Irradiance Sensor With Modbus RTU Output



A silicon solar cell can be used as an irradiance sensor, because the short-circuit current is proportional to irradiance. Our sensors are built out of a monocrystalline solar cell connected to a shunt. Due to the low resistance of the shunt the cell operates next to short circuit.

The temperature coefficient of the short-circuit current creates a small error.

The compensation is realized by using a specific temperature sensor laminated to the rear side of the solar cell. The measuring signals of short- circuit current of the cell and the resistance value of the temperature sensor are measured by a micro controller.

The calculated values of irradiance and temperature given onto a RS485 port with customer specification protocol. The electronic circuit is optimized for low power consumption.


The solar cell is embedded in Ethylene- Vinyl- Acetate (EVA) between glass and Tedlar. Plain integration into the top cover of the box Advanced weatherproof junction box made of UV resistant material with cable gland and screw-less terminal for the connection of the measuring cable, therefore, the sensor construction is comparable to that of a standard PV module. The electrical connection is realized by a 3m cable.



General Information
Solar Cell Monocrystalline Silicon (52 mm x 52 mm)
Current Shunt High precision shunt resistor directly soldered to the terminals of the cell
Operating Temperature -30°C to +70°C
Electrical Connection 3 m PUR Cable, UV and weather resistant
Power Supply 12 to 30 VDC (30 mA typically at 20 VDC)
Interface RS485 up to 19200 Baud
Protocol The sensor is connected via a 2-wire RS485 bus with open vendorindependent Modbus RTU protocol
Galvanic Isolation 1000 V between power supply and RS485 bus
Case Advanced weatherproof junction box made of UV resistant material
Dimensions, Weight 94 mm x 94 mm x 57 mm, approx. 200 g
Protection IP54
Irradiance 10…1500W/m2, Accuracy of monthly sums compared to a W.M.O. class 1 Pyranometer (e.g. CMP 11) according to ISO 9060: better ±5%
Drift Very small drift of <0.3%/ year
Electrical Connection  
Brown Power (+)
White Power (-)
Green RS485 Data (+) / A
Yellow RS485 Data (-) / B
Input 1 3S-WS-PLS, Wind speed sensor, 2 pin connector
Input 2 3S-AT-18B20, Ambient temperature sensor, 3 pin connector
Input 3 3S-MT-18B20, Module temperature sensor, 4 pin connector
Calibration Individual calibration of each sensors in the natural sunlight at AM 1,5 spectrum by means of a compatible calibrated reference cell.
Handling Case The sensor can be cleaned using a smooth cotton cloth, water and a mild cleaning fluid. Opening of the sensor case by the user or installation staff is not necessary. If the case is opened, we cannot guarantee the seal of the case anymore.
Modbus Specification  
Baud Rate 1200, 2400, 9600, 19200, 38400
Parity No, even, odd
Stop Bit 1, 2 (only at no parity)
Factory Default 9600 Baud, 8N1, address: 1




3S-WS-PLS Wind speed sensor, reed contact, pulse Datasheet
3S-AT-18B20 Ambient temperature sensor, DS18B20 Datasheet
3S-MT-18B20 Module temperature sensor, DS18B20 Datasheet
3S-PS-12VDC Power supply, 220VAC, 50/60Hz, 12VDC, 300mA
3S-Shield-A Solar Radiation Shield for Ambient Temperature Sensor PT100, PT1000, DS18B20 etc. Datasheet

Details of SEVEN Irradiance sensor

The irradiance sensor or PV pyranometer is a heat flux sensor used to measure the amount of solar energy in natural light and is particularly used in meteorology. It measures the power of total solar radiation in watts per square meter.

The solar irradiance sensor is a simple and inexpensive solution to monitor the performance of the solar system at any time. Entirely manufactured as a cell for the PV system and equipped with a temperature compensation system, the irradiance sensor measures precisely and reliably the energy supplied and the performance of the system. You will thus be able to benefit from the best performance for your solar panels.

Installation of SEVEN Weather Station

Irradiance sensor with Modbus RTU Connection

In terms of connection or communication with other sensors and dataloggers. Several types of irradiance sensors are available with different output signals such as the irradiance sensor with Modbus RTU connection and the irradiance sensor with analog output. In this text, we will focus on irradiance sensors with Modbus RTU connection.

First of all, Modbus is a serial communication protocol widely used by industrial electronic devices. In Modbus, the connection is established between a master (host) and slaves (devices connected to COM ports). The Modbus allows access to the configuration of the peripherals and to read measurements.

The irradiance sensor with Modbus RTU output is an advanced, weatherproof junction box made of UV-resistant materials. It is constructed from a monocrystalline solar cell connected to a high-precision shunt. It contains a Modbus output which is used to deliver the measurements obtained by the sensor to the datalogger via a RS485 cable. This type of Modbus irradiance sensors also has three input ports that allow the communication with three other sensors such as Wind Speed / direction sensors, Ambient / Module Temperature Sensors, humidity sensor, etc.

Irradiance sensor’s components

An irradiance sensor consists essentially of 3 main parts: Protective box, Photovoltaic cell, Electronic card/board.

The photovoltaic cell, which has a monocrystalline silicon structure, is the part that absorbs solar radiation. It has the same characteristics as a photovoltaic panel cell. Therefore, it behaves in the same way as the panel under the effect of light and heat. Then, with the help of a microprocessor, the electronic card gets the ability to collect the processed data. Because of the additional inputs that SEVEN Irradiance sensor has, the Temperature and Wind speed sensors can be easily connected to the electronic board.

SEVEN irradiance sensor and Photovoltaic cell

Irradiance sensor examples of use

The Modbus SEVEN irradiance sensor is used for Huawei weather stations; we have obtained Approval from Huawei for our entire weather station which includes the Modbus RTU irradiation sensor, wind speed/direction sensors, and ambient temperature/modules sensors. It is also used for GoodWe stations as it is compatible with its Ezlogger, and with all Modbus dataloggers. You may visit our Website for more information about our sensors and the other type of irradiance sensor, the analog one, which is compatible with too many brands such as Kaco, SMA, SolarEdge, etc.

As SEVEN Sensor Solutions, our engineers are available to provide customers with a remote setup services and information on anything they may need.