[Semi-OT] Solar-powered Stirling engines

There's a sort of "gee-whiz" article about generating electricity with solar-powered stirling engines in the August issue of
Discover magazine. The bad news is that the device they're describing is not a real product (yet), just a research project funded by a private investor.
The interesting part is that the technology they're describing is not new at all-- the only question is whether they can get the cost down to where they can find a market for it. Their target is 250 watts for $250.
Part of the project was designing a stirling engine that could be manufactured cheaply, and since the "fuel" doesn't cost anything, they were willing to sacrifice some thermal efficiency to get more "watts per dollar". The article says its about half as efficient as the best stirling engines, but *much* cheaper to build. They don't describe it in any detail, though.
For the solar part they're planning to use a 6'x9' array of small mirrors, automatically aimed by stepper motors (and somehow ganged together so they can use fewer steppers). By focusing the light on a small area, they can produce temperatures up to 1200 degrees farenheit. And because the array is relatively flat, they can cover it with glass or plastic to protect it from the weather.
My thought was that even if they miss their cost target, as long as the total price is low some people might buy one just to thumb their noses at the power company. They say a typical house would need between 4 and 8 of these, which would be a $1,000-2,000 investment. You might need demand-priced electricity to make it worthwhile economically (peak sunlight coincides with peak A/C loads).
Their website at <http://www.energyinnovations.com/ describes an earlier version of the product and says it will be on the market next year, but the Discover article sounded like they're now working on a completely different design (with more reflectors, and a rectangular array rather than round). Their web designer really likes the word "revolutionary"...
The basic concept is similar to some government-sponsored research described at <http://www.sandia.gov/ , but on a smaller scale. The Discover article quotes a guy from Sandia saying "In principle, this could work.... I'm going to stay skeptical until I see their data, but if they do pull it off, it could be huge."
BTW the magazine also has a brief article about people who collect sliderules, with photos of some unusual ones.
For some history on solar-powered steam engines, check out a book called "A Golden Thread: 2500 years of solar architecture and technology" by Ken Butti and John Perlin (1980). The first solar engine was demonstrated in 1866, and the first "practical" one was built in Egypt in 1913 (it was abandoned during WWI).
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Ron Bean wrote: (clip) You might need demand-priced electricity to make it worthwhile economically (peak sunlight coincides with peak A/C loads). ^^^^^^^^^^^^^ These cost calculations can be very tricky (and deceptive.) In order to use solar electricity in any real sense, you need a lot of storage batteries. They are very expensive, and their life may be too short for their cost. I mean they may have to be replaced before they have returned their investment in energy savings.
Where I live, they tried to distribute the peak load (afternoon) by installing time-of-use meters. The cost of electricity was very low in the morning, and high in the afternoon and evening. So I looked into the possibility of installing a lot of storage batteries, and then buying electricity in the morning and selling it back in the afternoon. It didn't work out, and the main reason was the batteries would not pay for themselves over a 20 year period when they would need replacing.
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Build your own batteries. It is extremely simple.
Cass

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<snip quoted message incorrectly placed at bottom>
But not easy or free, especially if you'r unhappy with lead fumes and toxic waste generation. You'd ideally want at least 1-200Kwh of batteries. That's around a tonne of batteries. That's one hell of a lot of 'home-made' battery construction.
--
http://inquisitor.i.am/ | mailto: snipped-for-privacy@i.am | Ian Stirling.
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wrote:

As well as topping up electrolyte, cleaning off corrosion, hydrogen fumes and lots of other icky, nasty details that some of the home-power types would just soon forget. And I'd say the 20 year lifespan that somebody estimated is overly optimistic, 5-10 years would probably be closer, less if you're using "free" recycled car batteries like some enthusiasts I've read were promoting.
What I'd like to know is if there's a solar-powered Stirling generator out there that's even close to what you get with a solar panel in terms of watts/square meter. They've always been on the virge of being practical since the '60s, I've still got a Popular Science mag somewhere from that era that had plans for a very small solar-powered Stirling engine. Kind of like fuel cells, the breakthrough was always going to be sometime in the next 5 years.
Stan
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Stan Schaefer wrote:

