Effects of side-wall air cooling on solar thermoelectric generation with high aspect-ratio, V-shaped P/N couples

Abstract

Solar thermoelectric generators (STEGs) often require long thermoelectric (TE) legs and efficient cooling at the cold side to increase the temperature difference across TE legs and, thus, the power output. We investigate the effects of direct side-wall air cooling of TE legs on the power output of STEGs fabricated with high aspect-ratio as well as V-shaped p-type and n-type TE couples without additional heat sinks. Wire-type metallic TE materials are welded together to create V-shape TE leg arrays without additional electrodes and attached to a ceramic plate with a solar absorber on top to complete the STEG. The power generation performance of the STEG is investigated with varying wind speed under concentrated solar irradiation. Finite element simulation is performed to further analyze the heat transfer and thermoelectric performance. We find that although sidewall air cooling helps to keep the cold-side temperature cooler in both natural and forced convection regimes, it can also lower the hot-side temperature to reduce the net temperature difference and, thus, the power output and efficiency. Partial thermal insulation of TE couples can further enhance the power output under forced air convection by keeping the hot side temperature higher. The developed STEG achieves a maximum power density of 230 μW/cm2 and a system efficiency of 0.023% under 10 suns with natural convection. The low efficiency was mainly due to the low ZT of the metallic TE materials used and the unoptimized leg length. Our simulation shows that the system efficiency can be improved to 2.8% with state-of-the-art Bi2Te3 alloys at an optimal leg length.