Why synthetic fuels face criticism: high energy use, high costs, and persistent pollution

Synthetic fuels are often considered “bad” for most road transport because they waste far more energy than direct electrification, remain expensive and scarce, and still emit harmful air pollutants at the tailpipe; their best use cases are niche sectors like long-haul aviation and parts of shipping. The debate matters now because governments and automakers are weighing whether to keep internal combustion engines alive with synthetic “drop-in” fuels or to prioritize direct electrification, and the choice affects emissions, air quality, and how quickly clean power gets built.

What “synthetic fuels” means today

Most current discussions center on e-fuels—liquid or gaseous hydrocarbons synthesized by combining hydrogen from electrolysis with carbon from captured CO2, then refined into e-kerosene, e-diesel, e-gasoline, or e-methanol. If all inputs (electricity for electrolysis and CO2 capture) are renewable and additional, these fuels can be close to carbon-neutral over their lifecycle. However, “synthetic” can also describe fuels made from fossil inputs via chemical synthesis, which do not solve the climate problem. Policymakers and engineers typically view e-fuels as a scarce, premium decarbonization option for uses that are hard to electrify.

The main drawbacks critics highlight

The following points summarize why synthetic fuels draw skepticism for mainstream road use and heating, even as they retain a role in some niches.

• Energy inefficiency: Converting clean electricity into hydrogen, then into liquid hydrocarbons, and finally back into motion in an engine loses most of the energy—cars on e-fuels consume roughly 4–6 times more electricity per kilometer than battery-electric vehicles.
• High costs and slow scaling: In 2024–2025, pilot-scale e-fuels typically cost several times more per liter than fossil fuels before taxes; building enough plants and renewable power to bend that curve will take years.
• Limited climate benefit without strict rules: If the electricity isn’t new and renewable, or the CO2 is taken from fossil smokestacks, lifecycle emissions can be far from net-zero.
• Air pollution persists: Burning e-fuels still produces NOx and some particulates, so they do not deliver the urban air-quality gains associated with zero-emission vehicles.
• Opportunity cost of clean electricity: Every MWh routed to e-fuels could displace much more CO2 if used directly—powering EVs, heat pumps, or clean industrial heat.
• Water and siting constraints: Electrolysis requires high-purity water and substantial power; concentrating production in windy/sunny regions introduces water sourcing, desalination, and transmission/logistics challenges.
• Risk of locking in old tech: Widespread e-fuel use in cars could prolong the life of internal combustion platforms and fuel distribution networks, slowing transition to more efficient systems.

Taken together, these factors make synthetic fuels a poor first-choice climate tool for sectors where direct electrification is already practical and rapidly scaling.

How inefficient are they, exactly?

Well-to-wheel comparisons illustrate the challenge. A modern battery-electric car typically delivers about 70–77% of the electricity from the grid to the wheels. An e-fuel pathway—electrolysis, CO2 capture, synthesis, refining, distribution, and engine conversion—usually ends up in the 10–16% range. In everyday terms, a car that needs ~20 kWh of electricity to drive 100 km as a BEV might require ~100–130 kWh of renewable electricity to travel the same distance on e-gasoline or e-diesel burned in an engine. That gap translates into higher system costs and far larger demands on the power grid.

Costs and availability in 2025

Even with falling electrolyzer prices and improving catalysts, e-fuels remain costly at small scale. Industry and independent analyses in 2024–2025 typically place e-kerosene and road e-fuels in the rough range of €3–6 per liter at pilot scale before taxes and credits, with substantial regional variance. Large, dedicated projects in very low-cost renewable regions could push toward the lower end later this decade, but building enough renewable generation, CO2 capture, synthesis capacity, and global logistics will take time. Policy incentives—such as the EU’s ReFuelEU Aviation mandates and U.S. clean-fuel tax credits—help seed supply but do not erase the fundamental efficiency penalty.

Emissions: climate and air quality

On climate, e-fuels only deliver deep reductions if producers use additional renewable electricity and source CO2 from the air or sustainable biogenic streams; using grid electricity with fossil intensity or capturing CO2 from a refinery flue undermines the benefit. On air quality, e-fuels still combust in engines and turbines, generating NOx and other pollutants. Some synthetic jet fuels with low aromatics can reduce soot and contrails relative to conventional kerosene, which helps climate and health impacts aloft, but they are not zero-emission.

Grid, water, and siting constraints

E-fuel plants work best where renewable power is abundant and cheap. That often means remote deserts or windy coasts, which adds transmission needs or long-distance shipping of fuel. Electrolysis consumes significant volumes of demineralized water; if desalination is required, that adds cost, energy use, and brine management considerations. All of this can be done responsibly—but it raises barriers to rapid, massive deployment.

Where they might still make sense

Despite the drawbacks for cars and buildings, synthetic fuels can play a useful role in specific segments that are difficult to electrify directly or require drop-in compatibility with existing hardware.

1. Aviation: Long-haul flights lack a near-term, scalable alternative; synthetic e-kerosene (a form of sustainable aviation fuel) is one of the few pathways that can cut lifecycle CO2 at scale if made with genuinely green inputs.
2. Deep-sea shipping and some heavy industry: Options such as e-methanol, e-ammonia, or synthetic diesel can decarbonize long-range vessels and specialized machinery where batteries are impractical.
3. Legacy and niche uses: Emergency services, remote operations, or classic vehicle fleets may rely on limited volumes of drop-in fuels while broader systems electrify.

In these cases, policymakers increasingly pair limited e-fuel mandates with strict “additional renewable power” and carbon-accounting rules to ensure real climate benefits while preserving scarce supply for the hardest problems.

Policy backdrop in 2024–2025

Regulators are trying to align scarce e-fuels with the sectors that need them most. The EU’s ReFuelEU Aviation policy ramps sustainable aviation fuel blending from the mid-2020s onward, with a dedicated sub-quota for synthetic e-kerosene rising over time. FuelEU Maritime, starting in 2025, tightens greenhouse-gas intensity for marine fuels, encouraging e-methanol, e-ammonia, and other low-carbon options. A separate EU arrangement allows sales of new cars after 2035 only if they run exclusively on certified carbon-neutral fuels—a narrow carve-out that remains contentious because of the efficiency and enforcement challenges. In the United States, clean-fuel production credits and SAF incentives help early projects but are time-limited and contingent on robust lifecycle accounting.

Bottom line

For most road transport and heating, synthetic fuels are a poor fit: they are energy-inefficient, expensive, and still pollute at the tailpipe. Their highest and best use is as a scarce decarbonization tool for aviation, parts of shipping, and a handful of niche applications—provided strict rules ensure truly renewable electricity and verifiable lifecycle CO2 reductions.

Summary

Synthetic fuels face criticism because they convert valuable clean electricity into motion very inefficiently compared with direct electrification, remain costly and supply-constrained, and do not eliminate local air pollution. They can still matter in hard-to-electrify sectors like long-haul aviation and deep-sea shipping, where drop-in compatibility is essential and alternatives are limited. Policy is increasingly steering scarce e-fuels toward those niches, while cars, vans, and buildings decarbonize faster and cheaper through direct electrification.