The Legacy of Pumped-Storage Hydroelectricity

Pumped-storage hydroelectricity isn’t new. In fact, it’s a century-old technology, first implemented in Switzerland in 1907. Today, PSH represents over 90% of the world’s long-duration energy storage capacity, totaling nearly 200 gigawatts globally in 2023 – earning it the moniker “the world’s biggest battery.” The core principle is elegantly simple: pump water uphill to a higher reservoir during periods of low demand or excess renewable energy generation, then release it through turbines to generate electricity when demand surges. This simplicity translates to efficiency, longevity, and relatively low operational costs.

“Pumped hydro is very mature,” explains Tamas Bertenyi, co-founder and Chief Technology Officer of RheEnergise. “In terms of long-duration storage—say, 8 to 10 hours—it’s incredibly low cost. There’s a hydro industry in most countries.” However, traditional PSH isn’t without its drawbacks. The primary challenge lies in scalability. Suitable locations – requiring both mountainous terrain and a consistent water source – are limited.

Breaking the Geographical Barrier: Introducing High-Density Fluid

RheEnergise’s innovation addresses this scalability issue head-on. Instead of water, the system utilizes a proprietary fluid, dubbed High-Density Fluid (HDF), which boasts 2.5 times the density of water. “It is so dense that if you threw a block of concrete into a pool of the fluid, it would float,” Bertenyi notes. This increased density allows for the construction of closed-loop systems requiring significantly smaller elevation differences – as little as 25% of the height needed for conventional PSH.

The development of HDF was a collaborative effort with the University of Exeter, led by the late Professor Richard Cochrane, a renowned expert in renewable energy systems. The team focused on engineering a mineral-rich fluid that was not only dense but also possessed manageable viscosity, environmental benignity, and minimal corrosive properties. This presented a unique engineering challenge: achieving sufficient viscosity for flow while maintaining the density needed to prevent unwanted migration in the event of a spill.

How Does High-Density Fluid Work in Practice?

To mitigate environmental risks, HDF is formulated as a suspension of particulate minerals rather than a dissolved solution. This ensures that any spillage would result in the particles settling and drying, minimizing the potential for soil or groundwater contamination. Furthermore, the fluid exhibits non-Newtonian behavior, specifically shear-thinning. This means its viscosity decreases under stress, allowing it to flow easily through pipes and turbines during operation, while remaining thicker when at rest.

“Given the system can generate the same energy output from gentler slopes and lower elevations than traditional pumped hydro, it makes far more sites viable worldwide—including low hills and urban fringe areas,” says Professor George Aggidis, a retired energy engineering expert from Lancaster University. “And its long-duration storage makes it suitable for balancing generation by renewables, a gap where batteries alone can be expensive.”

The pilot project features an 80-meter high reservoir, connected to a lower “swimming pool” style reservoir via 2.5-meter diameter fiberglass pipes. Both reservoirs are buried underground, with only the powerhouse – housing the turbine, pump, fluid management system, and electrical controls – visible above ground. RheEnergise envisions commercial projects utilizing two to four 5-megawatt turbines, targeting a 10-20 MW capacity.

Commercialization and Competition in the Energy Storage Landscape

RheEnergise is actively partnering with turbine manufacturers to develop modular turbines optimized for HDF. The company aims to deliver its first fully commercial system by the end of 2028, targeting independent power producers, utility companies, and energy project developers. However, scaling up will present challenges, including substantial civil engineering work, permitting processes, and complex coordination.

The energy storage market is also becoming increasingly competitive. Alternatives like sodium-ion batteries, flow batteries, compressed-air energy storage, hydrogen storage, and thermal storage are all vying for market share. Each technology offers unique advantages and disadvantages, and the optimal solution will likely vary depending on specific application requirements. What do you think will be the dominant long-duration energy storage technology of the future?

Will RheEnergise’s innovative approach to pumped hydro overcome these hurdles and establish a significant foothold in the rapidly evolving energy storage landscape? Only time will tell. But one thing is certain: the need for scalable, long-duration energy storage is more pressing than ever, and RheEnergise’s technology represents a promising step towards a more sustainable energy future. What impact do you foresee this technology having on the integration of renewable energy sources into the grid?

Frequently Asked Questions About RheEnergise’s High-Density Fluid Hydroelectric System

• What is High-Density Fluid and how does it differ from water in a hydroelectric system? High-Density Fluid is a proprietary mineral-rich fluid 2.5 times denser than water. This allows RheEnergise’s system to operate effectively with significantly smaller elevation differences compared to traditional pumped hydro.
• What are the environmental considerations surrounding the use of High-Density Fluid? The fluid is formulated as a suspension of particulate minerals, designed to settle and dry in the event of a spill, minimizing the risk of soil or groundwater contamination.
• How does RheEnergise’s system address the scalability limitations of traditional pumped hydro? By utilizing High-Density Fluid, RheEnergise can build closed-loop systems in locations previously unsuitable for traditional PSH, including low hills and urban fringe areas.
• What is the expected lifespan of a RheEnergise commercial system? While specific lifespan estimates are still being refined, the company anticipates a similar longevity to traditional pumped hydro facilities – several decades – due to the robust design and minimal corrosion potential of the system.
• What is the current timeline for the deployment of fully commercial RheEnergise systems? RheEnergise aims to deliver its first fully commercial system by the end of 2028, following ongoing partnerships with turbine manufacturers and project developers.