Most manufacturers of solar panels offer at least a 10-year materials warranty. The best solar panels come with a 25 or even 30-year warranty, which is a good indicator of how long solar panels last. Read on to learn more about the longevity of solar panels.
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That said, a study by the National Renewable Energy Laboratory (NREL) found that nearly 80% of solar panels still produced electricity after their 25-year warranty had expired.
Solar panel longevity is improving
The longevity of solar panels hasn’t changed all that much in the last few decades, unlike solar panel efficiencies. As such, older solar panels coming to the end of life might only be running at a fraction of their initial efficiency, but this could still be considerably lower overall than the most modern, high-efficiency panels.
For example, consider a solar panel from 20 years ago, when efficiencies averaged around 11%. Even if that panel has only lost about 1% efficiency each year, which is fairly standard, it will now be just 8.8% efficient (11 – 11/100 x 20 years).
In contrast, modern, high-efficiency solar panels, such as those from SunPower, are nearly 23% efficient. That’s a colossal difference. To run the math, a brand new SunPower panel with 22.8% efficiency is likely 159% more efficient than an 11% efficient panel bought in 2002:
(22.8-8.8) / 8.8 x 100 = 159.09%
What about that new solar panel, though? How long will it continue to perform at 22.8% efficiency? The answer is complicated.
How fast do solar panels degrade?
Solar panel manufacturers usually cite a degradation rate of 0.5-1% every year. This means that every year, a solar panel will be up to 1% less efficient than it was when brand new. After 10 years, the solar panel will be 10% less efficient.
For a panel that started out life at 20% efficiency, it would be about 18% efficient a decade later (20 – 20/100 x 10). After 20 years, this solar panel will still be about 16% efficient. A typical warranty guarantees, however, that a panel will work above 80% of its rated efficiency after 25 years. That means a panel starting out at 20% efficiency shouldn’t drop below 16% until after 25 years.
The trouble with long warranties is that we have no way of telling how efficient a solar panel will actually be in 25 years. So, how fast do solar panels actually lose efficiency?
While manufacturers’ warranties often cite a first-year degradation rate of 2-3%, then a subsequent annual degradation rate of 0.7%, a study by the National Renewable Energy Laboratory (NREL) found that the average degradation rate is around 0.5-0.8% each year. This means that by the end of a 25-year warranty, most solar panels were still operating at 75% or more of their original efficiency.
Interestingly, SunPower claims that its panels degrade at a much lower rate than many other solar panels. Using a methodology developed in partnership with NREL, SunPower calculated the median rate of degradation for its panels as just 0.2% per year. This is 70% less than the annual degradation rate for conventional solar panels.
What does it mean for a solar panel to degrade?
Degradation means to wear down, decay, or spoil. In the case of solar panels, degradation rates indicate a loss of efficiency, meaning the panels are less able to convert sunlight into electricity.
For example, a 250-watt panel following a typical degradation rate would still produce 200 watts at the end of its 25-year warranty. A 300-watt panel would produce 240 w, and a 160-watt panel 128 watts, and so on.
While some companies offer warranties guaranteeing up to 85% efficiency at the 25-year mark, or 80% at the 30-year mark, most offer a 25-year warranty at 80% efficiency. How much this matters to you will likely depend on how long you expect to use the panels, based on your own life expectancy, and if you have plans to move somewhere and not take your panels with you.
What about other defects in your solar array?
In addition to performance guarantees, most companies offer a separate workmanship or manufacturing warranty that covers defects. These can include defects in the frame or junction box.
The typical workmanship warranty is just 10 years, however. As such, it’s smart to check your setup before this warranty expires and consider starting a claim or getting additional insurance if you suspect a problem may be brewing.
Batteries, inverters, and other parts of the solar electrical system
Bear in mind, too, that solar panels are usually the most robust part of your home solar system. Batteries may need replacing every 3-10 years and are often the most expensive and complicated parts of a solar electrical system to maintain. Without proper care, batteries can fail in the first year after installation.
Some batteries are more forgiving, such as lithium batteries, which may only need replacing every 5-15 years. But lead-acid batteries are permanently damaged if they sit uncharged for long periods of time. It’s also essential to have a charge controller and proper safety disconnects if you have battery storage.
Many inverters also need replacing every 10-15 years, with most manufacturers offering a 10-year warranty on inverters connected to the electrical grid. Some offer an upgrade option of 20- or 25-years of coverage. This is a smart investment for most homeowners as you’ll likely have to replace your inverter at least once before your panels’ warranty expires.
Warranties are shorter on off-grid inverters. Typically, these last just 1-5 years, though some have options to extend up to 10 years. Beware the fine print of warranty extensions as some only cover parts, not labor. If you’re comfortable switching out an inverter yourself, this will matter less than if you’ll need to hire an electrician for the job.
Mounts, wiring, charge controllers, and other parts of the system may also need replacing, so it’s a good idea to check these are all secure and in good shape when your system is first installed. Poor installation is a key cause of system failures and inefficiencies. It’s also wise to perform routine checks on all elements of your home solar array. That way, you can catch any problems early, before they tank electricity output or imperil other parts of the system.
Final thoughts on how long solar panels last
While it’s fun to run the numbers and try to work out the likely efficiency of a solar panel after 10, 20, or even 30 years, the fact remains that most panels lose very little efficiency over their lifespan. Even after 25 years, most solar panels will still produce a good amount of electricity.
In short, then, while it’s good to check the degradation rate of panels before committing to an installation, chances are that other factors will weigh more heavily in your decision. If you live somewhere very hot or very cold, for instance, you may be better choosing a panel with a lower temperature coefficient and a slightly higher degradation rate, compared to a panel with a higher temperature coefficient and a lower degradation rate.
Finally, consider efficiency loss when sizing your system. A small system that barely covers your current electricity needs may not be sufficient for your needs in a decade or beyond. If you can size up, it may be smart to do this from the beginning, especially if your utility company is fair about crediting you for energy production.
You might, however, consider arranging your home solar array to make it easy to add panels at a later date. This assumes, of course, that new parts will be compatible with older parts. So, if your chosen panel manufacturer appears to be pulling out of the solar sector, it might be wise to purchase an extra panel or two before they close up shop (looking at you, LG!).