How solar EV charging works
A grid-connected PV inverter supplies the home’s AC system from the PV array. Its output can serve appliances, charge a battery, supply an EV chargepoint or be exported. There is no separate connection from the panels to the car.
A solar-capable chargepoint or home-energy controller measures the balance at the grid connection. When the home is exporting, it can increase the AC current offered to the EV. When household demand rises or PV output falls, it can reduce that current or pause charging.
The relevant balance is:
available surplus = PV generation − household demand − other charging loads
This is a live measurement rather than a prediction based only on the PV array rating. A nominally large array can have little surplus during poor weather or when other appliances are running. A smaller array can produce useful surplus during a quiet part of the day.
Equipment and compatibility
The basic arrangement needs:
- a PV system operating on the home’s AC installation
- a controllable Mode 3 EV chargepoint
- a compatible vehicle and charging lead
- a meter or CT at the correct measurement point
- a control connection between the measurement device and the chargepoint
- suitable commissioning access to the chargepoint, inverter and any home battery
The manufacturer may describe the function as solar, surplus, eco or green charging. Those labels do not establish how much grid import the mode allows. Check the operating description and available settings.
Some chargepoints provide the control themselves. Others depend on an inverter, home-energy-management platform or third-party controller. Product compatibility should cover the exact chargepoint model, inverter or meter, software service and vehicle. Sharing an app does not prove that all the devices use the same measurement or control logic.
The chargepoint’s normal electrical requirements still apply. Its circuit, RCD, open-PEN measure, cable route and site limit are not replaced by the solar-control function. The home EV charger installation guide covers the fixed installation and handover records.
Measuring import and export
The controller normally measures at the point where the home exchanges electricity with the grid. A CT must enclose the intended single conductor, face the correct direction and be associated with the correct phase. A meter must also be wired and configured for the intended boundary.
The correct location may not be immediately beside the electricity meter. The installer needs to understand:
- whether PV and the chargepoint are supplied through the same or different consumer units
- whether the property has more than one distribution board
- where a home battery connects
- whether the supply is single-phase or three-phase
- whether another building or submain sits inside the measured boundary
- whether an export-limitation scheme has its own measurement and controller
A reversed sensor can make the chargepoint increase demand when the home is importing. Measuring only one branch can hide loads elsewhere. Incorrect phase mapping on a three-phase installation can produce a plausible total while one phase is unsuitable.
Commissioning should create known import and export conditions and confirm the value and direction seen by the controller. It should also check the result when a substantial household load switches on.
Minimum AC charging current
Mode 3 AC charging communicates an available current to the vehicle through the control pilot. The standards minimum is 6 A per active phase. On a nominal single-phase UK supply, 6 A is approximately 1.4 kW.
The controller cannot keep reducing charging smoothly below the minimum. If the measured surplus falls below it, the chosen mode must:
- pause until enough surplus returns
- import enough electricity to maintain the minimum current
- combine PV with a permitted battery or grid contribution
The car may also take time to resume after a pause and some vehicles respond better than others to repeated starts. The nominal standards threshold is not a guarantee that every car will start and remain stable at precisely 6 A.
Three-phase charging raises the total minimum because the current applies on every active phase. Some systems can switch between single-phase and three-phase charging, but that transition has to be specifically supported by the chargepoint and vehicle. It should not be inferred from the Type 2 connector.
Solar-only and blended charging
A strict solar-only setting aims to avoid grid import for EV charging. It may pause frequently when cloud passes or household demand changes. It can work well when the car is parked for long periods and the owner does not need a fixed amount of energy by a near deadline.
A blended setting allows the grid to supply the shortfall below the charging minimum. Charging is steadier, but part of the session may be imported. The permitted import may be a fixed allowance, the minimum current or another product-specific value.