I'm not sure what you mean by "out there". If you mean available off the shelf, no, certainly not. If you want to build your own, however, it would be VERY hard not to get more power/sq. unit than the best photovoltaic systems do. The best PV systems claim 13% efficiency when new, many commercial-grade PV arrays run around 3%! Given all the associated loads having to do with water cooling the cold side of the engine, tracking the collector, etc. a 20% total system efficiency seems quite possible. Getting a 30% conversion to mechanical output is not extremely hard for small Stirling engines. But, you can't make it out of tin cans and string. The hot side will need to run at 600 C or higher, the cold side must have a huge thermal radiator to keep it as close to ambient temp as possible, you have to have a LOT of surface area in the heat exchangers, and in most cases you want to run pressurized working fluid to keep the engine as small as possible. (Smaller engines have less friction and heat losses, of course.)
Search the net, there are a lot of people experimenting with them. A few people are getting very serious, as individuals, in building working Stirling engines.
Jon
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On 5 Aug 2003 08:50:04 -0700, snipped-for-privacy@americanisp.net (Stan Schaefer) wrote:

IIRC and it has been awhile since I saw the numbers , the stirlings are about 35% efficient compared to 8 % for PV. They have PV's up to around 40% , but they don't say how much they cost and I'm sure they are pricey and you can't buy any. The stirlings run with hydrogen and cost about $100,000 plus the $150,000 tracker. There is a $250,000 concentrated PV tracker about 2 miles from my house that worked for about 3 months , 5 yrs. ago. I just don't see how they can effectivly cool it with static air and heat sinks, they should be about 100 degrees , its a good 100 degrees in the shade. Nevada Power won't talk to me and the company that made it, made it very clear that they don't want any help from me. They wanted to buy my guidance system at a ridiculously low price and I told them to get lost , might have had something to do with it. Let it stare at zenith ! Our federal tax $ at work. The DOE turned me down 4-5 times for a grant for frivolous reasons like my system would burn itself down if it stopped tracking. I tried to reply to them professionally like prosecuting a patent , but couldn't seem to answer such rediculous questions. I remember another one , they said that it couldn't possibly move and track with so few parts. Well, that seems weird , it works just great. Come out and check it out if you don't believe me. "We don't come out to Vegas..." That's a complete lie. They have the test site , EG&G , that $1/4 mil. junk , and gave $6 mil. to the senator to promote solar energy in NV. and he blew it all on paper work and wouldn't really talk to me. Oh, they said they culled it , the only Nevadan to respond to their RFP. They didn't even read it with that $6 mil. !
As soon as I get my tracker into production I'll take a closer look at stirlings. I found out that solar energy is very political and tight lipped. Finding any relevant information for a business plan is hopeless. Using the grid is also hopeless cause they will only pay 1 cent per KWH. Its booze , hookers , and bribes or do it alone.
I've said more than enough , sorry for the rant.
Edison said something about batteries ( they called them something else then) that didn't paint a rosey picture.
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"Cass wrote: Build your own batteries. It is extremely simple. And then he wrote: Sorry that I made a post that required someone to think or actually do something. ^^^^^^^^^^^^ I am THINKING about DOING. Would you be kind enough to outline the simple method you know. I am pretty good at doing simple things.
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Leo,
A lead-acid battery is very simple to build. Do some research on the Internet. All they consist of is modified lead, a water and sulphuric acid solution and a container.
Batteries were built in tubs long ago and every railroad station had some for its telegraph system.
I was just irritated at all of the nay-sayers as it is easy to try to pick something apart rather than do something. You know, easier to destruct rather than construct.
Cass

