Start Successfully Inspecting Solar PV Systems with Thermal Imaging Drones
This is the second part of the two-part series on the most effective and efficient ways to inspect a solar PV system with a thermal imaging UAV (drone) also equipped with a high-definition visual (RGB) camera. Read part one of the series here.
This article presents detailed information about technical requirements and best practices that you must follow to correctly inspect a solar PV system and obtain aerial inspection data (site imagery) to the highest standard. This is necessary for correct analysis and accurate and detailed inspection deliverables and reports. The following paragraphs will break down the correct inspection practices, and a post-inspection checklist created using best-practices from drone pilots with 100s of successful aerial PV inspections.
Best Practices to Follow During a Solar PV Aerial Inspection
Ground Sample Distance and Flight Altitude
Upon arriving onsite at the solar PV system, pilots should follow their standard pre-inspection checklist and review all hardware thoroughly to confirm it meets operating conditions. Before beginning the first flight of the inspection, pilots should re-confirm all flight specs are set up correctly in their flight planning software, there are sufficient levels of irradiance (600 watts/meter²) and that the right GSD (ground sample distance) and overlaps are set correctly for the solar inspection. GSD and overlap details can be found here. The GSD, or required image resolution for this inspection, is determined by the inspection level and deliverable requirements from the end-user/client. Many times pilots inform us that they are unsure of the level of inspection due to unclear requirements from the client. GSD specifies the level of detail of the inspection, a lower GSD equates to more detailed imagery, and in turn higher quality data. The level of inspection is predetermined and establishes the required altitude and GSD for the solar PV inspection. Read an article about GSD here.
Angling the Gimbal to Avoid Glare
After determining the correct GSD and altitude and confirming the irradiance levels, the pilot needs to adjust the thermal and HD visual imaging camera gimbal to prevent glare reflecting off of the solar panels and back into the camera, ruining the data. The gimbal also needs to be adjusted/rotated to capture data at the right angle and orientation to the solar rows. In addition, if the solar PV system is on trackers, the camera gimbal should be continually adjusted to be at the correct angle for data capture. Depending on the amount of time it takes to complete the inspection, the trackers could move several times as they follow the sun’s movement, and the gimbal of the drone should be adjusted regularly for this. Solar farms requiring less than an hour or two of inspecting, smaller than 10 MW, will only require you to set the gimbal in the beginning. Larger solar farms that require an entire day on-site to complete the inspection, sites as large as 30 or 50MW, will require several adjustments to the gimbal. When inspecting PV systems that are fixed-tilt ground mount, the gimbal will only need to be initially adjusted for glare and angle of the solar modules.
It’s important to constantly monitor the site while performing the inspection and pilots need to confirm the solar PV system is operating and producing energy during the entire inspection. If the site stops working and the inspection data will show nothing and be useless, requiring the site to need to be reflown when it is operating correctly.
One highly valuable practice that drone pilots inspecting solar farms larger than 1 or 2MW should follow is having multiple fully charged batteries and a battery charger with them, that can charge several batteries at once. Due to the size of some solar PV systems, it can require multiple battery changes to complete the inspection, and drone batteries run out of energy much faster than they charge. Following this, pilots should check the data quality during battery changes and remove the SD card that was just used on that mission and inserting a new SD card between each mission. In addition to checking the data, battery changes provide pilots an opportune time to reconfirm that irradiance levels haven’t decreased. Read about what correct data is in our Knowledge Hub. By regularly checking inspection data, pilots reduce the risk of needing to refly due to equipment malfunctions or data corruption, after already leaving the site. Images should constantly be backed up on a computer while in the field as well. There have been 100s of instances where the camera stops taking images partway through the inspection, and without checking the data in the field the pilot would need to figure out what area of the farm to refly after completing the inspection.
DJI TB60 Intelligent Flight Batteries.
Metadata and Avoiding Obstructions
When checking the data, pilots should ensure that the metadata is being correctly collected. The metadata must contain GPS location, relative altitude, gimbal pitch/yaw/roll, and a timestamp in each image captured during the solar inspection. Metadata is necessary for post-processing and to keep detailed records of the PV system condition and compare the change in site condition over time.