The control configuration records:
- the selected operating mode
- the grid-import allowance
- the delay before charging starts or stops
- the response when surplus rises or falls
- the manual override
- the behaviour after loss of meter or internet data
Use the product’s start, stop and control-margin settings to avoid repeated starting and stopping, then verify them with the installed vehicle. A mode name alone is not adequate commissioning evidence.
Coordinating the EV and home battery
An EV and home battery can both absorb PV surplus. If their controls work independently, each may react to the same grid measurement. The home battery may discharge into the car or the two controllers may repeatedly change direction around zero import.
Set an explicit order for the flexible loads. For example, the owner may want to preserve a backup reserve, charge the home battery for evening use, give the EV enough energy for tomorrow and then export the remainder. A different household may need the EV first.
The settings needed to implement the order depend on the equipment. They may include a battery reserve, EV minimum energy target, separate start thresholds or different delays. After changing a battery mode, confirm that it has not changed the source of EV energy.
Hot-water diversion and other controlled loads need the same treatment. Two devices independently trying to consume every exported watt are unlikely to maintain a stable priority without coordination.
Tariff charging, export and journey requirements
Solar self-consumption and charging cost are related but are not interchangeable.
Using a unit of PV electricity in the car means giving up any export payment that would otherwise apply. Importing during a low-price period may cost less than the export value in some tariff combinations, while other combinations favour direct solar use. Battery conversion losses also affect a plan that stores PV before transferring energy to the car.
Set the minimum energy or state of charge the car must have by departure. Solar charging can then be used for any flexible part of the session. Before a long or time-critical journey, a scheduled grid charge may be more reliable than waiting for uncertain daytime generation.
The EV electricity tariff guide explains how to compare the whole-home effect of import rates, export terms and smart-control eligibility. Current supplier rates should be checked when the decision is made rather than copied into a permanent chargepoint setting.
Avoid running active schedules in the vehicle, chargepoint and supplier service unless their interaction has been tested. One should be the primary scheduler. Electrical load management remains authoritative whichever service decides when charging is permitted.
Dynamic load management and export limitation
PV surplus control varies EV demand to improve on-site use. Dynamic load management reduces demand to keep the installation within an import or circuit limit. G100 export limitation controls generation or storage to keep export within an agreed limit.
These are different functions even if they share a meter, CT or controller.
PV output does not justify increasing the chargepoint’s configured site limit. Internal cables and switchgear still carry current according to their physical arrangement. Household demand can also rise suddenly while the EV is charging.
Where the property has an approved export-limitation scheme, the EV should not be treated as its fail-safe export control unless it is part of the documented design. The scheme must remain compliant when the car is absent, full, disconnected or not accepting charge.
Commissioning the complete arrangement
Commissioning should use the actual installation and, where possible, the owner’s vehicle. A sensible test covers:
- confirmed sensor direction and phase mapping
- known grid import and export
- surplus above and below the vehicle’s minimum current
- a substantial household load switching on and off
- the home battery charging, idle and discharging
- any hot-water diverter or second flexible load
- site load-management throttling
- loss of meter, CT or communications data
- vehicle unplug, reconnect and pause recovery
- the configured manual override
Record the observed grid allowance and the approximate delays before the chargepoint changes current or pauses. Confirm that a communications failure cannot defeat the electrical site limit.
The handover records the final sensor location, selected mode, battery and EV priority, configured site limit, fallback method, account ownership and administrator access.
Reviewing performance
Use half-hourly or finer interval data where it is available. Compare:
- PV generation
- grid import and export
- home-battery charge and discharge
- chargepoint consumption
- energy reported by the vehicle
The figures will not match exactly because they can cover different time intervals and measurement points, and conversion losses occur between the meter and traction battery. Compare the interval series rather than relying on a single daily percentage.
Unexpected grid import during solar mode may be intentional minimum-current support, a control delay, a household load or a measurement fault. Unexpected battery discharge into the EV usually points to the chosen priority or to two controllers acting independently. Review the settings and commissioning evidence before changing an electrical limit.