Solar Hot Water Heating

We often hear that solar thermal is quite cost effective, but if a person looks into the situation, it appears that solar thermal's primary use is for heating swimming pools and hot tubs. A recent publication by the EIA shows this chart:

In the chart above, the low-temperature solar heating units (140 degrees F or lower) are primarily used to heat swimming pools. Medium temperature solar thermal units (140 to 180 degrees F) are primarily used for heating hot water. High temperature collectors (over 180 degrees F) are primarily used to generate electricity for the grid.

In this Campfire post, we will talk about solar thermal hot water heating--the major part of the little blue bars in the above chart. Sales of solar hot water heaters have been growing since a tax credit for home installation became available in the USA in 2006. I will share some of what I found on the Internet, and ask what your experiences have been.

Tax Credits

Solar hot water heating has been growing in recent years, at least in part because a 30% tax credit which is available from the US federal government on systems that are certified by the Solar Rating Certification Corporation. State and local programs may be available as well. The tax credit is available both for units installed on primary residences and on secondary homes.

Active vs. Passive

There are two basic types of hot water heaters--active, which uses electricity to pump water through the system, and passive, which uses no pumps or electrical equipment. According to Real Green,

Because of their design, passive systems are the simpler of the two. They work essentially like a garden hose left out in the sun, except the container for the water is much, much larger. The sun directly heats the water in a large, rooftop tank, which then flows down into your plumbing system. If the water has not yet reached the temperature you’ve selected on your thermostat, your conventional water heater will need to kick in to finish the job. Passive systems are best suited for warm climates where your rooftop storage tank is in no danger of freezing.

Because of their simplicity, passive systems are usually cheaper and can last longer than active systems. The drawbacks are that they can be less reliable, and require a heavy water tank, or collector, to be mounted on your roof. (Depending on your roof’s design, this may require structural support.)

An active system stores water in a tank inside your house, and uses its pump to move either water or a “heat exchange” fluid through a “collector” on your roof. Collectors are the components of your solar water heating system it to heat your water. Used in freezing climates, the heat-exchange fluid is a non-freezing liquid that carries the sun’s heat from the roof to your tank, where it transfers the heat to your water. The fluid re-circulates to the roof to be heated again, while the water flows on to your tap. (This fluid is usually propylene glycol, which the FDA has approved as an additive in food and medicine. However, it is a suspected neuro- and respiratory toxin, according to the National Institute of Occupational Health and Safety.)

Although active systems are more expensive but more reliable than passive ones, you may still wish to keep your conventional water heater for a back-up. In fact, in many areas, local building codes require conventional back-ups, so be sure to check with your contractor or local government. Active systems using the “heat exchange” method are best for areas where freezing temperatures are likely.

Among the active solar water heating systems, there are two types, according to the US Department of Energy:

Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.

Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

According to the same source, there are two kinds of passive hot water heating systems:

Integral collector-storage passive systems
These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

Thermosyphon systems [require roof collection units]
Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.

Obstacles to Installation

According to the US Department of Energy, there are a variety of obstacles homeowners can run into. This is a list they note:

The matter of building code and zoning compliance for a solar system installation is typically a local issue. Even if a statewide building code is in effect, it's usually enforced locally by your city, county, or parish. Common problems homeowners have encountered with building codes include the following:

  • Exceeding roof load
  • Unacceptable heat exchangers
  • Improper wiring
  • Unlawful tampering with potable water supplies.

Potential zoning issues include the following:

  • Obstructing sideyards
  • Erecting unlawful protrusions on roofs
  • Siting the system too close to streets or lot boundaries.

The systems do require maintenance, and occasional replacement parts, especially if they contain electrical components.

Economics of Systems

How economic these units prove to be will vary by the part of the country, but one would expect them to always be significantly more economic than solar PV. This site says that solar water heating produces energy at 1/3 to 1/4 the cost of solar PV.

When you consider the cost, you will want to include the cost of the back up system as well. (Some hot water systems seem to be specially made as backup to solar hot water systems--for example this propane back-up unit for $599.) Besides geographical location, cost savings will depend on the local price of electricity or natural gas that your current system uses.

To get an idea about prices, I looked at the website of Solar Direct. The site lists three types of systems:

1. Warm Climate ProgessivTube - Solar Hot Water Passive System - No moving parts $1,700 to $2,600.

2. Moderate Climate Helio-Pak - Active Solar Hot Water, flat plate type - Tanks do not need to be installed above collectors - Uses electricity - $2,200 to $5,200

3. Cold Climate Trend Setter - Solar Hot Water Active, evacuated tube - Price range (including commercial) $6,000 to $17,000.

This is the map for which types of this particular vendor's products can be used where:

Obviously this is not intended as a recommendation for the above site--it just had some convenient cost figures available.

Questions for Readers

1. What has your experience with solar hot water heaters? Is it easy to find a contractor, and get around local ordinances?

2. Are the units proving to be cost effective?

3. What parts of the country / world should these units be considered for? It seem like these would be especially useful in parts of the world where temperatures don't freeze and a simple passive solar unit would work.

4. Are there any special issues that readers who want to try this idea should watch out for?

5. Are there any particular vendors or brands you have had good experience with?

6. Have you found any particularly good references on solar hot water heaters?

Also, readers who haven't installed solar hot water heaters, but have thought about the idea, may want to raise questions as well.

There is no doubt that of all the options available for capturing and using solar energy, passive solar hot water heaters give the best bang for the buck.

In Hawaii interestingly enough they are now mandatory.

Hawaii to Require Solar Water Heat in New Homes
Posted: 2010-01-04
Effective January 1, all new homes built in Hawaii will require the installation of a solar water heater to meet the state’s green building mandate, which was enacted in 2008 and slated to become effective in 2010.

Signed into law by the state’s Governor, Linda Lingle, the law actually requires energy-efficient hot water systems, but most builders and environmentalists agree this implies solar hot water, since no other residential type – including tankless water heating and heat pump water heaters – provides quite so much conservation bang for the buck, with greater reliability, as solar hot water.

The ruling is expected to save homes an average of 30 percent energy yearly over conventional homes with gas or electric hot water heating. This is good for homeowners, 30 percent of whose energy bill is devoted to heating water, and for Hawaii, whose almost total reliance on imported oil (99 percent in 2006, and little improved since) creates a precarious energy security scenario that has politicians nibbling their fingernails.

Here's a quick graphic I created that shows how a passive system works.

Solar hot water

In the diagram the hot water tank should be higher than the solar panel because hot water is lighter than cold water so if the water tank is lower the thermosyphon effect will never get going and there will be no circulation in the system. I also think is better to have the hot water line that goes to the tank go all the way to the bottom of the tank. And the hot water line that goes out from the tank should come out of the top of the tank because that is where the hottest water is.

In the diagram the hot water tank should be higher than the solar panel because hot water is lighter than cold water so if the water tank is lower the thermosyphon effect will never get going and there will be no circulation in the system.

Good points! Lousy graphic. Only works if you imagine you are looking down from above at a system on a roof.

well.... it's not termosiphoning, because he "installed" a boiler. when you're talking boiler, you're talking forced pumping, and it doesn't matter where the solar panel is, or if it's upside down.

but the main idea is clear, that of preheating water using solar panels, so that the boiler would use less gas / electricity

Arbelos, I believe you may be confused. The thermosyphon effect happens within the passive solar thermal panel (in the case shown, the ProgressivTube system). Once the hot water leaves the panel it must flow to a storage tank and to maintain the "passive" status that tank will most often be at a lower elevation to maintain gravity feed.

Take a look at the spec sheet for the ProgressivTube system from TCT Solar (the manufacturer of the system).

The US DOE EERE offers another great resource that shows how the cold water enters the solar thermal panels from the low side, exits from the high side after it has heated up, and then "falls" down to a storage tank at a lower level.

There are of course some options that have the storage tanks on the roof above the panel, but these systems are incredibly heavy (water in panel plus tank) and often not very practical for retrofits as you might have to increase the roof reinforcing to handle the extra weight.

Again, here's another good resource from the Florida Solar Energy Center.

Finally, here's my personal 2-cents on solar water heaters...they can be more cost effective than solar PV (though not always as you'll see in my situation. Ultimately, the devil is in the details which depend heavily on your household water consumption patterns as well as incentives from local, state, and/or federal goverments. My wife and I opted not to do a solar water heater at this particular time because we ran the calculations and with the amount of hot water we use, it would have taken us about 15 years to pay off the system (a ProgressivTube passive system linked to a tankless natural gas supplemental heater).

Instead we opted just to install the tankless natural gas system (approx. $850 main system + $200 parts + $200 installation - $350 local utility rebate = $900) for which we use approximately 4 therms of natural gas a month to heat our water at a cost of about $14/month (and this is with our new use which is higher due to washing cloth diapers for our baby). So if a really good solar water heater can reduce your water heating bills by 80% then we could save $11.20/month. We assumed adding a ProgressivTube system to our tankless booster would have added $2,000 to our other costs (after local and federal rebates). At $11.20/month this would take 14.8 years to reach a full return on our investment. I realize this calculation is assumes a constant cost for natural gas (not realistic) and a constant hot water consumption pattern in our house (also not realistic as our young family grows).

We ultimately installed a 3.5 kw solar PV system for which we've estimated between a 5-9 year return on our investment after rebates, etc. More importantly, our local utility pays us a flat rate per kWh generated so the payback does not depend on our household energy consumption like it would with solar water heating. No matter how much electricity we consume, we get paid the same for the PV...the energy efficiency and conservation we practice only make our investment that much better!

Know your specific situation and do the calculations to determine if solar water heating makes sense for you!

In a closed loop thermosyphon system the "heat engine" can be anywhere in the loop.

Arbelos, I believe you may be confused. The thermosyphon effect happens within the passive solar thermal panel (in the case shown, the ProgressivTube system). Once the hot water leaves the panel it must flow to a storage tank and to maintain the "passive" status that tank will most often be at a lower elevation to maintain gravity feed.

Take a look at the spec sheet for the ProgressivTube system from TCT Solar (the manufacturer of the system).

That's not a passive thermosyphon system shown there, it uses pressure from the mains to push water thru the panel when you turn on a hot water spigot.

Even if you are using water pressure from the mains to circulate the water shouldn't the hot water line come out of the top of the tank because that is where the hottest water is?

May not matter too much in something the size of a water heater. Any temperature gradient inside the tank wouldn't last long I would think...

I'll get the ball rolling here...

