Types of renewable energy sources

Hydropower: For centuries, people have harnessed the energy of river currents, using dams to control water flow. Hydropower is the world's biggest source of renewable energy by far, with China, Brazil, Canada, the U.S., and Russia the leading hydropower producers. While hydropower is theoretically a clean energy source replenished by rain and snow, it also has several drawbacks.

Large dams can disrupt river ecosystems and surrounding communities, harming wildlife and displacing residents. Hydropower generation is vulnerable to silt buildup, which can compromise capacity and harm equipment. Drought can also cause problems. In the western U.S., carbon dioxide emissions over a 15-year period were 100 megatons higher than they normally would have been, according to a 2018 study, as utilities turned to coal and gas to replace hydropower lost to drought. Even hydropower at full capacity bears its own emissions problems, as decaying organic material in reservoirs releases methane.

Dams aren't the only way to use water for power: Tidal and wave energy projects around the world aim to capture the ocean's natural rhythms. Marine energy projects currently generate an estimated 500 megawatts of power-less than one percent of all renewables-but the potential is far greater. Programs like Scotland's Saltire Prize have encouraged innovation in this area.

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Video credits: TED ED

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