Researchers Develop Device to Recover Waste Heat from Photovoltaic Units

Scientists from the University of Milano-Bicocca, University of Rome Tor Vergata, and Massachusetts Institute of Technology have fabricated a thermally-coupled electrically-separated hybrid thermoelectric, photovoltaic system (HTEPV)-based device based on a thermoelectric generator and a wide-gap perovskite solar cell. The device is said to recover waste heat from the PV unit and produce the additional power output.

Silicon solar cells dominate the PV market due to their high efficiency and low cost. However, they are susceptible to temperature, which can lead to considerable energy losses over the lifetime of solar panels. They can lose up to 20% of their room temperature efficiency to change in temperature. Of late, hybridization with thermoelectric generators (TEGs) has gained increasing attention. In HTEPV systems, TEG can recover the heat lost from solar cells to produce an additional power output and enhance the overall device output power and efficiency.

HTEPV systems have been the object of many studies and reviews. However, opinions on their effectiveness have been diverging. HTEPV systems have been reported as both very convenient and not suitable to increase PV efficiency.

The researchers chose three different types of solar cells for the experiment — perovskite, gallium indium phosphide (GaInP), and amorphous silicon (a-Si).

The hybrid system consists of a customized bismuth telluride TEG hot plate placed in thermal contact with a perovskite solar cell’s back with a surface area of 1 cm² employing a layer of Silicone-free thermal grease. The two units are thermally coupled but electrically separated.

The TEG cold side was attached with thermal grease to the vacuum chamber bottom. Its temperature was controlled with a K-type thermocouple for the final hybrid device. The chamber bottom temperature was controlled with a dissipation liquid circuit, fed with a chiller with adjustable temperature.  The solar cells were placed in thermal contact to the TEG top electrode employing a layer of thermal grease, and a K thermocouple was placed between the hot electrode and the solar cell bottom.  The J-V curves were recorded by a Keithley 2440 source meter controlled with a LabView program.

The researchers performed characterization on all three cells between 1 and 5 Suns to determine the effect of optical concentration on the temperature sensitivity. The solar simulator’s incoming power was constantly measured and adjusted with a certified reference silicon solar cell. A stainless-steel mask with known areas was implemented to evaluate incoming power density accurately.

Perovskites showed efficiency gains higher than 2% at all the optical concentrations, i.e., 2.64 % at 337.43 K, 2.90 % at 340.59 K, and 3.05 % at 343.13 K when compared to a-Si and GaInP. Maximum efficiency gains happened at moderate temperatures at around 340 K. This temperature is well within the range of temperatures commonly experienced by solar panels and does not imply the need for complex thermal management strategies. Thus, in this case, the HTEPV device is directly comparable and compatible with actual solar cells.

These enhancements were then experimentally confirmed for the case of perovskites solar cells, for which the highest gains were found to occur at normal operating temperatures of conventional PVs. This experimental evaluation accurately demonstrated the real potential of thermoelectric hybridization of solar cells.

Recently a team from Brown University said that they had developed a molecular glue that boosts the efficiency of perovskite solar cells.

Earlier, researchers at the Gwangju Institute of Science and Technology, South Korea, established a new method to increase perovskite solar cell’s efficiency by utilizing ions.