A proces powered by sunight, producing fuel through a direct conversion mechanism that doe not rely on living matter—this is the definition of an In Vitro photosynthetic process. Research into the theoretical problems conversion efficiencies and potential economic importance of such processes is both timely and of long-term economic importance. A fossile fuels become exhausted, new form of energy will have to be pressed into service. In Vitro photosynthesis offers the possibility of inexhaustible energy supplis, obtained in a more versatile and valuable form than those from solar/thermal processes. The following article reviews the most important In Vitro photosynthetic proces es and evaluate their respective efficiencies . The authors argue for a vigorous research programme to obtain essential information on which correct future economic decisions may be based.

In Vitro Photosynthesis

The second law of thermodynamics imposes a limit on the maximum efficiency achievable with any rectifier in converting radiation into dc power. By using the second law and Bose photon statistics, a general expression is derived showing that this efficiency depends upon the bandwidth and effective temperature of the incoming radiation. Only for completely coherent radiation can the conversion efficiency be unity. The theoretical implications are illustrated by examining specific thermodynamic cycles involving idealized recombination diodes and thermodynamically ideal rectifiers. The relationship between minimum bandwidth of radiation and bias voltage in a recombination diode is derived. The connection between conversion efficiency and Carnot efficiency is made clear.

Wolfgang Feist

Papers

Thermodynamical Limits on the Bandwidth and Conversion Efficiency of Incoherent Recombination Radiation from a Semiconductor Diode