Search

To bridge the gap between theoretically predicted and experimentally demonstrated efficiencies of solar thermophotovoltaics (STPVs), we consider the impact of spectral non-idealities on the efficiency and the optimal design of STPVs over a range of PV bandgaps (0.45-0.80 eV) and optical concentrations (1-3,000x). On the emitter side, we show that suppressing or recycling sub-bandgap radiation is critical. On the absorber side, the relative importance of high solar absorptance versus low thermal emittance depends on the energy balance. Both results are well-described using dimensionless parameters weighting the relative power density above and below the cutoff wavelength. This framework can be used as a guide for materials selection and targeted spectral engineering in STPVs.

Although spectrally selective materials play a key role in existing and emerging solar thermal technologies, temperature‐related degradation currently limits their use to below 700 °C in vacuum and even lower temperatures in air. Here a solar‐transparent refractory aerogel that offers stable performance up to 800 °C in air is demonstrated, which is significantly greater than its silica counterpart. This improved stability is attributed to the formation of a refractory aluminum silicate phase, which is synthesized using a conformal single cycle of atomic layer deposition within the high‐aspect‐ratio pores of silica aerogels. Based on direct heat loss measurements, the transparent refractory aerogel achieves a receiver efficiency of 75% at 100 suns and an absorber temperature of 700 °C, which is a 5% improvement over the state of the art. Transparent refractory aerogels may find widespread applicability in solar thermal technologies by enabling the use of lower‐cost optical focusing systems and eliminating the need for highly evacuated receivers. In particular, a shift to higher operating temperatures while maintaining a high receiver efficiency can enable the use of advanced supercritical CO2 power cycles and ultimately translate to an ≈10% (absolute) improvement in solar‐to‐electrical conversion efficiency relative to existing linear concentrating systems. [ABSTRACT FROM AUTHOR]

Abstract: Solar thermophotovoltaic (STPV) systems convert solar energy into electricity via thermally radiated photons at tailored wavelengths to increase energy conversion efficiency. In this work, we report the design and analysis of a STPV system with 2D photonic crystals (PhCs) using a high-fidelity thermal-electrical hybrid model that includes the thermal coupling between the absorber/emitter/PV cell and accounts for non-idealities such as temperature gradients and parasitic thermal losses. The desired radiative spectra of the absorber and emitter were achieved by utilizing an optimized two-dimensional periodic square array of cylindrical cavities on a tantalum (Ta) substrate. Various energy loss mechanisms including re-emission at the absorber, low energy emission at the emitter, and a decrease in the emittance due to the angular dependence of PhCs were investigated with varying irradiation flux onto the absorber and resulting operating temperature. The modeling results suggest that the absorber-to-electrical efficiency of a realistic planar STPV consisting of a 2D Ta PhC absorber/emitter and current state of the art InGaAsSb PV cell (whose efficiency is only ~50% of the thermodynamic limit) with a tandem filter can be as high as ~10% at an irradiation flux of ~130kW/m2 and emitter temperature ~1400K. The absorber-to-electrical STPV efficiency can be improved up to ~16% by eliminating optical and electrical non-idealities in the PV cell. The high spectral performance of the optimized 2D Ta PhCs allows a compact system design and operation of STPVs at a significantly lower optical concentration level compared with previous STPVs using macro-scale metallic cavity receivers. This work demonstrates the importance of photon engineering for the development of high efficiency STPVs and offers a framework to improve the performance of both PhC absorbers/emitters and overall STPV systems. [Copyright &y& Elsevier]