Solar Thermophotovoltaics

Abstract

In solar photovoltaics, design and optimization of a converting system are strongly determined by the sun spectrum and by the fact that there is no ‘reverse connection’ between a receiver and the sun. On the other hand, there is a possibility to vary the operating concentration ratio (in other words, operating current density of the p-n junction). In a TPV system, the optimization may imply a choice of the emitter spectrum and a possibility to return a nonabsorbed part of radiation from the receiver back to the emitter surface supplying it by an ‘additional’ power. One of the main common features in these systems is the following: in both systems, the energy source is characterized by a wide spectrum. This means that the most effective approach for improving the solar PV system efficiency – that is, the cascade approach – may be applied for the improvement of the TPV system parameters.

The investigations in the field of thermophotovoltaics started in the early 1960s [1], but the real advantage of the TPV approach has been demonstrated only in the past two decades. Theoretical and semi-empirical modeling [2–9] have shown that optimal band-gap energy is in the range of 0.4 – 0.6 eV in TPV cells designated for operation with black-body (grey-body) emitters at the temperatures of 1200 – 1500°C. Germanium and silicon were the materials at first suggested and applied to TPV conversion of radiation from fuel-fired emitters; however, the first TPV systems based on these materials have not gained their advantages such as low cost and commercial availability.