If you’re going to drop a few thousand dollars on anything - a car, a saltwater aquarium stocked with Clarion Angelfish ($2,500 each!), or solar panels for your home, you want to make sure that your investment is going to last.
Cars come with warranties, but expensive fish do not. Fortunately, solar photovoltaic equipment does come with warranties. However, even if a failure is covered by a warranty, the labor to replace it may not be, plus there’s the downside of losing power generation while waiting for a repair.
Understandably, if you’re thinking about going solar, wondering how long your equipment will last is a common question. This article will answer that question by addressing a few different aspects of solar panel longevity.
The answer is yes, solar panels will eventually stop working, but it may take several decades. The average solar panel warranty is 25 years, which is more than twice as long as it will take many people to recoup their investment. This means that your system will almost certainly be cash-positive if it lasts that long.
There’s a very good chance that your solar panels will last beyond 25 years, such as this solar panel from 1980 that is still working.
But even if it does, you should expect your solar panel to slowly degrade over time. Exposure to the elements, temperature extremes, and ultraviolet light will cause your solar panel to lose a little efficiency each year.
The amount of power efficiency that you can expect solar panels to lose over time is reflected in the power warranty that the manufacturer provides. Your solar panel will come with two different warranties: one that covers the manufacturing and materials, and a second warranty that guarantees the power production of the panel.
On the product sheet for your solar panel, look for a linear power warranty or linear performance warranty. It’s called linear because the solar panel is expected to degrade by a consistent amount each year. This warranty will stated as a percentage of the original power output.
For example, if the warranty is a 25 year / 80% power warranty, that means that after 25 years, the panel is guaranteed to have 80% of the power output as it did when it was new.
Some manufacturers also have performance benchmarks before end of the warranty. For example, Trina Solar includes a power performance guarantee at the first year, guaranteeing that the panel won’t lose more than 2.5% efficiency in the first year and 0.7% per year after that.
This is a good thing because it means that you don’t have to wait 25 years to show the manufacturer that the panel dropped below it’s 25 year performance guarantee. Every manufacturer has a different warranty, so be sure to read the datasheets for your product, which should always be available online.
Every solar panel we’ve reviewed has at least a 25 year / 80% power warranty. The best warranty we’ve found is offered by SunPower, which offers at 25 year / 92% power warranty with their E and X Series panels.
For a summary of warranties offered by the most popular solar panel manufacturers, read our article on how to find the best solar panels.
Solar panels don’t have any moving parts: they just sit in the sun and quietly generate electricity. That doesn’t mean that parts can’t break, though. High temperatures, low temperatures, exposure to the sun and the wind are all physical stresses that can cause cracking and corrosion that lead to failures.
The International Energy Agency performed a study that analyzed how solar panels fail in the real world. Here are the most common failures:
A solar panel is made up of several layers: glass on the front and sometimes the back, a layer containing the solar cells and wiring, and encapsulant layers on the front and back of the cells that protect the delicate photovoltaic layer by keeping out humidity and the elements.
The encapsulant is particularly important. To do their job, these layers need to be bonded tightly to the solar cells. Exposure to ultraviolet light and temperature swings can cause the encapsulant to lose adhesion. When that happens, air and moisture can get in, causing corrosion to the wiring and solar cells or even short-circuits.
Most solar panels have a layer in the rear called the backsheet. This backsheet is made of a polymer and prevents air, moisture, and dirt from entering the panel. This layer must be very strong because it’s exposed directly to the elements. In particular, when a panel is mounted on a rack, it must be able to resist high winds without breaking or losing its seal with the frame. This is true even if the panel is roof mounted, because there’s an air gap between the back of the panel and the roof surface that allows the wind to hit.
If the backsheet fails, water can enter, which can cause corrosion or short-circuiting. Moisture inside the panel can also cause damage in cold weather by freeze-thaw cycles that weaken the bond between layers, or even crack wiring and solar cells.
Solar panels have strength ratings for the backsheet, which is listed as a wind load or backside load in Pascals. The higher the number, the stronger the backsheet is. You can find this rating on the product datasheet.
The glass used in solar panels is tempered. Just like the windshield of your car, the glass used in solar panels is designed to be stronger than normal glass, and can windstand substantial rain and hail before breaking. Check the datasheet for your panel. It should list a snow load or frontside load in Pascals (Pa), which tells you how much force the glass can withstand from hail, or any other forces like a person standing on it.
2,400 Pa is the minimum rating you’ll see, but 5,400 Pa or even higher is common. If you live in a snowy area, you’ll want to pay attention to this rating and choose a higher rated panel if you can.
But no glass is indestructible, and a large enough hailstone, baseball, or rock will cause the glass to shatter. If that happens, the cells underneath can be broken, but even if not, rain will enter the panel and eventually cause a failure.
When a solar panel is operating, it develops an electrical charge that normally finds its way through the wiring and into your home. But a very small portion of that charge may leak out through the panel and the conductive aluminum frame. Depending on how the solar panel is grounded, that electrical leakage can drive sodium ions out of the panel’s glass layer and into the solar cells, causing damage.
PID damage takes years to develop, but is one of the more common reasons for failure. Frameless solar panels are resistant to PID.
Manufacturing defects, such as bad solder joints, or stresses that cause microcracks in the solar cells can result in areas of the panel that have higher electrical resistance. That higher resistance means higher temperatures, resulting in hot spots that can eventually cause damage to individual cells or the entire panel.
Hot spots can even result from shading, because shaded cells wired in series don’t pass electrical current, which then flows through the remaining unshaded cells. That extra current can cause heating and premature failure.
Fortunately, most panels these days have devices called bypass diodes that prevent high current when shading occurs.
Now that you know the common ways that solar panels can fail, you’re probably asking how frequently solar panels really do go bad?
Fortunately, failures are rare. According to a recent study by the National Renewable Energy Laboratory, the median failure rate for solar panels is 0.5% per year. You can read the study here (PDF).
Review of Failures of Photovoltaic Modules, International Energy Agency (2014). (PDF)