The GPM (Gravity Power Module) uses a very large piston that is suspended in a deep, water-filled shaft, with sliding seals to prevent leakage around the piston and a return pipe connecting to a pump-turbine at ground level. The piston is comprised of reinforced rock and in some cases concrete for low cost. The shaft is filled with water once, at the start of operations, but is then sealed and no additional water is required.
As the piston drops, it forces water down the storage shaft, up the return pipe and through the turbine, and spins a motor/generator to produce electricity. To store energy, grid power drives the motor/generator in reverse, spinning the pump to force water down the return pipe and into the shaft, lifting the piston. Hundreds of megawatt-hours per shaft can be stored with high efficiency, since pump-turbines have low losses and friction is negligible at modest piston speeds.
Tackling the cost issue, economic operation of the GPM system depends heavily on the construction cost of the shaft, which is surprisingly low. This is because the GPM system will require less excavation per storage capacity than many existing pumped storage hydro facilities and because that excavation uses proven technology from the open pit mining industry. A small footprint and unobtrusive operation will allow installations to be constructed even in dense urban areas.
Advantages include: modularity; use of existing technology; environmental compatibility; flexible siting; fast permitting; rapid construction; low cost per megawatt-hour; long lifetime; high efficiency; and a short time from project start to revenue.
The Gravity Power Module
Generating Power Storing Energy
GPMs (Gravity Power Module’s) will utilize Francis-type pump-turbines capable of providing high efficiency at high head(pressure) in both the pump and turbine modes. These same pump-turbines are also the core technology behind PSH and are traditionally custom designed using a trial-and-error iterative process that requires several years for development. However, a steadily improving knowledge of hydrodynamics and computational fluid dynamics (CFD), coupled with vastly improved computer capability, allows for different approach: CFD – based computer-aided design.