Evolution had already solved the hard part.
In the quiet chemistry of human skin lies a lesson older than civilization: the sun both wounds and sustains. Grace Han, a chemistry professor in Southern California, found in the molecular mechanics of sunburn a blueprint for storing solar energy—not as electricity, but as shape, tension, and potential. Her team's molecular solar thermal system has achieved an energy density surpassing lithium-ion batteries, offering a glimpse of a future where heat is stored without combustion, without emissions, and without the geopolitical weight of fossil fuels.
- A chemistry professor's personal encounter with California sunburn sparked a scientific insight: the same DNA molecules damaged by UV light could be engineered to trap and release solar energy on demand.
- The resulting molecular system stores 1.65 megajoules per kilogram—outpacing lithium-ion batteries—and demonstrated its power by boiling water in a lab vial, a small but electric proof of concept.
- Serious obstacles remain: the system requires deep ultraviolet light that barely reaches Earth's surface and uses hydrochloric acid as a chemical trigger, making real-world deployment far from straightforward.
- Researchers worldwide, including teams in Lancaster and Barcelona, are racing to build solid-state versions that could one day appear as window coatings, satellite films, or architectural heating layers.
- The entire global research community fits in a single conference room of 70 people—yet the field's momentum is unmistakably growing, buoyed by nature's own billion-year head start on the problem.
Grace Han moved from Boston to Southern California and quickly discovered the intensity of the Pacific sun. One evening, reading about DNA photochemistry, she noticed something: the molecules in human skin don't just absorb UV damage—they change shape under it, twisting into strained configurations before the body's repair systems restore them. She wondered whether that same mechanical transformation could be used to store energy.
The concept she was drawn to—molecular solar thermal, or Most—had existed for decades in theory. Specially designed molecules absorb sunlight, lock into a contorted shape, and release that stored energy as heat when triggered. It's a chemical mousetrap set by the sun. The appeal is profound: energy stored for months or years, no combustion, no emissions, no dependence on geographically concentrated fuel sources. But the technology had remained frustratingly difficult to perfect.
Han recognized that evolution had already done much of the engineering. Human DNA has been refined over millions of years to manage sun damage efficiently, and the molecules involved are extraordinarily small yet capable of storing remarkable amounts of energy relative to their mass. Her team's published results described a Most system achieving 1.65 megajoules per kilogram—surpassing the energy density of the lithium-ion batteries that power smartphones and electric vehicles. When her students tested it, they boiled water in a tiny vial using only the heat released from the molecular system. Kasper Moth-Poulsen, whose own leading systems had reached one megajoule per kilogram, called the result genuinely impressive.
The limitations are real. The system requires deep ultraviolet light at 300 nanometers—a wavelength that barely penetrates Earth's atmosphere—and uses hydrochloric acid to trigger energy release, a corrosive substance requiring careful neutralization. Han is working toward versions that respond to more accessible light and release energy without toxic chemistry. Other researchers, including John Griffin at Lancaster University, are developing solid-state configurations: window coatings that store solar energy and release it as warmth, or thin films for satellites and aircraft requiring precise thermal control.
Skeptics like Harry Hoster note that light-sensitive molecules must be spread thin for full penetration, and liquid-based systems require pumps that add cost and failure points. Heating an entire building with Most technology may never be realistic. But the science is sound, and the field—small enough that its entire global community gathered recently at a conference of just 70 people—is building momentum. The sunburn that first caught Han's attention may yet illuminate one of the hardest problems in the global energy transition.
Grace Han arrived in Southern California from Boston and quickly learned what sunburn felt like. The California sun was relentless in a way the Northeast never was, and after a few hours outside, her skin would begin to sting with the first warning signs of damage. She bought a wide-brimmed hat, sunglasses, and sunscreen—standard precautions for a chemistry professor who had done her homework on UV exposure. But one evening, reading about DNA photochemistry for pleasure, something clicked. The very molecules in her skin that were being damaged by the sun's rays were changing shape under that radiation, twisting into strained configurations before her body's natural repair systems kicked in. She wondered if those same molecules could be harnessed to store energy.
For decades, scientists have pursued what's called molecular solar thermal, or Most, energy storage—a system where specially designed molecules absorb sunlight, twist into a contorted shape, and lock that energy inside themselves. When triggered, they snap back to their original form and release that stored energy as heat. It's elegant in principle: a mousetrap set by the sun, sprung on demand. The appeal is obvious. Most systems could store energy for months or years without any emissions, without burning anything, without the geopolitical complications of fossil fuels. But the technology has remained stubbornly difficult to perfect. The molecules need to shift shape reliably and repeatedly. The trigger mechanism needs to work smoothly. And the whole system needs to store enough energy to be worth the effort.
