Wärtsilä’s 31H2: The First Large-Scale Engine Running on 100% Hydrogen

How the Wärtsilä 31H2 Engine Works

The 31H2 is not a small prototype. It is a medium-speed, four-stroke industrial piston engine built on the Wärtsilä 31 platform—an architecture whose diesel variant once held a Guinness World Record for efficiency .

The engine is a giant by car standards, measuring roughly 15 feet tall and 29 feet long. In its traditional form, it produces around 13,000 horsepower (roughly 9.8 MW), though output varies depending on the fuel .

The key to making a piston engine burn pure hydrogen is its combustion control system. Hydrogen burns with a very high flame speed and requires very little energy to ignite, which raises the risk of pre-ignition (knock) and backflash. The 31H2 manages these risks with a dedicated control system that adjusts parameters in real time to keep combustion stable across its full fuel flexibility range .

Engine Specifications and Dual Variant Strategy

Wärtsilä has adopted a two-pronged engine strategy for the hydrogen transition. Both engines are based on the same V31 platform but serve different needs:

• Wärtsilä 31SG-H2 (hydrogen-ready): This model is a direct evolution of the company’s natural gas engines. It operates on natural gas or a blend of up to 25% hydrogen by volume, without any hardware modifications—only control system adjustments are needed. It can be field-upgraded to run on 100% hydrogen when a customer secures a reliable supply .
• Wärtsilä 31H2 (pure hydrogen engine): This is a purpose-built engine designed from the start for full fuel flexibility—from 0% to 100% natural gas in hydrogen. The Bermeo test validated this engine running entirely on pure hydrogen .

Key performance metrics based on Wärtsilä’s documentation and public statements include:

• Output on natural gas: ~12 MW. A company spokesperson confirmed the V31 medium-bore engine produces 12 MW on gas .
• Output on 100% hydrogen: Lower than the gas rating. Wärtsilä had previously demonstrated sustained operation on pure hydrogen at around 70% of a typical marine engine load. The spokesperson noted that hydrogen-fired power output is derated compared to natural gas, though the exact reduction for the grid-connected test was not specified .
• Hydrogen blending performance: With a 25% hydrogen blend, the engine achieved 95% load in prior commercial tests. With a 17% blend, it was able to reach 100% load .
• Ramp time: The engine can go from zero to full output in as little as two minutes. This is a defining advantage over traditional thermal plants and makes the engine valuable for balancing intermittent renewables like solar and wind on the grid .
• Grid synchronization: Start command to grid synchronization occurs within 30 seconds .

The Role of Air Liquide’s Electrolyzer

The hydrogen used in the Bermeo test was not grey hydrogen produced from natural gas. Air Liquide supplied green hydrogen made via water electrolysis, a process that emits zero CO₂ when powered by renewable electricity. The company has deep experience here—its HyBalance facility in Europe is one of the first industrial-scale PEM electrolysis plants .

The hydrogen for the Bermeo demonstration was compliant with the EU’s Renewable Energy Directive (RED), meaning it met strict sustainability criteria. Air Liquide is also scaling up dramatically: it is building the 200 MW ELYgator electrolyzer in the Netherlands, designed to produce up to 23,000 tons of renewable and low-carbon hydrogen annually .

Commercial Validation: What the Bermeo Test Actually Proves

The Bermeo event, which took place in June 2026 with customers present, is not simply a laboratory experiment. Wärtsilä’s official press release describes it as the start of the engine’s “validation” phase. The company is operating the engine on Spain’s grid to demonstrate to power producers and industrial users that the technology can deliver firm, flexible, zero-carbon power under real-world conditions .

This validation is the last step before commercial orders. Wärtsilä expects commercial volumes to ramp up from 2027 . The company’s target is utility-scale power plants in the hundreds of megawatts range, built from multiple engine modules, much like how data centers and remote industries build out their power generation today .

A Six-Year Development Journey: 2020–2026

Wärtsilä did not jump overnight from natural gas to pure hydrogen. The company has run a systematic, multi-year testing program:

• 2020: Wärtsilä and WEC Energy Group completed the world’s first 25 vol-% hydrogen blend test on an unmodified 50SG engine. The engine ran for three days connected to the grid in Michigan and achieved 95% load on the blend .
• 2022: Expanded blend tests took place at Wärtsilä’s labs in Vaasa, Finland, and Bermeo, Spain. A commercial demonstration also ran at WEC Energy Group’s plant .
• 2023: A test with EPRI and WEC Energy Group on a 20 MW engine showed that 25% hydrogen blending produced better-than-expected efficiency and lower NOx emissions than anticipated, all without any engine hardware tweaks .
• 2024: Wärtsilä launched the world’s first large-scale 100% hydrogen-ready engine power plant concept. The design received Phase 1 H2-Readiness certification from TÜV SÜD .
• 2025: The company introduced the 31SG-H2 and 31H2 engine variants. It also achieved sustained pure hydrogen operation at roughly 70% of a typical marine load .
• June 2026: The Bermeo test—the first time a large-scale engine ran on 100% hydrogen while feeding a national grid .

The Cost Problem: Why €6.29/kg Matters

News coverage of the Bermeo test references a green hydrogen price of €6.29 per kilogram in Spain. This figure aligns with broader European green hydrogen cost estimates, which generally range from €5 to €8/kg depending on the cost of renewable electricity and how much an electrolyzer plant runs .

At this price, the fuel cost to generate electricity from pure hydrogen is significantly higher than burning natural gas. The engine’s value proposition, then, is not about cheap energy—it is about firm, zero-carbon, fast-ramping power that a gas turbine or battery alone cannot fully deliver. For industries with decarbonization mandates or where grid power is unreliable, that can change the calculus.

Where the Engine Will Be Used

Wärtsilä is pitching the 31H2 platform at several sectors that need exactly this combination of zero-carbon credentials and absolute reliability:

• Data centers: Data centers require firm, dispatchable backup and prime power. A hydrogen engine with a two-minute ramp time can instantly respond to grid fluctuations while meeting corporate carbon neutrality goals .
• Mining: Remote mine sites often operate on diesel power. A 100% hydrogen engine running on on-site green hydrogen produced from renewables offers a path to zero-carbon baseload without relying on a long-distance grid connection.
• Cement and heavy industry: These sectors have process emissions that are famously hard to abate. A flexible hydrogen engine can provide both the electricity and the high-temperature heat some industrial processes require.
• Textile manufacturing: In regions building out renewable hydrogen infrastructure, the engine offers a decarbonization route for the substantial power and heat loads required by textile mills.

Wärtsilä’s 31H2 engine is a piece of a larger bet: that green hydrogen can become the missing link between intermittent renewables and the industries that need electricity around the clock, no matter the weather.