The challenge with solar panels isn’t producing energy; it’s storing it, which is where molecular solar thermal energy storage offers a promising alternative.
Solar electricity disappears when the sun sets, and storing that energy usually requires expensive battery systems. Now, scientists may have developed a system that offers a simpler way to capture and reuse solar energy around the clock.
Solar panels themselves are very good at producing electricity, but they have two fundamental limitations. First, they are intermittent, meaning they only generate electricity when sunlight is available. Second, solar panels do not store energy. They only generate it. To store solar energy for later use, separate storage systems such as batteries are needed.
Researchers at the University of California, Santa Barbara, think they may have found a different solution to these limitations. It’s called molecular solar thermal energy storage. Instead of generating electricity and storing it in batteries, the system stores sunlight directly in molecules.
Scientists have developed a reusable liquid molecule that captures sunlight, stores it inside chemical bonds, and releases it later as heat when needed. The process begins when the molecule absorbs sunlight. The molecule then changes shape and stores energy inside its structure. You can think of it like compressing a spring: energy is stored while the molecule is in its high-energy shape.
Later, when triggered, the molecule returns to its original form and releases the stored energy as heat. In this way, the system works like a rechargeable solar battery, except the energy is stored inside molecules rather than electronic components.
The molecule at the center of the discovery is called pyrimidone. When sunlight hits the molecule, it changes shape and moves into a higher-energy state. In that state, the energy from the sun becomes trapped inside the molecule’s chemical bonds. The molecule can hold that energy until it receives a trigger, such as a catalyst or a small amount of heat. When triggered, the molecule snaps back to its original form, releasing the stored energy as heat.
Scientists often compare the process to something more familiar: photochromic sunglasses. When you step outside into bright sunlight, the lenses automatically darken. When you return indoors, they become clear again.
The change is reversible. Light causes the molecules in the lenses to rearrange and then return to their original state. Molecular solar thermal energy storage works on a similar principle. Instead of changing color, the molecules change shape to store energy and then release it when needed.
To design the new molecule, the research team looked to an unexpected source: DNA. The pyrimidone structure resembles components found in DNA that can undergo reversible structural changes when exposed to ultraviolet light.
By engineering a synthetic version of that structure, the team created a molecule capable of repeatedly storing and releasing solar energy.
Researchers also used computational modeling to understand why the molecule remained stable while holding large amounts of energy. Stability is critical for any energy storage material, since it must survive many charging and discharging cycles without degrading. The result was a compact molecule designed to store as much energy as possible while avoiding unnecessary structural elements.
One of the most striking aspects of the material is its energy density. The molecule can store more than 1.6 megajoules of energy per kilogram. For comparison, standard lithium-ion batteries store around 0.9 megajoules per kilogram in comparable thermal energy terms. That means the molecule stores roughly twice as much energy as traditional batteries.
Molecular solar thermal energy storage focuses specifically on storing heat rather than electricity. While electricity often receives the most attention in renewable energy discussions, heat represents a large share of global energy demand.
Heating buildings, producing hot water, and powering industrial processes all require thermal energy. Technologies that can capture sunlight during the day and release heat later could therefore help reduce reliance on fossil fuels.
In laboratory tests, the research team demonstrated just how powerful the stored heat can be. When the molecule released its stored energy, it generated enough heat to boil water under ambient conditions. Boiling water may sound simple, but it requires a significant amount of energy. Achieving this milestone shows that the stored solar energy is strong enough to perform real work.
That opens the door to practical uses for the technology. Future systems could potentially use the liquid molecules in rooftop solar collectors. During the day, sunlight would “charge” the molecules by storing energy in their chemical bonds. The liquid could then be stored in tanks until the heat is needed later.
Because the molecules dissolve in liquid, the system could circulate through pipes, much like the heating fluids used in existing solar thermal systems. Molecular solar thermal energy storage could therefore provide heat for homes, water systems, or even off-grid applications such as camping equipment.
Unlike conventional solar panels, which require separate batteries to store electricity, this system stores energy directly inside the material itself. The research is still in its early stages, but it demonstrates a promising concept: sunlight can be captured, stored in molecules, and released later on demand.
Scientists will now focus on improving the molecules so they absorb sunlight more efficiently and hold even more energy. Scaling the technology for real-world systems will require further development. Still, the idea of storing sunshine inside a liquid molecule shows how creative chemistry can contribute to the future of renewable energy.
As solar power continues to expand worldwide, innovations such as molecular solar thermal energy storage could help ensure that the sun’s energy remains available even after the sky goes dark.
