Scientists at Tianjin Chengjian University in China have fabricated an experimental photovoltaic device that integrates three different technologies aimed at improving its performance – a phase change material (PCM), a thermoelectric (TEG) generator, and thermal collector (T) devices.
PCMs can absorb, store, and release large amounts of latent heat over defined temperature ranges. They have often been used at the research level for PV module cooling and the storage of heat.
TEGs can convert heat into electricity through the “Seebeck effect”, which occurs when a temperature difference between two different semiconductors produces a voltage between the two substances. The devices are commonly used for industrial applications to convert excess heat into electricity. However, their high costs and limited performance have thus far limited their adoption on a broader scale.
“The system has good economic potential due to its excellent temperature control, high power generation, and energy efficiency, and is expected to be more widely used in the future as the cost of thermoelectric chips decreases,” the research's lead author, We Li, told pv magazine.
The system utilizes the PCM, TEG, and cooling water to absorb excess heat from the PV panels, effectively controlling the temperature of the PV panels and extending their service life. At the same time, the PCM provides a stable heat source for the TEG and the water-cooling panels provide a cold source for the TEG. The TEG generates electricity through the temperature difference between the two sides of the hot and cold sources, improving the PV system's overall power generation rate. The cooling water recovers the remaining heat to improve solar energy utilization.
The PV-PCM-TEG-T was constructed by placing an aluminum frame on the backside of the PV panel to form a cavity where PCM could be embedded and sealed with an aluminum plate. The TEGs connected in series were attached to the back of the aluminum plate with thermally conductive silicone. Furthermore, a water-cooling plate was deployed on the other side of the TEGs.
Image: Tianjin Chengjian University
The academics built an experimental prototype of the PV-PCM-TEG-T system and compared its performance with that of a reference PV panel without the PCM-TEG-T structure.
“In numerical simulations, the heat transfer of the PV-PCM-TEG-T system was numerically modeled,” Li explained. “Under 24-hour operating conditions, the PV-PCM-TEG-T system demonstrates higher temperature control compared to standard PV panels.”
The proposed system was found to have a 10.4% higher output power and a 1.9% higher power generation efficiency than the reference system. “Under the 24-hour simulation condition, the novel system’s temperature is significantly less than that of the standard PV panel, with a maximum temperature difference of 10.1 C,” the research group further explained. “The PCM thickness shows little influence on the temperature control ability, while a larger thickness of PCM increases the heat storage, thereby increasing TE power generation.”
“By comparing with standard PV panels under 3h radiation and 3h non-radiation conditions, the system can effectively control the temperature of the PV panels and enhance the power generation efficiency,” Li added. “The addition of TEG increases the power generation capacity; the circulating cooling water improves the temperature difference, enhances the thermoelectric power generation capacity, and realizes the recovery and storage of heat.”
The researchers presented the system in the study “Experimental and numerical study on photovoltaic thermoelectric heat storage system based on phase change temperature control,” published in Solar Energy.
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