Lake Sihwa in South Korea is home to the world’s largest operating tidal power station, using the tides to generate enough power for a city of half a million people. This regular rise and fall of the seas is more predictable than sunny or windy weather and can be forecast years in advance.

The technology for harnessing tidal energy has been around for more than half a century and the potential to create energy from the sea is huge. Yet tidal power only accounts for a tiny proportion of the global renewable energy mix. Presenter Graihagh Jackson finds out what’s holding tidal power back.