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DIY Solar Solutions for the Developing World
Robert Katz, 14 Jul 06

Question: What do you get when you combine an engineer-geek father with a development economist son? Answer: articles about non-photovoltaic, DIY solar systems in the developing world.

First, let’s de-mystify the jargon in my previous sentence – what I’m talking about here are cheap, do-it-yourself solar solutions that don’t rely on expensive photovoltaic panels. Engineers, including my dad, love this sort of thing, because it gives them a reason to continue tinkering with auto parts and plumbing supplies in a benevolent, Rube Goldberg-esque fashion. Development economists like me get excited because solar systems’ growth has historically been hindered by high fixed costs – cheaper, mass produced components and the application of local ingenuity can bring costs down.

Now, an article in MIT’s Technology Review magazine presents two new DIY solar solutions developed by – surprise! – some of the Institute’s grad students.

The first is based on reflective parabolic troughs and was designed by a returned Peace Corps volunteer who saw similar troughs used to bake bread during his stint in Lesotho:

The basic design of Orosz's solar generator system is simple: a parabolic trough (taking up 15 square meters in this case) focuses light on a pipe containing motor oil. The oil circulates through a heat exchanger, turning a refrigerant into steam, which drives a turbine that, in turn, drives a generator....The refrigerant is then cooled in two stages. The first stage recovers heat to make hot water or, in one design, to power an absorption process chiller, like the propane-powered refrigerators in RVs. The solar-generated heat would replace or augment the propane flame used in these devices. The second stage cools the refrigerant further, which improves the efficiency of the system, Orosz says. This stage will probably use cool groundwater pumped to the surface using power from the generator. The water can then be stored in a reservoir for drinking water.

The article claims that the system will cost “a couple thousand dollars,” which doesn’t sound cheap to me. In fact, the Solar Electric Light Fund claims that, for $500, they can set up a complete solar home system for one family – including lights, switches, bulbs, wiring, etc. (Aside: SELF is worldchanging in and of itself, helping rural communities acquire, finance, and install off-grid PV systems – check them out.)

The second MIT solar solution might be cheaper – it uses heat from a solar concentrator to drive a turbine originally patented by Nicola Tesla:

Rather than making complex, difficult-to-manufacture bladed turbines, Sun turned to the Tesla turbine, which consists of simpler flat disks stacked like records on a central shaft. The disks are carefully spaced to allow steam to flow between them. As the steam flows, friction between the steam and the surface of the disks causes them to rotate. "Once I have rotational shaft work, I can couple it to almost anything -- an air pump, compressor, fan, mixer, grinder, sewing machine, refrigeration compressor, and, to power those very few things that are truly electric in nature, an electric generator."

This sounds less expensive than the parabolic trough design, and its designer claims that an eight-year-old could assemble it. The article doesn’t indicate exactly how much the prototype will cost.

Neither system is ready for commercial do-it-yourself application, but both provide an interesting window into the photovoltaic-alternative world. I think the innovation is most encouraging – as yet, there is not a dominant technology in the solar energy universe. Lack of an industry standard keeps the fire going – students and innovators keep looking for ways to make energy generation cheaper, easier, and more efficient. And that’s music to my economist ears.

(HT to David Katz, AKA Dad)

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Comments

I would love to see how this translates into Watts/square meter as well as Watts/$, and to compare those to the same figures for both typical and high-end PV systems.

Any experts there have the means to calculate those numbers based on the data in this article and links??


Posted by: Ameet on 14 Jul 06

All that's great, but what you ought to compare it to is not PV, but other heat engines like for example, an opposed piston free piston stirling engine pumping its working fluid over a turbine-alternator.

Or, even easier, a bush thermocompressor doing the same.

I am betting that these are easier, cheaper and moe efficient, given the same heat source. So all you MIT guys prove me right or wrong, and I will try to do the same.


Posted by: wimbi on 14 Jul 06



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