On-Demand Solar Heating with Solid-State Solar Thermal Fuels
Carlyn McGill posted on January 11, 2016 | 6204 views
Spin-coating process that enables deposition of the solar thermal fuel polymer material from solution. (Image courtesy of MIT.)
Spin-coating process that enables deposition of the solar thermal fuel polymer material from solution. (Image courtesy of MIT.)
Researchers at MIT have developed a new process for absorbing and retaining solar energy for on-demand use.

“It is a material that is capable of absorbing photons (light) and storing their energy,” said MIT professor Dr. David Zhitomirsky.

Dr. Zhitomirsky is the project lead and the first author on a paper detailing the findings in the journal Advanced Energy Materials.

“Then, this energy can be released as heat on-demand, re-generating the original material, and this can be done many times.”

The platform for testing macroscopic heat release. A heating element is used to provide sufficient energy to trigger the solar thermal fuel materials, while an infrared camera monitors the temperature. The charged film (right) releases heat enabling a higher temperature relative to the uncharged film (left). (Image courtesy of MIT.)

The platform for testing macroscopic heat release. A heating element is used to provide sufficient energy to trigger the solar thermal fuel materials, while an infrared camera monitors the temperature. The charged film (right) releases heat enabling a higher temperature relative to the uncharged film (left). (Image courtesy of MIT.)

The researchers claim that storing solar heat in the form of a chemical change (instead of storing the heat itself) is the answer to long-lasting and stable storage. Now matter how effective the insulation, heat will always dissipate over time.

On the other hand, a chemical storage system can keep the energy in a stable molecular formation until it was time to be released. The release could be triggered by heat, light or electricity.

“Absorbing light results in a shape change in the molecules within these materials. The energy of the resultant molecule is higher than its initial energy, so upon reversion to the original state this energy can be released to the environment as heat,” Dr. Zhitomirsky explained.

“Importantly, the original molecule is recovered without degradation in this process.”

The process is based on polymers, cost-effective materials and common manufacturing technology. Previous attempts at chemical-based storage materials were based on liquid systems, which limited their application. This new approach, however, is based on solids.

Solar thermal fuel polymer film comprised of three distinct layers (four to five microns in thickness for each). (Image courtesy of MIT.)

Solar thermal fuel polymer film comprised of three distinct layers (four to five microns in thickness for each). (Image courtesy of MIT.)

Manufacturing the material is a two step process. The team used azobenzenes that change their molecular configuration when exposed to light. A small amount of heat reverts the azobenzenes back to their original configuration and enables them to release the previously stored heat.

Researchers changed the material’s chemistry to improve its energy density, its ability to create even, constant layers and its reaction to the activating heat pulse.

Although many vehicles have heating wires integrated into the back window, it is prohibited to have anything that could block the driver’s vision on the front window. Having this transparent polymer film manufactured into windshields would help melt ice or snow.

Dr. Zhitomirsky elaborated further on the importance of this energy storage system.

“It is an attractive additional method to harvesting solar energy. It is inexpensive and enables simultaneous energy harvesting and storage without additional equipment.”

“These materials could find a lot of use in rural areas and in third world countries, but also in urban first world environment where they can be integrated into clothing, for example.”

Do you have any ideas for other applications that could benefit from this material?

Comment below.

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