"Rod Speed" wrote in message
...

wrote in
message ...
Rod Speed wrote
Anthony Matonak wrote
News wrote

How much heat do PV cells emit on the back and front of the cells?

You could think of it this way. Typical PV panels are
around 12% efficient at converting sunlight into electricity.
This means that the other 88% is converted into heat.

Well, maybe 16 and 84%, eg 0.84x800 = 672 W/m^2 in AM2 sun.

...that would only be true if they were a perfect
black body absorber of all energy that falls on them.

But they are better than that.

Nope. Not even possible.

Rich Komp says the silicon is almost transparent to IR, and the
aluminum contact beneath is shiny, so PVs are a selective surface.

Waffle, the fact remains that all of what doesnt get turned
into electricity does not end up as heat. Plenty gets reflected.

The maximum efficiency ratings they are getting now are approaching 30%. In
normal production they are around 23%. The average cell is about 12%
efficient. Also, no matter what misguided brain fart you're having now Rod,
the rest of the sun's energy that is absorbed by the panel IS converted to
heat. In fact, the efficiency of solar cells decreases as the heat
increases so there are many people experimenting with methods, both passive
and active, to remove that heat and somehow convert that heat to electricity
as well. The measure of efficiency is not measured by the amount of energy
available, it's measured by the amount of energy produced compared to the
amount of energy used.

Here's a link discussing the heat loss:

http://www.nasatech.com/Briefs/Apr99/NPO20284.html

Now Rod, don't complain to me about how wrong you are now. You can complain
to the guys at Nasa about it.

You can measure the efficiency by taking the wattage being wasted as heat
and compare that to the wattage being output by the solar cell. If the rays
are reflected and have no impact on the process, they cannot be measured, so
the measurement is totally what is absorbed by the panel.

I don't understand why you wouldn't know how efficiency rates are
calculated. It's been common science for quite a long time now. It would
not be a true calculation of efficiency if they were to calculate the
efficiency by the total energy available. That's like calculating the
efficiency of a motor by calculating how much energy is output compared to
the amount of energy available in the entire gas tank when you only used a
quarter of a tank.