The bright future of solar powered factories

This is a guest post by Kris De Decker, founder and writer at Low-tech Magazine, an internet publication highlighting the need for elegant yet simple old and new sustainable energy technologies

Arun solar concentrator india

Most of the talk about renewable energy is aimed at electricity production. However, most of the energy we need is heat, which solar panels and wind turbines cannot produce efficiently. To power industrial processes like the making of chemicals, the smelting of metals or the production of microchips, we need a renewable source of thermal energy. Direct use of solar energy can be the solution, and it creates the possibility to produce renewable energy plants using only renewable energy plants, paving the way for a truly sustainable industrial civilization.

A large share of energy consumed worldwide is by heat. Cooking, space heating and water heating dominate domestic energy consumption. In the UK, these activities account for 85 percent of domestic energy use, in Europe for 89 percent and in the USA for 61 percent (excluding cooking).

Heat also dominates industrial energy consumption. In the UK, 76 percent of industrial energy consumption is heat. In Europe, this is 67 percent. I could not find figures for the US and for the world as a whole, but these percentages must be similar (and probably even higher on a worldwide scale because many energy-intensive industries have been outsourced to developing countries). Few things can be manufactured without heat.

Solar panels and wind turbines are no producers of heat energy

Blast furnace wikipedia The importance of heat in total energy consumption sharply contrasts with our efforts to green the energy infrastructure. These are largely aimed at renewable electricity production using wind turbines and solar panels. Although it is perfectly possible to convert electricity into heat, as in electric heaters or electric cookers, it is very inefficient to do so.

It is often assumed that our energy problems are solved when renewables reach 'grid parity' - the point at which they can generate electricity for the same price as fossil fuels. But to truly compete with fossil fuels, renewables must also reach 'thermal parity'.

Though today in some locations it may be as cheap to produce electricity with wind or solar energy as with gas or coal, it still remains significantly cheaper to produce heat with oil, gas or coal than with a wind turbine or a solar panel. This is because it takes 2 to 3 kWh of fossil fuel thermal energy to create 1 kWh of electricity, so it is at least 2 to 3 times cheaper to make heat by simply burning the fossil fuels directly than to use an electric renewable technology at grid parity.

Manufacturing wind turbines and solar panels requires heat

This means that solar panels and wind turbines will have to become two to three times cheaper than they are today in order to reach thermal parity with fossil fuels. This might sound reasonably possible, especially if you expect fossil fuel prices to rise. But consider this: even though they are intended to replace fossil fuels, renewable energy sources like wind turbines and solar panels are in fact dependent on a continuous supply of fossil fuels. 

Solar panels and wind turbines do not need fossil fuels to operate, but they do need fossil fuels for their production. You won't find any factory manufacturing PV solar panels or wind turbines using energy from their own PV solar panels or wind turbines. Why not? Because it is very inefficient (and thus utterly expensive) to convert electricity into heat. Yet to make solar panels and wind turbines, to produce steel and silicon for instance, heat is what is most needed. This means that the production costs of solar panels and wind turbines will be affected negatively by rising fossil fuel prices.

Arun 2 The same goes for batteries, which are an essential element of electric cars and renewable electricity storage, and for many other modern green technologies, like LEDs and heat pumps. They require heat for their production, and this heat can be delivered at least 2 to 3 times cheaper by burning fossil fuels than by using wind turbines or solar panels (cheap electricity from hydropower plants is also an option, but has limited potential). This is a fundamental problem, because we will have to produce new wind turbines and solar panels every 20 to 30 years, and new batteries every 5 to 10 years.

Renewable source of heat energy

The missing element in our sustainable energy strategy is a renewable source of thermal energy. Geothermal energy produces heat, but for now it is mostly economical in regions that lie on the boundaries of tectonic plates, as there temperatures are higher closer to the surface. Biomass is another option, but it faces many problems. If we were to try to provide an important share of heat demand by burning biomass, we would quickly come up against the limits of what the planet can produce. There is only one source of heat energy left, and it is a powerful and inexhaustible one: solar energy.

We tend to see solar energy as yet another way to generate electricity, using photovoltaic panels or solar thermal power plants. But solar energy can also be applied directly, without the intermediate step of generating electricity. Basically, harvesting direct solar energy can happen in two ways: by means of water-based flat plate collectors or evacuated tube collectors, which collect solar radiation from all directions and can reach temperatures of 120 °C (248 °F), and by means of solar concentrator collectors, which track the sun, concentrate its radiation, and can generate much higher temperatures. These can be parabolic trough systems, linear concentrating Fresnel collectors, parabolic dish systems or solar power towers. Almost all of these technologies were developed at the turn of the 20th century.

Solar thermal power versus solar thermal heat

Solar power tower The problem is that we mostly use this technology for the wrong purpose. In today's solar thermal plants, solar energy is converted into steam (via a steam boiler), which is then converted into electricity (via a steam turbine that drives an electric generator).

This process is just as inefficient as converting electricity into heat: two-thirds of energy gets lost when converted from steam to electricity. This is one of the main reasons why the use of solar thermal energy to produce electricity is only cost-effective in deserts.

If we were to use solar thermal plants to generate heat instead of converting this heat into electricity, the technology could deliver energy 3 times cheaper than it does today and become cost-effective also in less sunny regions. The crucial difference between solar thermal electricity and other renewables producing electricity is that solar thermal actually starts with heat energy. Thus, contrary to other renewables, the cost of heat energy using the technology is far lower than the cost of electricity, and so it can compete with burning fossil fuels at the thermal level.

Low temperature solar heat

This can be demonstrated by flat plate collectors and evacuated tube collectors, which are used for domestic hot water preparation and (to a lesser extent) interior space heating. This technology is used without any conversion losses and is cost-competitive with fossil fuels almost anywhere on Earth. According to the 2011 update (pdf) of the International Energy Agency's Solar Heating and Cooling Programme (IEA-SHC), solar thermal heat is now the second most important renewable energy source following wind, and a much more important energy source than photovoltaics and solar thermal power plants. Almost 60 percent of solar thermal heat capacity can be found in China and another 20 percent is in Europe. The US and Canada (where the main application is to heat swimming pools) account for less than 9 percent.

Renewable energies comparison capacity

Figure 1. Renewable energies comparison capacity

Sweden, Denmark, Spain, Germany and Austria have the most sophisticated markets for different solar thermal applications, including large-scale plants for district heating and a small but growing number of systems for air conditioning and cooling (using an absorption chiller). By the end of 2009, 115 solar supported district heating networks and 11 solar supported cooling systems were installed in Europe. Canada, Saudi Arabia and Singapore have also built a few large-scale solar heat systems for producing hot water, space heating and cooling. 

The potential of solar heat for industrial processes

Without a doubt, solar heat for domestic purposes should continue to be encouraged and a lot of potential remains. But it does not stop there. According to a 2008 report (pdf), which analyses the situation in Europe, the potential for solar heat in industrial processes is even larger than in the domestic market. About 30 percent of industrial heat demand in Europe is below 100 °C (212 °F), which could be delivered by commercially available flat plate collectors (< 80 °C) and evacuated tube collectors (< 120 °C) currently used for domestic purposes.

Another 27 percent of industrial heat demand requires medium temperatures (100 to 400 °C or 212 to 752 °F), which could be reached by improved versions of these collectors (up to 160 °C, see this document) and by commercially available solar concentrator technologies now mostly used for electricity production: parabolic troughs, parabolic dishes and linear concentrating Fresnel collectors.

Industrial heat demand

Figure 2. Industrial heat demand

This means that at least 57 percent of heat demand in European industry (or almost 40 percent of total industrial energy demand) could be covered by available and cost-effective technology using an inexhaustible renewable energy source that has no ecological disadvantages whatsoever. The capital costs (and embodied energy) of this would be much less than replacing a similar amount of fossil fuel energy use with solar panels or wind turbines. And of course, it could be done anywhere, not just in Europe.

Solar heat in industry: existing applications

Sopogy-micro-csp At low and medium temperatures, solar heat can be used for industrial processes in several ways. It can provide warm water for processes like bottle washing or chemical processes. Secondly, it can provide hot air for drying and baking processes, for instance in the food and paper industries. Thirdly, it can generate steam that can be fed into steam heat distribution networks, which are widely used in many industries. The interesting thing is that in all these applications, the existing industrial machinery and distribution infrastructure remains in place. Only the energy source is replaced.

Some manufacturers have started marketing their solar concentrator technologies for the use of heat generation in industry, in addition to their application as electricity generators. Examples are Sopogy (a Hawaian company that sells modular parabolic trough systems - picture above), the Solar Power Group (a German company that sells linear concentrating Fresnel collectors) and  HelioDynamics (an American seller offering similar technology - picture below).

Heliodynamics solar power Installations for the use of solar industrial process heat are still rare, but they exist. German heating systems manufacturer Viessmann installed 260 m² of its own flat plate collectors on its factory in France to provide hot water for a chemical process, taking a first step towards producing renewable energy using renewable energy. A solar thermal plant based on 1,900 m² of parabolic troughs provides steam for a pharmaceutical plant in Egypt. A similar solar thermal plant was built for a dairy plant in Greece. A food processing facility in California has 5,000 m² of parabolic troughs to produce steam used in the manufacturing process. Several industrial applications of solar heat have been built in India, using both flat plate collectors and concentrator technologies.

Arun solar concentrator A solar concentrator system called ARUN - a Fresnel parabolic reflector with point focus that delivers temperatures from 80 to 400 °C - has been installed in six industries, ranging from a dairy plant to an automobile manufacturer (picture on the left). India also has several large solar cooking facilities for community kitchens (schools, hospitals, factories, religious centres). The largest one consists of 84 parabolic dish systems reaching temperatures of up to 650 °C and producing up to 38,500 meals per day. The largest solar process heat application to date was recently installed in Hangzhou, China, where 13,000 m² of solar collectors on the roof of a textile factory provide hot water for a dyeing process. The Global Solar Thermal Energy Council is continually updating its list of new industrial applications of solar heat.

Renewables building renewables

The remaining 43 percent of industrial heat demand in Europe is above 400 °C (752 °F). These include many of the industrial processes that we need to manufacture renewable energy sources (wind turbines, solar panels, flat plate collectors and solar concentrators) as well as other green technologies (like LEDs, batteries and bicycles). Examples include the production of glass (requiring temperatures up to 1,575 °C) and cement (1,450 °C), the recycling of aluminum (660 °C) and steel (1,520 °C), the production of steel (1,800 °C) and aluminum (2,000 °C) from mined ores, the firing of ceramics (1,000 to 1,400 °C) and the manufacturing of silicon microchips and solar cells (1,900°C ).

These temperatures can be achieved by solar concentrator technology. Linear reflectors (parabolic trough systems and linear concentrating Fresnel collectors) are limited to temperatures of about 400 °C, but point concentrators can reach higher temperatures. These include parabolic dish systems, solar power towers, and solar furnaces - which are basically a combination of power towers and parabolic dish systems. 

Solar furnace france Solar furnaces can produce temperatures up to 3,500 °C (6,332 °F), enough to manufacture microchips, solar cells, carbon nanotubes, hydrogen and all metals (including tungsten which has a melting point of 3,400 °C). These temperatures can be achieved in just a few seconds - see this short video of a solar furnace melting steel. The most powerful solar furnace is the one at Odeillo in France, built in 1970, which concentrates the light of the sun 10,000 times and has a power output of 1 MW.

Solar furnace uzbeskistanMore than 60 heliostats (only one is seen on the picture above, in the lower righthand corner) direct the rays of the sun onto a parabolic mirror of more than 1,800 square metres, from which they are concentrated on a focal point with a diameter of only 40 centimetres in the tower in front of it. A similar solar furnace stands in Uzbekistan, built in 1976, but it is slightly less powerful due to lower solar insolation in the region. The picture on the right shows it in action, melting metal.

Solar furnace PSI switzerlandYou don't need such an enormous structure to achieve high temperatures. Several smaller solar furnaces have been built, often using only one heliostat. They reach similar or only slightly lower temperatures (usually between 1,500 and 3,000 °C) than the giants pictured above, though at significantly lower power outputs (between 15 and 60 kW). They can perform most of the same processes as the large solar furnaces, but processing smaller amounts of materials or chemicals.

Examples of smaller solar furnaces can be found at the Paul Scherrer Institute in Switzerland (pictured below right), the National Renewable Energies Laboratory in the USA, the Plataforma Solar de Almería in Spain, the German Aerospace Center in Germany, and the Weizmann Institute of Science in Israel (a solar power tower). They have concentration ratios between 4,000 and 10,000. In solar concentration, the temperature is proportional to the degree of concentration, whereas power will be proportional to size and efficiency (which is mostly determined by temperature). 

Solar energy improves product quality

Solar furnaces not only have the potential to replace fossil fuels for the energy-intensive production of construction materials, chemicals, and high-tech products like microchips and solar cells, but they also offer additional benefits because of their pure combustion and selective heating capacities. A 1999 research paper describes the manufacturing of silicon solar cells using a solar furnace, concluding that "solar furnace processing of silicon solar cells has the potential to improve cell efficiency, reduce cell fabrication costs, and also be an environmentally friendly manufacturing method. We have also demonstrated that a solar furnace can be used to achieve solid-phase crystallization of amorphous silicon at very high speed."

As opposed to low and medium temperature processes in industry, where only the energy source is replaced and the machinery and distribution infrastructure can remain in place, most high temperature solar heat applications require new machinery. Furnaces and kilns have to be rebuilt. Some efforts have been made. The Paul Sherrer Institute in Switzerland designed several solar powered lime and cement kilns (pdf), and research concluded that they could become cost-competitive with a fossil fuel powered kiln (pdf) following some further technological improvements. Again, the quality of the product turned out to be better using solar energy, eliminating combustion by-products.

