For nearly 100 years, pumped storage hydropower (PSH) has helped power the United States. Today, 43 PSH facilities across the country account for 93% of utility-scale energy storage. As the nation works to transition to clean energy, this hydropower technology will play a crucial role in achieving that goal.
Traditional PSH facilities contain two reservoirs, one at a higher elevation than the other. During periods of high energy production, excess energy can be used to pump water up into the higher reservoir. When energy demand is high, PSH facilities can release water from that higher reservoir into the lower pool. When the water flows downhill, it spins a turbine, running a generator and producing clean power. Now, water power experts are developing new approaches to the traditional PSH facility model and presenting new opportunities for hydropower.
The Furthering Advancements to Shorten Time (FAST) Commissioning for PSH Prize, which launched in 2019, challenged innovators to propose new solutions, designs, and strategies that would reduce the time, cost, and risk of commissioning PSH projects. Teams presented ideas focused on improving construction equipment, using new construction management methods and advanced manufacturing techniques, and implementing other groundbreaking ideas.
Three teams won the grand prize:
- Doug Spaulding of Nelson Energy and Golder Associates: Use of Modern Tunnel-Boring Machines for Underground Pumped Storage
- Gordon Wittmeyer of Southwest Research Institute: Accelerating PSH Construction with Steel Dams
- Tom Eldredge and Hector Medina of Liberty University: Modular Closed-Loop Scalable Pump Storage Hydro
These winners have continued advancing their work to improve PSH development by testing, completing further analysis, and identifying potential sites for their technologies.
Using Modern Tunnel-Boring Machines for Underground Pumped Storage
Historically, PSH facilities depended on a certain set of geographical features, like elevation differences or proximity to existing reservoirs or lakes. But what if PSH facilities were no longer limited by these landscapes?
Spaulding and team are working to solve this exact geographical challenge with their twofold concept: an underground construction method paired with practically placed PSH plants. The team proposed a construction method for underground PSH facilities using tunnel-boring machines (TBMs) to excavate channels between natural aquifers, mimicking the function of upper and lower reservoirs in a closed-loop PSH facility. Compared to traditional methods, TBMs require less construction, equipment, and time, which can reduce costs and decrease excavation time by 50%.
Typically, PSH facilities use underground excavation to create locations for the powerhouse (the structure containing pump-turbines connected to an electric generator) and penstocks (enclosed pipes for moving water), but Spaulding and his team’s innovation uses TBMs to build a PSH facility that exists and operates fully underground. These underground facilities could expand PSH to be more abundant in places like Texas or the Midwest, where the land is fairly flat and groundwater is plentiful. These areas also have sufficient and growing solar and wind energy infrastructure, with already existing transmission lines, meaning additional transmission infrastructure would likely not have to be built to support these projects.
Since the competition, the team worked with Pacific Northwest National Laboratory and Argonne National Laboratory to identify locations of groundwater sources, like aquifers, for potential underground PSH sites. They also produced economic and cost-benefit analyses for sites in the Midwest with reliable groundwater resources, potential head (the vertical distance that water falls), and proximity to transmission lines. The team is now considering potential sites to pilot their tunnel boring technique and underground PSH project.
Accelerating PSH Construction with Steel Dams
Wittmeyer and team focused on reducing the time and cost associated with constructing PSH facilities using modular steel dams to create reservoirs. Using modular construction, the steel dams would be built off-site, under controlled conditions, and using standardized, prefabricated materials. As a result, the team’s approach could reduce construction costs by one-third and cut schedules in half.
Since the competition, the team has developed new methods for installing modular steel dams based on a PSH facility’s anticipated capacity for power output and available head. The National Renewable Energy Laboratory supported the team by creating a tool that helps developers understand the associated costs for a PSH project’s specifications and materials—allowing them to ultimately choose which modular steel dam configuration is best for their site.
Wittmeyer is now working with experts at the Southwest Research Institute to create better structural designs for different types of modular steel dams.
Utilizing Modular, Closed-Loop, Scalable Pumped Storage Hydropower
The Eldredge-Medina team focused on modular, closed-loop, scalable PSH systems (mcs-PSH), where both upper- and lower-level reservoirs are isolated from a free-flowing water source like a river. They aimed to reduce the time and cost to build such facilities by standardizing components such as penstocks and water bladders, which serve in place of the upper and lower reservoirs.
After completing the FAST Prize, the Eldredge-Medina team focused on assessing their system’s performance by simulating water movement through their high-density polyethylene penstocks and water bladders (membranes). They also investigated pumping mechanisms that could be used to push water between the upper and lower reservoirs, or in this case, the membranes.
Additionally, the team performed an economic analysis to better understand costs associated with mcs-PSH. Through a comparative economic analysis, they looked into other benefits, like coupling solar power with PSH. While the analysis is not yet complete, the team estimated installed system costs with and without solar panels for system capacities ranging from 100 kW to 10 MW, and initial results appear promising for mcs-PSH systems.
The team is scouting potential locations in southwest Virginia where this technology could be successfully implemented, while continuing to further their research through membrane filter and design optimization tests.
The Eldredge-Medina team is looking ahead to their upcoming fatigue testing at the Liberty University School of Engineering. The test will evaluate the membrane filter performance so the team can analyze its lifespan and estimate costs of these small-scale PSH systems.
PSH technologies have made incredible advancements since first being used in the United States in 1930. Innovations such as those from the FAST Commissioning for PSH Prize continue to propel this technology forward and move the United States closer to achieving its clean energy goals.
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