A Comparison of the Environmental Effects of Open-Loop and Closed-Loop Pumped Storage Hydropower April 2020 PNNL-29157 Acknowledgments This work was authored by the Pacific Northwest National Laboratory (PNNL), operated by Battelle and supported by the HydroWIRES Initiative of the U.S. Department of Energy (DOE) Water Power Technologies Office (WPTO), under award or contract number DE-AC05-76RL01830. HydroWIRES Initiative The electricity system in the United States is changing rapidly with the large-scale addition of variable renewables. The flexible capabilities of hydropower, including pumped storage hydropower (PSH), make it well-positioned to aid in integrating these variable resources while supporting grid reliability and resilience. Recognizing these challenges and opportunities, WPTO has launched a new initiative known as HydroWIRES: Water Innovation for a Resilient Electricity System.1 HydroWIRES is focused on understanding and supporting the changing role of hydropower in the evolving electricity system in the United States. Through the HydroWIRES initiative, WPTO seeks to understand and drive utilization of the full potential of hydropower resources to help reduce system-wide costs and contribute to electricity system reliability and resilience, now and into the future. HydroWIRES is distinguished in its close engagement with the DOE National Laboratories. Five National Laboratories—Argonne National Laboratory, Idaho National Laboratory, National Renewable Energy Laboratory, Oak Ridge National Laboratory, and PNNL—work as a team to provide strategic insight and develop connections across the DOE portfolio that add significant value to the HydroWIRES initiative. HydroWIRES operates in conjunction with the DOE Grid Modernization Initiative,2 which focuses on the development of new architectural concepts, tools, and technologies that measure, analyze, predict, protect, and control the grid of the future, and on enabling the institutional conditions that allow for quicker development and widespread adoption of these tools and technologies. HydroWIRES also operates in conjunction with the DOE Energy Storage Grand Challenge,3 the vision of which is to create and sustain global leadership in energy storage utilization and exports, with a secure domestic manufacturing supply chain that does not depend on foreign sources of critical materials. Acknowledgments The report author is grateful for the financial and technical support provided for this effort by the WPTO, as well as the guidance and assistance provided by WPTO’s Dana McCoskey, Tim Welch, Alejandro Moreno, Samuel Bockenhauer, Hoyt Battey, and Miles Hall. The author also acknowledges the guidance and assistance provided by PNNL colleagues Rebecca O’Neil, T.J. Heibel, Alison Colotelo, Philip Meyer, Kendall Mongird, Dave Goodman, Susan Tackett, and Shannon Bates. The author thanks Nicole Samu and Shelaine Curd at Oak Ridge National Laboratory for their assistance with data and graphics from HydroSource.4 The author also thanks the six professional colleagues who conducted external reviews of the draft version of this report. Finally, the author dedicates this report to Mike Sale, a great friend and colleague and a true Hydropower Visionary. 1 https://www.energy.gov/eere/water/hydrowires-initiative 2 https://www.energy.gov/grid-modernization-initiative 3 https://www.energy.gov/energy-storage-grand-challenge/energy-storage-grand-challenge 4 https://hydrosource.ornl.gov/ A Comparison of the Environmental Effects of Open-Loop and Closed-Loop Pumped Storage Hydropower Bo Saulsbury April 2020 Results in Brief • Pumped storage hydropower (PSH) is characterized as either open-loop (continuously connected to a naturally flowing water feature) or closed-loop (not continuously connected to a naturally flowing water feature). All of the 43 PSH projects operating in the United States are open-loop, so the environmental effects of closed-loop are not well-documented. • This report: (1) compares the potential environmental effects of constructing and operating open- loop and closed-loop PSH projects; (2) describes how effects are avoided, minimized, or mitigated at existing and proposed projects in the United States and other countries; and (3) discusses the relative significance of the environmental issues. • The report concludes that the environmental effects of closed-loop projects are generally lower (i.e., more localized and of shorter duration) than those of open-loop projects because they: (1) are located “off-stream,” potentially minimizing aquatic and terrestrial impacts, and; (2) often have greater siting flexibility than open-loop projects. • In particular, the impacts to aquatic resources are typically lower for closed-loop projects than for open-loop, as