Bison Peak Pumped Storage

Bison Peak Pumped Storage would be a closed-loop project located in the Tehachapi Mountains in Kern County, California. The site is exceptional for a number of reasons. These include:

  • very high head (vertical drop) over a short distance, which makes for a more efficient and economical pumped storage project and lower water requirement;
  • proximity to thousands of megawatts of wind and solar resources in the Tehachapi Renewable Energy Zone;
  • a footprint entirely on private property.

The project was originally conceived at a scale of 1,000 megawatts, with water storage capacity of nearly 5,000 acre-feet. The concept has been significantly downsized, with scale at 360 to 480 megawatts (depending on lower reservoir alternative) and a fill water requirement of only 1,300 acre-feet.

Project Questions and Answers

Why this project, in this location?

California has one of the highest renewable energy standards in the nation. The vast majority of the energy meeting this standard is in the form of wind and solar energy, both of which are variable and intermittent in nature. The California grid is already seeing a significant amount of solar “over-generation” due to the fact that solar peaks mid-day, while the greatest need is in the early evening. Furthermore, significant amounts of fossil and nuclear generation are being retired. This leaves a need for both energy storage and for flexible generating capacity. Pumped storage offers both: flexible, fast-responding generating capacity that is fueled by surplus renewable energy.

Pumped storage costs vary widely from site to site. An economically viable site will offer high head (vertical drop) over a short distance. The higher the head, and the better to “length to head” ratio, the smaller the water requirement for the same energy storage capacity, and the smaller (and less expensive) will be all of the project components. Bison Peak offers heads between 2,100 feet (which would be highest in the nation) and 3,000 feet. A good pumped storage site will also have topography amenable to the construction of reservoirs with the smallest dams and amount of earth-moving required. Bison Peak meets these basic physical criteria extremely well.

Proximity to transmission is also an important factor. The Tehachapi Renewable Energy Zone is a crossroads of major transmission lines linking north and south, and supplying renewable energy to the L.A. basin and beyond.

Environmental and land use compatibility is critical as well. Bison Peak Pumped Storage would have a small footprint for its proposed generating and energy storage capacity, and impact would be primarily during the construction phase. Environmental review ramps up through the permitting process, with many opportunities for stakeholder input. If showstoppers are identified, the project cannot proceed. If there are negative impacts that can be mitigated, then mitigation plans are developed. In California, the environmental review process is particularly rigorous, and we look forward to taking the project through this stringent process.

A source of fill water is obviously critical as well. With the project downsized to a 1,300 acre-foot requirement, and with multiple sources available, it appears that the site meets this requirement. Confirming water sourcing is an ongoing high priority for project development.

What is a preliminary permit?

Nearly all pumped storage projects require a license from the Federal Energy Regulatory Commission before they can be constructed. A preliminary permit is the first step in the licensing process. It is essentially an announcement that a potential project is being studied, and it serves as a placeholder until a license application is filed. The term “permit” is misleading in that the preliminary permit does not actually grant the applicant permission to do anything. In fact, feasibility studies can be conducted without a preliminary permit, and the applicant always needs permission from property owners to enter their property to do any on-site studies.

Gridflex Energy, LLC prepared and filed a preliminary permit application on behalf of Covington Mountain Hydro, LLC (the project-specific entity) in the summer of 2017. FERC recently granted the preliminary permit.

There is a possibility that Bison Peak is among the few pumped storage sites that would not require a FERC license. We have filed a Declaration of Intention with FERC in order to get a determination on this. In the event that the project does not require a FERC license, we would have the option to either pursue FERC licensing or to forego FERC licensing, in which case permitting would be entirely at the county and state levels.

Doesn’t a FERC license convey the power of eminent domain? Will any private lands be taken under this process?

Theoretically, a FERC license (not a preliminary permit) conveys the power of eminent domain. That power would have to be exercised through federal court. However, no private developer of pumped storage that has been granted a FERC license has ever used eminent domain authority.

We believe that a project that could require the use of eminent domain has poor prospects of success. We fully expect that win-win land use agreements would be worked out with all property owners within the project footprint long before the project completes its permitting and licensing phase.

