Limiting efficiencies for photovoltaic energy conversion in multigap systems

Multigap systems are better matched to the sun's spectrum than single gap systems and are, therefore, more efficient as photovoltaic converters. This paper reviews the different thermodynamic approaches used in the past for computing the limiting efficiency for the conversion of solar energy into work. Within this thermodynamic context, the limit ranges from 85.4% to 95.0% depending on the assumptions made, Detailed balance theory provides a more accurate model of the photovoltaic converter. It leads to a limit of 86.8% for a system with an infinite number of cells, as already pointed out by other authors. In this work, however, we use the concepts of angle and energy restriction to emphasize that this limit is independent of the light concentration, Systems with a finite number of cells are also studied and their limiting efficiency is found to be higher than previously reported, Data for AM1.5 Direct spectrum, never computed before, are included.