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July 12, 2020

Solar first aid - the value of PV monitoring

How monitoring can lower PV O&M expenses

PV systems are first and foremost financial assets. The majority of projects are decided based on a financial model that indicates the cost of the PV system and value it generates over time – typically 20+ years.  

20+ years is a long time for an electrical system that is exposed to the elements 24/7. While minor degradation is taken into consideration in most financial models, there are many factors that can negatively impact performance over time. Little things like a growing tree nearby, module mismatch, and cable stress contribute to lower output - and the cumulative negative impact can be significant.

Do you know how your system is performing vs expectations?

The good news is that PV monitoring can detect and diagnose the most common performance and safety related issues. Module level monitoring coupled with software and data science can help protect your financial asset. Software can now detect if something is wrong, what is likely the cause, the impact, and the solution.

According to NREL, “monitoring is a powerful tool for understanding PV system performance.” Below is a list of some of the most common performance challenges that systems experience over time and what advanced, module level monitoring can do about each.

Changing Site Conditions

The design conditions of the site can change over time. Modules soil from dust, pollen, birds, soot and/or air pollution. Left unchecked, soiling can lead to localized hot-spot failures if it occurs unevenly. Trees growing nearby and construction of new facilities can cause shading of modules that previously were shade-free. If those shaded modules don’t have optimizers, one module can decrease the output of the entire string.  

With monitoring at the module level -as opposed to the inverter level -things like shading can be diagnosed down to the individual module. In some cases, it may make sense to retrofit any shaded modules with optimizers to ensure maximum output for the entire string. This is easy to do with Tigo’s flexible family of MLPE.

Module Changes

Modules degrade at different rates over time. Accordingly, mismatch from module degradation increases over time. As a result, strings of modules in an array – if they do not have optimizers – will perform as well as their worst performing module (NREL).

In addition to different degradation rates, there are module level failures that can also affect the entire string. These include diode failures, cell interconnection breakages, and damage to the modules from weather or external factors. In all of these instances, without monitoring at the module level, one module’s failure may not be noticeable. That one module going unnoticed over time can add up.  

Balance of System (BOS) Issues

Although inverter reliability continues to increase, it is one of the most frequent causes of PV performance loss. Unfortunately, an inverter loss affects all the associated modules. However, it is possible to perform some corrective maintenance such as inverter resets or communications resets remotely.

Another issue can arise from the electrical connections between the modules. These issues can be caused by water intrusion, soiling, and loose connectors from wind and general wear over time. Connector issues can cause high resistance and lead to performance issues as well as safety issues, including the risk of fire. With advanced monitoring, the increased voltages can be detected and even shutdown automatically to prevent catastrophic losses.

The benefits of module level monitoring

At Tigo, module level monitoring comes standard with every TS4-S, M, and O. Customers can view up to the minute energy, power, voltage, current and other key statistics at the module level through our monitoring platform - SMART. SMART also includes alerts to notify customers when it identifies issues and it recommends a course of action.  

Tigo’s TS4 platform of flexible module level power electronics (MLPE) can be retrofitted onto existing PV installations – to add monitoring and/or optimization in case module mismatch or shading are causing decreased output. For new installations, the TS4s can be included as a simple add-on or pre-bundled into the existing PV modules and inverter communications.  

To summarize, there are three primary causes for increased degradation with PV arrays: 1) changing site conditions, 2) module issues, and 3) balance of system issues. In all cases, advanced monitoring can help detect issues early and recommend solutions in order to minimize the financial impact of the underlying issue.  

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