System optimiztion of hot water concentrated solar thermoelectric generation

摘要

In this report, we describe the design of a concentrated solar thermoelectric (TE) system which can provide both electricity and hot water. Today''s thermoelectric materials have a relatively low efficiency (∼6% for temperature difference across the thermoelement on the order of 300°C). However since thermoelectrics don''t need their cold side to be near room temperature, (in another word, one can chose the particular thermoelectric material to match to the operational temperature) it is possible to use the waste heat to provide hot water and this makes the overall efficiency of the combined system to be quite high. A key factor in the optimization of the thermoelectric module is the thermal impedance matching with the incident solar radiation, and also with the hot water heat exchanger on the cold side of the thermoelectric module. We have developed an analytic model for the whole system and optimized each component in order to minimize the material cost. TE element fill factor is found to be an important parameter to optimize at low solar concentrations (<50) in order to obtain the highest amount of electric power generated per mass of the thermoelectric elements. Similarly the co-optimization of the microchannel heat exchanger and the TE module can be used to minimize the amount of material in the heat exchanger and the pumping power required for forced convection liquid cooling. Changing the amount of solar concentration, changes the input heat flux and this is another parameter that can be optimized in order to reduce the cost of heat exchanger (by size), the tracking requirement and the whole system. A series of design curves for different solar concentration are obtained. It is shown that the overall efficiency of the system can be more than 80% at 200× concentration which is independent of the material ZT (TE figure-of-merit). For a material with ZThot∼0.9, the electrical conversion efficiency is ∼10--%. For advanced materials with ZThot∼ 2.8, the electrical conversion efficiency could reach ∼21%.