Water pressure

Pressurising air - Sea Clam UK

air chambers, the outer faces of which are formed by flexible rubber membranes, were placed around a floating ring structure. Differential wave action moved the membrane in and out forcing the air to be interchanged between chambers. Wells turbines placed in the manifolds between the air chambers extracted power from the air flow. The rigid torus structure, 60 m diameter and 8m deep, acted as a stable reference body and was designed to be moored a few kilometres offshore. Typically, a 25 MW scheme deployed off the west coast of Scotland would feature 10 SEA Clam units and produce over 50GWh per year of electricity.

Electricity generation cost of the SEA Clam would be 8p/kWh, at 8% discount rate.

The Bombora is Vee shaped with the apex pointing to sea. The surface is a flexible membrane enclosing air. The air is in a series of cells and as they are compressed, the air flows and spins a turbine.

Pressurisin​g air - Bombora membrane

The Bombora device is submerged, located on the seabed in shallow water depths. It is designed to be lightweight and cheap.

Geotextile bags filled with sand can provide a cheap stable foundation platform.

The device has a ramp, and as the waves hit it, they rise up, increasing the pressure on the flexible membrane below. Normally when a wave hits a sandbank, water rushes back from the shore to help support the wave. However the idea here is to prevent this so the wave height, therefore pressure difference, is increased.

The membrane has a series of individual cells below it, along its length separated by diaphragms. The membrane directly transfers the wave energy to pressurised air (pneumatic) within the device.

 The design was inspired by the SEA Clam



Pressurising air - AWS-III

AWS-III is a multi-cell array of flexible membrane absorbers which convert wave power to pneumatic power through compression of air within each cell. The cells are inter-connected, thus allowing interchange of air between cells in anti-phase. Turbine-generator sets are provided to convert the pneumatic power to electricity.

A typical device will comprise an array of 12 cells, each measuring around 16m wide by 8m deep, arranged around a circular structure with overall diameter of 60m. Such a device is capable of producing an average of 2.5MW from a rough sea whilst having a structural steel weight of less than 1300 tonne. The AWS-III will be slack moored in water depths of around 100m using standard mooring spreads. Ref..