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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).

Practical Example

We first practically verified the accuracy of the calculations, so-called first-hand. On the right side of the picture you can see the solar panels of a 24V system for PLC power supply with LoRaWAN interface and a 24V submersible pump. After a year of successful operation (Spring 2019 - Spring 2020), we replaced the system with a more powerful 24V system with 4x300Wp panels for power supply:

  • PLC with LoRaWAN interface
  • 24V submersible pump
  • PoE PTZ camera
  • another PLC with LTE interface
  • 2 pcs of IO modules of the I&HAS system and for controlling the duck door

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.

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.

Devices Rated Power Input*
PLC IPLOG-G1-AI8.1 with LoRaWAN interface 4 W
24V submersible pump 150 W (turn on via LoRaWAN)**
PoE PTZ camera AXIS including PoE+ injector 14 W
PLC-IPLOG-G3-05-BI8.1 4 W
IO modules BI8.1-05 and RE8.2-05 3 W

*Measured by a multimeter during operation.
**The submersible pump in the borehole was not included in the total power input. It only turns on for a short time during sunny days, when there is excess energy from the PV modules.

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

LIGHT_ON - turns on the light with Modbus-TCP command
LIGHT_OFF - turns off the light by Modbus-TCP command
CAMERA_ON - turns on the PTZ camera with a Modbus-TCP command*
CAMERA_OFF - turns off the PTZ camera with 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 Power of solar panels for camera mode 24/7
2x 90 Ah 1200 Wp
Prague 2x 60 Ah 1200 Wp
Rome 2x 60 AH 600 Wp

Recommended METEL Products

Order Name Code Description  
OH8625 - OG1-LTE-POE 0-000-040 Cabinet designed for outdoor PLC installations of the IPLOG-G3 series in OFF-GRID systems. They are equipped with 2 shelves for placing a 90Ah battery and an overpressure fuse. Furthermore, DIN35 rails, terminals, fuses and cabling for easy connection, 1x PoE injector according to IEEE 802.3af / at, 1x MPPT regulator and surge protection, outdoor 2G/3G/4G-LTE antenna. Size: W600 x H800 x D250 mm.
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 working voltage up to 100V.


Updated: 13. 07. 2020