Solar panels don’t have any moving parts. They just quietly sit on your roof or in your backyard for a couple decades and generate electricity, day in and day out. How cool is that?
A study by the National Renewable Energy Laboratory shows that new solar panels have a failure rate of only 5 in 10,000 per year. This means that every year, a solar panel has a 0.05% chance of failing, or a total 1.25% chance of failing over 25 years.
That’s a very low number, but it’s not zero. So, while solar panels in general are extremely reliable, they aren’t indestructible. A solar panel is made of 60 or more silicon cells and many wires that are soldered together, all of which are sandwiched between multiple layers of glass and plastics. Heat, cold, rain, and physical punishment from wind and snow take their toll on these materials and can cause them to fail in different ways.
While there are no mechnical parts in a panel that can grind to a halt, differences in materials, manufacturing, cell technology, and quality control mean that some panels will last longer than others.
How can we figure out which panels are going to be the most reliable over the long run? One way is to wait a couple decades to find out, but that’s not very helpful if you want to install panels on your house this year. Another method is accelerated testing, which rapidly simulates the kind of stresses that a panel experiences in the real world. For example, the panels can be placed in an environmental chamber and subjected to hundreds or thousands of freeze and thaw cycles.
We’ll review the test results from one independent lab that does this type of testing, but first let’s quickly learn about the basic quality tests that all panels approved for home or commercial use in the US must pass.
The California Energy Commission sets requirements for the tests that solar panels need to pass in order for the projects that use them to be eligibile for incentives. Because California is the largest market in the nation for solar, the rest of the United States follows their guidelines.
There are two safety and qualification tests that a panel must pass.
One test is Underwriters Laboratories (UL) 1703, or 61730 for the newest panels. UL is a US-based safety certification company. Take a close look at any electrical device in your home, and you’ll probably see a UL certification logo on it.
The other test is IEC 61215:2005 for silicon panels or IEC 61646:2008 for thin-film panels. The International Electrotechnical Commission is an international standards organization with a role similar to UL.
There is some overlap between the two tests, but they both focus on electrical and fire safety, as well as basic stress tests that help to ensure the panels don’t have an early failure once installed in the field.
One example of an IEC 61215:2005 test is thermal cycling, where the panel is subjected to 200 temperature swings in a test chamber from -40°C to +90°C, and then checked for failures. This test attempts to replicate in a few weeks the kind of punishment a panel will experience in the real world: going from freezing temperatures in the winter to baking hot sun in the summer, as well as daily temperature swings over a couple decades, can cause wiring to crack or silicon cells to fracture.
Another test is the hail test, in which ten 1-inch ice balls are fired at 52 mph at the front of the panel. Hail is a particular problem in the midwestern US, especially “tornado alley”, and this test verifies the ability of a panel to withstand such abuse.
There are many other tests, but it’s important to understand that neither the UL or IEC tests are intended to guarantee the long term durability of a solar panel. Instead, they are designed to be safety tests and to test whether the panel is likely to fail early in its life.
To better predict long term reliability, you need accelerated testing. One organization that does this is PVEL, an independent lab.
PVEL is an independent lab that does reliability and performance testing for solar technology. Their main audience are companies and utilities that deploy large solar arrays, but that doesn’t mean a homeowner with a couple dozen solar panels can’t benefit from their research.
Their annual PV module reliability scorecard is the result of accelerated testing they perform on a wide selection of solar panels.
The PVEL tests are smaller in number but more severe than the UL and IEC tests. For example, the PVEL thermal cycling test involves 600 cycles in an environmental chamber that cycles between hot and cold temperature which is 3 times as many cycles as the IEC test.
Here’s a list of the tests performed:
The PVEL report confirms that solar panels are a very reliable product. 22 solar panel manufacturers made the overall top performers list. They include premium brands with 25 year product warranties that you might expect to make the list, such as Panasonic and SunPower.
Multiple Canadian brands made the list, including Silfab, Heliene, and Canadian Solar.
First Solar, a US company that is notable because they use thin-film instead of the much more common crystalline solar cells, is also a 2020 top performer.
But perhaps the most interesting thing about the report is that it shows the manufacturers that made the list over the past six years.
The two companies that have made the overall top performers list every year for 6 years? Two Chinese manufacturers: Jinko Solar and Trina Solar.
Close behind in the reliability rankings with top rankings in 5 of the past 6 years are three more Southeast Asian companies: Hanwha (South Korea), JA Solar (China), and REC Group (Singapore).
In the solar industry, Chinese panels are often dismissed as being cheap and lesser quality, but both Jinko and Trina Solar are among the largest solar manufacturers in the world. With so much manufacturing volume and experience, it’s actually not surprising that they’ve learned how to make a quality product.
The PVEL report also lists top performers in each test category, which can be useful if you want to buy a solar panel that does well in a specific category.
Low light and high temperature performance are two metrics that buyers often ask about. Low light performance isn’t just an issue for installations in cloudy environments - low light is something that every solar installation experiences every day, in the morning and evening.
7 manufacturers made the top performers list in this category. Not all of them are common in the US residential market, but they include Jinko, Panasonic, and Trina Solar.
Read my article on solar panels and low light performance to learn more about this topic.
Accelerated tests by independent labs such as PVEL provide useful data, but you should take any test with a grain of salt. Solar manufacturers may have multiple factories, and each factory might produce panels that perform differently, or quality could vary between different production runs from the same factory. Just because a product did well in a test isn’t an ironclad guarantee that you won’t get a bad panel.
Still, a long track record of high quality, such as with the top 5 companies listed above, is as good a metric as any for a consumer who is interested in getting a reliable product that won’t cause headaches years down the line.
Many shoppers in the US are interested in buying US-made panels. While many Chinese-headquartered companies are represented in the PVEL list, it’s worth noting that the location of the headquarters often has little to do with where the panels are manufactured.
In fact, Jinko (China) and Hanwha (South Korea) both do some manufacturing in the US. In addition, two Canadian companies on the list, Heliene and Silfab, have factories in the US.
Meawhile SunPower, a company headquartered in California, uses solar panels that are made in China.
To learn more about American-made solar panels and to see a more complete list, read our article.
You can download the 2020 PV Module Reliability Scorecard for free. If you’re using this to determine which panels to buy, read the report closely because it lists the specific models from each manufacturer that were tested.
To read more about how solar panels are stress tested, you can read a presentation from the National Renewable Energy Laboratory about IEC 61215 testing.