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California sun inspires energy storage breakthrough
Chemistry professor Grace Han's move from Boston to Santa Barbara led to a discovery in molecular solar thermal (Most) energy storage, achieving unprecedented efficiency in storing and releasing solar energy.
The science behind the discovery
Han, now at the University of California, Santa Barbara, noticed how DNA molecules in human skin repair sun-induced damage using an enzyme called photolyase. This natural process inspired her to explore similar molecules for energy storage.
Most systems rely on molecules that change shape when exposed to sunlight, storing energy in the process. When triggered, these molecules revert to their original form, releasing the stored energy as heat. Han's team identified molecules that could store significantly more energy per unit mass than previous attempts.
Record-breaking energy density
In a study published in February, Han and her colleagues demonstrated a Most system with an energy density of 1.65 megajoules per kilogram-nearly double the previous record. For comparison, this surpasses the energy density of lithium-ion batteries, which power most electric vehicles and smartphones.
During experiments, the system rapidly boiled a small amount of water in a vial, showcasing its potential for practical applications. Han described the moment as "remarkable," emphasizing the role of computational predictions by collaborator Kendall Houk at UCLA in guiding the research.
"When I actually saw the video and saw how quickly the entire solution was boiling, that was really remarkable."
Grace Han, University of California, Santa Barbara
Challenges and limitations
The system currently relies on ultraviolet (UV) light at a wavelength of 300 nanometers, which is scarce in natural sunlight. Additionally, the energy release trigger-hydrochloric acid-is corrosive and requires neutralization after use, posing practical challenges.
John Griffin of Lancaster University noted that the UV light requirement limits the system's immediate applicability. Han acknowledged these drawbacks but expressed optimism about refining the technology to respond to broader sunlight spectra and safer triggers.
Potential applications and future directions
The long-term goal of Most research is to decarbonize heating, a sector still dominated by fossil fuels. Kasper Moth-Poulsen, a leading researcher in the field, highlighted Most's advantages: it operates without combustion, can be deployed globally, and stores energy for years without significant loss.
However, challenges remain. The molecules must be spread thinly to allow light penetration, limiting the system's thickness to about 5 millimeters in optimistic scenarios. Liquid-based systems also require pumping mechanisms, adding complexity and potential points of failure.
Researchers are exploring solid-state versions of Most, such as transparent window coatings that could release heat to warm rooms or prevent condensation. Harry Hoster, a skeptic of Most's scalability for large-scale heating, suggested niche applications like warming temperature-sensitive components in satellites or aircraft.
"It's great science. It's beautiful that they managed to get this functionality right."
Harry Hoster, University of Duisburg-Essen
A niche field with growing interest
Despite its potential, Most technology remains a specialized area of research. John Griffin recalled a conference last year with only 70 attendees, representing nearly the entire global community working on the technology. However, the recent breakthroughs suggest growing momentum in the field.
Han and her team continue to refine their system, aiming to overcome its current limitations and unlock its full potential for sustainable energy storage.
