EV running cost per kilometre

The kilometre as the unit electricity is really bought in

The relation changes the unit of account. The charging page in this cluster prices a session — a battery window refilled at the wall — but sessions are irregular and hard to compare, while distance is what driving is measured in everywhere else: commutes, fuel economy figures, mileage allowances. Spreading the car’s rated consumption over the distance it describes, and pricing the result at a tariff, yields the cost of a kilometre — small on its own, decisive in aggregate.

The rated consumption is the vehicle’s energy label. Like an appliance label it comes from a standardised test cycle, which makes it fair between models and optimistic about your driving: speed, climate control, terrain and temperature all push a real car above its rating. The figure the trip computer averages over your actual driving is the honest replacement once you own the car — and be aware the rating and the trip computer do not always meter the same point in the chain, since energy lost in charging is priced by the wall even when the dashboard never saw it. The charging page carries that loss term.

Per-kilometre is the unit where drivetrains meet. The same quantity exists for the incumbent car — fuel consumed per distance, times the price of fuel — computed from your own receipts and the fuel price you actually pay, both of which are yours to supply, not facts a page should assert. Set the two per-kilometre figures side by side and the running-cost half of the switching decision is one subtraction, at your tariff and your fuel price rather than a brochure’s.

The pack also declares the reverse workflow: fix a cost per kilometre and the engine returns the consumption rating that produces it at your tariff. Run it with a target to get the rating to shop for; run it with the per-kilometre cost your own records imply — a period’s charging spend spread over its odometer distance — and it recovers the consumption your driving actually achieves, which is the rating audited against reality.

When this calculation is used

• Putting a number on the electric side of a switching decision, against the incumbent car’s fuel cost per kilometre from your own receipts.
• Comparing candidate EVs by what their ratings cost per kilometre at your tariff, which is the efficiency gap between them expressed as money.
• Pricing a commute or an annual distance: the per-kilometre figure scaled by the driving you actually do is the EV line of a household budget.
• Solving backwards — the declared reverse workflow — from a recorded per-kilometre spend to the real-world consumption it implies, as an audit of the rating.

Worked example

Price the pack’s anchor car: a vehicle rated at eighteen kilowatt-hours per hundred kilometres, charged at a tariff of fifteen hundredths per kilowatt-hour.

The engine returns the electricity cost of one kilometre. Read it beside the same quantity for the car it would replace — fuel per distance times your local fuel price, from receipts rather than brochures — because per-kilometre is the only unit in which the two drivetrains answer the same question.

Then run the declared reverse with your own records: spread a period’s charging spend over the distance the odometer added, enter that per-kilometre figure, and the engine returns the consumption your driving really achieves — the number to hold against the rating the brochure promised.

What each input represents

Assumptions and limits

• The rated consumption stands in for real driving: test cycles do not include your motorway share, your winters or your cabin heating, all of which raise the true figure.
• One tariff prices every kilometre — a car that splits its charging between a cheap overnight window and public chargers needs a blended rate to be represented honestly.
• Only electricity is priced. Battery degradation, tyres, insurance and servicing belong to a total-cost view; this page isolates the energy line of it.
• Whether charging losses are inside the entered consumption depends on where it was measured — a wall-side rating carries them, a dashboard average may not — and the choice moves the answer.

What the guards protect against

• A rated consumption of zero is refused — the pack ships that refusal as a declared test vector — because a car that consumes nothing per kilometre is not a rating but a missing entry, and pricing it would report free driving.
• The consumption is capped far beyond any passenger vehicle’s rating, which catches the neighbouring unit slips — watt-hours per kilometre, or kilometres per kilowatt-hour inverted — before they price a car an order of magnitude wrong.
• The tariff is capped far above any retail rate, so a price entered in cents where currency per kilowatt-hour belongs is refused as the hundredfold error it is.

Provenance

EV per-distance cost relation (consumption-rating convention)

The rated consumption per hundred kilometres is scaled to one kilometre and multiplied by the entered tariff to give the cost per kilometre driven; the declared reverse workflow solves for the consumption rating that produces a target per-kilometre cost.

A screening figure for a switching or shopping decision, not vehicle-cost advice — your receipts and your bill outrank any rating. What the page displays is computed after mount by the engine of a pack release whose signature is verified over its exact bytes; the pack carries the citation of record, and the page reports the verification state of the release it loaded.