ESS Tech's Path to Profitability: A Critical Pivot

Iron flow battery company ESS Tech Inc. had another unprofitable year in 2025. But the story isn't in those losses — it's in the direction of travel, the strategic bets the company is making, and whether those bets are large enough to matter.

For developers, investors, and utilities watching the long-duration energy storage (LDES) space, ESS Tech is one of the most closely watched tests of whether iron-based flow battery technology can survive the brutal early commercialization phase and emerge as a real infrastructure asset class. The 2025 results don't answer that question, but they do narrow it considerably.

The Numbers: Improvement Without Arrival

ESS Tech reported a full-year 2025 net loss of $63.4 million — a meaningful $22.8 million improvement over the $86.2 million loss posted in FY 2024. Operating expenses fell 33%, from $44.4 million to $29.7 million. Adjusted EBITDA came in at -$44.3 million, compared to -$71.3 million the prior year, a 38% improvement.

Those headline moves are real progress. A company that can cut its cash burn by more than a third in one year while keeping its technology development intact is doing something right operationally.

But the revenue figure is harder to spin. ESS Tech generated just $1.6 million in FY 2025 revenue — down 75% from $6.3 million in FY 2024. A company burning $44 million annually while generating $1.6 million in revenue isn't approaching a crossover point; it's racing against the clock. The improvement in gross profit (up 36%) reflects better unit economics, but you can't survive on unit economics alone when volume is this thin.

Context matters here. ESS made a deliberate strategic choice in 2025 to discontinue two of its smaller product lines — the Energy Warehouse and Energy Center configurations — and concentrate entirely on its larger Energy Base product. That pivot almost certainly suppressed near-term revenue. You don't rebuild a product portfolio mid-year and expect the top line to grow. But it's a bet that requires new deployments to start flowing through the books, and fast.

ESS went public via SPAC merger in 2021, at a moment when capital markets were writing blank checks to energy storage startups. The company's shares briefly touched $281.25. They have never come close again. Leadership has been clear that profitability is not imminent — which, given the numbers, is the only honest position to take.

The Google Partnership: Signal or Substance?

The most headline-worthy development is ESS Tech's involvement in Project New Horizon — a 5MW/50MWh iron flow system being deployed in partnership with Google and Arizona utility Salt River Project (SRP).

On paper, this is exactly the kind of deal that validates a technology. SRP selected ESS Tech through a competitive procurement process specifically targeting LDES technologies, which means this wasn't a favor or a pilot program handed out as charity. Google, meanwhile, has made long-duration storage a stated priority for matching its 24/7 carbon-free energy commitments — commitments that lithium-ion batteries, with their 2-4 hour discharge windows, simply cannot fulfill at scale.

A 10-hour discharge ratio (50MWh behind a 5MW system) is precisely the operating window where iron flow batteries are structurally competitive with lithium-ion — and Project New Horizon puts that claim to a real commercial test.

The timeline is worth watching closely. Design is currently underway, manufacturing is planned for 2026, and delivery is targeted for December 2027. That's a long runway, which is typical for utility-scale LDES projects but also means ESS won't see meaningful revenue recognition from this project for at least two years. For a company at this burn rate, the clock matters.

The insider angle here: utilities like SRP don't select new technologies for vanity. They select them because something in the cost-performance profile has shifted enough to justify the procurement risk. The fact that ESS won a competitive process against other LDES technologies — which now include a growing field of competitors spanning vanadium flow, zinc-based systems, gravity storage, and long-duration thermal — is a genuine proof point, not a marketing talking point.

VoltStorage: Acquiring the IP, Absorbing the Talent

The acquisition of VoltStorage GmbH, a German iron-salt battery developer, is strategically interesting for reasons beyond the patent portfolio.

VoltStorage was working on technology that overlaps directly with ESS Tech's core chemistry — iron and saltwater electrolyte systems for stationary storage. Acquiring their intellectual property reduces the risk of competitive encroachment from a technically credible rival and adds depth to ESS Tech's defensive patent position. In a market where the core electrochemistry is relatively well understood but the engineering execution is everything, owning more of the IP landscape matters.

More importantly, ESS gains the VoltStorage team's expertise in electrochemistry and materials science. These are not easy people to hire. Germany has a deep bench of battery researchers, and the VoltStorage staff bring academic and applied research backgrounds that could meaningfully accelerate ESS Tech's cost reduction roadmap — particularly on the materials side, where electrolyte cost and membrane durability are key levers.

Think of it less as an acquisition and more as a strategic talent absorption with an IP dividend attached.

The Germany connection also opens a door, if ESS chooses to walk through it. European industrial policy around battery storage is evolving rapidly, and having a technical team and IP base in Germany positions ESS Tech for potential European market entry without starting from zero.

Energy Base: The Only Product That Matters Now

ESS Tech's decision to stake everything on the Energy Base platform is either its smartest move or its most dangerous one — probably both.

Energy Base is designed for 12-to-14 hour storage durations, targeting customers like data centers and large-scale renewable energy operators who need storage that outlasts what lithium-ion can deliver. The logic is sound: the grid increasingly needs storage that can shift solar generation from midday to evening and overnight, and data centers running on power purchase agreements need something that can bridge multi-hour gaps in renewable availability.

The data center angle is particularly timely. Hyperscale operators are under genuine pressure to demonstrate credible 24/7 clean energy matching, not just annual renewable energy credit purchases. A 12-14 hour iron flow battery paired with solar is a real architectural answer to that problem. The Google partnership is, in part, a proof of that thesis.

The risk is concentration. By discontinuing the smaller product lines, ESS has eliminated the revenue diversification that those products, however modest, provided. If Energy Base deployments are delayed — by supply chain issues, by customer procurement cycles, by anything — there's no fallback revenue to cushion the burn. The cost-cutting has created more runway, but runway is finite.

What This Means for the LDES Market

ESS Tech's trajectory matters beyond its own balance sheet. It's functioning as an involuntary benchmark for whether first-generation iron flow battery companies can make the transition from demonstration projects to commercial deployment at meaningful scale.

If Project New Horizon performs well — if a 50MWh iron flow system delivers reliably at the utility level over multiple years — it changes the procurement calculus for every utility and developer evaluating LDES options. It gives SRP and Google a case study they can point to. It gives ESS Tech a reference project for its next hundred conversations.

If it struggles, the damage extends beyond ESS Tech. Every iron flow battery developer globally takes reputational shrapnel.

The appointment of Drew Buckley as CEO following Kelly Goodman's departure in early 2025 adds another variable. New leadership at a company at this critical juncture can mean sharper execution or strategic whiplash — the market will be watching how Buckley's fingerprints appear on the 2026 roadmap.

For investors and developers evaluating LDES technology today, ESS Tech represents a company that has survived its adolescence but hasn't yet proven its adulthood. The financial trajectory is improving. The strategic partnerships are credible. The technology has a defensible niche. What's missing is scale — and the next 24 months, anchored by Project New Horizon's manufacturing and delivery timeline, will determine whether ESS Tech gets there before its runway ends.

That's not a comfortable position. But it's an honest one.

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