Inside an artificial-intelligence data center, the electrical load swings in milliseconds as racks of accelerators switch between heavy computation and near idle. The grid and the backup systems around them were built for a steadier kind of demand, and the gap between the two has become a bottleneck for the companies racing to build the facilities.
Siemens said on Wednesday that it made a strategic investment in Skeleton Technologies, an Estonian maker of high-power energy storage, and secured the exclusive right to sell the company’s supercapacitors into the global data-center market. The two had worked together for years; the deal turns a supplier relationship into a distribution channel.
The size of the investment was not disclosed. It was enough to lift Skeleton’s valuation above $1 billion, making it Estonia’s newest unicorn, after the company raised more than 100 million euros, according to people familiar with the matter. Siemens has been a technology partner to Skeleton since 2022 and an investor since 2023, and most of the new money is expected to go toward expanding manufacturing in the United States.
Supercapacitors store and release energy in short, powerful bursts, a different job from the one batteries do. A battery holds energy for hours; a supercapacitor can absorb a spike and give it back before the equipment downstream notices. In a data center, that means buffering the surges that come when a rack’s power demand jumps, protecting both the machines and the grid connection behind them.
Siemens said the partnership covers the electrical chain from the grid connection to the AI rack. The products work with the alternating-current architecture most data centers use today and with retrofit projects, the company said, and they offer an upgrade path toward an 800-volt direct-current standard that the industry is discussing for future racks. Skeleton builds its devices on a proprietary material it calls Curved Graphene.
The timing follows the power shortage that has defined the AI build-out. Utilities are being asked to supply loads that arrive faster than transmission lines can be built, and operators have turned to on-site generation, gas turbines, fuel cells and grid-scale storage to bridge the gap. In recent weeks, American Electric Power agreed to build a 702-megawatt fuel-cell plant for Google under a 20-year supply contract, a sign of how far companies will go to secure electricity.
Skeleton was founded in Estonia in 2009 and has spent more than a decade selling high-power storage into buses, trucks, power grids and defense equipment before turning to data centers. Its pitch is that a supercapacitor is not a replacement for a battery but a complement to one: the battery supplies energy for a sustained load, and the supercapacitor absorbs the spikes that would otherwise wear the battery out or trip a breaker.
Data centers have become the demand story for the equipment. Their electricity consumption has climbed faster than forecasters expected, and utilities have told operators in several regions that new connections will take years. The pressure pushes designers toward ideas that shave peak demand rather than add supply, because a component that flattens a load spike can defer an expensive upgrade to a substation or a transmission line.
The industry has also begun to move toward higher-voltage direct-current power distribution inside the rack, a shift that companies building AI hardware have promoted as a way to cut losses and simplify the wiring that feeds dense clusters of accelerators. Skeleton’s products are built to work with that transition, which is one reason a large industrial supplier sees a market for them.
For Siemens, the appeal is a way to sell a higher-value component rather than commodity switchgear. The German industrial group competes in data-center electrical equipment with Schneider Electric, Eaton, ABB and Vertiv, and the market has grown quickly as operators add capacity. Siemens is not the only supplier trying to move up the value chain; each is looking for hardware that a customer cannot easily source from a second vendor.
The exclusive arrangement cuts both ways. Skeleton gains a global sales force and the credibility of a large industrial partner, which matters when the buyer is a hyperscaler with strict procurement rules. It also ties the company’s data-center revenue to a single distributor, and leaves it dependent on Siemens to scale demand as quickly as the market is growing. Skeleton does not sell this product to anyone else in the segment.
Whether supercapacitors become standard equipment in AI factories or remain a niche fix is the question the partnership is meant to answer. The answer depends on power density and on how quickly operators adopt the direct-current designs that make the devices more useful. Skeleton’s devices solve a real problem, but they are not the only solution competing for the slot. Batteries, flywheels and smarter power electronics all claim part of the same job.
For Siemens, the bet is that the bottleneck in AI has moved from chips to electricity, and that the company selling the components around the rack will earn more than the one selling the rack alone. For Skeleton, the unicorn label now comes with a single channel and a single partner. Both are counting on demand for power hardware growing faster than the number of companies able to supply it.
