Photovoltaic solar energy has become one of the most important renewable sources for electricity production in the energy transition context, but it still presents challenges due to intermittent solar production and fluctuating energy demand. Therefore, efficient storage systems are needed to ensure energy availability when demand increases. However, these technologies still do not perform optimally, mainly due to the heating they experience, which affects energy production and the durability of photovoltaic systems. Additionally, current storage technologies, such as batteries, rely on unsustainable materials.

An international research team led by ICREA professor Kasper Moth-Poulsen from the Department of Chemical Engineering of the Universitat Politècnica de Catalunya — BarcelonaTech (UPC) at the Barcelona East School of Engineering (EEBE) has now developed a technology to address both issues. It is the first hybrid device that combines a silicon solar cell with an innovative storage system called MOST, which stands for molecular solar thermal energy storage systems. The results of this research have been published in the journal Joule.

MOST consists of organic molecules that, when irradiated with high-energy photons such as ultraviolet light, undergo a chemical transformation and store this energy for later use. A particular feature of the system is that these molecules also provide cooling to the photovoltaic cell by acting as an optical filter and blocking photons that would normally cause heating and reduce system efficiency. In this way, the device allows both the generation of electricity and the storage of chemical energy.

Unlike other technologies that rely on scarce materials, the MOST system uses common elements such as carbon, hydrogen, oxygen and nitrogen, thus offering a more sustainable energy storage alternative.

Improvements in energy efficiency
The new device significantly improves energy efficiency. Experimental tests have achieved a record energy storage efficiency of 2.3% for molecular thermal solar energy. The integration of this hybrid system will also lower photovoltaic cell temperature by up to 8 °C, thus reducing energy losses due to heat and increasing efficiency by 12.6%. The combined device operates with a solar utilisation efficiency of up to 14.9%, which represents an improvement over the two hybrid solar systems operating independently.

Combining photovoltaic energy with molecular thermal storage will not only enhance energy efficiency but also help to reduce reliance on fossil fuels and minimise the environmental impact associated with other forms of energy storage, such as batteries based on scarce and polluting materials.

This hybrid device is expected to address the growing demand for clean energy and efficient storage, marking a step further in the energy transition.

The device has been developed as part of the ERC PHOTHERM and EU FET-PROACT MOST projects, with EU funding of 2 million and 4.3 million euros respectively. The study also involves researchers from University of Cambridge in the United Kingdom; Chalmers University of Technology in Sweden, and Institute of Materials Science of Barcelona (ICMAB-CSIC).

Reference paper

• 'Hybrid solar energy device for simultaneous electric power generation and molecular solar thermal energy storage' [Paper published in the journal Joule]