How Wave Star works

The Wave Star machine represents a solution to both the trivial and complex problems which, for years, have stood in the way of the development of commercially viable wave power technology.

The basic concept behind Wave Star is fundamentally different to many other wave power models. The machine does not form a barrier against the waves, with a view to harnessing all of their energy, but instead cuts in at right angles to the direction of the wave. In this way the waves run through the length of the machine, and their energy is exploited in a continuous process.

On either side of the oblong machine there are 20 hemisphere-shaped floats which are partially submerged in the water. When a wave rolls in, the first float is lifted upwards, and then the second and so on, until the wave subsides. 

The floats are each positioned at the base of their own hydraulic cylinder. When a float is raised, a piston in the cylinder presses oil into the machine’s common transmission system with a pressure of up to 200 bar. The pressure drives a hydraulic motor, which is connected to the generator, which produces the electricity.

As the machine is several wave lengths long, the floats will work continuously to harness energy.

When Per Resen Steenstrup heard about the Wave Star concept in 2003, he realised immediately that it fulfilled the four requirements which, in his opinion, a wave machine should meet:

Firstly, the machine should be storm-proofed. In the case of Wave Star, the machine automatically raises the floats up out of the water when the waves reach a certain height. As far as the full-scale machine is concerned this means that, in the event of wave heights of above eight metres, the floats will be raised to a safe position 20 metres above the surface of the water. 

As the machine is positioned in such a way as to cut in against the main direction of the waves, the wind will also normally be directed against the narrow end of the machine.

Per Resen Steenstrup’s second requirement is that the wave power machine should not be too heavy, thereby ruling out the production of the large-scale design, as heavy machines are expensive machines. Wave Star fulfils this requirement. A production price which, per megawatt, corresponds to that of the wind turbines has been calculated.

Thirdly, Per Resen Steenstrup has learnt, from his many years’ experience of the production of seafloor measuring equipment, that as few parts of the machine should be in the water as possible. Equipment which is submerged in seawater is extremely expensive to produce, not to mention expensive to maintain. The Wave Star machine meets this requirement by resting above  the surface of the water on steel pillars, and the only submersible parts of the machine are the fiberglass floats.

The final requirement is that the machine should be based on tried-and-tested technology, which ensures a more steady operation and faster project start-up, without an endless number of equipment tests. The Wave Star machine is fundamentally based entirely on tried-and-tested technology. It is fair to say that its hydraulic system is somewhat innovative, with its common transmission system, but all components used are tried-and-tested.

The critical parts of the Wave Star machine are housed in the generator casing on the bridge. The generator, computers and relays are located here under climatised conditions, which protects them against damage from moisture and salt spray. On the current 1:10 model, the equipment is exactly the same as for the full-scale model, only the generator is smaller.

A Wave Star machine is manufactured in its entirety on land, and then tugged out to the steel piles upon which it is to rest. The tugging is a relatively simple procedure, as the weight of the machine is carried by its own floats. The machine is positioned over the steel shaft, and then the float arms are raised, until it is resting on the shaft, where it is bolted on. When the machine is due to be serviced or requires repair, it is loosened and tugged back into land.

As Wave Star produces electricity via 40 independent floats, there is not a lot that can go wrong. If one float breaks, the remaining 39 continue to generate electricity. The machine can continue to generate electricity, albeit with a reduced effect, with up to 75 percent of the floats out of operation.

Wave Star in the main

Wave Star Energy’s wave machine is a so-called multi point absorber. That means a machine equipped with a number of floats which are moved by the waves to activate pumps, which press oil into a common transmission system, the pressure of which drives a hydraulic motor. The motor, in turn, drives the generator of the wave machine.

In the event of a storm the floats are lifted to a safe position – on the large-scale machine they will hang 20 metres above the surface. A sensor on the seabed ahead of the machine measures the waves and ensures that the storm security system is automatically activated. The floats can also be operated via the Internet.

The 1:10 model at Nissum Bredning has 40 hemisphere-shaped floats, each with a diameter of one metre. The model has a 5.5 kilowatt generator. The large-scale model will be equipped with floats of 10 metres in diameter and a three megawatt generator.

The larger the machine, the larger the waves it can withstand – and the greater the depth it can stand at. A rule of thumb says that waves can reach a height corresponding to 75 percent of the depth of the water before they break. The 1:10 model stands in water two metres deep. The large-scale model is designed to stand in water 20 metres deep.

The Wave Star machine generates electricity even from very small waves. For the 1:10 model, waves only need to be 10 centimetres high. Calculations and tests show that the wave machine produces energy around 90 percent of the time, and that it will run on maximum power 30 percent of the time. Each time the machine doubles in size, its power becomes around 11 times greater.

The commercialisation of the Wave Star concept will begin as soon as the 500 kW machine, which is currently under development, has produced satisfactory results in the North Sea. According to the plan this should be in the course of the next three to four years.

In order to be competitive, in comparison with wind turbines, the Wave Star machine needs to reduce its price per kilowatt hour four times. By comparison the wind turbine industry had to reduce its prices seven times to reach the price level at which wind turbine energy is today.