Researchers at UC Santa Barbara have managed to “bottle” the Sun’s energy, advancing renewable energy goals by enabling the storage of solar power in a novel format.
The work falls into an exciting new area of molecular solar energy storage, which has long struggled to deliver practical results. In their recent article in the journal Science, the team reports that, with advances in technology, achieving solar energy storage efficiency even higher than that of lithium-ion batteries is becoming possible.
All Power is Solar Power
A large amount of the energy available on Earth comes from the Sun. While human society is heavily reliant on fossil fuels, it could be argued that even these resources represent nothing more than long-term solar energy storage. Plants long ago absorbed solar energy through photosynthesis, allowing them to live and grow. Other creatures then ate these plants or the other creatures that ate them. Eventually, the biomass of these plants and animals was converted into fossil fuels such as coal and oil over millions of years, serving as a natural store of ancient solar energy.
However, using these fuels comes at a high environmental cost, especially in an era when catastrophic global climate change is a major concern. To mitigate this, humans have developed technologies to directly harness solar power, bypassing the environmentally destructive middleman of fossil fuels. Yet this solution has its own drawbacks, as access to the Sun’s rays is limited by the time of day and the weather. This is why the researchers have pursued a novel concept to capture sunlight for later use.
Bottling the Sun
The UC Santa Barbara team took a different approach from earlier solar storage concepts, which typically rely on bulky batteries and power grids. Instead, they focused on Molecule SOlar Thermal (MOST) energy storage, the use of chemical bonds to store solar energy. MOST researchers differ from traditional solar power researchers because their work focuses on converting light into chemical energy rather than electrical energy. In this case, the team’s subject was a modified organic molecule called pyrimidone.
“The concept is reusable and recyclable,” said lead author Han Nguyen, a doctoral student in the Han Group. “Think of photochromic sunglasses. When you’re inside, they’re just clear lenses. You walk out into the sun, and they darken on their own. Come back inside, and the lenses become clear again.”
“That kind of reversible change is what we’re interested in,” Nguyen continued. “Only instead of changing color, we want to use the same idea to store energy, release it when we need it, and then reuse the material over and over.”
Solar Energy Storage
“We prioritized a lightweight, compact molecule design,” Nguyen said. “For this project, we cut everything we didn’t need. Anything that was unnecessary, we removed to make the molecule as compact as possible.”
Pryimidone is a good subject because its structure is similar to that of a DNA component that undergoes reversible structural changes upon exposure to UV light. The energy stored in this artificial organic form is tremendous, roughly twice that of a standard lithium-ion battery, at 1.6 megajoules per kilogram. Crucially, pryimidone can store energy for years on end with no loss and release it on command.
After discovering this, the team partnered with UCLA’s Ken Houk to study how the molecule could achieve highly efficient long-term storage using computer models. They found that pryimidone stores energy in a manner similar to a spring, twisting itself into a strained contortion when subjected to sunlight, then releasing the tension energy as heat when hit with a catalyst.
“We typically describe it as a rechargeable solar battery,” Nguyen said. “It stores sunlight, and it can be recharged.”
Real World Solar Power Applications
These results are not just theoretical; the team has used their new approach to successfully boil water in real-world conditions. Previous work in the MOST field has struggled to achieve practical success.
“Boiling water is an energy-intensive process,” Nguyen said. “The fact that we can boil water under ambient conditions is a big achievement.”
The team sees the most practical application of their work in heating. They say that a primidone solution could be pumped through solar collectors and then stored in tanks to provide continual heat at night and in poor weather.
“With solar panels, you need an additional battery system to store the energy,” said co-author Benjamin Baker, a doctoral student in the Han Lab. “With molecular solar thermal energy storage, the material itself is able to store that energy from sunlight.”
With continued research, such promising developments using pyrimidone may ultimately lead the way toward a future of decentralized solar energy storage.
The paper, “Molecular Solar Thermal Energy Storage in Dewar Pyrimidone Beyond 1.6 MJ/kg,” appeared in Science on Science 12, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.