Solar Energy Breakthroughs: Storing the Sun's Power for On-Demand Use

Researchers have reported several distinct approaches to capturing solar energy, storing it chemically or thermally, and releasing it on demand for heating or electricity generation. These developments include molecular materials that store energy in chemical bonds and a wood-based composite that stores heat and generates electricity.

Molecular Solar Thermal (MOST) Energy Storage

Pyrimidone Material (University of California, Santa Barbara)

Researchers at the University of California, Santa Barbara have developed a material that stores solar energy chemically and releases it as heat. The material is a modified organic molecule called pyrimidone, representing a Molecular Solar Thermal (MOST) energy storage system.

"The material stored over 1.6 megajoules of energy per kilogram — enough heat to boil water under ambient conditions."

Mechanism
The molecule is designed to absorb sunlight and twist into a strained, high-energy configuration. It maintains this state until a trigger—such as a small amount of heat or a catalyst—causes it to revert to its relaxed state, releasing the stored energy as heat. The process is described as reusable and recyclable.

Design Inspiration
The molecule's design was inspired by a DNA component whose structure undergoes reversible changes when exposed to ultraviolet (UV) light. The team engineered a synthetic version of this component. Computational modeling was provided by Professor Ken Houk at the University of California, Los Angeles.

Performance
In experiments, the material stored over 1.6 megajoules of energy per kilogram. Researchers reported that the heat released was sufficient to boil water under ambient conditions.

Funding
The research was supported by a Moore Inventor Fellowship awarded to Associate Professor Grace Han in 2025. The findings were published in the journal Science.

ANI-MV Liquid Material (Northwestern University)

Researchers at Northwestern University have created a liquid material called ANI-MV that can harvest energy from sunlight, electricity, X-rays, or chemical fuels, store it for months, and release it on demand.

Mechanism
The material consists of custom-designed molecules containing an amino naphthalene unit (ANI) that absorbs energy and methyl viologen (MV) that stores electrons. Upon absorbing energy, ANI donates electrons to MV, causing molecules to form pairs called pimers. These pimers self-assemble into nanoscale ribbons that form a black gel. Exposure to air dissolves the gel back into a yellow liquid, allowing the material to be reused.

Applications
Researchers demonstrated that the charged gel could power chemical reactions in the absence of light, a process known as "dark photocatalysis." Potential applications include energy storage, environmental remediation, and adaptive soft electronics. The material operates in water and requires no metals or plastics.

Publication
The study, "Dynamic self-assembly mediated by stored and released electrons in pimer supramolecular polymers of chromophore amphiphiles," was published in the journal Chem on June 11, 2021. It was supported by the Center for Bio-inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy.

Wood-Based Solar Thermal Composite

Balsa Wood Material

Researchers have developed a material from balsa wood that can absorb sunlight, store energy as heat, and generate electricity after the light source is removed. The study was published in the journal Advanced Energy Materials.

"The material stored approximately 175 kilojoules of heat per kilogram and converted 91.27% of incoming sunlight into usable heat."

Material Development Process
The process began with balsa wood, selected for its internal structure of aligned microtubes. Lignin was removed from the wood, increasing its porosity to over 93%. The internal channel walls were then coated with:

Black phosphorene nanosheets, which absorb sunlight across multiple wavelengths and convert it to heat.
A protective layer of tannic acid and iron ions to prevent the phosphorene from degrading.
Silver nanoparticles to enhance light absorption through plasmonic effects.
Hydrocarbon chains grafted onto the surface, making it water-repellent with a contact angle of 153°.

The channels were subsequently filled with stearic acid, a bio-based phase-change material that stores energy by melting and releases it by solidifying.

Performance Characteristics
According to the study:

The material stored approximately 175 kilojoules of heat per kilogram.
It converted 91.27% of incoming sunlight into usable heat.
Thermal conductivity along the wood's natural grain was nearly 3.9 times more efficient than in other directions.
When paired with a thermoelectric generator, the system produced up to 0.65 volts under standard one-sun illumination.
The system maintained electricity production after the light source was removed by using stored heat to create a temperature difference across the thermoelectric generator.
The material demonstrated stability, with performance remaining largely unchanged after 150 days of solar exposure and 100 heating-cooling cycles.
It exhibited flame-retardant properties, self-extinguishing within two minutes when exposed to flame.
The surface demonstrated antimicrobial activity, preventing bacterial growth.

Research Context and Statements
The researchers described their work as "a scalable and environmentally friendly wood-based platform for advanced solar thermal energy harvesting." They stated that the design "integrates flame retardancy, superhydrophobicity, and antimicrobial activity, thereby mitigating dust adhesion and microbial colonization that would otherwise deteriorate the outdoor photothermal performance."

The researchers noted that previous approaches to storing solar energy as heat often involved stacking different materials, which can waste energy at material boundaries. This approach uses a single, modified material structure. The researchers avoided high-temperature carbonization, preserving chemical features for potential future modifications.

Potential Applications and Future Work
The researchers suggested similar designs might have applications in:

Heat management in electronics
Energy-efficient building materials
Off-grid power systems

The researchers indicated that scaling the system while maintaining desirable energy output requires further development. They also noted the approach could potentially be adapted to other nanomaterials and biomass structures.