Some Notes on The Midwest Renewable Energy Fair, Solar Ovens, And Small Wind

Since my dog has a broken leg, and my garden is reasonably under control, I decided this afternoon to drive the 20 miles from my cottage to Custer, WI, where the annual Midwest Renewable Energy Association Fair (MREA) was taking place. The organizers expected 15,000 people to attend. I went last year (amidst tornado sirens) to see Jim Kunstler and my initial sense was that this years fair was nearly identical to last, in terms of product booths, workshops and types of people attending. From the MREA website:

The Fair is the world’s largest renewable energy, energy efficiency, and sustainable living educational event of its kind

Below the fold are some of my observations and thoughts from a few hours at the energy fair.

Like last year, it was packed. The fair had hundreds of booths, from solar, wind, and geothermal alternatives, to gardening and small scale farming materials, to biofuel and farming books and magazines like Mother Earth News and Backwoods Magazine. Here's the exhibitor list (pdf) with phone numbers and websites of all the product vendors at the booths.

We only had a few hours so my friend and I spent most of our time talking to the several solar oven vendors. Solar ovens are selling like hotcakes in developing countries that have areas with no easy access to electricity, though here I get the sense they are still viewed as a novelty. There are the personal sized ovens (about 19x19x11 inches) that sell for under $200 and they also have the industrial cook-for-a-village size that are about $10,000. The large version concentrates reflection from panels on the side of a glass filled box. The smaller versions have the same shape/ratios, but the reflective panels are optional. Apparently (this was my first time shopping for solar ovens) the same mechanism that causes cars to get VERY hot when the windows are up is enough to generate 250-300 degrees in these glass and plastic ovenboxes. The reflective panels bump that temperature up a little more - one vendor said in the sun climate of Wisconsin, they could get to a maximum of 380 degrees, with the panels.

The other thing we were told is that these ovens are also used as water purifiers. Apparently boiling water kills pathogens in a few seconds, but 'pasteurization' occurs at lower temperatures for greater lengths of time (10 minutes was their guideline). cooking.JPG">

I was pretty impressed by the small oven and actually bought one (I chose this brand because I basically liked the people better). For me this was not an 'energy investment' decision, but my cottage gets hot in the summer and even hotter with the oven on. If I can cook outside, the house stays cooler. Also, the marketing seemed to suggest that food slow-cooked in this manner is tastier and healthier and apparently chicken and fish work great. Im sure I will save some electricity by using this product, but it struck me more as a sensible thing to do given all the free sunlight falling on my yard. Then again, my girlfriend bought one first and maybe my purchase had simpler explanations.

The fair also had numerous wind turbine and electricity conversion systems. The cost on the wind turbines I looked at was roughly $15-$20,000 and depending on the wind regime (see above) you live in had a payback time of 10-20 years by rough calculation. As wind 'return' increases with the cube of wind speed (as opposed to square), large scale wind turbines will have a better total return for society as there is an energy economy of scale - plus they can get higher up in the air accessing greater wind speeds.

One of the first questions people ask when buying a small scale wind turbine is 'what is the payoff time?', or how many years of electricity bills that I wont have to pay add up to the purchase price of the turbine? This question misses many aspects of the decision to buy a wind turbine. First of all, some people get satisfaction from harvesting renewable power from wind, irrespective of cost. If there is concern about grid interruptions or failures in the future, then owners of turbines and solar panels will not only have saved on electricity bills but also bought 'energy insurance'. To view the future electricity prices at an inflation adjusted version of today is straddling two paradigms and might be an excerise that keeps people from pulling the trigger on these items. Peak oil will likely result in the entire spectrum of energy prices having an upward shift. (Note: I dont know enough about small scale wind to recommend for or against it - though I am very certain that large scale wind will grow tremendously and be profitable in both energy and dollar terms).

The financial concept of duration comes to mind when assessing wind turbines. Duration is the weighted average of all future income streams on a bond and effectively measures the sensitivity of a bonds price to a shift in interest rates. If interest rates drop precipitously, one will make alot more money on a 30 year bond (12 year duration) than a 3 month t-bill (2.9 month duration). Similarly, if energy prices all shift upwards dramatically, those assets with the longest lifespan (duration in this sense) will have much higher payoffs. In other words, I am beginning to increasingly look at large purchases not only in dollar terms, but in energy terms. Given my view on the future energy landscape, I should be (and am) willing to pay more 'dollars' for things today if they are the correct energy decisions for the future. I wish more of corporate and policy decisions were made in this manner. I am going to look further into small scale wind - my impression is that many of the current menu offerings are more like toys, and not great harvesters of energy. If some of you know more on this, please post links and info.

In sum, the people I saw at the fair were not dissimilar to the crowds at other alternative fairs Ive been to in the past (though pretty different than my brother at a Midwest Medieval Fair in Ohio). I got the sense the average person at MREA were in Custer because living partially/wholly off the grid is a lifestyle choice and wanted to learn about the latest gadgets, meet with friends and learn more about the alt-energy tribe. I did not get the sense, either this year or last, that a majority of consumers attended because they see the peak-oil-writing on the wall and are trying to get ahead of the curve on energy independence.

It also struck me today that these solar PV and home wind systems are complicated enough that you almost need an engineer in the family or alot of training/experience to effectively get and use the energy harvested from the panels/turbines. I think its great to want to be more self-sufficient and that these fairs are attracting large crowds. But the days of many of your neighbors having solar panels and wind turbines seem far far away to me.

