Wave Energy

Background The possibility of generating electrical power from the sea has been recognized for many years (the first patent on wave energy conversion was issued as early as 1799, and, already in 1909, a harbour lighting system in California was powered with a wave energy system). However, significant research and development of wave energy conversion began only rather recently: in fact, although there was a renewed interest on wave energy after the oil crisis of 1973, it subsided again a few years later.

Five years ago, especially in Europe, the sector experienced a resurgent interest. Today, wave energy conversion is being investigated in a number of EU countries, major activity is also ongoing outside Europe, mainly in Canada, China, India, Japan, Russia, and the USA. Nascent wave energy companies have been highly involved in the development of new wave energy converters such as the Pelamis, the Archimedes Wave Swing, AquaBuOY, Oceanlinx, Wave Star, Wave Dragon, etc.


Wave Energy Potential

The global wave power resource in deep water (i.e. 100 m or more) is estimated to be ~ 1­10 TW (Panicker, 1976). The economically exploitable resource varies from 140-750 TWh/y for current designs of devices when fully mature (Wavenet, 2003) and could rise as high as 2,000 TWh/y (Thorpe, 1999), if the potential improvements to existing devices are realised. Global electricity consumption is about 15,400 TWh/y (BP, IEA), hence wave could supply up to 13% of current world electricity consumption which is equivalent to about 70% of what is currently supplies by hydroelectric schemes.


Cost

The predicted electricity generating costs from wave energy converters have shown a significant improvement in the last 20 years, which has reached an average price below 10 c€/kWh. Compared to e.g. the average electricity price in the EU, which is approx. 4 c€/kWh, the electricity price produced from wave is still high, but it is forecasted to decrease further with the development of the technologies.

Objectives

The most important objective for the wave energy sector is to deploy full size prototypes to prove performance at sea and to bring the technology to a point where it becomes comparible with other renewable energy technologies such as wind energy. This step is crucial in order to gain greater confidence in ocean energy as a reliable energy source. This requires suitable funding.

Technologies

Wave energy systems can be divided into 3 groups :

Shoreline devices: are fixed to the or embedded in the shoreline, having the advantage of easier installation and maintenance. In addition shoreline devices do not require deep-water moorings or long lengths of underwater electrical cable. The disavantage shoreline devices experience is that they experience a much less powerful wave regime. The most advanced type of shoreline device is the oscillating water column (OWC).

One example is the Pico plant, a 400 kW rated shoreline OWC equiped with a Wells turbine that was constructed between 1995 and 1999. Due to malfunction problems the testing programme was delayed. In 2003, the Wave Energy Centre, a Portuguese Association dedicated to the development and promotion of wave energy, refurbished the plant and restarted testing, resulting in real sea testing in September 2005. Based on the experience a 'wave energy breakwater' project is being developed at the Douro estuary in Oporto, Portugal mainly financed by the EDP-group.

Another wave energy system that can be integrated into a breakwater is the Seawave Slot-Cone converter (SSG). The SSG concept will then give the breakwater an added value in therms of income through sale of electricity. The SSG will provide the breakwater with infrastructure, including electricity and may be combined with fresh water production.

Near shore devices: are deployed at moderate water depths (~20-25), at distances up to ~500 m from the shore. They have nearly the same advantages as shoreline devices, being at the same time exposed to higher power levels. Several point absorber systems are near shore devices.

Offshore devices: exploit the more powerful wave regimes available in deep water (> 25 m depth). More recent designs for offshore devices concentrate on small, modular devices, yielding high power output when deployed in arrays. The AquaBuOY system is an example of an offshore wave energy device. The AquaBuOY system is a freely floating heaving point absorber system that reacts against a submersed tube, filled with water. Another example based on the overtopping principle is the Wave Dragon. The Wave Dragon used a wave reflector design to focus the wave towards a ramp and fill a higher-level reservoir. 

Sumber : http://www.eu-oea.com/index.asp?bid=425