A new type of hydroelectric energy system that doesn’t use water was cause for the champagne to flow in January when engineers at RheEnergise in the United Kingdom succeeded in driving a pilot project to a peak power of 500 kilowatts. The system is a fresh take on pumped-storage hydroelectricity (PSH) power, a century-old technology first implemented in Switzerland in 1907 that has since been adopted globally and grown into a major form of energy storage. In 2023, pumped storage provided nearly 200 gigawatts in global installed capacity—over 90 percent of the world’s long-duration energy storage. Hence its nickname: the world’s biggest battery.

PSH works by pumping water up to a higher reservoir during periods of excess electricity from renewables or when demand from the grid is low, and letting the water flow back down under gravity through turbines to a lower reservoir when demand is high. The simplicity of the concept makes PSH efficient, cost-effective, long-lasting, and reliable with relatively low running costs once constructed.

“Pumped hydro is very mature,” says Tamas Bertenyi, a cofounder and chief technology officer of RheEnergise. “In terms of long-duration storage—let’s say 8 to 10 hours—it’s incredibly low cost. So there’s probably a hydro industry in most countries of the world.”

But PSH also has its downsides. Besides high upfront costs and long construction times, Bertenyi says the biggest disadvantage is its lack of scalability. “You need a suitable mountain, and you need to have a river running along the bottom. You also need an alpine valley you can dam up, and there are just not a lot of sites where you can do that.”

To make PSH scalable, RheEnergise has revamped the technology by constructing a closed-loop system and replacing water with a proprietary fluid it calls High-Density Fluid, which has 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,” says Bertenyi.

In developing the fluid, RheEnergise worked with the University of Exeter in England, where Richard Cochrane (now deceased), a cofounder of the company, was a professor of renewable energy systems. The researchers sought to engineer a mineral-rich fluid that is not only much denser than water but has a manageable viscosity, is environmentally benign, and causes minimal abrasion or corrosion. That took “a lot of engineering and a lot of science,” says Bertenyi, because it raised two contradictory challenges: Have a low enough viscosity to flow like water but be dense enough to not go anywhere in the case of an accident.

How does RheEnergise’s High-Density Fluid work?

To reduce the fluid’s risk to the environment (from spills or entering the food chain), it’s formulated as a suspension mixture that suspends the particulate minerals, rather than dissolving them as a solution might. The fluid’s high density solved this problem: In the event of spillage, the particles will simply dry and settle, and not seep deep into soil or groundwater, according to Bertenyi.

RheEnergise formulated a dense yet low-viscosity fluid in its effort to make pumped-storage hydroelectricity possible in more places.RheEnergise

At the same time, the fluid—which is actually 80 percent solid particulates by mass—needed to have a viscosity as low as water to flow through pipes and turbines. Thus, the fluid was engineered to have a thick viscosity when it’s not moving, but have a decreased viscosity when pumped through a PSH system: a shear-thinning non-Newtonian behavior.

“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—not just mountainous regions,” says George Aggidis, a professor emeritus of energy engineering at Lancaster University in the U.K. “And its long-duration storage makes it suitable for balancing generation by renewables, a gap where batteries alone can be expensive.”

The pilot project consists of a higher reservoir constructed at a height of 80 meters, with fiberglass pipes 2.5 meters in diameter feeding a shared chamber; while the lower reservoir is a simple concrete construction, “basically a large swimming pool,” says Bertenyi. Both reservoirs are buried underground and connected by a steel pipe to form a closed loop, leaving just the powerhouse containing the turbine, pump, fluid-management system, and the electrical control system visible.

“We expect our commercial projects to use two or four 5-megawatt turbines, so 10 to 20 MW is the sweet spot,” says Bertenyi. Having achieved peak power with its pilot project, he says the company is working with partners to bring the technology to commercialization, including turbine manufacturers that will produce modular turbines engineered to work with its fluid. The company aims to deliver its first fully commercial system by the end of 2028. Potential customers include independent power producers, utility companies, and energy-project developers.

But RheEnergise can expect to face some challenges along the way. Besides being capital intensive, “larger scale deployment will require substantial civil works, permit requirements, and engineering coordination,” says Aggidis. “This is more complex than plug-and-play battery systems.”

Then there’s the competition. Aggidis points to sodium-ion and flow batteries, which are modular, fast to install and rapidly decreasing in cost. Other emerging technologies include compressed-air energy storage, hydrogen storage, and thermal storage that are also seeking to get a foothold in the rapidly expanding energy-storage market.

This post was updated on 25 February 2026 to clarify that RheEnergise’s name for its proprietary fluid is High-Density Fluid. High-Density Hydro, which was originally used, is the name of the company’s overall system.

Toshiba has carved out a significant share of the lithium-ion battery market in industrial, automotive, and energy sectors—despite championing a more expensive anode material with lower energy density. The Japanese company is using lithium titanium oxide (LTO) anodes as it competes with standard lithium-ion batteries to gain a foothold in price-sensitive markets including low-power vehicles, boats, and industrial equipment, where lead-acid batteries still dominate.

