The Tidal Stream Resource

The most detailed resource study yet carried out - by the DTI in 1993 - indicated that if all potential sites were developed, the total UK tidal stream resource could be about 60 TWh (ie 60,000 GWh or 60,000,000 kWh). Of this, 28 TWh - about half - could come from the Pentland Firth, representing 8% of total UK electricity consumption of 350 TWh. (In practice this might not all be realisable, for instance because of the need to leave shipping channels). The Pentland Firth tidal speeds average from 1.5 to 2.2 m/s - the highest in the UK and possibly the world - but the water depth is 60m or more, making potential energy capture huge but technically difficult. In fact, 63% of the tidal stream resource is estimated to be in waters deeper than 40m.

Shallower sites can be developed more easily but yield much less energy - an estimated 9 TWh near the UK mainland (3% of total consumption) and 4 TWh around the Channel Islands with no access to UK mainland demand. These sites can be developed first, but tapping into the Pentland Firth has by far the biggest long-term rewards.

Other resource studies have indicated accessible tidal stream energy for the UK of: 36 TWh from ten of the best UK sites (ETSU 2001) 34% of all UK electricity - ie about 130 TWh (Scottish Enterprise) 22 TWh - the UK 'technically extractable' resource (The Carbon Trust, 2005). This report points up the importance - and difficulty - of deepwater sites, and stresses the need for floating concepts to be developed. The world 'accessible tidal stream resource' has been put at 3% of the 3000 GW 'available' (DTI, 2002). This 90 GW (compared with a UK power capacity of 60 GW) could represent 200 TWh of energy, world wide.

Reference: Tidal Stream Energy Review, 1993, ETSU Report to the DTI carried out by Engineering & Power Development Consultants Ltd with Binnie & Partners, Sir Robert McAlpine & Sons Ltd and I T Power Ltd