- Researchers at Chalmers University of Technology discovered a molecule that stores sunlight as heat, inspired by the damage caused by sunburn on human skin.
- The molecule, norbornadiene-quadricyclane system, transforms into a high-energy isomer when exposed to sunlight, storing energy in molecular bonds.
- This energy storage innovation has the potential to decarbonize global heating systems, a critical step in reducing carbon emissions.
- The molecule remains stable at room temperature for extended periods, allowing it to retain stored energy for months, even in the dark.
- The breakthrough has shed new light on thermal energy storage, a field often overlooked in favor of batteries and solar panels.
On a sweltering summer afternoon in Lund, Sweden, a group of researchers at the Chalmers University of Technology were examining the effects of ultraviolet light on organic compounds when something unexpected happened. A flask containing a clear liquid warmed to the touch — even though it hadn’t been near a heat source. The molecules inside had been exposed to sunlight, and like human skin after too much sun, they had undergone a subtle structural change. But unlike a sunburn, this reaction stored energy rather than causing damage. The realization rippled through the lab: what if this wasn’t a curiosity, but a new way to trap solar heat for months, even in the dark? This serendipitous moment has since blossomed into one of the most promising advances in thermal energy storage, a field long overshadowed by batteries and solar panels but critical to decarbonizing global heating systems.
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A New Molecule That Stores Sunlight as Heat
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The compound at the heart of this innovation is called a norbornadiene-quadricyclane system, a pair of molecular forms that transform into each other when exposed to sunlight. When norbornadiene absorbs photons, it rearranges into quadricyclane — a high-energy isomer that remains stable at room temperature for extended periods. The energy isn’t lost; it’s locked in molecular bonds. Later, when triggered by a catalyst, the molecule snaps back to its original form, releasing the stored energy as heat. Researchers have demonstrated that this process can elevate temperatures by more than 60°C (108°F) on demand. What makes this remarkable is not just the efficiency, but the duration: the energy can be stored for months without significant loss. Unlike batteries, which degrade and require rare minerals, this liquid fuel can be cycled repeatedly with minimal wear. The system, dubbed MOST (Molecular Solar Thermal Energy Storage), is now being tested in residential prototypes in Sweden and could be scalable for industrial use.
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The Decades-Long Search for Thermal Storage
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For years, solar energy has faced a fundamental mismatch: peak production occurs during daylight, but demand for heating often peaks at night or in winter. Traditional solutions like insulated water tanks lose heat quickly, making long-term storage impractical. Phase-change materials and molten salts offer some improvements, but they’re bulky, expensive, or limited to high-temperature industrial settings. The idea of storing solar energy in chemical bonds is not new — researchers have explored photoresponsive molecules since the 1970s — but early versions suffered from low energy density, instability, or reliance on toxic solvents. Breakthroughs in synthetic chemistry and nanotechnology over the past two decades have changed the equation. By fine-tuning the molecular structure of norbornadiene with carbon-based side groups, the Lund team boosted both energy capacity and longevity. Their 2022 paper in Nature Energy showed a record energy density of 0.5 megajoules per kilogram, rivaling lithium-ion batteries on a thermal basis.
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The Scientists Behind the Sunburn Insight
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At the helm of this research is Professor Kasper Moth-Poulsen, a physical chemist whose curiosity about molecular machines led him to explore energy applications. His team’s focus on photoisomerization — the process by which molecules change shape under light — was initially aimed at developing responsive materials, not energy storage. But when they noticed persistent heat retention in their samples, they pivoted. “We realized we weren’t just watching a chemical reaction — we were seeing a battery built from molecules,” Moth-Poulsen said in a BBC interview. Collaborators across Denmark and China have since refined the catalyst that triggers energy release, using cobalt-based compounds to make the process faster and more controllable. What unites these researchers is a shared belief that decarbonization requires reimagining not just how we generate energy, but how we store and use it — especially in heating, which accounts for over 50% of global final energy consumption.
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Implications for Homes, Industry, and Climate
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If scaled, MOST technology could revolutionize how buildings are heated. Imagine solar collectors on rooftops charging a tank of liquid during summer, then releasing that heat months later during winter — no combustion, no emissions. Early pilot systems are being integrated into Swedish apartment complexes, where the stored heat supplements district heating networks. For rural or off-grid communities, this could eliminate dependence on heating oil. Industrial processes that require steady heat, such as food production or textile manufacturing, could also benefit. Economically, the system’s durability and use of abundant organic materials suggest lower lifetime costs than electric heat pumps in some climates. But challenges remain: improving catalyst efficiency, ensuring long-term material stability, and integrating with existing infrastructure. Regulatory frameworks for liquid energy carriers also need updating.
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The Bigger Picture
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This breakthrough underscores a crucial truth: the clean energy transition won’t rely solely on familiar technologies like wind and solar panels. It will depend on innovations that operate quietly behind the scenes — in molecules, materials, and systems design. Thermal energy storage has long been the overlooked half of the renewable equation. By addressing it with molecular precision, the MOST system exemplifies how nature-inspired chemistry can solve human-scale problems. As climate pressures mount, such interdisciplinary leaps — born from a sunburn, no less — may prove indispensable.
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What comes next is a period of refinement and real-world testing. The Lund team aims to commercialize the technology by 2027, with support from the European Union’s Horizon program. If successful, we may soon see solar energy not just lighting our homes, but warming them — long after the sun has set.
Source: BBC