Scientists at the University of California in the U.S. have developed a molecular system that can capture, store, and release solar energy without relying on conventional batteries or grid infrastructure, addressing a key limitation in renewable energy deployment.

The research introduces a modified organic molecule, pyrimidone, that stores sunlight in chemical bonds and releases it as heat when required.

The work represents a significant step in Molecular Solar Thermal (MOST) energy storage, a field focused on storing solar energy in stable molecular structures for later use.

Bio-Inspired Molecular Design

The research team drew inspiration from DNA to engineer the molecule. The pyrimidone resembles a structural component of DNA that undergoes reversible changes upon exposure to ultraviolet light.

By replicating and modifying this behavior, the team created a synthetic molecule capable of storing solar energy through structural transformation. The molecule absorbs sunlight and transitions into a high-energy configuration, remaining stable in that state for extended periods without losing stored energy.

The team focused on minimizing the molecular structure to improve efficiency. Unnecessary components were removed to create a lightweight and compact design. The resulting molecule operates without solvents and remains compatible with water-based environments, which improves its practical applicability.

The system is also designed to be reusable and recyclable, undergoing repeated cycles of energy storage and release without degradation.

High Energy Density

The pyrimidone-based system demonstrates an energy density exceeding 1.6 megajoules per kilogram (MJ/kg), approximately double that of conventional lithium-ion batteries, which are typically around 0.9 MJ/kg.

This positions the technology as a competitive alternative for specific use cases where heat, rather than electricity, is the required output. Unlike traditional photovoltaic systems that convert sunlight into electricity, this system stores solar energy directly as chemical energy and releases it as thermal energy.

The mechanism functions similarly to a mechanical spring. Upon exposure to sunlight, the molecule shifts into a strained, high-energy form.

It remains in this state until triggered by a catalyst or a small amount of heat, which causes it to revert to its original structure and release the stored energy as heat.

This reversible process enables repeated charging and discharging cycles, effectively functioning as a “rechargeable solar battery” for thermal applications.

Demonstration and Potential Applications

The study translated stored energy into a measurable output. The researchers demonstrated that the heat released from the molecule was sufficient to boil water under ambient conditions, a benchmark that has been difficult to achieve in MOST systems.

The experiment showed that the system could boil approximately 0.5 milliliters of water when triggered by an acid catalyst, indicating effective heat extraction and transfer.

This capability opens pathways for decentralized and off-grid applications. Potential use cases include residential water heating, where the material could be circulated through rooftop solar collectors to absorb sunlight during the day and stored in tanks for use at night.

The system’s compatibility with water also allows integration into existing thermal systems without requiring significant infrastructure changes. Additional applications include portable heating solutions for outdoor use and energy storage in locations without reliable grid access.

The technology also addresses a broader challenge in renewable energy systems: storage. Traditional solar installations require separate battery systems to store electricity, increasing costs and complexity.

In contrast, MOST systems integrate energy capture and storage into a single material, potentially reducing capital expenditure and simplifying system design.

In June 2024, researchers at Stanford University made progress on an emerging technology that uses liquid organic hydrogen carriers (LOHCs) to essentially create a ‘liquid battery’ for storing renewable energy from wind and solar power.

In 2022, researchers at Chalmers University of Technology, Sweden, developed a solution-and-neat-film-based Molecular Solar Thermal energy storage system (MOST) to capture solar energy and convert it into electricity on demand.