Scientists at the University of California Santa Barbara have developed a molecule that absorbs sunlight, holds the energy in chemical form for years, and releases it as heat when triggered — functioning, in the researchers’ own framing, as a rechargeable solar battery without electrodes or electrolytes.

The work describes a photoswitchable material that undergoes a reversible structural change when exposed to ultraviolet or visible light. That change traps the absorbed solar energy inside the molecular architecture itself, rather than converting it immediately to electricity or heat.

How the molecule stores sunlight

The mechanism draws on a class of compounds known as photoswitches — molecules that toggle between two stable structural isomers under light exposure. When sunlight strikes the material, the molecule snaps into a higher-energy configuration and stays there, storing the energy in chemical bonds rather than in a charged electrode or a hot fluid.

To release the stored energy as heat, an external trigger — such as a small amount of additional light or a catalytic stimulus — causes the molecule to revert to its original lower-energy form. The transition releases the stored energy as thermal output. The team drew inspiration from two well-understood reversible systems: the base-pairing dynamics of DNA strands and the photochromic compounds used in light-responsive eyeglass lenses.

According to the researchers, the molecule stores more energy per kilogram than conventional lithium-ion cells. Lithium-ion technology currently dominates portable and grid-scale storage, but faces constraints in energy density, degradation over charge cycles, and the need for thermal management systems. The UCSB molecule sidesteps the charge-discharge cycle entirely; it holds energy in a stable chemical state that does not measurably degrade over years of storage, the team said.

For context on how battery chemistry affects long-term performance, lithium EV batteries subjected to a US-developed heating protocol retained 93% capacity after 500 cycles — a result considered strong for conventional electrochemical systems. The UCSB approach avoids electrochemical cycling altogether, which could remove that degradation pathway entirely, though long-term field data does not yet exist.

Potential uses and practical constraints

The thermal output profile makes the technology most relevant to low-and medium-temperature heat applications: space heating, hot water systems, and industrial process heat below roughly 200°C (392°F). These sectors account for a substantial share of global energy consumption and are poorly served by electrical batteries, which store energy in a form that must be converted back to heat through a resistive element or heat pump, adding conversion losses.

A molecular solar thermal system, by contrast, delivers heat directly. The stored chemical energy converts to thermal energy in a single step at the point of use, with no grid connection required. That characteristic could make the material practical in off-grid or remote contexts where electrical infrastructure is limited.

Several engineering obstacles remain before the technology can scale. Synthesizing photoswitchable molecules at industrial volumes is currently expensive. The material must also demonstrate stability across thousands of charge-release cycles under real-world illumination conditions, not just controlled laboratory exposures. Researchers have not yet published data on how the molecule performs under diffuse light or partial shading — conditions that dominate most real solar installations.

Where the research fits in solar storage

Molecular solar thermal energy storage, sometimes abbreviated MOST, has been an active research area for roughly a decade. Swedish researchers at Chalmers University of Technology have pursued a norbornadiene-based photoswitch along similar lines. The UCSB work appears to offer higher energy density and a longer storage window than earlier MOST candidates, though direct side-by-side comparisons of specific energy values have not been published in the current reporting.

The broader solar energy storage field is pursuing multiple parallel strategies. Near-invisible solar cells 10,000 times thinner than a human hair address the capture side of the equation. Molecular thermal storage addresses the retention and dispatch side — a different problem with a different set of material constraints.

If the synthesis cost can be driven down and cycle stability confirmed at scale, the material could eventually be integrated into building materials, textiles, or passive heating panels that store daytime solar energy and release it overnight without any active electrical system involved.

The work was reported and published by Science Daily.