We explore the pros and cons of different methods used to inspect solar plants using drone thermography.
Drones are an important tool for the operation and maintenance of solar plants. Above combines drones, thermal imaging and software to identify and report module anomalies. Solar panels can develop defects that can be easily corrected if identified early. We believe it is important to know the advantages and disadvantages of each thermographic inspection method so that you can choose the most beneficial solution for your solar PV portfolio. To get started, we cover the basics of aerial thermography and the benefits of regular thermographic inspections.
Introduction to Aerial Thermography
For many solar PV companies, using drones for thermographic solar plant inspections is now an industry standard. Drone thermography provides a low-cost, highly accurate and 100% complete picture of a solar plant, down to a cellular level, reducing the reliance on manual string measurements and random ground-based thermography to validate the electrical integrity of the solar plant. This method can identify quality, construction, and commissioning issues at an early stage, and thus avoid early yield and revenue loss. Conducted at provisional acceptance certification (PAC), it provides an early health baseline for 100% of the modules as well as a comprehensive plan for the engineering, procurement, and construction company (EPC) to resolve any identified issues ahead of intermediate (IAC) or final acceptance (FAC), when a second thermographic inspection should be conducted. During long-term operation, drone thermography should be conducted annually to provide you with a timeline that can be referenced throughout the solar plant’s life span and can allow performance trends to be identified. Regular thermographic inspections identify issues that can be responsible for an underperforming solar plant and direct engineering resources straight to the issue to resolve.
High-quality thermographic and high definition visual RGB camera inspections, combined with an intelligent software solution, allow you to transition towards a preventative maintenance strategy instead of a reactive strategy. There are important factors to consider that affect the quality of the data collected and how the data is processed into actionable information for your team. There are two main methods of thermographic and visual data collection. One is the ‘Orthomosaic method’ and the other ‘Radiometric Video’.
Orthomosaic thermographic images are created by digitally stitching thousands of individual thermal photographs together, to create one image. Data for an orthomosaic thermographic inspection tends to be collected with the drone at a higher altitude, as the data processing to stitch the images together often fails if the camera is too close to the solar panels. Orthomosaic-type inspections are therefore commonly used to rapidly capture large areas of solar modules. However, this does not mean that an orthomosaic method is always the fastest method because the drone must fly slowly to capture still images. Moreover, the biggest disadvantage of this method is that the number of pixels per solar module is typically low, so data quality can suffer. This can mean that early-warning signs of issues might be missed, and other issues misidentified because the resolution is not good enough to accurately identify an issue.
Another disadvantage of this method of drone thermography is that the anomaly temperature gradient is hard to record accurately, meaning that the data has a short shelf-life as it cannot be accurately used in future historical data analysis. This inspection method will identify high impact anomalies, but it will not identify the more subtle anomalies. Many chronic or systemic module issues have subtle thermal gradients in the early years, so detecting these early and preventing further deterioration in module condition requires a more detailed methodology.
Radiometric Video Method
Above is one of the few companies that uses radiometric video to inspect solar PV plants. The methodology is to capture continuous radiometric video and visual RGB imagery during flight. This bespoke methodology provides highly detailed, cellular level data to our customers. Video capture has a high ‘frame rate per second’, often expressed in hertz. Using radiometric video means that, on average, our data analysis tools have 50 images of each module for thermographic analysis, compared to only 1 or 2 images with an orthomosaic approach. This has the benefit of raising the probability of capturing a good quality image of each module and secondly raising the confidence level of any temperature gradients measured.
Alongside this video methodology, Above’s patented temperature methodology ensures absolute temperature precision by recording the temperature and irradiance during the drone flight. This data allows Above to normalise the temperature gradient of each anomaly identified during the inspection. This is important because the thermal gradient will change depending on the level of irradiance at each time point in the drone flight, and comparison between anomalies in the same plant or across plants is impossible without normalisation.
This method enables solar plant managers and O&Ms to accurately sort module anomalies by temperature to prioritise resolving or identify issues for a warranty claim. Using this methodology Above can identify even the faintest temperature differences, which may be seen at very early stages of deterioration in module electrical performance. This level of data quality is paramount to future preventative maintenance regimes and to successful warranty claims, which often require IEC-compliant inspections. Above captures simultaneous high-definition (HD) visual video alongside the radiometric thermal video. The quality of this visual data enables our data analysis model to identify the root causes of certain thermal anomalies, for example, soiling, shading and module damage.
In summary, the radiometric video method of inspection delivers an incomparable level of insight into solar plant health. Above provides an end-to-end thermographic inspection solution for your solar PV portfolio. Our software SolarGain highlights underperforming modules at a solar plant level and underperforming solar plants at a portfolio level. This makes it easier for our customers to optimise their maintenance and operations strategies, and in turn, creates savings in performance improvements. SolarGain goes even a step further and allows our customers to take further action by adding root causes, creating punch lists, tracking the resolution status and viewing thermal reports on-site with our mobile tool EyeSite.
Above is ‘Solar Aerial Thermography’ certified, which means that we comply with the stringent requirements of the Solar Best Practices. Take a look at the Solar Best Practice website for more information.