Wallbox with surplus PV charging: what it must do and what you need
In short: With surplus PV charging, the wallbox charges the car only with the solar power that the house does not currently need. To achieve this, a meter at the grid connection measures the surplus, and the wallbox and inverter must work together. Most cars charge from 6 amps upwards, which equates to around 1.4 kW for single-phase and around 4.1 kW for three-phase. Automatic phase switching allows the wallbox to start charging once there is a surplus of just 1.4 kW. According to HTW Berlin, compared with uncontrolled charging, surplus charging can increase the proportion of solar power used for charging by an average of 25 percentage points.
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How PV surplus charging works
A photovoltaic system often generates more electricity at midday than the house currently needs. Without a storage system, this surplus flows into the grid. If there is an electric car in the garage, it can absorb it. A wallbox with PV surplus charging regulates the charging power so that the car charges using this surplus as much as possible. This page explains what needs to be compatible for this to work.
The wallbox must know how much surplus solar power is currently available. To this end, an additional electricity meter at the grid connection measures whether electricity is flowing into the grid or coming from it. According to HTW Berlin, the wallboxes use this to determine the surplus solar power within milliseconds (Wallbox Inspection 2025). Depending on the system, the wallbox either reads the meter itself or receives the value from the inverter.
If the surplus increases, the wallbox increases the charging current; if someone in the house switches on the hob or a cloud rolls in, it reduces the current. The ADAC recommends sourcing the components from the same manufacturer wherever possible, so that they are compatible with one another.
From what surplus level does charging begin?
An electric car does not charge at just any low power level. In accordance with the IEC 61851-1 standard, the wallbox reports a charging current of at least 6 amperes to the car. According to HTW Berlin, this results in:
| Connection | Minimum power at 6 A |
|---|---|
| single-phase | around 1.4 kW |
| three-phase | approximately 4.1 to 4.2 kW |
According to the ADAC, some vehicles only start charging from 8 amps. If the surplus is below the minimum output, the wallbox either does not charge at all or supplements the charge from the mains or a storage unit. How the wallbox behaves in this situation depends on the system and is specified in the manufacturer’s instructions.
Why phase switching matters
A three-phase wallbox, which always charges in three phases, only starts charging once there is a surplus of around 4.1 kW. On many days – in spring, in autumn and with smaller systems – this amount is not reached. An automatic phase-switching system charges in single-phase mode from 1.4 kW when there is little surplus, and switches to three-phase mode when there is sufficient electricity available.
- The ADAC strongly recommends automatic phase switching for efficient surplus PV charging. Without it, charging starts and stops constantly on days with fluctuating conditions, which some vehicles interpret as a fault and abort the process.
- In the 2025 Wallbox Inspection carried out by HTW Berlin, Fraunhofer ISE and ADAC, the wallboxes tested with phase switching in pure three-phase operation would, according to calculations, achieve a Wallbox Performance Index that is approximately 10 percentage points lower – a measure of cost savings.
- Limitation from the same study: Single-phase chargers in cars generally operate with lower efficiency than three-phase ones.
A single-phase wallbox does not require a switch; it charges from 1.4 kW anyway, but at a maximum of 7.4 kW.
What it achieves
HTW Berlin has analysed measurement data from 730 households (study ‘Solar Charging of Electric Vehicles’, April 2025). The proportion of solar energy used for vehicle charging averaged 53 per cent. Compared with uncontrolled charging at full power upon arrival, the proportion of solar energy can be increased by an average of 25 percentage points through dynamic surplus charging; this varies considerably depending on the household. How much this amounts to for you depends on when the car is parked at home: those who commute during the day rarely charge at midday.
The wallboxes in the range
All information is in accordance with the manufacturer’s data sheet and instructions:
| Wallbox | Connection, power | Surplus shop | Prerequisite | Phase switching |
|---|---|---|---|---|
| Fronius Wattpilot Home 22 J 2.0 | 1- or 3-phase, up to 22 kW | yes, from 1.38 kW | A compatible Fronius inverter on the same network and a Fronius Smart Meter; for inverters from other manufacturers, a Fronius Smart Meter IP at the feed-in point and no additional self-consumption controller, such as a battery | automatically |
| SAJ AC011K-AE-35 | 3-phase, 11 kW | yes | SAJ eManager and an SAJ storage system (H2+B2, HS2, AS2 or HS3) | automatically |
| Solplanet SOL 7.4H, 11H, 22H | 1-phase 7.4 kW, 3-phase 11 or 22 kW | Solar charging function optional | Energy meters | Not specified |
| Huawei AP07N-EU | Single-phase, 7.4 kW | yes | Compatible Huawei inverter with SmartDongle and Smart Power Sensor | Not applicable (single-phase) |
| Sungrow AC007E-01 | Single-phase, 7.4 kW | according to the data sheet in conjunction with Sungrow | As specified in the data sheet for single-phase Sungrow hybrid inverters of the SHRS series; confirm compatibility with the manufacturer | Not applicable (single-phase) |
All devices are listed under ‘Wallboxes’. Information current as of October 2026. The Fronius Wattpilot and the Huawei AP07N-EU have a Type 2 socket instead of a fixed cable; this requires a Type 2 charging cable, such as those from Fronius with lengths of 5 or 7.5 metres.
What to bear in mind
- Compatibility with the inverter: Check whether the wallbox and inverter are compatible according to the manufacturer. The table above lists the requirements; to find out which inverter is suitable for your system, see ‘Hybrid, string or micro inverter: which one is right for you?’.
- Meter at the grid connection: Without a meter at the grid connection, there can be no surplus charging; how the meter operates there is explained under ‘zero feed-in’ and ‘feed-in limitation’. Meters are covered under ‘Smart Meters for PV’: energy meters for inverters, and measurement sensors are also listed under inverter accessories; the manufacturer will specify which one is suitable for your system.
- Phase switching in three-phase wallboxes: this determines whether charging begins at 1.4 kW or only at around 4.1 kW.
- Storage and car: For systems with battery storage, specify whether the storage unit or the car is charged first. Information on how large a storage unit should be can be found under ‘Energy storage: How large should it be, and how much does it cost?’.
- Connection and registration: A qualified electrician will carry out the permanent connection to the domestic electrical installation. You can find out from your network operator whether and how you need to register the wallbox.
