alt.energy.renewable

In article <47be4a7f.398375@news.tpg.com.au>,
Mauried wrote:
>
>Its slightly better than PV, but not much.
>Which begs the question why isnt it many times better.
>Mirrors are more than 90% efficient at reflecting sunlight,
>so why is the plants cost in terms of dollars per watt so poor.
>
>The plant is going to cover 3 sq miles which equals 7.74 million sq
>meters.
>At 1000 watts per square meter the plant should make 7.7 GW if it
>was 100% efficient, but its only going to make 280 MW which makes it
>only 3% efficient.
>Where is all the energy lost.

Thermodynamics. Assuming it could capture all of the heat, it must
then convert it into electricity using a conventional heat engine.
The absolute limit on the efficiency of any heat engine is determined
by the temperatures of the hot side and the cold side:

Thot - Tcold
Max Efficiency = --------------
Thot

...where Thot and Tcold are absolute temperatures. In actual practice,
though, the efficiency of a heat engine is more likely to be worse:

Attainable Efficiency = 1 - sqrt(Tcold/Thot)

You would be lucky to have Thot as high as 838K. Tcold is 298K, best
case. That means you really can't expect to do better than to convert
40% *of the heat you can catch* into useful work.

--
Please reply to: | President Bush is promoting Peace and Democracy
pciszek at panix dot com | in the Middle East by selling Weapons to the
Autoreply is disabled | King of Saudi Arabia.