A DNA-inspired molecule out-performs lithium-ion energy density and could heat homes and water using nothing but sunlight
Science & Energy Technology Desk | March 2025 | 6 min read
Solar energy has a fundamental problem that no amount of panel efficiency improvement can solve on its own: the sun does not shine all the time. The gap between when energy is available and when it is needed has made storage the central challenge of the renewable energy transition. Batteries have been the dominant answer — but batteries come with their own limitations: raw material scarcity, degradation over charge cycles, fire risk, and an energy density ceiling that has proven difficult to push past.
A research team at the University of California, Santa Barbara has published findings in the journal Science describing a fundamentally different approach. Rather than converting sunlight into electricity and storing that electricity in a battery, their system captures solar energy directly as a chemical change within a specially engineered molecule — and releases it on demand as heat. The molecule outperforms lithium-ion batteries on energy density, is soluble in water, and is designed to be recharged by sunlight alone, repeatedly, without degrading.
It is early-stage science, and real-world deployment is still some distance away. But the architecture of the technology is genuinely novel, and its potential applications — from off-grid heating to residential hot water systems in sun-rich developing regions — make it worth understanding in detail.
The Numbers That Matter
| > 1.6 MJ/kg
New molecule energy density |
~ 0.9 MJ/kg
Lithium-ion battery energy density |
~ 78% higher
Improvement over lithium-ion |
What Is a Molecular Solar Thermal System?
A Molecular Solar Thermal system — MOST for short — is a category of energy storage technology built around molecules that can exist in two distinct structural states. In the lower-energy ground state, the molecule is stable and inert. When it absorbs sunlight, it transitions to a higher-energy state in which the absorbed energy is locked into the molecule’s chemical structure — not as heat, not as electricity, but as a kind of molecular tension. That tension persists until deliberately released.
The release trigger can be heat, a catalyst, or in some designs a specific wavelength of light. When triggered, the molecule reverts to its ground state and releases the stored energy as heat. The molecule is not consumed in this process — it returns to its original form, ready to absorb sunlight again. In principle, it can cycle through this process indefinitely.
The concept has been explored in laboratory settings for decades, but previous MOST materials suffered from two critical limitations: low energy density — meaning you needed impractically large volumes of material to store useful amounts of energy — and poor stability in the high-energy state, with molecules losing their stored energy too quickly to be practically useful.
The Pyrimidone Molecule: A DNA-Inspired Design
The specific molecule at the centre of this research is called pyrimidone. Its design was inspired by the structural biology of DNA — specifically by a naturally occurring DNA component that changes its molecular configuration when it is exposed to ultraviolet light. This natural UV-switching behaviour gave the research team a biological template to work from in engineering a synthetic molecule capable of the same fundamental trick at higher energy levels and greater stability.
The team collaborated with computational chemists at UCLA to model in precise detail how the pyrimidone molecule maintains its high-energy configuration without spontaneously releasing its stored energy prematurely. This stability modelling was central to the breakthrough — previous MOST candidates often failed because the energy-holding configuration was too transient to be practically useful. The pyrimidone design appears to have cracked that problem, remaining stable in its charged state until deliberately triggered.
| The Compressed Spring Analogy:
Think of the molecule in its ground state as a relaxed spring. Sunlight compresses the spring and locks it in place. The locked spring holds that energy indefinitely until you release the latch — at which point the spring decompresses and the stored energy is released as heat. The spring is undamaged by this process and can be compressed again. The pyrimidone molecule behaves in exactly this way, at the scale of individual atoms. |
How the Energy Density Compares
Energy density — how much energy can be stored per unit of weight — is one of the most important measures for any storage technology. Higher energy density means lighter, smaller, or more capable systems for the same mass of material. The pyrimidone molecule’s performance on this metric is what elevates this research above previous MOST work.
| Storage Type | Energy Density | Output Type |
| Lithium-ion Battery | ~0.9 MJ/kg | Electricity |
| Previous MOST Systems | < 1.0 MJ/kg | Heat |
| Pyrimidone MOST (new) | > 1.6 MJ/kg | Heat |
Surpassing lithium-ion energy density is a meaningful benchmark. Lithium-ion technology has benefited from decades of intensive industrial development and billions of dollars in optimisation investment. A new material exceeding its energy density at an early stage of development suggests considerable room for further improvement as the technology matures.
It is worth noting that energy density comparisons between different output types — electricity versus heat — are not straightforward. Lithium-ion batteries produce electricity, which is a highly versatile energy form. The MOST system produces heat, which is more limited in its applications. The comparison is most relevant in contexts where heat is the desired output — which, as it happens, accounts for a substantial share of global energy consumption.
The Boiling Water Demonstration
Abstract energy density figures are easier to contextualise through practical demonstration. To validate real-world usability, the researchers tested whether the stored energy in their material could perform a concrete task: boiling water under normal atmospheric conditions without any external energy input beyond what had been previously stored in the molecule through sunlight exposure.
