Animation tool and Q. E. measurements for estimating the optimum system efficiency of a TPV generator

• In order to achieve high efficiency in a thermophotovoltaic (TPV) generator, it is important that a high fraction of emitted photons with energies below the TPV cell band gap are reflected back to the emitter. This can be accomplished in several ways, and one possibility is to place an edge filter between the emitter and the TPV cell array in an elliptical optic design. By this arrangement the cooling demand on the TPV cells is reduced and the reflected radiation is reused in the emitter, the fuel demand is decreased. An animation tool, developed in the Excel program, for determining the optical availability in such a system has been presented previously. The animation components were a blackbody emitter, an adjustable edge filter, and an array of TPV cells. The tool was used to demonstrate the importance of an efficient filter and the usefulness of optics that makes the edge of the filter as sharp as possible. In such a system the TPV cells are the dominant cost. It is possible to tailor the selective filter in order to fit the bandgap of a certain TPV cell. For this purpose it is a great advantage to be able to measure the Quantum Efficiency Q.E. of the cell and how Q.E. changes at different temperatures. When this behaviour is known it is possible to tailor the selective edge filter in order to get higher efficiency. A simple measurement setup has been developed utilizing a lamp with IR reflector, a monochromator, a radiometer, and a heating system based on hot water. The animation tool has been further developed for estimating the optical efficiency, and more factors may be varied. The tool can now handle also the emittance of the emitter, absorption losses in mirrors and filter, as well as TPV cell characteristics such as adjustable Q.E., fill factor FF, and Uoc/(Eg/q).

Nyckelord

solenergi

TPV

optik

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