The second law of thermodynamics is applied to the entropy fluxes going into and out of solar power plants. It is discussed how clouds affect the entropy flux coming from the sun by redistributing the photons on a larger number of electromagnetic modes and thereby reduce the efficiency of the energy conversion in power plants. Under direct illumination the fundamental efficiency limit corresponds to the Carnot efficiency which is 94.8%. With isotropically scattering clouds the efficiency is reduced to a spectral average of 72.3%.
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For the same reason also the photons from the surrounding having an entropic temperature cannot contribute to power production.
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© 1998 American Institute of Physics.
1998
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