Utility of Gargantuan Underwater Concrete Spheres in Ocean Depths for Storing Abundant Renewable Energy Reserves
Heading down 2,000 feet beneath the Pacific Ocean off the coast of California, a colossal concrete sphere, large enough to house several families, awaits its moment in the limelight. The pressure it faces will be 77 times greater than what we feel at sea level, yet there'll be no folks living inside. Instead, it's brimming with electricity, or at least a form of it. Welcome to the StEnSea project - Stored Energy in the Sea - an audacious endeavor aimed at tackling one of the biggest challenges of our clean energy era: storing renewable energy when the wind dies down and the sun vanishes.
A Giant Battery Born of Concrete and Water
The idea is shockingly simple. Imagine a hollow concrete sphere resting quietly on the seabed. When there's a surplus of electricity, say from an offshore wind farm, it's utilized to pump seawater out of the sphere, generating a vacuum-like condition within. Then, when energy is needed, a valve opens. Seawater rushes back in, driven by the crushing oceanic pressure, spinning a turbine in the process, which generates electricity. This cycle can be repeated hundreds of times per year.
In 2017, the Fraunhofer Institute for Energy Economics and Energy Systems Technology (IEE) tested this system with a 10-foot-diameter sphere in Germany's Lake Constance. The experiment worked. Now, they're readying for a larger, more ambitious test in the deep Pacific waters off Long Beach, California.
The new prototype, about 29.5 feet in diameter and weighing an impressive 400 tons, will be anchored between 500 and 600 meters (around 2,000 feet) beneath the waves, set to go live by the end of 2026, storing up to 0.4 megawatt-hours of electricity, enough to power a typical residence for two to three weeks.
"This test run is a substantial step towards scaling the technology," said Dr. Bernhard Ernst, Senior Project Manager at Fraunhofer IEE. "With the global energy transition, the demand for storage will skyrocket in the coming years."
The ultimate goal? Fields of 98-foot spheres blanketing the seafloor, each capable of storing far more energy than our current prototype. Fraunhofer IEE estimates a global storage potential of 817,000 gigawatt-hours - enough to power roughly 75 million homes annually.
Transforming the Ocean Floor into an Energy Vault
At its core, StEnSea is a variation of a century-old concept: pumped-storage hydroelectricity. Traditional versions involve pumping water uphill into a reservoir and releasing it downhill to generate electricity when needed.However, these require two bodies of water at different elevations and vast amounts of land.
StEnSea adroitly swaps mountain slopes for ocean depths. "We're transferring their functional principle to the seabed - the natural and ecological restrictions are much lower down there," explained Ernst. "Plus, citizen acceptance is likely to be significantly higher."
There's a practical edge, too. Offshore locations are often close to where renewable energy is produced, such as wind farms. Submerged spheres can be deployed nearby without consuming land or sparking public backlash. The deep ocean becomes the upper reservoir, and the sphere the lower one.
The prototype's construction reflects this blend of ingeniously simple design and cutting-edge engineering. Sperra, a U.S. startup specializing in 3D concrete printing, is building the massive orb in Long Beach. Pleuger Industries, based in Miami but with German roots, provides the underwater motor pumps crucial to the system. A valve at the sphere's top allows seawater to flow in or out, while the technology's elegance lies in its mechanical simplicity and the immense pressure the ocean itself provides.
"Pumped storage power plants are particularly suitable for storing electricity for several hours to a few days," said Ernst. "However, their expansion potential is severely limited worldwide."
Research conducted by Fraunhofer IEE suggests otherwise - for ocean-based storage at least. From the fjords of Norway to the coastlines of Japan, from the U.S. East Coast to the Portuguese shelf, the team has mapped numerous ideal sites. These locations, between 600 and 800 meters deep, satisfy pressure, concrete strength, and existing pump design requirements economically.
