Ocean Power Technologies has spent its entire existence developing its power buoy technology designed to capture the energy of rolling ocean waves and turn it into electricity. The buoys the company has made differed in size but all of which worked with the same basic principle.

The buoy is anchored to the ocean floor. Atop is a float which rises and falls with the ocean swells. Below the surface is a spar and a heavy plate, which go far below the surface and resist bobbing up and down. As the float bobs up and down, it drives a hydraulic push rod into the spar, which drives an electrical generator. Because the power created in this way is wildly sporadic, the buoys use a system to convert it into constant AC power. The APB-350 stores its energy in a continuously charging battery pack.

The amount of power the buoy can generate depends on the state of the ocean — it can’t create power in seas that are glassy-calm, or in very rough seas when the waves are too high — Sea State 5, or about 13 feet, is the upper limit for Ocean Power’s buoys.

CEO George Kirby says each buoy can be designed for its deployment site, optimized to the average sea state there. If the waves get too big, they may break over top of the buoy instead of lifting it up to make power. Sensors onboard the buoy detect when the seas are too high, and the unit goes into “survival mode,” locking up and shutting down power generation to avoid damaging the machinery until the sea is calmer. Kirby compared the system to wind turbines, which can “pinwheel” freely in high winds, instead of generating power, to avoid damaging components.

Ocean Power Technology’s bobbing buoy is not the only method to capture the ocean’s energy that has been tried. A Scottish company, Pelamis Wave Power, has made power generators that lie on the surface of the water like a huge sea snakes. Hydraulic pumps within the undulating vessel drive generators. Pelamis has five of its units connected to a power grid.

At UC Berkeley, researchers have made a rubber or elastic carpet stretched across a grid of pumps and cylinders at the bottom of the ocean floor. The “magic carpet” is set for sea trials in 2016.

The Power Oyster, made by Scottish company, is a floating pump that sits just offshore. Each “oyster” has a huge flap that rises and falls with the waves, driving high-pressure water to an onshore turbine. Power Oysters have been at sea for two years.

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