From pv magazine Global
A research group from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a dynamically tuneable phase-change material (PCM) that can be used to store both thermal energy and electricity if applied in buildings.
PCMs are substances that absorb and release heat energy when they change phase and are able to store and release large amounts of latent heat over a defined temperature range. In the construction business, combining building materials with PCMs is an efficient way to improve the thermal energy storage capacity of construction elements.
“However, one problem with phase-change materials is that they typically work only in one temperature range,” the scientists stated. “That means two different materials would be needed for summer and winter, which increases … cost.” In order to address this issue, the NREL team changed the transition temperature (Tm) of a PCM using ions with very modest voltage requirements. The transition temperature is the minimum temperature at which a material changes its crystal structure to another.
A dual-ion battery (DIB) was utilised to electrochemically modify the concentration of salt in the PCM and, as a consequence, change its Tm in a reversible and dynamic manner.” In a DIB, a PCM with a high initial salt concentration and low Tm serves as the electrolyte for the device,” the scientists explained. “Electrochemical charging stores the cations and anions in the negative and positive electrodes, respectively.”
The PCM, salt, and electrodes were optimised to make the DIB work as a dynamically tuneable device. “It functions like a thermal and electric battery,” the research corresponding author, Gao Liu, said. “What’s more, this capability increases the thermal storage potential because of the ability to tune the melting point of the material depending on different ambient temperatures.”
The proposed technology is claimed to reduce the cost of storage, as the same material can be used for the whole year instead of just half of it. “If we use thermal energy storage, in which the raw materials are more abundant to meet the demand for thermal loads, this will relax some of the demand for electrochemical storage and free up batteries to be used where thermal energy storage cannot be used,” said research co-author, Sumanjeet Kaur.
All the details on the storage technology can be found in the study Dynamic tuneability of phase-change material transition temperatures using ions for thermal energy storage, which was recently published in Cell Reports Physical Science. “In large scale building construction, this combined thermal and electrical energy storage capability would allow the material to store excess electricity produced by on-site solar or wind operations, to meet both thermal (heating and cooling) and electrical needs,” the academics concluded.
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