Growing up on the farm in Australia in the late 70's, we had a wood fired boiler for hot water and space heating. We then put some solar hot water panels on the roof , three 5'x5' flat panels, and saw a significant decrease in our wood consumption. The area, near Canberra, the capital, has cool but sunny winters. The mid winter wood use went down a bit, the spring and fall wood use was probably halved, and in summer (lots of sun and no space heating) we never had to fire up the boiler, and actually had enough excess to divert some to the swimming pool.
We did get winter frosts, and the boiler and hydronic heating system already used a glycol/water mix, so this was easy to connect to the panels.
The panels operated without a hitch for the next ten years we were at that house, and saved me countless hours of woodchopping. And this was the 70's, todays panels deliver much better performance

Many houses in Australia had solar systems back then (and more do today) . When I first mentioned them here in Canada, people looked at like I was from another planet, but they are slowly gaining acceptance. For any cold climate, I would not use anything other than the evacuated tubes, they maintain performance in sunny days even at -20C.

The City of Vancouver has recently passed a building bylaw requiring all new houses to have ceiling rough ins for solar water heating.

The best advice I have heard, is to not oversize your system. You can never design it to completely replace conventional hot water, though it may do this in the summer. A well sized system will provide the bulk of your hot water in spring/fall.

If you are sizing for winter space heating, then make sure you have some way to "dump" the excess heat in summer, or cover the panels. I have heard of systems boiling in the summer!

As always, the cost/payback depends o what you are replacing. if it is natural gas, it's a long payback, if electricity, propane or oil, then it's quite good. Wood, well, it depends how much exercise you want to get, or want your kids to get...

Of course, hot water usage rate is also key for determining payback. When we investigated solar hot water for our home in Rhode Island, we could not justify the installation cost for our 2-person household. Our hot water demand is just not high enough to get a payback in our lifetime. I hoped that if we installed additional capacity for space heating, the investment might be justifiable.

Our home's construction is suitable for retrofitting such a system but my hopes were dashed when the discussion turned to how we would "dump" the excess heat in the summer. I was advised installing a pool or hot tub were the best options, otherwise a radiator with electric fans would be necessary. The contractor told me that covering the panels or taking the solar collectors out of service in the summer would be inadequate or impractical, even though I am handy with pumps and hydraulics.

For me, "dumping" the excess heat with a system that requires an external energy input such as electric fans was the deal breaker; cost estimate for entire system was $18k to $20k. The world would beat a path to the door of anyone who devised a method of sinking the excess heat cheaply and efficiently.

A note on trees, which are mentioned elsewhere in the discussion. We had to remove a 6 ft. diameter Northern Catulpa from the south side of our home due to rot; I hated to see it go because it shaded the house from the summer afternoon sun. I have been amazed by the additional passive solar heat that our house receives with this tree gone. Heating oil consumption is reduced by at least 20%, maybe as much as 30%. I would never have guessed that this tree, which had no leaves in winter, was so effective at blocking the sun's energy.

I hope that the increased heating in summer will not be so great as to overwhelm our ceiling fan cooling. I despise electric AC for home use at this latitude and we never needed it before we cut down the tree.

I suspect these systems can be installed for a lot less by a handy do-it-yourselfer.

In calculating capital cost, don't forget to deduct the cost of running a gas line if the only gas you are using is for water heating. This can save $1000 or more.

In calculating savings, if you are only heating water your payback will be good because you will be avoiding monthly connection charges for summer when you will be paying several times more fore service than for the actual gas.

The roof is a bad place to install these systems. You risk leaks and there are higher wind speeds. A ground mounted system can be better protected and you can repair it yourself. Most accidental household deaths are caused by falls.

A double plus good on your comment about putting the system on the ground.

It might be possible to get a really good long term roof installation if properly designed while building new but you are simply begging for leaks when you start building things on most existing roofs.

Any little accident these days means a humongous medical bill and elevated insurance premiums for years and years.

Most of us don't have the necessary climbing skills to be on a roof, especially as we get older.

But if there is no other suitable location I would still put one on my roof.

I'm hoping to install one in the side yard this year.And since we are retired we poor folks are getting screwed one more time by a regressive tax system and subsidizing our wealthier fellow citizens.

A third bonus of the ground mounted system, is that you can then do a passive one, with the collector tank directly at the top of the panels/tubes. You then run the cold feed to your regular hot water tank through the collector tank, so when you are using hot water the cold feed is pre-heated by the solar. If it is hot enough, the HW tank will not need to come on. Ditto for instantaneous systems.

In the US, to get the tax credit, you have to use a system that is certified by Solar Rating Certification Corporation. I suppose this is partly to keep homemade competition out. You may still want to do it yourself, but you should be aware of this issue.

Great point, and even if the system is certified, if you aren't using a licenced installer many inspectors can be a pain in the butt. If you are being inspected for tax purposes, make sure you have your ducks in a row.

Sure, but it is Equally important to note that homebuilts are very much possible, and can be pulled together from recycled materials such that the price and payback are far more appealing than a commercial unit WITH the rebates and the incentives.

Since I have no taxable income is it possible to transfer the tax credit to a vendor or installer?

One idea is to set up a business which owns the system and rents it to individuals. As I understand it, the business would qualify for some tax breaks for installing the equipment. The same sort of approach has been used with PV systems, where the company owns the panels and sells the power to the user or to the utility. I'm not sure about the details of either approach, so you are on your own.

E. Swanson

In Oregon, yes, you can just sell your tax credits to people (or companies) with tax liability. I don't know why they make it legal to do so, and don't just make the tax credits refundable, it seems like it would be a lot less work for the IRS than tracking tax credits that were generated by one person and claimed by another, but maybe they know that a certain amount of tax credits that could get sold don't actually get sold and so it saves them money...

Hi Gail,
Only the collector has to be certified by the SRCC under their OG100 program.

You can use the above mentioned $1K system with a commercial SRCC certified collector -- this makes it more like a $1.6K system, but since you then get the 30% federal rebate, it works out about the same, and you don't have to build the collector.

I'm probably a bit prejudiced because the $1K system is my design, but I think it makes a very attractive alternative to commercial systems that seem to be north of $8k these days. One wonders what is in these simple systems that justifies this kind of price.

The $1K system has provided 95% of our hot water needs over a full year in our very tough Montana climate -- this is a better solar fraction than great majority of commercial systems. Its not a difficult system to build, and any reasonably competent DIYer can do it. There are several examples shown of people who have successfully built these system and sent in descriptions:

I'm a retired airplane engineer, and I put quite a bit of effort into the design and testing of the system to insure good performance, simple construction,and long life -- there is a full description of the testing program and details on how to build it here:

My belief is that this industry really needs to work the cost of these system with simpler designs that can be manufactured in higher volumes and that take less installer labor. There is some indication that this may be starting to happen, but it seems very slow in coming. Being a very solar guy, I hate to say this, but the payoff for a solar water heating system for a family where the initial cost of the system is up toward $8000 is very long indeed -- maybe never. There are several studies out there that have looked at the economic return on these systems, and its not very good. Solar water heating is kind of a no-brainer, but we really need systems that are half the cost of today's systems -- at least that's my 2 cents.


Hi Gary, thanks for the link.

I'm one of the posters here who would rather build my own stuff whenever I can. I built my own PV trackers for about a third the cost of a "store-bought" tracker, and to date have had great success. The advantage to me is that if I can build it myself then I can repair/rebuild it myself. I also like salvaging and recycling stuff (my trackers are made from junked C-Band sattelite dish mounts. The great thing about your panels is that all of the stuff can be locally sourced. I already have most of the stuff in my junk pile, including five sheets of 6'X 3' low iron glass .

One modification to your design I plan to make involves the frame. Rather than use wood, I plan to use composite decking to avoid checking and warping. The materials are often available at building salvage yards. I also plan to use metalic silicone woodstove sealent as my heat transfer caulk. I also plan to build a jig for my log splitter to swage the fins. Maybe I'll send you a picture.

I've thought about using the plastic wood -- I think that it might work out well. As I see it:

- Should last close to forever

- No painting needed

- It would need protection from the high collector temperatures -- for example, a strip of the 1 inch thick polyisocyanurate (eg Atlas R-Board) along the sides. This is a good thing to do for the thermal performance of the collector anyway.

- Its heavy and not very strong (kind of floppy). This is probably only a problem when getting it into place -- its should be fine once its in place if its well supported by the roof or wall its mounted to. If mounted on a wall, it would want to be well supported.

I used the Trexs plastic wood product for cap strips on my large (6 bay) collector, and it has worked out very well -- it still looks like the day it went up after 5 years.

Some people use the galvanized metal sill plates that are made for buildings framed with steel studs for the collector frame.



You beat me to posting that link!

It was this article that led us to purchase a ProgressivTube system for our home in central NC 4 years ago. The unit itself is warranteed to 10F, but the supply and return lines are vulnerable. So I built a superinsulated box around the lines to encompass them into the thermal mass of the PT unit itself, and it has endured temperatures down to zero F with no problems.

We have since moved to the mountains of VA, and have installed the same system the same way here with the same results. In fact, I've installed the system for two neighbors as well. We just endured the coldest month anyone here can remember, with temps staying below freezing for days on end, and the systems were just fine.

Ours in NC for which I kept careful records provided us with 90% of hot water needs on an annual basis, and we only had an average solar window of about 3 hours! Our propane use for hot water went from 11 gallons/month to 1 gal/month. I cannot sing the praises of the PT too loudly, given my experience. No need for pumps or controllers or proplylene glycol. I believe this system would work in much of the country. No, not the far north from which I come, where the temps are far below freezing all winter. But we have just proved here in the Blue Ridge that it will take lows in the low teens and days in the 20's for several days running, as long as there is sun on the collector during the day.

All that said, I am so intrigued by the system that Moose linked above, that I am currently building one with yet another neighbor. I believe it could be customized to provide hot water without need for a back-up system, if the storage tank is sized large enough. Even if not, the instantaneous back-up heater will be doing very little work. Will let you all know how it turns out.

Here is another article I've found useful on solar hot water system basics.

We have had solar hot water panels for 28 years, and recently replaced the panels as there was some deterioration and one panel of four was lost to frost damage a couple of years ago. The original panels were reasonably effective, and clearly reduced electricity usage (off peak heating). Maintenance over the years has been occasional replacement of circulation pump or impeller, one repair of the controller due to a failed capacitor, and one replacement of heat sensors.

However, the heat input from the replacement panels is far greater, so much so that I should be putting shade cloth over one of them in summer. The tank can peak around 90C - You can just about make tea from the hot tap (and you definitely could if you were in the US!) The boost power is turned off unless we have 2 or more days of complete overcast (unusual here in Sydney). If I turn off the circulation pump, the panel temperature goes beyond 140C - I didn't like to continue the experiment above that temperature. The area of the new panels is slightly greater than the old, but the glass is better (low iron) and the panels seem to radiate less. They are flat panel construction, not evacuated tubes. The area is around 2msq.

The replacement panels with all sensors and controller cost around $AU1200, so not expensive.

My experience of solar hot water for 28 years is that it is very cost effective, and current panels are amazingly good, at least when new.

When looking around for replacement panels it seemed that evacuated tubes were favoured against flat panels. My experience is that flat panels are very effective, more than good enough, and much cheaper.

