An EV's dashboard efficiency describes energy used by the vehicle, while the utility meter sees additional charging losses. A useful home-cost estimate connects both sides.
Start with miles per kWh
Divide miles driven by vehicle efficiency in miles per kWh. That estimates energy delivered from the battery for driving. Use a long-term average rather than a single ideal trip.
Weather, speed, cabin heating, air conditioning, elevation, tires, payload, and towing can all move the efficiency number.
Account for charging loss
Energy is lost in the charging process and in battery conditioning. Divide battery energy by charging efficiency to estimate energy drawn from the grid. At 90% efficiency, delivering 90 kWh to the vehicle requires about 100 kWh from the utility.
Charging efficiency varies with vehicle, equipment, power level, temperature, and battery state. Treat a default percentage as a planning assumption rather than a vehicle specification.
- Battery energy = miles ÷ miles per kWh
- Grid energy = battery energy ÷ charging efficiency
- Charging cost = grid energy × electricity rate
Model the tariff you actually use
A flat electricity rate is straightforward. Time-of-use plans require separating charging into rate periods. Some plans also include demand charges or special EV rates.
Fixed household utility charges usually should not be assigned to the EV unless adding the vehicle caused the charge. Equipment purchase and installation are separate ownership costs.
Compare EV and gasoline fairly
Compare the same annual mileage and realistic efficiency for each vehicle. Energy cost is only one part of ownership; purchase price, depreciation, insurance, maintenance, taxes, and public charging may be more significant.
The Abelost comparison tool intentionally labels its result as energy savings, not total ownership savings.
Use real-world miles per kWh, include charging loss, and separate home electricity from higher-priced public charging.
Frequently asked questions
Why is grid energy higher than battery energy?
Charging equipment, conversion, battery conditioning, and other processes lose some energy. Dividing battery energy by charging efficiency estimates what the utility meter sees.
Should public charging be included in a home charging estimate?
Calculate it separately because public charging can use different per-kWh, per-minute, session, or idle fees. Combine the totals only after each charging location is modeled.
Sources and further reading
Sources support the methods and practical guidance above. Product specifications and local requirements should take priority for a specific project.
U.S. Department of Energy Alternative Fuels Data Center Official background on residential EV charging and charging equipment. ↗ FuelEconomy.gov Official vehicle efficiency and fuel-economy comparison information. ↗