Power across the Mersey15 June 2010
The Mersey tidal power project has passed a notable milestone with completion of the first stage of a major feasibility study. Further research is now underway to select the best scheme to start generating power across the Mersey estuary in 2020
The Mersey estuary has one of the largest tidal ranges in the UK and is a prime location for a tidal power scheme. It has a catchment area of over 4600km and includes the major cities of Liverpool and Manchester. Indeed, it has previously been shown that a substantial scheme in the estuary could satisfy the electricity needs of a large part of the Liverpool City region.
A noteworthy feature of the Mersey estuary, which makes it an attractive option for a tidal power project, is its narrow mouth. It is unlike most other estuaries which tend to become progressively wider towards the sea. Here, the narrow area extends from the estuary mouth to an area upstream of the Tranmere oil terminal, and its width varies between 1-2km. Furthermore, the deepest sections of the estuary are located in this area and the current velocities are greatest. There is very little mudflat exposure at the lowest astronomical tide. Upstream of the narrow area the width of the estuary increases significantly and the depth reduces. Extensive areas of mudflat are exposed at the lowest astronomical tide.
The basic geography of the estuary is important in the context of tidal power development. In other UK estuaries such as the Severn and the Solway Firth, the width of the estuary progressively increases towards the sea. The provision of a barrage or tidal fence in such estuaries is therefore associated with an increasing length of structure as the alignment is moved seaward. This increase in length is associated with an increased volume of water commanded and an increased quantity of energy captured. Movement of alignment in a seaward direction therefore increases both investment cost and energy yield, and a balance must be found between these two variables.
In the Mersey estuary the reverse applies. The movement of an alignment in a seaward direction increases energy capture and reduces the length of the structure required. Both these trends encourage consideration of alignments towards the downstream, narrow section of the estuary. A similar trend applies when tidal stream velocities are considered. In estuaries that widen in a seaward direction, the average stream velocities will reduce as you move downstream. In the Mersey the highest stream flow velocities are in the downstream, narrow section of the estuary.
For several years Peel Energy, in partnership with the Northwest Regional Development Agency (NWDA) and with the backing of the Mersey Basin Campaign, has been examining the development of a power scheme in the estuary. In 2006 stage 1 of the project got underway with a pre-feasibility report, which was completed in October 2007. This first stage was completed in January 2010 with the production of a long list of technologies to be evaluated in more detail.
Stage 2 of the scheme, the full feasibility study, began in September 2009 and is expected to be finished in January 2011. A feasibility report will be published in March 2011. The feasibility study is being led jointly by a consulting team comprising Scott Wilson, Drivers Jonas and EDF, on behalf of Peel Energy and NWDA. They are supported by a group of advisors including APEM, HR Wallingford, Regeneris Consulting, RSK, Turner and Townsend, the University of Liverpool and the Proudman Oceanographic Laboratory.
The study team has strived to include as many relevant technologies as possible in the assessment. Existing and emerging technologies for use in a range of water depths were examined, and consideration was given to work on tidal power generation from the Mersey stretching back nearly 30 years – schemes have emerged in the past for generating up to 700MW of electricity from the estuary. The study also took account of similar work being done to assess the possibility of generating power from the tides within the Severn estuary and of a related government-backed programme to promote new tidal power technologies, the Severn Embryonic Technologies Scheme (SETS).
Fourteen options for the Mersey were assessed and evaluated against a set of five criteria:
• 1: Estuary width and water depth: Can the technology be implemented in the Mersey estuary, given its width and water depth, while limiting impacts to acceptable levels, if necessary by adjusting the size of the scheme or modifying the operating conditions?
• 2: Water velocity: Will the technology be capable of generating a commercial quantity of energy from the natural tidal current velocities in the estuary?
• 3: Performance parameters: Has the performance of the technology been sufficiently studied to enable its energy output to be assessed?
• 4. Technology maturity: Will a prototype of the technology have been sufficiently tested (or will there be the financial and technical capacity to undertake such tests) in representative conditions, including adequate flow magnitude, physical scale and marine conditions, in time for the technology to be adopted as the basis of a commercial scheme in a planning application in late 2011?
• 5. Delivery: Will the technology have the support of a company with sufficient technical capability and financial security to enable it to be adopted as the basis of a commercial scheme in a planning application in late 2011?
At the end of stage 1, four main technologies were taken forward for fuller analysis and incorporation in scheme layouts in stage 2. This list may be revised and developed as the study proceeds and further information is available. The four technologies selected at this stage are:
• Horizontal axis turbines in an impounding barrage: This is a conventional barrage impounding the tidal range of the Mersey to obtain maximum energy yield, offering the most economic solution provided by a large diameter plant requiring deep water conditions. The concept could be further developed to command a reduced water level difference if required to limit impact on the estuary.
