Techie Project: Personal Solar Parabolic Collector

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Trip
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Techie Project: Personal Solar Parabolic Collector

Post by Trip » Thu Jul 24, 2008 2:24 pm

MIT Students Develop Solar Dish Hot Enough to Melt Steel
A parabolic collector consists of an array of mirrors focused on a singular point, which they heat to a high temperature. By placing water or another liquid at the collector, energy can be stored in the form of a phase transformation, and later harvested through a turbine generator.

However, parabolic collectors are still a relatively new field of research. Their true potential remains relatively unknown.
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I wonder if something of the sort could be built from scrap, for much less.

E.g. Large Fresnel Lens For Solar or Optics Projects costs only $30, and something similar might prove useful.

aristide1
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Post by aristide1 » Thu Jul 24, 2008 6:48 pm

Pluses - Appears to contain zero toxic chemicals, more than I can say for a photo cell.

Minuses - What's the lifespan of a mirror exposed to the elements?

sea2stars
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Post by sea2stars » Thu Jul 24, 2008 7:24 pm

".... parabolic collectors are still a relatively new field of research." Huh? Where has the author of that article been hiding?

Some links to take a gander at for DIY from a great site.
BuilditSolar

NyteOwl
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Post by NyteOwl » Fri Jul 25, 2008 12:27 pm

Indeed, solar "furnaces" are nothing new, except perhaps the technology [used] to make them. They have been around for 40 or 50 years at least. I built a little one in jr high school far too many years ago as a science project. It boiled water quite nicely. There are ven places where you can buy folding models for camping and hiking.

NeilBlanchard
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Post by NeilBlanchard » Fri Jul 25, 2008 6:23 pm

Hiya,

Another plus is a solar heat collector is much more efficient than a PV panel. And, you can store the heat much more easily than storing (large amounts of) electricity -- molten salt seems to be the thing for this.

I remember a national Geographic cover story that was about a parabolic collector -- in the 1970's. New technology -- pffuubbtt! :P

http://en.wikipedia.org/wiki/Solar_thermal_collector
http://www.pbs.org/wgbh/nova/solar/
http://www.powerfromthesun.net/chapter1/Chapter1.htm
The largest solar electric generating plant in the world produces a maximum of 354 megawatts (MW) of electricity and is located at Kramer Junction, California. This solar energy generating facility, shown below, produces electricity for the Southern California Edison power grid supplying the greater Los Angeles area.
Image

http://www.nrel.gov/csp/troughnet/solar_field.html
Mirrors or Reflectors

The most obvious features of the parabolic trough solar collector are its parabolic-shaped mirrors or reflectors. The mirrors are curved in the shape of a parabola, which allows them to concentrate the sun's direct beam radiation on the linear receiver.

All current parabolic trough power plants use glass mirror panels manufactured by Flabeg. The mirrors are second, surface-silvered glass mirrors (which means that the reflective silver layer is on the backside of the glass). The glass is a 4-milimeter-thick, special low iron or white glass with a high transmittance.

The mirrors have a solar, weighted specular reflectivity of about 93.5%. A special multilayer paint coating protects the silver on the back of the mirror. And each mirror panel is approximately 2 square meters in area.

The LS-3 collector features 224 mirror panels on each solar collector assembly. The 80-MWe SEGS IX power plant has 888 LS-3 solar collector assemblies and almost 200,000 mirror panels.

The glass mirror panels have performed very well during the operation of the SEGS (solar electric generating system) power plants. They've maintained high reflectivity and suffer low annual breakage rates. However, mirror breakage does occur and replacements have been relatively expensive. A number of alternative mirror concepts have been under development to reduce cost, improve reliability, or increase performance.

Trip
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Post by Trip » Sat Jul 26, 2008 5:56 pm

Thanks a lot Neil.

DryFire
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Post by DryFire » Sun Jul 27, 2008 2:38 am

NeilBlanchard wrote:Another plus is a solar heat collector is much more efficient than a PV panel. And, you can store the heat much more easily than storing (large amounts of) electricity -- molten salt seems to be the thing for this.
Comparing the efficiency of solar thermal collectors and PV cells directly really isn't fair. With PV panels you already have electricity and with thermal collectors you still need to convert the heat to work and then electricity. You need to look at exergy to make a direct comparison.

Even evacuated tube collectors are twice as efficient in their largest temperature difference (like trying to heat water in the winter-- efficiency is about 36%) when compared to PV cells which are 16% at best at their test conditions, and you loose 1/2% per rise in deg C of the solar panel from 25 C.

Sadly, 1kJ of heat (from any achievable change in temp) can never become 1kJ of work/electricity unless someone breaks the laws of thermodynamics.

aristide1
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Post by aristide1 » Sun Jul 27, 2008 8:55 pm

NeilBlanchard wrote:Another plus is a solar heat collector is much more efficient than a PV panel.
Eating broth with a fork is more efficient than PV panels.

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