Marine Power Systems’ CTO ‘decodes’ WaveSub power generation

The power generation principles of the recently launched WaveSub wave energy device were explained in detail by Graham Foster, the Chief Technology Officer (CTO) of the company that developed the device – the Welsh-based Marine Power Systems.

The quarter-scale WaveSub prototype was officially launched on October 13, 2017, in Wales, UK, ahead of planned real-sea trials at the marine energy test site FaBTest, off Cornwall.

MPS will try to demonstrate WaveSub’s power generation capacity across a broad range of sea conditions, installation and maintenance methodology, as well as survivability of the device.

The following are the words of Graham Foster who tried to shed more light on the power generation principles of the WaveSub wave energy device.

“A critical feature of any renewable energy generation device is its ability to capture energy efficiently. In our case, we knew we needed the WaveSub to be able to generate energy across a broad range of sea states.

We also knew that the subsurface orbital flow of waves is powerful but difficult to harness – most of the energy is underwater; this necessitates a more complex approach to efficient exploitation.

So how does the WaveSub capture this latent energy? And how does it convert it to electricity?

First, it is perhaps important to understand the key components of the WaveSub device. Measuring 100 metres long at full scale, the WaveSub comprises a series of cylindrical power capture floats and a rectangular reactor barge.

The power capture floats sit atop the reactor barge and all machinery, power and control equipment is housed on or in this barge. Four power take-off (PTO) lines connect each power capture float to the reactor barge. Taut mooring lines anchor the reactor barge to the seabed.

The power capture float tracks the orbital energy path, allowing it to harness energy through the entire wave cycle. A depth adjustability mechanism (also used to protect the WaveSub from storms) enables it to move to an optimum generation depth in the sea.

The depth adjustability is operated by a control system, which regularly monitors the sea state (wave height and period), thereby adjusting the float and reactor depth to an optimum location for energy generation.

 
To generate power, the WaveSub’s float tether lines are connected to hydraulic generators, so as the float moves with the waves, hydraulic energy is created. A hydraulic circuit then smooths this hydraulic energy and uses it to turn an electrical generator which outputs grid compatible electricity.

The WaveSub is the only device that currently addresses what we see as the four key challenges of wave energy generation.

Our techno-economic forecasting suggests that in time, the WaveSub will be in a strong position to compete with other renewable energy technologies including offshore wind.

The UK, currently a global leader in the marine energy sector would see a new maritime-based renewables sector emerge that brings new skilled jobs as well as contributing to carbon reduction commitments.

Ultimately, with government and investor support today, waves can join the sun and then wind to provide the clean, affordable and renewable energy of tomorrow.”