New material can store solar energy for years

Thin coatings made of this material can soak up solar energy in the summer months and provide heat to buildings in the winter without using fuel or electricity.

Making the transition from fossil fuels to renewable energy sources will be challenging. Perhaps the most important of these is storing energy from intermittent sources, such as the sun and wind. A new material whose properties allow it to capture and store solar energy for months at room temperature could be the answer. The material can release energy in the form of heat when needed.

The material reported in the Journal of Materials Chemistry in the article “Kieran Griffiths et al. Long-term Ambient Solar Energy Storage in MOF-based Solid Phase-Shifting Material.”, could be used to cover homes and buildings to store the heat of the summer sun for use during the winter months. Or it could lead to a heat storage system similar to a battery, but requiring no electricity or complicated mechanics.

Storing solar energy will be critical if it is to be used on a large scale. One way to do this is to store the electricity produced by solar panels in batteries. But batteries tend to be expensive and impractical for remote or underdeveloped regions. Storing solar energy in liquids by changing chemical bonds may be more compact and inexpensive.

A team from Lancaster University decided to explore the potential for energy storage in a metal-organic framework type material. These are solids with a highly organized crystal structure. They are very porous, so they can hold other molecules. Researchers are studying these materials for applications such as hydrogen storage or cleaning up oil spills.

The Lancaster team used a MOF created earlier by Japanese researchers. MOF pores contain azobenzene, a carbon-based compound that is excellent at absorbing light. Azobenzene also has properties that allow it to change shape when exposed to external stimuli such as heat or light.

When the researchers exposed the material to ultraviolet light, it absorbed energy, changed shape and held its shape, much like a spring holds energy. When exposed to external heat, the material released energy and returned to its original shape.

While other such light-sensitive materials store energy for days, the researchers’ tests showed that this material stores energy for four months. They estimate it can store energy for four and a half years.

In addition, MOF is chemically stable, so it can easily be stored or turned into coatings that can be applied to structures. “It also has no moving or electronic parts, so there is no loss in the storage and release of solar energy,” John Griffin, a senior in materials chemistry who led the study, said in a press release.

The researchers now hope to refine the concept by studying other MOF framework materials. “Our hope is that with further development, we can create other materials that store even more energy,” Griffin said.

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