Wallbox surplus charging – how to use PV power for your electric car

If you have a solar power system, you often feed excess electricity into the grid for just a few cents. However, this energy can be stored much more efficiently in your own electric car. We'll show you how this works and what you need to consider.

Charge excess PV power into the car instead of feeding it into the grid cheaply.

With wallbox surplus charging, you can charge your electric car using solar power that your household doesn't currently need. Instead of sending the surplus to the grid for a small fee, it goes into your car's battery, replacing expensive grid electricity. At PVundSO, experienced electrical engineers will advise you on how to effectively integrate your charging station with your own photovoltaic system. This guide explains how charging with surplus solar power works, what technology is required, and for whom the effort is truly worthwhile. This way, you can get the most out of every kilowatt-hour from your own roof.

What does excess charging mean for a wallbox?

Wallbox surplus charging describes charging your car with the portion of your solar power that remains after your household consumption. If the washing machine is running and the system is simultaneously producing a lot of electricity, the surplus doesn't go into the grid, but instead powers your vehicle. This significantly increases your self-consumption.

The difference to simple charging is significant. A conventional charge draws power regardless of whether the sun is shining or not. With wallbox charging, however, the charging rate is determined by the actual solar yield.

That's precisely where the financial advantage lies. Electricity you feed into the grid only earns you a small payment, while you pay significantly more for grid electricity. The effect becomes clear when looking at the numbers: you currently receive only a low single-digit cent amount per kilowatt-hour for electricity you feed into the grid, while grid electricity is often three to four times more expensive. Every kilowatt-hour you charge your car yourself therefore saves you real money and makes you more independent from your electricity provider.

This is how PV surplus charging works step by step

Solar charging requires three components working together: a photovoltaic system as the energy source, a measurement of the current surplus, and a wallbox that adjusts its output accordingly. Only this interplay makes solar charging possible.

If one of these components is missing, the wallbox simply continues charging at full power from the grid. Therefore, surplus charging depends entirely on the correct connection between generation, measurement, and charging point.

What role do the inverter and measurement play?

For the charging process to follow the surplus, the system needs to know how much electricity is currently available. This information is provided either by a smart meter at the grid connection or by the inverter itself. Without this continuous measurement, the wallbox doesn't know how much solar power it can send to the car.

Modern devices communicate directly with the inverter, often via an interface such as RS-485. This allows the wallbox to receive the data it needs in real time for clean charging with excess PV power.

Why the minimum charging power is important

Every wallbox has a minimum charging power below which it cannot regulate. Three-phase charging usually only starts at around 4,1 kilowatts, while single-phase charging starts at about 1,4 kilowatts. On cloudy days, the surplus power is often only sufficient for single-phase charging.

Therefore, the design of the wallbox plays an important role in how early you can actually use your surplus energy. The lower the minimum charging power, the more hours of sunshine you can ultimately utilize.

Dynamic excess charging and phase switching

With dynamic surplus charging, the wallbox continuously adjusts its power output to the available sunlight. If a cloud appears, it reduces the charging rate; if the sun shines again, it releases more power. This ensures that exactly the amount of energy currently available flows into the battery.

A wallbox with phase switching goes a step further. It automatically switches between single-phase and three-phase charging, depending on the available surplus power. This allows you to use even small amounts of electricity, instead of only starting charging once a high threshold is reached.

It's important to know that both phase switching functions are purely convenience features and not mandatory. You can charge with solar power even without phase switching; you simply start charging only when there's a slightly higher surplus. When buying a wallbox, however, pay close attention to whether and how it regulates the surplus. If in doubt, a brief consultation can help you determine which solution is best suited to your system.

What you need for a wallbox with surplus charging

For a wallbox to support surplus charging, several components need to be compatible. First and foremost is a sufficiently large solar power system that regularly generates excess energy. Without this foundation, the concept remains purely theoretical.

This also includes the appropriate metering technology and a wallbox for charging with excess PV power, which communicates with the inverter or the smart meter. Which one is ultimately the right one depends on your existing technology and your inverter. Our PV systems provide the solid foundation for this, because without sufficient generation, little of the surplus remains.

It's also crucial that the components can communicate with each other. If the inverter and wallbox are from the same manufacturer, coordination is usually particularly easy. This compatibility often determines how convenient everyday charging will actually be. Therefore, a wallbox for charging with excess PV power should always be considered in conjunction with the rest of the system. It's best to plan for this coordination from the outset to avoid costly modifications later.

