Scientists in Italy have discovered that trees generate an electrical charge every time the wind blows strongly enough to make their leaves touch one another.

The researchers, from the Italian Institute of Technology, have managed to harvest enough energy this way to power 150 LED lights from a single leaf.

We meet them, and others, who are trying to make use of untapped, natural sources energy.

We hear from a project trying to produce electricity from the interaction of fresh and salt water where rivers meet the sea.

And we talk to a geologist in Iceland, who’s helped dig nearly 5km beneath the surface of the Earth. At that depth, the temperature can be about 600C - the idea is to mine the heat and turn it into energy.