In addition, pilots should be wary of trees, buildings, and other obstructions throughout the duration of the flight. As well as high gusts of winds that could potentially blow the drone off course and into something. This will avoid any damages to the PV system, drone, other obstructions, and injuries. This will require the pilots to be attentive to the drone mid-flight, as well as the flight path that has been set. The possibility of unnecessary costs and insurance claims can be removed by remaining aware of the surroundings throughout the flight.
Post-inspection Checklist for Data-Processing Success
Before leaving the solar PV system that was just inspected, pilots should follow the listed best practices to ensure the captured data will be uploaded to the data-processing software platform quickly and successfully. Pilots need to perform a final data quality check before packing up and leaving the site to confirm all inspection data was collected correctly. Once completed, pilots may begin uploading the data into the Raptor Maps cloud-based platform using the uploader. When uploading data, clearly label all of the folders. The clearest way to label the data is “Site Name – Data Type (IR or RGB) – Mission Number – Inspection Date”. If pilots capture data with the FLIR XT2, XT1, or Duo Pro 2 it is best to upload the data in one image folder. This is because these cameras take simultaneous IR/RGB imagery and the data will be uploaded chronologically. If the camera does not capture RGB and IR imagery in chronological order, the two image types should be separated into individual folders for uploading. Any orthomosaic or oblique imagery should be separated into their own folders and uploaded individually. When uploading data to a cloud-based data-processing solution like Raptor Maps, it is best to limit uploading to no more than 1000 images at a time. Internet speeds can make uploading more images than this challenging. In addition to this, if the connection fails during the uploading process, the images won’t be uploaded and you will need to start over. Data sets of this size should be uploaded in batches. Each batch should be named the same, with the only difference being the batch number, for example, “Asset Owner’s Name – Site Name – Data Type – Date – Image set 2”.
An example of correct and incorrect camera alignment with the solar PV panels for data collection.
Start Aerial Thermography Inspections Today
Aerial thermography enables asset owners, asset managers, O&M teams, engineering firms, and EPCs to quickly, cost-effectively, and accurately gather data on the operating condition of a PV system. Aerial solar inspections are able to provide 95+% accuracy on sub-module anomaly detection and drastically increase visibility into a PV system. These inspections are also an effective way to catch systemic issues related to warranty claims. Using Raptor Maps for data analysis and deliverables, teams receive accurate and actionable reports that enable targeted and efficient site remediation plans. Also, all PV system inspection data and reports are stored in a centralized location, and creates a robust historical record of site condition over time.
Contact us today to learn more about the Raptor Maps software platform and the importance of aerial thermography and data analytics.
Innovation in the Solar PV Industry
The processes for inspecting solar PV systems has changed greatly over the last few years. Recently the use of a drone (UAV) or manned aircraft (plane) equipped with a radiometric thermal camera and high-definition visual camera to perform an aerial thermography inspection over a solar PV system has become widely adopted. This practice has proved to be fast, safe, cost-effective, and highly accurate; providing a 95-99% accuracy rate in the detection of PV system anomalies and defects affecting performance. Aerial thermography is a versatile inspection application, its uses include inspecting 100% of PV modules during commissioning, annual maintenance, investigative inspections for PV system underperformance and to support warranty claims related to module performance and degradation, amongst several others.
Raptor Maps originally wrote this guide in October of 2017. This is an updated two-part version of the guide, as both the drone and solar industries and practices have evolved. This article discusses the precautions and steps that should be followed before inspecting a solar PV system to prevent any issues that would discredit the inspection data and reports. The following paragraphs cover pre-inspection planning and the onsite pre-flight checklist.
Pre-inspection Planning and Equipment Requirements
For aerial solar inspections and any drone inspections in the US, the drone pilot(s) will need to obtain their Part-107 ‘Remote Pilot Certificate’ license, read more about this here. Pilots must have a capable payload to begin inspecting PV systems with drones. Using the right equipment is the foundation of correctly performing an aerial solar PV inspection.
