Whats the highest efficiency a Solar-thermal power system could have?
This document was inspired by two comments in the Introduction to Solar energy by John J. Hopfield and Jerry Gollub (1978), in which they explain the fundamental limits to the efficiency of photovoltaic systems. (PV can’t be better than 45% efficient, they show.) J.H. and J.G. say: The atmosphere is essentially a large heat engine that converts incident solar energy to mechanical energy with an efficiency of about 2%. And they point out that solar thermal electricity production (in which sunlight is first converted to heat) is far less efficient than an ideal photovoltaic system. I thought it would be fun to make a model, in the style of Hopfield and Gollub, pinning down the maximum possible efficiency of a solar-thermal power system. Then we can assess how impressive the 2% figure achieved by the atmosphere is. The maximum efficiency also gives insights into the huge `solar chimneys’ being considered in Australia. (A prototype in Spain generated about 1W per m^2.) We start with a syst
