Wave Energy in the North Sea


The Slow Mill is a Wave Energy Converter consisting of a floater with blades variably connected to an anchor on the seabed. Waves push the floater up and the blades away from the anchor. This way not only the up and down movement but also the back and forth movement of the waves is utilised. The blades go as deep as 4-5 m to extract wave power from below the surface as well. When the wave recedes, it takes the Slow Mill back to its starting position and a winch reels in the cable, preparing the device for the next work stroke. The entire unit follows the orbital or sometimes elliptical wave path but moves a bit slower than the wave, hence its name: Slow Mill.

One of the major challenges of converting wave energy into electricity is that wave motions are irregular and hard to follow. Some strategies adapt the resonant frequency in order to align the work stroke with the wave swell. The Slow Mill is rather light and follows the waves easily, harnessing both the heave (vertical) and surge (horizontal) motions. Its blades are designed to move more or less along the orbital wave path, even when waves hit at various angles and frequencies. It doesn't need to complete a return stroke to make a new work stroke as it just makes smaller or bigger circular motions, avoiding losses due to acceleration and deceleration while only using limited centripetal forces. 

The anchor is relatively large as forces during storms can become quite strong and the floater has to be pulled under the higher wave crests. But installation is rather simple as the design allows a small tug boat to quickly bring the anchor to the assigned location where it can be installed. The floater is lighter and could be installed right after or at the same time to minimise work at sea. Yearly maintenance is done by ffilling the anchor with pressed air and bringing it to sea level to clean, inspect and possibly repair the unit. The anchor will be made of marine quality concrete that boosts biodiversity and carbon storage to counter ocean acidification.