August 24th, 2020 by Tina Casey
For all the excitement over the next big thing in lithium-ion batteries, the simple fact is that plain old water is the only large scale, long duration energy storage medium available today in the US and in many other parts of the world. The challenge is that water batteries — aka pumped hydropower — require expensive new infrastructure, which limits their application. That could be about to change, and it looks like the US Department of Energy is determined to be the change maker.
But First, A Word About Seams
To get a snapshot of how pumped hydro fits into the national energy profile, let’s go back to last week when The Atlantic published an account of the Energy Department’s ill-fated Interconnections Seam Study under the title and subtitle, “How a Plan to Save the Power System Disappeared: A federal lab found a way to modernize the grid, reduce reliance on coal, and save consumers billions. Then Trump appointees blocked it.”
The Seam study was a wide-ranging, collaborative effort aimed at enabling more electricity to hop back and forth across the US, rather than getting stuck at a “seam” that splits the nation into two grids (Texas, unsurprisingly, has a third electricity grid all to itself). The study is part of the Energy Department’s ongoing grid modernization effort, which comes down heavy on the side of renewable energy and energy storage.
The Atlantic presented the story of the Seam study as a successful attempt to block clean power. Be that as it may, seam or no seam, more renewable energy has been making it onto the grid, partly with support from other Energy Department R&D programs. There is plenty more where that came from, and energy storage will play a larger role in the future as more wind and solar come aboard.
Long Duration Energy Storage On The Cheap
That brings us to the Energy Department’s push for more and better energy storage in the form of pumped hydropower.
For those of you new to the topic, pumped hydro can take advantage of renewable energy to pump water from a lower reservoir to an upper reservoir. When the local grid needs more electricity, gravity does the rest. Water from the upper reservoir scoots downhill to run turbines, and ends up in the lower reservoir.
Allowing for variables like evaporation, runoff, and planned releases, a closed loop pumped hydro system is also a nifty way to recycle water resources. The main point, though, is that bulk, long duration energy storage can provide bottom line support for new clean power projects.
That sounds simple enough, but the devil is in the details. A number of pumped hydro energy storage sites are already in operation around the US (pumped hydro currently accounts for a 95% of bulk, long duration energy storage in the US). Some of these facilities can be upgraded to allow for more green electricity production. However, building new pumped hydro facilities means building more infrastructure, and that’s where the bottleneck is.
Site selection and cost are both key roadblocks. Building the underground infrastructure required for conventional pumped hydro is a costly, tedious, high risk venture, and there is no one-size-fits all approach.
The Energy Department has gathered up stakeholders to take on the problem from a number of angles, including an initiative to standardize and modularize pumped storage, with an eye toward reducing costs and opening up more sites for development.
Look Ma, No Underground Powerhouse
Working with the National Renewable Energy Laboratory and other partners under a funding agreement of $1.8 million, Obermeyer is focusing on cutting costs and reducing the time it takes to deploy a new pumped hydro system (for those of you keeping score at home, the firms Microtunneling Inc. and Small Hydro Consulting are collaborating in the effort).
“Key to this new design is that it does not require an underground powerhouse, which is one of the more costly, risky, and environmentally impactful aspects of PSH [pumped-storage hydropower] construction,” NREL explained in a newly published article on its website last weekend.
An economic analysis of Obermeyer’s new design indicates that ditching the underground powerhouse would result in a 45% savings in construction costs, as the main feature in a 33% reduction in overall costs for the project.
“The team also verified the computational fluid dynamics analysis of the pump-turbine’s performance; the predicted round trip efficiency makes this technology highly competitive in the energy storage technology space,” NREL enthused.
Scalable, Modular Pumped Hydro Energy Storage: How Does It Work?
Obermeyer’s contribution to the cause involves a new reversible pump turbine design. In conventional pumped hydro design, the turbines are buried deep below the surface in an underground powerhouse. The Obermeyer turbine only requires a slim, well-like structure that eliminates much of the risk and cost associated with conventional powerhouse construction.
The well-building approach solved those problems, but it created another one. Obermeyer had to design a much more compact pump that could perform a 180-degree reversal in the flow of the water. In comparison, turbines in a conventional powerhouse only need to push the flow 90 degrees.
The R&D team expected a loss of efficiency from their extra effort, but instead they received a pleasant surprise.
“This novel arrangement required a coaxial diffuser, which unexpectedly outperformed a traditional scroll case diffuser and yielded a net efficiency bonus rather than the anticipated efficiency penalty,” observed Obermeyer Hydro president and chief engineer Henry Obermeyer.
Obermeyer cites the following advantages for its design:
“Submersible machines are compact and factory assembled and tested, reducing on-site work and construction costs.
“Energy storage within the power converter equipment provides virtual instantaneous transition between supplying and absorbing energy from the grid.
“Geologic risk and constraints are reduced, opening more potential sites to economical development.”
The team also took inspection and maintenance into account. The turbines can be raised by water pressure to allow for above-ground work.
The Long Duration Difference
Currently, just a handful of utility scale lithium-ion batteries are operating around the US, with the largest weighing in at the 30-megawatt range. That’s pretty good, but NREL is eyeballing pumped hydro for bigger energy storage projects — up to 100 megawatts.
Considering that only a fraction of existing dams in the US are used for power generation, an economical pumped hydro system could blow the field wide open for wind and solar developers.
A previous Energy Department study teased energy storage fans with the promise of a significant impact on the nation’s electricity grid for pumped hydro, if only the bottom line case could be made for constructing new facilities.
The study forecast only ran to 2020, though. With new developments like the Obermeyer turbine, the coming years could look quite different.
The results should be trickling in soon, so stay tuned for more on that.
As for the Seam study, it is still floating around on the NREL website for all to see.
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Image: “Obermeyer’s reversible pump turbine is enabling PSH projects to deploy with less substantial civil construction and equipment component costs. Illustration courtesy of Obermeyer Hydro Inc.” via NREL.
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