The material succeeded. This single demonstration addresses what has historically been one of the sharpest criticisms of MOST systems — that while they could store energy in principle, they could not deliver it at levels of intensity or volume sufficient for practical heating applications. The ability to boil water from stored solar energy changes that assessment.
Why Water Solubility Is a Key Design Feature
One of the practical advantages of the pyrimidone molecule that deserves separate attention is its solubility in water. Many promising energy materials are difficult to work with at scale because they require specialist solvents, operate only in solid form, or cannot be easily pumped and circulated through existing infrastructure.
A water-soluble MOST material opens up a straightforward system architecture: dissolve the molecule in water, circulate the solution through solar collectors during daylight hours to charge the molecules, then store the charged solution in insulated tanks for use when heating is needed. This design maps onto infrastructure that already exists for solar thermal water heating — a technology widely deployed in residential and commercial buildings across warm climates.
For regions where solar thermal water heating is already established, upgrading to a MOST-based system could provide meaningful advantages: longer storage duration, higher energy density per volume of fluid, and the ability to store energy collected on one day for use days later — something conventional solar thermal systems cannot achieve efficiently.
Potential Applications: Where This Technology Could Have Impact
Off-Grid Heating in Sun-Rich Regions
For communities without reliable electricity grid access, heating — for cooking, water sanitation, and space warming — is typically provided by burning biomass or fossil fuels. A self-contained MOST system that charges during the day and releases heat on demand overnight could provide clean, renewable heating without any grid connection or battery infrastructure. This application is particularly relevant across South Asia, sub-Saharan Africa, and rural parts of Latin America where solar radiation is abundant but grid access is limited.
Residential Hot Water Systems
Domestic hot water heating accounts for a significant share of household energy consumption in most climates. Current solar thermal water heating systems are effective but cannot bridge the gap between daytime solar collection and evening demand without supplementary energy sources. A MOST fluid circulating through a rooftop collector and stored in a tank could, in principle, deliver hot water on demand throughout the evening from energy collected during the day — or even from the previous day’s sunshine.
Industrial Process Heat
Many industrial processes require heat at temperatures achievable by concentrated MOST systems — food processing, sterilisation, materials drying, and low-temperature chemical reactions among them. Replacing fossil fuel-derived process heat with stored solar thermal energy represents one of the harder decarbonisation challenges in the industrial sector, and MOST technology could offer a pathway in thermally intensive but moderate-temperature applications.
Eliminating Separate Battery Systems
One of the more elegant aspects of the MOST approach is that the storage medium and the energy capture mechanism are the same material. Conventional solar electricity generation requires separate photovoltaic panels and battery storage systems — two distinct technologies with distinct failure modes, supply chains, and replacement cycles. A MOST system collapses those two functions into a single fluid, potentially simplifying installation, maintenance, and long-term cost structures.
What Still Needs to Be Solved
Scientific breakthroughs published in peer-reviewed journals represent important milestones — but they are rarely the last step before a technology reaches consumers. The pyrimidone research is compelling precisely because it has cleared several hurdles that have defeated previous MOST candidates, but a number of challenges remain before the technology could be commercialised at scale.
- Scalable synthesis: Producing pyrimidone in large quantities at commercially viable cost is an engineering challenge that has not yet been addressed
- Long-term cycle stability: Laboratory demonstrations of reversible energy storage are promising, but thousands of real-world charge-discharge cycles over years of use may reveal degradation behaviours not yet observed
- Temperature optimisation: Depending on the application, the temperature at which heat is released may need to be tunable — current systems release heat at temperatures determined by the molecule’s chemistry, which may not match all use cases
- System integration engineering: Moving from a molecule performing well in controlled lab conditions to a deployable system with pumps, collectors, tanks, and heat exchangers requires substantial engineering work
- Regulatory and safety assessment: Any new material entering consumer or industrial use requires safety and environmental assessment
Key Takeaways
- Researchers have developed a water-soluble molecule that stores solar energy chemically and releases it as heat on demand
- The material’s energy density exceeds 1.6 MJ/kg — surpassing lithium-ion batteries at approximately 0.9 MJ/kg
- The design was inspired by a DNA component that changes configuration under ultraviolet light
- In testing, the stored energy was sufficient to boil water without any additional energy input
- The molecule is designed to be repeatedly rechargeable by sunlight with no degradation in principle
- Primary applications include off-grid heating, residential hot water, and industrial process heat
- The research was published in the journal Science and received support from the Moore Inventor Fellowship
- Commercialisation will require further work on scalable production, long-term durability, and system engineering
— End of Article —
Disclaimer: This is an independently written analytical article based on publicly available scientific research and published findings. All content is entirely original. No text from any third-party publication has been reproduced or paraphrased.