A modification I am considering is adding a second glazing layer with perhaps a slightly narrower transmission window than the glass provided. On clear winter nights the panel temperature drops well below ambient, requiring water circulation to avoid freezing even on quite warm (10-14C) nights. The temperature drop is due to radiation into the cold night sky (we can have humidity of 20-30% at night here in winter). A second glazing layer would also reduce summer heat input a little, which would be a good thing.

If I move from here to a place without solar hot water, it'll be one of the first items I'll be adding.

Once again, Homepower is hard to beat as a reference on all things renewable. Here's an article for general understanding and selection of SHW systems:

Our system (currently undergoing an upgrade) is a simple "drainback" active system. The solar heated water is stored in a tank. Our domestic hot water is pre-heated through a heat exchanger in the tank and then goes through a tankless water heater. Most of the time the tankless heater doesn't turn on as the water is already at or above the 122 degree setpoint after going through the storage tank. The "drainback" system means that no water remains in the collector when the system isn't warm enough to produce hot water. The water just drains back to the tank. This eliminates the need for a glycol solution. The system also supplies our radiant floor heating.

Other great articles from Homepower:

Regarding storage and tanks: *

About types of collectors: * *

Pumps and plumbing: *

(asteric denotes subscription required, IMO worth it)

I just finished taking the Solar Technology course offered thru Caldwell College, NC. The course was rather basic and I took it with the thought of later applying for solar installer certification, which is available thru the North American Board of Certified Energy Practitioners (NABCEP). In some states, this certification is now REQUIRED before a person can install a system for client.

The problems of freezing and overheating can both be addressed with drain down or drain back active systems. Around here, in the mountains of western NC, the winter temperatures can be quite cold, thus one would need antifreeze in the panels if there's no way to remove the heat transfer fluid when heating is not available. In summer, if there's no draw on the hot water in the storage tank, high tank temperatures usually cause the controller to shut down the pump(s), thus the temperatures within the panels can become quite high. In one test I ran last summer, an experimental hot air collector run without air flow hit 300 F (149 C) with ambient temperatures near 80 F, a temperature which might occur in an efficient hot water panel when run without circulation. At these temperatures, the cooling fluid can boil and insulation can degrade. I had used polystyrene insulation, which melted...

E. Swanson

i snagged 4 copper panels[w/ tubes built in- but no glass or box frames] which came from 70's solar hot water heaters.

i think they are about 2 1/2' X 8'. we live where optimally we'd do the glycol[ mix], but i want to keep the system as simple as possible, & dollars are tight.

hadn't planned on moving forward yet so i haven't done much thinking/research. any particular suggestions, or links will be welcomed. i'll certainly look forward to the info this thread will have. thanks.


If you have simple manifold flat panels (pipe at bottom, pipe at top, connected by straight tubes) you can do a simple open loop drainback system. This is what we did with old '70s era panels from a hospital, $10 U.S. each. Eventually, the tubes began to delaminate (de-solder) from the flat copper plate (after over 30 years of use) and I have chosen to sell the copper and get newer, more efficient panels. The scrap value of the copper is more now than the panels cost new in circa 1977.

Old (25+ years) sliding glass doors have regular glass that is acceptable for use with these old panels. Be sure to use isocyan. insulation. Standard poly foam won't last. A good material for your frames is composite decking material (wood doesn't hold up as well over time). Use insulated PEX for plumbing to the panels.

In a drainback system the return (hot) line from the panels is above the water level in the tank. When the pump shuts down the water drains back to the tank through the pump. Just make sure that everything slopes back to the tank so no water remains in the panels to freeze. Not as efficient as newer closed loop systems, but you can make a lot of hot water on the cheap. Heat your domestic HW with a coil of copper tubing in the top of the tank plumbed in line with your regular water heater. I used 120 feet of 3/4" tubing in my system. Our system never gets above about 145F, plenty hot. We use a simple, well insulated polyethylene tank similar to this:

Simple poly water tanks are fine up to about 160F. Taller is better. This is a high volume medium temp system, on the cheap, but has been quite productive. I may convert to a modern high-efficiency system at some point, but alas, the economy may prevent that.

When not using prop.glycol solution I recommend using regular "boiler treatment", especially in open loop systems, to prevent corrosion of pump and fittings.

ghung thanks.
great info. my panels are hard to get to right now; & it's pouring or i'd look re the possible solder issue. i think they are as u say but i don't remember any solder between the tubes & panel- but i weld so i could maybe remedy that.

thanks for the detail on the collector boxes- makes all the difference in the world re not having to learn the mistakes the hard way. i have some sliding glass doors too.

the 120' coil of copper tubing is a little daunting but i have a large coil- 3/4 i think- i made for cooling beer wort; making 1/2 the job done. i will choose HW ---i guess...haven't brewed from scratch in 8 or 9 yrs.

i've thought a 12v pump with solar panel makes a good choice for this type system, & gives a lot of resilience.

thanks again, great helpful detail!

When our LPG water heater broke 3 years ago we replaced it with a solar water heater and no backup. The SWH is a passive thermosyphon model with 21 evacuated tubes and a 150 liter storage tank plus 30 liters in the solar tubes. This is for a house with 3 persons living in it. It has worked extremely well, with no backup the hot water temperature has only gone below 40 C on average 5-7 days per year, and even then it is still possible to take a shower without much suffering, but you have to take into consideration that it is installed in the south of Mexico where the ambient temperature rarely goes below 15 C.

It was very difficult to find a knowledgeable contractor, I ended up installing it myself, the installation instructions where very confusing, the hot and cold water lines were mixed up in the diagrams, and the vendor was not very helpful, he even discouraged me from getting one, it was only because I was determined to get one and knew what I wanted that I was able to buy one.

The cost of the SWH was about $600 USD plus installation, which I can't remember exactly but it was about an additional $100 USD. I figure that I am saving about $100 USD per year on LPG so it will pay for itself in 7 years or less because the LPG price keeps going up.

In conclusion I am very happy with my SWH. It requires less maintenance than a gas heater, its cheaper to operate and I figure the investment was better than putting the money in the bank.

7 years would be about a 14% ROI, right?

Who's got a better stock pick than that?

In terms of money, it depends what water heating method is being replaced.

I've been looking at solar thermal for a while, and unfortunately, it'd take 30+ years to pay back the difference between the cost of the solar installation and amount it reduces my gas bill at 4c/kWh

At my location, there is about 1200kWh/m² per year insolation. So a good set of panels will save me about €50 per square metre per year. Not a lot given they cost thousands (€5k+) for 3-4 m² systems.

Then there's the problem that most heat is required in winter when the insolation is at it's weakest.

It's *much* more cost effective for me to have lots of insulation installed everywhere I can and just take advantage of south facing windows.

If you have an electric water tank it might make sense financially though... Though again, you'd probably still be better off insulating it to death.

I'm amazed that there is no mention of solar pre-heating. It seems to me that solar hot water is being presented as an either/or option. In our case, we've had solar pre-heating for at least 25 years and have a heat exchanger in our wood heater that pre-heats the water in the winter. And, I might add that everything was designed and installed by me. There is a very detailed TOD archive on how I built my collectors some place. They follow the roof line and don't stick up.

Yes, I do have an intermediate tank (and in my case a pump - which draws all of 42 watts). Although I do have a differential temperature controller system, I've simply switched to turning the pump on when it is appropriate- either manually or via a timer.


As a PS, I do use my PV to heat the regular (220volt) water heater using a timer. I think it is in my key post A Trip to Todd's as to how it works. If you can't find it, and are interested, I'll post more.

Todd, I would like to see your collector design.

Also, many people don't know that you can hook a PV panel directly to an electric tank type water heater (not with the A/C connected, of course). You can buy D/C heating elements for most electric water heaters. Add a thermostat and you have PV direct heating. Not as efficient as thermal, but much simpler. Some folks use water heaters as a diversion load from their PV panels for after their batteries get fully charged.

As I mentioned above, our system is essentially a pre-heat system. Some people call this "in series". It is a great option because much of the time the conventional heater doesn't turn on. Even with a conventional tank type water heater you save a lot because the water is hot before it gets to the tank.

And this would be the place to again mention that there are people working with hybrid panels that are PV with waterjackets behind them to cool the PV, making it more efficient, and to pre-warm that water supply, offsetting the heating load for DHW (Domestic Hot Water)

In Maine, Ascendant Energy has installed a demo array of this approach at Chewonki foundation, which teaches many levels of environmental education and stewardship.



You can get an idea of what they look like by scrolling down the pictures in my key post, A Trip to Todd's. I also put up a post, probably three years ago, on exactly how I built them - they are made out of urethane foam although I have a better idea to replace the foam. I'll look for it if I have a chance; or you can.

On the HWH front, I actually use 220volt AC from my inverters although I know you can buy 12volt DC elements. Here's how it works: My battery bank and PV system (3.6kW) cannot handle continuous heating or it sucks the batteries dry in no time. However, I had played around running back and forth from the meters in the garage to the house to turn it on and off manually when the voltage got too low.

I said to my self, "Why not simply put in a cycling timer and 220v relay to do it automatically?" I made up a box with an Omron H3CR timer that feeds a relay for the HWH. For me, 10 seconds on and 13 seconds off does it if I have reasonable insolation.

Hope this helps.


BTW we're having snow and our wireless internet goes away now and then so I might not get back right away to answer any further questions.

Our house, which we bought in 2004, has a 'Copper Cricket' solar water pre-heater which is not made anymore. This system utilizes the 'geyser' principle in that the pressure from the heat itself drives the solar loop, with the collector above the water tanks. In other words, no moving parts, no electricity, no pumps, etc.

It's really too bad that the inventor (as I understand) ran into problems in the patent world and stopped making these systems. In our community there are 6 of these systems, some having worked without problems for ~20 years. All they generally need for maintenance is a flushing of the water loop every season, and, of course, a replacement tank if the tank shows signs of rusting through.

Mid summer brings electric bills $10-$20 lower than the bills in winter.

Hi Gail, SHW does indeed have the potential to provide cost effective renewable energy. It is a pity that in US so many of the heaters are used for swimming pool heating; in China, which has over half of global installed capacity of SHW, the majority heat domestic hot water systems (IEA, 2009).

For a summary of SHW from the UK's perspective, please download and share an academic article I wrote but did not publish on the subject, for which I received 72% at the University of Sheffield's E-Future's course. I believe this report, and the IEA's authoritative (2009) analysis of SHW presented here provide interesting and relevant background information on the true significance of SHW from an international perspective.

Keep the Drum Rolling, Robin

When we had nothing better to do (all crops were in), we dragged a defunct hot water heater from the scrap heap, peeled half the jacket and insulation back, painted that half of the naked tank black, rolled it onto a pallet against the south side of the pumphouse, with the bleed valve on top, ran a water line from a tee in the pumphouse through the wall to the tank inlet valve, and an underground water line from the outlet valve to the house, then built an insulated cold frame around the tank, with an aluminum frame window, also from the scrap heap.