Did you hear Kunstler speak? I would like to hear your impressions and comments, if so.

I talked to him before his speech last year but that was the day I had 400 miles to go to South Dakota so I skipped his talk - I had heard him 3 times before however, and each time was a completely different speech (though he did mention that we have a rail system that the Bulgarians would be ashamed of on all 3 occasions.)

Jim is a friend of mine. I think he has a better command of the English language than anyone I know and is a brilliant man in many ways (not in price/timing forecasts of DJIA levels...;) Like the rest of us he doesnt hold a crystal ball on what/when is going to happen, but he has a wide angle lens and 'gets it'.

Perhaps some don't realize; Kunstler was a celebrity FIRST, for years. I heard him speak on surburbia in the mid 90's.
He IS briliant and those of us with literary ( as opposed to scientific) backgrounds GREATLY appreciate what he brings to the discussion.


If you have a grid connected solar system like I do, you won't be protected from grid interruptions. Your system will shut down during a power failure to protect the safety of linesmen who may be working on the power line and not aware your system is feeding power into it. To protect yourself from power failures, you need batteries which are a whole new can of worms.

I agree that you need an MBA to figure out your expected rate of return. It depends on future power rates, interest rates, etc. I figure in the worse case, I have bought myself insurance against electricity prices spiking through the ceiling even if that event doesn't come to pass. I live in southern california. Only the Mojave desert has better sun and I think only the northeast has higher electric rates.

It doesn't take any brains to install a solar system. You make one phone call, write a big check, and a contractor will do everything. And it is maintainence free.

Could you trouble-shoot it yourself if you couldnt get the maintenance person out?

I'm not sure I'd want to mess with 360 volts of electricity if I can't get a licensed electrician out here. I'm an electrical engineer by profession, so I know what a volt, an amp and a watt is, but I don't deal with more than five volts. I'm pretty sure I could walk around with a multimeter and identify where the break in the circuit is. It worth noting that there are no moving parts, the solar panel output is guaranteed for thirty years and the inverter is guaranteed for ten years. Beyond that there are just wires and circuit breakers like any house would have.

You forgot to mention you were an electrical engineer!

In my opinion though, the important societal impacts will come from both the macro/policy scale and the micro/practical scale and hopefully in the twain shall meet.

I figure it all depends on what you wanna do with your electricity. Without batteries to store the energy you are using the grid for that purpose. What can you power with your solar cells directly? Probably not a computer, or microwave or mostly anything.

You can probably power lights (but during the day O.o?) or heating elements.

Of course I'm using the grid to store energy (well the grid doesn't store energy either but there's like a petawatt on the US grid at any one time). I'm grid connected anyways, batteries are a pain in the rear, and they paid me $3.50 a peak watt to do it. I dump all my power to the grid, run my house off the grid as always, and at the end of the year, me and the electric company will settle accounts.

If you are off grid, you will probably have batteries somewhere in your system. Remote traffic lights are powered by solar. There are solar powered cell phone battery chargers for backpacking and gabbing at the same time. Solar powered water pumps. Your energy reserve can be the gravitational potential energy of the pumped water rather than batteries. If you use solar power to heat a working fluid to run a heat engine, then the hot fluid is your energy storage and it can work all night long.

I just installed a 300v 3KW grid tie system on my garage.
I worked on wiring them to the combiner when it was dark outside, no light no power. I suppose if you had some way to cover them it would work also. It does not take much light to get some voltage, over 1 hour after sunset and it was at 14v.

Aren't there PV system controllers that can handle both a grid connection and battery farm? That's the sort of thing I'd want in a solar energy system.

The problem will solve itself.
But not in a nice way.

Yes there are. You'll spend a couple thousand more for the system controller and then a couple thousand on the batteries. And figure out where to put the batteries. And btw, the batteries only last a couple of years and then they need replacing. Your call, it depends how often your power goes down.

Battery life for expensive (andf heavy & bulky) nickel iron batteries is decades (perhaps a century under ideal circumstances). Chinese firm using German Varta tooling is only manufacturer that I know.

I would buy the PV now and make contingency plans for batteries.

A simple switch could go from grid connected/no batteries to off grid battery power. Use your IQ instead of the controllers IQ. Monitor over charging (I think Ni-Fe are immune).

Best Hopes for Renewable Power,


BTW, were there any microhydro booths ?

Not as such Alan. But they did have some old fashioned pull water out your well with a dutch style windmill.

I was trying to buy something called a sling pump to get micro-hydro from my river here, but I cant find any company that still sells them in the states.

Ever heard of a sling pump?

= hydraulic ram ?
I used to live in the same district as this guy and I know the pumps works good

The best microhydro designs in the world (IMO) are at

If you would like help in figuring out what to do, let me know.

Best Hopes for more MicroHydro,


Indeed. For those lucky enough to have land with a year round stream with the required flow and drop, MicroHydro is the gold standard for personal electricity generation. Low cost, low tech, and no batteries needed. For downunder:

Right. So here's my plan. Replace that hard to find hill and stream with a very simple stirling pump driven by biomass/solar. The rest of the microhydro is the same, you now have a biomass hill rather than a dirt/rock one. Your biomass/solar hill can be anywhere.

So, now you have it all. Except a really big hole in the ground which you use for hydo energy storage if you care to do a little digging.

