Ocean Energy Storage: One Startup's Innovative Approach

The Innovation of Subsea Pumped Hydro Storage

Manuele Aufiero’s early experiences involved family hikes near a unique reservoir situated in northern Italy. This wasn’t a conventional reservoir; it operated by continuously draining and refilling, utilizing pumps to elevate the water level during periods of low electricity costs.

A Century-Old Technology Gains New Relevance

Conversely, when electricity demand increased in neighboring cities, these pumps functioned in reverse, becoming generators as the water was released. This technology, known as pumped-storage hydropower – or simply “pumped hydro” – has been utilized for over a century.

The Scale of Pumped Hydro

These facilities represent some of the largest energy storage systems ever constructed by humankind. According to the International Energy Agency, globally, pumped hydro reservoirs currently store approximately 8,500 gigawatt-hours of electrical energy.

Pumped hydro is capable of generating electricity for extended durations, and its significance has grown alongside the increasing prevalence of intermittent renewable energy sources like wind and solar power.

Limitations of Traditional Pumped Hydro

However, the availability of suitable geographical locations for constructing pumped hydro reservoirs is limited. Ideal sites require specific topographical features.

“My passion lies with pumped hydro,” Aufiero stated to TechCrunch, “but its current capacity isn’t sufficient to meet the demands of expanding renewable energy integration.”

Sizable Energy: A Novel Approach

Driven by this challenge, Aufiero resolved to address the limitation by relocating the technology to the marine environment. He co-founded Sizable Energy, a startup dedicated to realizing this vision.

Recent Funding Success

Sizable recently secured $8 million in funding, led by Playground Global, with participation from EDEN/IAG, Exa Ventures, Satgana, Unruly Capital, and Verve Ventures, as exclusively reported to TechCrunch.

How Sizable’s Technology Works

The startup’s power plant design resembles an hourglass in form. Sizable’s concept employs two sealed, flexible reservoirs: one floating on the surface and another positioned on the seabed.

These reservoirs are interconnected by a plastic pipe and turbines. When electricity prices are low, the turbines pump highly saline water from the lower reservoir to the upper one.

Utilizing Density Differences

When the electrical grid requires energy, Sizable opens a valve. Due to the higher salt content, the water in the upper reservoir is denser than the surrounding seawater, causing it to descend to the lower reservoir.

This downward flow spins the turbines, effectively generating electricity. “Essentially, we are lifting a mass of salt from an energy perspective,” explained Aufiero. “However, instead of using cranes, we dissolve and pump it, as this is a more efficient and straightforward method.”

Scalability Through Ocean Deployment

By transitioning pumped hydro to the ocean, Sizable aims to enable mass production of the technology, a feat difficult to achieve with land-based installations.

“Constructing pumped hydro facilities onshore necessitates custom-designed concrete dams for each specific location, requiring adaptation of the technology,” Aufiero noted. “Offshore construction allows for streamlined production, with standardized components regardless of the deployment site.”

Testing and Pilot Programs

Sizable has conducted tests with a scaled-down reservoir model in wave tanks and off the coast of Reggio Calabria, Italy. Currently, they are deploying a pilot program focusing on the floating components, paving the way for a full-scale demonstration plant.

The company anticipates deploying several commercial projects globally by 2026.

Performance and Cost Projections

At full scale, each turbine is projected to generate approximately 6 to 7 megawatts of electricity, with one turbine installed for every 100 meters of pipe. Deeper sites offer greater storage capacity.

Each commercial site will incorporate multiple reservoirs. Sizable aims to provide energy storage at a cost of €20 per kilowatt-hour (roughly $23), representing about one-tenth of the cost of current grid-scale battery systems.

Synergies with Offshore Wind

This technology is particularly well-suited for integration with offshore wind farms, as sharing an electrical connection to the shore can reduce overall costs.

However, Aufiero emphasized that Sizable’s reservoirs can connect to any grid located near waters at least 500 meters (1,640 feet) deep.

The Future of Energy Storage

“We firmly believe that long-duration energy storage is crucial not only for integrating renewables but also for enhancing grid resilience,” he concluded. “Existing pumped hydro and battery technologies are insufficient to meet these needs; a novel solution is required.”