PV O&M Benchmarking: Planning for site performance management

Operations and maintenance (O&M) is often an overlooked part of PV system planning. Yet, proper O&M is critical to ensure a solar system performs as expected over its 20-year, or more, operating life. As the PV industry matures toward a Levelized Cost of Electricity (LCOE) metric that is on par with other forms of electricity generation, we must embrace a long-term view of system performance and cost. With proper system design, best-in-class equipment selection, and professional O&M management, PV site performance and costs can be optimized.  

So, why is the operation and maintenance function often overlooked in the early stages of PV system design and planning? A key reason is a lack of awareness of potential site issues and benchmarking data. There simply isn’t a mechanism to provide comprehensive, industry wide information in a lessons-learned format. With such a format in hand, designers would be able to see specific issues, probable root causes, and potential impacts on power production.

The following presents site issues collected from a contracted install base in 2009 and 2010 of North American PV sites. There are a number of methods that can be used to collect O&M data, however, here we pareto the top field issues and discuss the primary potential problems.

Key O&M findings
The Pareto chart shows the frequency of documented occurrences—not power losses—at PV sites during the period of study. The top four areas that can lead to power production losses as demonstrated by actual case data are examined. 

1. Unsealed enclosures & conduit
Left alone, unsealed enclosures and conduit can cause rust, corrosion, or ground faults that lead to future power production losses. For instance, heavy rain can cause erosion around the cement pedestal and electrical junction box. If the conduit in the box was improperly sealed, exposing entire underground strings to dirt and water, this could wash into the electrical box. Dirt and water in the conduit will likely lead to ground faults and trigger the inverter to shut down. The seal on the electric enclosures could also be compromised because improper seal material was selected. This material seems to be degrading from the weather or UV, and is crumbling when touched, leading to gaps between the enclosure and metal lid.

2. Hot & loose connections
Improper connections can create arcs and cause fires, leading to potential safety hazards for field service personnel, individuals connected to the site, or any unrelated parties responding to a problem. Some sites have more loose string connections in combiner boxes than others. For example, a combiner box with several connections that fail to meet the IAW torque specification. This is a simple matter to rectify; however, it’s unclear whether this was a recent occurrence or one that took place after the site was commissioned one year ago.

Regardless, a complete check of all combiner boxes on an ongoing basis helps mitigate the risk of loose connections. The high frequency of this occurrence points to the significance of string level performance monitoring. With a properly monitored system, faulty strings can be quickly located and repaired.

3. Tracking equipment issues
Many solar tracker issues are related to human error and can be resolved rather quickly. When electrical connections are loose in the tracker encoder boxes, there may be false encoder counts or lost encoder counts, causing the tracker to lose its position. In one case, the tracker encoder box had loose wires that caused an intermittent loss of tracker synchronicity with the rest of the system. The individual tracker, which is not aligned with the rest of the trackers, is marked in red. String level monitoring solutions will allow the O&M provider to detect an underperforming string, and assess the associated cost of lost production and the urgency of repair.

4. Under-performing & non-performing strings
String issues pose an immediate and direct impact on power production. The causes include blown fuses, failed power connections, connectors not tightened to torque specs, poorly performing strings, and grounded strings. Non-performing strings can be a result of failing connectors, as well. The connectors became disconnected despite a functional locking mechanism. This is most likely attributed to improperly joined connectors, which were eventually disconnected by excessive movement from wind or vibration. These issues would be easily detected with string level data monitoring solutions.

Conclusion
The examples presented here demonstrate the need for active O&M management and site performance monitoring. Consulting an experienced and knowledgeable O&M provider early in the design and planning process will help identify problematic design practices, proper equipment specification, and appropriate site data monitoring and performance management tools. O&M service providers not only understand specific equipment, but also the functional relationship among all parts of an entire PV system. In addition to maintaining the entire site, a provider should collect data, track and measure system performance, and address any non-conformances or irregularities before they impact power production. They will also offer a global perspective and provide industry benchmarking and recommendations based on a broad portfolio of sites under O&M contract to engineers and designers, ensuring maximum power production. 

As the collection of data grows, design teams will be able focus on issues that are important from a strategic or material selection point of view while, at the same time, benchmarking against the rest of the industry. The vision is to provide the market with unbiased, independent, and useful information to enable complete sharing of O&M issues that help all parties improve designs, drive down costs, increase power production, and support the growth of the PV market.


Casey Miller is the director of String Inverter and Site Solutions at Advanced Energy Industries, Inc. Matt Denninger has devoted nearly 20 years to the high-tech and renewable energy industries, holding leadership positions in sales, marketing, service, and senior management at Advanced Energy Industries, and other companies in the industry.
 
Advanced Energy Industries, Inc.
www.advanced-energy.com