In the house, we simply connected the new line to the hot water heater supply line via a tee and a gate valve that can be shut off if anything happens to the outside system.

The safety drain valve becomes the bleed valve in this arrangement; otherwise you may trap air in the tank, reducing heat efficiency and possible causing pipe hammer. To drain, disassemble cold frame, unhook the feed lines, and roll the tank over till the valve is on the bottom; open the valve. Needless to say, the valve inside the house should be shut off before working on the exterior system.

Perfect? No. But not an exercise in futility; this setup gets hot about half the year, and its use is as a pre-heater for the hot water heater. The electric bill has diminished as anticipated; we think we make back our original investment of about $40, three to four times/year.

Yeah ... I've done something like this too, and it's worked very well. If you're handy with tools it doesn't take that much work, and it certainly doesn't cost thousands of dollars. A simple system can still pay good dividends in energy savings.

Solar domestic water is good for Hawaii, Florida and southern California but not cost effective elsewhere.
Any place with any amount of cold weather needs high efficiency evacuated tube type with a pump and of course a back up water heater. An average apartment might use 40 gallons of hotwater per day which can be handled by a 40000 Btu (backup) gas hot water heater(50% efficient). Annually that's ~24000 cfh of gas per year or $200 per year.

In the northern half of the contiguous USA in Dec, Jan , Feb you can produce about
3500 Btu/month/sf, the rest of the year closer to 7000 Btu/ month/sf. In the summer, 150 sf of evacuated tube would produce 35000 Btu per day. A 150 sf evacuated tube system would cost ~$10000 and it might handle about 2/3 of the annual domestic water heating or $133 per year.
The payback isn't very good at current energy prices.


I have to agree with majorian that payback is dependent on location, system costs and incentives. In much of NY, if you have a natgas water heater, payback can be 30 years or more. However, with falling prices and tax credits people in much of the country can realize paybacks of well under ten years. Just a note, equivalent systems are much cheaper in other parts of the world. BTU to BTU, the Chinese pay 80% less than in the U.S.:

Solar water heating systems have become popular in China, where basic models start at around 1,500 yuan (US$190), much cheaper than in Western countries (around 80% cheaper for a given size of collector). It is said that at least 30 million Chinese households now have one, and that the popularity is due to the efficient evacuated tubes which allow the heaters to function even under gray skies and at temperatures well below freezing.

Payback periods tend to be much shorter if your hot water is electric. The way I see it, if you're always concerned with the bottom line, you're probably not much fun anyway. It's about choices. Many people will spend thousands on an ICE toy but wouldn't give solar hot water a second thought. I like that, with solar hot water and solar pumped spring water, most of the time I can take those long, hot, therapeutic showers, guilt free, zero carbon emissions and with no concern for costs. Pay it forward, America!

One of the further perverse things about solar hot water is that the better you are at water conservation (low flow, short showers, lowered temperature), the longer the payback time, if that is what you are most worried about.


That's an important point that's too often overlooked. Our electric water heater is sub-metered and the average daily usage of our two-person household is 4.5 kWh, or roughly 50-cents at current rates. (If I were to wash our clothes in cold water, we could do even better.)


One of the things that struck me when I was considering one of these systems is that up here in MN I would be getting plenty of hot water in the summer when I need it least and far less in the winter when I want it most. That didn't seem very efficient.

With PV, on the other hand, some of the highest need is in the summer when people turn on AC, so the maximum need matches the maximum availability of the source.

Yes - was thinking about the same thing here in Seattle. Except we don't have an AC for summer. With climate change may be we will have to get it soon ... had the hottest summer last year, with El Nino coming up doesn't look good.

I think an issue we have in Atlanta is that there are so many trees, not many homes get much sun, any time of year. I know we would have a hard time finding a place to put a solar water heater. Even on the roof, the amount of sunshine would be less than optimal.

Your trees likely save you more on air conditioning costs than you could ever save with SHW. SHW is not for everyone and is certainly sight sensitive. BTW, I grew up in Buckhead without air conditioning until the mid '70s. The house was in a thick forest that kept things cool and we just had an attic fan. I read a UGA report which said that since 1975 almost 70% of the trees in the 5 county Atlanta area have been "eliminated". Trees are very "green" things to have around.

Even if 70% of the trees were "eliminated", they grow back very quickly with all of our rain and long growing season. New subdivisions often look fairly bare. Twenty year old subdivisions usually have a lot of large trees, even if they were bare initially, because of the trees people plant, and all of the "volunteers" that come up everywhere.

We live in an older subdivision. The majority of the trees were left in place when the subdivision was built, and new trees were planted, so it is quite shady now.

Cutting down trees to install SHW may not be a good energy trade-off if you use air conditioning.

I also grew up in Atlanta.

Cutting down trees will definitely add to the available solar energy. That might increase your cooling costs, but there are other ways to address the problem. For example, paint your roof and walls white. But, you say, that's not esthetically pleasing. Well, that's just another example of the problem we have in our societal failure to understand the hard facts of physics. If you had no AC, because the electricity wasn't available, what would you do? How are you going to heat your water without natural gas or electricity? We've all got to learn to think outside the cultural "box" we've grown to accept over the past couple of centuries of development.

E. Swanson

We grow annual vines on the sunny sides of the house in summer. Beans, climbing peas, gourds, are all good choices. Ornamentals such as cardinal vines and morning glories are good seasonal shade too. We start things indoors to get a jump on mother nature. Use deer netting or string for the vines to climb on. Gourds can get pretty heavy, so plan accordingly.

I love that idea and plan to try it next year.

We used to live in Macon, GA, about 70 miles south and down stream from Atlanta. We would go up to Atlanta to cool off--it was usually about ten degrees cooler up there, mostly due to the elevation, I assume.

So it's all relative. The traditional ways to deal with summer heat in the south were rocking chairs on the porch, tall ceilings with ceiling fans, and the occasional skinny dip in the local creek or stream. AC has dramatically altered the architectural practices of the South in unsustainable (or at least uncomfortable, in an energy constrained/more sustainable world) direction.

Attic fans, regularly blowing air out of the ground floor and out through the attic, can also be very effective.

Ah, Macon, Atlanta's "Red-headed Stepchild". I did a lot of work on the grid there years ago. Poor old Macon has been semi-depressed for a long time. Maybe things have changed since I was there.

We spent less than $10 last year on string and seeds. Bought us a lot of cool. Not a bad EROI (energy reduced on investment).

Even on the roof, the amount of sunshine would be less than optimal.

Less than optimal sunshine and an insulated storage tank is all that you need as far south as Atlanta (at least for 10 months of the year).


Here's the results of one system in Maine, Majorian. (and there are many of them up here)

I used RetScreen software to calculate my Return on Investment, which works out at 4.6 years based on the design and site of my specific installation. Click the graph below to see a detailed report. Allowing for inflation and increasing propane prices it shows that after 25 years I will have saved over $11,000 in offset heating costs! Pretty impressive.

Add to that the security benefits of having a solar heating option in places where icestorms could isolate you from the Grid or Fuel deliveries, plus other uncertainties regarding availability or cost and the advantages compound. I don't know how you came up with Hawaii Florida and So Cal.. people are showing successes with this well up into Canada; the payback up here in Maine is consistently within ten years, and Guy Marsden (arttec site) seems to have done a bit better, with a chunk of help from the 25% rebate.

You must be paying a fortune for propane, which DOE says should cost about 60% more per btu than natural gas. SHW does much better against electric water heaters than gas does in payback.
$11000/25 years is $440 per year savings which indicates he was using a very big collector for a lot of hot water. (And how efficient were the solar collectors 25 years ago?)
At current prices a small family may be spending $200 a year in gas for DHW. Most people use the standby 25-50% of the time so the savings is less than $200 per year.
A $10000 system - $3000 credit/$200 = 35 years payback.

Ghung is right to say do SHW because you want to do it, not because it saves money. However, if you choose to spend your money on SHW first rather than insulation, air sealing, higher efficiency furnaces, storm or efficient windows etc. you will be less efficient financially speaking.

I think in deciding whether this is a reasonable thing for society to be doing, we should be looking at the payback without the tax credit. The government needs to collect more tax elsewhere, if it gives a rebate for this. Also, with the poor condition governments are in, it is not clear how many rebate programs can continue. If the payback isn't good without the tax credit, we really should be concentrating our efforts on parts of the country where the payback is better (and the systems are cheaper).

The tax credits make up, in part, for the subsidies available to the fossil fuel energy suppliers. They also offset the fact that we import lower cost oil from other countries, where there is excess production. Around here, we should all know by now that those oil imports are likely to decline in the near future, thus the tax credits are also somewhat forward looking, setting the stage for the future when the usual energy sources become much more expensive. Looking only at payback misses these points, as the economic calculations are basically rear mirror views of reality.

If the market calculated current cost estimates based on expected future availability of oil and other energy sources, we would probably not need subsidies. Instead, our economic gurus discount the future to the point that long term future problems are ignored.

Gail, surely you understand that by now...

E. Swanson


But if we have limited dollars to spend, it seems like we should spend them were they accomplish the most--and will probably last the longest. On this basis, the simplest passive solar heating units (without all the glycol) used where the temperatures are warm enough where freezing is not a problem would seem to have the best payback four our dollars.

If local governments are inspired to do more, in colder climates, that is OK too.

Gail my brother and sister live in Germany and my brother in law is friends with the owner of this company.

Disclaimer I'm not involved in any way with this company but I know that they have implemented systems all over the world. I can tell you that passive solar is viable in most places in the world without any incentives.

My uncle built a simple collector connected to an insulated tank on his farm in Brazil about 30 years ago no one gave him any incentive then and the system is still operational today.

Passive Solar Hot water works! Of all the forms of Solar Energy it is the one that makes the most economic sense.

The Oregon DOE says that we are equivalent to Florida in terms of energy savings. What they point out is that the incoming water temperature is much higher in Florida than in Oregon, so while the air temperature is also higher in Florida, you can just as easily raise the water temperature the same number of degrees with the same technology in both places which saves exactly the same amount of energy. Of course, in Oregon you'll use backup more often than in Florida but the point is that the payback times are very similar.

I paid $4000 for active flat plate collectors, installed. A well made flat plate can raise the water temperature 70F above ambient on a good day, (obviously if it rains all day they don't do anything,) which is more than enough for a place where it rarely freezes during the day, (in the summer the pump shuts off at 150F to keep the backup from tripping off.) Evacuated tube collectors are overkill in much of the US, and as you point out, quite a bit more expensive, but they can do 150F above ambient on a good day. I could see them being cost effective in places where the fuel supply was intermittent and expensive, (Alaska,) but otherwise I don't know why anyone uses them for domestic hot water.

