BACKGROUND PAPER 10
Turning the Tide: Tidal Power in the UK
Sustainable Development Commission, 2007
The Sustainable Development Commission (SDC) Report considers both tidal stream and tidal
range technologies and presents recommendations on proposal for a Severn Barrage. The best
tidal stream sites are in the north of Scotland and north Wales, Northern Ireland and the Channel
Islands. The tidal range resource is concentrated in the estuaries off the west coast of Britain,
including the Severn and the Mersey, as well as the Humber on the east coast.
All tidal technologies have a number of environmental, social and economic impacts that need to
be considered. In particular, the impact of a Severn Barrage on internationally protected habitats
and species is of great concern.
The UK also has an excellent tidal stream resource, and is leading the world in the development
of a wide range of tidal stream devices, several of which are at the testing stage. The UK must
‘stay the course’ in developing these technologies, as the export and climate change benefits are
potentially very large. Particular concern is expressed regarding the long-term ability for tidal
stream generation to connect to the electricity transmission system due to a lack of capacity. The
SDC believes that Ofgem and the Government must urgently increase the capacity of the
electricity transmission system to accommodate renewables over the long-term.
On tidal lagoons, the SDC found that there is a lack of available evidence on the costs and
environmental impacts, mainly due to the absence of any practical experience. The SDC have
called on Government to support the development of one or more demonstration project, which
would help provide real-life data on their economic and environmental viability.
Evidence suggests that there is minimal conflict between the potential development of tidal
stream, tidal barrages and tidal lagoons technology that could be deployed in the Severn. Small
scale tidal lagoon development could take place alongside a tidal barrage.
A Severn Barrage
A number of different barrage options have been proposed for the Severn Estuary, the SDC report
considers two of them in detail: the Cardiff-Weston scheme is one of the larger options proposed
and would have a generating capacity of around 8.64GW; the Shoots Scheme is a smaller
1.05GW proposal with an annual output of around 2.75TWh.
Generating capacity: 8.64 GW
Estimated cost of Construction: £15 bn
Annual average electricity output: 17 TWh
Contribution to UK electricity supply (2006 data): 4.4%
Estimate cost of output: 2.31 p/kWh (2% discount rate)
Estimate cost of output: 9.24 p/kWh (8% discount rate)
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BACKGROUND PAPER 10
Generating capacity: 1.05 GW
Estimated cost of Construction: £1.5 bn
Annual average electricity output: 2.75 TWh
Contribution to UK electricity supply (2006 data): 0.7%
Estimate cost of output: 2.58 p/kWh (2% discount rate)
Estimate cost of output: 7.52 p/kWh (8% discount rate)
The assumption is that both barrages would be operated on the ebb tide, with the addition of
“flood pumping” to increase the total energy output. This means that they would be generating
electricity for around 7-8 hours on each tide, and output would vary within this period. If built the
Cardiff-Weston scheme would generate 17TWh per year, which is equivalent to aroudn 4.4% of
UK electricity supply. This is the same level of output as would be produced by just over two
conventional 1GW power stations.
The report highlights the following potential benefits:
A national opinion poll showed that 58% of people across the UK were in favour of a
barrage and 15% against. Stakeholders at workshops in Bristol and Cardiff were also in
favour of a barrage as delegates felt that the benefits outweighed the disadvantages,
although there were a large number of concerns raised.
Electricity from a Barrage would make a significant contribution to the UK’s renewable
The variability in output from the Barrage is not a major problem for the electricity grid
and can be managed at very low cost.
There would be substantial flood risk benefits from a barrage but these are only marginal
to the economic case for its construction.
The case for new transport links, such as an additional road or rail link over a barrage, is
unproven and needs to be assessed looking at the net costs and benefits.
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BACKGROUND PAPER 10
There are a number of concerns over how a decision in favour of the Severn barrage might
impact on wider energy policy aims as well as a whole range of environmental concerns. In terms
of energy policy the SDC report highlights the problem that there is a risk that the development
of a barrage might divert Government’s attention away from the other necessary solutions to the
challenge of climate change. It also does nothing to support the decentralisation of our energy
system as a large amount of electricity generating capacity would still be based in a single
The Severn Estuary is a unique and dynamic environment. It has the second largest tidal range in
the world, combined with a high suspended sediment load, and has a number of special features,
including extensive areas of salt marsh, and mobile sandbanks. It is an important site for
migratory birds, and fir fish movements in and out of the estuary’s tributaries, such as the Wye
and the Usk. The Estuary is designated a protected site under national and international
legislation – EU Directives on Birds and Habitats Special Protection Area and a candidate Special
Area of Conservation. The Directives are intended to facilitate sustainable development by
ensuring that environmental objectives are adequately considered when proposals are put forward
that would negatively impact on protected habitats or species.