Equipment and Payload
The imaging system of a drone payload is the most important piece of equipment. A solar farm inspection requires a radiometric thermal camera, which can record the temperature of the solar modules and cells. Additionally, the camera must also capture the visual thermal imagery of each module. Best practices are to use a dual payload imaging system, which includes both IR and RGB lenses within the camera housing. Both the solar industry and Raptor Maps have standardized use of the 13mm thermal lens option but the 9 or 19mm lenses are also an option. The drone that carries the camera during the inspection should be an industrial-grade multi-rotor, such as the Matrice 200 series, or an enterprise-level fixed-wing, such as the senseFly eBee X.
Flight Planning Software
DJI Gound Station Pro flight planning software for solar PV aerial inspections.
Flight planning software is crucial to correctly perform a drone solar farm inspection. Flight planning software needs to allow for adjustment of every flight variable and pilots should become accustomed to using the software to meet the flight and data requirements needed for data-processing and to create inspection reports. Raptor Maps has created standard flight guidelines and data requirements for pilots to use to perform a fast and efficient aerial thermography PV system inspection. Flight planning software helps the pilot set an automated flight path and image collection rate. This enables consistent and accurate imagery collection throughout the inspection. The type of inspection (warranty, commissioning, preventative maintenance, etc.) dictates the automated flight path and image collection rate. Raptor Maps has used its years of experience performing and supporting thousands of aerial solar inspections to create three levels of solar inspection and flight parameters.
- Overview level inspections are high altitude and higher speed inspections that can identify large scale anomalies, with the smallest being malfunctioning modules.
- Standard level inspections are flown at a lower altitude and speed than an Overview but can identify both large and small scale anomalies, from offline inverters to sub-module issues.
- Comprehensive level inspections are flown to the IEC technical standards and are flown at the lowest altitude and speed of the three levels. This level provides highly detailed, granular sub-module level data, and absolute temperature accuracy of the strings and modules.
Depending on the level of inspection required for the project, the flight path software will enable the drone inspection to be performed correctly. Raptor Maps suggests DJI Ground Station Pro, DJI Pilot, or senseFly eMotion. Pix4Dcapture is another good option if pilots are already using this app. There are a variety of drone systems available today, read a list of supported hardware and payloads here.
Onsite Pre-flight Checklist
Before beginning any drone inspection, the pilot(s) need to perform a detailed pre-flight checklist. The first thing to check before beginning any solar PV system drone inspection is the onsite environmental condition. High quality and accurate thermal data require specific weather conditions, including clear skies and sunny weather or a slight overcast at the worst. Irradiance level onsite needs to be greater than or equal to 600 watts/meter2. Raptor Maps recommends purchasing an irradiance meter and using it for every drone solar farm inspection to confirm sufficient irradiance. If the irradiance is not checked there will be a negative impact on the data’s quality. Also, humidity should be less than 60%, and the wind speed below 15 MPH (6.7 /s)m. Aerial solar PV inspections cannot be performed hours after a rainstorm onsite. The ideal time for aerial thermography solar inspections is in the middle of the day but can vary based on the location of the solar plant, time of year, and weather conditions.
Energized Solar PV System
The PV system needs to be operating and energized during the drone inspection to collect accurate thermal data. Aerial thermography inspections can be performed throughout the year, even in the winter, but the window of time the inspection can be performed is much smaller several weeks before the summer solstice. For a more in-depth breakdown of the environmental conditions needed for a solar inspection, please watch episode 4 of the FLIR Systems and Raptor Maps webinar series “Thermal Drones and Solar Inspections”.
Pilots should ensure that these steps are carefully taken before beginning any drone solar PV inspection. Doing so will prevent the need for reflying due to poor or invalid data quality and wasted time on site which results in financial loss. In the second part of this blog series, the topics will cover best practices to follow during a solar PV aerial thermography inspection and a detailed post-inspection checklist, read part two here.
Raptor Maps recently released a case study that reports on five heavily impacted sites owned and managed by a large, U.S.-based asset owner. The owner’s solar portfolio totals more than 410 MW of PV assets across the United States. This case study analyzes five PV systems of over 280 MWs, ranging in size from 1 to 200 MWs, and site locations distributed across the U.S. The data capture (aerial inspection) and analysis (data processing and deliverables) was performed via a mixture of internal drone operations by the O&M subcontractor and turnkey aerial services delivered via Raptor Maps. The article below is an overview of each PV system covered in much greater detail in the full Portfolio Case Study.
