Power from the Ocean Floor?

As projected pressure ensues on oil and gas supplies, the search for alternative sources of energy continues. Ideally these should be "renewable" a term meaning that we do not need to depend on digging-up finite reserves, that will in consequence run-out at some future date open to speculation. They should not create pollution either, since building-up a pile of waste that will cause headaches for future generations also violates the defining contract of sustainability. Hence, wind-power, solar-power, geothermal-power and sea-power are particularly attractive propositions. Sea-power is normally thought of in its terms of providing energy through tidal-stream power or wave-power. These might be achieved via various forms of engineering contrivance, so for example, a tidal-turbine situated in the Bristol Channel or the Thames estuary (ignoring any impediment to shipping) could harness the energy of the tide as it rises and falls in river streams. Likewise, "rockers" could be placed almost anywhere around the coast of the U.K. mainland in order to harvest some of the energy from waves, as they migrate across the surface of the water.
However, it appears that there is yet another source of energy to be had from the sea. In Finland is a prototype one square metre plastic plate, connected to an hydraulic mechanism, and this is of the kind that the company, AW Energy, is installing in Portugal, at Peniche which is 100 miles up the Atlantic coast from Lisbon. The plates will be anchored to the ocean floor close to the shore at a depth of about 12 metres. They are intended to catch the back and forth motion of underwater swells, to produce kinetic energy which drives a piston-pump and is converted to electricity by onshore generator systems.
In contrast to other wave and wind-based technologies, the ocean-floor approach has the advantage that it is placed underwater, and hence out of sight and out of mind. Apparently, the idea originated from the company's founder, Rauno Koivusaari, who is a professional diver who worked on such projects as undersea cable installations. In the mid-1990's, he was exploring a shipwreck and narrowly avoided being hit by a metal bulkhead door that was flapping back and forth pushed by the deep-water waves. He realised that this kind of effect if harnessed could be used to drive power-production systems, and after a decade or so and a number of tests made by Finland's biggest energy producer, Fortum, along with other companies, and some trials at the European Marine Energy Centre in the Orkneys, now AW Energy is about to use the method to produce real electricity.
Unlike surface waves, underwater waves are more horizontal, and have a more regular and hence predictable pattern. In Peniche, 77% of the waves travel in the same direction, and this is why that particular location has been chosen to anchor the plates which are called "WaveRollers". As Ilkka Hominen (AW Energy) explains: " They will oscillate back and forth on an axle following the movement of the waves. A hydraulic pump will capture the energy and pass it on to a generator hosted in a small cabin onshore - the only visible part of the system." Combine several WaveRoller modules including the cabin which contains the equipment required to connect to the grid, and you have a power station. It sounds neat.
The full environmental impact of the WaveRoller appears to have been well thought through. For example, local fishermen believe that fish will actually be protected by the presence of these devices, and of course there is no hazard to shipping, unlike offshore wind-farms, say. The undersea waves fluctuate far less than surface waves or wind and so a more nearly constant supply might be expected. Routine maintainance and future refurbishment should also be more efficient, as work can be undertaken on one plate at a time, with minimal interruption to the overall output of the "plant". The lubrication of the hydraulics is even to be done using a vegetable-based oil!