New Pumped Hydro Energy Storage Project Enlists 3-D Printing

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For all the excitement over new kinds of batteries, pumped hydropower is still by far the single largest form of energy storage in the US today, just as it has been for the last 100 years or so. The technology could continue to dominate for the next 100 years, too. Pumped storage is getting a 21st century makeover,with modularity, 3-D printing and subsea construction in the mix.

The Bulk Energy Storage System Of Today, Yesterday

Pumped hydropower systems deploy an upper reservoir for energy storage. When needed, gravity does the work of sending water down to a generating station below. The reservoir can be replenished partly by natural rainfall and runoff. Otherwise, it is refilled by pumping water from a reservoir or river at a lower elevation, during periods when excess electricity is available (see more pumped hydro background here).

The first pumped hydro facility in the US dates all the way back to 1929, when the 29-megawatt Rocky River station went online in Connecticut. The Rocky River project also demonstrates how human-made pumped hydro reservoirs can do double duty as recreation areas.

New Twists On Old Energy Storage Technology

Pumped hydro has a couple of significant advantages over lithium-ion and other battery formulas. A pumped hydro system can store energy much longer than a battery array, and it skirts the supply chain issues that bedevil battery stakeholders. Nevertheless, the Energy Department lists only 40 or so pumped storage projects in the US.

One obvious obstacle to leap is the availability of suitable geography and water resources. In addition, even where the conditions are right for energy storage, pumped hydro proposals can run up against nature conservation and cultural heritage priorities.

Some innovators are looking to expand the field of accessible locations by repurposing abandoned coal fields, underground rock formations, and other unconventional sites. The US Department of Energy has also contributed to the energy storage innovation pot, in an effort to double the capacity of the nation’s current fleet of pumped hydro facilities. One example is the GLIDES project under the wing of Oak Ridge National Laboratory, aimed at opening up opportunities to deploy small scale, modular pumped hydropower technology.

75 Terawatt-Hours Of Pumped Hydro Energy Storage Potential

In the latest development, last week the Energy Department’s Water Power Technologies Office tapped the US clean tech startup Sperra for a $4 million grant that sends the pumped hydro energy storage field off in a new direction.

Sperra specializes in fabricating 3-D printed structures for subsea use, including anchors for floating solar solar arrays, offshore floating wind turbines, and wave energy converters.

With the $4 million award, WPTO has tasked Sperra with applying its technology to design and deploy a subsea energy storage device measuring 10 meters in diameter, to be positioned off the coast of California. The capacity of the demonstration-scale unit is just 500 kilowatts (or 600 kilowatt-hours), but the project has already caught the eye of energy stakeholders in Europe.

The German Ministry for Economic Affairs and Climate Action almost doubled the WPTO award with a grant of $3.7 million USD (about €3.4M), aimed at fleshing out the project with pumping and offshore wind turbine elements administered by  the applied research institution Fraunhofer IEE and the underwater pump specialist Pleuger Industries GmbH. The total of $7.7 million builds on previous funding for the project through the California Sustainable Energy Entrepreneur Development program and the New York State Energy Research and Development Authority.

In a press statement announcing the new awards, Sperra noted that the subsea energy storage potential of the US is somewhere around 75 terawatt-hours, more than double the estimated potential for comparable onshore pumped storage systems. “SPSH [subsea pumped storage hydropower) with 3D-printed concrete will accelerate the energy transition, employing local labor and using immediately available materials,” enthused Sperra CEO and Founder Jason Cotrell.

Other partners in the project include the engineering and design firm WSP USA along with Purdue University and the National Renewable Energy Laboratory.

Subsea Energy Storage: How Does It Work?

Sperra also notes that the California project builds on a longrunning subsea energy storage program of Fraunhofer called StEnSea, short for “Stored Energy in the Sea” (StEnSea)

As described by Pleuger, StEnSea began to take shape back in 2012 with the aim of adapting pumped storage for undersea deployment, leveraging the natural force of deep sea water pressure. In effect, the concrete structure fulfills the function of a lower reservoir, and water pressure pulls duty as the upper reservoir.

“The project utilises a unique approach to energy storage by placing hollow concrete spheres on the seabed at depths of 600 to 800 meters. When electricity demand is low, these spheres are emptied of water using PLEUGER’s specially designed submersible pumps to store potential energy,” Pleuger explains.

“During peak demand, water is allowed to flow back into the spheres, turning the pumps into turbines that generate electricity. This innovative method mirrors the functionality of traditional pumped storage hydropower but adapts it for the subsea environment, leveraging ocean pressure to store and release energy efficiently, Pleuger adds.

Pleuger notes that other initial targets for deployment include Norway, Portugal, Brazil, and Japan. In addition to subsea conditions, proximity to energy-hungry cities and seaports is another key element for site selection.

Many Roads To Subsea Energy Storage

If this is beginning to ring some bells, you may be thinking of a variation on subsea energy storage proposed by the Dutch firm Ocean Grazer, a startup that spun out of research at the University of Groningen back in 2014. The company’s “Ocean Battery” technology crossed the CleanTechnica radar in 2022 when it earned a Best of Innovation award at the 2022 Consumer Electronics Show in Las Vegas, partly on account of a business model that leverages the locations of pre-approved offshore wind farms.

In a departure from the StEnSea approach, the Ocean Battery is a closed loop system that deploys two reservoirs. The lower reservoir is a rigid structure made of concrete, buried under the seabed. The upper reservoir is a flexible bladder that sits on top of the seabed.

“Potential energy will be stored in the form of water under pressure in the flexible bladder. When there is demand for power, water flows back from the flexible bladder to the low-pressure rigid reservoir. This would in turn drive several hydropower turbines to generate electricity,” explains the engineering and consultancy firm Stantec, which is helping Ocean Grazer bring its technology into the demonstration phase.

When electricity demand is low, water will be pumped from the buried reservoir back up the bladder. That closed-loop design could help Ocean Grazer avoid environmental concerns related to the open-ended use of seawater, though that remains to be seen. Keep an eye on the sprawling OranjeWind offshore wind project in the Netherlands, where plans include a trial of the company’s subsea energy storage solution.

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Image (cropped): A new US energy storage project will adapt the power of pumped storage hydro to subsea locations near offshore wind farms and energy-hungry coastal cities, leveraging 3-D printing and the natural force of water pressure (courtesy of Pleuger Industries).