The US Department of Energy has been eyeing pumped hydro energy storage for a makeover, and it looks like they have a winner. Texas company Quidnet Energy just won a $10 million grant to put the finishing touches on a new type of “water battery” that deploys underground rock formations rather than having to rely on elevated reservoirs.
Storage of pumped hydro energy 101
For those of you new to the subject, pumped hydropower is an ancient one gravity based energy storage technology that has taken on a new relevance in the era of wind and solar energy.
The idea is to pump water to a higher reservoir when excess wind or solar power is available. When needed, water from the reservoir flows downhill to a power plant, where it spins turbines to generate electricity.
Pumped hydropower can run on a closed loop system, in which the same water circulates between the upper and lower reservoirs. Pumped hydro systems can also be designed as an open loop, where water is pumped from a river or other natural body of water to a reservoir and then discharged again after it leaves the power station.
Water batteries go underground
These “water batteries” are still an important part of the energy storage landscape in the US. Despite all the buzz about new lithium-ion technology and other emerging energy storage systems, pumped hydro still accounts for about 93% of utility-scale energy storage capacity in the US.
The Energy Department has 43 existing pumped hydro plants in the US and wants to double their combined capacity. The problem is that conventional water batteries involve a huge amount of above-ground infrastructure and they need a topography that resolves the difference in elevation. This makes it difficult and expensive to find locations for new facilities.
That’s true Why not? comes in. The company first came to the CleanTechnica radar back in 2019, when the energy department tapped the company to share in a funding round to develop new pumped hydro systems.
“The innovative technology can operate at higher temperatures than traditional PSH, achieve 95% mechanical efficiency (in both directions) and has the potential to reduce capital expenditure and energy storage solutions in relatively flat areas where conventional PSH may not be possible,” the energy department stated.
Since then, Quidnet has not slept behind the wheel. The new $10 million grant comes through the Department of Energy’s advanced ARPA-E funding agency, which focuses on supporting new high-risk, high-reward technologies.
“Quidnet Energy, Inc. (Houston, TX) will scale up its Geomechanical Pumped Storage (GPS) to a commercial system at CPS Energy, the largest US municipal utility,” explained ARPA-E.
“GPS uses the Earth as a mechanical battery by storing energy as pressurized water between layers of rock. The aim is to reduce the cost of long-term energy storage by 50-75% to enable more reliable and cost-effective use of renewable electricity generation resources,” they add.
Long-term underground energy storage solution to kill coal
That’s about it in a nutshell. While the concept is new enough to attract ARPA-E, the Quidnet model uses established mechanical systems and any terrain, as long as there’s a suitable rock formation below the surface.
“To use existing drilling and hydropower machines supply chains, Quidnet Energy reuses existing resources to find quickly deployable solutions to our most pressing energy and climate challenges,” explained Quidnet.
The company also points out that the underground system is a closed system that minimizes water loss through evaporation.
If all goes according to plan, CPS Energy in San Antonio will serve as a high-profile showcase for replication. The ARPA-E funding will enable Quidnet to scale up its pilot phase system to a 1 megawatt, 10 megawatt hour commercial system that can provide electricity for 10 hours or more.
That 10-hour time frame is a vital part of the Energy Department’s effort to push utility-scale energy storage systems beyond the capabilities of lithium-ion battery technology, which bogs down after several hours.
Of long duration energy storage enables utilities to integrate more wind and/or solar energy into their grids without compromising on reliability.
For example, CPS is count on more renewable energy sources. The area’s population is growing and CPS estimates it will need to add about 115 megawatts of generating capacity annually over the next few years. Meanwhile, the utility is aiming to decommission two of its oldest power plants by 2030, the 830 megawatt Sommers gas plant and the 1,345 megawatt Spruce coal plant. Three older gas units at the Braunig plant are also about to be shut down.
The water battery revolution has only just begun
In addition to developing innovative new systems, the country’s existing fleet of pumped storage facilities has room for expansion. For example, in 2018, Duke Energy upgraded a 30-year-old pumped-hydro power system to add another 300 megawatts of capacity.
Floating solar panels on reservoirs is another way to get more clean energy from existing pumped hydro infrastructure. In Germany, for example, the company Vattenfall has started a program to install solar panels on several of its pumped power plants.
In terms of locations for new storage facilities for pumped energy, brownfield development can also play a role. In Kentucky, the Rye Energy hydropower company is looking for old coal fields new pumped hydro reservoirs.
The Swiss company Nant de Drance illustrates a different approach to the location choice dilemma. They took advantage of underground caves to build a massive 900 megawatt pumped hydropower system. Using the existing caverns allowed the company to reduce construction costs for the underground powerhouse, though the project still took 14 years to complete.
Here in the US, the Department of Energy also supports the development of a new compact underground powerhouse that can fit into a sleek, good-looking structure.
The Energy Department is also counting on closed-loop systems of some kind to expand the country’s pumped hydropower capacity. That fleet of 43 existing pumped hydropower plants consists mainly of open loop systems. The Energy Department’s National Renewable Energy Laboratory recently conducted a GIS-enabled mapping study of millions of potential sites for new closed-loop systems. After filtering for cost optimization and other factors, the lab identified thousands of potential locations for new pumped hydropower implementation of energy storage in the US, including 11,769 locations in the contiguous 48 states and 3,077 locations in Alaska, Hawaii and Puerto Rico.
Of course, most likely only a small fraction of those sites are actually developable. Not much help is a concerted effort by state-level office holders to stem the flow of investor dollars sustainable energy projects. Still, the National Hydropower Association remains hopeful. In a report released last year, the organization wants to add something to this 50 new gigawatts to the national stock of pumped hydropower storage capacity by 2050.
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Photo: Geochemically pumped hydro energy storage system courtesy of Quidnet Energy.
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