When you buy solar panels for your home, it’s likely that the ‘lifetime’ of the system means the warrantied lifetime — 25 years. That’s how long the panel manufacturer guarantees a certain power output, and is generally the timeframe in which energy savings numbers are calculated.
That means that you could get much more out of the array then installers or panel manufacturers are willing to guarantee. It’s interesting to consider how many other products offer a 25 year warranty.
Over the system lifetime, panels lose about half a percent of efficiency per year, which means that after the warrantied 25 years they’ve lost a total of 12.5%. Panel manufacturer’s can’t claim the same power output at this point, so warranties naturally expire. After 25 years, a 10 kW system becomes an 8.75 kW system, and a 4 kW system becomes a 3.5 kW system.
The type of solar panel you have, as well as weather conditions and how well you maintain the panel, will affect how long it lasts. Crystalline panels last longer than thin film (see solar shingles and Different Types of Solar Panels), and will produce energy longer. Crystalline panels often have warranties for around 25 years.
Since solar panels don’t have moving parts, they have less wear and tear than other types of equipment, and that helps prolong their lifetime. Other parts of a solar system, like batteries, may occasionally need to be replaced, but the panels themselves should not have to be.
Solar panels do lose a little bit of efficiency (see solar panel efficiency) as they get older, but there are ways to maintain panels to make sure you’re getting the most juice out of them as possible. Keep tree limbs trimmed so they don’t start to shade panels or drop leaves on them. If you live in a very windy climate, you’ll have to take a little extra care to keep dust and dirt off the panels. Similarly, if you live in a snowy climate, you’ll want to gently brush snow off the panels to keep them functioning well.
The key to happy solar panels is access to sun, and if you provide that by keeping them clean and out of the shade, they’ll be working for you for decades to come.
You shouldn’t have to worry about purchasing new panels after 25 years, since they’ll continue to produce free power for a number of years.