Published on AE 868: Commercial Solar Electric Systems (https://www.e-education.psu.edu/ae868)

Home > Lessons > Lesson 11: Commissioning, System Monitoring, and Operation & Maintenance

Lesson 11: Commissioning, System Monitoring, and Operation & Maintenance

Overview

Lesson 11 Scenario

Imagine this: your crew has finished installing the PV system you designed and managed within the timeline of the project. The owner's manual is prepared and ready to be delivered. Your team is ready to connect the PV system to the utility grid. Upon arrival of the utility personnel, what are the steps to initializing the system the first time? Are there any procedures to be followed? The owner knows that because PV systems are installed outdoors, there must be some cleaning routine and checkups to ensure the system is operating at the maximum possible performance. What are the main maintenance considerations needed for any PV system? How will the owner know if the system is producing energy or not?

This lesson is a guide for PV professionals and system owners. The lesson will walk you through the basic understanding of the commissioning, operation and maintenance, and monitoring topics that relate to PV systems. This lesson prepares solar professionals to become PV system operators. Similar to any other construction that exists, O&M and monitoring are pivotal aspects of PV systems, and they are key components in driving the PV system to succeed under different operating conditions. Understanding the main concepts of O&M and system monitoring prolong the operation of PV systems and guarantee expected energy production throughout the systems' lifetimes.

Learning Outcomes

At the successful completion of this lesson, students should be able to:

  • Describe steps to commissioning a PV system.
  • Identify operation and maintenance tasks involved to maximize PV system output and operation.
  • Identify monitoring strategies of array, components, and warranty coverage.

What is due for Lesson 11?

Lesson 11 will take us one week to complete. Please refer to the Calendar in Canvas for specific timeframes and due dates. Specific directions for assignments below can be found within this lesson and/or in Canvas.

Complete the following Lesson Assignments:

  • Read through the Lesson Content
  • Complete the Required Reading Assignments:
    • Chapter 14, Photovoltaic Systems by James P. Dunlop (text)
    • Addressing Solar Photovoltaic Operations and Maintenance Challenges A Survey of Current Knowledge and Practices July 2010 [1]
    • SolarABCs-35-2013 PV System O&M Fundamentals [2]
    • PV System Commissioning [3]
  • Look over the Recommended Resources:
    • Budgeting for Solar PV Plant Operations and Maintenance Practices and Pricing 2015 [4]
    • PV Reliability Operations Maintenance (PVROM) Database Initiative 2014 Project Report [5]
    • Best Practices in PV System Operations and Maintenance [6] Version 1.0, March 2015
    • Solar Operations and Maintenance [7] videos produced by the Northern Mid-Atlantic Solar Education and Resource Center, part of The Pennsylvania State University
  • Participate in the Lesson 11 Discussion
  • Begin working on Final Project
  • Take the Lesson 11 Quiz in Canvas

Questions?

If you have lesson-specific questions, please feel free to post to the Lesson 11 Questions discussion forum in Canvas. While you are there, feel free to post your own responses if you, too, are able to help a classmate with a question. If you have questions about the overall course or wish to share and discuss any "extra" course related commentary (interesting articles, etc.), please feel free to post to the General Questions and Discussion forum.

 

Commissioning Procedure

After the installation of any PV system is completed and the inspection is done, the system will be ready to be plugged to the grid to transfer energy. That process is referred to as Commissioning the system. At the same time, the installer will hand the responsibilities to the owner or operator of the system.

There are steps and requirements to commissioning PV systems that vary depending on system size and complexity of design. However, there are general guidelines that apply to most systems.

Final checkout

The system should be checked thoroughly before the commissioning starts.

A highlight of the main electrical items to consider:

  • All disconnects are in (OFF) position during the final checkout.

  • Installation matches the design documentation.

  • Conductors, OCPD, and disconnect are sized appropriately.

  • Compliance with all local AHJ and national codes (including NEC) is met.

  • Terminals connections and screws are securely tightened. 


