Speaking of hydrokinetic energy, have you ever gone swimming in the ocean? Did the outgoing tide drag you from shore? Tides pack a powerful punch, and we can use them to generate electricity.
In 2012, one of the first tidal power projects in the United States began delivering power to the electrical grid. The project, an underwater turbine off the coast of Maine, was built by Ocean Renewable Power Co. The turbine resembles an old-fashioned lawn mower, but in essence is a type of undersea windmill. The turbine's foils rotate when the tide rushes in and out of Cobscook Bay near Eastport. The tides in the area are some of the highest in Maine, reaching 20 feet (6 meters). The $21 million generator can power 25 to 30 homes [sources: Sharp, Woodard].