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Most solar panel manufacturers will provide a 20-30 year product performance warranty. Here’s what you need to know about testing your solar panels for performance.
Solar panel performance warranties will guarantee that an individual PV module will output a certain amount of energy during the span of the panels life. Since all PV modules will degrade over time, the warranty is meant to assure the consumer that it won't degrade too much.
A basic PV module warranty functions like this. The PV manufacturer will guarantee a linear product warranty of perhaps 80% performance by the end of 30 years. This means that if you have a 300W module and by the end of 30 years, it cannot produce more than 240W at STC, then you would, in theory, be eligible for a warranty claim involving some level of payout, or a replacement panel.
Testing Your Solar Panels’ Performance
However, this typically makes the assumption that you will regularly test your panels to ensure that they are all functioning within the warranty specifications. It also assumes that you are able to measure your panel with STC ratings, which are typically only available within the laboratory setting. Given that most PV modules are out in the field, on rooftops, and far removed from any type of PV laboratory, it begs the question of how a homeowner or a typical contractor would actually perform a test in the field to ensure the panels are maintaining their warranty.
There are a few different ways that one could take care of a PV module performance warranty claim with a residential or small commercial sized system based on the inverter system that is being used. The first and most straight forward way to monitor the PV system is with a module level monitoring based inverter systems such as an optimizer system from SolarEdge or Tigo or a microinverter system such as Enphase or APSystems. The second and less effective system is the use of a string inverter with real-time monitoring of the input from individual strings of panels and the output of the overall system. The last and least effective way of checking the PV modules on the system is with a string inverter with no monitoring capability or a "dumb inverter".
1. Module Level Monitoring Using Optimizer/Microinverters
In the first scenario, if you or a client has a system with module-level monitoring such as a power optimizer based system from SolarEdge or Tigo or a microinverter system such as Enphase or APSystems you are in luck. This type of system allows the easiest method of testing modules to see if they are performing how they should be. This is simply because the system will be sampling the output and performance of the modules in real time. If there are any dips in output, a homeowner could easily see this from the monitoring portal provided by the inverter company. It would be important in this case to make sure that any dips in performance are not related to weather events, local shading, or uneven soiling. If an individual panel is discovered to be underperforming compared to the rest of the system, it should be easy to spot on the monitoring system and reported to the PV manufacturing company.
2. String Inverter Real-Time Monitoring
In the second scenario, if you or a client has a newer string inverter system such as SMA or Fronius, it may be possible to monitor real-time output from individual strings of panels. If data is collected in real time of the string output, you could get an idea of what the standard output of the system should be. If one string is underperforming and there isn't any logical external cause such as weather, shading, or soiling, it could be that one or more modules in the string has an issue. Something to note here is that in a typical string of panels if one panel is underperforming, it will limit the current output of the rest of the modules. This basically means that if all the panels are capable of producing 250W, but one panel is only producing 100W because of a performance issue, then it will limit the other panels in the string to producing about 100W. If this occurs, ideally, you could take an IV curve tracer and determine what the problem with the string is. If you don't have access to a tool like this, you would need to test each panel to see which one is bad. One way you could do this without the laboratory setting, is to take the modules out one at a time to see which one caused the whole string of panels to output poorly. This could be an overly exhaustive way to test the panels, but it may prove to be a good low-tech method to find the culprit.
3. No Monitoring
In the last scenario, if you have a PV string inverter with no monitoring, maybe because it is an older system, you will have to work the most to find if there is a single module performing poorly. In this scenario, you may need to purchase some type of monitoring hardware such as an IV curve tracer to test each strings output and start testing different panels to see which one is performing the worst. This will be the most time intensive option that may not result in clear data that you could provide to a manufacturing company to justify a warranty claim, but it could be worth a try.
For the second and third options above, it is a bit obvious that this may not be ideal for a homeowner who would like to simply check to see if the panels are outputting correctly, as it means that there will have to be some electrical work that must be accomplished. There is a solution here that one could do to take a preemptive approach to protect your system from possible warranty issues down the road. You could upgrade your system with Tigo power optimizers or a similar power optimizer product.
Tigo offers module-level monitoring on both their rapid shutdown solution and their optimizer solution. If you were to choose either option, you would increase the safety of the system and you would be able to gather PV module data at each individual panel and store it on the cloud in real time. In addition to that, if you were to choose the optimizer system, it would increase the overall system's output performance, which could justify the additional cost of the upgrade.
The reason I suggest this option is because I have personally talked with many PV system owners who have 10 to 20-year-old systems that are still technically under warranty but they don't have any way to know it because they don’t have module-level monitoring capability. When this is the case, their choices of monitoring come down to purchasing a IV curve tracer and manually collecting periodic data to make sure the system is functioning properly, or purchase a system like Tigo to upgrade the existing system and allow them to passively monitor the system in real time to see if there may be any warranty issues that should be taken care of.
Of course, either option isn't a 100% guarantee that you will be able to identify a problem panel, or that the manufacturer will honor a 25-year warranty, 20 years into the life of the product. But, it will be a way to increase the chances that your warranty is covered. And more importantly, it will allow you to know if your system is functioning correctly, which is the ultimate goal.
