Definition
Backtracking is the control algorithm in single-axis solar trackers that rotates modules against the sun's direction during early morning and late afternoon, preventing one row from shading the adjacent row at low solar angles. Recovers 3–5% annual energy.
Backtracking Mechanics
At low sun angles (early morning, late afternoon):
- Naive tracking aims modules toward the sun → casts shadow on next row.
- Backtracking rotates modules slightly off-sun → no inter-row shadow.
- Module receives less direct beam but avoids self-shading loss.
- Net positive recovery: 3–5% annual.
Sun-Angle Threshold
Backtracking activates when:
sun_elevation < arctan(module_chord / row_pitch_horizontal)Below this angle, naive tracking would cast row-to-row shadows.
Implementation
- Controller computes solar position from time + GPS.
- Knows row geometry (chord length, pitch, ground slope).
- Computes optimal tilt: maximum tracking until shadow onset, then backtrack.
- Smooth transition between modes.
Validation
Field commissioning should verify:
- Tracker angle vs. sun position log.
- Energy production matches simulation.
- Visual check at sunrise/sunset: no row-to-row shadows.
Key Takeaways
- Backtracking rotates trackers off-sun at low angles to avoid inter-row self-shading.
- Recovers 3–5% annual energy on typical utility-scale tracker plants.
- All modern utility trackers include backtracking; budget trackers may not.
- Calibrated against row geometry and terrain.
- Validation during commissioning is critical.
Frequently Asked Questions
5 commonly searched questions about Backtracking.
What is backtracking?
Tracker control logic that rotates modules off-sun at low angles to prevent self-shading between adjacent rows. Without backtracking, front rows shade back rows at sunrise and sunset.
How much energy does backtracking recover?
3–5% annual on a typical horizontal single-axis tracker plant. Higher recovery for tighter GCR or higher-latitude sites.
Do all trackers backtrack?
Modern utility-scale trackers (NEXTracker, Array Technologies, Soltec, Trina) all include backtracking. Old or budget trackers may not.
How is backtracking calibrated?
Controller computes solar position + row geometry continuously. Switches between maximum sun tracking and backtracking when sun angle below the threshold determined by row pitch and module chord length.
Can backtracking be mis-tuned?
Yes. Wrong row-pitch input or incorrect terrain slope can cause sub-optimal backtracking. Commissioning audits validate field behavior against expected.
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