Survey of Energy Resources 2007
Wave Country Notes
Between 1998 and 2004 the Danish Energy Agency operated the Danish Wave Energy Programme for supporting development projects initiated by inventors, private companies, universities etc. This covered a wide range of possible converter principles and provided developers with the facilities to have basic research carried out on their devices. At that time, the Danish Wave Energy Association was formed to disseminate information and promote activities for those interested in wave energy.
Several devices have been developed that have been tested at a small scale.
The Ecofys' Wave Rotor comprises a vertical shaft (or monopole) on which a rotor containing both slanted blades (similar to a Darrieus rotor) and horizontal blades. In waves, these experience hydrodynamic lift from the vertical and horizontal components of the motion of particles in the waves. This turns the rotor, which is attached to a 250 kW generator via a gearbox. The key innovations are that, apart from the rotor, there are no other moving parts in the water (the bearings and power take-off are placed 10 m above water level) and the same technology can also extract energy from tidal currents. The concept might also be capable of being mounted on existing structures in the sea. The device has been tested at a small scale in open-sea conditions and is scheduled for tests at 1/5th scale in 2007.
The Wave Dragon (a wave concentrating and overtopping device described in the Commentary) is a leading Danish technology. A 20 kW small-scale device is currently operating at Nissum Bredning, the Danish Wave Test Site, which has gained more than 19 500 hours of operating hours experience (www.wavedragon.net). Wave Dragon Wales, a subsidiary of the Danish parent company, is engaged in a project to build a 4-7 MW demonstration device in Wales (www.wavedragon.co.uk). It has formed a project development company, Tecdragon with a group of Portuguese and German investors with the purpose of developing a 50 MW wave energy project in Portuguese waters (www.tecdragon.pt). It has also secured funding from the European Commission for design of a multi-megawatt device.
Wave Plane International A/S
The WavePlane is another floating overtopping device that uses a number of channels for the water to move into, which also act as storage reservoir to smooth out the power. From these, the water is funnelled into a central turbine. Model tests have been carried out in various locations in the world but without any electrical generation. The company additionally proposes to use this device to oxygenate sea water and has representatives in seven countries (www.waveplane.com). This device is at the R&D stage.
Wave Star Energy
The Wave Star device consists of a long structure pointing into the oncoming waves, with a series of floats attached to booms on either side. As a wave travels down the structure, the floats rise and fall, each pressurising its own hydraulic cylinder, which is in turn connected to a common main that powers a central hydraulic motor and generator. The key innovations of the device are the ability to: raise the floats out of the water in large seas; place all the mechanical and electrical plant out of the water on the central structure; perform with only slightly diminished efficiency even when some floats are not functioning. The company, Wave Star Energy, has had a 1/10th scale device with 40 floats of one metre diameter generating up to 5.5 kW connected to the grid since July 2006 and has logged up over 4 000 hours of operation (www.wavestarenergy.com). It has plans for a 500 kW system for use in the North Sea to be installed in 2009.