(1) Aberthaw Tidal Power Station

2021 Outline Design by Edward Grist


What is it?

Aberthaw Tidal Power Station is a tidal barrage that crosses from Aberthaw in South Wales to Minehead in England. It is at the seaward end of the Severn Estuary where it joins the Bristol Channel.

The Aberthaw-Minehead tidal barrage provides two outstanding benefits.

  1. It has by far the largest tidal-power electricity-generating capability at a single location anywhere in Europe.
    With batteries it can produce up to 4,000 megawatts of electricity continuously (24/7) at a cost inherently much lower than all the alternatives.
  2. It provides primary protection against flooding for all of the Severn Estuary above the barrage at no extra cost.
    This includes Cardiff, Newport, Gloucester, Slimbridge, Avonmouth, Bristol, the Somerset Levels and Hinkley Point C. The price for 4,000MW continuous is £8 billion (A strike price of £40/MWh for 35 years). The price for 4,000MW tidal only, 16 hours per day, is £6 billion (£35/MWh for 35 years). The electricity-generating equipment can stop or control the magnitude of flow crossing the barrage. For present-day weather this primary flood protection is at no extra cost. Climate Change is likely to raise sea levels. If less than two metres the ‘root-tube’ length can be increased. All functions are then maintained including a full electrical output capability. For an increase of between two and five metres larger root-tubes can be added. Protection against flooding is maintained but electricity generation is restricted.

Why Aberthaw?

The Aberthaw-Minehead tidal barrage location has five inherent benefits. This makes the location ideal for a 4,000 megawatt ‘green’ tidal power generating capability.

  1. Electrical-power Generation
    The magnitude of the potential electrical-power generation capability is proportional to the product of the tidal height and the mass of water passing through a water-turbine. The Bristol Channel / Severn Estuary has the second highest tidal range in the world. At Lavernock Point the tidal range reaches about 14.5 metres in the Spring. At Aberthaw the tidal range reaches about 11.0 metres in the Spring. The magnitude and cyclic timing of the world’s tides are principally determined by the orbital path of the moon and the rotation of the earth.

    The gravitational forces produced during its transit cause any mass of water that is free to rise to do so and to attempt to move in the direction of the moon’s orbit. A narrowing west-to-east orientation of the channel into which it flows, such as the Severn Estuary, magnifies the resulting increase in level. The time taken for each tidal cycle varies. It is typically about 12 hours 20 minutes. Land-based hydro-generation often either replaces or works alongside waterfalls. The height through which the water falls dominates. In a choice of location, it is usually visually obvious where the maximum power generation potential exists. In tidal generation the tidal height changes simultaneously with the magnitude of the accompanying flow. The maximum power generation potential for a particular location is not immediately obvious.
    The volume of water that passes over the Aberthaw-Minehead barrage line as it flows back to the sea is much greater than that passing over the Lavernock Point to Brean Down barrage line. The area covered upstream of the Aberthaw barrage is more than 14.5/11.0 greater than that upstream of a Lavernock barrage.
    Combining the tidal height during electricity generation and the associated flowrate shows a barrage between Aberthaw and Minehead has the maximum potential for generating electricity in the Bristol Channel / Severn Estuary.
  2. Structural Height
    A reduction in structural height of approximately 14.5 – 11.0 = 3.5 metres compared with a barrage between Lavernock Point and Brean Down is a considerable cost advantage even when an increase in barrage length is included.
    Aberthaw to Minehead is the best location for power generation.
  3. Seismic Events
    All the large structures in the Bristol Channel must be designed to avoid unacceptable consequences that may arise from seismic events in the future. The Bristol Channel floor is, on occasion, subject to strong earth tremors.
    Earthquakes in or affecting the Bristol Channel - Severn estuary***
    table of siesmic events
    *** Data source: - The British Geological Survey, Centre for Ecology & Hydrology, Wallingford
    The foundations and related structures of the barrage must absorb seismic movement. Displacements along the length of barrage (ie shore to shore) are met with by providing adequate flexibility in structural steel cross member design. The shorter distance across the MFU is held rigid by a low-level beam to protect the crane rails from unacceptable separation. An Aberthaw Tidal Power Station with suspended water-turbine/generators can accommodate tremors up to Richter Scale 6.0.
  4. National Grid and Rail Access
    The Aberthaw coastline already supports electricity power generation. Aberthaw A opened in 1963, was decommissioned in 1995 and removed.
    Aberthaw B 1,580MW opened in 1972. Closure has not yet been agreed.
    A high-voltage connection from Aberthaw B to the National Grid pylon electricity distribution network exists. Upgrading and making use of this network simplifies the support structure requirements for the Aberthaw Tidal Power Station considerably.
    A legacy of past coal usage is a rail terminal that links Aberthaw B to the main rail network.
    An Aberthaw to Minehead barrage is in the best location for Grid and rail access.
  5. Sea and Road Access
    The deep-water channel down the Severn Estuary is particularly favourable to Aberthaw. Using a dockside where offloading is directly onto the barrage has many advantages. In particular delivering very large turbine-generators, cranes and structural steelwork for the barrage during construction. The M5 road direct connection to Avonmouth, and an existing dockside equipped with heavy loading facilities, simplifies delivery by ship.
    drawing of ship dock An Aberthaw-Minehead tidal-barrage ship dock
    Each of the two Shipping Channels can change function to become a ship dock. Raising the two bascule arms as shown forms a stationary waterway along the length of the shipping transit channel. The level can be adjusted and kept constant at a desired level by appropriate pumping. It is free from local currents, estuary waves and the worst ravages of Atlantic storms. Choosing to use the dock facility when the channel is closed during a four-hour tidal power electricity generation period makes economic sense. A link road between the M4 (junction 34) and A48 (near to Cardiff Wales Airport) is under consideration. In 2018 the choice between two routes was the subject of formal public consultation. On completion this will make visitor access to Aberthaw Tidal Power Station very simple. An Aberthaw to Minehead barrage is in the best location for sea and road access.
    CONCLUSION
    Aberthaw to Minehead is the best location for a tidal power generation barrage.

