Unique German light-harvesting tech stores solar power for months

Researchers at Johannes Gutenberg University Mainz (JGU) and the University of Siegen in Germany have developed a novel approach that enables efficient solar energy storage in specialized molecules or photoswitches. This energy can later be released as heat on demand, approaching more suited for heating applications. 

Photoswitches are molecules that absorb solar energy and store it in the form of chemical bonds, allowing the heat to be retained for weeks and months. While technology has been developed to absorb solar heat and store it in water or other liquids, it is only a matter of time before these fluids lose the heat and return to room temperature. 

With the world keen on switching to cleaner energy sources, we are seeing an uptick in solar and wind farm installations. But these can only supply electricity. According to the International Energy Agency (IEA) ‘s estimates, 50 percent of global energy consumption is spent on heating needs. 

Therefore, harnessing and storing the sun’s energy and using it for heating applications makes sense. This is where photoswitches work best. 

Overcoming shortcomings of photoswitches

Researchers at the University of Siegen first developed photoswitches a few years ago as a better alternative to storing solar energy in lithium-ion batteries. The team successfully demonstrated a higher energy storage potential in these molecules. 

However, there was a major shortcoming in their usage. These initial photoswitches would be activated only in ultraviolet (UV) light. Since UV is only a small component of the solar light spectrum, energy harvesting capabilities were limited. 

Recent research in this area by Siegen and JGU researchers overcame this shortcoming by allowing solar energy to be harnessed indirectly as well, much like in photosynthesis. This was achieved by incorporating a compound called the “sensitizer,” which increased solar energy storage efficiency by more than an order of magnitude. 

“The sensitizer absorbs light and subsequently transfers energy to the photoswitch, which cannot be directly excited under these conditions,” explained Christoph Kerzig, a professor of inorganic chemistry at JGU, in a press release. 

How did they do it? 

A team of researchers led by Kerzig used spectroscopy to understand photoswitches’ complex workings and the mechanism involved in each step. Till Zähringer, a PhD student in Kerzig’s lab, played an important role in the study, explored the system in great detail, and helped achieve more than harvesting with indirect light. 

“We could not only push the light-harvesting limit substantially but also improve the conversion efficiency of light to stored chemical energy,” added Zähringer in the press release. 

Photochemical reactions use sunlight to carry out different chemical changes but often see photons whose energy is lost through various channels. In Zähringer and Kerzig’s system through, each observed photon was able to trigger a chemical bond formation process, thereby increasing the energy conversion output, a rare feat. 

To validate that the approach was robust, the research team used the system through multiple charge and discharge cycles so that energy harvested from solar light was stored and utilized on multiple occasions, much like a real-world scenario. 

The research findings were published in Angewandte Chemie.