Surplus charging

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: Load management must be active so that charging rules are observed, ie the mode must be set to "load distribution", not "monitor".

You can set up a "Solar" type of charge rule for this purpose. Select "Solar excess" as the mode. As "Start current limit", select the excess electricity that the solar system should generate, from which this rule should apply.

Screenshot cFos Charging Manager Documentation - Surplus charging

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

In addition, you can specify an underrun time, ie the number of seconds that the current limit may be underrun after activating the excess rule before charging is stopped. In this way, charging is not interrupted in the event of short-term performance drops, for example due to passing clouds.

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

Tip: To ensure that your car is charged the next morning, you can specify a time-based rule in addition to the excess rule: Time, start: 21:00, end 6:00, electricity 6000. That means if the car still needs electricity at night to to be fully charged, you can either charge from the network or from a memory.

The excess electricity is the electricity that would be fed into the grid. In order to determine this, the cFos Charging Manager must be able to measure it. The following options are available for this:

Figure measurement concepts
  1. Either: Set up with a "Purchased electricity" meter. You install a (bidirectional) meter at the transfer point of the house connection. If this meter shows negative values, feed in and this current is available for excess charging. Suitable meters are, for example, Modbus meters or internal purchased electricity meters in your solar system (e.g. SMA Homemanager 2.0, Kostal Power Meter, E3/DC purchased electricity meters, etc.). So that the Charging Manager can calculate the purchased electricity independently of the charging of the electric cars, a meter with the "E-car consumption" role must be configured for each wall box in this configuration.
  2. Or: You measure your house consumption with a suitable meter without wall box(es) and without the generation capacity. Simple S0 counters are sufficient for this. The Charging Manager then subtracts the home consumption from the generation capacity and makes the remaining capacity 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, a slight grid purchase or feed-in can occur in the border area.

User Report on Surplus Loading with Shelly 3EM (PDF)
User report on excess charging with Solaredge

Balance surplus charging

If you know that the solar system can generate 4.2 kW of power or less, excess charging must be configured with a workaround. In this case, "balanced charging" is applied.

Note: Electric cars need at least 1.4 kW (ie 6 A) per phase in order to be able to charge. With three-phase charging, this results in 3*1.4 kW = 4.2 kW.

Below 4.2 kW of solar power, the power for charging must be redistributed from the three phases to one phase so that at least 1.4 kW are 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. Since the bidirectional meters of the energy suppliers work on a balance sheet, there is no mathematical purchase of the grid or feed-in.

Below 4.2 kW you have to switch off two fuses with which the supply lines to the EVSE are protected (only not the one with which the cFos Power Brain controller is protected). Caution: You may not switch individual phases on or off during the charging process. This can lead to the destruction of the car's charging device! If you do not use a meter on the EVSE that can resolve individual phases, you should, if possible, inform the Charging Manager that the car is now charging in one phase by setting the "Phases" configuration parameter accordingly. With a counter that can resolve individual phases, you can leave the phase setting on "determine".

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

Phase usage

If you use meters that record the electricity in phases, the Charging Manager (especially in single- or two-phase charging cars) can control the charging power in phases and thus optimize it. In the case of meters that only output one power value based on the number of phases used, the cFos Charging Manager allocates the power evenly to the phases, which leads to certain inaccuracies. In this case (and also in the event of sudden high consumption) you should set a sufficiently high power reserve. If you know which phases are actually being used, you can configure this for the meter or EVSE using the 'Phases' parameter. Automatic phase detection: If you set the 'Phases' parameter to "Determine" for a device without phase resolution, the Charging Manager tries to determine the phase usage per transition itself. For example, if a meter is attached to the EVSE, it takes over the phase use of this meter. If the power is clearly too high in relation to the number of phases, it corrects the phase usage from L1 to L1 + L2, or L1 to L1 + L2 + L3 or L1 + L2 to L1 + L2 + L3. If no further information is available, the cFos Charging Manager initially assumes 1-phase charging. This value determined in this way is used during the charging process and deleted again when the vehicle is unplugged. With excess charging, a three-phase charging car can lead to up to two short charging attempts until the Charging Manager has determined the correct number of phases. The aim here is to offer the highest possible functionality even without phase-accurate counters when cars with different phase usage are charged on a EVSE.

Power reserve

The control in a power storage always tries to minimize the grid consumption and the grid injection. You can tell this to the cFos Charging Manager by setting up a meter with the role "solar storage". In this case, a discharging storage is considered a generator (the meter shows negative power values), which means that this energy is available to charge the car. However, a charging storage (the meter shows positive power values) is not considered as a consumer because the storage stops charging immediately when the charging power is used for charging the electric car. So, for meters with the role "solar storage", the cFos Charging Manager ignores its consumption.

If your energy storage system does not have a bidirectional counter, you can install an external counter. Bidirectional Modbus meters are usually recommended, but depending on the arrangement of the meters in the installation, several S0 meters (or other unidirectional meters) can be used, which must be checked in each individual case.