In the tropics, the deep sea is cold and the sea surface is very warm. That temperature difference can be harnessed and turned into electricity. If we can improve the technology, this method of producing power could be a godsend for island nations reliant on expensive and polluting diesel for their power.

For more than a century, researchers have explored the idea of ocean thermal energy conversion. There’s nothing fundamentally new to the idea of extracting power from temperature differences. In fact, the underlying technology is similar to the way coal, gas and geothermal power plants create electricity, by using vapour to spin a turbine.

The challenge is finding the right spot, where the temperature differences make it worthwhile. That means relatively close to the equator – think north of Papua New Guinea, the Philippines and off the coast of southern Japan.

At present, pilot plants are only able to generate a fraction of what a large wind turbine can. But on the positive side, ocean thermal plants can generate power 24 hours a day.