Diagnosing Inverter Performance Issues

How to diagnose and solve inverter performance issues

Inverter underperformance should not be overlooked in the solar industry.

• According to KWH Analytics 2020 Solar Risk Assessment Report (page 12), it was found that inverters caused around 80% of non-weather-related production losses in commercial and utility PV systems.
• According to the Raptor Maps 2023 Global Inspection Report (page 12), inverter, combiner, and string-level anomalies accounted for about 77% of total PV system revenue loss.

Given these facts, it is extremely important to understand how to diagnose and problem-solve inverter-related issues to help improve the availability of PV systems. If you suspect that your system is experiencing underperformance, a good first assessment will include the inverters. Reliability and failure rates of inverters can vary depending on the brand, model, and installation quality, but failures in other system components can also result in inverter underperformance. Use this article to hone in on the solution.

Diagnosing

Typically, the systems monitoring portal/platform is the front line of defense in detecting and diagnosing inverter performance issues. Most Commercial and Utility PV systems have a robust monitoring portal that pulls all site/device data into a central logger, and the data is then sent to a server and then organized into a web-based software portal where approved users can access the data from any computer on the internet.

Inverter Communication Loss:

Inverter communication issues can be a symptom of a complete inverter production outage or just may be a loss of telemetry. Monitoring platforms can be configured to trigger alert icons and emails if this symptom presents itself. A quick way to manually check is to view the last timestamp of the inverter and compare it to the most recent timestamps of other devices onsite. 

To diagnose one step further and verify if the inverter communication issue is production-impacting or just communication related,  take a look at the total output of the meters with the total output of the inverters. If the meter total is reading higher than the inverter total (proportional to impacted inverter size), there is a good chance unit is producing. If there is no meter data in the monitoring portal to verify, dispatching is the only option for further diagnostics.

Fault Codes

Inverters come with internal computers and diagnostic systems that continuously monitor inverter performance on a multitude of levels. Some inverter diagnostic systems are more robust than others. If an event occurs in an inverter, the computer typically registers a fault code that is logged in the system for future reference. These codes are also pulled into the systems data acquisition system (DAS), and visible in monitoring platforms.

Alarms can be set up to detect and notify users when a fault occurs. If a fault is occurring on an inverter, use the fault code presented and cross-reference it with the OEM manual. The OEM manual will describe the alarm and troubleshooting procedure in more detail.

Under Performance:

Using an on-site weather station (such as Denowatts DTB), the monitoring portal can track a real-time benchmark for each inverter, typically referred to as the "Performance Index" or "Expected Index." This performance index can be applied to the inverter level in monitoring platforms and is a very useful tool for identifying a lower-than-expected-performing inverter.

These performance issues are more likely to slip through the cracks of remote operation centers due to the following:

• Usually smaller in impacted capacity,
• Harder to configure accurate and precise alerting mechanisms for
• Require a precisely installed and calibrated weather station that is tied to a granular PV system model in a monitoring platform.
  
  

Inverter underperformance can be a symptom of many different issues on site so it is important to look at the percentage/size of loss occurring, how and when it's occurring (i.e., data signature), and look at the system drawings to see what hardware failures could be causing that type of data signature. An underperforming inverter can be caused by any or more of the following conditions. 

- DC outage: such as a string or DC zone failure

- Inverter derating: could stem from overheating, curtailment commands, or internal defects.

- Inverter Mppt/Zone failures

- Tracker Rows Stalled (can be one or a whole block)

Action Plan

After looking over the symptoms and data signatures presented from the monitoring portal, an action plan should be put into place for a resolution. Typically, an action plan will either starts options that are available remotely and then a dispatch is initiated.

Remote Action:

A lot of information can be pulled from systems remotely these days as the industry matures and adopts more IoT (Internet of Things) technology. Inverter OEMs are deploying more and more propriety dataloggers that allow their operations team to remotely access the devices onsite for diagnostics.

Start asking these questions:

1. What information can be pulled from the system remotely to help diagnose the problem and minimize onsite troubleshooting time?
   1. Data Signature:
      1. How does the failure show up in the data?
      2. Are there any patterns?
      3. What hardware issue could be causing this type of pattern in the data that should be looked at onsite?
   2. Are there faults or status codes you can view from the monitoring portal?
   3. Have there been historical issues with this brand/type of equipment in the past?
   4. Reference OEM manuals for further information on what is being seen
2. Is there an "inverter smart-logger/gateway," and does the inverter OEM have access to the system? Inverter OEMs are deploying more and more propriety dataloggers that allow their operations team remote access for diagnostics. Sometimes these requests can result in a remote RMA, or they will request the O&M dispatch for further analysis. 
   
   Contact their support line and start a case. Information that will help them includes:
   
   1. Site name
   2. Device serial numbers
   3. Fault Codes
   4. Log Files

Dispatch:

A dispatch should be initiated once all remote action comes to a dead end. This involves sending a technician to the site for further troubleshooting of the issue. Adequate preparation ensures the success of a troubleshooting visit. Make sure the following is in place:

• Common spare parts stocked and the right specifications for the site (Fuses, MC4 connectors, spare modules onsite, etc)
• Specialized troubleshooting tools for the job are loaded in the truck (Multimeters, computers, etc.) 
• Inverter OEM has been notified if an RMA is suspected as the resolution
  
  

On-site Fix: This involves the instant resolution of the underperformance culprit in a fairly easy manner.

• Can it be fixed with a common piece of equipment? (String or combiner fuse, new MC4 connection, replacement module, breaker eset, replacement breaker, etc)
• Take notes on reoccurring issues and check system vitals before and after events occur.

Inverter RMA or Replacement

In the event of an inverter RMA, typically, everything else onsite has been verified acceptable with the installation and performance of the system. An RMA comes into play when the inverter is under warranty, and the root cause of the suspected issue is improper inverter operation.

Call the OEM, and they will walk the technicians through several checks to verify the proper installation of the device before recommending a replacement. Check the OEM manual ahead of time to ensure the installation is adequate.

• AC/DC voltages are within spec.
  
  • DC conductors are balanced between mppts, and their polarity matches inverter input terminals.
  • AC configuration matches inverters. (480V, Delta, WYE, etc.)
  • There were no grid-utility-weather events causing an AC/DC surge in the inverter.
• Installation quality
  • Spacing from other equipment, some inverters should not be mounted right next to each other.
  • Wire terminations are tight
  • No external damage from outside factors
  • Water-tight seals
  • There are no issues in the PV source or output circuit that could have led to an arc damaging the inverter.
    
    

Inverter underperformance can be quickly detected with the right tools, but solving the problems takes a little more time and money. Check out this article for more troubleshooting specifics on common causes of inverter underperformance.