BTW, a thermal machine designed to do nothing but pump water can be very very cheap compared to one made to do harder things like generate electricity.

The world is saved. I can now go down to New Orleans and happily eat myself to death as the gods fated me to do from the beginning.

Note the $38 dinner at the bottom, drink, tax and tip included in these. And the "Top Sixty" Ethnic restaurants (in a city of 250,000) This is the website of our "Talk Radio" food guy. #1 talk show in New Orleans, 2 to 5 PM weekdays,

Best Hopes for Fine Dining in New Orleans,


This reminds me ....

with a very simple stirling pump driven by biomass/solar.

And where are you buying this stirling engine?

Hey Eric. By now I would have thought that everybody knows that I MAKE stirling engines. I don't buy them. The ones I want ain't for sale. Have to whittle 'em out with a pocket knife on the back porch.

This one looks like and actually is a piece of pipe. Inside are the usual parts. They rattle around when the thing is heated. You use the rattling pipe to pump water.

A very old idea. Very simple. Very cheap.

And why aren't they being made and sold? Damned if I know. Especially when really crappy and really expensive stirlings are being funded by VC's, apparently the ones with way more bucks than brains.

Hey Eric. By now I would have thought that everybody knows that I MAKE stirling engines.

And many of us lack access to machine tools or even the knowledge of how a cutting tool can work harden metal, how toi hand sharpen a cutting tool, how to work a cutting path, et la.

And why aren't they being made and sold? Damned if I know.

The nitrogen charged, made from pressed sheet metal, 1 hp unit was claimed to exist by back in the last century.

Nate your sling pump appears to operate the same as an airlift pump. (Air bubble pump).
Looks like it has some advantages. Thanks

Well a friend told me that would be exactly what I could use on my property here but each time I google 'sling pump' I get advertisements for ladies shoes..

We got our sling pump from Lehman's. They also have
ram pumps,etc.

Nate, air lift pump explained(somewhat)

Wind mill driven air lift pump
My take is that there needs to be a below the water line tube that extends quite far below the air injection point, so the air will rise up the pipe and not bubble out of the bottom. This has to do with "lift" created pressure. Your sling pump would compensate for this lenght of tube via the internal coil.
You might try a ram pump- google has lots of hits. (and they are noisy)


I was looking to buy a fish farm in Wisconsin 10-12 yrs ago, near Richland Center, and the place for sale worked with 2 hydraulic rams. Low head spring, perhaps 7 ft drop on land. At spring, water went by ram to house and barn, rest of flow and spring to fish raceways. Botttom of raceways had another lg ram for filling stock/gravity watering pond.

Nice place, no electric at all-Amish I believe. Not quite right for fish (raceways dumped into each other, compounding any disease problem). Wonder what happened to it.

Nickel costs over $40,000/tonne - gyrated between $43,000 and $51,000 last week. It was only $9,000/tonne in 2000.

I guess that is not a realistic option for the masses.

By the way, the price of Nickel has a strong relationship to war or to expectations of war.

I don't really need a ton of it, just a few pounds in my NiMH or NiFe batteries.

And unlike petroleum, the metal is not irrevocably consumed by the system. It should continue to function for decades at least.

Lot's of battery chemistries each with advantages and disadvantages. My recommendation is not to use batteries unless you are off grid.

A simple switch could go from grid connected/no batteries to off grid battery power.

How do you power your AC appliances from DC batteries? If your inverter down not sense grid power, it will shut down.

I must disagree with the use of this site, it is very uninformative. It gives an energy density in terms of Watts/kg which is inane. Energy density is measured in Joules/Kg, the specific power of the device is watts/kg.

Being in engineering you should know this. Just like I do.

Feel free to disagree with the site. I just posted the link as a primer.

In the real world, 99% of solar houses use lead acid batteries. The rest, nickel-cadmium. Nickel-iron is a hundred year old technology, well known to people who make their living putting up solar houses, and have been found wanting.

Personally, I think all batteries suck. And I don't own a lead mine somewhere.

The cool thing about lead acid batteries is that they give off hydrogen. Collect it and combust! (its not a great deal but every little bit counts)

the uncool thing about lead acid batteries is how much they suck in terms of specific power and energy density.

only flywheels can get close to the energy density of hydrocarbons, and by gross energy flywheels are still a factor of 30 too low.

Energy Density of Some Materials (KHW/kg)

* Gasoline ------------------------ 14
* Lead Acid Batteries -------------- 0.04
* Hydrostorage --------------------- 0.3 (per cubic meter)
* Flywheel, Steel ------------------ 0.05
* Flywheel, Carbon Fiber ----------- 0.2
* Flywheel, Fused Silica ----------- 0.9
* Hydrogen ------------------------- 38
* Compress Air --------------------- 2 (per cubic meter)

Looks like you are thinking of carbon fiber flywheels. The energy density of hydrogen ought to include the weight of the tank needed to hold it, but it isn't my chart.

In a home solar situation, you don't care about mass. You buy literally a ton of batteries, stick them in a room somewhere, and they don't go anywhere.

You gotta wish that EEStor was for real: 54 kWh, 400 pounds, $4K. Density's around 0.3, and no worry about the number of times you recharge or the depth of discharge. Typical suburban household today is about 30 kWh per day, so one unit is almost two days worth, three days easily in an energy-efficient household. Don't even have to worry about volumetric efficiency -- for a residential application, it can be as big as a bathtub and it's not a problem.