Han realized that evolution had already solved many of these problems. DNA in human skin has been shaped by millions of years to handle sun damage gracefully. When UV radiation warps DNA molecules, an enzyme called photolyase repairs them with remarkable efficiency. Those same DNA-inspired molecules, Han reasoned, could be the key to a working Most system. They were tiny—incredibly small—yet capable of storing massive amounts of energy relative to their mass. She and her colleagues published their results in February, describing what may be the most promising Most system yet in terms of pure energy density. The numbers were striking: 1.65 megajoules per kilogram. That exceeds the energy density of lithium-ion batteries, the same technology powering smartphones and electric vehicles.
When Han's students conducted the physical test, they boiled water in a tiny vial using energy released from their molecular system. Han watched the video of the solution boiling rapidly and felt the weight of what they'd achieved. The work also relied heavily on computational predictions from Kasper Moth-Poulsen's collaborator Kendall Houk at UCLA, whose team modeled how the molecules would behave. Moth-Poulsen, who leads Most research teams in Barcelona and elsewhere, was genuinely impressed. His own best systems had achieved one megajoule per kilogram. Han's team had nearly doubled that.
But the system has real limitations. The wavelength of light needed to trigger the molecular shape-shifting is 300 nanometers—deep ultraviolet radiation so harsh that only small quantities reach Earth's surface from the sun. More problematic still, the chemical trigger used to reverse the molecules and release their stored energy is hydrochloric acid, a corrosive substance that must be neutralized afterward. Han acknowledges this isn't ideal. She's hopeful the system can be refined to respond to more natural light and to release energy without requiring toxic chemicals. The ultimate goal driving all this research is to decarbonize heating, one of the hardest climate challenges to solve. The world still burns fossil fuels for most of its heat. Most technology offers an alternative that stores energy chemically without combustion, and unlike fossil fuels concentrated in a few regions, it could work anywhere on Earth.
Other researchers are already thinking beyond the current limitations. John Griffin at Lancaster University and his colleagues are developing solid-state versions of Most technology, as is Han herself. Imagine a window coating that's transparent but can store solar energy and release it as heat to warm a room or prevent condensation. Or a thin layer applied to satellites or aircraft components that need precise temperature control. Harry Hoster at the University of Duisberg-Essen points out that the light-sensitive molecules must be spread thin enough for light to penetrate all the way through—perhaps 5 millimeters at most in an optimistic scenario. And if the molecules are suspended in liquid, that liquid needs to be pumped around the system, adding cost and complexity and more things that can break. Hoster remains skeptical that Most will ever heat an entire building, but he acknowledges the science is sound and the achievement genuine.
The field remains small. Griffin attended a Most technology conference last year with roughly 70 attendees—essentially the entire global research community working on the problem. But the momentum is building. Han's breakthrough suggests that nature's solutions, observed closely enough, can point the way forward. The sunburn that inspired her investigation may yet help solve one of the world's most stubborn energy problems.
Notable Quotes
When I actually saw the video and saw how quickly the entire solution was boiling, that was really remarkable.— Grace Han, describing her reaction to the energy release test
Most technology operates without burning anything, and could be made available anywhere on Earth, unlike fossil fuels concentrated in specific regions.— Kasper Moth-Poulsen, Most researcher at Polytechnic University of Barcelona
The Hearth Conversation Another angle on the story
What made you look at sunburn damage as a model for energy storage? That seems like an unusual connection.
I was reading about DNA photochemistry one evening, just out of curiosity, and it struck me that the molecules in my own skin were doing exactly what we'd been trying to engineer in the lab for years—changing shape under sunlight and then repairing themselves. Evolution had already solved the hard part.
So you borrowed the mechanism directly from biology.
Not borrowed exactly—inspired by. We used DNA-inspired molecules, not actual DNA. The key insight was that if nature had perfected a way to make molecules twist and untwist reliably, we should study how it works and apply those principles to energy storage.
The energy density you achieved is remarkable, but you mentioned the system uses hydrochloric acid to release the energy. That seems like a serious practical problem.
It is. We're aware it's not ideal. The acid works, but you have to neutralize it afterward, which adds steps and cost. We're actively looking for better triggers that don't require toxic chemicals.
And the UV light requirement—that's another barrier to real-world use, isn't it?
Yes. The wavelength we need is 300 nanometers, which is very harsh UV that barely reaches Earth's surface. We're hopeful we can engineer the molecules to respond to more accessible wavelengths, but that's still ahead of us.
If those problems are solved, what does a working Most system actually look like in practice?
Window coatings that store heat during the day and release it at night. Satellite components that maintain precise temperatures. Anywhere you need stored thermal energy without burning fuel. The real promise is long-term storage—months or years—which batteries can't do.