Every source of energy has its shortcomings. Some people think wind turbines are eyesores, fossil fuels aren’t renewable, and solar energy requires sunlight to work well and properly. Recently, a team at MIT and Harvard found a way to solve the problem of darkness for the use of solar energy. They used a “switchable” material capable of absorbing the sun’s heat and storing it in chemical form until it is ready to be released — on demand.

This material is made up of molecules called ‘azobenzene’, or more commonly known as ‘photoswitches’. They basically act like a traditional hinged light switch — one position for “on” and another for “off.” When exposed to sunlight, they change from one position to the other, creating stable energy that can be stored like thermal rechargeable batteries.

Allowing solar power to "work" at night.

It wasn’t enough to simply utilize azobenzene; the team had to figure out a way to pack the molecules close enough together to reach the desired energy density, or the amount of energy that can be stored in a given amount of material. Jeffrey Grossman, co-author of the paper describing this new process, and his team tried attaching the molecules to carbon nanotubes, or CNTs.

At first, they were disappointed because the layout achieved a packing density less than half of what the computer simulations showed that they would need for the desired output of heat. However, in the experiment, they saw a heat flow much greater than the initial logistics showed was possible with the current layout.

This unexpected result was due to the combination of the azobenzene with the CNTs. The molecules protrude from the sides of the CNTs and interweave with photoswitching molecules attached to adjacent CNTs, allowing the molecules to rest closer together than the computer tests showed. To put this into perspective: Computer models showed that packing azobenzene molecules onto the CNTs would provide a 30% increase in energy storage. The actual experiments produced a 200% increase.

“It could change the game, since it makes the sun’s energy, in the form of heat, storable and distributable,” said Grossman. Unfortunately, this doesn’t solve the issue of solar energy for lighting purposes. It can primarily be used for nighttime heating needs, like cooking or just staying warm. It isn’t efficient to use it for anything else.

Even if this development doesn’t solve our late-night green tech needs, it is still pretty revolutionary. Fossil fuels aren’t the only energy source that causes air pollution when burned. A large part of the world uses wood or feces to cook their meals or heat their home, leaving their airspace toxic and inhospitable. People living in these areas will greatly benefit from shipments of these thermal “batteries” that can be recharged by simply letting the sun do its job.