PV surplus charging: charge your EV with solar power, cheaply and intelligently
With a photovoltaic system, you generate electricity for your household, heat pump or battery storage – and, with the right wallbox, for your electric car too. The key question is not “Which wallbox offers PV charging?” but: Does the wallbox suit your PV system, your metering system, your energy management and your vehicle?
Key points at a glance
- Charging only uses the solar power that the house does not need at that moment.
- You need a PV system, a metering system, a compatible wallbox and a controller on the same network.
- Single-phase charging starts from around 1.4 kW of surplus, three-phase from around 4.1 kW.
Contents
- What is PV surplus charging?
- What do you need?
- Single-phase or three-phase charging
- PV surplus charging with a plug-in hybrid
- Prioritising PV, storage and heat pump
- PV surplus and dynamic load management
- Common mistakes when buying
- Checklist before buying
- Frequently asked questions
What is PV surplus charging?
An energy management system continuously measures how much electricity the PV system is generating and how much is currently being consumed in the building. If there is more solar power than the house needs, the system passes the spare power on to the wallbox. The wallbox starts or regulates the charging process automatically.
The priorities are usually set as follows:
- PV power supplies the consumers in the house first.
- Depending on the settings, a battery storage system is charged.
- The remaining surplus goes into the electric car.
- If the PV output is insufficient, the wallbox reduces the charging power or pauses.
This way your car charges with as much self-generated electricity as possible, without you having to intervene.
What do you need?
1. A PV system
What matters is not just the output in kWp, but how much surplus regularly remains during the day after deducting household consumption. Small systems can also make sense – the car then charges more slowly or only when there is enough sun.
2. A metering system
For PV surplus charging, the energy flow must be measured precisely. There are two ways to do this:
- Smart meter at the grid connection point: measures the current flow between house and grid and detects consumption from or feed-in to the grid.
- Current transformers at the inverter or in the distribution board: measure PV generation or individual circuits, usually in combination with an inverter or energy manager.
Both options work. What matters is that the system can correctly calculate the net power of the house or the PV surplus. The meter in the wallbox is not sufficient for this – it only measures the charging current.
3. A shared network and Modbus
All components must be connected to the same local network so that they can communicate reliably with each other:
- Inverter, smart meter, wallbox and energy manager are connected to the home network via LAN or Wi-Fi.
- Communication usually runs via Modbus (TCP or RTU).
- Depending on the system, MQTT, OCPP or manufacturer-specific interfaces are also used.
Modbus is particularly important because many inverters, energy managers and wallboxes support the standard. Without this basis, the wallbox does not receive reliable real-time data.
4. A compatible wallbox
The wallbox must be able to control its charging power dynamically and communicate with the controller or energy management system. Not every wallbox works with every inverter or energy management system.
5. A controller or energy management system
The controller connects the PV system, metering system and wallbox, calculates the surplus and controls the charging power. Two typical approaches:
- Manufacturer systems: for go-e wallboxes, the go-e Controller is a simple, well-integrated solution for PV surplus charging and load management.
- Manufacturer-independent home energy management systems (HEMS): open systems such as EVCC work independently of the manufacturer and usually integrate meters, inverters and wallboxes via Modbus on the local network.
Open systems are particularly interesting if different components are already in use or you want to expand later.
Single-phase or three-phase charging
A wallbox cannot use every small amount of PV power. With three-phase charging, the minimum power is around 4.1 kW; with single-phase charging, it is just about 1.4 kW. Single-phase charging therefore lets you use more PV power directly in the car, even when the sun comes and goes.
Whether your system can switch automatically between single-phase and three-phase depends on:
- wallbox and controller
- vehicle
- inverter or energy management system
- installation and configuration
Important: Not every wallbox and not every vehicle supports automatic phase switching. It is best to check this before buying.
