The Shockley-Queisser Efficiency Limit of Solar Thermophotovoltaic (STPV) Cells Using Different Photovoltaic Cells and a Radiation Shield Considering the Etendue of Solar Radiation

A theoretical model is developed to determine the Shockley-Queisser efficiency limit of solar thermophotovoltaic (STPV) cells with single- or double-junction photovoltaic (PV) cells and a simple radiation shield considering the divergence nature of concentrated solar radiation. A combination of adaptive parametric sweep and graphic-based methods is developed to solve the highly nonlinear correlations of energy and carrier transports in the theoretical model to find the optimized operating conditions of STPVs with high stability. The theoretical model predicts that the Shockley-Queisser efficiency limit of STPV under 1000x solar concentration and a simple radiation shield is similar to 50.1% with InGaAsSb PV cells, similar to 49.1% with GaSb PV cells, and similar to 53.2% with InGaAsSb/GaSb double-junction PV cells. The operating temperatures are similar to 1719.5 K, similar to 1794.1 K, and 1640.0 K, respectively. An observation from the modeling is that the energy loss due to the thermalization of hot carriers in the STPV with spectrally selected emitters is similar to 40% less than that in single-junction solar cells. Also determined from the modeling is that similar to 20% of the collected solar energy is still lost through thermal radiation, even with a simple radiation shield to block the radiative heat loss to the surroundings. Following this understanding, a further improvement in the Shockley-Queisser efficiency of STPVs can be achieved by adopting advanced designs of radiation shields that can separate the absorber of the STPVs far away from the aperture of the radiation shield without using a large-area absorber.