Energy · Deep dive

Rondo Energy

Heat batteries for industry: insulated stacks of refractory brick charged with cheap wind and solar electricity through toaster-style resistance heaters, storing heat at up to 1,500°C and discharging continuous 1,000°C+ air and steam to ethanol plants, cement kilns, chemical sites and breweries — a direct electric replacement for the gas-fired boiler.

emerging

The question that decides it: Rondo's brick battery only beats the gas boiler when it can charge on a few very cheap hours of electricity a day — the whole model is the spread between the six cheapest daily hours of power and local industrial gas per MMBtu. Does that spread stay wide enough, in enough geographies, for heat-as-a-service to pencil without subsidy — proven if Covestro's Brunsbüttel 100MWh unit starts up on schedule by end-2026 and the Heineken/EDP battery delivers contracted gas-parity steam — before Antora, which commissioned 5GWh at POET in May 2026 on a $550M war chest, defines the heat-battery category at roughly forty times Rondo's deployed base?

My take ★★ Very interesting ★ Interesting − Maybe ✗ Not interesting

Snapshot

Rondo Energy sells a heat battery: a steel box of refractory brick, heated to around 1,500°C by resistance elements running on the cheapest few hours of wind and solar power each day, that discharges continuous 1,000°C-plus air and steam to industrial plants at a claimed 97-98% efficiency. Founded in Alameda in 2020 by GlassPoint co-founder John O’Donnell, it has raised roughly $165M — including $80.6M of non-dilutive Breakthrough Energy Catalyst and European Investment Bank project funding (Jul 2024) — from backers including Microsoft, Aramco Ventures, SABIC, Rio Tinto and H&M. The world’s largest industrial heat battery — 100MWh, charged only by a 20MW on-site solar array — entered daily commercial operation at a California fuel-production site in October 2025, and a 100MWh unit for Covestro’s Brunsbüttel chemical plant broke ground in January 2026. It matters because industrial process heat is roughly a fifth of global energy use with no cheap electric substitute — and heat batteries are the first electrification play priced against the gas boiler, not the grid.

Founding story

O’Donnell spent fifteen years being right about heat and wrong about how to make it. After a first career in supercomputing and semiconductors, he co-founded Ausra (concentrated solar thermal, sold to Areva in 2010) and then GlassPoint Solar, whose enclosed-trough solar steam plants for oil fields — including the Miraah project in Oman — at their peak supplied more than half of all solar industrial heat in operation. Then solar PV fell about 90% in price over the period, undercutting every mirror-based system; GlassPoint went insolvent in 2020. O’Donnell’s response was to invert the loss: if PV electrons are now the cheapest energy on earth for a few hours a day, stop concentrating sunlight and buy the electrons — the problem becomes storage, and the storage medium industry has trusted for over a century is refractory brick checkerwork, the same regenerative brick stoves that have run in steel and glass plants since the 1800s. He founded Rondo in 2020, raised a Breakthrough Energy Ventures/Energy Impact Partners Series A in February 2022, and in June 2024 handed the CEO role to Eric Trusiewicz — an advisor since 2021 who had built the European business and become President in 2023 — moving himself to Chief Innovation Officer. The handoff doubled as a Europe-first pivot: Trusiewicz argues carbon prices and the post-2022 push off Russian gas make Europe the first market where heat batteries clear.

How it works

Charging is deliberately boring: electrical resistance elements — the company’s own analogy is toaster wire — convert grid or behind-the-meter renewable power to heat at effectively 100% efficiency and radiate it onto thousands of tons of stacked refractory brick, an alumina-silica recipe centuries old. The bricks store heat at up to 1,500°C and lose under 1% per day through the insulation (company figures, accessed Jul 2026). To discharge, blowers push air through channels in the brick stack; the air superheats to over 1,000°C and either feeds a heat-recovery boiler for industrial steam, is delivered as hot air, or — as at the SCG cement plant in Thailand — drives a steam turbine for around-the-clock electricity. Output is throttled simply by varying airflow. Rondo claims 97-98% of input electricity is delivered as useful heat — one-way electricity-to-heat, not a power round trip, which is exactly why it sells heat, not power. Two products: the RHB100 (about 7MW continuous heat discharge, 20MW peak charge, 15m x 12m x 12m) and the RHB300 (about 20MW discharge, 70MW charge, 40m x 15m x 12m). The economics-defining constraint: the battery charges in roughly the six cheapest hours of the day and discharges 24/7, so it needs a connection or array sized several times its heat output. Bricks and modules are manufactured on partner SCG’s refractory lines in Thailand, a 2.4GWh/yr plant announced in 2023 with a stated ambition — so far only an ambition — to expand to 90GWh/yr.

