EV charging

Why joint optimisation matters

The best charging plan depends entirely on your tariff. On a plan with a free or super-cheap window, the optimiser packs charging into that window. On a flat rate, it favours solar you’d otherwise export for little. With export-rewarding prices and V2G, it can even pay to charge cheap and sell back at the evening peak. Same car, same house — three different plans. That’s why the car can’t be planned in isolation from the house.

The fields

• EV battery size (kWh) — the car’s usable battery capacity (typically 40–100 kWh; check your car’s spec sheet).
• Charger rate (kW) — your home charger’s maximum speed. Common values: 1.8–2.4 (portable / wall socket), 7.4 (single-phase wallbox), 11 or 22 (three-phase).
• Charge now (%) — the battery level the car arrives home with. On multi-day forecasts, the car restarts at this level each time it plugs back in — your daily driving is baked into that number.
• Charge needed (%) by (each day) — the level you want by your departure time, every day. Set 100% for a full battery. The deadline is “best effort”: if it’s physically impossible (window too short, charger too slow), the simulator gets as close as it can rather than failing.
• Plugged in — when the car is home and connected. Overnight suits commuters; Daytime suits a car that stays home while you work elsewhere; Custom lets you set any window (a start later than the end wraps past midnight). The car only charges — or discharges — while plugged in.

Vehicle-to-home / grid (V2G)

With a bidirectional charger, the car can run the house or export to the grid when prices make it worthwhile. Turn on the V2G toggle and set:

• Driving reserve (%) — a floor the car never discharges below, so it’s always ready to drive.
• Discharge rate (kW) — the charger’s maximum export speed (often the same as its charge rate).

Battery wear (~5c/kWh) is costed into every discharge decision, so the car only discharges when the price spread genuinely pays — it won’t cycle your battery for pennies. On export-rewarding tariffs the optimiser can earn more than charging costs, and the results will show a net earning rather than a cost.

Reading the results

A headline card at the top of the results shows what charging cost with the optimised plan versus what the same energy would have cost charging naively from the grid, plus the petrol and distance your charge displaces. Below the home energy-flow chart, a dedicated EV chart shows charging (green), V2G discharge (red, below the axis) and the car’s charge (blue line) through the day.