Closed-Loop Pumped Storage Hydropower Supply Curves

Resource potential is often assessed in terms of geographic (or resource), technical, and economic potential—each of which represents a succession of additional complexity and input assumptions that leverage similar data and a common analysis flow.

This closed-loop PSH resource assessment is accomplished by first applying high-resolution digital elevation models (30-meter resolution) to identify potential upper and lower reservoirs within the technology parameters specified by the NREL adaptation of the ANU model. Design specifications include minimum 200-meter head height, a maximum 750-meter head height, discrete available dam heights of 40, 60, 80, and 100 meters, and a maximum conveyance length between upper and lower reservoir of 12 times the head height. This yields a large set of potential reservoirs with many overlaps.

Once the reservoirs are delineated, technical potential criteria are applied to appropriately limit the development areas. The current criteria eliminate any reservoirs that intersect existing water bodies and waterways; glaciers and ice-covered areas, protected federal lands; urban areas; critical habitat areas; or are within 1000 feet of a wetland. Optional criteria can eliminate reservoirs intersecting roads or farmland or allow reservoirs intersecting ephemeral streams.

The remaining upper and lower reservoirs after applying technical potential criteria are paired by comparing upper and lower reservoir capacity to be within 10% of each other, applying the 12X distance criteria, and finally evaluating total paired system cost. The paired reservoirs are then optimized for lowest cost systems to develop a non-overlapping reservoir data set for each combination of assumed storage duration (8, 10, or 12 hours in this data set) and optional technical potential criteria. Total costs include both hydropower site and transmission development. The site development costs are taken from ANU's pumped hydro energy storage cost model with costs adjusted to align with industry expectations published in 2020 Grid Energy Storage Technology Cost and Performance Assessment, U.S. Department of Energy Technical Report (2020). In addition, transmission spurline costs are taken from NREL analysis supporting the ReEDS model. See ReEDS Model Documentation Version 2020, NREL Technical Report (2021).

Ultimately, this exercise results in a spatially resolved characterization of the technical potential quantity, quality, and cost of PSH resources, which can be sorted to represent a "supply curve" for a specific scenario. The figure below plots the supply curve of closed-loop PSH cost versus cumulative generating capacity for the contiguous United States for 8-, 10-, and 12-hour storage durations and the default assumptions for where to prohibit or exclude closed-loop PSH construction. Resource and cost data binned by cost ranges is also included in the NREL Annual Technology Baseline beginning in the 2022 data year.

The latest (2nd generation) data set includes several updates and changes. Incorporating stakeholder participation and review, the updated data better reflects the range of technical possibilities for designing closed-loop PSH in the United States. It also integrates updated geospatial data where possible and includes multiple scenarios for storage duration, dam height, and several site exclusion criteria. While some changes limit the range of system specifications to better capture realistic design constraints, multiple dam heights and a lower minimum head lead to many more sites being identified in the 2nd generation data set.