Low-tech, open source solar concentrators

Solar fire 1Though existing solar funaces prove that anything could be produced using direct solar heat instead of fossil fuels, this is not yet possible in a cost-effective way (it is cheaper to use fossil fuels). However, since solar furnaces could produce all materials needed to build more solar furnaces, they might become cost-effective even without technical improvements if fossil fuels become more expensive.

Moreover, the capital costs of solar concentrators are decreasing quickly following some recent innovations aimed at simplifying the technology. These might not only lead to cheaper high temperature solar heat concentrators in the future, but they also make the use of solar heat for medium temperatures more affordable and competitive today.

The most spectacular example is the Solar Fire P32 (picture above and pictures below), a solar concentrator developed in 2010 by the French NGO the Solar Fire Project. It is an open source design (joining forces with the Open Source Ecology project), but the machine can also be bought for 7,500 euro - less than the price of an urban wind turbine.

Solar fire 3The Solar Fire P32 is built using simple, abundant and non-toxic materials. Contrary to most other modern green technologies, there is no need for rare earth metals or advanced tools that are not found in an average metal workshop. Essentially, this is a renewable source of heat energy analogous to home made windmills used to produce mechanical energy.

The machine can deliver up to 15 kW and can reach a focal temperature of 700 °C (1,292 °F), enough to melt (and thus recycle) aluminum, the material that is used to make its reflectors. This means that you could use a Solar Fire P32 to make another Solar Fire P32. Or almost. The receiver and the supporting structure are made of steel, which requires a higher melting temperature to recycle. However, the structure could as well be made of wood, bamboo, organic fibre or aluminum, and the steel receiver could easily be scavenged material. The use of glass improves the workings of the device, but is not strictly necessary.

The Solar Fire P32 is composed of 360 small mirrors with a total surface of 32 square metres, focusing sunlight on a steam boiler above them. The steam can be used directly to purify large quantities of water, boil milk, produce edible oils, make charcoal, bake bricks, make paper, and so on.

Increasing energy autonomy

Solar fire 6The steam can also drive a steam engine to directly power a water pump, oil and grain mills, cotton spinning, or any other stationary application requiring mechanical power. Connected to a steam generator, the machine can also generate electricity (up to 3 kW). These two last applications involve conversion losses, but they are interesting additions for those who want to achieve energy independence, especially in regions where there is lots of sun but no wind. The machine can produce heat, electricity and direct mechanical energy. 

The Solar Fire P32 is - in the first place - aimed at developing countries and designed to be cost-effective compared to burning coal and wood, reducing deforestation and pollution, increasing energy autonomy, and providing an energy source at the scale of traditional practices and small industries. It has been built in Mexico, Cuba, Burkina-Faso, Mali, India and Kenya, but also in Texas, France and Canada. Obviously, the design could also be useful in the developed world, where the supply of fossil fuels might not remain as easily accessible as it is today. 

Simplifying technology

Solar fire 5Apart from the additional equipment that is required to generate electricity, conventional solar concentrator technologies demand heavy capital investments for several reasons. Parabolic trough systems and parabolic dish systems require curved mirrors that are expensive to produce. Moreover, these mirrors cannot be manufactured locally and often have to be transported over long distances, increasing costs further. In both systems the curved mirrors are large and heavy, requiring rigid frames, strong foundations, powerful hydraulics and sophisticated tracking systems to follow the sun. In parabolic dish systems, the heat engine or steam boiler is part of the moving structure, increasing weight and thus making things even worse.

Solar power towers - which were invented in 1878 - solve some of these issues: they use nearly flat mirrors and all mirrors share one stationary receiver. But, they require the construction of a large tower building. Last but not least, all of these systems have very high land requirements because of overshadowing issues. Linear Fresnel concentrators use (mostly) flat mirrors, have simpler tracking systems and are more compact, but they can only reach temperatures of 250 °C (using relatively low-tech materials) or 450 °C (using sophisticated technology).

Sundrop jewelry melting glassThe Solar Fire is a Fresnel parabolic reflector with point focus, just like ARUN - but unlike that machine it is placed horizontally and the receiver does not have to be turned together with the mirrors, resulting in light weight and high wind resistance. The machine uses slightly curved mirrors, achieved by mechanical bending which can be done on the spot. Sun tracking of the mirrors is done by hand, eliminating the need for electronics and electric motors altogether (multiple mirrors can be turned at once using hand operated wheels). This might sound crude, but for industrial applications the machine has to be supervised anyway.

And because it is open source, it can be further improved by anyone. Eerik Wissenz, the designer of the machine, thinks this is the only way: "Companies pursuing patents for solar collectors have fallen into a complexity trap. Since solar energy is free it is far simpler to add 5 percent more surface area instead of creating complex machines too expensive to be commercially viable. Solar fire concentration is so simple it cannot be patented."

Low-tech solar furnaces

High temperature solar furnaces can be low-tech autonomous systems, too. One example is the large magnifying glass used by Sundrop Jewelry, which reaches high enough temperatures to melt coloured bottle glass into handcrafted jewelry. Of course the power output is low, making this installation useless if you want to produce industrial quantities of glass. But it shows that solar heat can be used on any scale.

Solar_sinter_01Another example is the Solar Sinter Project by Markus Kayser, in which glass is produced using only sunlight and desert sand. I would like to quote the artist here: "Whilst not providing definitive answers, this experiment aims to provide a point of departure for fresh thinking".


How can you power factories using an energy source that is not always available? Solar insolation varies throughout the day and the seasons, and there is no sun at night. Moreover, solar concentrator technologies only work with unscattered sunlight, which means that a passing cloud stops energy production. This raises two questions. Some industrial processes work fine with intermittent energy supply, but how do you guarantee an uninterrupted supply of energy to a process that requires it? And what do you do when there is no sun at all for a week?

There are three ways to deal with the intermittency of solar power. The first solution is to design hybrid systems: make solar and already existing energy sources work together. This is how most of today's solar thermal power plants work. In this scenario, which offers a solution for both short and long term storage, industrial processes are powered by solar heat whenever it is available. When it is not, solar energy is instantly replaced by fossil fuels or electricity. It is not an ideal solution, but it could save large amounts of energy. And we don't need new technology to make it work.

Sopogy thermal storage The second strategy is to store solar energy so that it can be used to smooth out industrial processes (analogous to a flywheel for smoothing out mechanical processes) and to guarantee energy supply on cloudy days or at night. Storage of heat is much cheaper and more efficient than storage of electricity. The most low-tech way is to store heat in well-insulated water reservoirs - another technology that is more than 100 years old. The disadvantages are that you need quite a lot of space, and that water storage only works up to a temperature of 100 °C (212 °F). There are more compact ways to store heat at higher temperatures, for example by using ceramics or phase-changing materials (certain salts). These storage media are already used in one solar thermal power plant, but they would be even more efficient if used in a thermal only system. Innovative technology could further improve heat storage.

Storing work instead of energy

The third way to deal with the intermittency of solar heat is to store work instead of energy. We let our factories work when the sun shines, and only when the sun shines. Just like we wait for a sunny day to do the laundry, we could wait for a sunny day to bake bricks, recycle metal or produce smartphones. Industrial production would be concentrated in summer months. Of course, there is a price to pay. Industrial production would be lower. But considering the fact that our energy and environmental problems are largely caused by overproduction and overconsumption of goods, this is not as far-fetched as it might seem.

Combining all three strategies could be a solution. In that scenario we would run part of our factories only when the sun shines (and when the wind blows), using heat storage, fossil fuels, biomass or electricity to smooth out industrial processes if necessary. Critical goods could be produced continuously combining solar heat and heat storage, fossil fuels, or biomass. Of course, not all climates are blessed with enough sun to make solar heat a viable option to power the whole industry. But since many people are now talking about outsourcing electricity production to desert regions, we could just as well move our factories to regions where there is plenty of sun. It is much more efficient to transport manufactured goods over large distances than to transport electricity.

Solar powered enhanced oil recovery

As always, a sustainable technology can be used for unsustainable purposes. Solar heat is a great way to get more oil out of fields that are now considered exhausted. Getting that remaining oil out using gas would cost more money and energy than the oil could return, but using a free source of energy changes everything.


At least one company specializes in this application. Glasspoint, a US firm originally founded to use solar heat for drying gypsum wall board, has seen remarkable growth promoting "Solar Enhanced Oil Recovery".

This has been tried before, but they use an innovative technology: parabolic trough mirrors suspended from the ceiling of enormous glasshouse structures that are equipped with robotic cleaning systems. Because they are protected from wind, sand and dust by the greenhouse, the mirrors can be made extremely light and without protective glass layers - lowering their costs and increasing their efficiency. The steam that is generated by the solar heat is pumped into the oil reservoir. The more sun there is, the more oil will come to the surface. Only 20 to 40 percent of an oil field can be recovered using standard techniques, but as much as 60 to 80 percent can be recovered using solar heat. In the end, solar heat could thus increase fossil fuel production and CO2-emissions.

Kris De Decker (edited by Rachel Meyer)

Sources, inspiration & more information:

Thanks, very informative.

Yes, a wonderful article.

BTW, see the campfire-driven fridge (that could be solar powered) developed by Adam Grosser here:Adam Grosser: A new vision for refrigeration (youtube video). (In 2007, Adam Grosser presented his research of a new, very small, "intermittent absorption" refrigeration system for use in third world countries at the TED Conference. The refrigerator is a small unit placed over a campfire, that can later be used to cool 3 gallons of water to just above freezing for 24 hours in a 30 degree Celsius environment.)

>In 2007....

That's over three years ago, so where's he at now with his project?

Probably stuck in 1927 with David Forbes Keith next to the Crosley IcyBall.

As this is about using 'heat' to do 'work' - the ISAAC Solar Ice Maker.

If one wants one today -

ISTR a scheme like that written up (Home Power?) which used CaCl2 as a solid sorbent for NH3 (here's a paper).  This eliminates the need for a water separator.  Bulk CaCl2 seems to sell for about 10¢/lb ($200/ton).

I think the lessons here are:

  1. Refrigeration is very low-tech.
  2. It can be done without electricity.
  3. It can be "stored" for days as isolated refrigerant and sorbent.

So who's mass producing the equipment we're discussing and where is it commonly used?

Nobody's making it.  Currently it's too cheap to use conventional refrigeration and batteries.  But such systems are simple enough to be built by amateurs, and in a crisis situation you can bet they would be.

A bit of a discussion about that over here:

And I note that you've been straightened out regarding the technology requirements.  Absorption systems were commercial products in the 1920's, and could have been built with 19th-century materials and practices.  All else that's needed is the knowledge that it can be done.

I'm not your average noob when it comes to refrigeration tech. I'm a former HVAC installer and refrigeration and heating serviceman.

Absorption systems are still commonly manufactured as small propane powered units in motorhomes and campers, and large scale commercial and industrial refrigeration systems.

Great.  How does that address the issue of what people would do if e.g. electricity was intermittent (as it currently is not) and they wanted their refrigeration to be reliable?

Much less material and less awkward to simply power a regular refrigerator with some PV.

How do you do this if several million people suddenly want PV too?  How do people invest in all that PV if they can't afford to maintain their electric grid?  Pushing PV as a civil-defense measure might work (keep things running if storms or sabotage take the grid down), but once the problems hit it's too late.

The beauty of absorption systems is that they are dumb.  They require no high-tech parts or sophisticated fabrication techniques.  They can be built from junk.  If you are looking for a fallback which can be implemented with local resources in a period of disrupted financial systems or supply lines, that's the way to go.

Oh sure, they're fantastic systems, yet all you can link to is instructions on how to make one. No citations that anyone in the world is mass producing them. They're fantastic systems, yet no one wants to take the plunge and mass produce them. Not even for charity for people in developing countries.
I wonder what the reason for that is....

"How do people invest in all that PV if they can't afford to maintain their electric grid?"

How will a society afford to maintain an ammonia manufacturing plant if they can't afford to maintain transmission infrastructure?

They're fantastic systems, yet no one wants to take the plunge and mass produce them.

Interesting question. Maybe concern about high pressure, noxious gas within the home? Can efficiency figures be met? I don't know but it does seem odd that if they are so good that we do not see them on the shelf. Mind you, look at all the kicking and screaming to get efficiency up for normal fridges, maybe it isn't that odd.


Good little subthread here.

I know the specialist service guy for RV absorption fridges in Calgary. He does a great business servicing these things. He also has a separate company that builds small RV trailers - and the fridges he puts in there - 12V marine fridges, that can be powered by a 30W folding solar panel and one car sized deep cycle battery.

His opinion - despite the apparent simplicity of the absorption fridges, they are just too high maintenance/low performance.

Now, this is not to say an absorption fridge can't be made reliable, but I think the key thing would be to move away from ammonia to some other less toxic, easier to use material.

If the performance parameters are such that it only needs to provide refrigeration, rather than freezing, then perhaps there are more options available.

Since no one has taken the plunge to produce such systems, maybe this would be an appropriate candidate for some government funding. Get a new, ammonia free, design made, at both small and large scale, and then start implementing them. There would be a large market in the southern US for these systems on all sorts of buildings, from schools to military bases. Given the large amount of fuel used by the military for A/C at bases, they might well be interested in joint funding for small, portable sun powered units.

I doubt we'll see any such action from any of the existing refrigeration companies - they are too heavily invested in what they currently do.

Although ammonia isn't something you want to breath high concentrations of, it's not environmentally harmful. It's a byproduct of our metabolism in small concentrations, and you might get a good whiff of it while turning a dry compost pile. It's not uncommon for folks putting only grass clippings or similar in a pile, to create an environment more favorable to bacteria that produce a lot of ammonia.

My first experience with an absorption system was as an HVAC installer working a remodel of a home in Bel Air Estates, an exclusive community in Los Angeles. I went to cut the refrigerant lines to let out the refrigerant, and was surprised to find they were steel. Not yet having been trained in refrigeration tech, I got a metal blade and proceeded to cut the lines. The resulting cloud of ammonia prompted a visit from the LAFD and the neighborhood evacuated.