A highlight of the main mechanical and structural items to consider:

  • Equipment is securely mounted (such as modules, racking, inverters, panels and disconnects and so on)  

  • Roof penetrations are properly weather sealed

  • Installations are matched to the manufacturer's specifications and recommendations. 


Other safety items to consider:

  • Applicable warning signs and labels are posted appropriately

  • The job site is clean and orderly

  • The documentation package is complete

  • Attention has been paid to details such as removing tools from the site before commissioning


Commissioning Procedure

When intending to start the PV system the first time, the procedure starts at the array and ends at the point of connection. This will reduce hazards and make the diagnostic and testing of subsystems easier in case there is a problem in the installation.

Reading

PV commissioning is a procedure that requires a lot of attention to details. Solar professionals are encouraged to refer to the required reading "PV System Commissioning" available on the overview page of this lesson.

1: Connect power sources to systems (this includes connecting PV module wire runs)

Considerations
  • AC and DC disconnects need to remain in “OFF” position 

  • Fuses are not connected

2: Test DC voltage and polarity

  • Make sure to use proper meter settings for DC

  • Test after connecting PV modules in series and measure

  • Expected voltage (from calculation of modules)

  • Voltage polarity

Considerations
  • AC and DC disconnects need to remain in “OFF” position

  • Fuses not connected as well

  • Watch for negative sign on meter that means lead positions of meter is not correct or circuit is not wired properly!!!


3: Test AC voltage at inverter output

  • Make sure to use proper meter settings for AC

  • Test Line to Line and Line to Neutral 

  • Compare with inverter AC voltage (specs sheet)
  • If inverter has settings for more than one connection, match your service setting for voltage

  • After this step, return fuses if applicable

4: Start-up procedure

  • Lift AC disconnect lever (inverter to grid)

  • Lift DC disconnect lever (PV to inverter) 

Considerations
  • Check with manufacturer’s manual for specific startup procedure 

  • Most inverters have Delay to check on grid and synchronize before connecting 


Operation and Maintenance (O&M)

Maximizing the performance of any PV system is one of the priorities of owners and integrators. This can be done with routine maintenance to ensure optimal operation conditions. Since PV systems can be owned by individuals, organizations, or utilities, there must be a set of practical guidelines to operate and maintain these systems to minimize downtimes and maximize the return on investment. The maintenance requirements vary depending on the system size, installation type, and locations. For example, stand-alone systems require more maintenance consideration due to the addition of batteries. Furthermore, manufacturers may provide maintenance guidance or procedure for components.

Maintenance Approaches

There are several major O&M approaches that exist in the market today, and each comes with tradeoffs. In simple words, each approach aims to achieve the three key goals of an effective O&M:

  1. Reduce costs
  2. Improve availability
  3. Increase productivity

There are three main strategies for maintenance: Preventative Maintenance, Corrective or Reactive Maintenance, and Condition-based Maintenance.

Preventive Maintenance (PM)

This strategy includes routine inspection and servicing of equipment to prevent breakdowns and unnecessary production losses. PM strategies can lower the probability of unplanned PV system downtime. However, the upfront costs associated with PM programs are moderate and requires more labor time, and the increased inspection and maintenance activity contribute to site wear and tear and perversely expedite system malfunctions.

Corrective or reactive maintenance

This strategy addresses equipment breakdowns after their occurrence to mitigate unplanned downtime. This strategy allows for low upfront costs, but it brings with it a higher risk of component failure and higher costs on the back end ( negotiating warranty terms). A certain amount of reactive maintenance will be necessary over the system lifetime, but this strategy can be minimized if more proactive PM and condition-based maintenance (CBM) strategies are adopted.

Condition-based maintenance (CBM)

This strategy uses real-time data to prioritize and optimize maintenance and resources and can be done through third party integrators and turnkey providers. Different CBM regimes have been developed by third parties to offer greater O&M efficiency. However, this comes with a high upfront cost due to communication and monitoring software and hardware requirements.

Routine maintenance Considerations

In general, most PV systems share basic maintenance elements such as modules, inverters, charge controllers, and batteries.

