Towards a near-field concentrated solar thermophotovoltaic microsystem: Part I - Modeling

Modeling of a near-field concentrated solar thermophotovoltaic (STPV) microsystem is carried out to investigate the use of STPV-based solid-state energy conversion as high power density MEMS power generator. Near-field radiation can be realized between two closely separated surfaces (order of radiation characteristic wavelength), resulting in the enhancement of the heat radiation flux orders of magnitudes higher than the blackbody limit, consequently increasing cell output power density. The near-field STPV model incorporates a photonic crystal absorber which transfers absorbed concentrated solar radiation to a tungsten emitter. Thermal radiation from the emitter illuminates an In0.18Ga0.82Sb photovoltaic (PV) cell generating electrical power; waste heat is rejected from the backside of the PV cell via a microcooler. Based on the model, the near-field STPV performance is estimated for different emitter-to-PV cell separation distances d(c), emitter temperatures T-e, and emitter/absorber area ratios A(R). Results from the numerical study showed significant enhancement of the heat fluxes due to tunneling of the near-field radiation, resulting in power densities as high as 60 W/cm(2) which is 30 times higher than the equivalent far-field power density for d(c) = 20 urn, T-e = 2000 K and solar concentration of x4350. For a emitter/absorber area ratio of A(R) = 1, the emitter/absorber thermal efficiency and the overall solar to electrical conversion efficiency were 73% and 15.5%, respectively. Higher power densities are achievable (up to 50 times that of far-field values) however cooling requirements and solar concentration could be a concern. (C) 2015 Elsevier Ltd. All rights reserved.