Imagine the joy of being the house in the neighborhood where the lights are still on, the heat still works, and people are eating hot meals, 24 hours into the blizzard-caused power outage :^)

All that takes is a domestic cogenerator and a battery buffer (assuming you heat with something other than electricity).

Three strange things about that table:

  • Hydrostorage could just as easily have been in units of kg, because water's roughly 1 kg/liter.
  • Why no head measurement for the hydro?
  • Fused silica is given as 4.5x as strong as carbon fiber.  I'm sure that's wrong.

The specific energy is 55 watt hours per kilogram. Not watts per kilogram. Thanks for pointing that out.

If you overcharge iron nickel batteries, you will electrolyze water into oxygen and hydrogen. The same thing will happen if you overcharge lead acid batteries but nobody is suggesting overcharging lead acid batteries.

how ya' doing...:-)
you said,
"I would buy the PV now and make contingency plans for batteries."

Or we could find some way to run a PTO (power take off) from our 240D to drive a gen set! :-)
(Don't laugh, I knew a guy who had it set up on a 3/4 ton Ford Diesel once, he had no PV solar, but he had a backup generator when the truck was in the garage!)

Another thought...a small backup generator with a propane (LPG) engine and a propane bottle. Clean, relatively quiet, and LPG will store forever (well, a long time...:-) A couple of power outages, go down and swap the bottle, pretty much like you do on your gas grill....

In fact, I am beginning to think that the ultimate home system, if a person can afford it, might be PV solar, grid tied, an LPG tank (as large as you can afford) buried in the yard, and backup heat and generator running LPG,
Add in the ultimate, a plug hybrid car that runs LPG as the fossil fuel...
hmmmm.....this could be interesting....:-)

Roger Conner Jr.
Remember, we are only one cubic mile from freedom

You forgot solar water/space heating (could piggyback off the solar PV) and the ground-source heat pump.

Given what I personally have in the pipeline, we are almost there with that plug-in hybrid being the biggest obstacle at the moment.

For co-gen propane, check out, for co-gen solar, see, and for the battery pack, see I'm still awaiting the propane co-gen. The other two are on my wish list.

One issue to consider is the controller. Simple controllers will shut down the system when there is no power coming in. More complex controllers will let the system switch to local power only in the case of a mains failure.

Second, you have to consider batteries. If you only need to worry about a short outage every few years perhaps you could get away with just a very small battery. It might be enough to run the freezer and fridge in the daytime while the solar cells are providing power and have a small battery for some limited lighting or running a radio at night. On the other hand, if you expect the power to be frequently unreliable for days at a time then you'll need to think about sufficient batteries to keep your life going during that time.

I also realised that if a bushfire takes out the mains power the 'smart box' won't let you use the roof current to power a water pump. Hopefully I've solved this problem by rigging up a quick connect pumping system driven by a petrol engine.

Hi Robert

In my hacky kind of thinking, I have been wondering if you can fool a grid tied inverter into operation in a power cut by supplying "grid" mains from a 12V battery-powered inverter. You'd have to disconnect from the real grid mains to prevent pushing power back on to the grid and putting maintenance operators at risk.

Carbon Coventry - UK

Hi Carbon,

Beats the crap out of me. Sounds like it will work. Around here your solar system requires a permit, is done to electrical code, and is inspected by the city and the utility before you get permission to turn it on. Nobody doubts that you can get a battery backup to work. We are just arguing about how much trouble it takes.

As a general philosophy, I take a dim view of people who jury rig around safety devices. Some day you'll have the manual switch in the wrong position.


One approach might be to have a battery powered inverter with a relay and controller, so that, if the inverter is up and the battery is charged, power will flow from the inverter, and, if not, from the grid. The relay needs to be fast, though, and the inverter needs to be able to handle your full load.

As a bonus, your equipment can be totally isolated from brownouts and grid fluctuations.

This approach 1) ensures that no grid interconnect is possible, and 2) vastly simplifies UL testing--for example, no need for surge immunity tests on the inverter output, if it can't be connected to the grid.

I suppose you'd need to worry about deep-discharging the batteries if your solar cells aren't capable of keeping them charged.

Disclaimer--I've only used this technique to ensure reliable power from a battery bank powered by grid-connected rectifiers.

No please do not do this. I spoke at length with a inverter manufacturer here in Australia, Latronics, on this very subject. Grid-tie inverters have anti-islanding routines that check to see if they are the only power source on the grid. They do this (I think) by attempting to change the phase of the grid power. If they can do it they reasonably conclude that mains has failed and they are alone (an island) and shut down. This sort of thing would do horrible things to the inverter that you had connected apart from the sychronisation problems.

Apart from this you would not want to be responsible for the death of a linesman working in probably appalling weather that skimped a bit on safety because he/she was in a rush to finish.

That's why the relay totally disconnects the newly created "island" from the grid. Your non-grid-tied inverter, still running, is totally isolated from the grid, and therefore incapable of harming any linesman.

There is never any connection between the grid and the inverter. The load is attached either to the grid or to the inverter, never both.

Of course, this approach means that you can't put power into the grid and get paid for it by the power company.

UL (a NRTL for the US) was OK with it.

However the grid tie inverter will probably still shut down as it will still detect that it is on an island.

