A concrete structure clings to the rugged western shoreline of the Isle of Islay in Scotland. Appropriately named the Limpet 500 (Land-Installed Marine-Powered Energy Transformer), it is the world’s first commercial wave power station and has been quietly producing electricity now for over ten years. Among its more mundane uses, the electricity produced is being used to power the world’s first wave-powered electric bus and a project is now underway to create the world’s first island hydrogen economy utilizing power from the Limpet.
A Modular, Easily Incorporated Power Plant
The Limpet’s design is essentially very simple. The concept was developed by Wavegen in collaboration with researchers from Queen’s University, Belfast and built with financial backing from the European Union. An open-ended bottle-shaped chamber is built into the shoreline, angled slightly downwards. This chamber captures the waves, causing the air in the chamber to be compressed and forced through the neck of the ‘bottle’ to drive a turbine, which in turn generates electrical power. As the wave subsequently recedes, air is sucked back into the chamber through the bottleneck, again driving the turbine.
To enable power to be generated from the wave as it enters and recedes, a special type of turbine is used. Named after its designer, Professor Alan Wells of Queens University, Belfast, the Wells turbine always turns in the same direction, regardless of the direction of airflow. The whole system utilizes the ‘oscillating water column’ principle, this time applied to air rather than water. This principle has also been applied successfully in other seabed-based power systems such as the Oyster.
The Advantages of the Limpet
The Limpet500 is designed for 500kW of power, which may seem small compared to large coal-fired or nuclear power stations but several units can be readily linked together to provide higher outputs and the Limpet does offer significant advantages over coal-fired and nuclear power stations.
- There are no fuel transportation costs and the fuel itself is essentially ‘free’
- There are no waste products for expensive disposal or long-term storage
- There are no emissions in terms of carbon or radioactivity at any level.
- There is no heat source, so no danger of steam boiler explosion or core meltdown.
- No operating personnel are required and maintenance requirements are low
- Once built, the unit requires very little further expense and its initial expense can be offset by incorporating units into seawall, harbour wall or breakwater installation or renovation projects
The units can supply the local community directly, obviating the requirement for long power lines to connect the national supply grid.
Supplying the local community enables the electricity produced to be charged at retail price instead of the much lower wholesale prices charged for electricity supplying the national grid. This enables the initial cost to be amortized much more quickly.
The Potential for the Limpet Wave Power Plant
Research conducted by Wavegen indicates that coastal waves, being wind and moon-driven, are a viable source of power on any coastline with wave-creating prevailing winds, i.e. coastlines falling within the temperate zones between the 40th and 60th parallels. Any shortfall on the small number of days, at these latitudes, that the sea is ‘quiet’ and wave energy is low, can be offset from power stored from excess production from other, more energetic days.
The development of marine energy is still in its infancy. Ten years of experience with the Limpet have already revealed that some small modifications to the shape of the power station and its position vis-à-vis the edge of the coastline or sea defences would improve efficiency by up to 14% and reduce the required structural mass, thereby reducing construction costs. Various efficiency-improving modifications to the blades on the Wells turbine have also been tested.
At the present level of marine energy development, many island, peninsular and coastal communities could already benefit significantly from Limpet technology, especially when conventional power plants are located significant distances away. With greater research and investment, this number is likely to increase.
Scotland, with one quarter of the potential tidal and one-tenth of the potential wave energy in Europe, is a world leader in marine energy development and has recently announced a raft of new projects, including seabed power arrays in the Sound of Islay and in the Pentland Firth.
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Martin Cross - A translator, former chef and marketeer, currently disabled. I write articles on food,, travel, politics, religion and technology.