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Leo,
Here is a useful link about lead-acid cells. You may want to research the patent office, too.
http://micro.magnet.fsu.edu/electromag/electricity/batteries/leadacid.html
I think the electrolyte that you mix is a solution of sulphuric acid and distilled water until you get a specific gravity of 1.260. I am not guaranteeing that I recalled that correctly. I know that one can make a L.A. battery hotter by running the s.g. up to 1.300 but the plates don't last as long.
Another thing you need is some separator material to put between the plates to keep them from shorting to each other.
Please let me know if you intend to build some/one as I may join you.
Cass

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plates
^^^^^^^^^^^^^ Cass, it is just as I thought. Your statement that building storage batteries is does not consider the many physical difficulties that come up when you go from the abstract to the concrete. The lead in a lead-acid battery is a special spongy form--not the lead used for joining cast-iron pipe. And the container has to be made of an acid resistant material like hard rubber or glass. The assembly of alternating layers of spongiform lead and porous insulator layers will involve techniques not known to the average shop worker. By the time you get your batteries, large enough to run a houshold, assembled and operating, I believe you will not say "It was easy."
Nor will you say,"They were cheap." I'll bet you can buy batteries of proven design cheaper than you can buy the materials and build them.
I don't think I am being a naysayer. I am being a realist. I don't think building a house is easy, either, even though the separate steps are not hard in themselves.
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Stupid me! I actually thought that you might be interested in building a very simple thing that is very simple to build.
Little did I know that your real intent is just to fight and pick nits.
You can build lead-acid cells much cheaper than you can buy them but you don't think so. So, buy them and quit trying to pick a fight.
By the way, I have built lead-acid cells and as I said, it takes a modified form of lead and I never said it took regular lead.
Now, run along and think that everything that you don't understand is hard.
Cass

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http://micro.magnet.fsu.edu/electromag/electricity/batteries/leadacid.html
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modified
Then please inform us of the details, and also specs such as life, internal resistance, capacity.. Maybe some photos too.
And BTW need I remind you, 90% of this group already has you in their killfile, you might want to keep calm lest you lose what little audience remains.
Tim
-- In the immortal words of Ned Flanders: "No foot longs!" Website @ http://webpages.charter.net/dawill/tmoranwms
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Tim,
Do you have a real purpose in your post? Or, is it that you just like trouble like a few on here?
I would provide pictures, my notes, details and sources of materials supply but since everyone has me in their killfile, there is just no point.
Now, buzz off.
Cass

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Leo Lichtman wrote:

This really won't work, except on the largest scale, due to the losses in the AC -> DC -> AC conversions. Some people at EPRI have been working on superconducting inductor energy storage for this purpose.
But, having a solar, wind or other system, and timing the heavy use of electricity (cooking, clothes drying, water heating) for the cheapest time, and allowing the solar, etc. system to supply all other needs can be a workable system.
Jon
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Have you ever looked into compressed air or pumped hydro? They are used on a commercial scale to help with peak demand.
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Stuart wrote: (clip) Have you ever looked into compressed air or pumped hydro? They are used on a commercial scale to help with peak demand. ^^^^^^^^^^^ I do know of one example of hydraulic peak-power storage. It is at a dam in northern California, where they use off-peak power to pump water back up into the fore-bay, so they can re-use it to handle peak loads. This is in the mega-watt range. They are able to make use of the turbines and dynamoes which were needed anyway to generate electricity. I don't know of any examples where this is done on a smaller scale, nor where the installation costs are justified by the off-peak load transfer function.
I don't know of any examples where compressed air is used to transfer peak loads. I would be interested in knowing of the ones you are familiar with.
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That would be interesting: cycle the pressure in a tank between say 0 and 500PSI, just hope you didn't get an aluminum tank! :-o
Tim
-- In the immortal words of Ned Flanders: "No foot longs!" Website @ http://webpages.charter.net/dawill/tmoranwms
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The scheme I saw involved storing compressed air in a hollowed out salt dome. I don't know if ever got off the ground though. I think that there are pumped hydro plants that use old mines as the lower "tank".
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I found and article about the plant at: http://www.platts.com/engineering/issues/Power/0011/0011pwrmcintosh.shtml
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