Product and business overview

The catalog is two boxes and a service. RHB100 and RHB300 heat batteries deliver steam, superheated air, or heat-plus-power, sold either as capital equipment or under Heat-as-a-Service, where Rondo (with infrastructure partners) owns the asset and the customer signs a long-term heat offtake. Around the hardware sits project development: pairing units with on-site solar (the Kern County unit runs solely off a 20MW array; the Heineken Portugal unit will be fed by EDP solar) and with grid-charging arrangements in volatile European markets. Application wedges so far: biofuels steam (Calgren), enhanced-oil-recovery steam (Holmes Western), cement heat-and-power (SCG Saraburi), chemicals (Covestro), brewing (Heineken), and — via the H&M investment (Jun 2024) — textile dyeing and finishing heat in Asian supply chains.

Business model and pricing

Rondo prices against the gas boiler, not against batteries: contracts are struck either at a fixed price per MWh of delivered heat or at a guaranteed discount to the customer’s gas-based heat cost (company materials, 2023-2025). O’Donnell has said the storage service itself targets roughly $30/MWh (Canary Media, 2023). The unit economics are a spread trade — buy the six cheapest hours of power, sell continuous heat at gas parity — which means revenue quality depends on electricity-price volatility, curtailed renewables, and local gas prices, none of which Rondo controls. Heat-as-a-Service converts that spread into infrastructure-style contracted cash flows, which is what unlocked the EIB debt (Jul 2024): Latitude Media reported that lenders required the cost- and schedule-certainty demonstrated by the first full-size California unit before committing. No revenue, backlog or margin figures have ever been published.

Traction over time

Read the series honestly: five years in, operating capacity totals roughly 135MWh across three sites — real, but every economic claim is company-sourced, and Antora commissioned 5GWh at a single POET site in May 2026.

Market analysis

Industrial process heat is about a fifth of global final energy demand and roughly 18% of global greenhouse emissions (WBCSD, 2023). Rondo cites the fuel bill itself as the prize; the investable market estimates are smaller: Global Market Insights pegs industrial heat decarbonization at $9.2B in 2025 growing ~9.4%/yr to $22.8B by 2035, and thermal-energy-storage-for-industry estimates cluster around $12.8B (2025) growing to ~$32.6B by 2034. Tailwinds: record renewable curtailment and midday negative prices, EU ETS carbon costs, European energy-security policy, and 45X-style manufacturing incentives. The structural headwind is American: peer-reviewed benchmarking published in 2025 (Applied Energy/NREL-linked) finds that at $4/MMBtu gas with boilers already installed, electrified heat with storage is uneconomic across most US regions; a Berkeley analysis (2025) counters that renewables-plus-storage could cost-effectively serve about a third of US industrial heat in favorable regions. Where it clears first is Europe and high-carbon-price niches — exactly where Rondo has redeployed.

Competitive intel

Antora Energy is the fight that matters: carbon-block storage plus thermophotovoltaics, ~$272M raised through 2024 and a reported $550M more in 2026 riding data-center demand, and — the number that stings — a 5GWh system commissioned with POET at Big Stone City, South Dakota in May 2026, under a long-term heat offtake financed by Grok Ventures. That is Rondo’s original biofuels wedge, taken at forty times Rondo’s deployed scale. Rondo’s counters are simplicity (brick and air versus carbon blocks in inert atmosphere) and delivery efficiency (98% heat versus sub-50% TPV round trips when Antora sells power). Brenmiller Energy (Nasdaq: BNRG) has ~103MWh installed of crushed-rock bGen storage and sells public-company bankability at lower temperatures. Kraftblock (Germany) uses recycled steel-slag granulate to ~1,300°C and is landing European food-and-beverage projects — PepsiCo’s Netherlands plant — on Rondo’s priority continent. Fourth Power ($19M DCVC-led Series A, Dec 2023) targets electricity-out storage via 2,400°C liquid tin — same cheap-power hours, different customers. Electrified Thermal Solutions’ conductive Joule Hive brick targets 1,800°C — cement-and-glass territory above Rondo’s range. And the incumbent is none of them: it is the installed gas boiler, plus plain electric boilers wherever power is cheap all day.