Why Now?

  1. Time critical UK constraints
    1. An investment in new ‘green’ electricity generating plant that will feed into the National Grid on or before the year 2030 to prevent a nationwide energy shortage.
    2. An investment in new ‘green’ electricity generating plant that will feed into the National Grid before the year 2025 to help meet global Climate Change targets.
    3. An investment in a barrage to provide flooding protection before the year 2025 to accommodate the level in the Bristol Channel rising by up to two metres as a result of increases in ocean levels. This could be caused if international targets on Climate Change fail to be met.
  2. UK Electricity generation in 2018
    The data given in the table below was recorded at 11.20am on Monday 22 nd October 2018. This was a cold day, but not severely cold one, with temperatures falling to 0C at one point.
    table of uk electricity generation
    The huge present-day dependence on the fossil fuels - coal and gas- is unacceptable.
  3. Aberthaw Tidal Power Station construction
    It takes six years to build following placement of order. This includes two years to produce final ‘approved’ designs followed by four years construction in the Bristol Channel where adverse weather conditions have to be allowed for.

    After three years of construction all flood protection measures could become operational and partial power generation would be possible.

    The estimated cost of Aberthaw Tidal Power Station is £8 billion. The estimated ‘strike price’ is £40 per megawatt hour applicable for 35 years.

    The Aberthaw Tidal Power Station barrage has an estimated design life of 70 years. Aberthaw Tidal Power Station can be constructed in time to ensure flooding protection to the Bristol Channel caused by Climate Change is provided if any necessary evaluations are completed to enable a placement of order before the start of 2021.
  4. Factors influencing timing
    In addition to recognising the need for urgency to meet global Climate Change commitments and the UK need to ensure a continuing uninterrupted electricity supply, the evaluation should recognise: -
    1. That the Aberthaw-Minehead tidal barrage produces up to 4,000MW of electricity at a very low cost.
    2. That water-turbines can respond in tens of seconds (in increments of 50MW up to 1320MW) to sudden energy demands from the National Grid. Water-turbines / battery storage. This is much faster than gas turbines coming on-line.
    3. Commercial opportunities afforded by the Aberthaw-Minehead barrage range from the obvious manufacturing work to the benefits flowing from a large influx of tourists from abroad.
CONCLUSIONS

Aberthaw Tidal Power Station must be operational before 2025. The 4,000MW tidal barrage is by far the most cost-effective means of generating electricity under normal conditions and of maintaining supply during unexpected system demand transients.

Appropriate action has to be initiated now to provide the following.

  1. A reliable electricity supply from the National Grid to consumers that is maintained at all times by recognising the demand for electricity is likely to increase and old power stations will need to be closed in the immediate future.
  2. Flood protection for all of the Severn Estuary is in place to meet both present needs and those potentially arising in the future. This anticipates an international failure to limit the influence of climate change.