Anyone driving an electric vehicle today feels the pinch of fluctuating grid electricity prices directly in their wallet. Combining your own solar system and wallbox offers the perfect technological bridge to free yourself from expensive public tariffs. Instead of feeding valuable electricity from your own roof into the public grid for a meager feed-in tariff, the clean energy flows directly into the vehicle’s battery. This not only protects the environment but also reduces the car’s ongoing operating costs to an absolute minimum. But how exactly does the interplay between these components work, and what do homeowners need to pay special attention to when planning in regions like Lower Saxony, Hannover, or Bremen?

How Does Charging an EV with Your Own Solar Power Work?

The technical principle behind coupling a solar system and wallbox is called intelligent PV surplus charging. A central electricity meter or smart meter in the home’s main service panel continuously measures how much electricity the photovoltaic system is generating and how much energy household appliances are consuming at that exact moment. If a surplus is generated on a sunny afternoon because the solar system produces more than the washing machine, refrigerator, and other appliances need, the system routes this excess energy directly to the charging station. The car is then charged 100 percent with clean, self-generated electricity.

Without this type of intelligent control, the charging station would simply start at maximum capacity as soon as the cable is plugged in. This often results in expensive grid electricity being purchased if clouds suddenly roll in during the afternoon or if the solar system does not yet deliver enough power in the morning. A well-designed system combining a solar system and wallbox adjusts the charging current in real-time to match current weather conditions instead.

Why Is Automatic Phase Switching Crucial for a Charging Station?

One of the greatest technical hurdles when charging with solar power is the minimum charging capacity of electric vehicles. The European standard dictates that to start a three-phase charging process, a charging current of at least 6 amps per phase must flow. This corresponds to a minimum output of approximately 4.1 kW. Smaller photovoltaic installations or larger systems on cloudy days in the Wolfsburg or Hannover areas often fail to reach this value during transitional seasons. Without additional technology, the charging process would constantly interrupt or unintentionally draw expensive electricity from the grid.

This is where automatic phase switching comes into play. High-quality charging stations can flexibly alternate between single-phase and three-phase charging. If the output of the solar system drops below the 4.1 kW threshold, the charging station automatically switches to single-phase charging. This allows the electric vehicle to be charged continuously and without interruption using pure solar power from a surplus output of just 1.4 kW. As soon as the sun shines brighter again, the system seamlessly switches back to the fast, three-phase mode.

What Role Does a Battery Storage System Play in Solar Charging?

A stationary battery storage system in the basement massively increases the flexibility of the overall setup. Commuters whose vehicles are not at home during the peak hours of sunshine benefit most from this intermediate storage. The home battery collects energy during the midday hours and makes it available in the evening or at night when the car is parked in the garage.

However, efficiency must be kept in mind here. Every storage cycle in a lithium-ion battery involves chemical and thermal conversion losses of around 10 percent. If the electricity is stored first in the home storage unit and then in the car’s battery, some of that energy is lost. The most economical strategy therefore remains directly charging the vehicle on weekends or while working from home. The home storage system should primarily cover the household’s evening baseload and support the car only with remaining capacities.

How Large Must the Photovoltaic System Be for an Electric Vehicle?

For reliable system dimensioning, a simple rule of thumb applies: add the annual electricity consumption of your household to the calculated driving electricity requirement of your EV, and divide this value by the regional PV yield. A typical electric car consumes an average of about 20 kWh per 100 kilometers. Based on a classic annual mileage of 15,000 kilometers, this results in an additional electricity requirement of around 3,000 kWh per year.

Driving Profile	Annual Mileage	Additional Electricity Demand	Recommended Minimum System Size (incl. Household)
Second Car	10,000 km	2,000 kWh	At least 6 to 8 kWp
Average Driver	15,000 km	3,000 kWh	At least 8 to 10 kWp
Commuter	20,000 km	4,000 kWh	At least 10 to 12 kWp
Frequent Driver	30,000 km	6,000 kWh	14 to 15 kWp and above

To ensure a sufficient buffer for power generation during changeable weather in regions like Bremen or Lower Saxony, it is highly recommended to always maximize the coverage of available roof spaces. The larger the installed kWp capacity of the solar system, the more frequently and the longer the threshold for pure surplus charging will be exceeded throughout the day.

Which Legal Regulations Apply to the Installation?

Installing a combined solar system and wallbox strictly requires execution by a certified specialist company. In Germany, according to the Low Voltage Connection Ordinance (§19 NAV), there is a strict notification obligation with the responsible local grid operator. Charging stations with a capacity of up to 11 kW only need to be registered with the grid operator before commissioning.

If a charging station with an output of 22 kW is to be installed, a simple registration is not sufficient. In this case, official approval must be obtained from the grid operator in advance, as the high load can place heavy punctual demands on local power grids. Furthermore, specialized companies check in advance whether the existing meter cabinet meets modern requirements or whether a digital electricity meter or smart meter gateway needs to be retrofitted due to statutory guidelines (such as §14a EnWG on the controllability of consumption devices).

Conclusion

Perfect synchronization of a solar system and wallbox requires precise planning tailored to your personal driving profile and roof areas. Rely on regional expertise and custom solutions right on your doorstep.

Would you also like to charge your electric vehicle as cheaply as possible with clean electricity from your own roof? PVPro Solar GmbH is your experienced partner for photovoltaics, electricity storage, and complete solar systems in the Lower Saxony region. Let our experts advise you now without obligation and secure your individual offer for a perfectly synchronized overall system.

Visit PVPro Solar GmbH for a free initial consultation!

Can you use pure PV surplus charging with any electric car?

Generally yes, because the charging process is primarily managed through communication between the energy management system and the intelligent charging station. The vehicle only needs to support standard charging protocols. However, it is important that the vehicle can handle low charging currents from 6 amps without issues and does not switch into an error mode during automatic phase switching by the charging station.

Is it worth purchasing a solar system and wallbox without home battery storage?

Yes, absolutely. Anyone who can charge their car primarily on weekends, while working from home, or during flexible afternoon hours can achieve excellent self-consumption rates even without an expensive battery storage system. In this scenario, storage losses are eliminated, meaning the directly charged kilowatt-hour from the roof achieves maximum economic profitability.

How does solar charging protect the battery of the electric car?

Charging via your own charging station with solar power takes place in the gentle AC alternating current range (usually between 1.4 kW and 11 kW). Compared to fast DC charging at highways, this generates significantly lower temperatures inside the battery. Additionally, the smooth power regulation adapted to solar yield ensures gentle charging, which can positively influence the lifespan of the vehicle battery in the long term.