Waves4Power AB is developing and selling wave energy systems. The heart of the system is our proprietary WaveEL buoy – a point absorber – where the energy of the waves are converted into electrical power. A wave power park consist of a large number of WaveEL buoys linked together in an optimized power generation pattern.
The Waves4Power system is based on years of experience and testing of wave power systems and from many years of marine service operations, resulting in a design which focuses on the SAFE concept.
WaveEL buoy THE HEART OF THE SYSTEM
- A buoy with a long vertical tube (the acceleration tube ) passing through it
- A water piston inside the tube connected to a power conversion system
- A mooring system allowing the buoy free vertical movement while securing it on station
- A dynamic cable connecting the WaveEL buoy to the collection hub and then via sea cable to the shore based power grid
The WaveEL buoy is a Point Absorber and as such is defined as a device with small horizontal dimensions in relation to the wavelength of the waves from which it is extracting energy. Due to their size point absorbers are known to survive well in the ocean as they do not fight the waves but ride them.
The device is best described as a very large pump where two masses are acting against each other. One mass is the buoy itself including the acceleration tube and the other is the mass of the water column inside the tube. Due to the difference in natural period for these masses – driven by the waves – they want to oscillate out of phase. By damping the relative movement – forcing them towards the same phase – energy can be captured by the conversion system. There are more or less sophisticated ways to establish this damping thus improving the energy output.
WORKING PRINCIPLE of the WaveEL buoy
The characteristic feature of the WaveEL buoy is the patented long acceleration tube. The tube – which is open in both ends – goes right through the buoy and is sticking down 30-35 meters below it.
As waves rise and lower the buoy with the attached tube, they will move differently from the water column in the tube. By placing a piston – connected to a hydraulic conversion system – in the tube, a gigantic pump is created.
The solution W4P offers is probably the most flexible on the market, a minimum depth of 40 meters is required, but other than that the buoys may be moored at essentially any depth or bottom conditions. Just like a weather buoy.
W4P has focused the concept on simplicity. By using standard components an inexpensive solution is reached with components that are well tested and with documented characteristics from well-known reliable suppliers.
When the buoy is still, the water line inside the tube will be at the same level as the waterline outside the buoy. The tubes lower opening is at such a depth that there is practically no turbulence from surface waves. Therefore the water column in the tube is hardly at all affected by the ocean wave action.
The buoy/tube unit represent one body of a two body oscillating system where the other body is the inert water mass present in the acceleration tube.
The conversion system utilizes a hydraulic cylinder as its pump. Its piston rod is connected to a large water piston placed inside the tube. The water piston’s motion relative to the buoy/tube is dampened by applying pressure in the hydraulic system, forcing the water piston to somewhat follow the buoy while pulling the water column along. The dampening force on the water piston needs to be set correctly between the two extremes – A: free floating with no dampening and B: totally locked – to efficiently harvest the energy in the waves.
A: Without damping of the water piston the buoy/tube unit will move freely while the water mass and water piston essentially stand still. The amplitude of the buoy/tube will be as great as the wave height. In this scenario no energy is captured.
B: If the water piston is locked completely to the buoy/tube it will force the water in the tube to follow the wave induced movement of the buoy/tube unit. The weight of the water mass that is now a part of the moving unit will reduce the speed and the amplitude of the motion of the system, with the same result – as in A above – that no energy is captured from the waves.
However between these two extreme conditions energy can be tapped by pressurizing the hydraulic system so that the movement of the water piston is dampened but not locked and thus making the water piston pull the water mass along but not quite being able to keep up with the buoy. The two masses will be moving out of phase making the hydraulic cylinder act as a gigantic hydraulic pump.
The hydraulic pump is connected to an accumulator feeding a hydraulic motor with a generator that converts the hydraulic pressure to electric power.