closed-loop projects are not continuously connected to any naturally-flowing body of water. This avoids the movement of water between reservoir and free-flowing water that drives many impacts of open-loop projects. For closed-loop projects, the impacts on aquatic resources are primarily related to the initial withdrawal of surface water for reservoir fill, which could reduce the availability of surface water for other uses. • However, for both above-ground and underground closed-loop projects using groundwater, impacts to geology and soils and groundwater could generally be higher than those of open-loop. Closed-loop projects using groundwater as the source for initial filling of their reservoirs and replacing evaporative and seepage losses may impact groundwater quality due to the effects on groundwater circulation patterns and chemistry. Impacts to groundwater quantity resulting from the large quantities of water necessary for reservoir fill and refill could reduce the availability of groundwater for other uses. • There is one specific circumstance in which the impacts of constructing the new upper reservoir and power generation facilities could be lower than those of constructing a new closed-loop project: open-loop projects where the lower reservoir was already constructed for other purposes and an upper reservoir is added later for PSH operations (i.e., an “add-on” project). However, the impacts of project operations would still likely be higher than for closed-loop because the add-on project’s lower reservoir is still continuously connected to and affects a naturally flowing water feature. v Executive Summary Background Pumped storage hydropower (PSH) is a type of energy storage that uses the pumping and release of water between two reservoirs at different elevations to store water and generate electricity (Figure ES-1). When demand for electricity is low, a PSH project can use low cost energy to pump water from the lower reservoir to the upper reservoir for storage. When demand for electricity is high, a PSH project can release water from the upper reservoir through a powerhouse to generate electricity. Traditionally, this meant that PSH plants generated power during the day and pumped at night, with modest diurnal or seasonal variation. Today, PSH pumping operations are changing to facilitate the integration of the tremendous growth of variable renewable energy (VRE) generating resources, especially wind and solar, on the U.S. grid. PSH facilities are often a least cost option for high capacity (both energy and power), long-duration storage, and can provide the flexibility and fast response that a high-VRE-penetration grid requires. PSH faces its own set of challenges in construction and operation, however, including high initial capital costs, long construction timeframes, uncertainty in revenue streams (similar to all storage), and potential environmental impacts. The U.S. Department of Energy’s (DOE) HydroWIRES initiative includes research to address each of these challenges. This report focuses on potential environmental impacts: specifically, the degree to which impacts can be reduced by using closed-loop pumped storage systems as opposed to the traditionally more common open loop systems. Figure ES-1. Generic comparison of open-loop and closed-loop PSH projects. (Source: DOE 2019) vii Closed-loop vs. Open-loop PSH PSH facilities can be characterized as either open-loop or closed-loop (Figure ES-1), with respect to their connectivity to other water bodies. DOE defines open-loop PSH as “continuously connected to a naturally flowing water feature,” and closed-loop PSH as “not continuously connected to a naturally flowing water feature” (DOE 2016; 2019). The term continuously is key in these definitions because some PSH projects are considered closed-loop even though they could withdraw water from naturally flowing surface water features initially to fill their reservoirs and periodically to replace evaporative and seepage losses. In contrast, open-loop PSH projects typically involve damming a naturally flowing water feature to create the lower reservoir. In its 2019 rulemaking on an expedited licensing review process for closed-loop PSH projects, the Federal Energy Regulatory Commission (FERC) defines certain qualifying criteria for closed-loop projects. Two of the criteria state that a project “utilize only reservoirs situated at locations other than natural waterways, lakes, wetlands, and other natural surface water features;” and “rely only on temporary withdrawals from surface waters or groundwater for the sole purposes of initial fill and periodic recharge needed for project operation” (FERC 2019a). The FERC criteria do not change the basic definition of closed-loop PSH; rather, they simply define