You would be far better to invest in a Xantrex SW3048E or similar that do all this without having to hack up a solution that may not work. The SW3048 will charge batteries and change automatically from grid tie to standalone. Outback do one as well.

or the Outback

....if energy prices all shift upwards dramatically, those assets with the longest lifespan (duration in this sense) will have much higher payoffs. In other words, I am beginning to increasingly look at large purchases not only in dollar terms, but in energy terms. Given my view on the future energy landscape, I should be (and am) willing to pay more 'dollars' for things today if they are the correct energy decisions for the future.

I wish more of corporate and policy decisions were made in this manner.

I think your analysis is correct, both in terms of the duration analogy and your expectation of increasing energy prices. However, the linkage to corporate and policy decisions may be weaker.

I don't think the problem is planners failing to incorporate expected rising energy prices in the planning process; rather it is failure to anticipate rising energy prices.

As you know, efficient market theory says that the price of a good on the futures market is the best available approximation of the price of that good over the given time period. It would be very difficult for government or corporate planners to use any other price in planning or they would be speculating, or taking on "risk" that is better left to others who are experts in it.

The same is true for the dollar. Many would argue that it is clear that the dollar will get weaker, so we should all try to reduce our future dollar exposure. However, the futures market shows that those who have actually taken a position, as a whole, don't have expectations of a huge swing in value.

I work in a giant finance company (not unlike ones you have worked for in the past) and we don't have any internal policy to treat future dollar or energy prices significantly differently from how the market treats them. (Although presumably certain entities within the firm are taking bets on the movements of these assets prices - however, as I noted above, on a net basis the financial world is not treating future dollar or energy prices significantly differently from how the market treats them). If those who should be best placed to speculate on future energy price increases aren't doing it, how could a government, which should be less capable of judging and bearing risk, justify it?

The solution is for the market to recognize higher energy prices, not to have the government and corporate sector try to outsmart the market.

I agree with everything you said (for once...;) The market is the tail that wags the corporate/policy dog.

The solution is for the market to recognize higher energy prices, not to have the government and corporate sector try to outsmart the market.

This is a large chunk of the big problem IMO. Many things conspire to allow the market to discount what will likely be a black swan event. Net energy decline, steep discount rates, recency effect, crowd mentality, reduced ability to think for oneself, etc, all have made it more difficult for the market, in aggregate, to connect the dots.

Yet oil and gas long dated futures made all time highs last week (and as I look tonight at energy flat, soybeans and corn making multi year highs and wheat making all time highs.) My sense is the grain market is pretty unprepared for peak oil as well.

I agree with everything you said (for once...;)

Sorry. I'll try harder next time.

How far into the future do futures markets actually go? If your investment is expected to last even one decade (like a car) let alone several decades (solar panels) one or two years is just the start. Does the market actually tell us anything directly about gasoline 5 years from now or electricity 10 years from now?


Oil futures markets go out to 2015, where prices are around $70. However, government and private forecasters make longer term predictions. The recent EIA report expects oil prices to be to be in a range of $28 to $90 in 2030!!! No wonder the markets are asleep! Of course, the incentivized smart folks will force the government forecasters hands with oil and NG prices, just like they do with interest rate cuts, etc. Already long dated oil futures are making new all time highs - higher even than during hurricane Katrina and Rita

Do we know the volumes for which these contracts are written?

Because if there are 100Mbb/day of contracts being written/sold for 2015 there might be a problem...

i wrote about oil futures, their volumes and implications here.

The december 2012 contract has open interest of about 17,000 contracts (source Each contract is 1,000 barrels, so 170 million barrels total contracts worth - current margin about $4,000 per.

Most oil is contracted for privately rather than on the spot market. These contracts typically have all sorts of clauses in them. If you've paid attention, Saudi Arabia has reduced deliveries to Asia almost every month for the last several months.

Ghawar Is Dying
The greatest shortcoming of the human race is our inability to understand the exponential function. - Dr. Albert Bartlett

I lived on a sailboat for two years sailing from UK to Australia (check it out if you want - I installed and maintained a power system that ran at 24V and consisted of:

1 engine alternator 12V DC engine starting circuit + 1 12V 150 Amp Hour (AH) battery.
1 engine alternator 24V DC 175Amp House circuit
1 3kVA diesel genset supplying 220V AC
4 75W solar panels supplying 24V
1 400W wind generator supplying 24V
1 water-towed generator supplying 600W at 24V
House Batteries: deep cycle, 500 AH at 24V

Managed by an Adverc battery management and smart charger/regulation system.

I ran refrigeration (what is the point of sailing round the world if you cannot have a cold beer or two?), lighting, water desalination, an autopilot, radar, VHF & HF comms and navigation electronics off that set up and needed 200-300 AH at 24V per day.

Not too difficult to set up and I was forced to do my own maintenance (electricians are hard to find 1500 miles from land!). I am an accountant, so if I can do it.......

Batteries are only good for 2000-3000 cycles. They need constant checking and maintenance. This meant checking cell voltages, electrolyte levels and specific gravity twice per week. One cell in one battery (each 12V/250 AH) failed in Grenada necessitating the replacement of the battery. It gets interesting checking electrolyte levels at sea. This should not be an issue if you are heading for the hills. Also, in a house I would install a weeks worth of power if I installed batteries. On the boat, I only had room for one day (max discharge practice was 50%, although permitted to go to 33%).

