Why E-Fuels Waste 84% of Their Energy — And Why That Still Isn’t the Whole Story

Explainer · Efficiency · Policy · August 2026

Why e-fuels waste 84% of their energy — and why that still isn’t the whole story

Critics say it takes five times more renewable electricity to drive a kilometre on synthetic fuel than on a battery. They are right.

Photo : Unsplash — libre de droits

Step one: follow one kilowatt-hour from the wind turbine to the wheels

The clearest way to understand the objection is to take a single kilowatt-hour of renewable electricity and watch what happens to it on each of the two routes. Every arrow in an energy chain has a cost. The question is simply how many arrows there are.

Put side by side, 16% against 72%. That ratio — roughly a factor of four and a half, often rounded to “five times more electricity” — is the entire objection. It comes from the International Council on Clean Transportation; the peer-reviewed engineering literature reaches 13% against 73% by the same method. Transport & Environment uses it to argue that supplying even a tenth of new car demand with e-fuels would consume an implausible share of Europe’s renewable build-out.

⚡ Battery-electric · city car 72% Reaches the wheels. Cheaper per kilometre, fewer moving parts, and the gap does not close with better electrolysers. For a car with access to a charging point, this is simply the better technology.

⚗ E-fuel · same city car 16% Reaches the wheels. Five conversion steps and a heat engine at the end. Anyone presenting synthetic fuel as the efficient choice for urban driving is stating something that is not true.

Step two: the question the ratio cannot answer

An efficiency comparison answers “which of these two should I choose?” It says nothing at all about situations where there is only one option on the table. That distinction is where most of this debate goes wrong.

Aviation is the clearest case, and the reason is physics rather than policy. Energy density — how much energy fits in a kilogram — is not something engineering improves incrementally. It is a property of chemistry.

The same reasoning governs deep-sea shipping, long-distance heavy freight, industrial process heat above roughly 800°C, off-road and remote equipment beyond the reach of any grid, and the roughly 1.4 billion combustion vehicles already on the world’s roads — which will not be replaced for decades, and which drop-in synthetic fuel can decarbonise without waiting for fleet turnover.

It is worth noting that the ICCT, which produced the 16% figure, explicitly endorses battery-electric aircraft for commuter flights of 9 to 19 passengers under 200 kilometres. The disagreement is not about whether batteries work. It is about range.

Deep-sea shipping — the second sector where the efficiency comparison has no second term. A container vessel on Rotterdam–Shanghai cannot carry the batteries. FuelEU Maritime, binding since January 2025, assumes e-methanol and e-ammonia as the compliance pathway. · Photo : Unsplash — libre de droits

Step three: the hidden premise in the objection itself

Here is the point both sides tend to skip. Ask why a 16% efficiency matters, and the honest answer is: because the thing you are losing is expensive. Wasting 84% of a cheap and abundant input would be untidy but tolerable. Wasting 84% of scarce renewable electricity is a serious argument.

The efficiency objection is therefore, at bottom, an argument about the cost of electricity. Every credible version of it — the ICCT’s, T&E’s, the academic literature’s — rests on that premise, usually without stating it.

Hydrogen accounts for roughly 55% of the production cost of a synthetic fuel. Made by electrolysis at today’s €3–6 per kilogram, the objection holds with full force. But electrolysis is not the only way to obtain hydrogen.

Natural geological hydrogen is produced continuously in the Earth’s crust by serpentinisation — iron-rich rock reacting with deep groundwater — and consumes no electricity at all. FDE confirmed 49.6% H₂ at 2,426 m in the PTH-2 borehole in Lorraine in June 2026, and targets €0.50/kg by late 2028, subject to REGALOR II certification expected in 2027. · Photo : Unsplash — libre de droits

What would prove this article wrong

Intellectual honesty requires naming the conditions under which the argument above fails. Three would do it.

One. If REGALOR II certification does not confirm a commercially recoverable Lorraine resource in 2027, the €0.50/kg premise collapses and the efficiency objection reasserts itself at full strength. Two. If natural hydrogen turns out to be geographically rare rather than widespread — a genuinely open question, which the European Commission’s Getech mapping programme across all 27 member states is designed to answer by 2027 — the pathway stays niche. Three. If battery specific energy reaches 1,500 Wh/kg at pack level, the aviation argument weakens considerably, although no credible roadmap currently shows that before 2050.

Readers should hold this publication to those conditions.

The honest summary

Nothing here requires abandoning the case for synthetic fuels. It requires making that case where it holds and conceding it where it does not. A publication that never states the principal objection to its own subject is not a reference source; it is advocacy, and readers are right to discount it accordingly.

The efficiency critics have won the argument about cars. They have not won the argument about aircraft, ships or the 1.4 billion vehicles already on the road — because in those sectors the comparison they rely on has no second term. And the economic force of their objection rests on a premise, expensive hydrogen, that Lorraine may or may not overturn in 2028.