We all know we need to switch to renewable energy sources such as wind and solar power if we are to prevent a global climate catastrophe. Currently, a third of our global electricity comes from low carbon sources, but the main issue is that we still use giant batteries for storage which contain metals that contaminate ecosystems. Emma Keeling traveled to the Swiss Alps to visit the Nant de Drance power plant that uses water to not only generate electricity again, but to store energy. This level of flexibility provides a vital solution to the issue of renewable energy storage.