TPV efficiency predictions and measurements for a closed cavity geometry

Abstract

A thermophotovoltaic (TPV) efficiency measurement, withii a closed cavity, is an integrated test which incorporates four fundamental parameters of TPV direct energy conversion. These are: (1) the TFV devices, (2) spectral control, (3) a radiation/ photon source, and (4) closed cavity geometry effects. The overall efficiency of the TPV device is controlled by the TPV cell performance, the spectral control characteristics, the radiator temperature and the geometric arrangement. Controlled efficiency measurements and predictions provide valuable feedback on all four. This paper describes and compares two computer codes developed to model 16, 1 cm2 TPV cells (in a 4x4 configuration) in a cavity geometry. The first code, subdivides the infrared spectrum into several bands and then numerically integrates over the spectrum to provide absorbed heat flux and cell electrical output performance predictions (assuming infinite parallel plates). The second code, utilizes a Monte Carlo Photon Transport code that tracks photons, from birth at the radiation source, until they either escape or are absorbed. Absorption depends upon energy dependent reflection probabilities assigned to every geometrical surface within the cavity. The model also has the capability of tallying above and below bandgap absorptions (as a function of location) and can support various radiator temperature profiles. The arrays were fabricated using 0.55 eV InGaAs cells with Si/SiO interference filters for spectral control and at steady state conditions, array efficiency was calculated as the ratio of the load matched power to its absorbed heat flux. Preliminary experimental results are also compared with predictions. an integrated test which incorporates four fundamental parameters of TPV direct energy conversion. These are: (1) the TPV devices, (2) specUal control, (3) a radiatioxdphoton source, and (4) closed cavity geometry effects. The overall efficiency of the TPV device is controlled by the TPV cell performance, the spectral control characteristics, the radiator temperature and the geometric arrangement. Controlled efficiency measurements and predictions provide valuable feedback on all four. This paper describes and compares two computer codes developed to model 16,l an2 TPV cells (in a 4x4 configuration) in a cavity geometry. The first code, subdivides the infrared spectrum into several bands and then numerically integrates over the spectrum to provide absorbed beat flux and cell electrical output performance predictions (assuming infinite parallel plates). The second code, utilizes a Monte Carlo Photon Transport code that tracks photons, from birth at the radiation source, until they either escape or are absorbed. Absorption depends upon energy dependent reflection probabilities assigned to every geometrical surface within the cavity. The model also has the capability of tallying above and below bandgap absorptions (as a function of location) and can support various radiator temperature profiles. The arrays were fabricated using 0.55 eV ...

Spectral Control for Thermophotovoltaic Energy Conversion

“…parasitic absorption at inactive cold side areas (e.g., grids, busbars, and gaps between TPV cells) 2. angular and polarization dependent radiator emissivity (i.e., non-Lambertian), 3. angular and polarization dependent front surface filter reflectivity 4. finite separation between radiator and TPV cell which alters the angular dispersion 5. cavity edge leakage or sidewall absorption These non-ideal cavity attributes complicate the photon recuperation process. In general, advanced numerical techniques such as Monte Carlo and photon ray tracing are needed to quantify the impact of these processes on TPV performance (Reference (42,43)).…”