The pump was ~$20 of the cost. There is a 20W solar panel (~$100) and the thermostat to turn it off when it gets too hot for the backup, and that is it for the controller. The big cost in the active system was the heat exchanger at ~$700.

The first year I had it, I played with it a lot, (I had the backup turned off for the summer without any problems at all,) but now I mainly ignore it and let it do its thing.

Its simply not true that evacuated tube systems are needed for cold climates. Flat plate collectors and evacuated tubes have very similar performance in cold climates.

You can download the SRCC certification test for dozens of flat plate and evauated tube collectors here:
They show very little difference in performance for collectors with the same collection area.
You can run this calculator (which is based on SRCC certification data), and compare actual performance for whatever sun level, and ambient and collector temperature you like:

Home Power magazine in their recent review of collectors came to the same conclusion.

There are a few sites/articles that compare flat plate and evac tube arrays located right next to each other and reach the same conclusion. Two them are listed here:


I have a brother with a 5 panel (4x8) solar thermal system. It heats his water and also has an exchanger that sits inline on his gas fired air furnace (retrofit). So he can run the blower only for the first few hours after a sunny day to heat the house with the btu's stored in his tank. WIth the proper orientation (south) and a good amount of windows, his furnace hardly runs on sunny winter days. He put this up when the first subsidies in Illinois were available around 2003-04. He has something like an 80 or 120 gallon tank (drain back style) which stores the hot water and their is another heat exchanger to heat his traditional gas fired hot water heater. From mid April through most of October the only gas he uses is for cooking. The first year, the gas company came out and to check to see if he diverted around the meter as his gas usage was down so dramatically as winter progressed.

The key is having the appropriate solar window to the sun and siting it properly, though with solar thermal this is a lot less sensitive that using solar pv. In many cases instead of using the solar PV rule of thumb of having the tilt at you latitude for fixed mounts, you generally want to plus that by 5-10 degrees to maximize for solar gain during winter. In summer, you will produce more btu's than you can use. As always specific site analysis always trumps rules of thumb, so if you have real cloudy summers and clear winters this may not apply.

It was a big missed opportunity after the 70's energy crunch when solar thermal was all the rage for a few years that more municipalities did not set up guidelines to require most subdivisions to have most of the homes orientated so homes were built with a south orientation for the long axis of the hours. Take a look at how older homes (100 + years were orientated). But then again, I am discussing suburbia...

There are a number of trade offs comparing evacuated tubes and flat plate collectors. Evacuated tubes are somewhat modular, so if a kids ball hits the panel you may break one or two tubes but the unit itself will continue to produce hot water. They are also capable of producing higher temps, though for most residential this is not a concern and if you don't have the proper storage, a waste. Also in high snow areas with inaccessible panels (roof), the snow will melt off the evacuated tubes faster than a flat panel. Flat panels will not produce as much heat (per sq. ft of area) as evacuated, but are less expensive.

Here is a link to the feds site

And the wiki

A couple of links of people who've designed their own homes with solar thermal (and PV). - He provides a journal of his house building and PV - Thermal design process and installs. (Caution, you may spend the next week reading his journal). Another journal of home building process and design. Allows builds and sells solar thermal monitoring solutions and parts you can use to make your own system.

Also in high snow areas with inaccessible panels (roof), the snow will melt off the evacuated tubes faster than a flat panel.

I think you have that backwards:
Flat plate panels melt the snow due to their high heat losses through the un-insulated glass. Evacuated tube collectors are so well insulated they do not melt the snow. If the south facing roof at your location does not routinely melt the snow during a typical winter, flat plates are probably a better choice. The evacuated tubes seem to work well under light-to-medium frost. And they will collect energy when half covered with snow (about half as much as when fully exposed).

I went looking for a solar hot water system in the summer of 2008 (I had just filled my fuel oil tank at $4.25/gallon). The local solar store had free two hour seminars each weekend, so I signed up for one. I also began doing on-line research - there is certainly no shortage of info on the web about solar hot water heating.

The guys at the solar store were great - good info - not pushy - just salt of the earth types. They came out for an estimate with some cool tools for calculating insolation, etc. Some trees would have to go...but the south facing roof was a winner. I looked at their proposal - good quality flat panel equipment installed by a well known local plumbing/heating/HVAC contractor. I signed up...and then it took 3 months to get the work scheduled due to the high demand.

They were in and out in a day, 3 roof mounted flat panels, glycol closed loop, AC controller, a new 110 gallon tank, wired and plumbed into my existing boiler (for backup). Neat, polite, personable people. All Stiebel-Eltron equipment. They took care of the town plumbing permit - also, I believe in Massachusetts, there is no sales tax on solar equipment, and (supposedly) a property tax exclusion for solar equipment added to your home. These were not factored into my decision, but nice added benefits.

Small problems...the trees to be removed were actually on my neighbor's property. They were supportive about the whole idea (I gave them most of the resulting firewood). But the tree contractor added almost $1000 to the cost....though I got some side benefit, landscape-wise. The guys put in the wrong glycol concentration and came back a few days later to drain and big deal...but I'm glad they caught can get well below 0F in western Massachusetts in the winter.

Just under $10,000 for the system. Minus $3,000 in state and federal tax credits. I figured the payback for a family of five at 5-7 years, a little longer now as the price of fuel oil has dropped. I self-financed, though the solar store guys did have a pretty good low interest loan deal with a community bank to spread the cost over 5 years. It gives me great pleasure to never hear the boiler run most of the summer. Like some of the other posters, I regularly see the panels at 180+F in the summer, and get home from work to find 110 gallons of 165F water in the tank (this will go about 2 days with my family - if it's sunny at least every other day in the summer, I'm not using any oil at all). In the winter...well it's New England...but on a sunny day in December the panels will reach 120F...still pretty good. I'd estimate I get 90% of my hot water "free" in the summer, and maybe 40-50% in the winter. Some behavior modification could maximize use of the solar gain (like showering in the afternoon, etc), but with 3 teenagers...I am just happy with the gains I get without rocking the boat.

Still very happy with the decision - zero problems so far - I took my time, and made sure I got quality equipment and contracting. I expect those panels to still be making hot water in 25 years. I also burn wood for heat, drive a small car, use CF bulbs...not necessarily for the green factor...but as financial decisions. The engineer in me finds it a challenge to try to reduce my family's oil/energy consumption. If you have a south facing roof (or room on the ground for the panels), a solar hot water system is a very practical, low maintenance way to harness the power of the sun.

I'm in Ohio and have had solar hot water for over ten years. I bought a used set of panels, contacted a local person who had been active in the 1980s, and got a system up and running for a total of about $3k. I've had to replace circulator impellers and one external heat exchanger - but had been warned that our water is so hard that without a water softener this was bound to happen. I estimate that it covers 1/2 to 2/3 of hot water needs for my family of four. The system has an on-demand water heater as backup; that unit modulates to only heat the incoming water to a set output temperature.

Since installing that system, I've helped install another 5 or 6 systems locally, always with people who wanted to learn themselves and were mechanically handy. I'm not licensed, and wish more people around here were. We pieced together used collectors and sometimes tanks, usually bought commercial controllers (Steca makes nice, fairly inexpensive units), and have tried glycol systems, drainback systems (careful about freezing and getting good draining; ask me what happens if you don't), and systems integrated with radiant floor heating. Everyone is happen with what they have.

For me personally, I still get a little thrill on a sunny day when I see that the pump is running and that I am getting "free" hot water. That's worth something as well. Although it's not going to work for everyone, as an acquaintance in Germany told me twenty years ago when I first learned about solar hot water systems, "nobody asks about the payback time for the sunroof on the car or for the granite countertop in the kitchen; you do it because you want to." I'm afraid we still often hold renewable energy technology to a higher economic standard than many other things we undertake daily.

When it comes to payback I look at it this way.

On the third day of a power failure, how much would you pay to have hot water?

There are some people (in high rises, for example) who will be without any water on the third day of a power failure. These folks aren't likely ones who would benefit from passive solar hot water, though, I expect.

But a neighbor might..

One of the GREAT benefits of distributed electric generation and heating being widely developed is that it increases the likelihood that someone nearby has SOME access to Hot Water and Power.

A friend of ours up in the White Mts was giving his neighbors turns in the shower after the 97 icestorm, when everyone else was dark and cold. His panels melted clear and were producing heat THAT SAME DAY.

Our apartment buildings in Portland are starting to load up with Solar Hot Water systems, what with those convenient flat rooftops.

Speaking of neighbors, I wonder if anyone knows of situations where someone with a good, large, unobstructed southfacing roof put up a system large enough to serve not only themselves but neighbors. Would/could the economy of scale off set the additional plumbing?

Another question--we hear a lot about regular advances in PV technology; are there any major breakthroughs in hot water solar in the works that anyone has heard of?

RE: Economies of Scale

Almost related, a friend was in a Co-Housing group in Oakland area, they were able to develop Solar water heating as a bigger package that served the cohousing community, not just individual families.

There are certainly also neighborhood groups that are buying together to leverage bulk sales.

One advance (prob not considered new any more) is that Evacuated Tubes are orientable tube to tube, so an off-angle roof can correct in its best sun angles..


By the way, today is said to be the statistically coldest day in the Northern Hemi., lagging the Solstice by a month, and it being sunny on the Maine Coast, my humble little hot air collector (Black felt filter/collector under glass) is now blowing about 100f with ambient temps around 35. Got two more under construction and glass to make maybe 15 more..


Another kind of economy that has not been much touched upon is that wich comes from combined systems.

My guess is that there are going to be a lot of electric vehicles around that need charging within a decade, and that combined heat and power systems will also become common.

A relatively small ng or propane powered generator built so as to capture the waste heat and funnel it into a large hot water storage reservoir could use the same reservoir as the solar hot water system.Such a system could charge your car very economically and efficiently during the colder months as well as contribute substantially to the household space heating load.It might even supply all the necessary heat.

You could also run it for awhile if there happens to be a long cloudy spell during the off season , and you would have your own backup electrical system in case of an outage.

Such a system might also be able to earn you some money by selling juce to your utility during peak load conditions except in the hottest part of the year, when there might be very little use for the hot water as the solar collector would be cranking along under those conditions.

Such small scale (micro) combined heat and power systems are already available.
Here's an example from Honda. Honda has been selling them since 2003.

E. Swanson

We live in southern Ontario and have two active panels ground mounted off the back of our home. The installation is described in greater detail in the posts on my blog at

In the winter, I estimate that solar provides 25% of our domestic hot water (with the balance electric) while in the summer it can supply close to 100%. The issue is not outside temperature (the insolation does not differ that much). The percentage of sunny days does differ a lot summer to winter.

Our system cost approximately $5,000 Canadian installed by a professional installer.

We put in an Indirect circulation system over a year ago in Auckland NZ.

