BMW funds battery-less solar storage

January 12, 2016 // By EETE Automotive
Solar storage has for too long been focused on converting photons to electricity, according to a Massachusetts Institute of Technology (MIT) project funded by BMW. For instance, if your purpose is to use the solar-to-electricity-battery process to later defrost your windshield, wouldn't it be much more efficient to cut out the middle-man and store the solar photons inside the transparent polymer inside every windshield, then later release it directly as phonons (heat) for defrosting?

That is the concept of MIT's professor Jeffrey Grossman, postdoctoral researcher David Zhitomirsky, and doctoral candidate Eugene Cho and their solar thermal fuel polymer--a transparent film that can be sandwiched between the two layers of glass on your cars windows (which is already done for safety--so they don't shatter). The transparent film stores the solar energy by varying its molecular configuration--a engineered reaction to light--then releases the heat on-demand as it relaxes back to its "normal" chemical configuration.

The layer-by-layer solar thermal fuel polymer film comprises three distinct layers (4 to 5 microns in thickness for each) which are cross-linked to enable building up films of tunable thickness. (Source: MIT)

"This material can be engineered to have many different specific properties, but in its current version is absorbs UV [ultra-violet] photons to change its shape into a high-energy form, then when it snaps back into its low-energy shape it releases phonons--vibrations--that instantly heat up their surroundings," Zhitomirsky told EE Times in an exclusive interview.

Of course, there are many other applications of such as solar-to-solid-fuel conversions, such as in a memory that uses a laser to change the shape of the molecule from a 0 to a 1 and back again, but BMW funded the research at MIT specifically because a great deal of electrical energy is wasted in an electric vehicle (EV) defrosting its windows, sometimes reducing the EVs range as much as 30 percent. But by releasing the stored heat inside the windshield as phonons, the ice touching the windshield could be liquified, allowing the windshield wipers to easily remove any amount of ice or snow that had accumulated overnight.
At MIT they of course targeted BMWs application, but also can envision using the polymer in many other applications, such as weaved into clothing that can "charge up" while in sunlight then release the charge as heat when, say a skier, moves into the shade.

"You could even