The Sofar Solar Wallbox in the solar network

A suitable example from our product range is the Sofar Solar Wallbox. It is a three-phase charging station with 11 kilowatts and communicates directly with the Sofar inverter via an RS-485 interface. This allows charging to be specifically aligned with your own solar power supply.

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The app lets you conveniently control your Sofar Solar Wallbox , schedule charging times, and keep track of your data. When used with a Sofar solar system, charging is automatically adjusted to the available solar power. Our electrical engineers will be happy to discuss the extent to which charging can be automated with your specific system.

The charging station is robustly built, with IP65 protection and IK10 impact resistance, making it suitable for harsh outdoor conditions. You authorize charging via RFID card or app, maintaining control over who is allowed to charge. This provides an honest assessment instead of relying on advertising claims. Whether your 11 kW wallbox will operate fully automatically or rely on a charging schedule depends on your inverter, metering system, and usage patterns.

Excess charging with and without energy storage

Even without a home battery, surplus charging works as long as your car is plugged into a wallbox during the day. The electricity then flows directly from the solar panels into the vehicle's battery, which essentially acts as a large storage unit. However, this isn't practical for many commuters who charge in the evening.

This is where a home energy storage system comes in. It buffers the day's excess energy and releases it later when the car is parked in the garage. You can find suitable devices in our energy storage category.

In practice, the question often arises whether to charge the home battery or the car first. You determine this prioritization according to your needs. Those who also want to use the surplus energy for hot water or other appliances will find further ideas in our guide " Making Effective Use of PV Surplus ." A battery also increases the period during which surplus energy is available for charging. Instead of only charging at midday, you can then also charge with stored solar energy in the early evening. Especially for working people who are rarely at home during the day, this often makes the difference between theory and real-world solar charging.

For whom is surplus charging via a wallbox worthwhile?

A wallbox with solar surplus charging is particularly worthwhile if you regularly charge at home during the day or use a battery storage system. Those who only charge their car at night and don't have a battery storage system benefit significantly less from excess solar power.

The size of your system and your driving profile also play a role. The more surplus electricity you regularly generate and the more flexibly you can charge, the greater your savings will be. With low feed-in tariffs and high electricity prices, self-consumption is now more cost-effective than before.

A simple calculation illustrates this. If you charge just 2.000 kilowatt-hours per year with your own solar power instead of from the grid, the savings quickly add up to several hundred euros. Over the system's lifetime, this amounts to a four-figure sum. As experienced electrical engineers, we'll take a close look at your specific situation. Our article "Charging an Electric Car with a Balcony Power Plant ," which explains the principle on a small scale, also shows what charging with your own electricity feels like in everyday life.

Frequently asked questions about surplus stock

Which wallbox is suitable for charging with excess PV power?

A wallbox that can regulate its charging power based on surplus energy data is suitable. For this, it must communicate with the inverter or a smart meter. The frequently asked question, "Which wallbox is suitable for charging with excess PV power?" is therefore answered by the available interface and the desired convenience features.

Is surplus charging possible without storage?

Yes, as long as your car charges during the day. Then the excess solar power flows directly into the vehicle. Without a battery and without daytime charging, however, little of the excess power remains in the evening. Those who work flexibly from home can use the midday hours specifically for charging and thus get a lot of solar power into their car even without a battery.

What are the real benefits of dynamic overcharging?

Dynamic surplus charging ensures that charging follows the sun's energy supply and no additional grid electricity is purchased. This allows you to charge as cheaply as possible and increase your self-consumption without having to constantly intervene manually.

Is it worth using excess charging with an 11 kW wallbox?

A three-phase 11 kW wallbox charges quickly, but needs sufficient sunlight for pure surplus charging. A real-world test of your wallbox's PV surplus quickly reveals whether your system often generates enough surplus power for three-phase charging or whether a battery storage system would be worthwhile.

Conclusion

With wallbox surplus charging, you can turn cheaply fed-in solar power into affordable mileage for your car. This requires a photovoltaic system, a surplus measurement device, and a wallbox that communicates with your inverter or smart meter. Convenient features like dynamic control and phase switching extract even small amounts of power from your system. The Sofar Solar wallbox can be aligned with your solar power supply via its interface with the Sofar inverter. Our electrical engineers will be happy to discuss the extent to which this can be automated in your specific situation.