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FA-93666 / Solar tracker geometry / Open access

Overcast diffuse flat stow: diffuse fraction definition · case 01

Clear-sky conditions send the plant flat and overcast conditions keep it tracking.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The beam fraction is computed instead of the diffuse fraction.

THE FAILURE

The beam fraction is computed instead of the diffuse fraction.

Unsuccessful approach: Dividing by ghi + dhi double counts the diffuse component.

Case contract

ghi <= 0 returns [0.0, night]. Diffuse fraction df = dhi*100/ghi percent (may exceed 100 with sensor noise). df >= thresh_pct: [0.0, 'diffuse']. If blend > 0 and df > thresh_pct - blend the angle is ideal*(thresh_pct - df)/blend ('blend'). Otherwise [ideal, 'track']. Angles rounded to 3.

Why this case matters

Single-axis and dual-axis solar trackers turn a sun direction into actuator commands; a sign, frame or limit mistake points a whole plant away from the sun or into a mechanical stop.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(ghi, dhi, ideal, thresh_pct, blend):
    if ghi <= 0:
        return [0.0, 'night']
    df = (ghi - dhi) * 100 / ghi
    if df >= thresh_pct:
        return [0.0, 'diffuse']
    if blend > 0 and df > thresh_pct - blend:
        return [round(ideal * (thresh_pct - df) / blend, 3), 'blend']
    return [round(float(ideal), 3), 'track']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [200, 900, -30, 70, 0], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [200, 160, 0, 70, 20],
   [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [0, 80, 0, 70, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [400, 80, 45, 80, 10], [45.0, 'track']],
  ['regression: diffuse fraction definition (partial repair)', [400, 900, -30, 70, 20],
   [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 2', [100, 0, 0, 70, 0], [0.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [100, 100, 45, 60, 20], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [100, 160, -50, 80, 20],
   [0.0, 'diffuse']],
  ['control 1', [200, 160, 25, 70, 0], [0.0, 'diffuse']],
  ['control 2', [800, 160, -50, 80, 20], [-50.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [400, 0, 0, 80, 0], [0.0, 'track']],
  ['regression: diffuse fraction definition (partial repair)', [400, 400, 0, 80, 10],
   [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [0, 60, 25, 80, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [100, 100, 45, 70, 10],
   [0.0, 'diffuse']],
  ['control 1', [400, 400, 0, 80, 10], [0.0, 'diffuse']],
  ['control 2', [100, 400, -30, 70, 0], [0.0, 'diffuse']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
boundary: diffuse fraction at threshold[30.0, 'track'][0.0, 'diffuse']Failed
boundary: blend band lower edge[30.0, 'track'][30.0, 'track']Passed
normal: clear sky[0.0, 'diffuse'][-45.0, 'track']Failed
regression: diffuse fraction definition[-30.0, 'track'][0.0, 'diffuse']Failed
regression: diffuse fraction definition (partial repair)[0.0, 'track'][0.0, 'diffuse']Failed
control 1[-30.0, 'track'][0.0, 'diffuse']Failed
control 2[0.0, 'night'][0.0, 'night']Passed

SHA-256 / 388afab6e623fa1a289751a230c574ee1e7e0228484beb5961bf4d2b1aafc237

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(ghi, dhi, ideal, thresh_pct, blend):
    if ghi <= 0:
        return [0.0, 'night']
    df = dhi * 100 / (ghi + dhi)
    if df >= thresh_pct:
        return [0.0, 'diffuse']
    if blend > 0 and df > thresh_pct - blend:
        return [round(ideal * (thresh_pct - df) / blend, 3), 'blend']
    return [round(float(ideal), 3), 'track']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [200, 900, -30, 70, 0], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [200, 160, 0, 70, 20],
   [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [0, 80, 0, 70, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [400, 80, 45, 80, 10], [45.0, 'track']],
  ['regression: diffuse fraction definition (partial repair)', [400, 900, -30, 70, 20],
   [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 2', [100, 0, 0, 70, 0], [0.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [100, 100, 45, 60, 20], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [100, 160, -50, 80, 20],
   [0.0, 'diffuse']],
  ['control 1', [200, 160, 25, 70, 0], [0.0, 'diffuse']],
  ['control 2', [800, 160, -50, 80, 20], [-50.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [400, 0, 0, 80, 0], [0.0, 'track']],
  ['regression: diffuse fraction definition (partial repair)', [400, 400, 0, 80, 10],
   [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [0, 60, 25, 80, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse fraction definition', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse fraction definition (partial repair)', [100, 100, 45, 70, 10],
   [0.0, 'diffuse']],
  ['control 1', [400, 400, 0, 80, 10], [0.0, 'diffuse']],
  ['control 2', [100, 400, -30, 70, 0], [0.0, 'diffuse']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
boundary: diffuse fraction at threshold[30.0, 'track'][0.0, 'diffuse']Failed
boundary: blend band lower edge[30.0, 'track'][30.0, 'track']Passed
normal: clear sky[-45.0, 'track'][-45.0, 'track']Passed
regression: diffuse fraction definition[0.0, 'diffuse'][0.0, 'diffuse']Passed
regression: diffuse fraction definition (partial repair)[0.0, 'track'][0.0, 'diffuse']Failed
control 1[0.0, 'diffuse'][0.0, 'diffuse']Passed
control 2[0.0, 'night'][0.0, 'night']Passed

SHA-256 / 5d45affd348d8fe433c117a243dbc0ca9605e95f1a5c39da3a2d0ccfb8bd2a1e

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Deterministic stipulated toy contract for teaching; no claim of conformance with any standard, vendor protocol or production controller. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:57.211743+00:00.

Case digest / a51ad71e944fe9b92b9cff498225f7473551257ef8d273ea455a205a61283f49