Resources:
Renvu Solmetric PV IV Curve Tracer
IV curve test with Solmetric
Renvu Tigo TS4-R-O
Solar panel performance warranties will guarantee that an individual PV module will output a certain amount of energy during the span of the panels life. Since all PV modules will degrade over time, the warranty is meant to assure the consumer that it won't degrade too much.
A basic PV module warranty functions like this. The PV manufacturer will guarantee a linear product warranty of perhaps 80% performance by the end of 30 years. This means that if you have a 300W module and by the end of 30 years, it cannot produce more than 240W at STC, then you would, in theory, be eligible for a warranty claim involving some level of payout, or a replacement panel.
Testing Your Solar Panels’ Performance
However, this typically makes the assumption that you will regularly test your panels to ensure that they are all functioning within the warranty specifications. It also assumes that you are able to measure your panel with STC ratings, which are typically only available within the laboratory setting. Given that most PV modules are out in the field, on rooftops, and far removed from any type of PV laboratory, it begs the question of how a homeowner or a typical contractor would actually perform a test in the field to ensure the panels are maintaining their warranty.
There are a few different ways that one could take care of a PV module performance warranty claim with a residential or small commercial sized system based on the inverter system that is being used. The first and most straight forward way to monitor the PV system is with a module level monitoring based inverter systems such as an optimizer system from SolarEdge or Tigo or a microinverter system such as Enphase or APSystems. The second and less effective system is the use of a string inverter with real-time monitoring of the input from individual strings of panels and the output of the overall system. The last and least effective way of checking the PV modules on the system is with a string inverter with no monitoring capability or a "dumb inverter".
1. Module Level Monitoring Using Optimizer/Microinverters
In the first scenario, if you or a client has a system with module-level monitoring such as a power optimizer based system from SolarEdge or Tigo or a microinverter system such as Enphase or APSystems you are in luck. This type of system allows the easiest method of testing modules to see if they are performing how they should be. This is simply because the system will be sampling the output and performance of the modules in real time. If there are any dips in output, a homeowner could easily see this from the monitoring portal provided by the inverter company. It would be important in this case to make sure that any dips in performance are not related to weather events, local shading, or uneven soiling. If an individual panel is discovered to be underperforming compared to the rest of the system, it should be easy to spot on the monitoring system and reported to the PV manufacturing company.
2. String Inverter Real-Time Monitoring
In the second scenario, if you or a client has a newer string inverter system such as SMA or Fronius, it may be possible to monitor real-time output from individual strings of panels. If data is collected in real time of the string output, you could get an idea of what the standard output of the system should be. If one string is underperforming and there isn't any logical external cause such as weather, shading, or soiling, it could be that one or more modules in the string has an issue. Something to note here is that in a typical string of panels if one panel is underperforming, it will limit the current output of the rest of the modules. This basically means that if all the panels are capable of producing 250W, but one panel is only producing 100W because of a performance issue, then it will limit the other panels in the string to producing about 100W. If this occurs, ideally, you could take an IV curve tracer and determine what the problem with the string is. If you don't have access to a tool like this, you would need to test each panel to see which one is bad. One way you could do this without the laboratory setting, is to take the modules out one at a time to see which one caused the whole string of panels to output poorly. This could be an overly exhaustive way to test the panels, but it may prove to be a good low-tech method to find the culprit.
3. No Monitoring
In the last scenario, if you have a PV string inverter with no monitoring, maybe because it is an older system, you will have to work the most to find if there is a single module performing poorly. In this scenario, you may need to purchase some type of monitoring hardware such as an IV curve tracer to test each strings output and start testing different panels to see which one is performing the worst. This will be the most time intensive option that may not result in clear data that you could provide to a manufacturing company to justify a warranty claim, but it could be worth a try.
For the second and third options above, it is a bit obvious that this may not be ideal for a homeowner who would like to simply check to see if the panels are outputting correctly, as it means that there will have to be some electrical work that must be accomplished. There is a solution here that one could do to take a preemptive approach to protect your system from possible warranty issues down the road. You could upgrade your system with Tigo power optimizers or a similar power optimizer product.
Tigo offers module-level monitoring on both their rapid shutdown solution and their optimizer solution. If you were to choose either option, you would increase the safety of the system and you would be able to gather PV module data at each individual panel and store it on the cloud in real time. In addition to that, if you were to choose the optimizer system, it would increase the overall system's output performance, which could justify the additional cost of the upgrade.
The reason I suggest this option is because I have personally talked with many PV system owners who have 10 to 20-year-old systems that are still technically under warranty but they don't have any way to know it because they don’t have module-level monitoring capability. When this is the case, their choices of monitoring come down to purchasing a IV curve tracer and manually collecting periodic data to make sure the system is functioning properly, or purchase a system like Tigo to upgrade the existing system and allow them to passively monitor the system in real time to see if there may be any warranty issues that should be taken care of.
Of course, either option isn't a 100% guarantee that you will be able to identify a problem panel, or that the manufacturer will honor a 25-year warranty, 20 years into the life of the product. But, it will be a way to increase the chances that your warranty is covered. And more importantly, it will allow you to know if your system is functioning correctly, which is the ultimate goal.
Resources:
Renvu Solmetric PV IV Curve Tracer
IV curve test with Solmetric
Renvu Tigo TS4-R-O
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