Sea source

A simple, robust and reliable wave power generator that operates like a hydroelectric power station is to be installed on Orkney this August.

Designed and built by Edinburgh-based company Aquamarine, Oyster is a unique hydroelectric wave power system. It has two main components — a wave-powered pump, which delivers high-pressure water, and an onshore hydro-electric power plant, to which the water is delivered. The system is designed to have few components so it is easy to maintain.

Oyster has been designed for use in waters about 10m deep to maximise accessibility for maintenance and reduce exposure to the extreme wave heights found offshore.

Near-shore wave conditions are more consistent than those of deeper water as shallower water filters out the most energetic seas and reduces the directional spread of the waves, enabling the pump to capture a higher percentage of power across the most commonly occurring sea states.

This ensures there is consistent power generation to the grid in most sea-states, countering a criticism of some forms of renewable energy.

The peak power generated by each Oyster pump is between 300kW and 600kW, depending on location and configuration. The system uses materials and components that have already proved reliable in the hydroelectric industry. It has a design life of 20 years and is monitored remotely to ensure it is working consistently and at optimum levels.

The design consists of a large pump, or power capture unit, which is fixed to the seabed and extracts energy as it is moved back and forth by passing waves. This energy then drives double-acting pistons, which deliver pressurised seawater to onshore hydro-electric plant, as is done in conventional hydro-electric generators.

The Oyster pump is designed to swing away from large waves to keep generating power in extreme conditions. It interacts directly with the amplified surge component in near-shore waves, meaning it also captures power efficiently in small seas.

Oyster pumps can be mass-produced cheaply and be installed and removed within 24 hours, cutting the costs of deployment. They are silent and contain no toxic substances. Aquamarine estimates each will provide a saving of about 500 tonnes of CO2 each year, based on Carbon Trust estimates of saving 0.43kg CO2/kWh for electrical production. The company’s goal is to deliver commercial wave farms around Europe’s Atlantic coast and beyond. It is also working on designs for a wave-powered Oyster desalination system, and there are plans for a scale model test of such a unit later this year.

Aquamarine aims to produce a system that can provide both clean power and water as well as cutting carbon emissions from desalination plants, which are heavy users of electricity. The island communities rely on the import of expensive fuel and people living in areas where fresh water is scarce could gain significant benefits.

‘We have been carrying out research and development at Queen’s University in Belfast for the past five years,’ said Dr Sian McGrath, business development manager at Aquamarine. ‘The serviceable parts of the system are onshore, meaning that it has 365-day accessibility and is less expensive to maintain. The section of the device that is at sea is very simple.’

The firm’s chairman is Allan Thomson, founder of marine power company Wavegen. ‘He came out of retirement to set up Aquamarine and commercialise Oyster as he recognised the potential of the technology,’ McGrath said.

According to recent research by the World Energy Council, the global market for wave power technology could be worth as much as £500bn in the first half of the 21st century.

During this year’s tests, Aquamarine will analyse the module’s performance and check it against predictions from scale and numerical models. This will take place alongside tank testing, cost engineering and further research and development of the prototype hydroelectric plant and first Oyster pump. It plans to install additional Oyster pumps to increase the total capacity to more than 3MW at the Orkney site.