The SDC outline the following points in relation to the environmental considerations:
A Severn barrage could lead to a loss of biodiversity, resulting in the need for a
compensatory habitats package to maintain the overall integrity of the Natura 2000
The EU Directives provide a clear and robust legal framework for achieving sustainable
development and therefore compliance with the Directives is a central condition for a
sustainable Severn barrage
Providing compensatory habitat would be a very significant undertaking on a scale
hitherto unprecedented in the UK, but this would have to be an integral part of any
It is clear that the barrage would have a major impact on the local environment. There would also
be a number of impacts on local communities and the regional economy, and a high risk that
unsustainable ancillary development would take place alongside any barrage project. The SDC
has therefore laid down a series of tough conditions which a Severn barrage would have to meet
in order to be considered sustainable.
A Severn barrage must be publicly led as a project and publicly owned as an asset to
avoid short-termist decisions and ensure the long-term public interest
Full compliance with European Directives on habitats and birds is vital, as is a long-term
commitment to creating compensatory habitats on an unprecedented scale
Further investigation of the ‘environmental opportunity’ that might exist for combining
climate change mitigation with adaptation through a habitat creation package that actively
responds to the impacts of climate change over the long term
Development of a Severn barrage must not divert Government attention away from much
wider action on climate change
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BACKGROUND PAPER 10
The SDC believes that there is a strong case to be made for a sustainable Severn barrage and that
this should be pursued as part of a major drive to reduce emissions substantially over both the
short and the long term. A robust climate change and sustainable energy policy is an essential
pre-requisite for development of a barrage and there is the potential for a Severn barrage to be
used as a symbolic example of the scale of action that is requierd as part of a comprehensive and
radical programme on climate change.
A Severn Barrage or Tidal Lagoons? Friends of the Earth (Jan 2004).
The table below summarises the main details of the schemes:
Barrage Lagoons (largest scenario)
Power generated 17-19 TW hours/year 24 TW hours/year
Average output 1.95 – 2.17 GW 2.75 GW
Capacity 8.64 GW 4.5 GW
Emissions avoided 4.6 – 5.1 mtC per year 6.5 mtC per year
Impounded area 185 square miles 115 square miles
Aggregates required 13m tonnes 200m tonnes
Design life Min 120 years Min 120 years
Generation cost 5.5 pence/kWhour 2.0-2.5 pence/kWhour
Electricity generating tidal lagoons located in the Severn Estuary could provide an economically
attractive and environmentally acceptable way of supplying up to 7% of England and Wale’s
electricity consumption with lost-cost, low-carbon electricity.
There are a large range of potential environmental and economic benefits and disbenefits
associated with siting lagoons or the proposed Severn barrage in the Estuary. However, initial
comparisons strongly suggest that lagoons could be significantly less extensive and
environmentally damaging and more cost effective and powerful than the Barrage. Lagoons
would not directly impound the ecologically highly valuable inter-tidal areas of the Estuary and
would generate twice as much per square mile than the Barrage. Every tonne of aggregate used in
lagoon construction would enable the generation of three times more electricity than a tonne of
coal burnt in a power station.
Lagoons would not impede shipping but the Barrage could provide a novel transport link. Both
technologies would generate significant quantities of low-carbon electricity close to large
populations. However, the unit generation cost, output timings, storage capabilities and smaller
capital costs of lagoons are likely to be far more attractive to private investors and consumers.
Environment Agency – comments on Severn Barrage proposals
Insufficient consideration has been given to the environmental implications of the Barrage in the
debate so far, in particular the degree of protection afforded by the EU Birds and Habitats
Directives. They support the Government’s position stated in the 2003 Energy White Paper, “that
plans for a Severn Barrage would raise strong environmental concerns and we doubt it would be
fruitful to pursue it at this stage”. As the Government’s statutory advisors on environmental
issues the Environment Agency, together with Natural England and the Countryside Council for
Wales, do not see a basis for changing that view (May 2006).
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