0.86MW Rooftop Solar PV System in New Jersey
This rooftop PV system was inspected for the asset owner by Raptor Maps’ local turnkey services. The inspection took one hour to complete including set up, flight, and demobilization. This inspection uncovered 4 hot cells, 6 cracked modules, and 1 offline inverter. These anomalies were impacting more than 5% of the site’s production capacity and estimated to result in $1,800 of annual revenue loss if not addressed. Performing the rooftop inspection via aerial thermography prevented any inspection related injuries and greatly minimized the amount of time required by the field technicians to be onsite for their inspection and repairs. The O&M subcontractor utilized Raptor Maps’ platform and the detailed anomalies map to quickly identify the modules and inverter requiring a further look and send the exact number of repairmen and supplies to remediate all issues.
6 MW Ground Mount DG Solar PV System in Minnesota
This 6 MW PV system was inspected as part of the annual preventative maintenance scope of work using Raptor Maps turnkey services and local, professional, and experienced drone pilots. The inspection uncovered 490 anomalies, categorized into 16 anomaly types, and amounting to 2,853 affected modules. Instances of shading due to the tree line was one of a few major issues identified by the drone inspection, impacting the performance of more than 2,200 modules. Equipped with this data, the O&M team was able to quickly and accurately create a detailed plan to resolve all major PV system anomalies causing performance issues and impacting revenue.
RGB Imagery of shading impacting the PV system
13 MW DG Solar PV System in South Carolina
This site was inspected by the O&M subcontractor responsible for operating and maintaining this plant. The O&M team had built an internal drone program in 2019. They found the large amounts of data generated by the drone inspection difficult to analyze and organize and began using the Raptor Maps data-processing and reporting platform shortly after launching their drone program. Using Raptor Maps’ Flight Guidelines and Data Requirements, the O&M’s internal pilot managed all data capture (flights) and uploaded the imagery for automated data processing and report generation. The thermal drone inspection and reports uncovered 1,826 anomalies, across 9 categories, totaling more than 2,300 affected modules. The final reports identified and localized 10 malfunctioning strings, 379 diode faults, and over 400 cases of vegetation problems across the northwest side. The detailed reports and HD color imagery (RGB) enabled the O&M team to effectively assess all 400 cases of vegetation and is now utilizing Raptor Maps flight guidelines and data processing software to perform regular aerial inspections to maintain optimal site conditions.
RGB Imagery of some of the cases of vegetation that impacted the PV system’s production.
79 MW Utility-Scale Solar PV System in Arizona
The O&M subcontractor managing this utility-scale plant, as well as other large solar assets in the region, had a very tight timeline to complete all aerial thermography inspections before their site visits. Though this O&M subcontractor had an established internal drone program, they outsourced the aerial inspection to Raptor Maps’ turnkey services to free up their labor resources for other needed activities. By utilizing our turnkey services, we handled the aerial inspection, data analysis, and delivered them a report, allowing the O&M subcontractor to focus on other sites they managed. Upon inspection completion, the report identified 50 inverter faults, resulting in over 4% of annual production loss if left unrepaired. The O&M team knew that the site was facing inverter issues due to internal monitoring signals, but the exact number and locations were unclear. The O&M team prioritized their time onsite to resolve the numerous malfunctioning inverters and were able to reduce labor costs by deploying only the necessary number of technicians and resources to resolve all major issues.
199 MW Large Utility-Scale Solar PV System in California
This utility-scale PV system’s O&M vendor was alerted by their system monitoring software that the site was significantly underperforming in various blocks. Due to the large size of the site–more than 1000 acres– and difficulty in locating the string and module-level faults using field walks and IV-Curve tracing would be too expensive. In addition to the costs of these methods in both time and labor resources, they decided to use the faster and cheaper drone inspection option. The O&M subcontractor consulted with Raptor Maps regarding what level of aerial inspection would be appropriate for this investigative inspection and chose a two-phase inspection. The first aerial PV inspection would be a high-level, Raptor Overview level inspection to quickly identify and localize major issues impacting performance as well as heavy concentrations of lower priority faults. After the completion of the first phase, the second deployment would be a Raptor Comprehensive level inspection, targeting heavily impacted areas of the site to collect more detailed analytics on the anomalies causing the performance issues. The report identified thousands of performance issues across 6 categories, totaling 3,114 anomalies. There were almost 20,000 impacted modules resulting in over 7 MW of production lost and almost $300,000 of annual revenue loss if left unresolved for the next 12 months. The O&M team utilized Raptor Maps interactive map and a printed out copy of both the .PDF and Excel spreadsheet reports to create a detailed remediation plan. The site manager was able to deploy their team to every anomaly without wasting time locating the box or module. The team was able to resolve all major issues impacting system performance within a few weeks and return the PV system to optimum production levels.
