Evopod completes trials

The Evopod is a device for generating electricity from coastal tidal streams, tidal estuaries, rivers and ocean currents and rather than being attached to the seabed it offers a unique floating solution for tidal energy generation. The designers, Oceanflow claim that this type of solution offers a much cheaper and easier form of tidal generator because intervention in the event of failure is much easier with a floating solution.

Now the Evopod development has moved further ahead with the completion of 6 months of winter deployment reportedly without problems. For floating units Oceanflow claims that it is important that the floating platform supporting the turbines does not pick up motions from passing waves and that the turbine can be kept away from wave action in average sea conditions. The small waterplane area struts and deeply submerged nacelle of the Evopod ensure low motion characteristics and optimal alignment with the water flow. In addition the streamline struts avoid wake interference with the turbine.

The Evopod is tethered to the seabed using a catenary spread mooring system with simple pin-pile or gravity anchors. Mono and twin turbine Evopod units for deployment at coastal sites exposed to harsh wave climates employ a swivel mooring connection that allows the free floating device to maintain optimum heading into the direction of flow.

The Evopod was initially moored in the relatively sheltered waters of Strangford Loch in Northern Ireland for trials. The next stage was to test the system in more exposed waters and last August the Evopod was moored in Sanda Sound which lies between the Island of Sanda and the Mull of Kintyre off the West Coast of Scotland. The successful completion of these winter trials have demonstrated Evopod's low motions and survivability characteristics in the moderately fast flowing (4 to 5 knots) tidal site, which in the winter months is also exposed to a harsh wave environment from the Atlantic and Irish Sea.

The floating platform's streamline surface piercing struts and turret mooring ensure that the device always faces into the flow whatever the wave direction while the small water-plane area of the struts and the device's deeply submerged tubular hull ensure that the unit has very low motions compared to more conventional surface floating platforms or buoys. The unit rode out a particularly severe "weather bomb" storm in December which combined spring tides with record breaking wind speeds and wave heights.

Graeme Mackie, Oceanflow's Managing Director, said, "We are extremely pleased with E35's performance in harsh sea conditions over the winter. The device's low motions and survivability in the roughest of seas fully validated Oceanflow's decision to develop semi-submerged platform technology for its Evopod tidal turbine".

The E35-01 unit deployed in Sanda Sound was fitted with a 35kW rated generator driven by a 4.5m diameter turbine. The next stage will be to connect this unit in Sanda Sound to the grid via an umbilical and subsea cable connection later this year. The umbilical and seabed power cable will also transmit data to the company's onshore control and monitoring container which is sited 0.75 nautical miles from the device's moored location.