Scientists in Sweden have integrated a PV device with a molecular solar thermal (MOST) energy storage system, which acts as an optical filter and coolant for solar cells. The proposed combination achieves a 0.2% higher PV efficiency and a solar storage efficiency of 2.3%.
A group of researchers led by Chalmers University of Technology in Sweden has fabricated a hybrid polycrystalline solar cell that a molecular solar thermal (MOST) energy storage system that converts the high-energy photons underutilized by the cell into chemical energy.
In the proposed system configuration, the MOST unit acts as an optical filter and coolant for the PV cell. It is placed on top of the solar cell and is based on a solution of photo-switchable organic molecules that flow through a microfluidic chip that can store the high-energy photons through a photoisomerization process.
“This process involves high-energy blue and ultraviolet photons to convert parent molecules into high-energy metastable photoisomers, the scientists said. “The energy stored in MOST photoisomers can then be used as a backup energy source, either as a heat source or for the generation of thermoelectric energy.”
In the study “Hybrid solar energy device for simultaneous generation of electrical energy and storage of molecular solar energy,” published in Joulethe research group explained that they tested three different MOST system configurations based on three norbornadiene-quadricyclane (NBD-QC) molecules called NBD1, NBD2 and NBD3. Each molecule had different photophysical properties.
Through a series of experimental tests, the academics found that the optimal performance of the device was achieved with the NBD3 molecule, thanks to its “superior” absorption and heat prevention capabilities.
Tested under standard lighting conditions, the solar cell achieved a conversion efficiency of 12.6%, which according to the scientists is 0.2% higher than a reference solar cell without the MOST system. This was possible thanks to the cooling effect of the MOST on the operating temperature of the cell, which decreased by 8°C from 53°C to 45°C.
The tests also showed that the hybrid PV MOST system was able to operate at 14.9% solar usage efficiency and 2.3% solar storage efficiency. “The combined MOST-PV system demonstrates the ability to produce more consistent power output over different periods, from daily to seasonal cycles,” the research group emphasized. “Theoretically, the system can be configured to circulate different materials throughout the day to optimize efficiency.”
Looking ahead, the scientists said they will work to identify small and large-scale cycling tests with efficient catalysts and develop more red-shifted NBD candidates to bring storage efficiency closer to the theoretical limit of MOST systems. “In addition, investigating techno-economic trade-offs in hybrid technology is critical, such as balancing efficiency between the MOST system and the PV cell and considering thermal effects,” they concluded.
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