Five years after a $60 million bet, Malta Inc. is building its first commercial-scale plant in Spain. The question is whether the market for week-long energy storage will arrive before its backers' patience runs out.
The industrial town of Puertollano, Spain, roughly 150 miles south of Madrid, isn't the sort of place venture capitalists typically watch for proof points. But for Malta Inc., a Cambridge, Massachusetts company that emerged from Alphabet's experimental X division seven years ago, a 14-megawatt-hour plant now taking shape there represents something between vindication and a very public test.
Malta has been promising, essentially, to turn molten salt and steam turbines into a grid-scale battery. Not the lithium kind that charges your phone or stores a few hours of solar power—this is storage measured in days. Eight of them, if the engineering holds. It's an audacious premise, one that attracted Facebook co-founder Dustin Moskovitz, oil major Chevron, and Bill Gates–backed Breakthrough Energy Ventures. And it's taken a notably long time to get from blueprint to breaking ground.
The company announced a $50 million Series B on February 24, 2021. A typical venture trajectory might've seen rapid hiring, additional funding splashes, maybe even IPO chatter by now. Instead, Malta expanded that same round to $60 million six months later, added a quiet $21.61 million Series C in late 2023 that never warranted a press release, and, according to its LinkedIn profile in April of this year, still employs somewhere between 11 and 50 people.
That's a lean outfit for a technology aiming to reshape how grids manage renewable intermittency.
Industrial-Scale Physics, Startup-Scale Burn
The core concept sounds straightforward, at least until you sketch the thermodynamics. Malta's system uses electricity to run a heat pump cycle in reverse: thermal energy gets stored as molten salt on one side (hot) and chilled liquid on the other (cold). When the grid needs power, the temperature differential drives turbomachinery to generate electricity. Think of it as a Carnot engine repurposed for multi-day energy arbitrage.
The round-trip efficiency hovers around 55 to 65 percent AC-to-AC, according to a 2023 presentation to the Electric Power Research Institute. Lithium-ion systems routinely hit 90 percent. But that comparison misses the point, Malta's backers argue. Lithium excels at same-day cycling—charging on midday sun, discharging into evening peaks. Malta is betting on a future where grids need something closer to seasonal balancing: storing excess wind in March to cover a calm week in April, or bridging multi-day weather systems when neither solar nor wind shows up.
Whether utilities will pay enough for that capability—duration over efficiency—is the bet.
The company spun out of X in December 2018 with a $26 million Series A led by Breakthrough Energy Ventures, the climate investment vehicle Gates launched in 2015. For two years, Malta stayed largely in stealth, assembling partnerships with industrial heavyweights who could lend credibility to the molten-salt handling and turbomachinery components. A July 2021 development agreement with Siemens Energy brought in turbo-generator expertise. Bechtel, the global engineering giant, signed on for project execution that December.
By August 2022, Malta had a lab-scale pilot running at Southwest Research Institute in Texas, funded partly by a $2.6 million grant from ARPA-E, the Department of Energy's advanced research arm. All the pieces for a commercial demonstration were theoretically in place. What followed, though, was another two years before serious site work began.
The Second Round That Barely Made News
Malta's Series C closed on December 1, 2023, pulling in $21.61 million from much of the same investor syndicate—Alfa Laval, Siemens Energy Ventures, Piva Capital, Proman, Breakthrough Energy, Chevron Technology Ventures. The company issued no announcement. The funding surfaced through MarketScreener's transaction reporting, a detail that suggests either strategic discretion or a round that didn't warrant fanfare.
CB Insights also lists a $23.99 million Series D dated January 13, 2026, though as of late April, this remains unverified—no press release, regulatory filing, or company confirmation has emerged to substantiate it. Perhaps it's real and simply unannounced; perhaps it's a data artifact. Either way, Malta's capital path looks less like a rocketship and more like a methodical trudge.
The undisclosed strategic investment from Trafigura—one of the world's largest commodity trading houses—landed in June 2022. That's the kind of backer that makes sense for a technology requiring molten-salt supply chains and industrial-scale offtake agreements. Trafigura trades energy; Malta proposes to store it for a week at a time.
Spain, Finally
The Iberia storyline began to coalesce in mid-2024. Malta signed a memorandum of understanding with Spanish banking giant BBVA in June of that year to explore financing for a demonstration plant. By June 2025, BBVA confirmed in a corporate update that Malta had established a subsidiary—Malta Iberia PHES SL—and secured a power purchase agreement backing the Puertollano project.
A month earlier, in October 2024, Malta struck a strategic partnership with Cox Energy (formally CA Infraestructuras Energía 2023 S.L.U.), a Spanish renewables developer, which also took an equity position. And in that same month, CEO Ramya Swaminathan, who had shepherded the spinout from X, stepped back to a senior advisory role. Phil Delleville, a renewable finance veteran who joined Malta in 2022, took over as president and chief executive.
Leadership transitions at climate tech startups can signal either maturity—bringing in the operator who can scale—or trouble. In Malta's case, the timing aligns with the shift from R&D to deployment. Whether that's smooth or fraught will become clear in Puertollano.
The Market That Might Exist
Malta competes, if you can call it that, in the long-duration energy storage niche alongside Form Energy's iron-air batteries, Highview Power's cryogenic systems, and Energy Vault's gravity blocks. It's a small club, and the market they're all banking on is largely theoretical. The Long Duration Energy Storage Council estimated in its 2024 annual report that global grids will need somewhere between 1.5 and 8 terawatts of LDES capacity by 2040. Hitting even the low end of that range would require a roughly 50-fold scale-up from today's project pipelines.
That kind of growth doesn't happen without policy tailwinds—offtake contracts that value duration, capacity payments decoupled from round-trip efficiency, procurement mandates that recognize the grid reliability benefits of multi-day storage. Some of those structures are emerging in California and Europe. Most are still works in progress.
Malta has collected its share of recognition: a finalist nod at the Platts Global Energy Awards in September 2024, a spot on TIME's "Top GreenTech Companies 2025" list. Mindshare doesn't pay the bills, but it helps when you're asking utilities to bet on turbines and molten salt instead of stacking lithium cells.
The Wait, and What Comes Next
Five years from Series B to first commercial demonstration is a long gestation for venture-backed climate tech. Then again, Malta isn't trying to optimize software or improve battery chemistry at the margins. It's asking industrial supply chains to deliver heat exchangers, steam turbines, and salt-handling infrastructure at grid scale—and asking grid operators to rethink how they value storage altogether.
The Puertollano plant is rated at 14 megawatt-hours. Company materials from 2022 have suggested full-scale deployments could hit "more than 100 MW" and "1,000+ MWh," which translates to something closer to a week of storage at modest discharge rates. Whether Malta gets to build plants at that scale depends on how the Spanish project performs, and perhaps more importantly, on whether the market for week-long storage materializes at the pace its backers envisioned back in 2021.
For now, the proof sits in an industrial town south of Madrid. And the clock, having already run five years, keeps ticking.
