West Somerset Lagoon
West Somerset Lagoon (WSL) is a proposed tidal range power scheme in the Bristol Channel. The lagoon will be located off the coast of West Somerset between Minehead and Watchet. The proposed location is 10km downstream of the Severn Estuary areas with special environmental designations (SACs & SPAs). The lagoon will not contain any large rivers, although it will contain a few streams. The lagoon is outside the main shipping channel, which runs up the deep water channel off the Welsh coast, thus there should be minimal direct impact on shipping.
WSL will generate electricity on both ebb and flood tides. The generators will be used as pumps to increase high water levels and lower low water levels which will result in high and low water levels within the lagoon area broadly similar to or slightly higher and lower than existing. The energy output from WSL is estimated to be 6.5 TWh per year.
The lagoon enclosure will be formed from large reinforced concrete caissons, prefabricated in existing port facilities in the Bristol Channel / Severn Estuary and towed to site, and short lengths of embankment in the shallow water near the landfalls. The proposed layout consists of 125 bulb turbines of capacity 20MW, thus providing a total generating capacity of 2500MW, and sluiceways with vertical lift gates.
National Grid (NG) have advised that the electrical grid in the South West is being upgraded to accommodate Hinkley Point C power station. There will be a new sub-station at Sherton which is expected to have spare capacity of 4000MW and, based on present knowledge, the WSL output can be connected at Sherton.
Most of the potential environmental issues to be considered are identified in guidance received from the Environment Agency (EA). Whilst there are a number of issues to be considered and mitigated where appropriate, in particular marine and migratory fish, nothing which is likely to be a “show stopper” has been identified so far. The scheme has been discussed with the RSPB who raised no immediate objections.
The lagoon will provide control of basin water levels, thus storm surges can be excluded if they coincide with spring tides. Also, large waves will be excluded by the enclosure walls. Thus there should be a benefit to coastal protection. Also, the scheme is designed to accommodate a sea level rise of 0.7m and could be modified in the future if this figure is expected to be exceeded.
Local councils, landowners, environmental and statutory bodies, businesses and the general public will all be consulted formally in the next stage of study. Based on initial discussions, it is believed that the scheme is likely to be supported by most. The lagoon will lie just outside both the Exmoor National Park and the Quantocks Area of Outstanding Natural Beauty. Informal discussions held with representatives of both suggest that neither is likely to object in principle.
Road access to each landfall will need to be constructed. This will need detailed discussion with landowners, residents groups, local councils and highway authorities. In addition, upgrading of parts of the A39 road which carries heavy traffic in the summer, will be considered.
The current capital cost estimate, including 15% contingency, is £8,500M at 2019 prices and the estimated construction period is 5 years to first power and 6 years to full power. The required Contract for Difference (CfD) payment, calculated from a private sector financed financial model to give an IRR of 12.5% with a CfD contract duration of 35 years, would be around £100 per MWh. Clearly this is not competitive with recent offshore wind bids at around £40 to £50 per MWh. However, it is similar to the CfD for the new nuclear power station Hinkley Point C.
The majority of revenue for WSL will come from electricity sales. Other sources of income could include floating solar in the basin and leasing of areas for local retail and marine activities. Potential non-energy benefits for the community include employment on the construction and operation of the scheme, an all tide floating marina and associated developments at Minehead, improvements to Watchet Harbour, increased tourism and a reduction in flood risk and coastal erosion.
The major influence on future electrical demand will be the UK government’s commitment to net zero carbon emissions by the year 2050. The required electrical generation capacity is expected to increase by around 50% by 2030 and by 100% or more by 2050. It is likely that offshore wind and solar will make up a substantial proportion of the new capacity. However, these two technologies alone are unlikely to provide the required large increase in capacity. New nuclear capacity seems likely to provide some of the new capacity. Power from tidal range in the UK can provide an important component of a diversified future electrical supply.
Tidal range power schemes are expected to have a life of 100 years or more, as is the case for hydro-power schemes. For tidal power long-life has been demonstrated by La Rance in France which has now been operating for more than 50 years and is expected to continue for many more years. Methods of financing investment provide no credit for an operating life beyond about 30 years.
A method used to finance major long life infrastructure is called Regulated Asset Base (RAB). Government are currently considering RAB for nuclear power stations, which have a design life of 60 years. Tidal range power has similar features except that its design life is about 120 years. Thus, it seems reasonable to consider RAB for tidal power.
A Development Consent Order (DCO) now has to be used for all Nationally Significant Projects. The necessary consultations and desk and field studies have to be carried out before an application is made. An Environmental Impact Assessment (EIA) is a key part of an application. The EIA and DCO process is likely to take around 4 years, with a target to start in 2021 and complete in 2025. The construction start would then be in 2026, with first power in 2031 and full power in 2032.
Preliminary studies are planned for the WSL scheme to be carried out later in 2020, to provide an independent review of the scheme and of the investigations carried out to date and to prepare a detailed scope of work for the EIA, DCO and marine licence.