How Long Do Solar Panels Last?

Solar is a long-term decision, so it makes sense to ask how long the equipment will hold up. The good news is that panels are among the longest-lasting things you can put on a house.

This article goes deeper on lifespan than our guide to how home solar works: how slowly panels age, what wears them out, how the other parts compare, and what the warranties cover.

How long do solar panels last?

Solar panels last 25 to 35 years on average. That figure comes from a Berkeley Lab survey of solar industry professionals, cited by the U.S. Department of Energy, and it has grown from about 20 years in 2007.

Lifespan doesn't mean the day a panel goes dark. A panel has no moving parts, and it doesn't shut off when its warranty ends. It keeps turning sunlight into electricity, just a little less each year. That's why a 25-year warranty is a promise about the first 25 years, not an expiration date.

The Department of Energy also notes that most U.S. systems are still early in their expected lifetimes. Home solar took off fairly recently, so many of the panels on New England roofs have decades ahead of them.

How much do solar panels degrade each year?

Degradation is the slow loss of output as a panel ages. It happens to every panel, and it is gradual, not a sudden drop.

NREL's review of nearly 2,000 field-measured degradation rates found a median loss of about 0.5% a year. Some panels in the study lost more, which pulled the average up to 0.8%, but the typical panel lost about half a percent.

Climate matters too. A later NREL study of about 8 gigawatts of large U.S. commercial and utility-scale systems found that those in cooler climates lost about 0.48% a year, compared with 0.88% in the hottest zones. Those were large systems, not homes, but the pattern makes sense: heat is hard on panels, and New England's climate is easier on them than the desert Southwest.

Your monitoring app is the easiest way to keep an eye on this. Compare each month with the same month in earlier years, not with last month, since the seasons change production far more than aging does.

What wears solar panels out?

Panels sit outside for decades, and a few things slowly wear on them:

• Heat. The Department of Energy notes that solar cells generally work best at low temperatures, and that extreme heat can damage the cells and other panel materials, shortening their lifetime.
• Ultraviolet light. Years of sunlight slowly wear on the materials that seal and protect the cells, which is part of why output drifts lower over time.
• Moisture and freeze-thaw cycles. Panels heat up and cool down every day, and water that gets into a damaged seal can freeze and expand. Standard panel tests include repeated heating and cooling, damp heat and humidity-freeze cycles for exactly this reason.
• Physical damage. Panels have historically survived most hailstorms, according to the Department of Energy, but very large hail can damage them, and impacts can crack cells without breaking the glass. Stepping on panels, falling branches and hard tools on the glass can do the same.

You can't control the weather, but you can avoid adding to the wear. Keep people and tools off the panels, and leave rooftop work to professionals. Our article on solar panel maintenance covers the little upkeep a system needs over its life.

Do inverters and other parts last as long as the panels?

Not always. A solar system is more than panels, and each part has its own lifespan and its own warranty. Inverters, which turn the panels' power into the kind your home uses, often carry shorter warranties than panels and may need service or replacement during the system's life.

The type of inverter matters too. Microinverters sit under each panel, while a string inverter serves a group of panels from one box, usually on a wall. Our comparison of micro-inverters and string inverters explains the trade-offs.

What do solar panel warranties cover?

Most panels come with two separate manufacturer warranties:

• A product warranty covers defects in the panel's materials and workmanship, such as a failed seal or a faulty junction box.
• A performance warranty covers degradation. It promises that the panel will still make at least a stated share of its rated output by the end of the term.

The terms vary by manufacturer and model. One major panel maker, for example, offers a 12- or 25-year product warranty and a 25- or 30-year performance warranty depending on the panel. A performance warranty that runs longer than the product warranty is common, so read both.

When you compare quotes, ask for each warranty in writing: how long it lasts, what it covers and who you call to make a claim. Our guide to going solar, step by step covers what else to compare.

Will your roof last as long as your solar panels?

It should. Panels that last 25 to 35 years need a roof that can go the distance under them. If the roof wears out first, the panels have to come off so it can be replaced, then go back on.

That's why the roof gets checked before anything else. Our article on how old a roof can be for solar covers our rule of thumb and the signs that matter more than age. If your roof is near the end of its life, our roof + solar package replaces it as part of the project. Roofs installed through that program come with a 50-year warranty, so the roof is built to outlast the panels on top of it.

What happens when solar panels reach the end of their life?

When panels finally come down, they have a few places to go. The Department of Energy describes three options: reusing panels that still work, refurbishing or repowering a system with newer equipment, and recycling.

Recycling processes already exist for the most common panel types. In the U.S., recycling still generally costs more than sending panels to a landfill, so it remains an area of active work. Panels contain valuable materials, and the Department of Energy sees recovering them as a way to strengthen domestic supply chains.

For most homeowners going solar today, that day is decades away. What matters now is choosing equipment and a company that will stand behind it for the long haul. To see what a system would cost and save on your home, our guide to what solar costs and saves is a good next step, or call us at (508) 507-2908.

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