POWER June 2022 Intl - 31

SOLAR POWER
40-minute flight duration per inspection.
Based on preconfigured flight routes,
the UAV can complete the inspection
of 1 MW of solar modules in about one
hour (actual time varies according to different
setting parameters). Imagery can
not only be viewed on the controller in
real time through the UAV's built-in WiFi
connection, but it can also be simultaneously
stored in the camera memory,
which allows further processing through
professional software for report compilation
purposes.
Anomaly Cases and Insights on
Thermal UAVs
Below we will share a few cases showing
three types of anomalies as seen
from a thermal UAV, which include a
PV module string anomaly, a single PV
module/diode anomaly, and an anomaly
due to environmental factors.
PV Module String Anomaly. A PV
module string anomaly poses the
greatest threat to power generation.
Depending on the scale of the power
plant, as many as thousands of modules
can suffer from this type of anomaly,
bringing considerable loss to the plant.
Therefore, PV module string anomaly
deserves particular attention.
Normally, PV module strings are
not maintained on a daily, weekly, or
monthly basis, so it is difficult to detect
anomalies right away. Even though
anomalies can be judged by looking
at the increased or reduced amount
of power generation as shown on the
monitoring system, this does not work
when an anomaly occurs right at the
beginning when the power plant is up
and running, since there would be no
differential figures for comparison. It is
suggested, therefore, to use thermal
imagery to locate anomalies whenever
power generation abnormality is
detected from the monitoring system,
rather than wait for routine inspections
to be completed. This can help prevent
unnecessary power losses.
Figures 1 and 2 are thermal images
showing two types of PV module string
anomalies. They depict a single-string
anomaly and multiple-string anomaly,
respectively. Because circuit anomalies
in single strings or small-scale strings
do not significantly impact power generation,
they usually go undetected
without installation of a string monitoring
system. Also, this type of anomaly
is not only nearly impossible to be detected
by the naked eye, but it is also
difficult to be detected with handheld
June 2022 | POWER
3. This thermal image shows an anomaly of
a diode circuit. Courtesy: ECOVE
thermal imaging tools. However, with
aerial thermal imaging by a UAV, anomalies
can be quickly spotted.
Single PV Module Anomaly or
Diode Circuit Anomaly. Figure 3 is a
thermal image showing a diode anomaly.
This anomaly can neither be spotted
under visible light nor be detected
through a monitoring system. They can
only be spotted with thermal imaging,
either by handheld thermal imaging
tools or thermal UAV. Again, thermal
UAV is far more efficient in this respect.
Anomalies Due to Environmental
Factors. Some environmental factors
contribute to the loss of power generation,
including biological contamination
(Figure 4) and tree or building shadowing.
Even though these types of anomalies
can be detected visually during
routine
inspections,
thermal
imaging
brings far more detection efficiency.
Once the anomaly is spotted, operators
can refer to the power generation
figures as shown on the monitoring
system to further determine the type of
module cleaning plan or vegetation removal
plan needed. Anomalies caused
by environmental factors do not pose
as immediate threat to equipment function;
however, if left untreated or uncleaned,
there may be partial hotspots
on PV modules, which in the long run
would affect power generation.
UAVs Save Time and Optimize
Performance
From our experience, thermal UAVs
can help solar power
plant maintenance
operators save at least half the
time required to perform manual inspections.
The dual-camera modules
on the UAV can not only take thermal
images, but also capture visible light
images. This can aid inspectors when
analyzing the images, as defects or
www.powermag.com
4. This thermal image shows an anomaly of
PV modules due to biological contamination,
affecting normal power generation. Courtesy:
ECOVE
anomalies shown on both pictures can
confirm problems, helping to identify
causes and avoid misreadings.
Another feature of thermal UAV is
that it can conduct full range inspections
and area screening. The screened
results can then be post-edited with
professional software to produce complete
images of the entire solar power
plant in gray scale and in thermal
mode. Comparison between gray-scale
and thermal images is recommended
because sometimes an anomaly seen
on a thermal image is not necessarily
a real anomaly. Gray-scale images provide
a way to double-check and avoid
misreading the results.
Lastly, pre-configured flight routes allow
thermal UAV to accurately inspect
the same areas every time, reducing
the chance of human error during
inspection. Quality and standardized
data is especially important if the operator
wishes to develop a database for
future machine learning programs.
Challenges remain for carrying out
solar farm inspections with thermal
UAVs, including ambient temperatures,
sunlight angle, and UAV flight
parameters, which could either reduce
the validity of inspection results or
impact results judgment. But overall,
thermal imaging through UAVs is a
great maintenance tool for solar farms
in that it can locate anomalies with
precision, save more than one half of
the inspection time than when done
by hand, ensure inspection staff security,
and provide useful data for future
smart applications. ■
-Cheng Hong Tsai and Jie-Ming Yang
are senior engineers with ECOVE, a CTCI
company that provides environmental
services, specializing in energy-fromwaste,
waste management, wastewater
recycling, solar power, and PET
(polyethylene terephthalate) recycling.
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http://www.powermag.com
POWER June 2022 Intl

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