PV surplus charging with a plug-in hybrid
Many plug-in hybrids only charge on a single phase, often at a maximum of 3.7 kW. For PV surplus charging, this can even be an advantage, because charging starts at a lower PV output. What always matters is what the vehicle can accept – not the rated power of the wallbox. Clarify the permissible phase imbalance and the electrical installation with your qualified electrician.
Prioritising PV, storage and heat pump
The same solar power is of interest to the household, battery storage, heat pump and car. Typical strategies:
| Goal | Sensible priority |
|---|---|
| Highest possible self-consumption | Household consumption, storage, car |
| Charge the car as much as possible during the day | Household consumption, car, storage |
| Low grid load | Household consumption, dynamic wallbox control |
| Maximum PV utilisation in a business | Fixed priorities for vehicles, storage and consumers |
There is no single best setting. If you are out during the day, you need something different from a household with a home office or a business with several company cars.
PV surplus and dynamic load management
The two complement each other but serve different purposes:
- PV surplus charging optimises the use of your solar power.
- Dynamic load management protects the house or business connection from overload.
An example: the PV system delivers 8 kW, and at the same time the heat pump and oven start up. The system detects the higher load and automatically reduces the wallbox power. With several charging points, load management distributes the available power and often avoids an expensive upgrade of the grid connection.
Common mistakes when buying
“The wallbox has Wi-Fi, so PV charging works.”
Wi-Fi alone is not enough. What matters are compatible interfaces, a suitable metering system and a working control system on the same network.
“A meter in the wallbox is enough.”
No. The meter in the wallbox only shows the energy going to the vehicle. For surplus charging, the power at the grid connection point or the PV generation must be measured.
“22 kW is automatically better.”
For PV surplus charging, what counts above all is how finely the wallbox can be regulated dynamically and whether it suits your energy management system.
“PV surplus charging works with any wallbox.”
That is not true. Always check compatibility before ordering – especially if you already have an inverter, battery storage or smart home system.
“The car only ever charges with sunshine.”
In everyday life, a combination often makes sense: prefer PV surplus, but allow grid power if necessary before a planned departure.
Checklist before buying
- Which PV system and which inverter do you have?
- Is there already a battery storage or energy management system?
- Which metering system is installed?
- Are all components on the same network and do they support Modbus or comparable protocols?
- Does your vehicle charge on a single phase or three phases?
- Should charging continue automatically with grid power when there is little sun?
- Is there a heat pump, air conditioning or other large consumer?
- Will a second wallbox be added later?
- Is dynamic load management required?
Which wallbox suits your PV system?
For many households with a go-e Charger, the go-e Controller is an easy-to-integrate solution for PV surplus charging and dynamic load management. For multi-brand setups, open energy management systems are a good choice: they integrate different components via Modbus on the local network and can be expanded later.
The right solution always depends on your existing installation. Ideally, before buying, send us details of your PV system and inverter, battery storage or energy management, vehicle model, house connection, desired wallbox power and number of charging points to onlinesales@ampion.at.
Conclusion
PV surplus charging turns your electric car into a flexible consumer within your own energy system. What matters is that all components work together on the same network with clean communication via Modbus or comparable standards. With the right combination of metering system, controller, wallbox and vehicle, your car charges when the most self-generated solar power is available – and your house connection stays protected.
Frequently asked questions
From what PV output is surplus charging worthwhile?
There is no fixed minimum size. What matters is how much regularly remains after deducting household consumption. Single-phase charging can start from around 1.4 kW; three-phase typically requires more than 4 kW.
Can I do PV surplus charging with any wallbox?
No. The wallbox must be compatible with a suitable controller or energy management system and be able to control its charging power dynamically.
Do I need battery storage?
No. With storage, the main question is priority: should the car or the storage be charged first?
Does it also work with a plug-in hybrid?
Yes, if the wallbox, controller and vehicle are compatible. Since many plug-in hybrids charge on a single phase, charging starts with a smaller surplus.
Can I still charge quickly?
Yes. Many systems offer different charging modes: pure surplus charging, combined charging with limited grid consumption or fast charging at full power.
