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STR-21G Sun Tracker

The compact sun tracker are perfectly suited to support all kinds of Global, Diffuse and Direct Radiation measurement sensors. Besides the standard EKO sensor mounts various mountings are available. EKO Instruments improved STR-21G with fully automated set up procedure through a GPS receiver providing increased reliability and enhanced functionality.

From sun rise to sun set the compact Sun-Tracker guarantees accurate sun tracking and pointing of the attached solar sensors. The 2-axis tracker automatically adjusts to the sun’s position by the sun sensor closed-loop control system, even if the tracker is not oriented or leveled properly.

The Sun Tracker comes with a small tripot that offers a stable surface for the measurement equipment. When AC power is not available on site a 24 VDC low power version can be used to run the EKO Sun-Tracker from a solar powered battery system.


  • Easy and accurate set up by automatic retrieval of position and time (GPS)
  • Standard Integrated Sun sensor for accurate tracking and easy alignment
  • Power consumption less than 10W
  • Easy installation and operating without need of a computer
  • Continuous clock synchronization enabling permanent reliable and accurate positioning of the solar radiometers measuring direct, diffuse and global irradiance
  • RS-232 serial interface for extended position control and status information
Solar Sensors


Model STR-21G Single Arm
Motor Stepping motor
Driving technology Harmonic Drive
Pointing accuracy < 0.01° (Solar Elevation: 0 to 87°)
Angle resolution 0.009°
Rotation angle Elevation-angle(-15° to +95°) Azimuth-angle(0° to +/-180°)
Torque 12 Nm
Payload 7kg balanced
Tracking mode Sun-sensor mode and Calculation mode are automatically switched.
Tracking accuracy of Sun-sensor mode 0.01°
Sun-sensor field of view +/- 15°
GPS Sensor measurement accuracy Horizontal Position: Below 15m (2drms). GPS Positioning
GPS Sensor positioning start time < 5min. (depends on the recieving condition.)
LED Indicator Power, GPS status
Environmental Protection IP65
Temperature range -40~+50°C (-30 ~ +50°C at cold start)
Altitude for solar position calculation No Limitation
Communication RS-232C, 9600bps, 8N1
Power requirement AC100 to 240V, 50/60Hz, 20W DC21 to 32V, 20W for DC optional Sun Tracker (*Power consumption <10W)
Dimension 430(W) x 380(D) x 440(H) mm
Weight 14.5 kg

*Power consumption under normal load and operating conditions @ 25°C.

Standard STR-21G

  • Single arm STR-21G Tracker with built in GPS
  • Four Quadrant Sun Sensor which automatically compensates for mechanical misalignment
  • Pyrheliometer Mount (suitable for any pyrheliometer model)
  • Levelling Tripod with spirit level
  • Diagnostics and control software

Sun Tracker Options

  • Various top mounting plates for all common pyranometers or pyrgeometers models
  • Additional pyrheliometer mounts
  • DC operating version (18 - 30 VDC / 15W power consumption)
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