EngineerHub.orgWhat this scheduler does
The model calculates the battery energy required, determines the EV power available in every half-hour, and ranks available energy by marginal cost. Surplus solar is treated as zero-cost; negative-price grid periods can rank even lower. The result is compared with charging immediately at the maximum available power.
How to build a charging plan
Enter when the car is plugged in and the next departure time. Overnight windows can cross midnight.
Use battery percentages, or estimate the energy needed for tomorrow's driving distance.
Select charger power, main fuse, household load and optional solar. Use realistic simultaneous demand.
Start with a simple tariff preset, then replace it with the prices and variable charges that apply to your contract.
Start simple: use the Night-rate commuter preset, change only your plug-in time, departure time, battery need and electricity prices, then refine the household-load assumptions.
Vehicle, home and tariff
Example scenarios
Charging requirement
Home import limit
Household demand and solar
Electricity tariff
Enter energy prices in currency/kWh. Taxes and network charges should be included if they vary with consumption and are avoidable.
Quick paste: paste 24 hourly values separated by spaces, commas, semicolons or line breaks, starting at 00:00.
Smart-charging result
| Strategy | Battery energy | Grid energy | Cost | Peak import |
|---|
Tariff, household load and charging timeline
Price is shown in the upper band. The lower chart shows household grid import and the additional EV grid import. Green markers identify EV energy supplied from surplus solar.
Scroll horizontally to view the complete charging window.
| Time | Price | House load | Solar | EV power | Grid import | Battery energy | Cost |
|---|
Worked example: overnight commuter charging
A 75 kWh battery rises from 35% to 80%, requiring 33.75 kWh in the battery.
An 11 kW charger shares a 3 × 25 A supply with the household and keeps a 10% reserve.
The smart schedule moves charging into the lowest-cost feasible periods and compares the result with charging immediately.
Background
Engineering basis, assumptions, interpretation and practical limitations.
Replace the example prices with the hourly or time-of-use rates that apply to your home, including relevant energy taxes and variable network charges.
Choose values that represent simultaneous demand, not monthly average consumption. Heat pumps, water heating, cooking and sauna use can sharply reduce charging headroom.
A schedule alone cannot respond to unexpected household demand. Dynamic current control requires compatible charger hardware and a correctly installed meter or current sensor.
Winter heat-pump demand and summer solar production can create very different charging opportunities even with the same tariff.
Battery energy required: Ebat = Cusable(SOCtarget − SOCstart)
Available EV power: PEV,max = min(Pcharger, Pimport,limit − Phouse + Psolar)
Battery energy in one step: ΔEbat = PEVηΔt
The optimization is a simple least-cost allocation: surplus-solar segments are assigned zero cost, while grid-energy segments use the entered tariff. All segments are then ranked from lowest to highest marginal cost, so a negative grid price can rank ahead of zero-cost solar.
- Half-hourly steps and constant values within each step.
- One charging window, no battery preconditioning or taper near high state of charge.
- Three-phase household demand and solar are assumed balanced. Chargers below 10 kW are treated as single-phase; 11 kW and 22 kW chargers are treated as balanced three-phase loads.
- No charger minimum-current, phase-switching, reactive-power or thermal-derating model.
- Solar output is an idealized clear-sky shape, not a weather forecast.
- Solar export value, battery degradation, fixed charges and demand charges are excluded.
Frequently Asked Questions
Practical questions about assumptions, inputs, interpretation and limitations.
It ranks available half-hour charging energy by marginal cost while respecting charger power and household import headroom.
No. The included tariffs are illustrative. Enter the prices from your own contract, retailer or market-price source.
The model limits charging to calculated headroom, but real protection requires compatible dynamic load management and a correctly designed installation.
The window may be too short, the charger too small, or household demand may leave too little electrical headroom.
Not always. If exported solar has value, enter that value as an opportunity cost.
Use battery percentage when the car reports a reliable state of charge and you know the desired target. Use driving distance for a simple estimate of tomorrow's energy need.
Use the avoidable price for each kWh, including energy, taxes and variable network charges where applicable. Fixed monthly charges do not change with charging time.
Charging from surplus solar may give up export revenue. Entering that value lets the scheduler compare solar use with cheap grid periods more fairly.
No. It produces a planning schedule. Automatic control requires compatible vehicle or charger hardware and the correct tariff data.