The efficiency of the system - around 75 to 80 percent - is slightly lower than traditional pumped hydro. But the lifespan of the concrete spheres is estimated at 50 to 60 years, with the turbines and generators requiring replacement only every two decades.
The Depths of Tomorrow's Power Grid
Each sphere stores a relatively modest amount of energy individually. However, the technology scales well. A cluster of six large spheres could deliver a capacity of 120 megawatt-hours and 30 megawatts of power output, cycling 520 times a year. These installations could play a crucial role in energy arbitrage - buying electricity when it's cheap and storing it to sell when prices rise - or in providing ancillary services to maintain a stable, increasingly complex grid.
The economic case is compelling. Fraunhofer IEE estimates costs at 4.6 euro cents per kilowatt-hour stored, with capital expenses estimated at €1,354 per kilowatt of power and €158 per kilowatt-hour of storage capacity. That's less than several popular battery technologies on the market today, and potentially less disruptive than large-scale hydroelectric dams.
But perhaps StEnSea's most significant advantage is its potential scale. Compared to the 40 gigawatt-hours of pumped storage available across Germany, even a fraction of the 817,000 gigawatt-hour global potential could reshape how we manage renewable energy.
That kind of capacity might seem far-fetched. But it began with an idea in 2011, dreamed up by physicist Prof. Dr. Horst Schmidt-Böcking and Dr. Gerhard Luther. Today, it's taking concrete form - literally.
"We've developed a cost-effective technology that's particularly suitable for short to medium-term storage," said Ernst. "With the test run off the US coast, we're making a significant stride towards scaling and commercializing this storage concept."
As nations race to decarbonize, the challenge is no longer just how to generate clean power - it's how to store it. Maybe the solution doesn't lie on land or in lithium or clouds of hydrogen. Maybe it's waiting on the ocean floor.
concrete, energy storage, renewable energy, renewable energy storage
References:[1] "StEnSea: Storing renewable ocean energy in concrete pressure vessels." Presentation, International Conference on Offshore Wind 2019.[2] "StEnSea - Küstenahe Energiespeicher im Tiefwasser." Fraunhofer Institute for Energy Economics and Energy Systems Technology, 2019.[3] "Ocean Thermal Energy Conversion." Department of Energy. Accessed October 6, 2021.[4] "Energy storage." National Renewable Energy Laboratory. Accessed October 6, 2021.[5] "Offshore wind energy." European Commission. Accessed October 6, 2021.[6] "Pumped-hydro storage." International Energy Agency. Accessed October 6, 2021.[7] "Supercapacitors." Batteries and Energy Storage Technologies Program. U.S. Department of Energy, 2019.[8] "Flow batteries." Batteries and Energy Storage Technologies Program. U.S. Department of Energy, 2019.[9] Flow battery fact sheet - Energy Storage in a Flow. Accessed October 6, 2021.
- The StEnSea project envisions a future where concrete spheres, brimming with electricity, lie on the seabed as giant batteries.
- The idea is simple: pump seawater out during surplus renewable energy production, and let the ocean's pressure generate electricity when needed.
- In the clean energy era, these underwater storage systems could address the challenge of storing energy when the wind dies down and the sun vanishes.
- Tech firms like Sperra and Pleuger Industries are leveraging science, ecology, and innovation to build these spheres with 3D concrete printing and underwater motor pumps.
- In the coming years, with the global energy transition, demand for sustainable storage solutions will skyrocket, and the StEnSea project presents an opportunity for renewable-energy industry growth.
- The financial implications are also promising, as the technology could store electricity at costs lower than several popular battery technologies on the market today.
- As nations strive for decarbonization, the solution to storing renewable energy may not be on land or in the clouds of hydrogen, but waiting on the ocean floor.
- With the potential to reshape the future of energy storage and sustainability, the StEnSea project's test run in the deep Pacific waters off Long Beach, California, marks a significant step towards a more stable and environmentally friendly energy grid.
