How to store the sun in a crystal for months
Completely replacing fossil fuels with renewable energies, as required by climate change and the depletion of oil resources, will not be achieved without rising to several complicated challenges, starting with storing the energy produced by intermittent sources such as sun and wind power. These energies must be stored if they are to be rolled out on a wide scale.
An advantageous and inexpensive solution, especially for areas that are far from producing regions or less well equipped, would consist in keeping these energies in fluids, altering the molecules’ chemical bonds.
The good news: researchers from Lancaster University in the United Kingdom have just discovered a revolutionary material capable of capturing and storing solar energy for months at room temperature, and releasing it in the form of heat on demand. Their discovery has just been presented in the review Chemistry of Materials.
Applied to buildings, this material could store the heat of the sun in summer and release it in winter. It operates like a kind of heat battery, but without electricity or added mechanics.
Crystal to store energy
The scientists studied the energy storage potential of a type of material known as a metal-organic framework (MOF), a kind of crystal with a highly organized structure. These MOFs are porous and can absorb other molecules, and some are already used to store hydrogen or clean up oil spills.
The MOF used by the English researchers was produced by Japanese researchers. Its pores contain azobenzene, a carbon-based compound that strongly absorbs light and easily changes shape when it is stimulated by an external factor.
Exposed to ultraviolet light, the MOF absorbs and stores its energy, changing shape just like a coiled spring retains energy. Under a heat source, it returns to its initial shape while releasing the energy accumulated.
Even better, it stores this energy for four months, a period that could be extended to four and a half years, according to the researchers. Its chemical stability and ease of storage mean that it could be used to manufacture coatings that can be applied to buildings without any electronic or mechanical parts and with no energy loss.
The next step is improving the concept with other MOFs to store even more energy.
« Long-Term Solar Energy Storage under Ambient Conditions in a MOF-Based Solid–Solid Phase-Change Material », Chemistry of Materials, November 25, 2020 - pubs.acs.org/doi/10.1021/acs.chemmater.0c02708