AE 868
Commercial Solar Electric Systems

Monitoring

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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, part of The Pennsylvania State University.

Reflection

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

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