First introduced in 2008, Toshiba’s SCiB batteries are now available as single cells, modules, and packs that can be configured in series or parallel to match voltage and capacity needs. For example, the Type 3 module can be linked in series to deliver over 1,000 volts and roughly 40 kilowatt hours. As energy storage systems in industry, for example, SCiB batteries are used to reduce grid-frequency changes in substations, and as battery storage for renewable energy systems; while in transportation, it can be found powering electric ferries and battery-powered locomotives.

In October, Toshiba launched its SCiB 24-volt battery pack designed to replace standard industrial lead-acid batteries in Japan’s cost-conscious mobility market, and which can be adapted to similar form factors used overseas.

Advantages of LTO Anodes

Toshiba’s SCiB 24-volt battery pack can be deployed as a standalone unit or configured in series and parallel.Toshiba

Though LTO carries a premium price tag, “it provides a long life of over 20,000 cycles, greater safety, rapid recharging, and it can operate as low as -30 °C,” says Shigeru Shimakawa, a technical fellow in Toshiba’s battery systems engineering department. These are key advantages for competing in the 24-volt lead-acid replacement market, he says, because lead-acid batteries are heavy and bulky, charge slowly, and have short life cycles—though low cost explains their continued popularity.

Yasushi Midorikawa, a senior manager of battery sales and marketing at Toshiba, explains how LTO’s advantages compare with those of competing graphite-based lithium-ion batteries. Any lithium-ion battery charges and discharges energy by moving lithium ions from the anode to the cathode and back again. The difference is that graphite anodes store the ions between tight carbon layers, which slows their movement. LTO, by comparison, has a three-dimensional tunnel structure that provides more space for ions to move freely and safely at high speeds, which allows it to charge faster.

That said, graphite operates at a lower potential relative to lithium than LTO, giving it the advantage of a higher cell voltage and energy density. “A higher potential reduces the energy density of a cell,” says Neeraj Sharma, a professor of chemistry focusing on battery materials at the University of New South Wales Sydney, in Australia. “For example, when comparing graphite and LTO with the same cathode, the graphite cell will have a higher energy density. Generally speaking, this means you need more LTO-cathode cells to get the equivalent energy density of a graphite cell.”

But during fast charging or at low temperatures, lithium can be deposited on the graphite anode, a condition known as lithium plating. Over time, this plating leads to the growth of dendrites, tiny needles of metallic lithium that can damage the anode, reducing its ability to hold and release ions efficiently, which shortens the battery’s cycle life compared to LTO.

“Lithium-ion plating is a key failure mechanism for graphite-based lithium-ion batteries,” says Sharma. “And it is often associated with battery fires, risks, and safety.”

Toshiba is trialing swappable 24-volt battery packs with LTO anodes for electric motorbikes in Bangkok.Toshiba

Battery-Swapping Innovations

Toshiba is testing its 24-volt battery pack in Bangkok as a replacement for lead-acid batteries used in electric motorcycle taxis. Last year, the company teamed up with Naturenix, a Tokyo-based battery technology startup specializing in designing fast-charging lithium-ion battery pack systems for small electric vehicles. Together, the companies conducted a proof-of-concept (PoC) service test that allowed drivers of electric motorcycle taxis to swap battery packs at a charging station.

“From the resulting test data, we estimate a battery life of over 10 years is possible even in Bangkok’s hot climate,” says Haruchika Ishii, a business development fellow in Toshiba’s battery division. “And if specialized maintenance is used, this could be extended to about 18 years.” He adds that from December to March 2026, a new phase of testing will begin with a paid service supporting 100 motorcycles using five charging stations.

Yet even with these promising results, Toshiba faces a well-entrenched rival. Honda Motor Company has already established a battery-swapping business in Asia and elsewhere. As early as 2019, Honda began testing its lithium-ion Mobile Power Packs in motorbikes and scooters in the Philippines, Indonesia, and Japan. In 2022, commercial operations commenced in Japan and then in Bengaluru, India, and Honda has since broadened the business to Delhi and Mumbai, as well as Thailand and Europe.

But Toshiba says its approach to the battery-swapping business is different. “SCiB’s long life and fast charging—80 percent of capacity in six minutes—changes the economics of electrification, making a subscription model possible for battery as a service,” says Ishii. Typical lithium-ion batteries degrade relatively quickly, making a subscription model less practical, he says. “Also, swapping a SCiB battery is optional—not essential, because charging time is so quick,” he adds. “So fewer charging stations will be needed.”

Toshiba is also eyeing small boats. In October, Yamaha Motor began testing the technology in an electric sightseeing boat servicing the port of Yokohama, Japan. The vessel previously used lead-acid batteries powering twin electric propulsion systems produced by Yamaha, but the batteries had to be exchanged for fresh ones after every trip. Now, each propulsion system is powered by a SCiB 24-volt battery pack configured in a set of two in series and six in parallel, delivering 5.76 kilowatt-hours for a combined total of 48 volts and 11.52 kWh. As of this writing, the companies said it was too soon to provide test results.

For certain use cases, Sharma says SCiB looks to be a good, safe competitor to lower-cost lithium-ion batteries when it comes to replacing lead-acid ones. “Key advantages compared to lead-acid batteries is its higher energy density, so you can have the same energy density with a smaller footprint, and it can perform for a longer number of cycles,” he says. “As for graphite-based lithium-ion batteries, SCiB is safer and so more suited for certain applications.”