A hybrid device has been created that combines, for the first time ever, molecular thermal solar energy storage with silicon photovoltaics. The special battery achieves a storage efficiency of 2.3% and up to 14.9% total utilization of solar energy
Photovoltaic Thermal Battery: New Performance Records
The heat generated by solar radiation can negatively affect the performance of photovoltaic cells, leading to efficiency losses of around 10% to 25%. An international research group sought to turn this problem into an opportunity for progress. How? By creating a special photovoltaic thermal battery, a hybrid system can prevent cell overheating by utilizing the “excess heat” for energy purposes.
This isn’t the first time solar batteries or storage systems that can produce electricity from the sun have been mentioned. However, compared to past research, the system devised by scientists from Chalmers University of Technology in Sweden and Universitat Politècnica de Catalunya – Barcelona Tech in Spain is based on a new approach and functionality.
Led by Professor Kasper Moth-Poulsen, the group created its photovoltaic thermal battery by integrating a crystalline silicon solar cell with a special storage device called MOST (which stands for MOlecular Solar Thermal).
MOST Storage System: How Does It Work?
The MOST system consists of a microfluidic chip through which a solution of photo-switchable organic molecules flows. These molecules can store sunlight as chemical energy through a process called photoisomerization.
Specifically, when high-energy blue and ultraviolet photons (typically <450 nm) hit the surface of the MOST, they convert the parent molecules into other molecules with the same chemical formula but with higher energy. This energy can be stored “within them” or used as a reserve source, either directly as heat or for thermoelectric production. One of the characteristics of MOST molecules is that they do not interact with other photons, making them transparent to wavelengths above 450 nm.
In other words, when placed above a solar cell, the thermal storage system allows most of the relevant photons to reach the silicon wafer while retaining high-energy photons that cause photovoltaic overheating.
Thermal Storage Based on Norbornadiene
The international research team succeeded not only in creating a functioning photovoltaic thermal battery but also in achieving notable performance compared to the state of the art. “Previous studies on hybrid architectures […] have shown improved combined efficiencies,” the publication in Joule states. “However, the reported data on the efficiency of thermal solar energy storage in MOST systems varied only from 0.5% to 1.1%. In this work, we achieve […] up to 2.3%, which is, as far as we know, a new world record.”
The secret? Using a norbornadiene derivative as the organic molecule, which shows good performance in various fields, including the quantum yield of photoisomerization.
Photovoltaic Thermal Battery: How Efficient Is It?
The new device significantly improves yield. Experimental tests reached a storage efficiency of 2.3% for molecular thermal solar energy. The integration of this hybrid system can lower the temperature of photovoltaic cells by 8 °C, thereby reducing energy losses due to heat and increasing efficiency by 12.6%. The combined device operates with a solar utilization efficiency of 14.9%, representing an improvement over two independently operating solar hybrid systems.
“Combining photovoltaic energy with molecular thermal storage will not only improve energy efficiency but also help reduce dependence on fossil fuels and minimize the environmental impact associated with other forms of energy storage, such as batteries based on rare and polluting materials,” explains the Spanish university. “This hybrid device is expected to meet the growing demand for clean energy and efficient storage, marking a further step forward in the energy transition.”
