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Solar concentrated power generation (~5kW)

  1. Feb 22, 2008 #1
    I want to look into the feasibility of manufacturing "dirt cheap" solar powered electricity generators for small businesses and households in sunny third world countries.

    Small electric generators of any kind are obviously uneconomic compared to a central grid. But vast rural areas, including small and medium inland cities, in poorly developed countries have no working grid at all. And as big cities grow rapidly, even grids in large cities are insufficient outside city centers. I've noted that when electricity supply is time limited, priority is given to evening and night time (for household A/C, TV and light purposes). Especially small businesses active daytime therefor all must have their own small diesel generator (for small office or shop A/C and PC, refridgerating food and/or running some machine et cetera). As oil prices rise, economic activity is squeezed a bit extra hard in these already pretty depressed areas.

    Solar power cuts fuel costs completely. And they should be easier to maintain. To not have to transport the fuel to rural areas is a blessing in itself. Just clean the the reflector now and then!

    The classic concept is a parabolic reflector which heats a stirling engine. The problem is that stirling engines don't seem to be easy to come by. They are rare and expensive. And the are not easily manufactured ad hoc, are they? If anyone knows otherwise, I'd be happy to hear of it!

    What about using a steam engine instead of a stirling engine? Efficiency is lower but construction is simpler. Are solar powered steam engines a good idea from an engineering point of view? (There's no lack of water in the (sub)urban areas which is the main market).

    Concerning the reflector, I suppose it could be cheaply produced as a (precision) parabolic plastic mold painted with a reflective metal layer. But basically, the larger it needs to be, the further away must the focus and the engine be. This might be a problem for a heavy engine.

    A fresnel lens on the other hand, could allow for the engine to stay fixed on the ground. Are fresnel lenses hard to come by? I can hardly find a price example online. How are they manufactured really?

    The solar tracking device cannot be an important problem. I would guess that a fail safe system with light sensitive sensors which continously finds the location of the sun, is better than some preset calender system. Cheap electronics could help save a lot of hazzel for many users.

    The vast majority of household and small business diesel generators I've seen in this potential market, have between 1 kW and 5 kW capacity. So a solar powered generator of 5 kW would meet existing customer expectations and habits. Solar radiation is about 1.3 kW per square meter at Earth orbit. This would represent a reflector/fresnel area of 3.7 square meters, i.e. a circle with 2.2 meter diameter, for 5 kW. But what efficiency should one roughly count on? I suppose losses occure in atmosphere, reflector/lens, engine and generator. But reflector/lens losses are negligible, right? 25% efficiency would mean that a 4.3 meter diameter reflector/lens would be required for 5 kW. That might be just about where the limit for practicality lies.

    For households, it would be nice to charge car batteries or such for use in the evening and night. For this purpose, less than 5 kW could suffice well.

    I hope that this isn't too off topic for the forum, and that someone has opinions of any kind to share. Thanks!
    Last edited: Feb 22, 2008
  2. jcsd
  3. Feb 23, 2008 #2
    How about visiting my blog. http://hubpages.com/hub/solar-reflector

    I have presented a dirt cheap way of making a solar concentrator.

    Its really easy to build. I have tried it myself. It took me approx. 15 minutes to boil water.

    With good cheap heliostatic controls it can work wonders.
  4. Feb 23, 2008 #3
    Nice do-it-yourself example!

    I wonder, could one use "chrome spray" with good effect? How does one know that it reflects invisible heat radiation as well as visible light? It would be very easy to apply and maybe not more expensive than buying metal sheets. A drawback is that it might wear off.

    To get the parabolic shape (in quantity), I assume that plastic molding is the way to go. Having individual mirrors and adjusting them with screws might not be suitable for hazzle free consumer use.

    Btw, a second smaller reflector at the focus of the larger one, allows for concentrating the beams on a fixed point on the ground (for example through the center of the large reflector). The point being that heavy heat-to-power transforming equipment doesn't need to hang out in the air and turn around with the sun. So there is hardly any advantage of a fresnel lens.
  5. Feb 23, 2008 #4
    I am not sure but chrome spray is more expensive then using aluminium sheets. I dont know very well how much a new mold would cost. Can you please tell me how much would it cost if I try to make the model as mentioned in my article by using chrome spray and plastic molded parabolic dish.

    May be plain sand can be used to make a parabolic surface and on it we can pour molten shiny metal e.g. aluminium.

    There are a number of possibilites but third world solutions need to be experimented before we can say something for sure that whether they are cost effective and cheap or not.
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