SHAFTS/KIDSTON PUMPED STORAGE PROJECT | BTS


Table 1: Key Parameter


Maximum static pressure (intake) Maximum generation net water head Turbine Type


Maximum generation output


Maximum static pressure (Tailrace) Total Storage Capacity


Value


274m head 223m


Reversible Francis Turbine (vertical axis) 250MW


122m at the transition 1.870 MWh guaranteed for at least 6 hours (143,000 homes)


With the flow in each direction, up or down, there


are hydraulic friction losses (‘head losses’). When water flows downwards, there is only a net head remaining at the turbines to generate electricity to send out to the power grid. When the powerplant moves the mass of water back


up, energy is taken from the grid, including extra to overcome the friction. The benefit of having a choice of conveying a mass


of water either up or down through the pipelines or tunnels at a pumped storage project site comes from electricity economics rather than physics. Having the water fall to generate electricity is more valuable at times of need in the power network, either to help meet demand or quickly stabilise the transmission grid. When demand is much less, so is the cost of taking electricity from the grid to pump the equivalent mass of water back up, ready for next time. Usually, the upper and lower bodies of water are


natural bodies of water or can be impounded. Rarely, other bodies are examined for possible use to hold water, like disused quarries or surface mines. It can be that the position of the upper and lower


reservoirs only require surface pipelines to run between them, linked to a surface power plant. But, in some locations, they need tunnels to join them to convey water flow, passing through turbines placed in underground powerhouses, in caverns.


The Kidston arrangement In the case of Kidston, the renewable sources at the energy complex are solar power (50MW existing installed capacity with another 270MW in feasibility stage) and wind power (200MW in development). These will be used to supply electricity to pump water from the lower to the upper reservoir. The lower reservoir is called Eldridge Pit and the


upper reservoir is Wises Pit (see Figure 1). The Wises Pit then effectively acts as the ‘battery’ storing energy that can be released when energy demands peak. At the detailed design stage, Mott MacDonald was


working in a joint venture with GHD. The design JV was working for a construction JV of McConnell Dowell and John Holland, which has a contract with Genex Power. Andritz Hydro designed and supplied the pump turbine and associated hydromechanical equipment.


UNDERGROUND WORKS Figure 2 shows the planned underground works for the Kidston PSH scheme. The spiral main access tunnel (MAT) drops about 200m at a gradient of 1 in 7 to the underground powerhouse caverns; the two intake shafts are 230m depth and 4m i.d. transferring water to the penstock chambers, which are 30m long reducing in section from 4m wide to 2.5m; the powerhouse cavern housing the turbines is 18m wide, 85m long and 45m high; the project also has a smaller transformer


Above left, figure 2: Planned underground works Above right, figure 3: Location of steelwork alongside the powerhouse September 2023 | 11


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