• A tidal gate comprising Hydromatrix turbines and creating a very low head barrage: A barrage operating at a low head difference, below the operating range of conventional horizontal axis plant. The tidal gate solution employs small diameter units and will therefore be suitable for a shallow water application.
• Vertical axis, cross-flow or horizontal axis, ducted stream flow machines in a tidal fence: A partial or continuous barrier across the estuary will constrain the tidal flow and increase the velocity locally to drive the stream flow generating plant.
• A spectral marine energy converter (SMEC) forming a tidal fence: SMEC is an innovative tidal fence concept developed by VerdErg Ltd based on the Venturi effect. It is suitable for low flow velocity conditions. It potentially requires deep water conditions depending on the final configuration of the generating plant.
The selected tidal power scheme for the Mersey must meet three prime objectives:
• It has to be capable of generating a meaningful amount of electricity at a price that the country can afford.
• The direct impacts on the environment, shipping, local businesses and communities must be kept to acceptable levels (in determining their acceptability, measures may need to be provided to mitigate or compensate for the impacts).
• It should be to the maximum possible benefit of the region in a socio-economic and environmental sense.
An important socio-economic benefit of the scheme would be the development of the skills, facilities and the supply chains required to establish the region as a recognised centre for renewable energy development. Other benefits might be local infrastructure improvements and the creation of leisure and tourist opportunities.
Speaking for the NWDA, Stephen Broomhead, Chief Executive, said: “The Mersey tidal power project has the capacity to provide both national and regional benefits. It stands to make a significant contribution to reducing the UK’s carbon emissions, essential if we are to counter the effects of climate change. At the same time, it will undoubtedly have a positive effect on the region in terms of promoting growth and reinforcing regeneration.”
In the next stage of the feasibility study, indicative sites within the estuary where the different technologies could be best deployed will be identified and possible scheme layouts established. Once this is done it will be possible to move the assessment forward on three fronts. There will be an economic analysis that looks at the likely energy yields of the different schemes set against their anticipated construction and operating costs. Each of the schemes will be evaluated from the standpoint of their impact on the natural environmental, a crucial part of the study in an area internationally recognised for its ecological richness and diversity. And there will be a socioeconomic analysis focused on the effects of the different schemes on the shipping industry, businesses and local communities.
“Throughout the course of the process, in the run up to a planning application, the project team will engage extensively with everyone that has a stake in the project,” said Anthony Hatton, Development Director of Peel Energy. “We will be totally open about the different options under consideration and will seek to stimulate a discussion that includes local authorities and organisations, especially people who live in the areas surrounding the possible scheme sites.
“Comments and feedback on any aspect of the project will be welcome at any time. At this stage we are specifically asking for any additional information on relevant technologies or reference information that will assist with the study,” he added.
A key stakeholder advisory group and an environmental advisory group have already been set up to help guide the decisions being made and review the findings of the study as they emerge. The consultation exercise will be widened in the future as the feasibility study progresses and the candidate schemes are more fully defined.
Peel Energy has a generating portfolio of more than 3GW comprising tidal power, wind, biomass and multi-fuel plants. www.peelenergy.co.uk
The NWDA works to deliver economic success in this region of England. It is working towards a low carbon economy by ensuring the region reduces its environmental impact, adapts to climate change and capitalises on key business opportunities. www.nwda.co.uk
For more information see www.merseytidalpower.co.uk
|Mersey - points for consideration|
When selecting a preferred choice for tidal power generation across the Mersey, consideration has to be given to the following factors:
Water quality- This has been a significant issue for the Mersey estuary for some time. The Water Framework Directive has classified the area as a heavily modified waterbody with unsatisfactory quality. Improvements have been made over recent years and a river basin management plan is underway, which predicts that some water bodies within the Mersey catchment will achieve good ecological status before 2015. The Mersey tidal power project has to ensure that these plans are not compromised by the chosen power scheme.
Natural environment - Large parts of the estuary and Liverpool Bay are European Community designated protected areas for conservation. The area is also rich in wildlife, particularly birds. Any tidal power scheme here is likely to have some effect on water levels and will alter habitats. This will be a key issue for the siting, design and operation of the chosen scheme.
Shipping - The Mersey estuary has nine shipping destinations and is the third busiest estuary in the UK. Site selection must also take into account tankers using the Tranmere oil terminal which need to turn in the river.
Geology - A deep and variable bedrock profile has been identified as a significant geotechnical constraint in the Mersey estuary. A feature of the area is the presence of deep valleys called Tunnel Valleys formed by subglacial or englacial meltwater flowing under great hydrostatic pressure beneath ice sheets.
|Severn Embryonic Technology Scheme (SETS)|
The first River Severn tidal power consultation was launched in the UK in January 2009. A £500,000 government fund was established for developing schemes incorporating embryonic technologies which may offer less environmental impact than those shortlisted for the Severn estuary.