We ran the genset every day! To get the renewables to work well (and be grid independant) you would need 10 times the solar we could carry and a much bigger wind generator. I would size the solar at a minimum of four times daily requirements using winter sunshine information and I would be checking wind in the area very closely before investing in a wind generator. If you work on the basis that it might be working at capacity for 20% of the time that would be average.

Otherwise the system as a whole was adequate and reliable.

It one thing to be an accountant working on a 24V system and another thing to be an accountant working on a 360V system or a 120V/240V system. To me, the issue isn't difficulty but risk.

disconnect the ground
figure out how to bypass the battery bank

The genset was 220V AC available throughout the boat on an AC circuit, but usually applied to the smart charger. The boat could also accept 110V and 220V AC shore power. So there were high voltage AC circuits on board.

There were in fact 4 circuits in total: 12V DC engine start circuit, 24V DC House Circuit, 12V Comms Circuit (through 24-12 stepdown from the house circuit) and a 220V AC circuit supplied either by shore power or from the on board diesel genset.

I was always "scared" of the AC circuit and used to isolate it completely before working on it.

Solar panels always generate power if they are illuminated. You can't just pull the circuit breaker and be isolated.

They cover the active surface with black paper in the factory. Until they got the system all installed and tested, they don't remove the paper.

I guess I can check connectivity at night with a flashlight and an ohmmeter. But the problem may not show up when the system is powered down.

So you were using between 200 and 300 watts average.

That's a hell of a lot for a very small space (it's about what I use for a 2-bedroom duplex, including electric hot water).  It sounds like you should have aimed at efficiency first, before renewables.  LEDs for all running and most cabin lights, low-power transcievers (or dedicated receivers so you can leave the transmitters off), etc.  Don't know what you'd do about the radar if you have to run it all the time.

Great post Nate. Good to see the MREA and Energy Fair get a main post here on Oildrum.

"you almost need an engineer in the family or alot of training/experience "

Go to their homepage and you can take 1-5 day workshops that will get you the training you need. If you still feel less than competent you will at least understand the market place and the systems themselves.

"my impression is that many of the current menu (wind turbines) offerings are more like toys, and not great harvesters of energy. If some of you know more on this, please post links and info."

Contact the object of this article at the MREA. He could send you some reprints of articles he's done in magazines like Home Power etc on these and more concerns you might have or come up with over time. MicK is one of the best in the business in the world, IMHO.

I think you touched on one of the more important points here - economies of scale - for wind turbines.

An interesting concept... the Rural Electrification Program Redux (farms were buds on the tree (grid) and now may bloom to become the "leaves" ... ????) - see pick at bottom of article linked above:

Although some have been critical of relying on the rural landscape for siting public utility wind machinery, such practices have created revenue streams for willing farmers. Owned by a consortium of Eastern Wisconsin Utilities, this project consisting of two 600-e CWM (cold-weather modified) turbinees sits on the Zirbel family farm in Glenmore, Wisc. Over their first three years of operation, the two windmills generated 7,089 megawatts of electricity and displaced an estimated 6,175 tons of carbon dioxide, 26 tons of sulfate, and 25 tons of nitrogen oxides.

Glad you bought a solar oven. One of my favorite investments and low tech enough to fix or make yourself in a pinch.

I tend to cook frittatas, stews and soups, beans, steam vegetables, bake chicken and fish.

White rice can get mushy if not done carefully, brown rice more reliable. Lentils are a fast cooking legume.

Cooking in a solar oven and bathing from the solar shower give me great, nearly guiltless, pleasure.

Here are directions for making a solar oven from a pizza box:

It's a low-tech, 1-2 hour project. My wife led a girl scout troop and they did this.

How great would that be if all the parents in the country did this as a project with their kids, taught them about solar power, where it comes from, how it works, etc.. This is what kids could be learning about - thanks for the link.

Nate Hagens, you are owed a proper thank you, what a fun and interesting article, and your PDF of the exhibiters was EXCELLENT as a tool, I have it saved to my hard drive, just a great resource! :-)

The American Solar Roof site with it's PDF files alone has kept me reading for hours!! :-)

Thanks again! Roger Conner Jr.

Roger, thank you.

From time to time one has to stop trying to pointing out whats wrong with the forest and just focus on one tree.

Glad you learned some things.

Did you see anything of note in the solar H2O heating realm? I am thinking that would be the first thing beyond my wood stove that I would put in.

All the talk of PV intricacies had me wondering the same thing (about solar thermal, that is). From when I've read, it seems that (unlike our colossal liquid-transport-fuels problem) there are some genuinely promising advances in PV that might actually be expected to hit the marketplace within the next 3-5 years.

Unless you really expect that the S will HTF within that time frame, it seems to me that right now the two best investments for a home (or commercial building) owner are

a) lots of insulation, and
b) solar-thermal hot water,

in that order. Unlike PV (and somebody knowledgeable please correct me if I'm wrong), it seems like solar thermal is a mature, stable technology, with no dramatic advances expected in the foreseeable future, and way more efficient at harvesting watts than the current (sorry :-) state-of-the-PV-art.

That's what I'm pushing for in our small northeast-US condominium building, anyway: insulation this year (currently none, yikes!), and solar hot water sometime after that.

