Pumped Storage

Reversible pump turbines have strict design-specific submergence requirements to suppress destructive cavitation and must therefore be installed well below tailwater level, typically in an underground powerhouse. Such facilities are expensive and require suitable geology. The cost of the required underground construction may not be justified for pump turbine installations of less than several hundred megawatts.
Obermeyer Hydro’s improved pumped storage configuration, by comparison, requires only the construction of a simple vertical well to position a novel (patent pending) submersible pump-turbine/motor- generator sufficiently below tailwater to suppress cavitation. Neither the penstock nor the tailrace tunnel need be extended to extraordinary (and expensive) depths. Sufficient submergence is readily provided to permit use of a compact and efficient single stage pump turbines directly connected to economical variable speed motor/generators. Multiple machines may be installed in conjunction with a single penstock. The simple underground structure may be constructed under a wide range of geological conditions. Geological risk is further mitigated by the fact that a limited number of borings can reliably characterize the entire excavation.
Obermeyer Hydro’s compact pump turbines can be factory assembled or final assembly may be accomplished on-site, depending on shipping constraints. In either case, all tasks requiring personnel access to the machines can be accomplished above grade. Lowering the machines into operating position and raising them to perform inspection or maintenance is accomplished using auxiliary water pressure acting on a hoisting piston beneath each machine.

The submerged reversible pump-turbine has the following advantages when compared to conventional reversible, ternary machines, or separate pumps and turbines in a buried powerhouse:

• Submersible machines are compact and factory assembled and tested, reducing on-site work and construction costs.
• Energy storage within the power converter equipment provides virtual instantaneous transition between supplying and absorbing energy from the grid.
• Geologic risk and constraints are reduced, opening more potential sites to economical development.

Reversible pump turbines with ratings of 1 MW to 100 MW, depending on head, may be economically installed with this reduced-civil-works approach.

Obermeyer Hydro, Inc. worked with the National Renewable Energy Laboratory (NREL) with support from the Department of Energy (DOE) on the development of Cost Effective Small Scale Pumped Storage Configuration. This work was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Water Power Technologies Office, DE-FOA-0001455 Award Number DE-EE0008014