Molecular solar storage and the promise of MOST technology
Capturing and storing solar energy efficiently and compactly remains one of the central challenges in sustainable energy research. In recent years, molecular solar storage systems, known by the acronym MOST, have emerged as a promising solution.
MOST technology stores solar radiation in the form of chemical energy using a photoactive molecule. The molecule acts as a molecular photoswitch. When exposed to light, it undergoes isomerization into a high-energy metastable photoisomer. When triggered by an external stimulus, the molecule releases the stored chemical energy as heat.
In theory, this creates a rechargeable thermal battery capable of shifting solar energy use over longer timescales than conventional photovoltaics. The main challenge has been identifying the ideal molecule that balances energy density, absorption spectrum, kinetic barrier, quantum yield and long-term stability.
From DNA architecture to engineered pyrimidone
Practical results have remained limited, but new research conducted at the University of California offers a potentially significant advance. A team led by Professor Grace Han developed a bio-inspired MOST system drawing from the structural architecture of DNA.
The researchers engineered a pyrimidone-based molecular solar storage system. Pyrimidone is a ketone derivative of pyrimidine, a molecule structurally related to components found in DNA and capable of undergoing reversible structural changes after exposure to ultraviolet light.
The team designed a synthetic version of this framework, creating a new photoswitch that stores solar energy stably, even for years, and releases it reversibly on demand. Specifically, pyrimidone stores energy in a metastable Dewar photoisomer, formed through excitation at 300 nm.
“We prioritized a lightweight and compact molecular design,” said Han Nguyen, lead author of the study. “For this project, we removed everything that was not essential.”
Record energy density for molecular solar storage
The result represents a significant step forward for molecular solar storage. The new MOST system achieves an energy density exceeding 1.6 MJ/kg, roughly double that of a standard lithium-ion battery, typically around 0.9 MJ/kg. This marks the highest value reported in previous experiments.
Designed with sustainability in mind, the system operates without solvents and remains compatible with aqueous environments. It also addresses a longstanding obstacle in the field, the controlled extraction and transfer of stored heat.
When catalyzed by an acid, the Dewar isomer releases enough heat to bring water to a boil.
“Boiling water is an energy-intensive process,” Nguyen added. “Achieving it at room temperature is therefore a major accomplishment.”
This capability opens pathways for practical applications ranging from portable heat supply, such as for camping, to domestic water heating. Because the compound is water-soluble, it could also enable a new generation of solar thermal collectors.
The research, titled “Molecular solar thermal energy storage in Dewar pyrimidone beyond 1.6 MJ/kg,” was published in Science.