This was in 1980, before refrigerants had to be recovered.

There was a time when natural gas powered absorption refrigerators were relatively common in homes. As far as what your friend says, I think the weakest link in an absorption system is the burner. Usually something a simple cleaning will take care of. Following is a link to a company selling absorption refrigerator/freezers recommended for PV:

The following site has answers to just about any question one might have about absorption systems, although it looks like a natural gas industry website (annoys me):

Any encouragement to burn more fossils annoys me.

How will a society afford to maintain an ammonia manufacturing plant

You can make ammonia by decomposition of urea.  It's also a widely-used agricultural chemical and doesn't require an intact just-in-time delivery system.

No citations that anyone in the world is mass producing them. They're fantastic systems, yet no one wants to take the plunge and mass produce them.

You want a new one?  Here's a product description.

There's currently no market for absorption backup systems, because the people who need backup are using generators instead.  Folks who are predicting a fast collapse ought to realize that people will shift to make use of what's available; if gasoline goes away, the generators won't work but the rocket stoves will.

Edit:  Here's an NYT blog item on liquid-dessicant dehumidifier systems.  Conditioning air with less electricity (or possibly none, if the system is regenerated with solar heat) is one way to have more good out of less FF use.

A very interesting article, but I question your statement.
A large share of energy consumed worldwide is by heat. Cooking, space heating and water heating dominate domestic energy consumption. In the UK, these activities account for 85 percent of domestic energy use, in Europe for 89 percent and in the USA for 61 percent (excluding cooking).
About 40% of energy consumption is derived from oil used mainly in transportation with a small amount used for heating and electricity production. Another 30% is derived from burning thermal coal to generate electricity. A small amount of coal is used to produce cement and steel. About 20% energy consumption is from natural gas, approx a third being used to generate electricity. An additional 5% is from hydro, nuclear and wind delivered as electricity. Biomass accounts for <5%,used mainly for heating and cooking.

While space heating, hot water heating and cooking dominate dominate domestic energy consumption in some regions, air conditioning is also important and much heating and cooling uses electric heat pumps. Some cooking (microwaves,electric ovens), electric kettles, lighting, refrigeration use electricity.

The energy used to recycle aluminum, copper and other base metals is minor compared to the electrical energy used in initial electrolytic production. In US and EU a lot of steel comes from recycling scrap in electric furnaces.

It is simply not not worth mentioning the heating and cooling of buildings, when thinking about our energy future. Buildings must be built to require no energy at all to keep their temperature comfortable. It is easy possibly to build a house requiring less then 10% energy for this purpose, compared to current average, at no extra costs.

There is another area with great potentials for the future. Many of our materials are produced by high temperature industrial procedures, while similar materials are created in living creatures at body temperature. Using such bio-chemical procedures in industries, may reduce heat requirement a lot and may also make solar heating more feasible.

Unfortunately the future is going to contain pretty much all of the buildings that exist now - and those buildings are going to have to be heated and cooled. They represent a large investment and can't be replaced immediately as if they never existed.

They can be insulated.

Assuming a building has a sound skeleton sitting on a sound foundation and has an economic purpose, i.e., a tenant, then investing in insulation is practical and easy.

Whether or not the interior design and mechanical systems are renewed, it is a straight forward job to increase dramatically the thermal resistance of the walls:
1. Remove old cladding, as necessary
2. Install impermeable membrane continously over wall sheathing
3. Install brackets to hold semi-rigid stone wool insulation and to hold cladding
4. Install insulation
5. Install cladding: cement board; corrugated steel...

Conceptually similar methods are regularly employed to add insulation to all sorts of roofs.

Thus, what you have is a building structure now waterproofed, with a continous layer of 'external' insulation and therefore no thermal bridging to supplement whatever was the preexisting insulation value.

We should be glad we have all these older buildings around, already standing.

Reaching the zero (or near to zero) heating/cooling energy requirement is easier with newly built houses. However, it is still possible to make wonders with old houses.

Just some examples of extreme old houses:

Our house is also more than 100 years old. We are near to finish renovating it with 20 to 30 cm thick insulation, triple glazed windows and with heat recovery ventilation. Our modest target is to reach the 30-40 kWh / m2 / year heat requirement.

Energy need of buildings is really no reason for headache. It is the only area, where requirement for external energy source can be nearly eliminated with low tech methods. Transportation, industry and agriculture is much harder problem.

Can you possibly link to the heat recovery ventilation system you are installing.

If not I'll eventually search Google.

I don't know what bdi is putting in, but you might also search on "air-to-air heat exchanger." e,g,

The HE100 seems to have a cross-flow heat exchanger. Countercurrent is better.

There are heat exchangers made from plastic and metals, but a new direction is to make them from paper-like materials, to allow recovery of air humidity not only heat.

Thanks for the link. As an HVAC tech in the plains states I'm just trying to keep abreast of technical innovations.

Worst job I ever had. I hated crawling, working in tight spaces, but most of all, I loathed working with fiberglass.

Most of the HVAC systems I saw were absolute crap.

A look at you link and further links from a Google search indicates this is a German product.

I have not found explicit confirmation of this technology being available in US ... will keep my eyes open.

At any rate, you seem to be on the cutting, if not the bleeding, edge of application of the technology.

Good for you !

Thanks for the reply !

I am just an enthusiastic amateur from Hungary, applying passive house techniques on the reconstruction of our house.

Passive house is a standard developed in Germany. They build houses with no (or almost no) heating/cooling by applying only low tech solutions. (actually, the heat recovery ventilation machine is the only active component, also not too complicated: a heat exchanger, two ventilators and some electronics) It is a well tested system, with tens of thousands of houses already built with this technique mainly in Germany and Austria. Surprisingly, it is not necessarily more expensive than building a traditional house.

If you are interested in it, you can start at wikipedia ( and external links at the end. Passive House Institute is also present in the US now.

If building a new house, I think it is stupid not to make it at least a passive house. If someone is brave enough, may target zero energy house, which will be the standard in Europe for new buildings from 2020. (2018 for public buildings)

I am familiar with Passive House specs in general from Germany.

Thanks for the personal info, as I am at the moment, mostly an enthusiastic amateur as my professional capacity only nets me about 40 hours a year. This is working on very, very staid and traditional US residential heating and cooling systems.

Unfortunately the future is going to contain pretty much all of the buildings that exist now - and those buildings are going to have to be heated and cooled. They represent a large investment and can't be replaced immediately as if they never existed.

As far as cooling is concerned you can certainly use PV power on your roof.
And thinfilm PV-module costs start meanwhile at $0.90/W:

And if you don't have a heat pump and no insulation and need some warmth, you can always dress for the season.

I also question the premise of the article. HVAC systems are pretty efficient compared to thermal+heat exchanging alternatives. Also, I've done a fair bit of work in the PV industry, there are no thermal steps required for thin film PV and for silicon PV, the thermal steps mostly uses electricity (induction furnaces). Today it makes more sense to use natural gas fuel reverb furnaces, but if the price of natural gas rose 2x, then silicon refiners could easily switch to electrical alternatives. Finally, the premise that manufacturing solar requires heat and thus PV can only be manufactured without fossils when it becomes 2-3x cheaper is truly flawed. PV is currently expensive not because of the embedded energy but because of all the non-energy expenses (labor, supply chain inefficiencies, depreciation, etc). This is clear when you consider that the energy payback of PV systems can be under 1 year and is almost always under 2.

On a much higher level, I reject the premise that the world needs low tech solutions for our energy problems. When you see how efficient modern solar manufacturing facilities are, you realize that any energy crises would only increase demand for the product rather than force the facility to shut down.

Then why don't you use solar panels to produce solar panels?

Because they aren't currently at grid parity compared with the lowest cost base load electricity. As soon as this is no longer the case, PV electricity (along with whatever other electricity generation is available on the transmission side of the grid) will be used to produce solar panels. You don't believe that making PV panels from wind generated electricity (as happens in parts of the world today) means that the manufacturing of PV panels is deeply flawed do you?

You mean that there are PV solar panel manufacturers using only wind turbines to produce their PV solar panels? Would be great. I am curious to know them.

Back 'round the 1st go on this 'energy shortage' there was a Massachusetts company making solar PV which bragged (just before they were bought out by what became BP Solar as I 'member) they were using their off spec PV to power the plant.

I believe you're referring to Astropower, (in Delaware), who at one time had the largest PV array on a building in the U.S. Astropower went bankrupt, the assets were sold to GE,
and somehow now Motech (a Taiwanese company) is in their former module assembly building.

BTW BP solar has shut down its Fredericksburg Maryland plant as of late too.

While I'm responding (quickly)...
Re the "1999" paper of using solar heat for making PV cells.
(a) it's from 1996 (went online in 1999 - the year of the dot com boom/crash).
(b) that was a long time ago in PV land - nobody uses gold contact anymore, etc.
(c) any manufacturer worth their CAPX (Capital Expenditures) is going to be running 24x7,
and solar heat is hard to store, especially at diffusion furnace or ink firing temps temps (800+ deg. C).
(d) modern furnaces for PV use are all electric, so they are clean and can be precisely controlled
(1996 is a long time ago in PV equipment land, 3-4 generations of most things)
(e) many processes in current, industrial PV production are only electrically powered
(silicon nitride deposition for Anti-Reflection Coating and surfaced passivation is either Plasma Enhanced Chemical Vapor Deposition or sputtering as one critical example. Another is that edge isolation of the junction is commonly done with an electrically powered laser.).
(f) the experiment led to the development of Rapid Thermal Processing, using high intensity lamps to do all this stuff, with better controllability, and on demand 24x7.

Written by eric blair:
Back 'round the 1st go on this 'energy shortage' there was a Massachusetts company making solar PV which bragged (just before they were bought out by what became BP Solar as I 'member) they were using their off spec PV to power the plant.

Solarex of Frederick, Maryland, partly powered their production with their own product. SOLAREX FADES AWAY, Green Energy News, March 27, 2010, Vol.15 No.1. I have 8 SXP-44's (polycrystalline PV) that today produce the same amount of power that they did 20 years ago when new.

You mean that there are PV solar panel manufacturers using only wind turbines to produce their PV solar panels?

Besides that you won't find anyone, who solely uses coal power to mine and ship coal and to produce coal power plants either...

This car factory is wind powered:

This Chinese PV-module manufacturer has a 1000 kW PV facade:

This tire manufacturer has a 7400 kW PV system on its roof:

This car manufacturer has a 11800 kW PV system on its roof:

I was not asking for car manufacturers or tire manufacturers using solar energy. I was asking for PV solar panel manufacturers using wind turbines and solar panels to produce their solar panels. You post a picture of a Chinese PV-module manufacturer that has a 1000 kW PV facade. You give no link or additional information. So, what I would like to know: does this Chinese factory uses these solar panels to produce its solar panels? Or does it use them to operate the lighting and the air conditioning?

Besides that you won't find anyone, who solely uses coal power to mine and ship coal and to produce coal power plants either...

That's a weird reply. We have fossil fuels on one side, and renewables on the other. Coal plants rely entirely on fossil fuels - what kind of fossil fuels has no importance. If renewables rely on fossil fuels, however, they cannot be an alternative to fossil fuels. But whether solar PV panels manufacturers are powered by wind turbines or solar panels or any other renewable energy - that has no importance.

The point is that simply because a factory doesn't use energy produced from the product it manufacturers doesn't mean that the energy technology isn't sound. As was mentioned previously, coal excavation primarily uses electricity only a fraction of which comes from coal plants. Nuclear uses very little nuclear power in the construction or operation of nuke plants. Many people who work at bicycle factories drive to work.

Muscle builders used to think they should only eat protein because "you are what you eat". This is narrow thinking and should be avoided.

In Europe, nuclear power uses quite a lot of nuclear power for doing the uranium enrichment - the facility is in France and the French grid is about 80% nuclear. But I appreciate this isn't quite the point you're making.

It can be helpful to reduce the pictures and link to larger ones, since they may create bandwidth issues for some members.

All the best,

What makes you think that all the citations you provided are disconnected from the grid and getting all their power from intermittent solar and wind?

I don't care if they get all their trons from the panels. It would be nice if the plant was net zero, i.e. exports as many trons as it imports. But, even so, purity of source is a standard we won't have to meet for several decades. Its usually used as a mechanism for dismissal.

Fetuses, rely on their mothers bodily functions. Infants rely on their parents for years. Should we abort all fetuses, because they are not in isolation viable at conception?

The Japanese and the Algerians have a project "Sahara Solar Breeder" to make PV from PV and sand.

Sounds interesting? Something I have long thought MENA should be investing their vanishing oil wealth in.


Because electricty is fungible. Makes much more sense to use the grid for 24/7 poower. Many high tech processes require 24/7 operation, and the avoidance of heating/cooling cycles for equipment. Now if a solar manulfactuerer wants to greenwash, he could always build/finance a utility scale PV plant that produces the same annual output as the plant. But the PV supply chain is distributed. Producers of solar silicon are usually not producers of panels. Then you purchase mounts glass electrical connectors etc. So you end up with an industrial microcosm of general industrial production.

This question usually devolves to argumenting that PV is impure, because it is difficult to purify the supply chain. That probably won't happen until fossil fuels aren't used at all in the wider economy.

Neil, it is true that many heat processes are powered by electricity, but that does not take away the fact that these are heat processes, which could be powered more efficiently by solar energy. The numbers mentioned show the significance of heat energy in industry and households, regardless of how this heat energy is produced - they speak for themselves, no?

You mention air conditioning and cooling: these are probably the most interesting applications of solar heat, using (for instance) an absorption chiller. Cooling is mostly needed when the sun shines.