History and evolution

• 2020 — Founded in Alameda, CA by John O’Donnell after GlassPoint’s insolvency; Trusiewicz joins as advisor early 2021.
• Feb 2022 — $22M Series A (BEV, EIP).
• Mar 2023 — Calgren 2MWh unit enters commercial operation; company claims world’s highest-temperature thermal storage.
• Aug 2023 — $60M Series B from an unusually strategic register: Microsoft, Aramco Ventures, SABIC, Rio Tinto, SCG, Titan, SEEIT, John Doerr.
• Jun 2024 — Founder-CEO handoff to Trusiewicz; H&M Group invests for textile-supply-chain heat.
• Jul 2024 — €75M ($80.6M) Breakthrough Energy Catalyst grant plus EIB debt — the EU’s flagship cleantech financing duo — for three European projects.
• Oct 2024 — First 100MWh unit energized at Holmes Western Oil, Kern County; environmental criticism follows.
• Oct 2025 — Kern County unit reaches daily automatic commercial operation on solar-only charging.
• Nov 2025 — SCG Saraburi cement unit operating in Thailand; Heineken/EDP 100MWh Portugal contract signed.
• Jan 19, 2026 — Covestro Brunsbüttel groundbreaking; operation due end-2026.

What people say

The case for. MIT Technology Review (Oct 2025) treated the Kern County unit as evidence thermal storage has crossed from pilot to infrastructure; Latitude Media (2024-2025) credited the build’s cost- and schedule-certainty with unlocking EIB infrastructure lending — a first for a heat-battery startup. Customers supply the operating proof points: Calgren says Rondo heat cuts its ethanol carbon-intensity score 22-23 points without process changes (2023), Covestro frames the Brunsbüttel unit as 10% of site steam and 13,000t CO2/yr (Jan 2026), and repeat strategic money — SCG, H&M, Breakthrough twice over — reads as conviction from buyers, not just VCs.

The complaints. The loudest criticism is where the flagship sits: environmental groups attacked the choice to debut clean heat at a Kern County enhanced-oil-recovery operation, arguing renewable steam that pushes more crude out of the ground extends fossil infrastructure (Canary Media, Oct 2024; CleanTechnica’s Oct 2025 verdict was literally titled good news, bad news). The economic skepticism is structural: 2025 benchmarking finds electrified heat with storage beats a $4 gas boiler almost nowhere in the US, so the home market rarely pencils without curtailed power, carbon pricing or LCFS credits — and charging a 100MWh unit needs a 20-70MW connection in a queue-constrained grid. Skeptics add: every efficiency and parity number is company-sourced, no revenue or backlog is disclosed, the 90GWh factory remains a 2023 press release, and Antora’s POET deployment plus reported $550M raise (2026) suggest the scale race already has a leader — and it is not Rondo.

Outlook: the open question

For Rondo to work, the spread has to be real and repeatable: the gap between the six cheapest daily hours of electricity and local industrial gas prices must stay wide enough, in enough places, to sell heat at or below gas parity while servicing infrastructure debt. The near-term tests are concrete and dated: Covestro’s Brunsbüttel unit starts up on schedule by end-2026 and hits its 10%-of-site-steam duty, the Heineken/EDP unit delivers contracted solar-charged steam in 2027, and at least one of the three EIB-funded projects refinances or repeats without new grant money — grant-supported firsts becoming bankable seconds is the entire heat-as-a-service thesis. If those hold, Rondo owns the category’s most conservative, most financeable design — brick, air and steel, lender-legible — in the one region where policy does the price work, with SCG ready to stamp out capacity.

