Storing electricity from wind and solar is the part of the green transition nobody likes to talk about, mostly because the answers are either boring or enormous. You can build a lake on top of a mountain and pump water uphill when there’s spare power, or you can park a warehouse full of lithium batteries next to the wind farm and hope the chemistry behaves.<\/p>\n
China has a third option up and running on its coast now, and it doesn’t look like either one. North of Shanghai there’s a 148-meter concrete tower that stores a wind farm’s electricity by stacking 35-ton blocks on top of each other, and it does the whole job without a single lithium cell inside it.<\/p>\n
The building sits in Rudong, in Jiangsu province, right on the edge of the Yellow Sea, and from a distance you’d swear it was an unfinished apartment block. Almost forty stories of gray concrete, no windows, the kind of structure you drive past without a second glance. Inside, it’s a battery. Not in the chemical sense your phone uses, but in the original sense of the word: a thing that holds energy until you need it and then hands it back. T<\/p>\n
he energy here is stored as height, which is about as old-school as physics gets. The Swiss technology company behind it, Energy Vault<\/a>, calls it the world’s first commercial gravity battery, and the design magazine Domus<\/a> recently went out to look at the thing in person.<\/p>\n The mechanism is almost insultingly simple once you see it. When the wind farm next door is making more electricity than the grid wants, motors inside the tower use that surplus to haul heavy blocks up toward the top of the structure. The blocks just sit up there holding their position, which in engineering terms means they’re holding potential energy the same way a boulder at the top of a hill is. When demand on the grid spikes and the power is actually needed, the blocks come back down in a controlled descent, spinning generators on the way and pushing electricity back onto the line.<\/p>\n That’s the entire loop. Charge by going up, discharge by coming down. The blocks themselves are the clever part. Each one weighs roughly 35 tons and they’re cast from recycled material, mostly waste concrete and industrial aggregate, which is a polite way of saying the storage medium is rubble pressed into bricks. A system of mechanical arms and cables shuffles them around inside the tower, both straight up and sideways, restacking them in whatever order keeps the structure balanced. The rated capacity is 25 megawatts of power and 100 megawatt-hours of storage, which works out to about four hours of full output before all the blocks are back on the ground. Four hours happens to be the awkward window where solar drops off in the evening but everyone gets home and switches everything on, so it’s a useful number rather than an arbitrary one.<\/p>\n Concrete is quietly having a moment as an energy material, by the way. MIT researchers recently turned ordinary concrete into a working structural supercapacitor that stores electricity and lights an LED<\/a>, which is a different trick entirely but points at the same instinct: stop treating the gray stuff as dead weight and start asking it to do a second job.<\/p>\n Here’s where the “world’s first” claim needs a footnote, because gravity storage is not new and anyone who tells you otherwise hasn’t met pumped hydro. Pumping water up to a high reservoir when power is cheap and letting it fall back through turbines when power is expensive is the exact same idea, and it currently accounts for somewhere around 90% of all the energy storage capacity on the planet. Mountains have been moonlighting as grid batteries since the early 1900s. China itself just broke ground on an enormous water battery high on a Tibetan mountain<\/a> that runs on precisely this principle, two stacked lakes and a lot of elevation.<\/p>\n What makes the Rudong tower a genuine first is the part where no water is involved. It’s the first commercial, grid-scale gravity storage system that pulls off the trick with solid blocks instead of a reservoir, according to Energy Vault. That distinction matters more than it sounds. Pumped hydro needs a mountain, two bodies of water and a very particular kind of geography, which is why you can’t just build one wherever the grid happens to need it. A block-stacking tower needs a flat patch of ground and a building permit. You could in theory drop one next to any wind farm or substation with no elevation required, and that flexibility is the entire pitch.<\/p>\n The technology belongs to Energy Vault, founded in 2017 by a group of Swiss researchers and now trading on the New York Stock Exchange under the ticker NRGV. Energy Vault didn’t pour the concrete or pay for the Rudong tower, though. It licensed the design and collects a 5% royalty on the project’s revenue, while the building and operating is handled by its partners: China Tianying, a Shenzhen-listed company that put up the money and constructed it, and Atlas Renewable, which holds the licensing agreement.<\/p>\n That arrangement explains why this landed in China rather than Switzerland. China is the largest and fastest-growing energy storage market in the world, partly because it’s adding renewable capacity faster than anyone else and partly because the government requires a certain amount of storage to be built alongside it. Energy Vault says it has nine of these EVx towers planned across China, totaling more than 3.7 gigawatt-hours, with additional units under construction beyond Rudong. Comparable block-stacking and weight-based projects have been proposed in several other countries, but none of them have reached commercial operation yet. The first gravity tower to actually interconnect with a national grid did it on the Chinese coast, and it didn’t get there quickly: construction started back in March 2022, survived two Covid-related work stoppages in its first year, and reached full grid interconnection in December 2023. The system was also named one of TIME’s Best Inventions of 2024, which is the kind of outside nod that suggests this is more than a press-release rendering.<\/p>\n A battery that never wears out is still worthless if it gives back far less than you feed it, so the figure that actually decides whether any of this scales is round-trip efficiency: how much electricity comes back out compared to what went in. Energy Vault is targeting above 80% for the Rudong system, which would put it ahead of compressed-air, thermal and flow-battery storage and roughly level with pumped hydro. For reference, the company’s first and much smaller tower in Switzerland, wired up in 2020, measured above 75%. Whether the big one in Rudong holds that 80% in day-to-day commercial use is the figure that separates a clever curiosity from a real grid asset, and it’s the one engineers will be checking first.<\/p>\n The other half of the pitch is that the blocks don’t care how often you use them. Concrete doesn’t degrade the way lithium chemistry does, so the tower is rated for a 35-year lifespan with no self-discharge, meaning the energy stored as height doesn’t quietly leak away while it sits there waiting. A lithium pack loses a sliver of capacity every cycle and slowly bleeds charge just sitting on a shelf. A stack of rubble does neither, which is the sort of unglamorous advantage that adds up over three decades.<\/p>\n It’s a good enough story that Energy Vault is already exporting the design. In May 2026 it signed a development agreement with Eskom, South Africa’s state utility, to build a 25MW\/100MWh system the same size as Rudong, using a next-generation version it calls EVx 2.0 that the company says can eventually scale up to 4 gigawatts, according to Energy Storage News<\/a>. That’s a long way from one tower on the Yellow Sea, and South Africa hasn’t put a timeline on it, so the distance between signing a deal and pouring a foundation is still very wide.<\/p>\n The honest read is that Rudong has spent the better part of two years quietly lifting and dropping blocks on the coast while the rest of the industry argued about lithium supply chains and which battery chemistry wins. It’s grid-connected, it’s passed its charge and discharge testing, and recent reporting describes it as operational, which makes it the first thing of its kind anywhere. Whether the next forty-story battery gets built comes down almost entirely to whether the next one is cheaper to pour than this one was, and concrete, for all its many virtues, has never once been famous for getting cheaper. Still, it’s worth keeping in mind the next time someone insists the only way to store green power is to stack up a warehouse of lithium and cross your fingers.<\/p>\n","protected":false},"excerpt":{"rendered":" Storing electricity from wind and solar is the part of the green transition nobody likes to talk about, mostly because … <\/p>\nThe tower stores power by getting heavier<\/h2>\n
Pumped hydro has done this for a century, just with water<\/h2>\n
Switzerland drew it up, China actually built it<\/h2>\n
Eighty percent is the number everything rides on<\/h2>\n