Virkjanir 

There are primarily two types of tidal power plants used. A power plant that utilizes streaming speed of the ocean and a power plant that utilizes the drop height of the ocean. Tests are being done with many types of streaming power plants but the most common are machines that are similar to a windmill. The density of the ocean is roughly 800 times more than air and because of that are the spades much shorter in the ocean . The spades turn when the sea streams past and they drive a turbine that produces electricity. The production depends on the tides and stops on the slack water until the stream has got enough speed again. Usually the water mills need flow rate up to 1 meter per second to start production. Desirable streaming speed is considered to be between 1 – 4 meters per second.