Hi Mike,

We can get into the intricacies of solar thermal hot water heating. Yes, it is cheaper per watt harvested. I have a natural gas hot water heater so I'm paying a third as much for water heating energy as electricity energy. Think about it, to make electricity they burn natural gas and throw two thirds of the energy away. So in terms of dollars, it's a wash.

In the simplest design, you have a black tank on the roof, a siphon so no moving parts, and then run municipal water up to the tank and after it is solar heated back into your standard water heater. The water heater has a thermostat and maintains your hot water at a constant temperature using fossil fuels. Scalding yourself is an issue. At a minimum you need to have an engineer see if your roof can support a water tank, and it might need propping up.

In the northeast, you'll need to run antifreeze to the tank and use a heat exchanger to heat pure water. That will run up the costs.

My take on politics is that they'll reduce the subsidy on photovoltaic at the same rate as it becomes affordable.

Hmm, I guess if you're already using NG for water heating you're in pretty good shape efficiency-wise, and the decision between PV or solar-thermal becomes less of a slam-dunk.

Our building (just outside Boston) has 6 2-bedroom apartments (12 adults, 3 children) in a 3-story flat-roofed building with decent insolation. We use oil for both domestic hot water and (steam!) heat; we just recently replaced the 40-year-old furnace & tankless hot-water setup with a new boiler and ~150(?) gallon tank.

As I mentioned above, I think the absolute low-hanging fruit is insulation. But after that, my thought was that we should add maybe 300 gallons of HW storage (based on 25 gallons/person/day) fed by ~400 square feet of collector (based on 1.33 square feet of collector per gallon of storage, which I read as recommended for our location/latitude).

The technical complications for our particular situation, as I see them, are:
1) the roof is ~30 feet above the basement - I had hoped to simply power the pump via direct PV rather than the expense/complication of a controller, but not sure if this is feasible given the head required
2) It seems to make a lot of sense to have the storage tank in the furnace room, close to the existing hot-water tank, but we only have a standard-sized door opening, so this may mean we'd need to have a custom tank fabricated (I assume from stainless steel). If we go this route, my thought was to have a ~120-150 gallon tank within a larger tank (outer tank/water jacket volume also ~150 gallons, for a total of ~300), run the cold-water supply into the inner tank, and run the (pre-heated) output from this inner tank into the existing water-heater input. To collect the solar energy, circulate a non-toxic anti-freeze solution from the larger, outer (jacket) tank up through the collectors & back.

My thought was that this would provide decent thermal-exchange efficiency with a minimum of complication (i.e. would not require any big coils of copper heat exchangers). Any solar-thermal mavens out there - does this sound like a good plan? Any input appreciated...

Hi Mike,

It sounds like you have thought about this more than I have. I do not have a solar water system and I'm an electrical engineer not a plumber. My two cents.

1) Stainless steel is not a very good conductor of heat. About a tenth that of copper. They wouldn't make heat exchangers out of big coils of copper if they didn't have to. Can you get an aluminum inner tank and will it have the strength to hold 300 gallons of water?


Solar hot water pumps exist. They cost money and take power. This one is 100 watts and five hundred bucks. Photovoltaic panels run five bucks a watt for just the panel, never mind the pump and the controller.

Out here I'd create a siphon using municipal water pressure but it don't freeze here.

3) What is the collector on the roof made of? I have a friend who made a swimming pool water heater out of polyvinyl plastic. One day the pump got turned off or the power went out and the thing melted. But it was cheap.

Thanks Robert,

I didn't know about the relative thermal conductivities of SS vs. copper. I was thinking stainless because I'd like whatever we put in to last for decades... but maybe a simple SS storage tank with the supply to the regular HW tank running through a big coiled copper heat exchanger is the way to go.

I think one of the advangates of running a pump from PV is that it does away with the need for a controller - when the sun is shining, the pump is running, and when not, not. But I don't know how well PV-driven pumping would work for the volume and vertical rise we would be working with.

And we don't have anything in place yet - I'm just in the (wishful) thinking phase at the moment...

I'm out of my league here. I assume an electric pump is just an electric motor driving a piston or other positive displacement chamber. But I don't know. I realize there is a zillion kinds of pumps.

So anyways you got a PV panel. The output voltage is more or less constant. The output current for maximum efficiency depends on the light level, more if it is sunny, less if it is cloudy.

Ok, so it is driving a DC electric motor. The electric motor wants to spin at a constant rate per minute proportional to the voltage, and will try to draw whatever current it takes to spin that fast which depends on how how much load is slowing it down. There is one magical current that produces maximum efficiency.

But notice you don't know how much current there is. It depends on the weather. Either you assume it is sunny and then on a cloudy day you don't have the torque to lift that much water 30 feet. Or you assume it is cloudy and then on a sunny day all that excess power is converted into heat somewhere in the wiring. Until something melts.

I'll take an educated guess that there is no way this is going to work without electronics. At a minimum, a motor controller.

If you don't need high flow I'd run a 12v system through a deep cycle lead acid battery with a charge controller eg
Even better if you can also put a max limit on the pumping time. I've run a standalone system for 2 years without a glitch. The small solar panel is on the roof of a garden shed (independent of the 240v house system) and the 12v bilge type pump is from a marine shop. It pumps around a ton (1000L) of water a day for trickle irrigation.

As far as what to get first, I'll drop in my regular aviso..

