There is a wide range of different technologies to harvest energy from the waves and tides. Here are a few of the leading contenders.
One of the most tested designs for gathering energy from waves is the Pelamis wave energy converter, which is installed in Portugal and the U.K. Below what's visible here are three hydraulic motors driven by the motion of the waves to generate electricity. This device, called the P2, is able to generate 750 kilowatts. The idea is to chain several together to make wave farms able to generate tens of megawatts of power, enough to supply thousands of homes.
Here is a photo of a tidal generator being tested by Ocean Renewable Power in the Bay of Fundy, Maine. This 60-kilowatt system is generating electricity, but it is not connected to the grid. Instead, it charges batteries that are transported to the Coast Guard, which use the energy to charge emergency vessels, according to the company. The project is also monitoring the effect on the ecosystem, including fish. The company is seeking to raise money now to have its next-generation device connected to the grid next year. The technology is designed to work on rivers, ocean, and deep water tidal currents.
Updated on November 17 with the correct kilowatt rating.
This is a photo of the first version of the Oyster, which is now generating electricity to the grid off the coast of Scotland. When moved by the waves, the machine pumps water onshore, where it turns a hydrogenerator to make electricity. Aquamarine Power, its manufacturer, is now working on a second-generation device it hopes to deploy for testing next year. It will have fewer moving parts and be modular so it can be more easily maintained. A single machine can produce 800 kilowatts of constant power.
Ocean Power Technologies is testing its wave power device at a military base in Hawaii. The PowerBuoy product generates electricity by converting the movement from the waves into usable energy. The system includes a number of sensors to monitor and is connected to the land with a cable, allowing designers to monitor the device over the Internet.
U.K.-based Atlantic Resources has different tidal energy converters, including this giant machine, called the AK-1000. It was placed in the waters of the European Marine Energy Center in Orkney in August.