Largest tidal array in the world to be built in Scotland  

Wired has a report on the progress of tidal power in Scotland - Largest tidal array in the world to be built in Scotland.

Western Scotland will see the world's largest tidal array constructed off the coast, as the first large-scale rollout of tidal energy generation.

A trial with one 30m turbine, the HS1000, anchored to the ocean floor in a fast-flowing channel near the Orkney Islands, raised one megawatt of electricity -- enough to power around 500 homes. Now, Scottish Power is planning on building two farms of turbines off the Scottish coast.

The project at the Sound of Islay should hopefully generate 10MW, and then the later project off Duncansby Head (the most northeasterly point of Scotland) should generate around 95MW. While individual turbines have been trialled across the world, the arrays will be the largest of their kind, with local communities having their power provided by renewable tidal sources.

The turbines -- built by Andritz Hydro Hammerfest, a Norwegian firm -- represent a tricky engineering challenge. Considerations for wild plants and fish means that the blades can't move too fast, and the turbines must be located in areas where there is a reliably fast current travelling at at least 2.5m/s (such as the Sound of Islay, a narrow passage between the Scottish mainland and the island of Jura).

Once a suitable location has been identified, a giant steel frame is lowered to the seabed and secured. The turbines are between 40 to 100 metres below the surface of the sea, so theoretically pose no danger to shipping. The turbines are designed to turn in both directions to generate power, giving a constant supply of electricity.

Some have estimated that around ten percent of the UK's total energy needs could be met with tidal arrays -- and the long-dreamed-of Severn Barrage alone could meet five percent of UK demand if numerous engineering difficulties are overcome.

As with many renewable energy technologies, the initial costs can be prohibitive. Scottish Power estimates the cost of the turbine farm to be around £70 million.