Wave power

 Water is 784 times as dense as air. You may have experienced this at the beach by getting knocked down by a relatively small wave. Some inventors have been at work taking advantage of this power.

In all the talk about new sources of renewable energy, solar and wind power have dominated the conversation, with biofuels coming in third. Hydroelectric power is a long established renewable energy option, but limited to very specific locations and restricted by environmental concerns. Wave power is just starting to show its potential, with a few installations on the coasts of Europe.

There are three basic types of wave power generators: bobbing buoys, bending buoys, and water column devices.

Bobbing buoys are basically big floats, either under water or on the surface. They travel up and down with the waves and transfer the energy of their motion though rods or cables to generators fixed to the sea floor or in the buoy itself. Ocean Power Technologies is developing the latter type of device and is in the early stages of a 1.39 MW project off the coast of Spain.

Bending buoys float on the surface and undulate with the waves, bending at their hinge points and transferring power with pistons that resist the bending. There is only one manufacturer of these right now, Pelamis.

Water column devices are installed on the shore, with a large diameter tube extending below the surface of the water. When a wave comes in, the rising water pushes a column of air up the tube and through a turbine. As with the bending buoys, there is only one company developing this model, Wavegen.

There are also a few companies developing a kind of modified hydroelectric system where waves are guided into a narrow area to make them taller. They splash over a wall and then are run back through the wall to a lower level through turbines.

Wavegen has the longest track record, with its 500-kilowatt LIMPET installation on the coast of Islay in Scotland. It has been feeding the island grid since 2000. Before that, an experimental 75 kW unit operated from 1991 to 1999. Wavegen just received approval in January for a 4-megawatt near-shore installation in Siadar Bay on the Scottish Island of Lewis.

Here’s a clip of the exhaust port on an installation on the Island of Pico in the Azores.

Pelamis has had more recent successes, with a 2.25-megawatt installation just off the northern coast of Portugal. They also have a 3-megawatt facility in development off the Orkney Islands just north of the Scottish mainland and a 5-megawatt installation planned for the west coast of Cornwall.

Here’s a video of one of their sea trials:

There are two significant benefits of wave power, to my mind. One is its relative predictability compared to wind and solar. The oceans are like a great flywheel for energy. Since wave energy devices are dependent on an oscillating energy source, they have inertial or pressure storage built in to make up for that oscillation. Arrays of wave power collectors average out their output. This means that wave power doesn’t suffer from the momentary power variations imposed on wind and solar by wind gusts or passing clouds. This means that wave generated power outputs tend to vary slowly and predictably by the hour or day.

The second significant benefit of wave power is its density. The Wavegen installation in Islay was designed for wave intensities of 25 kilowatts per meter of shoreline. That works out to a megawatt per 40 meters (131 feet). It doesn’t take a lot of shore or breakwater to produce serious power. The northern Atlantic and Pacific coasts of the United States and Canada offer a potential bonanza of clean, consistent power.

The State of Maine, for example, has 3500 miles of coastline. If one-half of one percent of that, 17.5 miles, were used for wave power generation it would amount to over 700 megawatts. There must be at least 17.5 miles of breakwaters and seawalls in Maine that could accommodate oscillating water column devices, and it would take up no shoreline at all if the floating devices were used.

Wave power is still in its early stages and needs to be accelerated through the inevitable period of technological diversity, shakeout, and further development of surviving designs. The U.K., Portugal, and Spain are leading the way in wave power development. The U.S. and Canada should look to our coasts for power and promote the technology on this side of the energy-dense Atlantic.