All renewable energy sources are strong contenders for the title of ‘greenest energy source’ since they harness carbon-neutral sources of energy such as the Sun or wind and don’t cause air pollution, putting them leagues ahead of coal or gas power.
Picking a clear winner is, however, tricky. Once you consider the emissions associated with their manufacture and installation, hydropower has the lowest carbon footprint, according to one major study.
But there are also many other environmental impacts to bear in mind. For example, building hydropower dams can cause disruption to river ecosystems, while manufacturing solar panels typically involves toxic chemicals.