Efficient, low-cost solar thermoelectric cogenerators comprising evacuated tubular solar collectors and thermoelectric modules

We have designed a solar thermoelectric cogenerator (STECG), which can supply electric power and heat simultaneously, by adding thermoelectric modules to the heat pipe in evacuated tubular solar collectors. A pilot experiment shows that the STECG can generate 0.19 kW h of electrical energy and about 300 l of hot water at 55 °C in 1 day when the figure of merit of the thermoelectric module, ZTM, is 0.59 and solar insolation is less than 1000 W/m2. A theoretical model for accurately predicting the thermal losses, collector efficiency and electrical efficiency of the STECG is also presented based on energy balance and heat transfer equations. For thermoelectric modules with ZTM = 1, when the solar insolation, wind velocity, ambient temperature and water temperature are 1000 W/m2, 1.3 m/s, 25 °C and 25 °C, respectively, the collector efficiency, output electrical power and electrical efficiency are calculated to be 47.54%, 64.80 W and 1.59%, respectively. The results show that STECGs combining heat pipes with thermoelectric modules in evacuated tubular solar water heaters are economical and practical, making them suitable for commercial production.