The metric shouldn't be converting PV electricity to heat. Rather, it's more appropriate to compare the best thermal generation from solar to the best fossil application. For example, solar water heating is much more efficient than using PV to heat water. It's also MUCH cheaper. Folks China, Greece, Egypt, already do this and even rick folks in the US use solar water heating for their pools, homes, etc. I think similar arguments could be made for CSP for industrial applications, mid-level concentrating systems for light industrial applications, solar ovens, etc.

"Cooling is mostly needed when the sun shines."

Mostly. I'd argue it's most needed when there's heat+humidity, which often means clouds at some point in the day, and a major loss of generation from solar when it's obscured by clouds. It's always going to need some sort of backup.

"Cooling is mostly needed when the sun shines."

Mostly. I'd argue it's most needed when there's heat+humidity, which often means clouds at some point in the day, and a major loss of generation from solar when it's obscured by clouds. It's always going to need some sort of backup.

Well, smartass, there's always a need for backup ... like the stored solar energy in any variety of things, including fossil fuel.

I can testify, that where I live (Calif), peak elec demand closely follows the rise in temps in July and Aug. We're using many thousands of megawatts for AC in CA right now. I think absorption cooling could be a great solar application... and make ice so cooling can continue into the eve. Like a lot of things, the high initial cost is holding us back especially while morons are saying cut cut cut. We need to invest invest invest in solar.

It would be nice to see some packaged systems for evacuated tube solar absorption chillers going into homes and businesses everywhere. I haven't run across any lately

>and make ice so cooling can continue into the eve

Actually I believe ice is made for all of the following day and into the evening. Example: Enough ice is made on Monday afternoon to be used for Monday night, all of Tuesday, and perhaps into Tuesday evening if necessary. I'm not a total noob at debating this subject. The following is a block away from me, and uses a thermal storage A/C system: The image is of Eastside High School, Lancaster, Ca. The solar installation is part of the largest PPA agreement with a utility and installed at multiple locations within a school district in the United States.

IMO, the approach we're taking involves an unsustainable consumption of materials and doesn't sufficiently solve the issues with incinerating fossils for energy.

I'm one of those damn pro nuclear power guys. If I didn't think it was a superior alternative, I'd be all arguments in favor of solar and wind.

I'm one of those damn pro nuclear power guys. If I didn't think it was a superior alternative, I'd be all arguments in favor of solar and wind.

Even if nuclear is a superior alternative, that does not mean it is *always* a superior alternative.

Nuclear is only feasible in large installations, that seem take take a long time to build, needs a supply of fuel, and also create a waste storage/security issue. It also needs highly skilled people to build operate and maintain, and decommission thee facilities, let alone handle them after Fukishima type incident.

Solar systems can readily be built at small scale, in a short time, have no waste, and do not need highly skilled people.

This makes them ideal for remote and/or low tech places that have lots of sun - which just happens to describe many third world countries.

Do you really think nuclear is a "superior alternative" for politically unstable places like Libya, Egypt, Somalia, Ethiopia, Nigeria, Afghanistan, etc or earthquake/tsunami prone places like Indonesia, New Guinea, Solomon Islands, Haiti etc?

The following is a block away from me, and uses a thermal storage A/C system: The image is of Eastside High School, Lancaster, Ca. The solar installation is part of the largest PPA agreement with a utility and installed at multiple locations within a school district in the United States.

That's a nice pic, but I'm not sure what I'm looking at. You say PPA so I assume it's a PV array. I said I'd like to see some solar thermal absorption chillers working.

>That's a nice pic, but I'm not sure what I'm looking at.

So it's actually a crappy pic, which I'd acknowledge. There's actually a lot going on there. The school is one of California's latest (cost over $200,000,000), and the solar topped canopies are a popular trend. The one agreement involving the imaged school, is actually one of a 10 school project. California has some of the most ambitious renewables mandates in the world, so there's an explosion of renewables installations. One of the gimmicks used to meet the mandates are power purchase agreements (PPAs), and the installation of solar topped canopies at California schools have become a popular method and location for those. I think there's at least 20 school installations just in my town, and at least 60 across the state.

Perhaps tomorrow I'll image some windfarm porn. Also near me is one of the largest wind resource areas in the world, and there's some major expansion of it going on. Over the weekend I drove past the area where all the equipment is being staged. Monopole sections, nacelles, and blades all lined up in one location.

IMO, the approach we're taking involves an unsustainable consumption of materials.

Actually, a thin-film silicon PV-module contains about 0.6 gram/m2:
That's about 0.6 gram silicon for a 100 W thin-film panel.
At 1500 sunhours/year and 30 years lifetime, that's 7500 kWh/gram silicon.
For comparison: Current nuclear power plants only produce 38 kWh/gram uranium.

And silicon is non-toxic and available in abundance (28% of earth crust):

Carbon is at 0.03% and Uranium235 at 0.0000013%

The 0.6 grams of silicon is minuscule compared to the balance of the panel; one might as well rank PV panels by GJ per gram of dopant.

Current nuclear power plants only produce 38 kWh/gram uranium.

U-235 releases about 6.5*1010 J/g when struck by thermal neutrons (including the losses to U-236 formation), so that figure must be starting from natural uranium and include the conversion losses from heat to electricity.

Fast-spectrum reactors make ~100 times as much uranium usable, and thorium reactors will utilize about 99.85% of thorium (about 0.15% winds up as Pu-238 after 6 neutron captures).

Of course, both sides of this are rather ridiculous.

The silicon argument reminds me of the oft repeated statements by hydrogen enthusiasts that it is the most common element in the universe--true, but utterly irrelevant as our access to vast clouds of the stuff millions of light years away is...rather limited.

On the uranium side, one must always wonder what is left out of such calculations:

the energy to find, mine transport, process the stuff?

the energy needed to decommission the plants?

the energy needed to 'safely' store the spent fuel for essentially ever?

the energy needed to evacuate citizens from ever-widening exclusion zones after the inevitable 'accidents'?

the energy needed to pay industry shills to make ridiculously optimistic claims about their toxic industry on sites like this?


Of course, both sides of this are rather ridiculous.

I agree (however, the problem with hydrogen is not the abundance-issue, but the cost-of-electrolysis-and-energy-consumption-issue).
But sometimes it just needs to be pointed out, that renewables actually need very little material, since this 'uranium-beats-everything' gets really tiring, especially given the fact that a gram of silicon can produce significantly more electricity than a gram of uranium.

But important is the fact that PV-modules start meanwhile at $0.90/W (and still falling):
(My efficient household is at 300 kWh/person and year. So with less than $300 of PV-modules per person, I can power my household for the next 30 years and even give some extra electricity to the grid - compare this with your health insurance bill for the next 30 years...)

Is this the whole of your argument?

The energy per gram of material?

And to what end? Ignoring the lack of "good" locations for fission reactors, ignoring the known demonstrated failures of Man to be able to operate fission plants safely - how does this energy fact address the long term lack of 'economic'
Phosphorous, the erosion of topsoil, idiots playing games with fiat money? At what point does "growth end" on a finite planet?

Stating "the material has this much energy per gram" is on par with the joke.

" A physicist, a chemist and an economist are stranded on an island, with nothing to eat. A can of soup washes ashore. The physicist says, "Let's smash the can open with a rock." The chemist says, "Let's build a fire and heat the can first." The economist says, "Let's assume that we have a can-opener..." "

For those that might be interested in California's CAISO state power generation, they also report out the contributions by wind and solar to the grid in MW:

It shows that today, using some cherry picked times:
Midnight to 4am, 2GW from wind.
10a to 2p, 400MW+ from solar.

etc... ;)

For my thoughts on the discussion:
1. I am not so concerned that an individual plant or office is net zero
2. I am interested in larger-scope communities getting more and more contributions from renewables.

CA is generating ~5% renewable from wind and solar. What percentage is imported hydro? Seems there is plenty of room to grow.

CA is generating ~5% renewable from wind and solar.

Well, it's not really 5% from wind and solar (a little less than 4%). It could be a lot more than in the next few years if funding comes through for a bunch of approved projects.

A few things:

- The Cal ISO area is not the whole state... 80+ percent. Major utilities not part of Cal ISO include LA County DWP and SMUD (Sacramento Municipal Util Dist).

- For any point in time, wind varies from nearly 10 percent (like around 4am sometimes) of the load to around zero. Yesterday happened to be a big day for wind. A good day we get about as much as geothermal. Yesterday we got almost 50% more from wind than geothermal (32 gwh v. 22 gwh) in Cal ISO area.

- California has a lot of hydro installed ... around 14,000 megawatts. Capacity factor is not very high (depends on season) but I think it averages ~25 percent.

- Large hydro is not included in the 33 percent RPS mandate. If we hit the 33 percent target (doubtful) in 2020, we'll actually be closer to 50% renewables (depending on weather etc... lots of rain and mild temps can double the percent contribution of hydro). Last year large hydro made 14.6% of elec power generated in-state. Other renewables contributes a similar portion, but this is mostly geothermal, small hydro, and biomass.

see )

- We get some WAPA power, which is mainly federally owned hydro (10,000 megawatts to 15 western states ... see ). This goes to municpalities for stuff like mass transit (BART get WAPA power).

- We also get some power from the largest nuke plant (Palo Verde) in the US, which is in AZ and part owned by CA utilities.

- Hydro imports can be substantial but depends on weather. Last year not much imported hydro -- less than 4%, mostly from the north (WA and OR).

In my local area EMBUD, it appears a great deal of effort is going into making biogas from sewage. There is enough biogas to run the plant and add power to the grid, which reduces fees to ratepayers.

Interesting times for power generation. I cannot believe we used to dump all this energy down the drain literally in the past. We were running waste treatment plants with electricity made from fossils when our waste had plenty of energy content.

Apparently water distribution in CA uses 10% of electricity in the state. That seems like a ripe area to exploit with intermittent renewables, which can pump water when the sun is up or the wind is cranking. Of course in the old days wind was used to move water around. This should be the way things go in the future as well.

Actually, water distribution use less than 10% of the electricity, but total water related energy use is much higher;

The Calif energy commission looked at this in a 2005 report on California's Water-Energy Relationship and found;

As California continues to struggle with its many critical energy supply and
infrastructure challenges, the state must identify and address the points of highest
stress. At the top of this list is California’s water-energy relationship: water-related
energy use consumes 19 percent of the state’s electricity, 30 percent of its natural
gas, and 88 billion gallons of diesel fuel every year – and this demand is growing.

The single biggest energy consumer is actually heating water, followed by "supply and conveyance" meaning the aqueducts. Urban distribution and sewage collection and treatment are decent users too.

Bottom line - if Californians learned to use less water, and less hot water, they would save a lot of energy. The author of this report concluded that if they want to save electricity, they are better of changing toilets and showerheads than light bulbs. Getting rid of some of those lawns wouldn't hurt, either.

Yair...I've said it many times and it's probably boring but why don't the Yanks use Aussie style solar water heaters...simple low-tech that works. The one on my roof has worked with no maintainance for over twenty years.


I can't give you figures, but a lot of in state hydro is along the California and Los Angeles aqueducts. They generate electricity where they can, but the aqueducts also consume a lot of electricity. California's single largest draws of current are electric motors used to pump water along the State Water Project.

Sounds like an instant invitation to work on a redesign with pumped Hydro storage that will both store renewable energy sources, and then reapply them directly as pumped (nee, gravity fed) water to satisfy a greater portion of the system's needs.

Pumped hydro schemes already exist as part of The State Water Project. Like most pumped hydro schemes, it's primarily used for excess nightime generation. The Castaic Lake/Pyramid Lake scheme. Water isn't pumped and stored for days of use, it's pumped and used the following day.

Ideally, you want to use what you generate, since you don't take X excess MWh of generation, use it for pumping water, and then get it all back. When we're discussing renewables, we're discussing a large amount of material and cost used to generate relatively small amounts of power.

>A small amount of coal is used to produce cement

Also used is petroleum, natural gas, and increasingly tires. I can't envision it done with solar or solar providing the heat directly or indirectly for any industrial process that requires very high temperatures from WITHIN a kiln used to heat non metallic substances. Many industrial processes that source electricity for the heat required, are processes that take more hours than the sun shines in a day.

"The energy used to recycle aluminum, copper and other base metals is minor compared to the electrical energy used in initial electrolytic production. In US and EU a lot of steel comes from recycling scrap in electric furnaces"

Aluminum and other metals can't be recycled into high quality alloys unless the feed material is pure or is already the alloy desired. Only the highest grades of copper can be made back into the highest grade of copper without electrolytic refining to produce a pure product. Bare bright copper can be made melted back into copper pure enough to produce wire from, but tin plated wire is often made into bronze alloys. It would have to be electrolytically refined to produce a high quality product. General steel scrap isn't made into high quality steel alloys. Too many contaminants. Primary iron from ore is made with coal.

Sure, I can envision some commercial and industrial processes powered by solar....some of the time. I'd be willing to bet that all the solar on a Costco's roof can't provide all the energy required for just its food court.

"General steel scrap isn't made into high quality steel alloys. Too many contaminants." This is incorrect.
Specialty steel, is made in batches from graded scrap via electrode or vacuum induction electric furnaces. Small amounts of pure elements are added in relatively small amounts at the last step to get the chemistry right. Poor this into molds. Remelt in vacuum arc furnace one or more times to produce high-tech alloys i.e tool steel, Inconel etc.


Provide a citation for that.

"Small amounts of pure elements are added in relatively small amounts at the last step to get the chemistry right"

Adding elements to the melt to get the desired characteristics doesn't remove the undesired elements that will affect the character of the steel they're trying to produce. You're contradicting yourself and confirming my comment when you type: "Specialty steel, is made in batches from graded scrap" To make a high quality or specialty steel, a manufacturer doesn't just begin with shredded autos or white goods, they begin with carefully selected scrap ("graded"), and/or dilute with primary steel

There's a reason why there's grades of scrap with low prices paid for low grades, and high prices paid for high grades.

