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Summary

Terrain-Aware Backtracking (TABT) is an advanced algorithm introduced in PlantPredict Version 12 that optimizes single-axis tracker angles accounting for local terrain slopes, row-to-row elevation differences, and neighbor shading interactions. TABT calculates optimal angles on a per-row basis rather than applying uniform backtracking.

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Inputs

NameSymbolUnitsDescription
Uncorrected Tracker Angleαuncorr\alpha_{uncorr}degreesIdeal tracking angle before terrain correction
Ground Coverage RatioGCRGCR—Ratio of module width to row spacing
East Neighbor SlopeβE\beta_{E}degreesTerrain angle to eastern neighbor (positive = upslope)
West Neighbor SlopeβW\beta_{W}degreesTerrain angle to western neighbor (positive = upslope)
Tracker Tilt Angleβt\beta_tdegreesN-S tilt of tracker rotation axis due to terrain
Sun Positionθz\theta_z, γs\gamma_sdegreesSolar zenith and azimuth angles

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Outputs

NameSymbolUnitsDescription
Terrain-Corrected AngleαTABT\alpha_{TABT}degreesOptimized tracker angle for sloped terrain
Shade Condition—booleanIndicator if row would be shaded at uncorrected angle

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Detailed Description

TABT proceeds through four main steps: shade condition detection, optimal angle calculation, neighbor interaction accounting, and stow logic handling. For each row, TABT calculates whether the current tracker position results in shading from neighbors using the shaded fraction calculation: fshade=max(0,GCRsin⁡(αcurrent)+tan⁡(βneighbor)cos⁡(αcurrent)−cos⁡(θz)GCRsin⁡(αcurrent))f_{shade} = \text{max}\left(0, \frac{GCR \sin(\alpha_{current}) + \tan(\beta_{neighbor}) \cos(\alpha_{current}) - \cos(\theta_z)}{GCR \sin(\alpha_{current})}\right) where βneighbor\beta_{neighbor} is the terrain slope to the relevant neighbor (East or West depending on sun position). If fshade>0f_{shade} > 0, the row is shaded and TABT calculates a corrected angle. The optimal angle minimizes shading while maximizing cosine of angle of incidence: αoptimal=arctan⁡(tan⁡(θz)cos⁡(γs−γt)−tan⁡(βneighbor)GCR)\alpha_{optimal} = \arctan\left(\frac{\tan(\theta_z) \cos(\gamma_s - \gamma_t) - \tan(\beta_{neighbor})}{GCR}\right) This equation accounts for sun position (θz\theta_z, γs\gamma_s), tracker axis orientation (γt\gamma_t), terrain slope to neighbor (βneighbor\beta_{neighbor}), and array spacing (GCRGCR). TABT provides two stow strategies when optimal angle cannot eliminate shading. Option 1 (Terrain-Aware Angle, default) applies calculated optimal angle even if partial shading remains, minimizing shading while maintaining near-optimal angle of incidence. Option 2 (Terrain-Aware Stow) moves to full stow position if shading detected, eliminating all direct beam shading but potentially reducing diffuse capture. An optional stow-when-past-zero constraint prevents tracker from rotating past horizontal when correcting: if  sign(αoptimal)≠sign(αuncorr): αTABT=αstow\text{if } \, \text{sign}(\alpha_{optimal}) \neq \text{sign}(\alpha_{uncorr}): \, \alpha_{TABT} = \alpha_{stow} This prevents trackers from “flipping” orientation during correction, reducing mechanical wear. When TABT is enabled, PlantPredict automatically activates 3D transposition calculations to account for row-specific sky-view factors, terrain-dependent ground-reflected irradiance, and varying diffuse irradiance due to shading geometry.

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References

  • Anderson, K. S., & Jensen, A. R. (2024). Shaded fraction and backtracking in single-axis trackers on rolling terrain. Journal of Renewable and Sustainable Energy, 16, 023504.
  • Khan, M. R., et al. (2020). Optimizing single-axis tracking on sloped terrain. IEEE Journal of Photovoltaics, 10(4), 1053-1062.
  • Gueymard, C. A., & Ruiz-Arias, J. A. (2016). Extensive worldwide validation and climate sensitivity analysis of direct irradiance predictions from 1-min global irradiance. Solar Energy, 128, 1-30.