Scientists are trying to bottle solar energy and turn it into liquid fuel

As a pump cycles the fluid through transparent tubes, ultraviolet light from the sun excites its molecules into an energized state. The light rearranges bonds among the carbon, hydrogen and nitrogen atoms in the fuel, converting a compound known as norbornadiene into another called quadricyclane — the energetic Mr. Hyde like version. Because the energy is trapped in strong chemical bonds, the quadricyclane retains the captured solar power even when it cools down.

The energy system works in a circular manner. First, the liquid captures energy from sunlight, in a solar thermal collector on the roof of a building. Then it is stored at room temperature. When the energy is needed, it can be drawn through the catalyst so that the liquid heats up.Yen Strandqvist
To extract that stored energy, Moth-Poulsen passes the activated fuel over a cobalt-based catalyst. The Hyde-like quadricyclane molecules then shapeshift back into their Jekyll form, norbornadiene. The transformation releases copious amounts of heat — enough to raise the fuel's temperature by 63 degrees Celsius (113 degrees Fahrenheit).

If the fuel starts at room temperature (about 21 degrees C, or 70 degrees F), it quickly warms to around 84 degrees C (183 degrees F) — easily hot enough to heat a house or office.