It's even more important for aluminum, zinc, and copper.

I'm not sure exactly what your point is. The original point was about energy inputs, right?

Isn't it correct that recycling scrap eliminates the very high energy inputs required to reduce raw ore which is found in an oxidized state?

I was initially responding to: "In US and EU a lot of steel comes from recycling scrap in electric furnaces"

This is true, but I was merely pointing out that specialty steels aren't made from general steel scrap. Too many contaminants. It's not like copper, in that you can't electrolytically refine it to a high level of purity. You know, to remove undesired trace alloy contaminants and other impurities.

Outside of specialty scrap steels, like 600 inconel, 304 stainless, or other steel that can be sorted to one specific alloy, heavy steel is the highest grade of scrap. Everything else is low grade and it's reflected in how much you'll get paid for it.

If you had enough cheap process heat, steel could be separated into pure iron, pure nickel and everything else via the carbonyl process.

It's rumoured that Australia's six aluminium smelters pay 3-4c per kilowatt hour of electricity. That's a round the clock price so that it includes for example 2 a.m. on a windless night during an overcast week. Ironically the fear is that the molten salt in the crucibles will lose heat and set hard. I doubt this proposal can get anywhere near that electricity price or reliability of supply.

Manufacturing might have to return to a system like the days of sailing ships when a flag was flown from the mast when conditions were right to set sail. Before any kind of factory attempts this I suggest an apartment block get all its HVAC and appliance energy from a solar thermal plant. No fossil backup and no ongoing subsidies. If the residents can cope with the vagaries of supply then I guess a factory could also.

Unfortunately, this solution is impossible for aluminum smelter that must operate all time.

Manufacturing might have to return to a system like the days of sailing ships when a flag was flown from the mast when conditions were right to set sail.

Many will. But some that have thermal issues or tolerance issues won't. A papermill for example - the big metal drum has to be kept spinning otherwise gravity deforms your drum and you have to re-machine it.

Big steam turbines ditto, but that doesn't mean you have to keep spinning it at 100% of rated speed all the time.

Yair...with respect Eric, you are thinking BAU. Some manufacturing processes will have to be altered.


Yeah, as Scrub also implies.. it seems like that is a technology begging for a redesign or a rescaling.

Heaven forbid we scale down paper production.. I grew up between two Boise Papermills, Rumford Maine and Berlin, New Hampshire. Oxford county sorely misses the jobs, but not the stink or the dead fish bobbing down the Androscoggin.

I'm sure there's a better way to make those drums. Probably pricier at the outset, and only cheaper in a long-term view.

You have a pulley or sprocket which allows a small motor to keep the shaft turning at a few RPM.  This prevents the shaft from deforming and going out of balance under gravity loads.

That's similar to the relatively small energy inputs required to keep aluminium liquid during smelting.

He did say in the original post about using the Solar Fire to melt (recycle) aluminium, not to smelt it. Melting of scrap can easily be done in batch loads during the day.

However, if the objective was to smelt aluminium from alumina then you would need to design for higher temperatures and add electrolysis. This would be much more complicated, and can be done, but solar fire, as built is a pretty good start - there is no shortage of scrap aluminium.

Kris de Decker wrote:
"In that scenario we would run part of our factories only when the sun shines (and when the wind blows), using heat storage, fossil fuels, biomass or electricity to smooth out industrial processes if necessary."

That would be an interesting reversal of the 24/7 pattern in heavy industry. Heavy industry moved to 24/7 processes in the late 19th century as fossil fuel based heat sources could not be simply turned on or off each working day. Hence shift work and a lot of social, safety and productivity problems as humans are mostly daylight animals. If solar heating can be switched on and off as easily as you showed in the video's a number of critical processes can be moved to daylight hours again. Some processes like blast furnaces will need to be continuous off course but for me this would be a major gain with a move to solar heating in industry.

Interestingly, when people in developing countries get solar charged lamps, many of them use the light for extending the hours they work so they can make a buck.

As pinted by other, there is many alternative to solar to produce heat that are more efficient. Simple heat pump with a COP of 3, will have the same efficiency as a fossil fuel heating system. As for industrial process, induction heating and similar process are way more efficient than burner. Even for building application, life cycle analysis I have seen is not favourable to solar unless it is passive. Most of the time better insulation end up to consume more less energy over life time.

A CoP of 3 cannot be achieved beyond a relatively small increase in temperature over ambient.  Once you're talking about process-heat temperatures of 200°C or more, heat pumps are no longer cost-effective.

A remark on physics. Thermal radiation scales as the fourth power of absolute temperature, the statement that temperature is proportional to concentration isn't correct. In open air systems, convection is a serious source of heat loss.

I have a plastic fresnel lense similar to that shown in the Jewery making example. It easily reaches 2000-2500F (a penny melted in five seconds), but I've only achieved superficial melting of iron. So the highest temps require taking steps to reduce convective heat losses.

I think for most usues of industrial heat, at least in the OECD, the convienence of electricty is valued. So far the cost of energy versus the cost of labor and capital is such that operating only when the sun shines isn't economically viable in the OECD. I do like the idea of trying to exploit this for industrial use, even if only supplemental when the sun is shining. I just don't think it will be easy to achieve much penetration, until fossil fuel becomes several times more expensive.

You will need a cavity with an aperture to reduce your convection and reflection and radiation losses.

Like on this solar stirling engine, this type of setup is 85% efficient at taking in the solar energy.

Yes, I agree. Using a reflector instead of a lense, lets you make the collector upside down, which means if it is in a cavity it will inhibit convection. A lense like mine is more of a toy than a prototype of an industrially useful technology.

I've been toying with solar oven and smelting systems where you use multiple Fresnels in combination with mirrors in order to have control over both concentration AND beam direction.. so that you can combine several fresnel/mirror pairs to aim towards the same target, enhancing the temp levels more than a single lens..

The trick for me is intially in finding cheap fresnels with a long enough focal length to allow for the additional throw required.. the surplus fresnels from rear-proj tvs and such seem to focus in at under 6 feet or so. (and of course a longer throw means, for the home experimenter, being MUCH more careful about designing a system that won't allow people to get burned or blinded by this silent power source..

Have you been toying with providing the shielding atmospheres necessary when smelting?

Sorry, but I just can't envision concentrated solar being used as a substitute for high temperature electric or fuel powered kilns.

I can imagine adding a capability to add solar heat, so as to avoid some of the fuel demand. Thats a far different thing than going to 100% solar. These would be called hybrids, but obviously more than half the energy would still be supplied by fuel/electricity, so its not a huge efficiency upgrade.

It might not be that hard toadd to a kiln, have a port/window through which concentrated solar can be directed when it is available, and closed otherwise.....

>have a port/window

There's a reason high temperature kilns are lined with refractory bricks, and any sort of hole used to introduce additives, gases, catalysts, etc, is something only temporarily opened.

Have you considered changing your member name so that challenging comments aren't that much more likely to be taken as intentionally snarky incendiaries? When we see the name 'smartass' at the head of a comment, how do think the rest of the conversation is going to be taken, or where it is likely to head? It's tough enough around here to create a constructive and adult conversation without that sort of distraction..


There are clearly some 'home-scale' forms of melting, casting and refining simpler metals and small volumes that would apply to my earlier comment.. and holding that up against the overall high-energy industry of metals refining is part of why this conversation keeps getting stalled out by unnecessary presumptions that what is being proposed either in the keypost or in my pretty clearly 'home experimenter' ("Surplus TV Lenses"..) submission as "Solar can replace ALL large industry tasks" ..

It can do what it can do, and is clearly up in the metal/glass melting temps and is used as such.. since even the keypost showed people already doing such things, then why is it necessary to make it sound like it's not worth approaching, since all I've added is a different way to configure lenses/mirrors in order to affect form factor, perhaps system size?

"It can do what it can do, and is clearly up in the metal/glass melting temps and is used as such.. since even the keypost showed people already doing such things"

That's twice you used the word "clearly", but I'll bet you can't find one citation of hobbyists or home experimenters doing anything practical in the way of refining or fabricating metals or glass using concentrated solar power.

One can do more with a pocket sized torch than what dozens of folks are videotaping themselves very awkwardly doing with large fresnel lenses.

Perfect examples would be found on the website of the king of goofing with fresnel lenses; The Greenpowerscience dude. It's facepalm inducing watching him awkwardly do things with fresnel lenses, like melt tiny amounts of brick, a penny, make popcorn, melt a bit of glass, and stretch it out into worthless threads.

I have fresnel lenses too, and I like to goof around with them, but I'm not under any kind of illusion that I can do anything practical with them. Large scale demonstrations of what one can do with concentrated solar are over 50 years old. It didn't result in any practical uses in industry solely because fossils are cheaper.

It's about time you read the article that you are commenting on. All these thing you cannot imagine using concentrated solar heat have been demonstrated, and are being demonstated. The only thing is that they're not cost-competitive: it's cheaper to use (cheap) fossil fuels.

You're imagining things that are not in the article. You're seeing an image of a small CSP project and imagining it's a working kiln or furnace. There's no such thing in the article, it's all hope and conjecture. Look at an existing kiln, blast, or arc furnace, and ask yourself how can you get that same heat inside of that same kiln or furnace using CSP. CSP schemes are heated from the outside, and kilns and furnaces are usually sealed atmospheres lined with some sort of refractory material and heated from within.

I'm just trying to be realistic here. I can see CSP used do provide process heat for some applications, but not for others. How would you transfer the heat from CSP to the inside of a refractory lined, insulated, and sealed kiln or furnace?

Read the article. Start at "Renewables building renewables", stop at "Low-tech, open source solar concentrators". Follow the links. Then come back.

We should concentrate on low to medium temperature process heat, it can be done with existing technology. But while they are obviously not around the corner, solar powered high temperature processes could be an extra option. If I read what can be done with the solar furnaces operated by universities now, then I can imagine that in some decades we are able to design, indeed, solar powered industries. If you let the engineers design them. If we can build nuclear power plants, then we can build sophisticated solar powered factories and rewire our production processes.

"..solely because fossils are cheaper."

And what was that thing I heard about fossil fuels?.. and where are we headed with them?

And if you can melt a little stack of pennies with ONE of these lenses and no Thermal Retention or Refractive Brick, etc, in a couple minutes.. then what I suggested above, not rocket science at all, but just to find ways of orchestrating multiple Fresnels and Redirecting Mirrors in order to increase either the temperature or the target area so you can heat up more mass, or higher temp materials.

Those torches are great, as long as you can get the gas refilled. If you're on a remote farmstead, and it's a couple years after the Home Depots have shuttered, and THEY had shuttered all the smaller suppliers that used to carry tanks of propane or butane or MAP? gas.. etc.. you might be turning to your Mirrors and Lenses to make that smoke.

You think nukes will hang on.. I think they are as vulnerable to the complex supply chain economics that would make getting a simple tank of Acetylene more and more difficult/prohibitive.. and that we would be smart to have some other processes in hand, even if they seem sorta wimpy and 'aw shucks!' from our fading perch on the high-energy post.

You want acetylene?  Neither charcoal nor lime are hard to find, and electric arcs aren't difficult to make.  The traditional engine-driven arc welder can be run off wood gas or biogas, too.

It'll be a long time before it gets hard to weld things.

It'll be a long time before it gets hard to weld things.

We’ve done some testing on torch tip gas volume requirements. For most applications, including cutting inch thick steel a #0 torch tip or a #0-3 cutting tip is adequate. A 1,000 liter per hour electrolyzer will support these applications. 1,000 liter s per hour requires 16 amps at 240VAC. P8.

>And if you can melt a little stack of pennies with ONE of these lenses

If you understood everything behind the smelting or refining of metals, you wouldn't be thinking it's as simple as melting some metal in open air. BTW, the pennies you usually see folks melting are newer pennies, which are made of zinc. Zinc has a relatively low melting point.

Do you know anything about welding? If you understood why shielding gases are necessary, that would clue you in.

"..solely because fossils are cheaper."

And what was that thing I heard about fossil fuels?.. and where are we headed with them?

Sure, the very phrase "fossil fuels are cheaper..." [than solar] is absurd. It is an absurd comparison.

I've thought about how this might be re-framed... perhaps referring to non-renewables as "capital sources" and renewables as "income sources." If you are paying the rent with capital, you are going broke. You need to pay the rent with income, not capital. You need to invest capital to develop income.

I'm assuming most readers here understand that in saying "Fossil Fuels are Cheaper", I'm just framing this issue within the Short-term Mindset in which most energy decisions are still getting made.. but it's worth remembering the assumptions I've left unclarified..

Still, it's quite easy for someone (and it happens here daily) to explain just how cheaply they can set everything up with NG or whatever, and show that for their purposes, running with FF is clearly to their benefit. Being prepared with useful tools and systems that anticipate the toppling of that Regime is clearly not their department.

Try indirect heat? Used NG-fired radiant tubes in sealed annealing furnaces at old Al Tech facility in Dunkirk, NY. Ran exo-endo atmospheres just fine. Don't have numbers for thermal efficiency.

I have a small flexible 11x11inch from Edmund scientific, that in bulk was around $7. It would require some support, as I think it was designed to be glued onto glass. My bigger lense from the proj TV (I presume thats where it came from) is well under F1, so it isn't suitable for ganging up with others. Yes, I think the safety thing is important, I winced when I saw that picture of the jewlery maker, with his head, and bare hands so close to the focal point and work material. Do note that some materials rather than melt, fracture because the heating is very fast and uneven. Thermally created mechanical stress can cause some objects to shatter. I tried to melt a quartz crystal yesterday, but instead of melting, hot chips fly off....


Yes, clearly one needs to create an enclosed/insulated area with some thermal mass to store and smooth the incoming energy.. and this would also become part of the structure that placed the operator in such a way that they are shielded from crossing the focused beams and seeing it hitting its target, so the eyes aren't vulnerable..

