Optimisation of self-generated PV energy with a car battery and intelligent charging management

Step by step.

In order to optimally use the self-generated PV energy, it is important to use the energy surplus flexibly, especially during times of high PV yield. One way to absorb the surplus is to use a car battery as a flexible energy storage system. However, there are some important aspects to consider, especially with regard to charging the vehicle.

To achieve this goal, a logic group is used in the EIBPORT for control. Communication with a charging station (wallbox) takes place via the APP MODULE in conjunction with a corresponding Smart Home app. Direct communication between the control unit and the wallbox enables dynamic charging that takes the PV energy yield into account.

Implementation of intelligent charging management with sample configuration
To enable you to create an individual solution, an example is described below that can serve as a basis. The configuration is carried out in the logic editor of the EIBPORT, while the interface to the charging station or wallbox is set via the APP MODULE. Various Smart-Home APPs are available for selection here, both manufacturer-specific and the generic Modbus-TCP-Connect Smart-Home APP.

Two outputs are available for specifying the charging power:

  1. The available charging power in watts (W), provided the wallbox can be controlled with it.
  2. A percentage value indicating the possible charging power in relation to the maximum charging power.

This example does not yet take into account: The monitoring of the battery level, and the automatic stopping of the charging process when the vehicle is fully charged.

The charging of the car battery is carried out with variable power. Depending on the available values of the wallbox, the entire status of the car battery can be monitored in addition to the power monitoring for charge control and, if necessary, other functions such as the charging time or the battery level can be used for control.

About the functioning of the logic group
The measured values of the performance recording are stored in a cache every minute and forwarded from there to a statistics element. Ten values are recorded in this element and the mean value is calculated, which is then sent every ten minutes. The averaging and the 10-minute interval are used to smooth the measured value for the switching threshold and the power specification for charging.
The user sets an upper and lower switching threshold, whereby the lower switching threshold can be provided with an offset to prevent premature switching back. Otherwise, the value "0" is entered. This ensures that charging is not aborted too early, even if the PV surplus range is left. During charging, the measured power value must be corrected by the power value of the wallbox so that the switching thresholds are not influenced.
The correction is based on the feedback from the wallbox and occurs even if the power specification for charging is higher. Enabling "ON" activates the logic group, while enabling "OFF" stops the logic group and sets the switching command to the wallbox to "OFF". An integrated start value is required to ensure that the logic group has a defined output value.

Input values (settings of the user):

  • Counter Charging station: This is the charging power that is read out by the wallbox via the APPMODULE and can be specified or preset by the wallbox. The measured value is positive. (EIS9, DPT 14.xxx 4 byte float)
  • Counter current power: These are the power values of the house connection meter (bidirectional meter). Positive values represent consumption (power drawn), while negative values represent yield (power fed into the public grid). (EIS9, DPT 14.xxx 4 byte float)
  • Release: This setting activates the pulse generator to start the logic group. For "OFF", the pulse generator is stopped and the switching command to the wallbox is set to ".OFF" set. (EIS1, DPT 1.xxx)
  • Feedback switching: This is the feedback signal, for example from the wallbox, to indicate that it is in charging mode. If there is no active feedback, the same group address used to switch the wallbox is used. The feedback from the wallbox triggers the power equalisation with the extracted power from the wallbox. (EIS1, DPT 1.xxx)
  • Switching threshold: This is the limit value for switching to the "Shop" mode. Only negative values are possible (level of feed-in), which would normally be fed into the public grid. The user can define from which value charging should start, so that the battery is also charged when the yield is lower. (EIS9, DPT 14.xxx 4 byte float)
  • Power OFF Offset: Only positive values are used here to determine the value at which charging should be stopped. The limit value results from the sum of the switching threshold and the power OFF offset. (EIS9, DPT 14.xxx 4 byte float)
  • Maximum power charging: The maximum charging power is set here to specify a percentage value for the charging power. (EIS9, DPT 14.xxx 4 byte float)


Initial values:

  • Value Energy Charging: This is the group address for the available charging power in the PV surplus area. If there is no surplus, the default value is 0 (no charging). (EIS9, DPT 14.xxx 4 byte float)
  • Switching (charging): This is the group address for switching charging on or off. (EIS1, DPT 1.xxx)
  • Power control: This is the group address for the available charging power in percent in relation to the maximum power of a wallbox. If there is no surplus, the default value is 0 % (no charging). (EIS5, DPT 6.xxx 1 byte)