
Light and Heat: Giant Fresnel - ph0rque
http://www.brotherswhitney.com/2008/11/light-and-heat/
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dick
Hey, glad you like it! There are a couple of hypothetical solar energy
possibilities, but neither's really worth the time.

The first is concentrated photovoltaic (CPV), based on the idea that lens is
cheaper than silicon, so why not concentrate a larger area onto a smaller
chip? The issue here is thermal- if a cell has 15% efficiency, then it
necessarily rejects 85% of the energy as heat so significant cooling is
required.

The second is solar thermal or steam generation. Heat water until a phase
change occurs, then use the expansion to drive a turbine. It's not
particularly safe or easy to do on a hobbyist basis.

As ars peripherally mentioned, the Fresnel essentially produces an energy
rate. The thermo take-home is that there IS no maximum temperature, except
perhaps the surface of the Sun. That makes the (incorrect) assumption that you
have a perfect absorber with no convective or radiative losses. My current
kiln design should nearly eliminate convective losses, and will greatly reduce
radiative by refocusing the lost energy.

Come check it out at Maker Faire!

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ars
Very impressive - it's a good thing large sheets of plastic with ridges are so
expensive.

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ryanwaggoner
Is there some kind of opportunity here for solar power?

~~~
ars
No. The power (energy rate per area) is very high, but the total energy is
not.

~~~
ph0rque
But there _is_ opportunity in making a solar-fired kiln (mentioned in the
article), and produce pure silicon from sand and carbon. The article mentions
1500C, but I'm not sure if 1800C is attainable with the method. Also, (lack
of) vacuum might be a problem.

