TPV efficiency predictions and measurements for a closed cavity geometry

Abstract

an integrated test which incorporates four fundamental parameters of TPV direct energy conversion. These are: (1) the TPV devices, (2) spectral control, (3) a radiatiodphoton source, and (4) closed cavity geometry affects. 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 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 performance predictions (assuming infinite parallel plates). The second, utiliies a Monte Carlo Ray-Tracing 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 are 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. Preliiary experimental results are also compared with predictions.

0.52 eV Quaternary InGaAsSb Thermophotovoltaic Diode Technology

“…The test was run in vacuum to eliminate conductive and convective heat transfer. Reference [24] gives details of the test apparatus.…”

“…In this section, preliminary results on back surface reflector InGaAsSb TPV diodes utilizing epoxy bonding and total substrate removal are presented 23,24 . Figure 6 shows the schematic for a device fabricated by bonding with transparent epoxy a grid patterned N/P InGaAsSb TPV diode to a GaSb handle substrate, which has a predeposited gold reflector.…”

Realistic modelling of TPV systems

“…The efforts relating to TPV system simulation up to 1998 were summarized by Coutts [1]. The potential of the Monte Carlo method was first demonstrated by Gethers and Ballinger [2,3]. The program RACER-X includes temperature gradients on the radiator, polarization and angle-dependent reflectivity.…”

Thermophotovoltaic Spectral Control

“…TPV system design introduces unique photonic issues, which affect efficiency and power density. For example, a TPV converter necessarily involves some sort of cavity [5]. From a photonic viewpoint, the key TPV cavity attributes are: 1. parasitic absorption at inactive cold side areas (e.g.…”

“…grids, busbars, and gaps between diodes) 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 diode which alters the angular dispersion 5. cavity edge leakage or sidewall absorption These non-ideal cavity attributes complicate the photon recuperation. 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 [2,5].…”