Last month the tidal power industry moved a step forward when, on the publication of the 2007 Energy White Paper, Trade Secretary Alistair Darling stated the government was intending to actively encourage tidal power development. Predictable and consistent, they view it as an important source of renewable energy for the future.

Partly funded by the Department of Trade & Industry (DTI), The Sustainable Development Commission (SDC) is currently carrying out a major study on tidal power in the UK, covering a range of tidal technologies, their efficiency as well as their environmental and ecological impact.

The SDC report will also include an in-depth assessment of one of the white paper's main proposals for the harnessing of tidal power; the Severn Barrage. Construction is proposed across the Severn Estuary and the location was selected due to its tidal range of nearly 14 metres, making it the best location in the world after Canada's Bay of Fundy.

The Severn Barrage

The Barrage method of harnessing tidal power uses the potential energy from the difference in height between high and low tides. The barrage is normally built across a river estuary and is designed to trap a high tide of water, then allowing it to drive a set of turbines and generate power. The largest current example of this technology in the world is at La Rance, Brittany - and it is a thirtieth of the size of the proposed Severn project.

Since the barrage was initially proposed in 1849 there have been a number of different plans submitted for its location and structure along with varying functions. These have typically included transport links, flood protection and harbour creation. However, recent plans have focused on tidal power generation as they key fuction, whereas previously it was seen as a useful but minor part of the proposal.

The current plan, submitted by Welsh Entrepreneur, Gareth Woodham, proposes to stretch the barrage ten miles across the Seven Estuary linking Lavernock in South Wales to Brean Sown, near Weston Super Mare. Planners say the barrage could be constructed within eleven years, powering 200 turbines and generating 5% of the UK's energy needs.

The barrage would also provide a massive economic boost in the area. Secretary of State for Wales Peter Hain stated the barrage could create up to 35,000 jobs during its construction and 40,000 jobs in the longer term due to the increased economic stability it will bring.

Opposition to the Severn Barrage

However, The Renewable Energy Centre along with many environmental groups including Friends of the Earth, fear that the change in water level the barrage will create is certain to have a serious detrimental effect on a unique and important aquatic and shoreline eco-system.

Consideration must also be given the amount of carbon dioxide which will be produced during the construction of the barrage, and how many years it will take for the renewable energy it produces to offset these emissions.

Richard Simmons, founder of The Renewable Energy Centre commented "There is no question that the Severn Barrage could generate a large amount of sustainable and renewable energy; however research must be done into the impact such a large structure will have, on the local eco-systems as well as people and businesses in the area.

He continued "It is not before time that a major proposal of this kind has been seriously considered if we are ever to meet our carbon emission targets but it is important that we remember that the Severn barrage was dismissed in 2003's white paper. With advancing technology and the emergence of less damaging alternatives, the barrage could be even more of an unwise proposal now. Sub-surface turbines that harness the flow in naturally occurring tidal streams for example, could generate far more energy and cause little environmental harm".

Tidal Streams are fast flowing volumes of water caused by the motion of the tide. In a similar way to wind turbines, the kinetic energy from the tidal stream can be captured by a generator which relies on the tides to power underwater generators. Compared with constructing a tidal barrage, these have the advantage of being much cheaper to build and would not have such a high impact on the environment and ecosystems.

Friends of the Earth have also proposed alternative tidal technologies, principally the construction of tidal lagoons in the Severn Estuary. Each lagoon would be capable of producing electricity by filling and draining through turbines but without blocking the whole estuary. Initial research has shown that lagoons could also generate significant amounts of renewable power but at a considerably lower cost and less impact on the surrounding environment. For example, unlike a tidal stream generator the barrage could kill high numbers of fish trying to cross it or disturb nesting sites.

Whichever route the Government decides to take it is important to look at the bigger picture regarding world climate change. The tidal power of the Severn Estuary has the potential to produce up to 15GW of peak power, effectively replacing the need for 3 nuclear power stations.

The recent white paper confirmed that the Government has recognised the related problems associated with tidal power and that it will be studying the findings and recommendations of the Sustainable Development Commission (SDC) report when it is released in September, before announcing what it considers to the next best step.

Further information on wave and tidal technologies can be found at:

• www.therenewableenergycentre.co.uk/wave-and-tidal-power/

• www.TheRenewableEnergyCentre.co.uk

• www.sd-commission.org.uk/pages/tidal.html