The Symphony Team proved to be able to convert the energy of waves into mechanical- and electrical energy in the earlier Archimedes Wave Swing (AWS) development. With the AWS development, several EU projects and assisting other wave energy converters (WEC), we have 20 years of experience which really counts.
Only two key components
With Symphony we introduced a number of innovative technologies which replace the function of critical parts existing in other designs. The Symphony WEC contains in the end only two critical or key components. These are the structural membrane and the turbine. Both are new patented technologies. Our two key technologies replace a number of critical parts of the AWS, like the bearings, the endstops, the hydraulic piston, the linear generator and the large air volume.
Although the Symphony key components are novel, they are believed to be well designed and tested. The membrane is designed build and tested by Trelleborg. The turbine is being assembled (end 2017) and will be tested extensively in Q1 2018. The development and test of the key components are performed within the EU H2020 project WETFEET.
The next step after testing the turbine and the membrane separately is to build and test the turbine and the membrane together in a dynamic test rig. Then the turbine can act both as pump and turbine in one cycle.
After all components are tested individually, a complete demonstrator will be assembled at a scale of 1.5m diameter and ca 7m heigh. This device is going to be tested for at least full season (12 – 18 months). The demonstrator is small enough to work on low costs but large enough to be direct scalable to medium size devices.
The demonstrator will be tested in a sheltered area where small vessels can be used to install and service the device and the tests can focus on functional performance.
Although it seems a straight forward path, the steps taken should be prepared with caution. More mechanical and electrical engineering is needed. For instance on the cooling of the electronics in a closed underwater compartment. Symphony is discussing these types of issues with interested industrial partners.
The working principal
Relevant background of wave energy is found here. The working of Symphony can be explained shortly as a device with an internal spring that resonates at the wave frequency. Already small waves will attenuate the Symphony motion up to the full stroke. The generator damps this motion by extracting electrical energy.
The system is placed ca. 6 meter under the neutral waterlevel, it will experience a pressure field under the wave crest. This will push the outside hull down and comperes the air inside. Under a wave trough the air will expand and push the outside up a gain.
If the natural frequency of the system is close to the wave frequency, it will be able to abstract energy from a larger area. Tis is called point absorption in wave energy literature. This phenomenon has been studied extensively, but not many devices have been able to apply it. Because it is potential destructive. As the device charges itself with energy it will hit the mechanical endstops and destroy itself. In this device the endstops are integrated in the shape in which the membrane rolls. This gives the endstop the characteristic of a stiff spring. A buffer, that not dissipates the energy, but gives it back. By doing so it causes a small delay which lowers the intake of energy. A fully passive control of the kind you need to follow the KISS principles. Below graphs that came from the design study performed by a student of the Technical university of Twente is given.
the black line is the wave, the blue line the motion of the outer part. With these waves it uses constantly its full stroken options. On the right bottom graph the spring characteristic with the stiff spring at the end is shown.