WaveRoller concept

WaveRoller wave energy device under water - cropped WaveRoller wave farm in operation during high tide.

WaveRoller is a device that converts ocean waves to energy and electricity. The machine operates in near-shore areas (approximately 0.3-2 km from the shore) at depths of between 8 and 20 meters. Depending on tidal conditions it is mostly or fully submerged and anchored to the seabed. A single WaveRoller unit (one panel) is rated at between 500kW and 1000kW, with a capacity factor of 25-50% depending on wave conditions at the project site.

The story behind the invention

The simple yet very powerful idea for the design of WaveRoller came in a moment of enlightenment when Finnish professional diver Rauno Koivusaari was exploring a shipwreck. He noticed that a very heavy flat piece of the ship’s body was moving back and forth, driven by the energetic under-surface surge of water, the ocean waves. Since that first moment of insight the WaveRoller design has gone through multiple cycles of building prototypes, testing them in laboratories, conducting highly sophisticated simulations and numerical modelling, and finally deploying the test devices in the real ocean environment to make observations, adjust the scale and repeat the development cycle.

How it works

WaveRoller behaves in essentially the same way as the flat part of the wreck that Rauno observed. The back and forth movement of water driven by wave surge puts the composite panel into motion.

To maximize the energy that WaveRoller panel can absorb from the waves, the device is installed under water at depths of approximately 8 – 20 meters, where the wave surge is most powerful. The panel spans almost the entire depth of the water column from the sea bed without breaking the surface. This ensures that the panel does not protrude onto the seascape and prevents the creation of material inefficiencies that would put additional load on the structure.

As the WaveRoller panel moves and absorbs the energy from ocean waves, the hydraulic piston pumps attached to the panel pump the hydraulic fluids inside a closed hydraulic circuit. All the elements of the hydraulic circuit are enclosed inside a hermetic structure inside the device and are not exposed to the marine environment. Consequently, there is no risk of leakage into the ocean. The high-pressure fluids are fed into a hydraulic motor that drives an electricity generator. The electrical output from this renewable wave energy power plant is then connected to the electric grid via a subsea cable.

Power production and operations

The power output from a single WaveRoller device, or in other words output from a single panel, ranges between 500 and 1000 kW. The differences in power production result from the local wave resources (see more in Wave energy resources globally).

When multiple WaveRoller devices are installed at a single site, we talk about wave farms or arrays. These farms can include tens of devices, so that part of the infrastructure of the site is distributed among the machines, thus reducing the cost of an individual unit. Since each WaveRoller is equipped with an on-board electricity generator, the output from many devices can be combined via electricity cables and a substation. Large wave farms have nominal capacity of a utility-scale power plant.

One of the unique features of WaveRoller that ensures its cost effectiveness in delivering reliable power output is its distinctive operation and maintenance concept. WaveRoller units feature large ballast tanks that are filled with air so they can be floated to their deployment locations. These tanks can be flooded with water to submerge the unit. Although the wave energy converter remains fully submerged during regular operation, it can be easily re-floated on the surface for maintenance by emptying the ballast tanks. There is consequently no need for complex, costly and potentially hazardous diving operations when maintaining WaveRoller. Additionally, the device can be installed or serviced without additional costly equipment such as large cranes or jack-up barges.