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Report 1 of 5:
Turning
The Tide - Scotland
Fossil fuels such as coal and oil are not renewable over the span of human generations, and their use may be increasingly limited by environmental concerns over global warming and acid rain. To meet the energy needs of a growing world population, engineers in coming decades will be challenged to generate power economically from renewable energy sources. Despite the fact that nearly 75% of the Earth’s surface is covered with water, waves are a largely unexplored source of energy, compared with the progress that has been made in harnessing the sun and wind.
Wave energy
It has long been recognised that near shore wind and wave resources offer outstanding potential for generating renewable power. This, coupled with growing public concern regarding the long term environmental impact from fossil fuels, has resulted in a considerable commercial opportunity for an economically viable renewable marine power technology.
Waves are a free and sustainable energy resource created as wind blows over the ocean surface. They are a store for solar and wind energy. The greater the distances involved, the higher and longer the waves will be. Energy is stored in this way until it reaches the shallows and beaches of our coasts where it is released, sometimes with destructive effects.
Wave power and the environment
Until recently, the commercial use of wave power has been limited to small systems of tens to hundreds of watts aboard navigation buoys. As the buoy heaves up and down in waves, the oscillating water column (OWC) in the centre pipe of the buoy's hull acts like a piston, alternately pushing air out the top of the pipe and drawing it in. This pneumatic power can be converted directly to sound through a foghorn, or indirectly to light by spinning a turbine-generator, which charges an electrical storage battery.
Wave power modules are built to harness energy from waves and transform it into electrical power. By absorbing the incoming energy, power modules create an area of calm water behind them, contributing toward coastal defences and producing a valuable area for other commercial and recreational marine activities. This protected area can be used to create self-financing harbours and breakwaters. Their installation can bring positive environmental and economic spin-offs, such as protection of threatened areas of coastline or provision of an environment suitable for aquaculture development.
Artificial reefs substantially improve the local marine bio-density, attracting shoals of fish and providing habitats for the colonisation of commercially valuable species. Wave power modules can act as these artificial reefs and also have the potential to improve the local inshore marine harvest. Benefits will be greater in areas presently sparse in marine life and devoid of suitable substrate for settlement.
Wavegen
Established in 1992, by Professor Alan Wells FRS inventor of the Wells Turbine, Wavegen has developed a range of energy modules for clients to exploit the unlimited wave energy resources in the shoreline, near shore and offshore environments.
Wavegen modules capture waves converting the stored energy back into pressurised air which drives a turbine. The turbine rotates a generator transforming this movement into electrical energy. In operation, the air driven turbo-generator is the only rotating component, reducing plant maintenance to a minimum.
This technology leads the way in harnessing the vast untapped resources of the world’s oceans. The units are capable of generating electricity at a price that is competitive with fossil fuelled power stations and other renewable energy sources. Furthermore, the Wavegen modules generate power which is emission free.
Wave Power Devices
Wavegen’s power devices are comprised of two basic elements - a collector to capture the wave energy and a turbo generator to transform the wave power into electricity.
The Collector and Oscillating Water Column (OWC)
Oscillating water column devices use a pneumatic Wells turbine to collect energy from an artificial ‘blowhole’. In this design, a large structure is built, usually on or near the shore, containing a chamber with an opening to the sea below the water line, into which seawater is free to enter and leave. As waves strike the device, the water level within the chamber rises and falls, pushing air out through an opening at the top. This column of air, contained above the water level, is alternately compressed and decompressed by this movement to generate an alternating stream of high velocity air in an exit blowhole. If this air stream is allowed to flow to and from the atmosphere via a pneumatic turbine, energy can be extracted from the system and used to generate electricity.
Power Take Off – the turbo generator
Wells turbines are used to power the electricity generators. These turbines have the unique property of rotating in the same direction regardless of the direction of fluid flow around the turbine blades. This design allows the turbine to spin both as air is expelled from the chamber by the rising water and as it rushes back in when the wave subsides. Thus, the turbines continue turning on both the rise and fall of wave levels within the collector chamber. The turbine drives the generator, which converts this power into electricity.
The LIMPET
The LIMPET (Land Installed Marine Powered Energy Transformer) generates 0.5MW of power for local or island communities and is designed to operate right on the shoreline.
Pelamis wave energy converter
Wave energy increases with distance from the shore. The Pelamis wave energy converter is a device that has been designed by Ocean Power Delivery. It 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 the joints is fed down a single umbilical cable to a junction on the seabed. Several devices can be connected together and linked to shore through a single seabed cable.
Control of the restraint applied to the joints can be 'turned-up' in small seas where capture efficiency must be maximised or 'turned-down' to limit loads and motions in survival conditions. The complete device is flexibly moored so as to swing head-on to the incoming waves and derives its 'reference' from spanning successive wave crests. A 750 kW device will measure 150 metres in length and 3.5 metres in diameter.
Wave power applications
- Electrical power generation
- Coastal protection
- Harbour development
- Satellite oilfield power
- Aquaculture development
- Desalination
Shortage of drinking water is a cause of much suffering and a major limitation to agricultural development in many parts of the world. Wave power devices can provide supplies of potable fresh water through on board seawater desalination to help alleviate these problems. This is of particular value in dry coastal areas with strong wave regimes.
The regular and powerful wave climates found in many locations where water shortages exist, result in ideal locations for the generation of power from waves. Many of these peripheral locations currently rely on diesel generators to provide electricity to power their desalination plants. It is in these regions in particular that the benefits of wave power are considerably magnified.
Benefits of wave power
- Oceans cover three quarters of the earth’s surface and represent a vast natural energy resource in the form of waves.
- The World Energy Council estimates that energy, equivalent to twice the world’s electricity production, could be harvested from the world’s oceans.
- In the UK alone it has been estimated that the recoverable wave energy resource exceeds total UK electricity demand.
- If less than 0.1% of the renewable energy within the oceans could be converted into electricity it would satisfy the present world demand for energy more than five times over.
For further information, please contact:
Intermediate Technology Development Group would like to thank Wavegen and Ocean Power Delivery for providing the original material on wave power.
This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
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