SHPEGS — DIY Solar/Geothermal Electricity

rohar writes "SHPEGS is an open design not-for-profit project to design and prototype a base-load renewable electrical generation system suitable for moderate climates and built from common materials. The design centers around creating a local geothermal source with an efficient solar thermal water heater system and can be scaled from single residence to mega-scale. The heliostat system used in Europe's first solar thermal plant could be used in a scaled-down SHPEGS system with Practical Solar's small scale heliostats."

Efficiency?

[mdsolar]

I read though the site and found many calculations but I'm trying to figure out the actual efficiency of converting solar energy to electricity. I don't mind if the hot water out gets counted at 100% but I'm guessing that per unit area this does not do as well as silicon PV at 15%. If there is a table that gives this kind of comparison, can someone please point it out? Thanks.
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Rent solar power: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]

Let's see a prototype

[Animats]

That thing has an incredibly complex cycle, with losses all along the chain. There's ammonia, water, steam, air, and hot oil involved, with heat exchangers all over the place. The paper attached to it doesn't describe the basic thermodynamics in any real detail. It's sort of like a solar-powered Rankin cycle system. [nrel.gov] But much more complex, and without solid justification for the extra complexity.

This might be credible if they had a working prototype, even a little one. A prototype in the 1 KW range would be about right. That's a backyard project. A 1KW plant would need about 10 square meters of collector mirror, which isn't too hard. Then they'd have something. All they have now is hype.

Developing World Application

[FromTheHorizon]

I currently live in Indonesia, where people commonly burn rubbish - including farmers who burn the husks from rice production. Although this certainly isn't the most environmental form of waste management, I feel that if they are already burning rubbish, at least they could collect the energy from the burning?

Would it be possible to build a simple generator to convert the energy into electricity?

Re:Developing World Application

[rohar]

This is a very interesting project [mit.edu] by a group of MIT grads [synergeticpower.org] that implemented a very cheap solar thermal system out of salvage automotive components (power steering pump, alternator, etc) for low cost deployment in developing countries.

The SHPEGS additions to this type of system (thermal storage, convection tower) could also be implemented cheaply from common materials and salvage parts.

Can anyone help with the math?

[Bodhammer]

I recently read an article about solar power in Wired magazine: http://www.wired.com/wired/archive/13.07/solar.htm l [wired.com]

The article mentions a new design for a concentrator that only uses two motors. To quote the article -

"Then, in a weekend flash of inspiration, a young Caltech physics grad named Kevin Hickerson figured out how to reduce the number of motors needed to move 25 mirrors independently, a major cost factor. Instead of two motors for each mirror - the traditional approach - Hickerson's solution requires only two motors for any number of mirrors. The key is a mathematical curve known as the conchoid of Nicomedes (named for the ancient Greek mathematician, who discovered it). A grid of ball bearings arrayed to match the conchoid is attached to a frame inside the Sunflower. As the motors move the frame, the bearings control each mirror's position individually."

I have found this but it is not helping me much:

http://nvizx.typepad.com/nvizx_weblog/2005/08/conc hoid_of_nic.html [typepad.com]

I have been unable to locate a more detailed explanation of the system and I'm not sure if this basic math is patentable. My advanced math skills are very rusty and I'm not quite sure where to start to understand this. I have an idea that this technique might be useful and I want to understand how to design such a frame. I did look at the concentrator page here: http://www.sandia.gov/pv/docs/PVFarraysConcentrato r_Collectors.htm [sandia.gov] but it was not much help.

These articles as well also have some implications for the benefits of a simple energy source:

http://science.slashdot.org/article.pl?sid=05/09/1 2/1621204&tid=126&tid=14 [slashdot.org]

http://www.time.com/time/magazine/printout/0,8816, 1101299,00.html [time.com]

Also, this today triggered my interest again:

http://www.renewableenergyaccess.com/rea/news/stor y?id=46765 [renewablee...access.com]

I want to understand how to make a spreadsheet or something that would allow me to input number mirrors, focal length, size and it tell me shape, size a location of pivots. Can you explain it to someone who hasn't touched calculus in 18 years? I want to build a cheap one on my roof!

Re:Likely not worth it...

[mdsolar]

It is true that heat retention improves with scale linearly and delta T can be increased with scale, but the cost goes up with volume (linear scale^3). One nice aspect of this system is that you might build it to last a few centuries in the below ground hardware so that the cost per unit time is low. It is difficult though to arrange multi-generational financing of this duration so the first users have to carry the install costs.

PV scales as you say, but the cost comes down a lot with large scale manufaturing, and the cradle-to-cradle-to-cradle aspects of recycling the PV look pretty positive so it carries reduced costs forward but in a way that spreads them without having to work out new finacial instruments.
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