Water energy works by powering turbines that turn generators to produce electricity. Turning the turbines requires water movement, such as rivers flowing downstream, waves or tide changes. In addition, scientists are working on methods of removing heat energy from the ocean water.
Water wheels have a long history that dates back to ancient China. The water wheel transfers energy to move a grinding stone in order to mill grains. Turbines offer greater efficiency than water wheels. Many hydroelectric plants use dams to form lakes in order to increase the force of the water flowing through the turbines. The dams also ensure water supplies in times of drought. However, there are developing concerns about the long-term effects of building dams on rivers.
Wave energy can also generate electricity. Buoys or other floating devices catch the water energy with each passing wave. As of June 2013, the first of this type of generating plant is under construction in Oregon. Upon its completion, developers expect the plant to use 10 buoys to provide power for up to 1,000 homes.
In areas where there is a large difference between high and low tides, power companies build dams to trap water when the tides are at their highest. The water then flows back through turbines to generate electricity, just like with any other turboelectric plant.