Scientists from MIT have created a new type of solid material that does exactly that

Solar projects are usually focused on generating electricity, but we could arguably save more power by storing heat. Scientists from MIT have created a new type of solid material that does exactly that. When exposed to sunlight, it assumes a "charged" state that can be maintained for long periods of time. However, when triggered with a small burst of heat, the material reverts to its original chemical composition, releasing a much larger amount of heat energy. Since the film is thin and transparent, scientists think it could be useful in the near future for defrosting your car's windshield and could one day heat your home or even your clothes.