Design, manufacturing and indoor/outdoor testing of a hybrid thermoelectric-concentrator photovoltaic mono-module at unprecedented ultra-high concentration levels

Hybrid concentrator photovoltaic-thermoelectric systems aim to increase the conversion efficiency of sunlight to electricity by recovering part of the waste heat generated in the photovoltaic cells by means of thermoelectricity. They are in a research stage, with many theoretical predictions of their potential benefits, especially when increasing the light concentration ratio, but few experimental demonstrations. They have been never tested under ultra-high concentration levels (>2000x). In this paper, the results of an experimental assessment of the state-of-the-art technology to develop such hybrid systems under extreme concentrations are presented. A hybrid mono-module was designed, manufactured and tested under ultra-high concentration both indoors and outdoors. Indoor experiments used a steady light sun simulator for effective low concentrations from 1.3 to 17.2 suns and a multi-flash simulator for geometric concentrations from 476x to 3600x. Outdoor experiments covered concen-trations between 476x and 2066x. A conventional concentrator photovoltaic-only mono-module was also tested outdoors for comparison purposes. The experimental characterization of the prototype showed that some opti-mistic values used in the theoretical predictions (such as the temperature coefficients of the solar cell, the thermoelectric efficiency or the optical efficiency of conventional concentrators) cannot be fulfilled with the current commercially available components. Results of the outdoor measurements exhibit a similar energetic behaviour of the hybrid system compared to the conventional system at 476x. For higher concentrations, the performance of the hybrid system is poorer than that of the conventional system due to a faster degradation of the optical, thermal and electrical behaviour. The solar cell was damaged when it reached 194 degrees C at 2066x outdoors. The study sheds light on the limits of the current technology and identifies improvement research areas: optical systems for ultra-high concentration, solar cells with a wider operating temperature range and lower temperature and series resistance losses, thermoelectric generators with higher figure-of-merit and inno-vative cooling systems. These areas need to be explored to reach experimentally the potential benefits of this technology.