What would sink it: the spread closes or the race ends before Rondo scales. US gas at $4/MMBtu keeps the domestic market shut; European industrial contraction or softer carbon prices shrink the one market that clears; interconnection queues can strangle 20-70MW charging connections. And the competitive clock is loud — Antora is deploying at gigawatt-hour scale with roughly three times Rondo’s lifetime capital, in Rondo’s own launch vertical. Watch whether Rondo lands a confirmed growth round in 2026-27 (the unverified $1.6B Series C chatter resolving into a real financing or into silence), whether the 90GWh SCG expansion gets a date, and whether any customer ever discloses the actual delivered price of Rondo heat. The physics is settled; the arbitrage is not.

How a challenger would attack it

Out-finance the spread trade. Rondo’s model lives or dies on a spread it doesn’t control — six cheap hours of power against local gas — and its scaling machinery is thin: no disclosed revenue or backlog, a 90GWh factory that remains a 2023 press release, three operating sites totaling ~135MWh, and a first EIB-financed cohort that still leaned on a Breakthrough Catalyst grant. Antora has already shown the attack works: pick one vertical (biofuels steam), sign a long-term heat offtake, bring project finance at scale, and commission 5GWh in a single build while the rival celebrates 100MWh. A new challenger repeats that but sharper — arrive as a developer with a capital markets desk, not a hardware vendor: standardize one battery design, pre-arrange infrastructure debt against offtakes, and lock up the customers whose load profiles pencil (curtailment-adjacent ethanol and food plants) before Rondo’s Europe-first pivot returns home. The technical flank is temperature: Rondo delivers 1,000°C+ air but cement and glass want more — Electrified Thermal’s 1,800°C conductive brick shows the segment above Rondo’s range is open. And every claim Rondo makes is company-sourced; a challenger that publishes third-party-verified delivered-heat prices and efficiency data makes Rondo’s undisclosed economics look like something to hide.

Same playbook, new buyer

Same brick, different offtaker. The nearest unclaimed buyer is the data center: Antora’s reported $550M round is explicitly riding that demand, and heat batteries that firm cheap renewables into round-the-clock energy fit campuses desperate for clean firm supply — but Rondo deliberately sells heat, not power, because its 98% efficiency claim dies in a power round trip. That constraint is the follower-proofing: pivoting to electricity-out means abandoning the one number the whole pitch rests on. Within heat, the open geographies are the sun-drenched, gas-importing industrial belts — India, Vietnam, Mexico, the Gulf — where PV is cheapest, gas is priced off LNG imports rather than $4 Henry Hub, and the H&M textile-supply-chain thesis already points: dyeing and finishing steam in Asia is a real wedge Rondo has only gestured at. A regional player manufacturing locally (as Rondo does with SCG in Thailand) and selling heat-as-a-service against imported LNG faces a wider spread than Rondo sees in Europe, without EU permitting or interconnection queues. Rondo can’t chase every geography at once; its capital and credibility are committed to three dated European proof points through 2027.

Sources and further reading

• Rondo Energy turns on first major thermal battery — at an oil field (Canary Media, Oct 2024)
• Rondo Powers Up World’s Largest Industrial Heat Battery (PR Newswire / Rondo, Oct 2025)
• Rondo Energy announces €75M project funding with Breakthrough Energy Catalyst and the European Investment Bank (PR Newswire, Jul 2024)
• Rondo Energy Secures $60 Million from Global Giants and Leading Climate Investors (PR Newswire, Aug 2023)
• What Rondo’s first full-size unit means for heat batteries (Latitude Media, 2024)
• Inside Rondo’s European debut with new CEO Eric Trusiewicz (Latitude Media, 2024)
• Groundbreaking for Innovative Heat Battery at Covestro’s Brunsbüttel Site (Covestro, Jan 2026)
• Rondo Energy to deploy 100 MWh heat battery for HEINEKEN, powered by solar from EDP (PR Newswire, Nov 2025)
• Antora and POET Commission 5 Gigawatt-Hour Thermal Battery Project (Antora Energy, May 2026)
• Good News, Bad News As Rondo Energy 100 MWh Heat Storage Facility Goes Live (CleanTechnica, Oct 2025)
• What a massive thermal battery means for energy storage (MIT Technology Review, Oct 2025)