PV module

A thorough inspection of PV modules can be done visually by the owner or installers. Main signs to look for when inspecting a PV system include:

  • Physical damage to frame and glass
  • Delaminating or change in color of the module's outer layer due to separation of bonds between glass and frame that allow moisture or corrosion to seep into the modules

  • Burned connections inside module (hot spots) 

  • Grounding corrosion of wires or frame

  • Array mount weakness or corrosion


Shading control

As we learned in lesson 2, shading can significantly reduce the electrical output of PV array. Even after a careful site evaluation is performed before installing the system, a routine maintenance is recommended to avoid:

  • Soiling

  • Tree growing

  • Leaves and debris accumulation


Battery maintenance

Batteries are considered one of the most maintenance intensive components in the PV system. We discussed in lesson 4 that lead-acid batteries are still widely used in PV systems and a special maintenance attention is needed. A careful consideration and review of the manufacturer’s maintenance recommendations is important to ensure safety on the site.

Electrical Equipment Maintenance

Besides visual inspections of inverters, chargers, transformers, and all other electrical equipment; there are other industry tools that can be used to find the weak points of the system. An infrared (IR) thermometer can be used to find the points where higher temperatures occur, such as circuit breakers, terminals, wires, and others. 

Maintenance plan

A checklist of all required maintenance tasks and their recommended intervals to ensure best economic scheduling is referred to as a maintenance plan. The intervals can vary according to the site condition and system type. For example, a PV array installed in the desert requires more frequent scheduled cleaning of modules due to dust and soil accumulation.

Note:

An example of the O&M is shown in the Solar Operations and Maintenance videos produced by the Northern Mid-Atlantic Solar Education and Resource Center, part of The Pennsylvania State University. (The link is located under "Recommended Resources" on the Overview page.)

Reflection

What is the main cause of system downtime in any PV system?

Click for answer...

ANSWER: Inverters

Note:

More information about the recommended maintenance strategy practices in terms of frequency for main elements and main causes of downtime are available for students in Table 3 and Figure 2 on the EPRI report on “Addressing Solar Photovoltaic Operations and Maintenance Challenges: A Survey of Current Knowledge and Practices” posted on the Overview page of this lesson.

 

Monitoring

PV systems consist of different components to transfer energy. Measuring the electrical parameters at certain intervals can help gather more information about system operating status and alert users to possible problems. As we discussed earlier, measuring the output of the system is essential for production-based financial incentives offered by federal and local agencies. 

The traditional monitoring method entails simply comparing actual energy generation to that predicted from the simulation software. The advantage of this approach is simplicity, affordability, and reliability. There are multiple levels at which a PV system can be monitored. Depending on system size and type, they can be classified as:

Inverter Monitoring

Inverter-level AC and DC monitoring offers insights into an inverter’s status, given the strategic location of the inverter to monitor the performance of the PV system. Nowadays, most inverter manufacturers embed their devices with monitoring functionality.

Advantages

  • Relatively low costs (for central inverter) 

  • Monitoring of DC power being fed into the inverter

  • Monitoring the level of AC power being produced on the back end

  • The efficiency of power inversion 


Disadvantages

  • Limited level of resolution

  • Information gathering, which must be done either manually on-site or via remote Ethernet link established through the inverter’s communications port, can be time consuming and labor intensive.


Array Monitoring

Going a level deeper into the system, array monitoring involves information from DC circuits located in various sections of a PV array.

Advantages

  • Provides an additional level of data with a relatively small upfront investment. 

  • It can isolate array level problems to a more specific array segment


Disadvantages

  • A single shaded or faulty panel is not easily recognized. Several panels will need to fail before a detecting a problem. 


String Monitoring

A little closer to the modules, string level monitoring narrows the focus even further to individual strings of modules.

Advantage

  • Failure or shading of one panel in a string is easily located


Disadvantages

  • Additional monitoring complexity
  • Increases installation cost


Module Monitoring

Once we reach the module, Micro Inverter Level Monitoring is installed at the PV module level. They are more common in smaller systems than large commercial or utility scale.

