How much energy does a car really take out of the ground?
An interactive well-to-wheel comparison of six powertrains — battery electric, hydrogen by electrolysis, hydrogen by steam reforming, petrol, diesel and hybrid. Every link in the chain is a slider carrying its own source, and the Sankey diagram, the overall efficiency and the running cost are recomputed live.
By Robin Girard, MINES Paris — PSL.
Open the current version — v1.0.
It runs entirely in your browser, from a single file. Nothing is sent anywhere.
What it is for
Three method choices decide the headline number more than the engineering does, and the tool lets you move each one and watch the answer change:
- the perimeter — the same electric car reads 21.9% well-to-wheel and 48.6% plug-to-wheel, and the second figure is the one that reaches the brochure;
- the primary-energy convention — physical content, substitution or direct equivalent, which moves the same French-grid car from 17.6% to 41.4%;
- the type-approval cycle — the JEC publishes both NEDC 2015 and WLTP 2025+, and the WLTP demands 19% more useful work for the same 100 km, so efficiencies jump while consumption barely falls.
Default values reproduce the JEC Well-to-Wheels report v5 (JRC, EUCAR and Concawe, 2020), the European Union’s reference study, which simulates the same C-segment vehicle in every powertrain — so the comparison is honest at equal service. Each chain closes on the JEC’s published consumption to within 0.2%.
Why it is worth checking
Every slider carries the source of its value underneath it, and where sources disagree the disagreement is shown rather than averaged away — including two places where the JEC contradicts itself. Peak efficiency and cycle-average efficiency are always distinguished, in both directions: a petrol engine advertised at 50% delivers 42% in production and around 20% over a real cycle, and an electric drivetrain advertised above 98% measures 63.9% over the WLTC.
Source code, sources and the reproducible figures: git.persee.minesparis.psl.eu/energy-alternatives/car_efficiency
Content under CC BY 4.0, code under the MIT licence — reuse it in your own teaching, translated or cut up, and say where it came from.
Versions
Each minor release keeps its own permanent link, so a link given to a class still opens the model it was given against.
Page updated 2026-08-25.