RGB Imagery of tracker issues discovered in the aerial inspection.
The client added Raptor Maps’ turnkey services and to support their O&M subcontractors in early 2019. Within nine months, over 340 MW of sites were flown, analyzed, and reported on. They utilized the versatility of aerial thermography and data analysis through both turnkey services and software. In addition, the asset owner decided to add their O&M subcontractors that self-perform drone inspections to their Raptor Maps account. This enabled the O&M subcontractors to upload, analyze, review, share, and host their drone inspection imagery in a central place and access it as needed.
Download the full case study here!
Begin Improving Portfolio Profitability
Asset owners share the interest of maximizing a site’s production with its investors. When key steps are taken to improve asset management and operational efficiency a portfolio’s performance increases and savings are passed onto investors. Comprehensive level aerial thermography inspections enable asset owners to quickly and easily acquire extremely detailed analytics, improve efficiency, and reduce operating costs.
More Granular Data on the PV Systems’ Current and Historical Operating Condition
Comprehensive level inspections through Raptor Maps turnkey services helps teams quickly begin using aerial thermography, a cost-effective, fast, and accurate solar PV inspection method. Inspection deliverables include sub-module level analytics on 100% of the modules and detailed classifications of every identified anomaly. This increase in site data enables teams to make data-driven decisions to improve site efficiency and productivity. The Raptor Maps software platform also serves as the system of record, allowing each inspection record to be easily referenced and compared against previous inspections and other data layers including asset monitoring and asset management records.
Multiple anomalies affecting a PV system’s production, captured at a comprehensive level inspection through a thermal camera.
Improving Efficiency within Asset Management and O&M
Asset owners are able to utilize Comprehensive level inspections and the granular analytics produced to be more efficient across their organization. They are able to direct their O&M teams to focus on the most pressing issues within a site or portfolio. This level of analytics provides locations of each anomaly enabling their O&M teams to deploy labor to specific anomalies and reduce or even eliminate unnecessary hours spent remediating anomalies with a very little performance impact. In addition, the aerial inspection data allows teams to use this system of record to compare this data layer to other layers, including system monitoring data, and precisely dial in the causes of underperformance. In the case of a newly commissioned PV system, asset owners can quickly assess the overall condition, investigate issues related to warranty or performance, and begin the remediation process before teams are demobilized from the site.
Raptor Maps Software displaying the location, severity, and category of anomalies impacting the PV system’s production.
Reduce Operating Costs
Portfolio owners are able to reduce O&M costs with Comprehensive level aerial inspections. This inspection procedure replaces the need for labor-intensive exploratory I-V curve tracing or assists the process and direct teams to the problem areas. With the addition of HD visible spectrum imagery captured during the aerial thermal inspection, on-site field walks to identify damaged modules and performance issues related to soiling or shading becomes unnecessary. Exploratory handheld thermal imaging of modules by field techs also becomes redundant work because 100% of every module is documented in a radiometric thermal image with temperature values available for analysis. In turn, O&M teams are able to spend less time troubleshooting the cause of issues detected in system monitoring and spend it remediating them instead.
Multiple anomalies affecting a PV system’s production, captured at a comprehensive level inspection through a thermal camera.
Turnkey Comprehensive aerial thermography services (inspection and detailed reports) offer Asset Owners the ability to quickly and accurately inspect their PV systems without mobilizing field crews. The increase in granular data on a site’s operating condition enables them to improve operating efficiency and in-turn reduce operating costs. Raptor Maps provides turnkey services to asset owners around the world, providing inspections and site reports within days of requests. To learn more about our turnkey services or our data analytics software, please contact us at email@example.com.
Click Here to Read our extensive solar industry case study: Portfolio Case Study.