Thursday, January 10, 2008

Whither Carnot Efficiency?

An interesting story about a new method of generating solar power from the inventor of the super-soaker. The article claims efficiencies of 60 % are possible.

As some of the comments point out this idea might not be feasible. The Carnot efficiency of a heat engine is given by:

efficiency = 1-(T COLD/T HOT)

(with absolute temperatures used)

The article suggests temperatures as high as 600 degrees centigrade. So (assuming T COLD is room temperature):

1 - ((273+25)/(600+273)) = 0.66.

Giving a theoretical efficiency of 66%.

Of course it's possible there is some error in my understanding of the article and/or theory.

However the endoreversible process is a slightly more accurate method of measuring the efficiency of a heat engine (at least according to the Wikipedia article), which is given by:

efficiency = 1 - (T COLD/T HOT)^0.5.


efficiency = 1 - ((273+25)/(600+273))^0.5 = 0.41

Giving a theoretical efficiency of 41%, rather less than as advertised.

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