Solar Tracker Row Backtracking

Sun Position

Time of day 12:00

Site latitude 35°N

Array Geometry

Ground coverage ratio (GCR) 0.50

Live Readouts

Sun elevation

0.0°

Tracker angle

0.0°

Shading loss

Relative output

How it works

Utility-scale solar farms mount panels on horizontal single-axis trackers (HSAT): each row rotates about one north–south torque tube to follow the sun east→west through the day. For a north–south axis, the rotation angle that points the panel normal straight at the sun ("true tracking") is:

θ_true = atan2( sin γ·cos α , sin α )

where α is solar elevation and γ is solar azimuth from south — both computed here from a standard equinox solar-position model: sin α = cos φ·cos H, sin γ = sin H / cos α, with H the hour angle (15°/hour from solar noon) and φ the site latitude.

Near sunrise/sunset θ_true is large, and adjacent rows start casting shadows on each other. The industry-standard fix is backtracking: back the panel off its ideal angle just enough that neighboring rows never shade one another, given the array's ground coverage ratio GCR = panel width ÷ row pitch:

critical angle = acos(GCR)
if |θ_true| > critical:
   θ = θ_true − sign(θ_true)·(|θ_true| − critical)
else: θ = θ_true

This simulation computes the actual shaded fraction of each row by projecting its up-sun neighbor's panel edges along the real sun ray onto the row's own tilted plane — exact 2D shadow geometry, not a lookup table. Two competing losses are shown separately:

Shading loss — power lost because part of a row sits in a neighbor's shadow. With backtracking ON this is always ≈0%.
Cosine loss — power lost because, with backtracking engaged, the panel is no longer pointed exactly at the sun. This is the real trade-off tracker firmware makes: a small alignment penalty in exchange for eliminating shading entirely.

Toggle backtracking off to watch shading losses spike at low sun angles and tight row spacing (high GCR) — exactly the failure mode backtracking exists to prevent.

Sun below horizon

Sun ray Unshaded row Shaded row

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