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Ocean Energy

Ocean Energy, or Wave Energy

Wave energy is produced when electricity generators are placed on the surface of the ocean. The energy provided is most often used in desalination plants, power plants, and water pumps. Energy output is determined by wave height, wave speed, wavelength, and water density.

To date, there are only a handful of experimental wave generator plants in operation around the world. The articles on this page explore the world of wave energy and its possible applications.

PowerBuoy

The PowerBuoy is the wave energy device designed by Ocean Power Technologies (OPT). There are two larger scale PowerBuoys currently in development. They are known as the PB40ES and the PB150.

The PB40ES is a 40kW utility scale device that is capable of generating a sustained maximum output of 40kW.  The PB150 is the company’s first utility scale PowerBuoy with a 150kW rating. It is being made in Scotland and will be tested at the European Marine Energy Centre, Orkney. The size of the PB150 is 115ft tall by 46ft beam.

How It Works

The PowerBuoy works as the rising and falling of the waves causes it to move up and down. The resultant stroking action is converted by a power take-off to drive an electrical generator. The power that is generated is transmitted ashore via an underwater cable. The PowerBuoys generate power when the wave height is between 1.5 and 7 metres and sensors will detect waves that are too large and will shut the system down automatically.

Wave Treader

The Wave Treader device has been developed by Green Ocean Energy Ltd. Each device attaches to an offshore wind turbine where the pile foundation and the tower connect. This then allows the offshore turbines to generate both wind and wave power. The testing for this device will begin this year. The projected peak power rating for each device has been quoted at over 500kW.

How It Works

The Wave Treader is a device measuring 50m long and 20m beam and comprises a fore and aft arm holding sponsons that are attached to the transition piece. The device can rotate and move vertically in the waves and this motion moves hydraulic cylinders that are attached between the arms causing the hydraulic fluid to pulse and spin hydraulic motors. The motors operate electric generators and the electricity will be exported through the cable shared with the wind farm.

Oyster 2

The Oyster 2 is the name of the wave power device developed by Aquamarine Power. The Oyster 2 is the improved version of the first generation device called the Oyster. The Oyster 2 measures 26m long by 16 m beam and it is capable of a generating capacity of 800kW. Three of the devices are being deployed at the European Marine Energy Centre (EMEC) in Orkney where it is hoped they will generate a consistent 2.4MW of electricity.

How It Works

The Oyster 2 is a hinged flap that is designed to operate in shallow water of around 10m in depth near to the shore. The flap sways backward and forward in the waves and this movement drives two hydraulic pistons to push high-pressure water onshore which will drive a conventional hydro-electric power plant.

Pelanis

The Pelamis Wave Energy Converter is a semi submerged structure that consists of articulated cylindrical sections. In the water it resembles a serpent except these serpents are 180m long and 4m in diameter. Each machine is rated at 750kW and, depending on the wave resources available will produce an average of 25-40% of the full rated power per year. A new model of the Pelamis, the P2, has recently been successfully tested at the European Marine Energy Centre (EMEC).

This device was developed for the E.ON utility and the test completes the first phase of a work-up programme. A commercial scale wave energy project is currently under early stages of development off the southwest coast of Shetland. Called the Aegir Wave Power Project the proposed farm will contain anywhere from 14 to 26 Pelamis devices to make a generating capacity of 10 to 20MW. The project is planned for commission in 2014.

How It Works

The hinged joints of the Pelamis provide the movement from the waves. The joints are resisted by hydraulic rams and they pump high-pressure fluid through hydraulic motors to drive electrical generators to produce electricity. The electricity is fed from the device down a cable to the sea bed where several devices are linked and the power is fed back to shore through a single cable.

BioWAVE

The bioWAVE is the wave power device developed by BioPower Systems. The device is rated at 250kW and it mimics the actions of some of the marine life in order to generate electricity. The devices are designed to move and sway with the movement of the ocean making them relatively lightweight and lower cost.

In March 2010 the company secured land access and onshore development rights for a commercial-scale wave energy site near the town of Port Fairy, Victoria in Australia, giving it access to the wave power resources produced by the Southern Ocean. This site is intended to provide the company with the location to test its 250kW bioWAVE device. The intention is to then use larger 1MW bioWAVE devices to create an array capable of 100MW of installed capacity.

How It Works

The bioWAVE is based on the swaying motion of underwater sea plants. As the device moves back and forth the movement creates hydrodynamic interaction allowing for maximum energy absorption. There is little information available that satisfactorily explains exaclty how the process converts the wave movement into electricity at this stage.