Write a summary of the article Tidal Power and Hydropower.
The motion of the ocean, through both waves and tides, provides a potentially vast and reliable source of energy-but there are significant challenges in converting it into electricity. Several pilot projects are underway to harness wave energy and to design sustainable tidal systems, but this is a relatively new technology. Recognising this constraint, the Ecofys scenario assumes that ocean power accounts for only 1 per cent of global electricity supply by 2050. However, it is likely to provide a significantly larger percentage in some particularly suitable areas, like America's Pacific Northwest and the British Isles.
Wave and tidal power installations could affect the local marine environment, coastal communities, as well as maritime industries such as shipping and fishing. It is critical that appropriate sites are selected and technologies developed that minimize any negative impacts.
Hydropower is currently the world's largest renewable power source, providing nearly one-fifth of all electricity worldwide. Large-scale hydropower plants store water in a reservoir behind a dam, and then regulate the flow according to electricity demand. Hydropower can provide a relatively reliable source of power on demand, helping to balance variable sources like wind and solar PV.
However, hydropower can have severe environmental and social impacts. By changing water flow downstream, dams threaten freshwater ecosystems and the livelihoods of millions of people who depend on fisheries, wetlands, and regular deposits of sediment for agriculture. They fragment habitats and cut off fish access to traditional spawning grounds. Creating reservoirs means flooding large areas of land: 40-80 million people worldwide have been displaced as a result of hydroelectric schemes.
The Ecofys scenario reflects these concerns with a relatively small increase in hydropower. Hydropower would provide 12 per cent of our electricity in 2050 compared with 15 per cent today. New hydropower schemes would need to meet stringent environmental sustainability and human rights criteria, and minimize any negative impacts on river flows and freshwater habitats.