Repsol and Horse Powertrain say they have developed a hybrid powertrain system that can cut fuel consumption by up to 40% when paired with 100% renewable gas. If validated in real-world driving, that would rank among the more aggressive efficiency claims for an internal-combustion-based architecture running on alternative fuels. But Europe’s documented gap between laboratory test results and actual road performance raises questions about how closely any test-cycle result will translate once drivers leave the test bench.
How the Hybrid-Plus-Renewable-Gas Formula Works
The core idea is straightforward: combine an advanced hybrid drivetrain with a fuel that qualifies as fully renewable under European Union rules. By pairing electric-assist hardware with synthetic or bio-derived gas, the system targets deep cuts in both tank-to-wheel energy use and lifecycle carbon intensity. The companies have not detailed the full test context in the sources cited here; in Europe, efficiency and CO2 figures are typically discussed using standardized type-approval cycles such as the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). That distinction matters because WLTP numbers and real-world consumption are not the same thing, and the difference directly affects how much fuel a driver will actually save over the life of a vehicle.
The European Commission’s Directorate-General for Climate Action has published evidence on real-world fuel consumption showing that on-road values for cars and vans are on average around 20% higher than WLTP type-approval figures. That gap means a large lab-reported improvement may be smaller on actual roads, and could vary further if drivers frequently operate outside the test cycle’s assumed speed and load patterns. The finding does not erase the benefit, but it forces a more honest conversation about what consumers and fleet operators should expect when these powertrains reach production vehicles, especially in mixed urban–highway use where hybrids often behave differently than they do on test cycles.
EU Renewable Energy Rules Behind the CO2 Claims
Any claim that a fuel is “100% renewable” in Europe depends on a specific legal framework, rather than a marketing slogan. The cornerstone is Directive 2018/2001, widely known as the Renewable Energy Directive, which sets binding rules for how biofuels, bioliquids, and renewable gases must account for greenhouse gas emissions across their full lifecycle. Annex V of the directive sets out calculation methods that producers use to demonstrate greenhouse gas savings. Without meeting the directive’s lifecycle accounting rules and minimum savings thresholds, a fuel generally cannot be counted toward renewable targets and related eligibility frameworks under the EU’s reporting approach.
This matters because the carbon accounting is not a simple tailpipe measurement. The directive requires tracking emissions from feedstock cultivation, processing, transport, and combustion, using detailed formulas laid out in the Annex V methodology. A renewable gas that scores well under these rules can legitimately claim near-zero net CO2 on a lifecycle basis, even though the engine still produces exhaust gases every time the vehicle is driven. For Repsol and Horse Powertrain, this regulatory architecture creates a path to market their system as a low-carbon alternative without full electrification, particularly if they can show high lifecycle savings compared with fossil fuels. The risk is that buyers may not grasp the distinction between lifecycle accounting and zero tailpipe emissions, which are fundamentally different measurements and are treated differently under other EU regulations that focus on what actually comes out of the exhaust.
Where Europe’s New-Car Emissions Actually Stand
The hybrid powertrain announcement lands against a backdrop of declining average emissions from new vehicles sold in Europe, driven primarily by rising electric vehicle registrations and tightening CO2 standards. Provisional 2023 data from the European Environment Agency shows that CO2 emissions from new cars and vans continue to fall as battery-electric and plug-in hybrid models gain market share. That data is collected under Regulation (EU) 2019/631, which sets fleet-wide CO2 performance standards for manufacturers and uses WLTP-based reporting as the official measurement, meaning that the same lab–road gap that affects Repsol and Horse Powertrain’s claims also shapes how regulators view industry progress.
Yet the trajectory is uneven, and conventional powertrains still dominate the road. Battery electric vehicles pull the average down sharply, while combustion and mild-hybrid models account for a large share of registrations in many EU member states, particularly where charging infrastructure is limited or electricity prices are high. A hybrid powertrain running on renewable gas occupies an awkward middle ground: it offers real efficiency gains over a standard gasoline engine, and potentially deep lifecycle CO2 cuts if the gas meets the directive’s criteria, but it cannot match the zero-tailpipe profile of a battery EV under current fleet-averaging rules. For automakers struggling to meet tightening CO2 targets, the technology could serve as a compliance bridge, especially in segments like commercial vans or long-distance fleets where full electrification is more challenging. Whether that bridge is durable will depend on how quickly EV infrastructure expands and how regulators treat renewable fuels in future revisions of CO2 standards.
The Real-World Gap That Could Undermine the Promise
The persistent divergence between lab results and road performance is the single biggest vulnerability for any efficiency claim tied to WLTP testing. The European Commission’s real-world fuel consumption publication, produced within the Commission’s climate policy work, summarizes on-road fuel consumption and CO2 data and reports that real-world values are on average around 20% higher than WLTP type-approval figures. That pattern, observed across vehicles and model years covered in the report, suggests the issue is systemic rather than limited to a few outlier models. Cold weather, aggressive driving, cargo loads, and air conditioning use all push real consumption well above the controlled test environment, while urban congestion and frequent short trips can erode the advantage of hybrid systems that rely on steady-state operation for peak efficiency.
For a hybrid system claiming 40% lab savings, this gap is not trivial. If the powertrain’s electric-assist calibration is optimized for the WLTP cycle’s specific speed and load profiles, real-world degradation could be even steeper than the 20% average, particularly in markets with harsher climates or hilly terrain. Diesel hybrids, gasoline hybrids, and plug-in hybrids have all shown varying degrees of this effect, with plug-in hybrids historically exhibiting the widest gap because owners often skip charging and run on the combustion engine alone. Independent, on-road validation from entities working within the Commission’s broader climate policy framework will be essential before the 40% figure can be treated as anything more than a best-case benchmark. Without transparent, real-world data, there is a risk that ambitious lab claims could fuel consumer backlash if promised savings fail to materialize at the pump.
A Bridge Technology or a Regulatory Dead End?
The deeper strategic bet behind Repsol and Horse Powertrain’s project is that advanced combustion technologies running on renewable fuels can complement, rather than compete with, electrification in the European transition. The legal text of the Renewable Energy Directive, as consolidated in the Official Journal, explicitly envisions a role for renewable fuels of non-biological origin and sustainable biofuels in cutting transport emissions, especially where direct electrification is difficult. In freight, long-distance travel, and regions with constrained grids, a hybrid system using certified renewable gas could deliver meaningful emissions reductions more quickly than waiting for full battery-electric coverage. For fuel suppliers like Repsol, such powertrains also preserve a long-term market for liquid and gaseous energy products, provided they meet the directive’s sustainability and greenhouse gas criteria.
However, the same regulatory architecture that enables renewable fuels could also limit their long-term appeal in light-duty vehicles. Current CO2 performance standards for cars and vans focus on tailpipe emissions, not lifecycle accounting, which means that a hybrid running on renewable gas still counts as a combustion vehicle in fleet averages. Unless future revisions explicitly recognize lifecycle savings from certified renewable fuels, automakers may find that investing heavily in such systems delivers diminishing regulatory returns compared with accelerating battery-electric rollouts. That tension leaves Repsol and Horse Powertrain’s hybrid concept at a crossroads: it could emerge as a pragmatic bridge technology for specific use cases, or it could become a niche solution if policymakers, investors, and consumers converge on a zero-exhaust future. The answer will hinge on how quickly Europe can scale charging networks, how strictly it interprets tailpipe-focused rules, and whether real-world data ultimately supports the bold efficiency claims now being made in the lab.
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*This article was researched with the help of AI, with human editors creating the final content.