We chose the indirect system but we use water as the heat transfer fluid for 2 reasons.

1. Not being glycol, if the closed circuit happens to leak you only get water leaking into water. A plumber mate told me horror stories of a family that had used glycol, had a leak and the whole family came down with a range of neurological symptoms.
2. By using one charge of water in the closed loop we get only one dump of dissolved chemicals into the loop. If you use direct circulation each new flow of water brings new chemicals that get deposited to shorten the life of the system or require more frequent cleaning.

The system we have also has a reverse flow setting for places where there are light frosts. It moves water from the tank through the loop to keep it from freezing.

We get value from it all year round but we essentially turn off the electricity to the tank from about mid November till the end of February.

It uses mains pressure for the tank and the backup coil is half way up the tank so that it heats the least amount of water possible to keep the temperature up when the solar is short.

Only thing missing is PV backup for the pump which needs about 25 watts; that's next on the list.

I would love a bit more info about your experience and installer/vendor. we are just north of Auckland and are looking at options at the moment.
Regards, Jed.

We have a solar water heating system, in Austin. I bought it as a kit from (their web site seems to have imploded to just a phone number, but my experience with them was good). Total cost was about $3,000 since I installed it myself; this is a good do-it-yourself project for those who are moderately handy. The cost is about twice that if a contractor installs it.

The system has a 4x10-foot panel, an electric water heater with a heat exchange loop inside it also, pump and controller. The controller compares the temperature in the panel with the temperature in the tank; when the panel is 10 degrees hotter, it turns on the pump. The hot water from the panel flows through the heat exchanger loop and heats the water in the tank. Basically the pump runs all day when the sun is shining. The panel loop contains about 3.5 gallons of water and Noburst non-toxic antifreeze [car antifreeze is toxic and should not be used], although fluid in this loop is contained and normally should never mix with house water.

From about April until sometime in October, I turn off the electricity at the breaker, and solar provides all of our hot water. In the winter, sometimes electric backup is needed, but the solar helps a lot. In summer, the system can even get too hot and boil over. There is a "tempering valve" to add some cold and prevent scalding; the tank temperature sometimes gets up to about 160 F.

Our house is all-electric. Electric water heating used to use about 13 KWH per day, or about $40 per month, so the payback is 4+ years, with 30% Federal tax credit. Definitely cost-effective. The pump and controller only use about 0.3 KWH per day, or $1 per month.

Compared to photovoltaic solar, which we also have, the solar thermal saves as much electricity as a 3 KW solar PV system generates, at maybe 1/5 the cost.

Solar water heating is a no-brainer if your water heater is electric or propane. Even with gas water heating, it is worth considering.

I installed solar hot water on my house and wrote this article

It is happily working still, and will for many years more.

The sites I find most useful ...

Air collectors are also being developed for space and hot water storage

My hot water panels thermosyphoning into my house hot water tank

My current solar thermal project ...

We installed a wood-burning cooking stove just over 12 months ago. At the time we considered installing a solar hot water system but the cost to retro-fit our old cylinder in our 100 year old house was going to be prohibitive. To put it in context, approximately NZ$5000 for solar hot water vs NZ$2000 to plant 2 acres in firewood trees made it an easy decision (while I'm still young and fit enough to harvest firewood comfortably).

As it turns out, we've left the electric element switched off for a year and never missed it. The wood stove provides almost unlimited hot water and we only have to use it once every 2 or 3 days for cooking to not run cold. The fuel is all sourced on our property and is arguably still solar power, it's just that the trees do all the hard work converting it for us :-)

When our old water cylinder comes up for replacement, solar hot water will definitely be something we look at, but however you look at it, the luxury of taking a long hot bath or shower when it's raining and the fire's going is a truly guiltless pleasure.


I did a DIY installation at my home near Cambridge UK.

The system is composed of 40 47x1500mm vacuum tubes mouted on the gable end of my house as I don't have a South facing roof. The system is pressurised to 2 ba. I also installed a twin coil 210 litre cylinder. The old cyliner needed replacing anyway so I only consider the additrional cost not whole cost of the cylinder in my calculation. The system is pumped with a standard central heating pump (40w). I also have a small radiator as a heat dump in the loft to. Circlating water is diverted into this if it exceeds 75 degrees in temperature. However with a 210 litre tank this only opened up 1-2 times last summer.

Total installation cost was about £1250-£1300 plus 3 days labour (mine).

Back up system is a circuit from the central heating boiler which is 91% efficient.

In summer the solar provides virtually all my hot water. In winter it operates as a pre heater adding typically 10-15 degrees to the bottom half of the tank.

Pay back is marginal against mains gas in a condensing boiler. I reckon on about 9-10% against current prices.

nick, I live 40 miles to the South of you with an almost identical system, there are few SHW systems in our area and I thought mine was the only one on a vertical wall. Even though I have the HVAC qualifications/skills I didn't install it myself as substantial grants from both local and state Government more than paid for the authorised labour.

I am retired and need places to invest money so I am looking for a good low risk return on any investment (not necessarily the return of the investment in the short term). Since May 2006 the pump has run for >3700 hours, about 1000 hours per year, mostly in the summer months 'cos of our lattitude/grey winter skies.

When the panels are running I reckon they are absorbing ~2Kw so saving me £0.20 x 1000 = ~£200 per year. £200 on around £2000 investment is 10% tax free, one of my better investments - the panels are maintenance free and I expect them to last indefinitely, with maybe a new pump every 20 years or so. As the UK gas/oil/coal will be all gone in 10 years or so I expect the return on my investment to improve year on year with no effort on my part - think long term!

Hi Xeroid

Totally agree with your setiments. I am glad I put it in. In view of where this Country is going I have also put in 450mm of loft insulation, cavity wall, and a high efficiency wood burning stove.

I cook with gas however my gas consumption is down to less than 5000kwh per annum. Electricity is 3500 but then i work from home 2-3 days per week.

Yes I agree once installed there is little or no effort required. In contrast chopping and stacking wood is a task that soon loses its novelty.

I have a similar system to yourself and Nick (I am also near Cambridge). My self-installed vacuum-tube roof system preheats water via a glycol/water loop through a conventional hot water cylinder, which I plumbed in-line with the existing hot water cylinder. The circulation pump and heat dump fans (I use a car heater matrix) are 24V DC which is powered from a PV system. The PV system is rated at 750 Watts, and seems adequate to run a freezer and a fridge in the summer, but I have a charger which runs during off-peak tariff to make up any shortfall.

The SHW system cost me about £800 (no controller in that price). It's too early to tell what the performance is, only commissioned in the Autumn, but it looks like 3-4 kWH of hot water heating at the equinox on a sunny day.

In our low energy house, in North East of France we installed a very efficient system based on a heat pump working for heating the house and the water for the showers etc…with 5 m2 of solar panels connected to this system to assist in winter and to insure the autonomy from May to September. The fluid heated by the sun give its calories to the secondary loop via an heat exchanger, we limited the temperature to 62°C in order to avoid incident for users.
The make of the heat pump is StiebelEltron and solar panels Buderus both German manufactured equipment.
In fact when you heat the water in winter it is thermodynamically with a performance factor from 3.4 to 2.2, if it is very cold (below -12°C) regular thermal heating is helping the system (all integrated in the main machine”). A secondary feature of this system is the ventilation system of the house with also a heat exchanger between the air intake and the air exhaust.
All this equipment cost about 20 k€ where you can deduct 4 k€ from your taxes.
It works very well! Off course in a very well insulated house, which is in my opinion the first thing to do before investing in “fancy” and “efficient” technologies.
Hope it will help.
Otherwise I agree that at least solar pannels for heating should be an obligation in areas where the sun is "sufficient".

Here is the documentation for my low cost batch system installed not too far from Toronto Ontario Canada
I am rebuilding the collector box this year and will redo my tracking data.

Central New York State here. Two old Salvaged panels built on racks on the ground. Wood stove hooked up for winter Hot water. System works great and back up is an electric tea kettle! Wish I knew how to put a picture in. Donn

Get a free account at a picture sharing site like .
Upload your picture to the site. Open your picture in photobucket. On the left you will see a list of sharing options. Click on the html option. This should copy the html code for your picture (to your clipboard). Open a reply window in TOD and paste the html code to the reply. If you did it right, when you preview the post your picture should come up. Keep pictures small (less than 600 X ???) (to not overload the thread), or the picture won't fit peoples' screens.
Good luck!

Insulating , air sealing, higher efficiency furnaces, efficient windows, PV system, solar hot water, hybrid vehicle, etc.

Maybe 10% of the population can afford to do one of these in this current economic climate, less going forward. Maybe 1% can afford to do all the above.

How does this discussion even warrant the pixels and bandwidth? Other than technophiles fascination with "cool things".

Unless the discussion includes solutions that apply for at least...say 30% to 40% of the population, any of this fun stuff will be completely bowled over by the other 90% of humanity that can't afford to play your games.

I am not just being "holier than thou" nor simply contrarian or pessimistic, We need to keep our eye on the real issues and not get too distracted.
There are hundreds of tech blogs that focus on the specifics of all the alternatives. It seems to me that TOD has the potential to look a little deeper, more big picture, that is what made this site standout in the beginning.

The Campfire series was initiated so that these topics could be addressed from the perspective of oil depletion. That is a perspective that won't necessarily be found on the hundreds of other tech blogs.

It was also in response to requests from this community, and the editors graciously obliged.

If you don't find value in them, don't read them. It's really that simple.

Maybe eeyore should take a cold shower!

As I recall, eeyore was not the cheeriest of Pooh's friends.

But really, most environmental and many other energy related groups, though promoters of solar and other alternatives, do point out that conservation is generally by far the best payback both monetarily and in terms of energy savings and CO2 reduction.

It would be great to see a rating system presented and discussed here in terms of price, eroei, CO2 reduction...

(But note that I am not volunteering to bell that cat.)

Has any one seen my tail? I lost it somewhere.

"I am not just being "holier than thou" nor simply contrarian or pessimistic,"

Yes you are.

All these struggling folks you talk about ARE ALREADY paying for Solar Equipment and Insulation as we speak. They're just not getting them. That money is going into Oil, Gas and Electricity deliveries. And that money 'that they don't have'- will keep going out for those energy supplies again and again, while with the Solar and Weathersealing stuff, it would go out ONCE.

I'm sorry this is so hard for you and so many other people to take in and accept. A solar hot water setup is not a Techno-toy or a Complex 'Gadget'. It's more expensive on setup, but often free to operate. People will finance to get a pricey truck that they 'need' to get to work, this is NO different, only at the end of a decade (insulation faster, PV slower), this technology can have entirely paid off the investment you made in it, and the energy just keeps coming in through it. PROFIT, actual profit!.. get that? That truck might have been 'worth it', or an essential expense, but such 'perceived essentials' rarely make us back the money we put into them.. just another Sunk Cost of doing business.

