solar heat to electric

[hansvonlieven]

im sorry but the maximum effeciency of electricity from solar heated water is 9.3%? considering PV panels can tap 15-30% and they see usually one spectrum of light where as a black coated solar heat collecter collects multiple light spectrums.... that doesnt make sense! not even with the science of resistance or loss of energy!

Heat is only a small part of the spectrum absorbed by the black panels. The rest is wasted, hence the poor performance.

Hans von Lieven

[The Eskimo Quinn]

Stick with it mate, you can radiate heat into an object all day long until it melts, but you can only use so much light from the sun for PV due to cell limits. The day PV cells are worth anything is the day they can match infra red absorbsion.

The principle is basic physics, heat absorbsion is not restrcted where solar cell tech in PV cells converting sunlight to electricity to heat is very restrictive and the reason it takes large panels just to watch a televsion.

The huge false pretence of a solar hot water system is that the solar cells create the heat, when the heat absorsion into the black construct of the panels and cells provides many times the heat of the electrical production of the panel they are on. that is why there are no solar hot water systems in the arctic, because they rely on that heat absorbtion more than the current created.

EG: on a 35 degree day, a solar panel of any kind, can not produce more electricity than a on a 40 degree day, not a bit not ever. The restriction is the limit of our current cell tech.

Go for it.

[sm0ky2]

a single lense can focus the solar-heat into an intense beam, capable of increasing your solar energy collection exponentially. 

from the same 15 inches of sun-lit area you can get a LOT more heat.

one idea im working on is going to use a conical-shape, like those things you put around a dogs neck.
with mirrors, all focusing the light up onto a 2" downward facing mirror.
This technique is used in 'solar ovens'
reference: Solar Death Ray experiments, and subsequent links, including a large military project
http://www.solardeathray.com/

Then have a 7.5-inch lense (with a hole cut out for the 2" mirror in the center)  on top of the cone, chosen with an appropriate focal-point, such that all the light collected is directed onto a 1-2" area down the center of the cone. perhaps onto a black,heat collection rod or perhaps even small a flat 'panel', giving me a small intense solar collector.
Summertime is comming up, and we get a WHOLE lot of sun here in Kansas!!


Concerning the carnot cycle,another way to look at it is:
the maximum efficiency =  1 - (Tc/Th)
which is still 0.0927  or <10%
UNLESS - you include a work factor for the heat while you are transfering it, such as in a rankin cycle.
the equation would then look like
efficiency = Work / Heat Input.    Which (at least theoretically) can be up to 100% efficient heat transfer.

Sterling engines are theoretically 100% efficient. - provided that ALL of your heat goes into the hot side of the engine.
However, In practice, we note that sterling's are not actually 100% efficient, because there is some heat output on the 'cold' side. meaning that not all of the heat was transfered into 'work'.

these guys here are doing some pretty fun stuff with it.
http://www.ergenics.com/

[ben8807]

Evacuated tube solar collectors have the best heat absorption ( >90%) because they don't have convection losses.  If you really want to do this I recommend either some sort of magnification or evacuated tubes.

Then there is your choice in heat engine. Solar steam would be nice if there were off the shelf steam engines. Also piston team engines require lubrication which then in a closed cycle can foul your boiler. Doable but not the easiest way to go.

Stirling engines work great at high temperature differences, but at lower temperature differences they are a bit more lackluster. Also the machining and R&D gets expensive because again they are not off the shelf parts.

I think the best option right now is an organic Rankine (steam) cycle using refrigerant. Scroll compressors can be used as expanders with minor modifications. Then you just need a feed pump which can be any pump that provides the pressure and flow with seals that withstand refrigerant. Then for the best efficiency you need some regenerative heat exchangers, but again off the shelf parts.

Would be doing it myself, but R&D costs still make it cheaper to buy my electricity. Don't forget you will be buying each part you use at least twice since initial testing will probably poke some holes in your design, also you will need to figure some sort of grid tie or battery tie system.

Good luck! Post results if you try it!

Edit: Bad grammar

[hartiberlin]

The best thing would be solar cells, that could convert low infrared emissions to electricity.

The PN-layerjust must be selected this way, that it is the most optimized for the infrared
wavelength..We have to find the right materials to do this or use
millions of small diodes which have noise at this temperature to rectify the noise
on a silicon chip.

Lookup what Paul is doing with his diode arrays.