Identifying and Addressing Underperforming Solar Assets: Page 2 of 3

Preventative Maintenance

While desktop analytics are a crucial tool for identifying underperforming assets, KPIs are ultimately limited in resolution. The fog of uncertainty is always present. This is why periodic preventative maintenance (PM) is a core component of an O&M program.

One approach to PM is to use highly trained PV professionals who can cut through the fog to unveil a wealth of information. The benefit of this approach is that it can identify subtle module-level defects, reveal systemic issues that may be undetectable via IR imaging, confirm warranty failures with IV measurements, and identify any safety issues that may exist with wiring and other aspects of the array. In many cases, it may be difficult to find qualified professionals to inspect all the fielded PV assets in a large fleet. While less highly trained professionals are more readily available and can conduct inspections at lower costs, the quality of these inspections can be lower. If you take this approach, you run the risk of overlooking subtle yet critical performance issues.

While there is no substitute for in-field investigations, relying exclusively on boots-on-the-ground inspections is an expensive and labor-intensive PM solution. If you have hundreds of assets distributed over thousands of square miles, your PM program would need to employ dozens of vendors and manage myriad contractual obligations to inspect every asset. It is also difficult to standardize inspection techniques and report data using this approach.

Standardize PM activities across your fleet. Aerial thermography in tandem with aerial visual inspections addresses many of the issues associated with traditional approaches to PM. With a few exceptions due to restricted airspace, asset managers can scan an entire fleet with one unified process. The resulting data integrates smoothly with analytics platforms. These data streams are extremely valuable as they provide a mountain of data that are easily mined for insights into asset performance.

The histogram in Figure 1, for example, shows the percentage of modules presenting faults for more than 200 PV assets based on aerial inspection results. Although there is some spread to the distribution of results, the bin with the lowest fault rate contains the highest number of sites. There are also two notable outliers in these results, which we flagged for further analysis. While it is theoretically possible to obtain these same data using traditional boots-on-the-ground inspections, doing so would be time intensive and costly.

Drilling down into thermal scan details, we can not only identify submodule issues but also differentiate between a faulty diode versus failure in a cell string. These results are useful for identifying and remediating performance issues and also reduce safety risks by identifying dangerously hot modules that would otherwise go unnoticed. Zooming out from individual components, we can review data across the fleet and look for trends. As an example, fleet-level thermal scan results show that performance impacts due to hard shading—often associated with foreign objects on top of PV modules—are higher at elementary schools than at middle or high schools, suggesting that younger children are more likely to throw objects onto solar canopies, causing hot spots. The ability to quantify subtle impacts like these improves performance models and the accuracy of risk assessments early in the project development cycle.

Corrective Maintenance

A distribution such as the one in Figure 1 clearly identifies underperforming sites relative to the fleet population. You can use these results to both flag sites with performance issues and prioritize remediation efforts. By ranking KPIs across the portfolio, for example, you can create an initial remediation priority list, which you can refine to optimize your corrective maintenance (CM) efforts.

Focus remediation resources where they are needed most. All else being equal, the first priority is generally to fix those assets that are losing the most revenue. However, you may also want to address sites together within a specific geographic region to optimize logistics and management costs. It is also important to consider equipment warranties, as you may need to prioritize corrective maintenance at sites with equipment nearing the end of the warranty period to leave time to engage with the manufacturer.

In many cases, it is efficient to leverage a site’s existing O&M provider to conduct CM activities. This is especially true when PM inspection results provide a clear understanding of the underlying performance issue and the location of the problem. Since aerial inspection reports indicate the precise location of each fault down to the module level, the repair team can use this report as a map, which expedites the remediation process.

Use expert investigators where appropriate.  As a PM inspection reveals greater scale, complexity, or potential implications of performance issues, the site may require more-detailed investigations. In the case of the two outlier sites in Figure 1, the owner engaged an independent engineering (IE) firm specializing in PV performance audits to conduct detailed ground-based investigations. The case studies that follow illustrate that this level of investigation is warranted where project stakeholders suspect unknown systemic or potentially systemic issues that require an exact diagnosis to determine next steps.

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