Meet 'photoswitches,' a breakthrough set of materials that act as their own batteries...
“Some molecules, known as photoswitches, can assume either of two different shapes, as if they had a hinge in the middle,” MIT researchers said in statement about their paper published in the journal Nature Chemistry.
“Exposing them to sunlight causes them to absorb energy and jump from one configuration to the other, which is then stable for long periods of time.”
To liberate that energy all you have to do is expose the molecules to a small amount of light, heat or electricity and when they switch back to the other shape they emit heat.
“In effect, they behave as rechargeable thermal batteries: taking in energy from the sun, storing it indefinitely, and then releasing it on demand.”