While I agree that leak-sealing and insulating should be happening immediately and continually, my vote is to own some nominal amount of PV watts also as soon as possible. If you find yourself in 'crunch time' along with the rest of us, is there really any doubt that PV prices will skyrocket? Already the supply is hard-pressed to meet demand, and while the Silicon supply issue seems to be getting addressed and developers have been announcing the crap out of improved technologies for PV, why would anyone think that the price for this won't still rise to meet a potentially phenomenal coming demand for massively more product? Wait til suburbia feels a handful of outages, or starts getting the rate increases that Connecticut has bearing down on them. The orders will flood the suppliers, and at that point and for a while, product quality might even stagger a bunch. I think people will look longingly at $5/watt and wonder why they thought that was so high..

Solar Heating is certainly a great deal, and stands to do a lot of work for less investment than PV.. but Solar Heating I can largely make from scraps and readily available local materials. Not so for PV.

Anyway, that's my angle on it. I've got a measly 250w of PV at this point. I can run chargers, lights, radios, some tools etc on them.. a lot of stuff that I'd be hard-pressed to do with any quantity of Hot Glycol..

But I am also all over the solar ovens/water purifiers/dehydrators etc. I have collected rigid foil insulation panels and glass for my first oven and solar shower.. just need a big tank and some time!

Bob Fiske

I've presently got a high efficiency LPG water heater. While LPG is more efficient than electric, it is also a petroleum product, and we all know the issues we can expect with that in the future.

I am thinking that I would keep the LPG heater, but use it just to supplement/boost a solar heater on cold/cloudy days, and to provide hot showers in the mornings. My thinking is that I could put a timer on the LPG heater to be off from mid-morning through late afternoon, and also from around midnight to 5AM or so. The rooftop solar collector would kick in and heat the water during the day. I would schedule my laundry and dishwashing loads for early evening, spread out over the week, to take advantage of the solar-heated water. If worse comes to worse and LPG becomes too expensive or unavailable then I shower in the evenings as well.

Because I wouldn't be trying to use solar to provide 100% of our heated water 24/7/365, I am thinking that I could get by with a smaller, less complicated, and less expensive system.

Any thoughts about this plan?

Most solar DHW systems use them as preheaters, with supplemental heaters for the cloudy periods and tempering valves in case you've got a surfeit.  Look up some designs before you roll your own; I suggest starting with the back issues of Home Power.

One possibility is an on-demand hot water heater with a bypass valve. No wasted fuel when not needed.

I think Bosch makes an LPG one designed to "top up" teh temperature from a solar hot water heater.

After a winter without hot water (rarely below 32 F/ 0 C) I am not sure hot water is quite the essential most think. Even in a colder climate, a solar hot water should keep the water tolerable.

Best Hopes,


My wife has no problem with buying a new laptop, but she looks a bit askance when I mention buying a terribly energy efficient acoustic guitar at a similar price. Is she wrong or is there something hear that I am missing?:>?

tell her your purchase will give you both a higher HROI (Happiness Return on Energy Invested)

Beyond that, your question gets at the meaning of life, which is too difficult to answer even for theoildrum gang.

If you want to understand the meaning of life I don't recommend TOD, but do advise watching this film:

"The Meaning of Life" 1983

In my local video store, I found the 25 year anniversary double disk set, which made it even more meaningful.

Being 42 this year, I also appreciate it.

..or was that Douglas Adams?


The system that I am going to install soonish takes advantage of a new grid tie inverter from Latronics. Unlike most grid-ties it works on 48V PV input voltage. This puts the voltage in the range of off-the-shelf inverters and battery chargers.

I will have the solar PV array wired at 48V(nom) feeding the grid through a PV Edge 1200W. My essential services, lights computers etc, will be powered on a separate circuit from an automatic changeover switch that selects either mains (normally) or UPS inverter(mains failure).

The separate UPS 48V 600W inverter will be powered by a small 48V battery bank forming what is essentially an uninterruptable power supply (UPS). When there is mains power the battery bank will be charged through a mains 48V power supply feeding a Plasmatronics PL20 solar controller.

For normal mains outages (2 to 8 hours) there will be no need to do anything as the battery will comfortably supply the load for this time. If the outage extends (1 to 2 days) the output of the Solar PV array (48V) will be switched from the input of the Grid Tie inverter to the input of the PL20 thereby charging the batteries and allowing it to supply the load whenever the sun is shining.

For really extended outages (1 or 2 weeks) a generator can be connected, switching out the mains entirely, and can supply all loads and charge the batteries.

If anyone is at all interested I can supply the plans (in Visio) for my system and the calculation spreadsheet to estimate the system size that I have written for MS Excel. Just indicate your interest and I will post them to my blog.

You are producing 1200 watts at 48 volts. If I did my math right that is 25 amps. I have a 3.7kW system, 10 amps at 360 volts. Building Code requires 10 gauge wiring for 10 amps. The average home in America burns 30 kWhs a day, mine burns half that. I realize you don't have to back up the whole house, just the fridge and the furnace blower and a few essentials. Anyways, you probably already realize you need really thick wires and there are always trade-offs.

Fortunately I do not have furnace blowers or anything like it in Perth, Western Australia. We are blessed with very mild temperatures. In summer it gets quite hot however our house is very cool and it has an evaporative airconditioner that draws 200W or 300W just to move air through.

Also with 240VAC as standard 1200W is 5 amps of current into the AC wiring. Mind you the battery connection wires as you mention are best to be as large and short as possible.