Frequently Asked Questions

+ Why haven’t there been any new pumped storage plants built in the US recently?

All the large existing plants in the US were built from the 1960’s through the 1990’s during an era when it made economic sense to use low-cost, night-time ("off-peak") nuclear energy or coal generation for pumping, and to use the stored energy during the day ("peak") when it could replace expensive oil-fired generation. In the 1990’s, natural gas became the fuel used in most new power plants. The difference in price between off-peak and peak shrank, making energy storage less economically viable. Fracking further reduced the cost of producing peak power with natural gas. Today, the shift to low/zero-carbon electric power from renewable resources like wind and solar, along with a need for new dependable generating capacity during shifting peak/off-peak times, is creating a new need for utility-scale energy storage. Pumped storage hydro has an important role to play in meeting this need.

+ Why do pumped storage plants take up to a decade to develop and build?

Pumped storage plants take a substantial amount of time to develop. One reason is that each site and project is unique. As complex civil projects, they require several stages of site-specific engineering, with each step being progressively more detailed. Permitting also takes time. Since most pumped storage projects require a license from the Federal Energy Regulatory Commission (FERC), they must meet stringent federal environmental standards (along with all applicable state and local standards). The timeline for scoping, studies, agency and public review is significant. Construction time is also significant, typically taking 4 to 6 years. This is due to the size and complexity of civil works, including reservoirs and underground works like tunnels and the powerhouse.

+ Are there actually any good sites left for new pumped storage in the US?

Yes. However, ideal pumped storage sites are rare. A developable pumped storage site must have the right combination of physical features, low to moderate environmental sensitivity, proximity to transmission lines, and a source of fill water, among other factors. There must also be a nearby market for the kind of products and services that a pumped storage plant offers.

+ Don’t pumped storage projects have large, even unacceptable, environmental impacts?

Any pumped storage project will have an impact and alter a landscape, if only within a small area. However, every project is unique and its impacts and sensitivities will vary widely from site to site, project to project. As with any kind of facility, site selection must be done carefully, avoiding areas that are too sensitive from biological, social, cultural, recreational, visual, and other standpoints. In addition to careful site selection, the project concept (i.e., features, footprint, access, etc.) must consider what is likely to be acceptable. Where projects are taken forward into development, studies must be undertaken to determine what the impacts of construction and operation would or could be, what steps can be taken to minimize and mitigate impacts, etc. The developer must also consult stakeholders and agencies early, often, and throughout the entire development process. rPlus Hydro takes great care to select sites that entail lower risks for environmental and land use conflicts.

+ How much water do pumped storage projects use? Isn’t this a problem in arid regions?

Pumped Storage Hydro represents a non-consumptive water use. The water use of a pumped storage project includes (a) the amount needed during the construction phase, (b) the amount of water used for the ongoing operation, and (c) make-up water for evaporation and seepage. Total water need will be driven primarily by project size, desired storage duration, and project head (vertical drop). Head has a direct relationship to the amount of water needed. rPlus pays great attention to the water sourcing aspect of our projects. The fill water amount for each of our projects ranges from 2,000 acre-feet to 10,000 acre-feet. It’s critical to note that this is not an annual or “consumptive” volume, but a one-time fill or the amount needed for cycling up and down in the pumped storage operation. Generally speaking, the amounts of water needed for rPlus’ proposed projects are very small in relation to resources and consumptive uses in their respective areas. In some areas, we are considering the potential for covering reservoirs in order to reduce or virtually eliminate evaporation loss. And for at least one project, we are also looking at the potential to use treated effluent (wastewater) as a project fill source.

+ What economic benefits do pumped storage projects create?

The capital investment, construction requirements, and long lifespan of our projects means that they produce very significant economic benefits for local communities. Projects will employ 300-500 construction workers for a period of 4-5 years, with the multiplier benefits of that spending translating into significant local income. During operation, projects are expected to employ up to 35 full-time staff. Personal and property tax revenues will also be significant, with most projects being capital investments of $1-3 billion and having useful lives greater than 75 years.

+ Who is FERC and what is their role?

FERC is the Federal Energy Regulatory Commission. Most hydroelectric projects require a license from FERC before they can begin construction. Since even closed-loop pumped storage projects fall into the category of “hydropower,” most pumped storage projects will require a FERC license. FERC conducts the Environmental Impact Study process that is ultimately needed for most pumped storage projects. FERC may or may not be involved in the early development stage, depending on the process that the project is using. The initial license that FERC issues is typically for a period of 50 years.

+ Can pumped storage reservoirs be used for recreation (e.g., fishing?)

For most new reservoirs built specifically for pumped storage, as in the case of “closed-loop” projects, the reservoirs are sized only for power operation and can experience dramatic elevation changes throughout any given day. For safety and other reasons, they are not available for recreational use.

+ Don’t pumped storage plants use more energy than they produce? How efficient are they?

As with all energy storage technologies, there is some loss of energy in the round-trip cycle of pumped storage operation. The value added to energy by being able to store it, along with the services provided by the pumped storage plant, more than makes up for the energy loss. With regard to efficiency, most new pumped storage plants will have round-trip efficiencies of 77-80%.

+ Why do we need pumped storage hydro when we can use large-scale batteries?

Both technologies will play a vital part in the modern energy transition. Batteries are playing a growing role in utility portfolios. Batteries are more modular and can be built faster. However, there are different use cases and distinct advantages for both batteries and pumped storage hydro. Wherever utilities have good opportunities for new pumped storage, that pumped storage easily earns its place in the portfolio and helps to diversify the technology base.

+ Has pumped storage technology advanced over the decades since it was first employed?

Yes. The first advancement in pumped storage technology was to combine separate pumps and turbines into a single, reversible unit. In the 1990’s, variable-speed equipment was introduced, allowing a much wider range of operation in pumping mode, among other performance enhancements that help pumped storage with its new mission of integrating renewable energy sources. A more recent advancement involves the use of full-size frequency converters for pumped storage units, affording additional performance enhancements for variable-speed units.