Advantage

  • Provides more information about each individual module in the PV system. 


Disadvantage

  • Not very cost competitive due to the huge number of inverters


An example of monitoring is shown in the video (22:47) produced by the Northern Mid-Atlantic Solar Education and Resource Center, part of The Pennsylvania State University.

Monitoring Methods for PV Systems.
Credit: This video was produced by the Northern Mid-Atlantic Solar Education and Resource Center [8], part of The Pennsylvania State University.

Reflection

Is micro inverter monitoring level suitable for utility scale PV systems?

Click for answer...

ANSWER: No, due to the large number of modules. String and Inverter level are more feasible.

Lesson 11 Discussion

Lesson Discussion
Activity Details
Assignment Post original entry:
In this lesson, we covered PV systems monitoring concepts. Based on previous discussions, we learned that PV systems classification can include more specific market sector, such as:

  1. Solar installation for rural off-grid application
  2. Residential rooftop for grid-tied application
  3. Utility Scale PV installations
  4. Shared solar for communities
Based on the monitoring methods presented in the lesson, discuss which approach is more suitable for your systems. Support your choice of monitoring level with facts and references.

Post comments:
Respond to two different opinions of others' posts. (For example, if you choose Option 1, you need to respond to one post for Option 2 and another post for Option 3 or 4.)
Requirements, Submission Instructions, and Grading For more detailed instructions about the discussion component of this course, including how you will be graded, please visit the Discussion Activity [9] page.

 

Final Project Introduction

This week, you will begin working on your Final Project. This will be a two-week project.

Final Project
Activity Details
Assignment This final project will highlight the main concepts we discussed in the class. The questions are designed to evaluate your understanding of the basic PV system design principles and the impact that the additional PV might have on the utility grid.

Visit the Final Project [10] page for the complete details of this assignment.

Note: You will not be submitting this project within this lesson. You will be submitting the entire project at the end of Lesson 12.

Summary and Final Tasks

Let's revisit the scenarios from the beginning of the this lesson. By the end of this lesson, you should be able to communicate well with the utility personnel to insure that safe commissioning steps and procedures are followed before starting the PV system. Furthermore, you should be able to address the main O&M and monitoring questions the client asked at the beginning of this lesson. At this point in the class, our solar professionals are loaded with all basic information for design and installation of any PV systems with different sizes and types.

Being a solar professional requires a broad understanding of technologies and strategies in addition to solar design and installation knowledge such as: project management, financial analysis, communication, maintenance scheduling, monitoring networks and communication for data acquisition systems, and the list goes on.

In the next lesson, we will wrap up our class by discussing the impact of PV systems on the utility grid. As more PV are being added to the grid, there must be technical challenges to consider and understand when dealing with utilities to better negotiate and understand their requirements. So stay tuned!! See you next week.

Reminder - Complete all of the Lesson Requirements!

You have reached the end of this lesson. Before you move to the next lesson, double-check the list on the first page of the lesson to make sure you have completed all of the requirements listed there.


Source URL: https://www.e-education.psu.edu/ae868/node/954

Links
[1] http://assets.fiercemarkets.net/public/smartgridnews/1021496AddressingPVOaMChallenges7-2010_1_.pdf
[2] http://www.solarabcs.org/about/publications/reports/operations-maintenance/pdfs/SolarABCs-35-2013.pdf
[3] http://solarprofessional.com/articles/design-installation/pv-system-commissioning?v=disable_pagination
[4] http://prod.sandia.gov/techlib/access-control.cgi/2016/160649r.pdf
[5] http://energy.sandia.gov/wp-content/gallery/uploads/dlm_uploads/SAND2014_20612_PVROM.pdf
[6] http://www.nrel.gov/docs/fy15osti/63235.pdf
[7] https://smartenergyacademy.psu.edu/solar/open-education-resources#OandM
[8] http://www.solarcenter.psu.edu
[9] https://www.e-education.psu.edu/ae868/890
[10] https://www.e-education.psu.edu/ae868/974