NREL's longevity of solar study: Key takeaways

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 money for over half of your system's lifetime.

But warrantied production is one thing, and actual performance is another altogether. So, how well do panels 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.

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 risen 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 to determine 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 system, with samples of residential, commercial, and utility-scale projects.

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

Solar systems meet or exceed performance expectations

Looking at the study's conclusions, 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 in the study performed within 10 percent of their predicted power output, with many even outperforming expectations.

Solar panels rarely fail.

Solar panel failures were extremely rare, with only 0.2 to 0.02 percent of panels experiencing 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.

The degradation of solar panels is extremely slow.

Finally, the researchers also found that most systems degrade approximately 0.7 percent yearly. 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; instead, 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 study's findings were largely positive, the researchers identified 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 of these in your solar system.

Quality installations improve solar system reliability.

Similarly, the study also found that installation quality significantly impacts overall system reliability – you must hire an experienced installer with 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.

Stay on top of your system's maintenance!

Finally, the data suggest that proactive approaches to system maintenance are highly effective in preventing problems. If you notice something unusual about your system's performance, notify your installer and get it inspected!

The NREL study provides an illuminating look into the reality of solar panel longevity. Through a thorough examination of roughly seven percent of the 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 invest in a solar system, you can be confident that it will produce reliable, affordable, and clean energy for decades.

Many of the most common issues identified by the NREL study can be avoided or eliminated by a high-quality installation process. Are you 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 ensure you get 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.