Pelamis Wave Power technology

The P-750 Wave Energy Converter (Pelamis WEC) is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all of the joints is fed down a single umbilical cable to a junction on the sea bed. Several devices can be connected together and linked to shore through a single seabed cable.

The machine is held in position by a mooring system, comprising a combination of floats and weights which prevent the mooring cables becoming taut.

Energy purchase and supply

Initial life cycle analyses that have been carried out indicate that a wave energy converter operating in a good wave resource (40 kilowatts per metre annual average wave energy level) will have an energy payback period of less than 20 months with a life cycle emission of approximately 25 grams per kilowatt hour.

Under these conditions a Pelamis WEC will offset the production of approximately 2,000 tonnes of CO2 from a conventional combined-cycle gas power station each year.

Environmental impact Materials

The largest proportion of material weight within a Pelamis WEC is accounted for by the main structure, which is made of mild steel, and ballast, currently in the form of washed sand. There are smaller quantities of various other metals and materials which make-up the machine and its components including: copper, stainless steel, rubber, bearings and plastics.

Corrosion and fouling protection

Unlike a vessel, where marine growth causes drag and therefore increased fuel costs, a Pelamis WEC is stationary and any increased drag due to marine growth is negligible. Therefore the system is largely tolerant of growth, meaning that antifoulants – a chemical agent added to paint to prevent encrustation by aquatic organisms such as algae or barnacles – are not required over the entire submerged structure.

A marine paint coating is applied to structural steel surfaces in the atmospheric and splash zone and cathodic protection is applied to areas of the structural steel components in the submerged zone using sacrificial anodes.

Liquids and pollutants

Within the power take-off systems on board the Pelamis WEC are volumes of hydraulic fluid. PWP uses hydraulic fluid which is biodegradable in the marine environment. In the unlikely event that a leak of hydraulic fluid occurs within the power take-off module there are two levels of egress/ingress protection on all leak points, both of which would have to fail to allow water to ingress to a point where fluid could escape to the outside environment. PWP also uses biodegradable transformer fluid.

Other distinguishing features Reliability and multiple redundancy

Unlike many generators, which lose all generating capacity through single point failures, the Pelamis WEC has been designed to be a fault-tolerant system with the incorporation of multiple levels of redundancy throughout all systems (structural, moorings, hydraulics, electrical and control).

Additionally failure paths, where possible, have been engineered to end with inherently safe modes so that the survivability, station-keeping and in most cases generating functionality of the system is not compromised. The Pelamis WEC can therefore continue generating electricity safely, in many cases with little or no loss of performance, even with multiple failures within its systems.

Intervention strategy can then be tailored to maximise economic performance of the farm using in-house software which Pelamis has developed, rather than being driven by a simple need for earliest possible recovery.

Future outlook

Pelamis Wave Power has recently been commissioned to provide another of its machines, a Pelamis P2, for commercial use by German energy utility E.ON.

At the time of printing, Enersis had issued a letter of intent to PWP for a further 20 megawatts of Pelamis equipment to expand the initial Aguçadoura project to a larger scheme. Development work for the second phase project is already under way.

Funding arrangements and acknowledgements

PWP has raised some £40 million ($68.47 million) to fund the development of Pelamis technology from a variety of financial and industry backers. Major shareholders include Emerald Technology Ventures, Norsk Hydro Technology Ventures, BlackRock Investment Managers, 3i, Carbon Trust, Nettuno Power, Tudor BVI Global Portfolio and Scottish Enterprise.