The Churchill Barriers in Orkney, UK link a series of small islands on the east side of Scapa Flow and they were built during World War II to form a protective barrier against submarine intrusion after the sinking of the battleship Royal Oak by a German submarine in 1939.
The barriers have changed the tidal flow in the surrounding waters considerably and now there are plans to harness the tidal flow potential to generate electricity.
Orkney Islands Council has invited interested parties to pre-qualify for a competition to obtain a concession for the installation of tidal energy technology across two sites at Churchill Barriers. Pre-qualified developers will compete to design, build, operate and finance a tidal energy generation scheme at Churchill Barriers No. 1 and/or No.2.
Although work started on the barriers in 1940 they were not completed until 1945 at the end of the war. Largely Italian prisoners of war were used for the construction work under the guidance of contractor Balfour Beatty that entailed dumping 250,000 tonnes of locally quarried rock into the 20 metre deep channels and then topping these with 66,000 large concrete blocks. The four barriers in total extend for close to 2 miles and they are topped by a road that now provides a transport link between the islands.
The tides run strongly through the islands in this area and to the south in the Pentland Firth they are some of the strongest tides around the British Isles. The potential for harnessing some of this tidal power to generate electricity has been assessed and consultants estimate that with tidal energy turbines installed at Barrier No.1 it would be possible to generate an estimated 16.7MW when the tide is running at full flow whilst 8.6MW could be generated at Barrier No.2.
Any scheme proposed by companies interested in developing this site for tidal energy must allow for maintaining of the road transport link across the barriers at all times and also reduce the existing wave overtopping risk at Barrier No.2 which has led to closure of the road in the past.
It is recognised that allowing the water to flow through the barriers to generate the tidal power will have an effect of the overall tidal flows in the region but this effect is considered to be acceptable. A wide variety of tidal generator concepts will be considered and they could include building bridges over the generators and using both vertical and horizontal turbine systems. It is estimated that the pay-back time for a tidal generator could be anything between 10 and 30 years.
At this stage the Orkney Islands Council has issued a notice to establish if there was any developer interest in developing the potential tidal energy generation scheme at Churchill Barriers.
By Dag Pike
