Theoretical limits for radiant energy conversion

Theoretical limits for radiant energy conversion are dealt with in two categories: i) Those associated with the second law of thermodynamics ii) Those associated with specific energy level schemes (photochemical system). Particular emphasis is placed on the conversion of solar radiation into work although luminescence and laser emission are also discussed. Attention is given to the calculation of the entropy of solar radiation, both using experimental data and a theoretical model. The theoretical model developed uses diluted black-body radiation (D.B.R.) which is introduced in detail here for the first time. In dealing with photochemical limits a kinetic manylevel model is developed including the role of a metastable triplet state in the energy conversion process. Stimulated emission and other terms are included so that the model is valid even in equilibrium conditions. An ideal solar cell model is derived from the photochemical case and acme basic photovoltaic equations are seen to follow directly from photochemical arguments. A detailed study of the spectral distribution of solar radiation is included so that new conclusions concerning meteorological effects are possible. For example limiting efficiencies and optimum solar cell bandgaps are derived for overcast conditions and for operation undersea.