Solar Power Plants Air Thermography

fault detection

in solar power plants

Solar Power Plants Air Thermography, aerial drones are used for fault detection and localization in PV plants. While drones help to scale, automate and accelerate the detection of faulty areas within a large SPP site, it should be noted that such techniques may lack the resolution to detect subtle component artifacts or identify specific failure modes. This type of inspection by drones is classified as a simplified inspection procedure of the entire PV array to find modules of PV subarrays with noticeable problems.

In case the imaging is performed using a fast carrier, the camera’s moving speed should always be chosen according to the time constant of the camera’s IR detector to avoid smearing effects. When used for PV modules and system, common IR camera bolometer detectors on common IR camera bolometer detectors may appear at a movement speed of 3 m/s.

For wide-area imaging, such as drone use, consider radiation and system stability, especially if the images will be stitched together and not individually mapped to system performance (instantaneous DC array current).

Ensure that the geometric resolution requirements are met, especially if the distance between the IR camera and the PV module is large. If the requirements are not met, there may be a deviation in the procedure.

Perform the simplified inspection on the entire PV array to find PV modules or arrays with visible problems. A detailed inspection is then performed on these PV modules. This partial and detailed inspection can be agreed in the contract with thresholds to decide what kind of case in the simplified procedure will warrant the detailed approach described in this document.

Emisivity

The ability of the surface of a material to emit energy by radiation proportionally.

It is the responsibility of the qualified thermographer to estimate the emissivity of the surface under investigation, especially in the case of detailed inspection. The emissivity of a surface depends on many factors. Most of them are less relevant to the given task, such as the full spectral range of the (LW)-IR camera, surface and ambient temperature, surface geometry, etc.

For simplified review the most important dependencies and some common values for common surface and ambient temperatures, non-perforated surfaces and (LW)-IR camera pass are given. It should be noted that the less common MWR-IR cameras differ significantly.

Software for Evaluation

Using software in the review, it is possible to transfer the radiation intensity values measured by the IR camera to absolute temperature values. Calculations can be done directly using the IR camera software which updates the temperature effects on the screen and in the saved file.

Care must be taken when interpreting any temperature values because they may not be absolute temperatures if the correct parameters have not been set. To obtain temperature values, it is necessary to set certain parameters, in particular

1. Emission,
2. Reflected warmth,
3. Temperature level and range,
4. Different measuring tools for temperature data under minimum, maximum and arithmetic proportioning value specification (e.g. point measurement, polygons)

Assessment

The following measurements and observations are important for evaluation or verification:

1. Maximum temperatures,
2. Temperature differences,
3. Temperature profiles,
4. Cloud, cloud movement, cloudiness,
5. Wind speed and direction,
6. Mechanical stress, contamination before the installation history log file,visual inspection
7. Radiation and DC load of the system,

The results and recommendations of previous inspections should also be taken into account.

Exact temperatures cannot be determined during a simplified thermographic inspection of a PV plant. They are assessments of specific thermographic models. A detailed inspection with suitably qualified personnel should be carried out to assess absolute temperatures and temperature differences.

Evaluation of IR Images

Anomalies are classified and evaluated according to a known thermal model. Measurement of absolute and relative temperature values is not necessary but can complement thermal models as a plausibility check.

An algorithm should be used to determine the highest temperature in the images. This can be done using different types of tools in the camera and image processing software, such as “free hand point” or “maximum point in an area”.

To calculate the average temperature of areas using the camera and image processing software, use different tools such as rectangular, circular or polygonal areas.

Taking into account measurement uncertainty, point anomalies and average values of extended areas can be measured.

Absolute temperatures in PV generators vary due to differences in PV array, time on site, wind position and convection.

For much more detailed information about the Thermal Anomalies detected by MapperX software, please see our article.