The preliminary permit application indicates that the upper reservoir would be at the top of Covington Mountain but there are three lower reservoir alternatives. Why?

We have identified three possible locations for a lower reservoir, and all three were included in the application in order to be clear on all the possibilities we were considering. Each one is very different from the others in terms of location, access, construction requirement, and vertical drop from the upper reservoir. One lower reservoir site would be selected after additional studies and consultations are conducted.

If this project continues through development, how long would it be until construction begins?

If the project were to progress at maximum pace, we expect that it would take at least three years to complete licensing and permitting activity. It could take longer, however, because the pace of development activity is driven in part to success in marketing the project to regional utilities.

Doesn’t pumped storage require more energy to pump than it generates?

Yes. It is not an energy source, but functions like a giant battery, with a round-trip efficiency of 75-80%. The reason why it makes sense to use it is to make much more effective use of renewable energy. In order to have dependable generation, utilities cannot rely on wind and solar alone. Natural gas is a common “firm” power supply in California. However, natural gas combustion is not free and it produces greenhouse gases. It also has no ability to make more effective use of renewable energy.

Pumped storage, by contrast, can take energy produced by windfarms at night and shift that energy to daytime availability. It can take solar energy produced at 1:00 PM, when it is peaking but not as useful, to the late afternoon peak demand period. It can switch from pumping to generating rapidly, depending on system conditions. It can also provide grid support services on a 24 x 7 basis. For all of these reasons, and because it is such a long-lasting resource, a good pumped storage site (like Bison Peak) is an excellent long-term power resource.

How much water would this project require? Where would it come from? What about evaporation loss?

As currently proposed, the project would require 1,300 acre-feet of water for the closed-loop pumped storage cycle. That water would either come from groundwater sources within the project footprint (if confirmed available), or purchased from a local water agency (either the Tehachapi Cummings County Water District or the Antelope Valley-East Kern Water Agency). If the latter, a temporary water supply line would be required.

We are investigating the possibility of cutting evaporation loss by 90% or more through the use of floating disks similar in nature to the “bird balls” used by LADWP to cover some of its reservoirs.

What about seismic concerns? How do they affect the viability of the project?

Seismic risk will be a key focus in engineering reviews and design, and state of the art design would be employed. Any dams would need to satisfy the requirements of the California Division of Dam Safety.

Aren’t batteries falling in cost and able to meet California’s need for energy storage?

Utility-scale batteries have been falling in cost, but they remain more expensive than pumped storage projects with the quality of a Bison Peak. This is particularly true as the storage duration requirement exceeds the few hours of storage for which batteries are economical. One of the biggest advantages that pumped storage has over batteries is lifespan: battery cells have estimated lifespans of 5 to 15 years, depending on utilization pattern. A pumped storage plant has a useful life of 60 years or more (virtually none have ever been retired).

There are also growing concerns about what to do with spent battery materials (recycling of lithium ion batteries is still at an early stage of development), and with the impacts of mining lithium, cobalt, and other minerals used in utility-scale batteries. Thus, the investment in Bison Peak Pumped Storage would be a far better deal for ratepayers and for the environment than would batteries at an equivalent scale and capability.

Would the project be constructed exactly as it is described in the preliminary permit application?

Not necessarily. The preliminary permit includes a preliminary design concept. Elements can change along the way through the development and permitting process depending on feasibility studies, engineering studies, stakeholder input, and environmental reviews. This includes the composition of dams, the diameters of conduits, and precise placements and sizes of elements.

Are there other projects like this operating in California?

Yes. These include Helms Pumped Storage (1,200 megawatts operated by PG&E), Castaic Pumped Storage (1,500 megawatts operated by LADWP), and Lake Hodges (40 megawatts operated by SDG&E). The first two have far larger footprints than Bison Peak would have because they are much larger in generating capacity, have significantly lower heads, and have longer storage durations than are required in today’s energy market.

How can I follow what is happening with this project?

We will periodically update this web page as the project proceeds. Interested parties can follow the progress at the FERC licensing level by registering for notifications at  The docket number assigned to Bison Peak is P-14850.

How can I reach Gridflex Energy directly with questions or comments about this project?

You can contact Matthew Shapiro, CEO, at, or via phone at (208) 246-9925.