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Powering through: 2020 NREL study reveals the true longevity of solar

One of the most common statements you’ll hear us say about solar is that it’s a great investment. Among many reasons, we say this because solar panels last a long time. Most solar panel manufacturers now offer warranties between 20 and 25 years, with some going even longer. The average payback period in the US is around eight years, meaning you’ll save substantial amounts of money for well over half of your system’s lifetime.

But warrantied production is one thing and actual performance is another altogether. So, how well do panels actually perform as they age? A 2020 study by the National Renewable Energy Laboratory (NREL), PV field reliability status—Analysis of 100 000 solar systems, provides some compelling insights. 

Key takeaways

  1. The NREL study found that over the course of their lifetime, solar panels are extremely reliable, with most systems performing as expected (80-90 percent within 10 percent of predicted output, and many exceeding predicted output)

  2. Module failures are low (0.2-0.02 percent), and most systems degrade in the 0.7 percent per year range

  3. Many of the most common causes of failure can be avoided with a proactive maintenance approach and installation best practices

  4. Find the most experienced installers on the EnergySage Marketplace!

What was the purpose of the NREL study?

Before we look at the results, it’s important to understand the background and purpose of NREL’s study. The number of solar panel installations has been rising dramatically in recent years, with more than half of all installations occurring in the last three years. With this dramatic increase in the adoption of solar, many current and future solar shoppers are asking questions about reliability. However, large scale data sets measuring the performance of solar systems over time are rare, making these questions difficult to answer definitively. A team of researchers from NREL and the Lawrence Berkeley National Laboratory (LBNL) analyzed one such data set in order to find out just how reliable solar panels are. They used data from 100,000 solar systems in the US, or roughly seven percent of the US fleet in 2019. The data included annual production data for five years for each of the systems, with samples of residential, commercial, and utility scale projects.

What were the key findings of NREL’s study?

Let’s take a look at the results of the study, and most importantly, what they mean for you as a solar customer.

Solar systems meet or exceed performance expectations

Looking at the conclusions of the study, there are some significant positive takeaways. One of the most important statistics for you as a consumer is that 80 to 90 percent of the systems included in the study performed within 10 percent of their predicted power output, with many even outperforming expectations.

Solar panels rarely fail

Additionally, solar panel failures were extremely rare, with only 0.2 to 0.02 percent of panels experiencing a failure. This means you can be extremely confident in the ability of your system to perform as expected for the duration of its warranty period and even beyond, as several systems older than 30 years were included in the study.

Degradation of solar panels is extremely slow

Finally, the researchers also found that most systems degrade at a rate of approximately 0.7 percent per year – essentially, the natural wear and tear experienced by the panels will result in a loss of less than 1 percent of system efficiency each year, an almost negligible amount. These data points are not from lab tests; rather, they come from the real experience of over 100,000 solar systems in the US, and therefore provide strong evidence of the longevity of solar panel systems.

Inverter failures are the most common cause of solar system issues

Although the findings of the study were largely positive, the researchers did identify a few common issues in systems, with inverter failures being the most common cause of larger issues with solar systems. Often, inverter issues stem from a failure to adhere to installation best practices: inverters need to be shaded for maximum longevity. The figure below shows NREL’s findings of the most common hardware issues in solar systems, with inverters leading the pack. However, note that none of these issues have an occurrence rate higher than one percent, meaning you are highly unlikely to see any one of these in your solar system.

This figure from NREL displays the different hardware issues identified in the study by occurrence and lost production. No issue has an occurrence of over one percent for residential systems!

Quality installations improve solar system reliability

Similarly, the study also found that installation quality has a large impact on overall system reliability – it’s critical that you hire an experienced installer who has the necessary expertise to set your system up for success. The following figure shows common project issues identified by the NREL study – the two most common, construction and delay, can be mitigated by choosing a quality installer. Note again that none of these issues occur in more than one percent of systems, highlighting the reliability of solar systems in general.

This figure from NREL shows the most common project-related issues identified in the study. Again, none of these issues occur in more than one percent of residential systems!

Stay on top of your system’s maintenance!

Finally, the data suggest that proactive approaches to system maintenance are extremely effective in preventing problems: if you notice something unusual about your system’s performance, notify your installer and get it inspected!

The bottom line

The NREL study provides an illuminating look into the reality of solar panel longevity. Through a thorough examination of roughly seven percent of the entire US solar fleet, the researchers found that solar panels are extremely durable throughout their lifetime. The vast majority of systems performed within ten percent of output expectations, and system failures fell well below one percent. If you choose to make the investment into a solar system, you can be confident that it will produce reliable, affordable, and clean energy for decades to come.

Visit the EnergySage Marketplace to find high quality installers for your solar system

Many of the most common issues identified by the NREL study can be avoided or eliminated entirely by a high quality installation process. Looking for the most reputable solar installers for your solar system? Check out the EnergySage Marketplace for up to seven quotes from pre-vetted installers in your area! By comparing quotes, you can make sure you’re getting a system that fits your needs at the right price.

PS: want to read more about the study? You can find the full text of the document here, and a write-up of the report (“PV field reliability status—Analysis of 100 000 solar systems”) in PV-tech.


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