Pumped-Storage of Hydroelectricity
The UK in line with Europe and many other developed countries is facing a number of challenges in the energy generation sector which is predominantly brought about by the government’s aim to reduce greenhouse gas emissions, increase energy security and to move generally towards a more sustainable, low carbon economy. The government’s focal point for achieving these aims is an introduction of large-scale off-shore wind development programme which are now well underway. To support these developments and to link the new generation facilities on the Scottish Coast, the Irish Sea and in the South West and East with the large areas of consumption in the South east and Midlands, the upgrade of the transmission network is planned costing an estimated £10b. It is furthermore essential to link the large-scale intermittened generators (off-shore and on- shore wind farms) with balancing plants many of which are still in planning or construction.
The upgrade of the UK’s transmission network is hampered by the need to obtain way leaves, planning and to overcome local objections to HVC routes.
The proposed Pump-Storage Hydroelectric (PSH) system can address some of these issues and partially avoid the need for the transmission network to be built to peak demands.
The pumped-storage hydroelectric plant uses the hydrostatic water pressure at sea levels off Scotland or the Irish Sea at a depth of 500 m. The plant could be fed from excess electricity generated by off-shore or, depending on the grid connection point and where available on-shore wind farms. A typical plant will have the following structure:
The storage will be provided by separate caverns (tunnels) dug in a solid geological layer deep under the sea bed. The (typically) twin tunnels will be drilled at a depth of 400 to 500 m. The tunnels will have a diameter of 12 to 15 m. The tunnel drilling machine will be taken through the inspection and access shaft coast side. The tunnel drilling machine will be used to dig the tunnels over a length of approx. 50 km below the off- shore wind farms. The turning cavern for the drilling equipment will be built at the end of the storage tunnels sea side. This cavern will later house the electricity generating equipment, the room for the electrical connection plant and the stilling basin below the intake, outlet, air, inspection and access shaft.
The intake, outlet, air, inspection and access shaft sea side will be built in parallel with drilling the coast side shaft using a pressurised caisson for deep-sea work
After the completion the PSH plant, sea water will be allowed into storage tunnels through the inlet shaft and passes through the electricity generating turbines, filling the storage tunnels. The pressurised air is discharged through the coast side air shaft. At times of excess wind capacity, the turbines work in reverse and pump out the storage tunnels again taking in air from the coast side air shafts.
As an example, the supply shaft on someone of the german island (in the North Sea off Germany) is used for air in and outlet. Furthermore, a factory workshop is built on top of the coast side shaft which contains a crane for supply of equipment to the turbine hall. The coast side shaft is separated from the storage tunnels by an air-tight access hatch.
The storage tunnels off the island will also be used as HV cable routes for connection of the off-shore wind farm. It will only be necessary to lay undersea cables from the island to the shore.
The PSH facility will have a minimum capacity of 2,180MW with a storage volume of 12m m3. This is comparable to pump storage facilities built in mountain areas (e.g. Goldisthal, Germany). The capacity can generally be increased by adding additional storage tunnels.
We have secured the international patent (for the EU region and world-wide PCI) for the construction of a PSH plant. The patent is based on a feasibility study covering technical and economic issues. The next step will be a location study and the investigation of the opportunities in the UK market place. This needs to include cover an investigation of the regulatory environment under which a PSH plant will have to operate, the type of corporate entity that will be able to operate the facility and an assessment of the impact on the market. It will also be necessary as part of the market analysis for the UK to assess the potential for savings in the transmission network upgrade necessary over the next decade to link the planned off- and on-shore wind farms in Scotland, the North and Irish Seas as well as the South East and South West of England with the consumer location in the South East and the Midlands.
Based on the results of the location studies and the analysis of the UK market place, a number of outline designs will be produced as the basis for a planning application under Section 36. This will go in parallel with necessary public consultations which are not expected to be controversial due to the near invisibility of the plant, the lack of any impact on the transport system and the non-invasive nature of the plant to the coast line and the sea bed. The feasibility study will then be completed by a financial appraisal of the project.
The overall development is split into three phases. They are:
We expect that the location study and UK market analysis can be carried out over the next six months. This will be followed by the preparation and submission of planning application, the conduct of the public consultation process and the decision process under Section 36. This process is expected to take another 18 to 24 months.
The construction of the storage tunnels will be carried out using similar tunnelling drilling equipment used for building the Eurotunnel, the London Jubilee Line and other comparable engineering projects. The twin-storage tunnels could be built either in parallel or in sequence depending on the available finance. As a comparative the Channel Tunnel consists of three bores with two 7.6-metre (25 ft.) diameter rail tunnels, 30 metres (98 ft.) apart is 50 kilometres (31 miles) in length and took 2 years to be built.
In addition, the construction of the service shafts, the turbine hall as well as commissioning of the plant is expected to take another 2-3 years. Thus the overall construction programme from completion of the feasibility stage to commissioning is expected to take 6-7 years depending on specifics of the rock formation found in the various potential locations.
There are options to optimise the build programme by building some of the tunnels in parallel. This could allow the commissioning of 50% of the capacity after only 4-5 years which would assist greatly in the financing of the projects.