Hydroelectric energy is water energy. Moving water contains an enormous store of natural energy, whether the water is part of a running river or waves in the ocean. Think of the destructive force of a river breaking its banks and causing floods or of tall waves breaking on a shallow coastlines, and you can visualize the amount of power involved.
This energy can be harnessed and converted to electricity, and the generation of hydroelectric power does not produce greenhouse gas emissions. It is also a renewable energy resource because water is constantly replenished through the Earth's hydrological cycle. All a hydroelectric system needs is a permanent source of running water, like a creek or river. Unlike solar or wind energy, it can produce power continuously, 24 hours a day.
TheWorld Energy Council estimates that wave power could produce two terawatts of energy each year. This is twice the world's current electricity production, and is equivalent to the energy produced by 2,000 large oil, gas, coal and nuclear power stations. The total renewable energy within the world's oceans, if it could all be harnessed, would satisfy the present world demand for energy more than 5,000 times over. But until now, harnessing wave power was only a theoretical possibility. In fact, the technology is still under development, and it's too early to estimate how soon it will significantly contribute to the global energy picture.
In 2003, 16 percent of the world's electricity was produced by hydropowerplants. Hydropower harnesses the energy of water going from a higher to a lower level (i.e. water running downstream). The greater the drop in elevation, the faster the water flows, and the more electricity that can be produced.
Unfortunately, the dams that go with large scale hydropower can drown ecosystems. Water needs of downstream communities, farmers and ecosystems should also be taken into account. Plus, hydro projects can be unreliable during prolonged droughts and dry seasons when rivers dry up or reduce in volume.
However,small-scale hydro systems can produce plenty of electricity without needing the large dams. Classified as "small", "mini" or "micro" depending on how much electricity they produce, small hydro systems capture the river's energy without diverting too much water away fromits natural flow.
Small-scale hydropower is an environmentally benign energy source with large growth potential, but it won't reach this potential unless we give it a chance. See the Take Action page for how you can be part of the solution to climate change.
For a detailed overview of the issue related to dams check out the report by the World Commission on Dams.