Explanation of the factor 11
Froude’s Law says that the effect will increase according to the size uplifted to the power of 3.5. Why is this so? When the Wave energy converter is built in double size, it will receive a wave front that has double the width. If the device is placed in a wave climate with an average wave height that is doubled from 1 to 2 meters, the power in the waves will be raised by 2 uplifted to the power of 2.5 which equals 5.56. The double width device then receives 2 x 5.56 = 11.3 x more power.
Facts on the Wave Dragon
At Nissum Bredning in Denmark a 1:4.5 scale Wave Dragon prototype launched in 2003 was the world’s first floating grid-connected wave energy conversion device. It weighs 200 tonnes, is 57 meters wide and is made of steel. The test unit has accumulated over 20,000 hours of experience supplying electricity to the grid. At the moment, the Wave Dragon is not producing due to a breakdown. EUDP funding allows the team behind Wave Dragon to pursue the modeling and design of the full-scale device in spring 2011. The demonstration project will be installed off the Danish coast with an almost twice as large device to follow in Wales.
Wave energy concepts
There are four overall types of wave energy extractors.
1. Oscillating water column - These devices contain a chamber where the water level changes as waves go in and out. As the water level changes so does the pressure, which causes air to flow through the turbine. This generates electricity.
2. Attenuator or linear absorber – These devices, also called attenuators, use less than the full amount of energy in a wave. The linear absorber structure is oriented roughly parallel to the direction of wave propagation and is composed of multiple sections that rotate in pitch and yaw relative to each other. This motion is used to pressurize an internal hydraulic fluid. This fluid turns a turbine that is coupled to a generator to produce electricity.
3. Overtopping terminator - A terminator is a device that reflects or absorbs all the energy in a wave. One type of terminator is an overtopping device that uses a floating reservoir structure, typically with reflecting wings to focus the wave energy. As waves arrive, they overtop the device and are restrained in the reservoir. The head of the collected water as it flows back out to sea turns conventional low-head hydro turbines, and the turbines are coupled to generators to produce electricity.
4. Point absorber - These devices capture energy from the ”up and down” motion of the waves. They may be fully or partially submerged. They are small compared to a typical wavelength and can absorb energy from all directions.
Read more about wave energy devices, the challenges and opportunities at LORC Knowledge lorc.dk/knowledge/wave-energy