I've got a Solar space heater running upstairs for FREE, blowing 105 degree air into the house every day it's sunny. I built it myself from scraps and basic hardware store stuff, and the fan runs on Solar PV. It's got doors to cover it in the summer so it doesn't fry up when I don't need the heat.. someone above said his contractor thought putting covers over panels was prohibitive. Man, I guess he'd never heard of Tarps or Hinged Boards before.

It's not that complicated. The Sun is hot, and we just get to grab a little bit of it. Find some stuffing, proper curtains and some caulk, and you can KEEP more of it, too.

Jokuhl - What you did (though you say free then you say things like PV, Blower, Hardware store) is admirable but is only an option for an even smaller percentage of the population than the store bought solutions.

My point is that these technocopian love feasts always end up giving the impression that the only thing getting in the way of a beautiful Sustainable tomorrow is doomers. I say the thing getting in the way is the VAST majority of the rest of the population for whom these "solutions" are not an option.

I don't deny that all the silver bullets are important, beneficial, and necessary. Im am just saying that the bottle neck we are approaching has an almost 100% likelyhood of pulling the rug out from under them.

Now back to your regular scheduled show Tech Talk.


I get it, and I tend to agree with you to a large extent.Not more than a very small percentage of the population has the wherewithal to do anything along these lines in the short term.

But every little bit does help.

And if teowacki doesn't arrive soon,these systems will become very common after another decade or so.From little acorns ....

To be clear, I said it's 'RUNNING for free', which is the central point. Yes, I bought a few items, including some cheap ($200) Harbor Freight Chinese Panels that are still vastly oversized for this application (15 watt fan), but it turns on with the sun and turns off when the box is not putting hot air into the house any more.

This is nowhere near the tech complexity of your basic clock radio or cordless phone. These solutions would take an enormous energy/financial burden off of many people, and are about as complicated to live with as a thermostat.

The idea that a local handiman being able to build such units does nothing to make it less available to his community. I don't expect every Lawyer and ESL teacher in Maine to figure out how to build and install them. A couple of carpenters or underemployed plumbers around, and you can see a market for reasonably priced, locally built systems. How does that make it a techno love-feast?



I get your point too.Certainly a lot of this stuff can be successfully home built.

There is really in my opinion only one really whopping big barrier to that happening.

Our society has mostly been kidnapped and hogtied by liberal yahoos who think the solution to every single little problem OF ANY SORT is another bueracracy that costs us an arm and a leg to oversee hangnail problems.

I could make an excellent living doing about six different kinds of work except it's against the law for me to do any of it without about fifteen different pieces of paper, which I cannot obtain except at a huge expenditure of non productive work and expense.So I occasionally change out an electric service panel , or install a pump, or butcher a pig, or sell five pounds of sausage, or borrow a transit and mark a property line for a nieghbor who wants to build a fence, or advise someone at risk of a heart attack and diabetes in respect to thier diet.So I have broken enough laws in the last year to have all my net worth consumed in fines and to earn an EXTENDED vacation courtesy of the regulatory gods in the fine facitilies operated by the dept of corrections.

But I beg every body to remember that the govt is your Mommy and is ready , willing, and eager to save you from the evil depredations of your nieghbor hood handy man , who after all undoubtedly made extra copies of the keys to the lock you had him install five years ago so he can comeback and KIDNAP YOUR LITTLE GIRL TONIGHT while you sleep.

Now it's been a few days since any body has given me any serious grief here and I'm in a bad mood and looking for an excuse to drag out MY flame thrower, so have at it, all you liberal pinko godless commies. ;)

Now if anyone gets the idea that I'm running a risk here let it be known that I commit these crimes only with and for people known to me personally for at least two decades who believe in omerta-silence.But that means I can't do enough business to earn a living-not that I want to or need to, being retired, healthy , and debt free , with a very low maintainence lifestyle.

Whew! You sure are spoilin for a game of tag, Mac!

I'm going to be obnoxious and not give it to you. Ornery old cuss!

I actually know a lot of commie pinkos around here who can build and fix their own stuff, but this is Maine, maybe that makes it OK.

But to come back to the issue, I don't see that much in the way of building your own hot water or hot air gear. You might not be able to give customers that paper that lets them get their rebate or something, and I suppose some places will want to issue a building permit for such work, but I'd hardly think that's all so onerous.

But believe me, I'm an 'under the radar' guy, too. I don't want to spend time filling out forms and registering for special programs. I want a hacksaw in my sweaty palm, and plenty of bandaids nearby.

Kumbaya, Tovarishch!

Of course I know you are already on my side Johkul.;)

My point is that almost anywhere now to do almost anything you must get a permit, and with the permit comes the liscenesed contractor, etc ad infinitum.

I like to let some of the more liberal types have it the way old southern women dealt with men who tried to cop a feel-they used a hat pin when he got close enough a second time.The man couldn't say anything at all, knowing he was in the wrong.

My little rant is for the benefit of those who don't yet realize that the govt is NOT supposed to be our mommy.

Give them thier way for another generation of so and they will insist on everybody coming in and getting fingerprinted and filling a date plan ala a flight plan before you can go out with the opposite sex.

You may be ok for a while yet in Maine but you must realize that you are at high risk of being overwhelmed politically in the next few years by folks who move to places like Maine or my Va mountians to escape the society they built elsewhere.The trouble with all these dumb sobs is that they immediately register to vote and start agitating for more govt- so thier new home can be just like the place they left.

Not a nickel's worth of work can the local handy men get out of the many tens of millions of dollars worth of construction and maintainence going on around here yet even after the recent crash.But if things keep getting worse, we will have our revenge when they all go broke and are unable to commute here for the weekends or keep up thier mortgages.

Funny thing about your typical well educated liberal-they believe in multiculturalism of a very strange sort-anything goes anyhere they AREN'T, but where they ARE, only THIER culture is permitted.

NOW OF COURSE I DO RECOGNIZE THAT ABOUT HALF OF OUR NEWCOMERS ARE PLAIN OLD MONEY GRUBBING NEOCONS.Most of THEM don't know what multiculturalisim IS , or what a neocon IS.But they do know what a water and sewer system is and a shopping center, and a country club, and they are more than willing to join hands with thier strange bedmates, the newly arrived liberals, and work like hell to turn this part of the world into another place thier children will want to flee.

A POX on the lot of them!!

Your otherwise excellent posts are getting a bit loony with your increasing hatred for we liberals (progressive, actually)
Now it's you and Johuhl et. al. against anyone liberal???
C'mon, I'm here because of the need for "US" all to find solutions.
I don't give a rat's patootie about your politics, I'm here to learn shit.

Sorry if I've been obscure in my Sarcanol. My wife HATES it when I do that. But pure pride keeps me from EVER explaining my jokes with a smiley. Pure Contrariness!

I'm about as Bleeding Heart as they get.. and I went nearly nuts watching the Inauguration to see them cut to a shot of George Lucas singing along to 'Blowing in the Wind', or one of my other anthems.. I swear to God ("..and may she keep me safe in Her great, Black hands.", as Garrison Keillor once told the Washington press club)

Anyway.. it rolls off. I like Mac, and hope that the 'Socialist Agenda' stuff is said with at least a glimmer of a twinkle in his eye.

Power to the People! (Obey your thirst!)

(I trust my credentials have now been reviewed and accepted.)

Credentials reviewed and in order.
I like Mac, too....

And dude, you put my workshop to SHAME!

You've built some very fun toys!


Thanks, Bob
The creepy part is, they all work so far.
Next project is to finish the beer can solar air heater.
It's on hold until and IF we ever get more sun.
And, tho' it was really hard drinking all that beer, I did it for science....

Luv Ya, Mac, but I too take exception with something you said. It was conservative Repubs who put all of our codes, permits, inspections and enforcement into place here. Had to be them, 'cause that's all we've ever had.

1. It's about the REVENUE.

2. It's about who to blame if things go wrong.

3. It's about the REVENUE.

Better to replace 'Liberals' with 'middle class busybodies' in OFM's original comment. Here in the UK they seem determined to regulate everything down to what colour your underpants are while at the same time waving the Daily Fail around screaming that it's all a European plot [In the UK Europe seems to have much the same usage by right-wingers that Commie does in the US]. It's unbelievably counterproductive here - for example I can replace a broken single glazed window pane like for like without needing a building inspection but if I want to change the whole thing for a decent double glazed one I need a five minute inspection that costs nearly as much as the window. Thus people don't bother (or ignore the code which makes selling your house hard).

Reno, Ghung,Bing;et bong, yes it's all with a twoinkle in my eye and a belly laugh and I attack he republicans quite freqeuntly.

Reguklars wiil know that I support many liberal initiatives such a single payer health care, tough fuel economy standards, clean air and water laws, civil rights, etc.

I would actually pass for a liberal , and have for long periods, except for the one thing-the libera solution seems to almost always tend to more govt-and that way lies paralysis and stagnation.
Somewhere around here is documentary proof that I was once a long haired hippie,and amember of the ACLU.

And for every single item my liberAl targets (this week) are trying to ram down my throat, there is a counterbalancing item the neocons are forcing on us all too.If the liberals were to stay in power long enough to get around to it for instance they would probably decriminalize smoking pot for instance-why should we have to submit to such a ridiculous invasion of our personal freedom and privacy as pot prohibition?

My point is to remind everybody that localism, self reliance, and consequently survival are going to depend on family, nieghbor, and community rather than non productive bueracracy -and Bingley is correct ,"middle class busybodies" is closer to the truth.

I hereby promise in the interest of fairness and balance to attack only neocons for the next thirty days.

Hi Mac,
In all honesty, I'm pretty pissed at both sides. The Repubs are the party of mean, and the Dems the party of clueless.
Here we recently had a nice windfarm shot down because of the rightist NIMBY's, and rumor has it the Sierra Club is going to sue to stop a wonderful solar thermal plant north of town. (I guess they haven't heard of Peak Oil or Climate Change?)
Nobody wants to address these serious problems or that we have so little time to fix things.
I agree with you fully, it's going to be a local and neighborhood fix. The gov's are bankrupt, and not daring enough to work outside the 'norm' so it's our joyous task to try and help.
Thanks for your above reply, and the 28 1/4 days coming of not sniping at Libs.
I do enjoy your posts...

I'm sorry this is so hard for you and so many other people to take in and accept. A solar hot water setup is not a Techno-toy or a Complex 'Gadget'.

But...but...if it's not a complex gadget then it can't possibly be a workable solution for an industrialized society. That plus the fact that it just ain't sexy enough and we've always heated our water either with fossil fuels directly or by electricity from our power company. There's no way anything other than that could possible work! And don't let the communists take away the profits from the power companies because it is just plain Unamerican.