Have you looked at and the idea of one of the FreeBSD developers
If its just an oven - Scheffer dishes. Can track the sun via a wind up clock mech.

Its cool stuff. But I worry that the safety aspects might be problematic. Seems like it would be easy to screwup and get burned....

1st rule - avoid looking at the device when in operation.

Any energy handling device runs the risk of getting hurt. People burn themselves on stoves all the time.

Scheffer dishes are deployed in other nations, odds are someone has some safety data they can report.

And again, don't look at the spot where the sunlight is concentrated. Damage like looking at a welder's arc or the sun directly can result.

Thanks for the links, eric.

I've been collecting old C-band sat dishes, have a couple of the old 12' Curtis Mathis dishes with the beasty mounts; heavy duty adjusters for elevation, declination, azimuth, and sometimes you can find them with the actuators still working, though new actuators (12-36 VDC) aren't too expensive. The original feed horns are strong enough to support quite a bit of weight, already focused pretty well, and could be made telescopic for adjusting.. Single and dual axis trackers aren't too pricey, made to operate the actuators. I need to scrounge enough reflective material to cover one of the dishes. Planning a concentrating water heater/oven someday, a mutifunction concentrator.

Then you'll like this one.

And you are quite welcome - happy to share the link'n love.

Wow! Lots of useful stuff there, and I'm halfway done. Thanks again!

I would love to see some more information/comments on the application of solar to agricultural drying applications. I understand that this doesn't fall precisely into "industrial" but we do have plenty of "industrial agriculture" and drying consumes large amounts of energy and must take place in widely distributed areas around the globe.

Does anyone have any numbers on the total amount of fossil fuels used in drying agricultural and forest products. (Does Kris' total industrial use number already include these application?) Drying consumes a lot of energy and these processes, because of the low temperatures involved, are perhaps ideal candidates for some of the solar technologies mentioned in this article.

Here are a couple of links from a quick Google search to start the conversation.

Solar Heat for Grain Drying (Purdue University)

In Indiana, the energy used to dry corn is estimated at 7.65 trillion BTUs per year-a fuel equivalent of 85 million gallons of LP gas! A rather significant amount of this fuel equivalent could be provided by solar energy. `Tapping into the sun' would not only help conserve dwindling fossil fuel supplies, but also hold down your drying costs in the face of increasing fuel prices.

Natural Drying of Forest Biomass for Energy (Forest Energy Blog)

Due to fluctuating fossil fuel prices the use of forest biomass for energy is expected to increase considerably in the future. Today, the demand for high quality wood fuel products such as chopped firewood or pellets has increased price pressure on these products. In order to make the production more cost-effective new methods to optimize their production have to be found. Drying of raw material in the forest in order to improve the quality of the raw material and to reduce transportation costs can considerably improve the overall efficiency of the supply chain. It also enables longer storing periods and decreases GHG emissions and dry matter losses during storing.

Design for lumber dry kiln using solar/wood energy in tropical latitudes (USDA Forest Products Laboratory)

Developing countries with a timber resource that can be manufactured into finished products either for local use or export often lack the capital to build high-cost dry kilns. Many of these countries are in the tropics where solar radiation and ambient temperatures are high. The low-cost solar/wood energy lumber dry kiln described in this report was designed and tested by the Forest Products Laboratory (FPL) for such countries where solar dry kilns can be built and operated at low cost.

One of my favorite designs is sort of a solar amphitheater for the farmstead/community center, where a few focused heliostats sit amid a semicircle of Applications, if you will, and the duty-cycles of the collectors can be programmed to serve whichever Applications need some heating time.

Applications along the semicircle could include,

-Woodshed/Kiln for curing either firewood or Building Materials (whatever you need, really.. soggy boots? Quick Drying of a Painted or Varnished Object..

-BakeOven Room (also Boiling, Crockpots, Deepfrying.. other cooking processes)

-Sauna/ Showers/ Bath

-Laundry Washing

-Laundry Drying

-Small Industry Rooms (Heat Drying, Ironing, Melting/Casting, Soldering/Welding??

-Stored Heat Medium (for living space heating and washing)

-Stored Heat Medium/High (for cooking, etc)

And the combination of collectors would be able to aim at these neighboring tasks either separately or in conjunction, depending on the requirements, speed of heatup vs heat maintenance, etc..

It's good to keep in mind how smart modern controls can be. one of my favorite concepts is a big field of small heliostats, each with a control that decides which of the many small power towers it will point at as the sun moves. So each heliostat will swing from one to another tower as logic demands, and the whole field of heliostats is always near full utilization, unlike the present ones in which a huge power tower is surrounded by dumb heliostats that only point at it, and so during part of the day are not fully effective.

So of course, a logical extension is what you suggest, you put any one of those targets up the pole when you need what it does--like boil teapartys.

I looked at my own home layout and I have a great opportunity to put some of those smart heliostats in the north field, all putting their watts on the side of our house. But somehow my wife is a bit timid about x kilowatts on her wood shingles.

BTW, my cheap pool heater domestic hot water layout works great. No propane all summer. Plenty of very hot water. Everybody should do it. Everybody should be FORCED to do it.

Oh yeah, you reminded me of the other main use, which would be for lighting.. toss a de-concentrated beam at a spot (fireproof) on the house which channels a lightpath to a few main rooms..

Whatever.. like you said, the control tech is quite simple now.. even using basic Transistors for comparators gives one lots of options.


Actually, Bob, it seems to me that this general idea of a lot of small smart heliostats is so good and so versatile that we (ie, you) aughta hammer on it a bit harder. I visualize cities covered with them, programmed to switch targets from here to there as is best to do for the moment.

So here we have a wallmart, and all around it we have heliostats stuck on the sides of buildings, or hills, shining their light on a solar/freezer on the wallmartroof that keeps all those consumers happy, well lit and all that.

Then, after a few more K years of evolution, we might at last figger out that it would be smarter to just relax, forget the wallmart part altogether, and just go back to doing things only when its the right time of year where they take no work to do, like islandboy says below god intended us to do.

PS. I took a mirror out in the north field, aimed it at my wife's home office ceiling to lighten up her bookkeeping tasks a little, and heard the resulting shriek from 100 meters thru a pretty thick wall. Conclusion, too much is too much.

I think the idea of using solar to provide heat for some industrial purposes is great. Sure, you can criticize the idea by saying that it won't work (currently) for smelting aluminum (compared to cheap electricity in Australia) but that is ignoring a lot of places where it could work, even just as a suplement.

Could anyone recommend a design of a solar oven that works well in the tropics? Importing one isn't an option and I have tried a couple of times to make one but my instruction following and construction skills are not the most formidable (I haven't glued my hand to my face in years so I am getting more competent but...).

My household is a great example of where a solar oven would be great. I don't work in the middle of the day and have a balcony that is exposed to the sun so it would be easy to replace lunch's gas with solar, reducing the frequency at which I must go hunting for a gas refill. Cooking gas is cheap (10BsF) but not always availlable --last time I had to get a refill I spent 270BsF in taxis and 8 hours before finding a store that was in supply.

I think that scene you paint, finding gas, would be a perfect short film, set in one of those 'Silver Aircar Cities of the Future'...

Reminding me of the Swedish woman who said of America.. "Your conveniences aren't very convenient!"

Eat The Weeds: cooking with solar:

I watched it ... just great. Thanks.

Could anyone recommend a design of a solar oven that works well in the tropics?

Back when we had profiles - I had such info in it. (many in India) (the pressure cookers)

I made a Cookit, early this year, and found that it made excellent cooked rice and beans. Long slow cooks, much better than on the stove. I used foil on cardboard and a foggy night destroyed it :( Now it is the rainy season I am not trying but I have saved the old fridge carton to make some replacements in the dry season. I am trying to find better reflector material but no such luck yet.


I've seen them made with the fold up reflectors used in vehicles to protect the interior from the sun.

I think it's 3M that's been mass producing reflector film material for a while now. I think it's going to be used as the cheaper substitute to silvered glass mirrors used in concentrated solar schemes.

I haven't built more than the occasional 'quick solar defroster' with them, but I have a growing collection of Aluminum PiePans.. since my wife likes to make Pie and Quiche, but hasn't made the hurdle of doing her own crusts. But I've been keen to make a shallow parabolic form to remold those into reflector dish-parts, and I'd have to imagine they would assemble into a great oven. That heavy gauge Disposable Baking Pan Aluminum is fairly offensive and wasteful in it's original use, but could become a very durable Solar Oven. I'd make these pans into Hexagons, possibly, with wire-frames on each, to be assembled into the dish. (The fun part is coming up with a clip, hinge or linking approach that makes setup and breakdown of this easy, solid, and non-destructive of the parts. Afraid I don't have one handy to try to offer at the moment, tho' I am fond of clothespins, velcro, buttons and little magnets.. or maybe those tight little clips that hold on the "HELLO, My Name Is!" Tags. They might be very good for connecting pieces like this.)

My buds in the 'NewEngland R2D2 builders club' have also been perfecting the art of polishing Aluminum down to mirror shines with ultrafine grits and lubricants like wd-40.

Instead of cardboard, consider finding some 'Coroplast', the corrugated plastic that's used for temporary signage along the roads, like political campaign signs. (Usually PolyPropylene and Polyethylene, tho' many polymers are used in this form for Greenhouses and other things) After the election season, I scavenge piles of that, which makes a great weatherproof construction material. I also grab the wire hoops that hold up the cardboard Pol. Signs.. Usu 3/16" steel wire.. great for a lot of needs.. likely including framing up structures for Solar Ovens!

Thanks for the suggestions guys but we don't have anything high tech, such as sheet aluminium, around here :) The only Coroplast I've seen is in pre-formed archive boxes and expensive that way. I'm thinking of trying mylar gift wrap to fix on the carton, let it dry all the way through then varnish the back side of the carton. I may well be getting busy after the rainy season so I might just make a simple Cookit for now and look towards using old mirrors from the bazaars for the reflector once I move. Oh, adding square panels above the original petals gives it a good boost.


Mirrors is a really good idea, if you ever see those cheezy full-length ones thrown in the trash after one corner gets chipped.. or heck, even if it's broken right in half.. the Meatloaf doesn't care!

But I'm surprised you don't see those cooktrays around.. you know, the big throwaway aluminum pans used for a pile of ribs at a picnic? I thought they were in park trashcans everywhere.. alas.

I think the mylar could be great, though.. maybe come up with a tri-fold frame from old dowels or empty screen frames or such, and when folded open the whole thing stands on its own.

It all comes down to what spare materials you can get your hands on. I've even toyed with gluing a bunch of Mica onto Thin Plywood for a reflector, if you have that sort of mineral in your streambeds, etc..

The trays are expensive and only appear at Thanksgiving and Christmas. Ply might be an idea, varnished first. Not seen mica but I'm not sure why you'd use it, it doesn't strike me as very reflective.


Solar heat is a great way to get more oil out of fields that are now considered exhausted. Getting that remaining oil out using gas would cost more money and energy than the oil could return, but using a free source of energy changes everything.

I don't think this would be such a great use of solar energy. I don't think this particular technology "changes everything." Do you know of anyone doing this?

I know of a pilot project using solar troughs to provide steam for steam flooding. It's located in central California. EDIT: It's cited in this posted article we're commenting about.

I think it'd need fossils for back up much of the time, unless someone can explain to me why it's advantageous to only inject steam when the weather is cooperating.

As I look at the project, I'm wondering how much grant monies was used to fund it. Really, mirrors INSIDE a greenhouse? Is that really necessary?

Does the steam injection need to be 24/7? Variable rate (of oil extraction) is essentially very similar to storing energy as product. I'm not even sure if the well output varies quickly enough, would the varaiation even be noticed? With this sort of input, in theory you could extract oil at well under EROEI of one.

I don't think this would be such a great use of solar energy. I don't think this particular technology "changes everything." Do you know of anyone doing this?

It would seem that the oil producign country of Oman disagrees with you, posted in today's Drumbeat;

Oman Awards Contract for Mideast’s First Solar Oil-Recovery Site

Petroleum Development Oman, a third owned by Royal Dutch Shell Plc, awarded a contract to GlassPoint Solar Inc. to build the Middle East’s first solar plant generating steam to boost output from aging oil deposits.
The 7-megawatt, four-acre site will deploy enhanced oil recovery, or EOR, technology, injecting steam into oilfields to loosen denser crude, according to an e-mailed statement today from Fremont, California-based GlassPoint. Previous such operations have burned natural gas to produce the steam.

This is about as good an industrial application for solar steam as you will find. Unlike a factory process, this does not require 24/7 steam, it just requires X million btu's of steam per day or week. It does not need to be "dry" steam for a steam turbine, or be highly treated water for recirculating - it can even be done with seawater!

I think that Glasspoint is onto a good thing here.

This field, as set up for 7MW, could also desalinate about 80,000 gallons of seawater per day - enough for a town of about 2000 people.
It could also treat the same amount of sewage per day, producing clean water and dried sludge - suitable for burning or composting

Another process that could be adapted to use this, and keep the NG just for backup, would be ethanol production - from the malting and mashing of grain to heating the fermentation to the distillation itself.

As mentioned above, crop and lumber drying, and many other drying processes could be run by this, as could commercial/hospital laundry, food processing etc etc. Any process that needs steam is a candidate. Whether there can be full substitution or only daytime depends on the process in question, and the alternative fuel prices, but the more you look, the more applications you can find.

It would seem that the oil producign country of Oman disagrees with you, posted in today's Drumbeat;

Nice find there, Mr. Nash. The better point is about other uses for the solar ... like desal. So, I'll qualify what I wrote. If it's built dedicated to blowing the last drop of oil out of the ground, then I don't like it. If they can use it for other things, eventually, then it seems more palatable.

