Energy systems

Why this matters

Each energy system fails in its own way. A whole string running warm and a single hot module have different causes, line joints heat up with current, wind turbine blades erode at the leading edge, and gas leaks are invisible to the eye. Reading the pattern correctly sends the repair team to the right place with the right equipment.

Solar farms

Outdoor thermography of PV modules is covered by the technical specification IEC TS 62446-3:2017, which includes clauses on classes of abnormalities and a table of module thermal patterns. The detailed criteria are in the standard itself, which must be obtained for real work. This module practises a principle common to all of them: compare a module with modules of the same type under the same conditions.

from statistics import median

temps = [[45.0 + 0.1 * ((i * 7 + j * 3) % 5) for j in range(10)] for i in range(4)]
temps[1][6] += 12.0                     # single hot module
temps[3] = [t + 4.0 for t in temps[3]]  # whole string warm

array_median = median(t for row in temps for t in row)
for s, row in enumerate(temps, 1):
    s_median = median(row)
    string_flag = "string warm" if s_median - array_median >= 2 else ""
    hot = [f"module {m} +{t - s_median:.1f} K" for m, t in enumerate(row, 1) if t - s_median >= 5]
    print(f"S{s}: median {s_median:.2f} °C ({s_median - array_median:+.2f} K) {string_flag} {' '.join(hot)}")

S1: median 45.20 °C (-0.10 K)
S2: median 45.25 °C (-0.05 K)  module 7 +11.8 K
S3: median 45.20 °C (-0.10 K)
S4: median 49.20 °C (+3.90 K) string warm

Power lines, wind turbines and pipelines

• Power lines: loose or dirty joints have higher resistance and heat up with the current flowing, so inspect at high load and record the current at the time. Corona is inspected with UV cameras (module 2)
• Wind turbines: the review by Memari and colleagues (2024) summarises drone and deep-learning inspection for cracks, leading-edge erosion and delamination of blades. The turbine must be stopped and the rotor locked before flying close
• Gas pipelines: optical gas imaging (OGI) has criteria in EPA 40 CFR 60 Appendix K (2024), such as the camera’s band overlapping an absorption band of the target gas. TDLAS sensors tune a laser across a gas absorption line and compute concentration from the Beer–Lambert law (Lin and colleagues, 2022)

Pipeline patrol frequency

The US rule 49 CFR 192.705 is an example of setting patrol frequency by class location, which depends on the density of buildings near the pipe: the more people, the more frequent the patrols, and road or railway crossings are patrolled more often than elsewhere.

MIN_PER_YEAR = {  # class location: (at road/rail crossings, elsewhere) minimum per year
    1: (2, 1), 2: (2, 1), 3: (4, 2), 4: (4, 4),
}
segments = [("A", 1, 2.4, False), ("B", 3, 0.6, True)]   # name, class, km, has road crossing
for name, cls, km, crossing in segments:
    crossing_n, elsewhere_n = MIN_PER_YEAR[cls]
    n = max(crossing_n if crossing else 0, elsewhere_n)
    print(f"segment {name}: class {cls}, {km} km -> at least {n} patrols/year")
plan = max(max(MIN_PER_YEAR[c][0] if x else 0, MIN_PER_YEAR[c][1]) for _, c, _, x in segments)
print(f"one patrol plan covering the whole route: {plan} times/year")

segment A: class 1, 2.4 km -> at least 1 patrols/year
segment B: class 3, 0.6 km -> at least 4 patrols/year
one patrol plan covering the whole route: 4 times/year

Module lab

Common mistakes

Summary

• Compare modules with their own group, separating module-level from string-level anomalies, which have different causes
• Inspect power lines at high load together with UV; stop wind turbines before flying close; use OGI or TDLAS for gas pipelines
• Pipeline patrol frequency depends on class location; a single-route plan uses the frequency of the most demanding segment
• Detailed criteria are in the standards and the asset owner’s requirements; drone findings must be confirmed on the ground

Check your understanding

1. A string median is 46 °C and one module is 53 °C. What is the difference from the median?
2. A whole string runs uniformly warmer than the array. What should be checked first?
3. Why should line joints be inspected at high load?
4. Under the US rule example, how many times a year must a class 3 segment with a road crossing be patrolled?
5. What property must an OGI camera have under Appendix K?