Statistical Mechanics of Solar Energy Conversion

This chapter deals with the general class of processes in which solar energy is absorbed and in which the absorbed energy is converted in multistage processes until it is eventually in a storable form. Several such processes are discussed, as well as the difficulties of modeling the processes in the framework of statistical mechanics. The description pays special attention to loss mechanisms, including the temporal aspects. Possibilities and limits for optimization, arising from both absolute limits and from irreducible losses, are also discussed.Furthermore, the connection between statistical mechanics and information theory is analyzed in the context of solar energy conversion. In this context, the usefulness of the exergy concept, as an efficiency measure inthe analysis of solar energy conversion processes, is discussed. The results for the exergy, of general incoherent photon exergy as well as for a more general kind of radiation field, are reviewed.The conversion of black-body radiation, in the form of free photons within a certain volume, is used as a benchmark case. Several problems with this widely used model are described.It is clear that the actual achievable exergetic efficiency is in some cases considerably less than for the ideal benchmark case and also that the difference is not quantifiable with the existing models.