We need to get going with renewables, and using solar to eek out the oil sends an ambiguous message. It might be good to leave a little oil in the ground for future generations in case they need it for oh it don't know what.

But the points about using solar thermal are all good, it seems. We tend to hear about using solar to make electricity. The best payback is still with solar thermal, including plain old flat plate collectors for domestic hot water -- still way under-utilized. We saw efficiencies of 40 percent or so, which is 2 to 3 times the efficiency of PV.

While rambling on the subject, here is a comparison of Heliodyne flat plate collectors vs. evacuated tube.

BTW, I sold tons of those Heliodyne flat plate collectors in the 1980s -- a lot of them still working great. Tomorrow (AUG 10), we have techs out for a minor repair to a 70-panel system I designed and sold in 1984.

So, I'll qualify what I wrote. If it's built dedicated to blowing the last drop of oil out of the ground, then I don't like it. If they can use it for other things, eventually, then it seems more palatable.

Agreed absolutely. I suspect the decision in the Glasspoint examples is simply that it is cheaper than NG is , or perhaps than NG will soon be. When the Bakersfield system runs out of oil to extract, it could be re-purposed to other things, like crop drying, ethanol, etc. I really think there is a lot of potential there.

One change I would like to see to tax rule, to really encourage these things, would be to allow a 100% write off of capital used for renewable energy systems. This then matches the write off to the spending - all up front. Then the Berry Petroleums would do another one the next year, and the next, and so on. The gov still gets its tax money eventually, but can afford to take a longer view than the companies. Even if the company goes broke, chances are that someone will take over and operate the solar facility,a s once built, it just makes lots of energy.

Good to hear you are in the solar business - do you have a website for it?. My father put flat panel collectors on the roof of our farmhouse in Australia in 1978 - they are still working.

I am with you on tube-v flat panel. The tube systems always struck me as a very interesting, high tech, high efficiency approach, but not worth the cost. Just like the Solar Fire guy says, it is cheaper to go with a lower tech system and simply add more area, if needed.

The major plumbing contractor in my town does installs of both tubes and panels, and he says that people with large houses and lots of money and want the "best" system go with tubes, and people who are pragmatic and want the most hot water for the least amount of resources (=money) go flat panel.

And pragmatism is the element that I see emerging in things like Glasspoint, and Solar Fire. The high tech approaches seem to prove only that they are too expensive to be worth doing, whereas these guys started with the premise of it has to be cheap enough to be implemented, and the efficiency is secondary, at best.

A similar approach was sued by Carrier/United Technologies in developing their PureCycle ORC energy systems. Their approach was that waste heat or low grade (unused) geothermal, is free heat, so they need not be too concerned about how efficiently their system used it, as, presently those heat sources were not being used at all. so their approach was to engineer their system as simple as possible, use as many existing. off the shelf components ass possible, to keep the cost/kW down, and thus the ROI up - and this has worked out very well. The project decisions are not made on energy efficiency, but cost efficiency, something that many of the high tech developers seem to miss.

best hopes for appropriate solar!


yesterday there was some interesting dialogue about pyrolysis and bio-char. Could solar thermal be used in that kind of process. How small could one make it? In countries like India water hyacinth are a major problem with regard to waterways. Seems to me if one can use switch grass as a feed stock one might be able to use water hyacinth for pyrolysis using solar thermal. That would essentially be the an incredible solution. Provide rural employment in the harvesting of the water hyacinth, create a bio fuel, produce bio char and free up the waterways.

Certainly under concentrated sunlight, just about anything that can give off volatile gases that can combine exothermically with oxygen, will burn -almost instantly. It could be messy though, gases given off are likely toxic, and they could dirty-up the optics.

My comment is a little off topic, but it is related to the subject under discussion-solar thermal capture and use.i have finally finished my solar domestic hot water system.It is doing a bangup job of supplying 100 % our domestic hot water needs so far.How well it will perform over the winter is yet to be seen.

Exclusive of my own labor, it cost only about nine hundred dollars to build it.A major part of that was for the copper tubing.It will be saving lots of kilowatt hours for several decades at least with only very minor repairs anticipated.

I am ready now to build a solar cooker.

I would appreciate any other members with links to sites having plans for well designed cookers posting them.

I'm especially interested building in a parabolic collecter with the focal point INSIDE the dish, so the collecter can be covered and the pot placed under the cover glass, but I have not yet been able to find the measurements necessary for the proper curvature of the collecter.

Thanks in advance.!

I posted a link in this thread from Eat The Weeds. He has 4 solar cookers, and despite being a popular guy, he seems to respond to most questions directed at him at his youtube account.

A parabola has the formula Y=X*X. The slope of that line is 2X. When the slope is equal to 1, the surface of the dish is inclined at 45 degrees, and the reflected rays will be horizontal. So with the sun directly overhead the focus will be at x=0, y=.25. You can scale it up or down to fit your needs. If you let the radius by the sqareroot of a half (.707), then the height is a half, and the focus is inside.

Follow the Sheffler dish links. You can copy what is already working for others.

Try here

See my comment above about the Cookit, I used a tube of chicken wire inside a turkey oven bag as a container and a spayed black aluminium pot inside for the cooking. Stood the pot on a wire pot stand inside the chicken wire. No problem boiling, had to use an oven bag as polythene just melted.


Built It Solar has all kinds of plans for solar-related projects, including cooking:

Nice going on the water heater, OFM. There are some great links for solar cookers folks have given. One thing I noticed in your post: I think you may be trying for too high a temp trying for a focus of a parabola. There is no need for that type of precision for a solar cooker.

I recommend watching this video. Although it is for a pre-made commercial product, you will get some good ideas here:

You might check out this guy's good idea.

He figured out that you can use two simply curved mirrors to get the focusing effect of a compound curved dish.

I particularly like the solar wheelbarrow.

It could work almost perfectly.

The receiver can just be a black metal vessel, and you load the wood in, and you will get out of it char, tar, and gas. The gases can be run through a condenser, and if you put them through a copper mesh catalyst, you will get methanol, equivalent to 1-4% of the original wood weight. Some of the gases are non condensible, but can be burned as gas fuel for cooking, steam or an internal combustion engine.
The tar may be useful depending on the wood. Pine produces pine tar, used for waterproofing ships, cross country skis, as skin/scalp dermatitis treatments, can be a fuel, and on and on.

the charcoal, of course, can be buried for biochar, or used in your Weber to produce the best barbecued meat you are ever likely to have (I suggest good steaks marinated in Scotch and Worcestershire sauce, but that's just me).

The condenser will produce not only methanol, but all sorts of other liquid stuff, acetic acid, and so on, which could be separated and used, but, other than the methanol, this is not likely to be worth it.

However, if you take the condensate and put that onto the charcoal before using it as biochar, you are inoculating the charcoal with lots of good food for the soil bacteria.

All of this, except for the biochar in soil part, is how they used to do it in Scandinavia with Pine pitch making - just fill a metal vessel with the wood, make a fire under it, lead the top vent from the vessel to the fire underneath, and have a drain at the base of the vessel on one side to collect the tar. Centuries old stuff.

The difference with solar, is that you will get higher yields, as you don;t need to burn the wood, or the off gases, to run the process.

You'll see me being a negative Nellie throughout this thread with regards to smelting or refining metals, or making cement, but I can imagine concentrated solar being used for lower temperature processes like what you describe.

You could do it using a solar trough scheme. The vessel would of course be the linear receiver, and material could be fed into one end and driven along the pipe using an auger.

I agree that while it is interesting that we have demonstrations of how solar can be used to melt/smelt metals, or even make cement, there are far more low and medium temperature processes that can be done first.
There may be situations, like the islands and cement discussed below, where local conditions make it worthwhile, but in the current context of westernized countries, there are many, many applications of bulk heat where solar can work.

If NG goes back up over $8/GJ (MMbtu) then we will start to see some more interest in them.

You'll see me being a negative Nellie throughout this thread with regards to smelting or refining metals, or making cement

All one needs to do is the calculations of the energy needing to be delivered into the target area (watts per meter) VS the watts per meter of solar to see direct solar to the high energy smelting/cement making isn't gonna happen in industrial sizes.

PV electochemical refining can happen. Less than .5 volt to get pure copper as I remember.

A concentrated solar thermal electricity generation scheme with storage could pull off batches of arc or induction furnace steel or other metals much of the year.

The oil/gas/coal is old solar energy, processed into a far more stable form then photons, then released as an impulse.

Rather than picking up some post-processed stuff and saying "Oh hey, lets value this at the cost of me just finding it"
humanity should have been thinking "This is made of photons. From long ago. What is its value if I had to take this kind of thing from photon to the release of the energy".

Humans have therefore grown far beyond the carrying capacity of the cycle of photons and its ability to design for failure as demonstrated by the un-insurability of fission reactors without the Government backing of Price-Anderson.

it is very inefficient (and thus utterly expensive) to convert electricity into heat.

I'm afraid I stopped reading at this point.

The conversion of electricity to heat is just about the most efficient energy conversion known - very nearly 100% efficiency. And using electricity to move heat around can get you six times as much heat as the electricity you use.

If heat becomes expensive, heat recovery will become economic, and manufacturing processes will become continuous rather than batch. There isn't a problem.

But you have to produce the electricity first, no? Then how much of your 100% efficiency is left?

But you have to produce the electricity first, no? Then how much of your 100% efficiency is left?

You have a point in that solar thermal processes usually produce a much higher percentage of the available energy into usable energy... for example a thermal collector might capture 40% as opposed to 15% for PV.

However, the equation has changed some in recent years. Copper prices have skyrocketed while PV panels have dropped in cost substantially.

The cost per sq foot of collector of copper flat plate is roughly double that of PV. A contractor-installed system will run less than $70 per sq ft for PV -- probably double that for copper flat plate. If this trend continues, it may become cheaper to heat water with PV than copper.

would it make sense to replace the copper with aluminum?

would it make sense to replace the copper with aluminum?

I haven't seen any aluminium collectors -- it might work though. I've heard of some collectors that use a mixture of aluminium and copper.
A Google search on

aluminum copper solar collector

presents a long list, e.g.

That makes sense.

Aluminium has essentially 100% replaced copper for cooking - I suspect the same will happen in other heat transfer applications where materials cost is a big factor.

The cost per sq foot of collector of copper flat plate is roughly double that of PV.

Yes, but the energy collection can be double or triple, so it comes out similar.

I think it's only fair to compare complete systems, at this point.

It is certainly very easy and convenient to convert Electricity to Heat, and we do it all over the place.. but the volumes of WattHours involved really only work in a world with a lot of cheap watts. It seems quite likely that Electricity Rates might not be sitting in this range for much longer. What then?

Look at a Space Heater driven by PV, or a Space Heater driven by CSP Solar Electricity, and then at any form of Direct Solar Heating, and I'm sure it's clear which would be the most economical source of that heat.

This is a subject that I have wondered about myself from time to time and it is nice to see someone give it some deeper thought.

It might not be the 1st world where these things will be first put into practice. Some countries (island nations, in particular) have especially high energy costs, and using solar power to make cement for example might be more economic than importing oil or natural gas.

I can't envision a solar kiln making cement clinker. Those giant things are fired from within directly with various kinds of fuel, and lined with refractory brick.

Those island nations probably import their cement, along with many other essentials.

Sure, but the point here is that this may allow them to make these essentials themselves. If island X has the appropriate raw ores at hand, like limestone, then they can produce the cement themselves, Better yet, if they have pozzolanic volcanic ash - which was the basis of Roman concrete, then they can make better cement still. There are *many* islands have volcanic ash/pumice deposits, though they may not all be pozzolanic.

The smaller the island, the more expensive their cement imports will be. This is not to say solar furnaces are there yet, but this could still be a good application for them. meanwhile, there are many other applications of solar energy for the island nations, from cooking to desalination to metal melting/recycling. Cement production can come later.

My island nation happens to be very rich in limestone and has had a cement factory since 1952 so, the majority of all the cement used since then has been locally produced. All the fuel used to fire the kilns has always been imported as has "many other essentials".

Having been built at the height of the expansion of the oil age, the plant originally used oil to fire it's kilns. During the 70s oil shocks and all the subsequent ones, this became a source of very unwelcome escalations in the price of local cement. Eventually, changes were made to allow the use of coal as the fuel.

The plant is an imposing (hideous) structure set against the the backdrop of the hills at the eastern end of Kingston's natural harbour. The road that leads to both the international airport and the southeastern end of the island goes right between the plant on the north and it's sales office, finished product storage silos, delivery yard, wharf and coal storage shed. As a result anyone who has passed through the airport cannot avoid noticing it.

In recent times I have often wondered if the abundant intense sunshine could be used in some sort of concentrating solar kiln, to produce cement in a more sustainable way. As I have said many times before, I am constantly reminded of how much heat energy is present in solar radiation by the concrete slab roof of my apartment, currently at 32.6°C(91°F) on it's way down to somewhere between 30 and 31 °C (86-88°F) that, it should get to about 8:30am (EST). It then starts it's relentless rise to somewhere above 35°C (95°F) by 8:00pm, an hour after sunset! Although clouds and rain reduce the output of my solar PV, they offer a welcome reprieve from the heat.

Alan from the islands

It's been nearly four years since this concerned dad of three great kids first visited here, looking for answers, perhaps a splinter of hope. But still we're proposing business-as-usual objectives with "new" technology (it isn't really new, fundamentally) that will never scale up nor truly be sustainable.

Until the PTB voluntarily steer us away from the "growth is good" mantra (unlikely) that many here also fail to consider, I'll continue to remain pessimistic about our global prospects. Do we really think there'll be the trillions $$$$$ available anytime soon, all things considered?

Matt B

Probably not.

A collapse seems to be unavoidable as is the resulting chaos.
However, unless the climate kills us off, there will be a time after BAU.
It is then when all the stuff discussed here becomes vital.

