With the cFos Charging Manager and a solar system, you can make sure that your car is (almost ^(*)) only charged when solar surplus power is available. Surplus = generation minus household consumption.

Note: In order for charging rules to be observed, load management must be active, i.e. the mode must be set to "load distribution", not "observe".

You can set up a "Solar" charging rule for this. Select "Solar surplus" as the mode. For "Start current limit", select the surplus current that the solar system must generate for this rule to apply.

The rule: Solar, start current limit: 6.5 A(6500 mA), "solar surplus", this activates surplus charging with the available surplus from a feed-in of 6.5 A.

In addition, you can specify an undercut time, i.e. the number of seconds that the current limit may be undercut after activating the surplus rule before charging is stopped. In this way, charging is not interrupted in the event of short-term power drops, e.g. due to passing clouds.

You can read the solar surplus by setting up the "Surplus (VM)" virtual meter in the Charging Manager. You can also set up a "Grid Demand (VM)" virtual meter, which shows how much electricity is currently being drawn from the grid.

Tip: If your PV system no longer generates the minimum power required for charging in winter or during the transitional period, you can also specify a value below 6000 mA as the starting current limit. In this case, the system will charge with solar surplus with partial grid supply.

Tip: To ensure that your car is charged the next morning, you can specify a time-based rule in addition to the surplus rule: Time, start: 21:00, end 6:00, current 6000. i.e. if the car still needs electricity at night to be fully charged, you can either charge from the grid or from a storage unit.

The surplus current is the current that would be fed into the grid. To determine this, the cFos Charging Manager must be able to measure it. The following options are available for this:

1. Either: Set up with a "grid supply" meter. You install a (bidirectional) meter at the transfer point of the house connection. If this meter displays negative values, you feed in and this electricity is available for surplus charging. Suitable meters include Modbus meters or internal grid reference meters from your solar system (e.g. SMA Homemanager 2.0, Kostal Power Meter, E3/DC grid reference meter, etc.). In order for the Charging Manager to be able to calculate the grid consumption independently of the charging of the electric cars, a meter with the "Electric car consumption" role must be configured for each wallbox in this configuration.
2. Or: You measure your home consumption with a suitable meter without wallbox(es) and without the generation power. Simple S0 meters are sufficient for this. The Charging Manager then subtracts the domestic consumption from the generation power and makes the remaining power available for charging.

The generation power can be measured with an extra meter. Alternatively, you may be able to read the values from your solar system directly. Please refer to our list of currently supported devices.

^(*) Due to measurement and calculation inaccuracies, there may be a slight grid reference or a slight feed-in in the limit range.

Step-by-step instructions for setting up PV surplus charging (solar surplus charging)

User report on surplus loading with Shelly 3EM (PDF)

User report on surplus charging with Solaredge

Balance surplus charging

If you know that the solar system can generate a maximum of 4.2 kW of power, excess charging must be configured with a workaround. This involves the use of "balanced charging".

Note: Electric cars require at least 1.4 kW (i.e. 6 A) per phase to be able to charge. For three-phase charging, this results in 3 × 1.4 kW = 4.2 kW.

Below 4.2 kW solar power, the power for charging must be redistributed from the three phases to one phase so that at least 1.4 kW is available on this phase. For example, if you feed in 500 W of solar power on all phases, you can draw 1500 W on a single phase. As the energy suppliers' bidirectional meters work on a balanced basis, there is neither grid consumption nor feed-in.

Below 4.2 kW, you must therefore switch off two fuses with which the supply lines to the wallbox are protected (only not the one with which the cFos Power Brain Controller is protected). Caution: However, you must not switch individual phases on or off during the charging process. This can lead to the destruction of the car's charging system! If you are not using a meter on the wallbox that can resolve individual phases, you should, if possible, inform the Charging Manager that the car is now charging in single phase by setting the "Phases" configuration parameter accordingly. If you have a meter that can resolve individual phases, you can leave the phase setting set to "determine".

If you want to charge the car again later independently of the solar surplus, switch on the switched-off fuses before the charging process and deactivate the solar surplus charging rule in the Charging Manager. Then you can charge with the normal power.

Tip: With the cFos Power Brain Solar Wallboxes (from firmware version 1.23.3), you can realise surplus charging with automatic phase changeover.

Setting the "Phases" parameter

The cFos Charging Manager needs to know which phases the car is charging on (e.g. single-phase or three-phase) in order to

• be able to calculate the utilisation of the individual phases for load management, and
• to decide when the minimum charging current per utilised phase is reached in the event of excess PV charging and charging is activated.

If the wallbox does not have a (possibly attached) meter with phase resolution (e.g. cFos Power Brain with S0 meter, Tesla Wall Connector, etc.) and you always charge the same car, then you should set the phases as the car actually uses them. If you charge different cars, set the phases of the wallbox to "Determine". With "Determine", the cFos Charging Manager attempts to determine the phases actually used. It normally knows whether the respective meter or wallbox offers phase-by-phase resolution of the currents. For example, an S0 meter only provides pulses per kWh of total power and no values for the individual phases. Such a meter therefore measures the total power and allocates it to the set phases. From the point of view of the wallbox, single-phase charging cars always use phase L1 (even if this is installed phase-rotated in relation to the domestic grid) and two-phase charging cars always charge on phases L1 and L2.

The "Phases" parameter set for the wallbox is also used to predict the phases actually used when a new car is plugged in. With "Determine", the Charging Manager initially assumes single-phase charging and switches to two-phase or three-phase charging if necessary. After unplugging, the forecast starts again with single-phase.

With PV surplus charging of three-phase charging cars, this means that the cFos Charging Manager starts charging too early with the "single-phase" forecast when solar power increases. It then detects three-phase use after a few seconds and pauses charging if the solar surplus is too low until enough power is available for surplus charging. To ensure that this works, the undershoot time (which can be set in the charging rules) is limited to 15 seconds in the first 2 minutes of charging. If you want to avoid this brief switch-on, you can set the phases in the wallbox settings to the phases actually used. If you change cars, it is advisable to create RFIDs with the "Overwrite phases" function in the Charging Manager and use them to tell the Charging Manager which phases the car is charging with when the charging cable is plugged in.

Power reserve

The controller in an electricity storage system always tries to minimise grid consumption and grid feed-in. You can inform the cFos Charging Manager of this by setting up a meter with the role "Solar storage". In this case, a discharging storage system is considered a generator (the meter shows negative power values), i.e. this energy is available for charging the car. However, a charging storage system (the meter shows positive power values) is not considered a consumer because the storage system stops charging immediately when the charging power is used to charge the electric car. The cFos Charging Manager therefore ignores the consumption of meters with the "Solar storage" role. You can choose between "Storage All" and "Storage Home" for the role of the storage meter. With "Storage Home", the discharge of the storage tank is not used for surplus charging, which avoids deep charging cycles of the storage tank. You can find more options for using the meter here.

If your electricity storage system does not have a bidirectional meter, you can install an external meter. Mostly, bidirectional Modbus meters are recommended, but it may also work with several S0 meters (or other unidirectional meters) depending on the arrangement of the meters in the installation, which has to be checked in each individual case.