WHERE people have talked for many years about the potential for the sea to one day substantially replace fossil fuels as our main source of electricity, making it happen has proved more challenging.

While wave power looked more promising in the early years, now tidal is considered to be two or three years in front. The current leader looks to be Norway's Hammerfest Strom, whose HS1000 1MW device, currently testing in Orkney, has been commissioned by Scottish Power to form the first array in the world with 10 turbines off Islay. Although it is said to have encountered some costly installation problems this year during device tests, it is due to go into construction next year.

It is one of four projects named by the Scottish Government last month as "finalists" in the Saltire Prize, which will award £10 million to the company that achieves the greatest amount of electrical output over a continuous two-year period. Behind it comes MeyGen, also focused on tidal and owned by a consortium that includes Australian developer, Atlantis Resources. MeyGen is building an array off Caithness that will also begin next year.

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The other two projects belong to Scottish wave developers Pelamis and Aquamarine, respectively off Sutherland and Lewis.

Behind this leading pack are various others, including tidal players Marine Current Turbines and Rolls-Royce-owned TGL, and Pelamis, which will provide turbines for developments by Scottish Power, E.ON and Vattenfall off Orkney and Shetland. Others to watch include Orkney's own ScotRenewables, with a tidal device.