Thermal challenges on solar concentrated thermoelectric CHP systems

We report thermal challenges based on our experiments on a solar concentrated combined heat and power (CHP) generation system. The system is designed to harvest solar radiation as a renewable energy source. The electrical power is generated by a thermoelectric (TE) module and the wasted heat from the module is recovered with a water cooling heat exchanger behind the module. The goal is to achieve a water temperature that is useful for hot water residential applications while generating some electricity. This CHP system includes optical solar concentration to obtain a lower cost per performance [$/W] applying the higher heat flux to the thermoelectric generator, which was theoretically calculated in our previous work. The results are compared with the generic analytical optimization model. For the experimental apparatus, we used a Fresnel lens for the optical concentration. The previous analysis showed that matching of both electrical and thermal resistances of the TE module and the load resistance are key factors. We optimized the load resistor to get the maximum electrical power from the TE generator. The thermal resistance match appeared to be quite challenging, due to the non-uniform profile of the energy flux on the TE module. This yielded inhomogeneous power generation for each thermoelement in a TE module and resulted in significant degradation to power output. This can be improved with appropriate heat spreader at the TE hot plate and/or with optical optimization of the Fresnel lens. The harvested combined power was more than 53% of the received solar with the thermally non-optimized module, while 0.44-0.46 W of electricity was generated by the TE module with a center temperature difference of 143-152°K between the hot side and the cold side of the TE module. The extensive calculation for the thermally matched design (optimum) of the TE module suggests that the same system can produce 10 times as much electrical power.