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Intelligent OFF-GRID system controlled by PLC - variant with PoE support

Compared to systems powered from a 230V network, solar OFF-GRID systems have a significant disadvantage in an unstable energy supply. Any unnecessary watts will result in increased demands on the capacity of the backup battery and the size of the solar panels. The advantage in such a situation is an intelligent solution with a PLC, which helps to reduce system consumption by an automatically running program:

  • Measuring station - The PLC turns on the power supply to the sensors only for the duration of the measurement
  • Surveillance PoE+ camera - The PLC turns on the PoE power supply of the PTZ camera on request (SMS, Android/iOS application) or automatically after the arrival of the alarm from the PIR (see our MPPT chargers with MODBUS interface).

When designing a solar OFF-GRID system, it is necessary to deal with its correct dimensioning so that:

  • the battery absorbed enough energy to run the system even on days with clouds, snow and rain,
  • photovoltaic panels ensured a sufficient supply of energy throughout the year.

Below you will find a brief overview of the steps and the most important risks that must be considered in the calculations. The resulting values depend on the total annual total of incident solar energy at the installation site. The system designed for central Italy will therefore certainly be insufficiently dimensioned for a similar installation in the Czech Republic or Poland.

Example of dimensioning a 12V OFF-GRID system with a fixed PoE camera

Step 1: Calculate the energy intensity of the system

First, find out the maximum power consumption of the connected devices and calculate the daily consumption of the system from it.

Camera MOBOTIX M26 - power consumption up to 5 W,
PLC with LTE interface IPLOG-G3-21 - power consumption up to 4 W,
PoE+ injector POE-PSE-30 - power consumption up to 1W

Maximum power consumption of connected devices = 10 W
Daily system consumption = 10 x 24 = 240 Wh

There are situations when it is not necessary to have all devices in 24/7 mode, but it is enough to turn them on only when needed. In such cases, we recommend creating a control program in the PLC that turns the device on / off:

  • on request
  • according to the set time
  • when other conditions are met

In addition, IPLOG PLCs can be easily integrated into third-party software and applications. The picture below shows, for example, the control buttons directly in VMS Obseron:

LIGHT_ON - turns on the light with Modbus-TCP command
LIGHT_OFF - turns off the light with Modbus-TCP command
CAMERA_ON - turns on the PTZ camera with a Modbus-TCP command*
CAMERA_OFF - turns off the PTZ camera with a Modbus-TCP command*
* The commands control the PLC relay, through which the 12V power supply is connected to the PoE+ injector.

Step 2: Calculate the size of the backup battery

Use the page: . It contains useful maps with annual totals of incident solar radiation and a form for determining the appropriate size of the battery and PV panels. The table below shows the results for three different locations.

Location Probability of battery charge at the end of the day Battery size / /erformance of PV Panels
60Ah / 350Wp In 10% of days, the battery may be discharged below 40% of the capacity. We recommend creating a program to save energy when discharging the battery below a critical value.
Prague 60Ah / 350Wp In 6% of days, the battery may be discharged below 40% of the capacity. We recommend creating a program to save energy when discharging the battery below a critical value.
Rome 60Ah / 350Wp The system is oversized. It is not necessary to create an energy saving program in the PLC.

Recommended METEL Products

Order Name Code Description  
OH6425 - OG1-LTE-POE 4-000-004 OH6425-OG1-LTE cabinets are designed for outdoor installations of PLCs of the IPLOG-G3 series in OFF-GRID systems. They are equipped with a shelf for battery placement and an overpressure fuse, as well as DIN35 rails, terminals, fuses, an outdoor 2G / 3G / 4G-LTE antenna, a BM-MPPT series charger and surge protection.
Industrial PLC with LTE interface and IO of choice in ONLINE CONFIGURATOR.  


Recommended accessories from other manufacturers

Order Name Description  
VICTRON gel batteries In OFF-GRID systems, only use batteries designed for cyclic operation. From our own experience, we can recommend Victron gel batteries, which are characterized by long life.
 BlueSolar VICTRON
Solar polycrystalline panels for systems with a working voltage of 12V.

Limitations and Risks

  • The maximum input voltage of the MPPT charger is 30V
  • The maximum recommended size of the connected panels is 350Wp
  • The lowest operating temperature is usually -20 °C (limited by battery)

For greater performance USE.


Updated: 13. 07. 2020