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FA-93686 / Solar tracker geometry / Open access

Overcast diffuse flat stow: night detection · case 01

Clear-sky samples with no diffuse reading are reported as night.

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

ROOT CAUSE

Night is detected from the diffuse sensor instead of global irradiance.

VERIFIED REPAIR

Detect night from ghi <= 0.

Unsuccessful approach: Treating dhi > ghi as night hides overcast readings that should go flat.

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 dhi <= 0:
        return [0.0, 'night']
    df = 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: night detection', [400, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [800, 20, 0, 70, 20], [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: night detection', [800, 0, 0, 80, 20], [0.0, 'track']],
  ['regression: night detection (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: night detection', [800, 0, 0, 70, 0], [0.0, 'track']],
  ['regression: night detection (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: night detection', [400, 0, 0, 80, 0], [0.0, 'track']],
  ['regression: night detection (partial repair)', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [100, 40, -50, 70, 0], [-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: night detection', [200, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, 25, 80, 20], [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[0.0, 'diffuse'][0.0, 'diffuse']Passed
boundary: blend band lower edge[30.0, 'track'][30.0, 'track']Passed
normal: clear sky[-45.0, 'track'][-45.0, 'track']Passed
regression: night detection[0.0, 'night'][-50.0, 'track']Failed
regression: night detection (partial repair)[0.0, 'diffuse'][0.0, 'diffuse']Passed
control 1[0.0, 'diffuse'][0.0, 'diffuse']Passed
control 2[0.0, 'track'][0.0, 'track']Passed

SHA-256 / 401a54784a5ac362f39a469303d341bea551e183c3f7ce02cb91dc530e05400a

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 or dhi > ghi:
        return [0.0, 'night']
    df = 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: night detection', [400, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [800, 20, 0, 70, 20], [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: night detection', [800, 0, 0, 80, 20], [0.0, 'track']],
  ['regression: night detection (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: night detection', [800, 0, 0, 70, 0], [0.0, 'track']],
  ['regression: night detection (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: night detection', [400, 0, 0, 80, 0], [0.0, 'track']],
  ['regression: night detection (partial repair)', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [100, 40, -50, 70, 0], [-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: night detection', [200, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, 25, 80, 20], [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[0.0, 'diffuse'][0.0, 'diffuse']Passed
boundary: blend band lower edge[30.0, 'track'][30.0, 'track']Passed
normal: clear sky[-45.0, 'track'][-45.0, 'track']Passed
regression: night detection[-50.0, 'track'][-50.0, 'track']Passed
regression: night detection (partial repair)[0.0, 'night'][0.0, 'diffuse']Failed
control 1[0.0, 'night'][0.0, 'diffuse']Failed
control 2[0.0, 'track'][0.0, 'track']Passed

SHA-256 / 333754623f377fbd287d9b361aad4c071260bff54c9fd205a5122d2bb9b9b278

3 / The verified repair

Exit 0
"""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
    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: night detection', [400, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [800, 20, 0, 70, 20], [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: night detection', [800, 0, 0, 80, 20], [0.0, 'track']],
  ['regression: night detection (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: night detection', [800, 0, 0, 70, 0], [0.0, 'track']],
  ['regression: night detection (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: night detection', [400, 0, 0, 80, 0], [0.0, 'track']],
  ['regression: night detection (partial repair)', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [100, 40, -50, 70, 0], [-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: night detection', [200, 0, -50, 80, 10], [-50.0, 'track']],
  ['regression: night detection (partial repair)', [200, 900, 25, 80, 20], [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[0.0, 'diffuse'][0.0, 'diffuse']Passed
boundary: blend band lower edge[30.0, 'track'][30.0, 'track']Passed
normal: clear sky[-45.0, 'track'][-45.0, 'track']Passed
regression: night detection[-50.0, 'track'][-50.0, 'track']Passed
regression: night detection (partial repair)[0.0, 'diffuse'][0.0, 'diffuse']Passed
control 1[0.0, 'diffuse'][0.0, 'diffuse']Passed
control 2[0.0, 'track'][0.0, 'track']Passed

SHA-256 / eb3f8b20915f50df6d900be865fddb0ee79a189ba8e6473628e3d6887f15a0a4

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 2026-09-29T14:51:57.457623+00:00.

Case digest / 8bf878f8e625bb4313d180a7b9794c8f45edef2147e132ad617b75486ea72cd8