At least that is my hope.

As for your gloominess, I can relate.
It's no fun to be Cassandra.

Solar power distributed thru district heating networks never became more then experiments in Sweden. What has worked out well is summer heating of hot tap water at camp sites, summer pool heating, reheating of too shallow or too densely drilled grund source heat pump wells and combinations with wood pellet heating to avoid a need for inefficient low power running of the "boiler".

Some, perhaps manny, district heating networks could be run with a slightly lower temperature in summertime and utilize solar heating but manny of the large systems have a summertime excess of heat from garbage incinerators and industrial waste heat. Where I live are prices lowered in the summer to increase consumption and heat is donated for free too a giant outdoor pool since its cheaper then building a cooling tower.

There has been large scale experiments with storing summer heat in large insulated water cisterns and one with a giant torus shaped bedrock chamber to get the best volume/surface ratio. Such high temperature systems turned out to be too expensive and have too large losses. There are sometimes suggestions to build such for storing free excess heat from industries. A fair number of district heating networks have 12-48 h storage cisterns to even out the load and they can be large.

Most large scale heat storage systems work with low temperatures. The biggest one is at the Arlanda airport in a natural layer of ground water rich gravel. At summertime is cold water drawn from it to chill the airport and reinjected as warm water and at wintertime is warm water drawn from it to heat the ground at the ramps etc and reinjected as chilled water.

Btw, conversion from electricity to heat is almost perfectly efficient and even in hot systems such as induction heaters, arc-ovens and plasma generatots are the losses fairly small. The problem is that electricity is scarce and can be used for even more valuble processes then simple heating. One way to solve the problem would be to cheat and move the high temperature processing to areas with abundant hydro power or stable societies with nuclear power and then be content with using solar PV or other for running communications, lighting, microwave ovens, light industries, small scale AC, etc.

I have been thinking about this subject a lot recently. It was part of my motivation for attending the Intersolar North America trade show recently in San Francisco. The primary reason was to get some "face time" with inverter manufacturers to see which ones might support grid interconnections for Jamaica's 110V 50Hz residential power supply (only three or so countries on the entire planet that have this combination of voltage and frequency). I was also on the lookout for low cost pre-configured off grid systems that would be affordable for very poor people who's only choice might end up being a little bit of renewable electricity or none at all. Then, there was the chance I might run into something that is not on my radar at all.

I was very disappointed by the lack of solar thermal applications apart from water/pool heating and a couple of utility scale trough/Fresnel mirror projects including Areva Solar. I have been noticing applications in my neck of the woods that, could benefit substantially from concentrated solar thermal process heat in the range of 100°C to 400°C. These include food processing, baking, institutional cooking and plastic forming/injection moulding. The key feature is that, these processes require heat above the boiling point of water up to the melting point of most plastics. I have come to conclusion that there is a dearth of ready made solutions because, the economies with the engineering and manufacturing resources to provide large scale solutions, do not have the resource (sunlight) year round with pretty much all of them being in temperate climates and having to deal with this season called winter. In addition several of these economies either have had and in some cases still have, access to abundant indigenous fossil fuel resources. This produces a particular paradigm of a energy (heat) source that is reliable, affordable and available to the users on demand.

In the tropics our situation is fundamentally different. This was brought home to me very forcefully, during a solar water heating course I attended the week after Intersolar. A great deal of time was spent on freeze protection for systems. This is NOT an issue at all in the tropics, certainly not at sea level. We just don't experience freezing temperatures ever, unless at extremely high altitudes. We also don't have large variations in hours of sunlight, varying from 11 hours in the "winter" to 13 hours in the summer. Some tropical countries have no indigenous fossil fuel resources at and most(all?) tropical countries are not nearly as industrialised as the leading industrial nations. I would venture to say that none of the worlds heavy industries (ship building, trains, automobiles, earthmoving/farming/construction machinery, metals and glass) have traditionally existed in the tropics. (why is that?) So, the resources are different and the needs are different.

I must say that Peak Oil awareness has led to an entirely unorthodox view of things. It strikes me that we have become totally accustomed to doing things whenever we want to, wherever we want to (skiing in the desert in Dubai). The old saying "Make hay while the sun shines" has almost completely lost it's original meaning, evolving into "make use of opportunities when they present themselves". I suppose that, as we enter a world of post peak everything, that old saying will regain it's original meaning and we will have to make things when the (renewable) energy resources are available to make them. As inconvenient as this may seem to us now, Peak Oil (everything) means a lot of things are not going to be as convenient as we have gotten used to.

If we start to put the infrastructure in place now, we may end up in a position where it will be possible to manufacture things that we will otherwise not be able to manufacture in the absence of abundant fossil fuels.

Alan from the islands

>The key feature is that, these processes require heat above the boiling point of water up to the melting point of most plastics.

So do the best steam turbines, yet they're used in solar thermal schemes. The receiver tubes on parabolic troughs can heat thermal fluids to over 700F.

Although it is perfectly possible to convert electricity into heat, as in electric heaters or electric cookers, it is very inefficient to do so.

With respect to cookers, that's not always the case -- induction hobs are typically two, three or four times more efficient than gas at point of use because all of the energy is transferred to the cooking vessel as opposed to being absorbed by the supporting grates and surrounding hardware or, more critically, lost around the sides of the pot.

Even at full flame, our portable induction hobs easily outperform the 4.5 kW burners on our gas cooker. As a simple test, I boiled 0.2 litres of room temperature water using both fuels. To make the comparison as fair as possible, I selected a large frying pan for the gas burner to ensure maximum heat transfer and a standard size pot for the induction unit. The induction hob brought the water to a rolling boil in two minutes and twenty-eight seconds using a maximum of 1,119-watts at 114-volts and consuming a total of 0.04 kWh. The gas hob completed the same job in two minutes and forty-three seconds -- a difference of just fifteen seconds -- but, in the process, used four times as much energy, i.e., 4.5 kW of propane versus 1.12 kW of electricity.


Interesting... Seems like there's an opening for more efficient gas burners (or even pots themselves); you could be onto a $$$ winner there! ;)


One of the side benefits of switching from propane to electric is that our kitchen stays cooler during the summer months and we don't have to run the extractor fan nearly as much, so less conditioned air is being sucked out of our home (with propane, the combustion by-products given off pretty much meant that the fan ran continuously whenever one or more burners were in use).

BTW, I obtained our first induction hob by redeeming credit card points and the second I bought on Kijiji for $20.00; with luck, you can get set-up at a reasonable cost.


Honestly, my middle aged a** has never heard the word "hob" used in The States. Today I learned something new.

I think I have a great question. How would your induction stove compare to a microwave for heating water?

I poured 200 ml of room temperature water into a small bowl and placed it into our microwave. On high, it took two minutes and thirteen seconds to bring this water to a rolling boil. I don't have the ability to plug our microwave into a power monitor as it's a built-in unit, but it's a Panasonic inverter model and the nameplate tells me that it uses 1,430-watts and supplies 1,100-watts of cooking power. Assuming that the actual draw is, in fact, 1,430-watts, this suggests its energy usage was 0.053 kWh.

Our nine year old inverter microwave has a theoretical conversion efficiency of 77 per cent (1,100-watts/1,430-watts) whereas the one used in the Treehugger link below has a conversion efficiency of 67 per cent (900-watts/1,350-watts).


If what we read is to believed, the current generation of Panasonic microwave ovens are even more energy efficient -- 91 per cent, according to: Induction hobs have a conversion efficiency of 80 to 85 per cent, although I've seen claims that suggest it could be as high as 90 per cent (e.g.,


Thanks for the great reply. BTW, I think the newer microwaves in addition to being more efficient also use less copper and aluminum. They don't use giant MOTs anymore.

I'm going to have to look up the new tech later on. I remember a geek with a youtube channel that had dismantled one with the newer electronics.

Hey, do the induction appliances have a setting so you could cook as low and slow as a crockpot?

A wild guess: the crockpot will be much more efficient, as it's heat input is within an insulated chamber, which will also prevent heat loss during the very long cooking period far better than a steel pot.

My guess would be that it's more inefficient, since the crock pot isn't directly heated, and it's not that well insulated.

Sounds like a bad crockpot!

A crockpot is one of those rare cases where it is worth getting the plug-in appliance, rather than (or in addition to) stovetop one. My electric crockpot sits inside the insulated metal surround, with the heating element at the bottom. After six hours, the outside of the jacket is still warm, and only the glass lid is hot, and the condensation on the lid forms a seal around the rim of the lid, eliminating air leakage.

For a cheap consumer item, I think it is spectacularly energy efficient, and is the *only* way to do a good corned beef - add good slosh of Scotch and plenty of peppercorns.

I have seen the cast iron stovetop/dutch oven type used for a solar cooker, and it is quite effective, as long as you keep the sun on it for several hours.

Have you actually done the math to see if it's more efficient than an induction plate? The induction plate is heating the pot directly, and a crockpot is heating very indirectly. It only has a minimal amount of insulation. About 1/2 inch.

"I have seen the cast iron stovetop/dutch oven type used for a solar cooker, and it is quite effective, as long as you keep the sun on it for several hours"

4 hours for a 4 pound chicken.

a crockpot is heating very indirectly.

?? What do you mean?

The ceramic pot is heated by the element in the base of the crockpot jacket, so that counts as indirect heating. Induction heating uses the electric(magnetic?) field to heat the metal directly.

However, since I don't have a Kill-a-watt meter, or an induction plate, I can't do that comparison.

I can confirm the crockpot jacket has about half an inch of insulation - exactly half an inch more than a stove top one. So while an induction plate may transfer the heat slightly more efficiently, the uninsulated crockpot will lose more heat to its surroundings - and I suspect this will more than make up the difference.

We are splitting hairs here - both are relatively efficient - and delicious - ways of cooking.

Hi Paul,

Swing by your local Canadian Tire and pick up one of their blueplanet energy monitors ( which retail for $24.99. One of the nice things about this device (beyond its low price and ready availability) is that it has an internal battery backup so you won't lose your data if the event of a momentary power cut or if you should need to unplug it for any reason. The other thing is that it shows the actual runtime of the appliance as opposed to the total elapsed time since it was last reset. So, for example, the one that monitors our electric water heater was reset on July 23rd, some 446 hours ago, and it shows that the water heater has been energized for 57:30:26 hours during this time and consumed a total 73.01 kWh.


There's someone in this thread that might compare the two for us. I'll ask, you know, for science.

Gesh, the sacrifices we make in the name of science... OK, I'm making scalloped potatoes in our Rival Smart Pot 38601. It's rated at 275-watts and plugged into a power monitor, so I should know the final results within another four to six hours depending upon how long it takes to get the job done (right now, it's pulling a steady 250-watts at 116-volts). Off hand, I can't say this thing is very well insulated -- just twenty-five minutes into the test and the exterior surface is already 39.8°C.

The Verdict: Total cook time: two hours and forty-five minutes. Total energy use: 0.69 kWh. Exterior surface temperature (sustained): 53.5°C.


Ahh, but how did it taste? That is the real point of the exercise, and the best part of science, when food and science overlap.

When my my high school physics teacher taught us JJ Thomson's "raisins in a plum pudding" theory of electrons, he said we would investigate this by experiment in our next class.

Sure enough, in our next class, we made raisin and plum pudding - quite possibly the best electrons I have ever tasted!

Even though the theory was proven incorrect, the results were great.

Best hopes for the science, and art, of cooking!

Btw, 275 watts seems pretty reasonable to me. A metal pot on the induction plate, simmering away (even at 275 watts) would likely have a higher surface temperature still.

I will pick up one of those devices at Canadian Tire tomorrow - thanks for the tip.

The meal was great, thanks. In practical terms, 275-watts has proven to be excessive as whatever you cook has a tendency to stick and burn (I've noticed that on the four and six hour settings the heating element never cycles off). The stoneware liner has cracked so I'll be looking for a replacement model with a lower rated wattage, ideally 200-watts or less, and hopefully one with better side wall insulation.

Update: I picked up a slow cooker at Sears for $18.89 after all discounts (a clearance model that normally sells for $69.99). This unit is rated at 170-watts or about 100-watts less than the one it replaced. I cooked five boneless/skinless chicken breasts with enough vegetables for four meals for 0.55 kWh. Our toaster oven at 1,500-watts would have consumed perhaps two to three times that and I'm guessing our convection oven (5,300-watts) ten times.


All have a "simmer" or low power setting, but I wouldn't consider them a suitable replacement for a crockpot or even an electric kettle. On the flip side, we eat a lot of stir-fry and if you cook using a wok, an induction hob can't be beat.


A flat bottomed wok, right?

Actually, round, and that's one of the great things about induction. A round bottom wok won't work with a standard electric element or smooth top as there's little direct surface contact and they're not all that more efficient with gas because much of the heat is lost around the sides. With induction, 100 per cent of the energy is transferred directly to the wok and the wok itself becomes the heating surface.


So you have to hang on to the wok so it won't roll off? I have to ask, because I have a traditional style one, which I love to cook in. I used to be a restaurateur, so everything I have is heavy commercial stuff. I couldn't resist getting a nice heavy wok for home use while on a shopping spree for my restaurant 20 years ago. I can't ever get the thing hot enough though. A lot of folks don't know just how much heat your local Asian restaurant's wok is heated up to. Commercial wok stations put out so much heat, that they are cooled with a curtain of water flowing down a back splash and onto the surface surrounding the wok.

I have to get me one of these induction plates. It's my new quest.

If you're interested in commercial-grade equipment, consider the performance of the induction wok featured in this video:

For a portable unit (120 or 240-volts), see:

And I have to apologize... our wok is flat bottom, not round.


Water-cooled wok burners are a significant drain on the water supply and sewage systems of Sydney (and no doubt many other places). The local water authority has invested quite a bit in persuading restaurants to switch away from them when renovating.

A Cookit is good for that application.