Irradiance RSR3
Irradiance, Inc.
P.O. Box 381374
Cambridge, MA 02238-1374

RSR3 Rotating Shadowband Radiometer

Modern solar array modeling codes require separation of direct and diffuse sunlight, but trackers are big, heavy, power hungry, and expensive. The Irradiance RSR3 Rotating Shadowband Radiometer operates by momentarily shading a fast-response photodiode pyranometer with a motor-driven band. Direct, diffuse, and global values are output by industry-standard Modbus RS-485 interface for compatibility with common solar and meteorological sensors.

RSR3 Manual [PDF]


Each new RSR3 is calibrated against our reference pyrheliometers. After sufficient filtered data is collected to measure the unit's DNI bias, the new calibration factor is programmed into non-volatile memory. Annual recalibration is recommended.

RSR3 Test Site Current Conditions

Theory of Operation

The RSR3 distinguishes direct and diffuse light by momentarily shading the sensor. The difference between shaded and unshaded is the direct illumination.

12v Power & Modbus RS-485 Data

The RSR3 is powered by 12v DC and outputs data via Modbus RS-485. It can be daisy-chained with complimentary sensors including pyranometers and meteorological sensors. Modbus RS-485 is available on most modern dataloggers and can be added to many older models. (Shown with network interface not included.)


Global, Direct, and Diffuse are read directly in W/m^2. Operational status (GPS location/time, temperature, input voltage, motor current, etc) and raw scan data are available on higher modbus registers.

RSR3 Accessories

An RSR3 can be complimented by a compact meteorological sensor and a global horizontal pyranometer and we offer the following compatible mounting hardware:

24" Aluminum Meteorological Sensor Arm

This can be used to mount a meteorological sensor, typically on the polar side of the RSR3, level with the base of the RSR3. For more accurate wind measurement, a separate tower and dedicated sensor is suggested.

Offset Aluminum Pyranometer Arm

Mounts a standard pyranometer at approximately the same height as the RSR3 sensor to minimize interference.

Two Meter Tripod

A sturdy tripod built out of aluminum tubes and stainless steel fittings, with wide foot pads to mount an RSR3 and accessories on any surface.

About the Company

Chris Kern has been principal of Irradiance since 2016 and is the designer of the RSR3. Previously he studied computer science at Brown University and worked as software engineer at Google.

The RSR3 is a modernized version of the Irradiance RSR2 and Ascension Technology RSR, invented by Dr. Edward Kern, founder of both companies. Dr. Kern has now retired from Irradiance but is available for consulting via KRNLPWR.

©2022 Irradiance, Inc.