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a new chemical composite developed by researchers at MIT could provide an alternative. It could be used to store heat from the sun or any other source during the day in a kind of thermal battery, and it could release the heat when needed, for example for cooking or heating after dark.
A common approach to thermal storage is to use what is known as a phase change material (PCM), where input heat melts the material and its phase change -- from solid to liquid -- stores energy. When the PCM is cooled back down below its melting point, it turns back into a solid, at which point the stored energy is released as heat. There are many examples of these materials, including waxes or fatty acids used for low-temperature applications, and molten salts used at high temperatures. But all current PCMs require a great deal of insulation, and they pass through that phase change temperature uncontrollably, losing their stored heat relatively rapidly.
Instead, the new system uses molecular switches that change shape in response to light; when integrated into the PCM, the phase-change temperature of the hybrid material can be adjusted with light, allowing the thermal energy of the phase change to be maintained even well below the melting point of the original material.
The rate of cooling can be controlled.
Grace G. D. Han, Huashan Li, Jeffrey C. Grossman. Optically-controlled long-term storage and release of thermal energy in phase-change materials. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-01608-y
(Score: 5, Informative) by Anonymous Coward on Wednesday November 22 2017, @03:45PM (1 child)
At one point I studied a number of the phase change heat storage materials. There are various salts with convenient melting points around "room temperature" which can store solar energy during the day and keep a house warm at night. One of the major problems with these is that the compounds degrade over freeze thaw cycles, separating into layers that no longer have the original thermal properties.
Clever researchers at MIT worked out that storing the phase change material in thin horizontal layers would greatly reduce or eliminate this separation/striation. They made ceiling tiles (looked like a normal hanging acoustic ceiling) with a few layers of material in thin horizontal plastic bags. Have forgotten the thickness, perhaps a few mm thick for each layer.
When combined with horizontal window blinds that reflected sunlight up to the ceiling, they built a super-insulated, passive-solar test building in Cambridge, MA. This was c.1980 and it worked well for many years. It was a little more expensive than normal construction, but perfectly practical otherwise. Not only do you save the cost of heating fuel, you also reclaim the floor space taken by furnace or boiler. I believe they installed some electric baseboard heaters for backup that might be required if there were several cold & cloudy days in a row--but because of the super-insulation, the power required was relatively low.
(Score: 0) by Anonymous Coward on Wednesday November 22 2017, @04:47PM
I think it's all really cool.