As for Tarps, yeah we in Florida have heard of them that's what we we're given to fix our roofs with after a hurricane ;-)

I think that most of the value of these posts comes from the sharing of the insights of those who have tried the systems with others who might consider the idea. Readers of The Oil Drum come with a fairly different perspective than those from other sights.

Hopefully, the post plus the comments can give readers at least a few hints as to what they may be up against, and where they can get additional information.

Just a quick thought about 'the other 90%' who can't afford techno-toys. If SHW can regularly get up to 180F in Aus/NZ/USA/Can/UK/Mex (did I miss anyone?) can it also be used for water purification? I realize that the temp would need to get above boiling, but it seems to me that:

A - most of the poor 90% live in the tropics (if we're talking globally)
B - the tropics rarely get cold (that's why they're tropical)
C - high ambient air temperature + lots of sunlight = ideal conditions for boiling water (because who likes parasites anyway?)

I've seen a few campfire discussions about solar cooking, and have read about economic development projects (mostly in impoverished parts of India) around solar cooking, so what about solar water purification? Given that one in six (correct me if I'm wrong) people doesn't have access to clean water, solar water purification (SWP) could be much more useful (and cheap) than things like LifeStraws. Any thoughts?

I think that is a good idea, and you don't even need to boil the water to kill all pathogens, 30 minutes above 70 C is enough so any decent SWH should be enough.

Here's a link to my simple winebox solar rice cooker, which reaches over 220 degrees.
Total cost of original design was under 50 cents, most of materials are throwaway stuff.
I'm guessing you could do 4 or 5 batches of purified water on a good sunny day, and double that with two cookers.
Quad with 4....etc.
It takes just under 2 hours to cook 20 oz of rice, and while it cooks it should sterilze the water at the same time.
My latest model now uses 3 each 1-square foot glass mirror tiles, total cost 5 bucks, and they should last nearly forever if they don't get broken. Now I silicon the 3 mirrors together at edges to hold them in place, and Lynford made a beautiful set of wood edges to help secure the glass and help prevent breakage. Thanks Lynford!
Now if we can ever get some sun here, will start testing the new model.

eeyores, you are quite correct, as a UK citizen I know that on average we use ~112KWh of primary energy per person per day (US citizens usse about twice as much) only a very few percent comes from non-fossil fuel. Nick2w and I appear to be doing the same things and trying very hard to reduce our carbon footprint, but I for one don't come anywhere close to the UK Government target of ~34% reduction by 2020 from current levels - at the lattitude of the UK we all have a precarious future as we are now into major overshoot with no way back to the way things were in my childhood.

But I should be able to have a hot shower in the summer months at least.

You are right, only 10% of the world can afford* to these any one of these things in the current economic climate. Of course, if we limited our discussions to things that everyone could afford, we couldn't even talk about food, since ~20% of the planet is starving. It wouldn't be much of a blog either, and it wouldn't appeal to a lot of the people that read it currently: if you look at the average readership around here, (they did a survey once,) we tend to be highly educated, make above average incomes, white, male, and from developed countries. Not that I'm saying everyone is, but the point is that the number of people that can afford* these sorts of things are quite a bit higher among the readership. And if the blog doesn't appeal to the readership, then what is its point of existing?

*I've got a friend who makes a similar amount of money as I do, who also has a partner who makes a similar amount of money as I do, (I'm single,) and thinks that I'm rich to put solar (PV&DHW) panels up. My friend spends $4/day on coffee, I drink tap water. My friend has a new car, I have a 8 year old bicycle. My friend wants to buy a new house, I'm working on my old one, etc, etc... I make priorities about what I want to spend my money on, just like everyone else does. One of the things that I don't own is a car: it is a significant expense, (even if it isn't a hybrid.) I still manage to go to the store, get to work, (15 miles from my house,) and go to the average of 3 different destinations/day that normal people do, I just take the bus, ride a bike, and yes, a couple times a year rent a car, or get a taxi. Most people in the US own a car, although almost no one needs* one personally: the people that live too far from their jobs to ride a bike or take the bus could* always move closer, and the people that have to shuttle their kids around should make them walk: the chances of them getting kidnapped while walking are less than the chances of them dieing in a car accident, and far less than the chances that they will develop health problems from lack of exercise. Certainly some businesses need cars, although a lot less than currently own them; when they installed my solar panels two of the people showed up with a big van full of tools and parts, but two of the people showed up on bicycles, they lived in my neighborhood, and everything that they needed was in the van anyways, but most companies, (and their employees,) would send 4 vehicles for that trip. My point is that a car isn't actually a necessity, it is a luxury, yet most people own one anyway. So when people say they can't afford to insulate, (which isn't very much money in the first place: I spend more money on a blind date than I spent insulating my entire floor,) it is very rarely because they truly can't afford it, but more likely because they don't want* to, it just isn't a priority* for them. As for air sealing: The payoff for the simple stuff is often less than a year, and since most renters have one year leases, the real question is can they afford* not to?

Honoured Eeyore

Caulk costs $6 Can a tube. Plugging holes is the first step and gives a great return in energy efficiency. Caulking holes in walls and attic floors does not require much money at all. It also does not require much knowledge (I knew nothing about it when I started, I learned from two cheap paperback books from Taunton Press). It does not require much strength or health (I've been doing it while in a surgery queue with bad B12 anemia and a bunch of lymphoma biopsies, some days I feel like crap and am as weak as a kitten). It does require time (that's how I spend my weekends), patience, observation, a willingness to learn and attention to detail, all of which are FREE. Sealing the convection cell between the cracked foundation wall plate and the chimeny chase has greatly improved our house. I feel much fewer drafts (and I hate a draft), the spouse is going around gloating "The furnace is on much less, I know it. We're saving money." I figure if the spouse's sense of the furnace running less is correct (spouse has very good hearing so I don't see why not), we're paying for the cost of the caulk, foam and putty and stucco patch in one winter in fuel savings.

Solar thermal can be used very cost effectively for space heating as well. My system consists of a seven large flat plate collectors rated at 275,000 BTU/day, a pair of DC circulators powered by a small 50 watt PV panel, and 95 tons of sand in an insulated chamber under the floor. Runs of PEX tubing embedded in the sand transfer the heat as in a conventional hydronic system. Since it takes a long time to heat this much sand, I can start collecting heat in August when a lot of solar heat is available. By the time cloudy, cold weather sets in November the sand bed is at 85 degrees F. Even in a year like this one in which sunny days are few and far between, the sand bed cools only to the low 70's by late January. Room temperatures right now are in the mid 60's without any supplemental heat. When outside temps are really low we use a small wood stove to take the chill off. I anticipate we might burn half a chord this winter.

This system can be thought of as an unregulated mechanical heat pump: any time the sun shines it makes and circulates hot water. Other than the PV panel it utilizes technology that would have been familiar to any engineer working in the golden age of the steam engine. Since it uses no grid electricity it has no operating costs. System components have a 25-30 year life expectancy. I anticipate that I will need to change out the water/glycol mix in about 15 years at a cost of around $500, which is the only maintenance anticipated during the life of the system. Total installed cost minus the 30% federal tax credit was about $16K, which compares favorably with a conventional gas-fired hydronic heating system. It also provides about 75% of our domestic hot water needs. It's simple, reliable and mature technology and easy to explain to tradespeople (and building inspectors).

It should provide my family with free heat for the rest of my life (I'm 65); what's not to like?

really nice system. thanks. our problems are not primarily engineering/tech!


I have thought about something along these lines myself.How long do you expect the pex buried in the sand to last, and how will you replace it?Moving that much sand in a confined space is going to be a very tough job.Changing out the rest of the system might not be very hard at all.

Also what kind of insulation did you use? Is your sandpit watertight?


I used oxygen barrier Swedish PEX which is said to have a 30-50 year service life. The glycol (DowFrost HD) contains a pH buffer and a corrosion inhibitor which should foster maximum longevity. I doubt I'll be around when it finally fails but replacement would require jack hammering out the slab and moving around a lot of sand. I've had to redo the PEX once already before the slab was poured. The temps were in the teens when the sand was placed and two of the six runs were damaged when we had to pickaxe trenches through the frozen sand. I discovered the leaks when I pressured tested the loops before tying the rebar for the slab. Surprisingly, it took less than a day for a three man crew to dig up all the tubing, patch the two holed runs and replace the sand.

The walls of the structure are ICF (Insulated Concrete Forms) rated at R29, The walls extend 3 feet below final grade and sit on 9" footers. I placed 6" of 1" limestone rock between the footers and then 3" (R15) of EPS rigid insulation. A foil/bubble/foil blanket covers the foam and acts as both a radiant and radon barrier. The sand went on top of this. An exterior perimeter footing drain with a sump pump keeps the water out. No problems so far.

This system was developed by a guy named Bob Ramlow in Wisconsin. He has designed and engineered dozens of sand bed installations for builders all over the country and teaches classes on solar water heating design. For $600 he and his son in law provided full engineering drawings, a detailed parts list, step by step instructions and online tech support. A local plumber and I did the installation. You can find his site at

I have a solar hot water system in Stockholm, Sweden 59° 19′N, 18° 4′E.
It is a Active systems using a “heat exchange” circulation system and glycol throw flat collector on the roof, the collector is 10 m2 and then I have waterstorage with 1000 l, used for both hot water and heating.

The system vill give me all energy from the sun from end april to september, the rest of the year a use district heating as a complement. But the system vill start produce some energy starting in february.
I built the system 1995 and it has worked well all the time.
Electric heating is about 17 cent/kWh and district heating is 13 cent/kWh and the sun give me about 3000 kWh/year and it is also heating the bassment during the summer.

Hi, for any one in the UK
Or are very good on prices
For Ireland. or are very good on prices
Tubes are best suited to area with less than 900Wm2 annual solar iradiation.You can check your location on NASA web site
Both suppliers have a lot of good material on sizing /plumbing/ installing for the DIY capable person. For Europe be sure panel/tubes have SOLAR KEY MARK
If you want independant back up in case of mains failure a cheap way to to it is to power controler trough a Computer UPS similar to those supplied by APC or THRUST

Other than the obvious question "why are you heating hot water?" I'm impressed by the responses.

However, my question is has anyone used ethanol as a working fluid (antifreeze)? It seems safer, tastier and easier to obtain than glycol. The motor fuel ethanol plants will be very good moonshine producers soon, but I'm sure a little could go to hot water production...

I live in Central NY. I tried in 2005 or so to do solar. I looked at hot water and PV electric for our house.
It didn't work out for PV because the best place for the array was in the road set back and the town wouldn't let me build anything there.
Our south exposure isn't that great for the solar domestic hot water. Our roof slope faces west. We also have some pretty good sized trees in the east (back) yard.
In the end the consultant didn't seam to enthused to do it and I thought the cost was pretty high. About $8,000. Collectors facing west wasn't ideal.
Re-fi the mortgage last year made the most sence to spend money to save some money.
I guss my point is not all sites are created equal :)