Maximum efficiency of solar energy conversion

Owing to the energy scattered or absorbed by the constituents of earth's atmosphere and self‐absorption in the outer layers of the sun, the spectrum of solar flux at earth's surface is different from that of a blackbody. Consequently, the second law of thermodynamics for heat engine cycles operating between thermal reservoirs needs to be revised to determine the maximum conversion efficiency. A thermodynamic model similar to those for multi‐temperature plasmas and non‐isothermal particle‐exchange heat engines is proposed to estimate the maximum conversion efficiency of a mechanical or solid‐state heat engine subject to a radiation flux not having a blackbody spectrum. An example is given to illustrate the calculation of the maximum power that can be converted from a solar flux with considerable gas absorption. Copyright © 2011 John Wiley & Sons, Ltd.