Do solar panels wear out over time?

Adding solar panels to your home is a long term investment. But for that investment to work out, your solar equipment needs to last. One question people often have is: do solar panels wear out over time?

The answer is that solar panels have a limited lifetime, and they do wear out over time. There are two categories of solar panel degradation to know about. The first is a small loss in power generation each year as the solar cells in the panel degrade, which is normal in all solar panels. In fact, if you check the datasheet for your panel, you will see this listed. The second are unexpected failures such as potential-induced degradation (PID) that would be covered by the solar panel warranty.

In this article, we’ll cover this topic in depth and give you some tips to look for when selecting a brand of solar panels for your home.

Normal power degradation in solar panels

As solar panels are exposed to sunlight, they start to slowly degrade. Intense sunlight, heat, and thermal cycling (temperatures alternating between hot and cold) over the years causes microscopic damage to the silicon cells and to the metal connections between cells.

The result of this normal degradation is a reduction in electricity production over time. Earlier solar panels would have relatively high annual loss of power - 1% or more per year. But modern solar panels are much more robust. At the worst, solar panels today will normally lose a maximum of 0.7% power production per year.

Meanwhile, premium solar panels on the market today will lose no more than 0.25% in efficiency every year.

This is pretty remarkable when you think about the fact that solar panels are outside year-round and have to stand up to all kinds of extreme weather and extreme temperatures.

Find out the power degradation for your solar panel

If you look at the technical datasheet for your solar panel (which should always be available on the manufacturer’s website), check the warranty coverage. The warranty for a solar panel has two parts:

• The product warranty, which covers manufacturing defects that cause the panel to failure prematurely. The shortest product warranty period you should expect for a home solar panel is 10 years. The best panels have 25 year product warranties.
• The power warranty, sometimes referred to as a linear power guarantee, guarantees the minimum amount of power that the panel will generate after a given number of years. Virtually all home solar panels on the market today include a 25 year power warranty.

If you are on a manufacturer’s website and looking for the warranty details for a solar panel, keep in mind that the fine print for the warranty is often included in a separate document.

Power warranties for popular solar panels

When you look into the details for a solar panel power warranty, you’ll see that there are two important numbers:

• The length of the warranty. For any solar panel on the market, this should be 25 years or more. If you find anything else, avoid that panel!
• The power output guarantee, which is the power output that is guaranteed at the end of the warranty period. This is listed as a percentage of the power output when the panel was new.

For example, a 300 watt panel with a 25 year / 80% power warranty should still be able to generate a maximum of 240 watts after 25 years.

Of the solar panels that are currently on the market, the lowest power warranty we’ve found is 25 year / 80%. Meanwhile, the best panels on the market have a 25 year / 92% power guarantee.

Solar panel power warranties have two parts

In addition to the warranty duration and the overall power guarantee, if you read the warranty details for a solar panel, there is almost always a separate rating for the amount of power degradation expected in the first year.

This is because new solar panels wear out a little faster when they’re new, and then settle into a steady degradation for the remainder of their lifespan.

For most solar panels, the first year power degradation is between 2-3%. After that, you can expect the annual power degradation to between 0.25-75%.

If you read the fine print of a manufacturer’s warranty, it will have language the describes this two-part power degradation. Here’s an example for the Trina Solar warranty:

For Monocrystalline Products (as defined in Sec. 1 b):3.0% in the first year, thereafter 0.68% per year, ending with 80.68%in the 25thyear after the Warranty Start Date.

Other manufacturers have similar language. Here’s another example from SunPower, which currently has the best power warranty on the market:

...the power of the PV Modules will be at least 98% of the Minimum Peak Power rating for the first year, and will decline by no more than 0.25% per year for the following 24 years, so the power output at the end of the final year of the 25th year warranty period will be at least 92% of the Minimum Peak Power rating (the “Guaranteed Peak Power” rating).

List of warranties for popular solar panels

Here’s a summary of the warranties for some of the most popular solar panels currently on the market. The column labor included tells you if the warranty covers not just the replacement of the panel, but the cost of installation as well.

The difference between 80% and 92% degradation

While the overall percentage of power loss for any solar panel is relatively low, by the end of your solar panel’s lifespan the difference between a premium panel with a 92% power guarantee and a cheaper one with an 80.2% guarantee ends up being fairly significant.

For example, let’s say we have a 360 watt panel. SunPower has the best power warranty on the market with a 92% guarantee after 25 years. At the other end of the spectrum, there are many manufacturers with a guarantee of about 80% - for example, Yingli offers 80.2%.

With a solar panel that started at 360 watts of output, here’s what it would look like after 25 years:

It ends up being a fairly significant drop. But one thing to consider is that SunPower panels are among the most expensive on the market. Whether that higher cost is economically worth it is something you should discuss with your solar installer.

Do solar panels in storage wear out?

Solar panels wear out because of exposure to the sun and elements. Sunlight causes chemical changes in the silicon cells that reduces their efficiency over time. Exposure to the elements causes wiring to fail, and moisture can get inside the panel, causing corrosion. This means that if solar panels are kept in climate-controlled storage, they will not wear out in the same way that solar panels in active service do.

What causes solar panels to wear out prematurely?

In addition to the expected wear-out of solar panels over time, there are a couple types of degradation that cause unexpected failures.

Potential-induced degradation (PID)

PID is a type of solar panel degradation that is caused by high voltage current leaking from the solar cells into the frame. From a technical point of view, it’s caused by sodium ions migrating from the glass to the solar cells. This process is accelerated under high temperature and humidity conditions.

PID can cause output to drop or, in extreme cases, for the panel to fail completely.

Manufacturers have come up with different strategies to cope with PID.

Other failures

Some other types of failures include hot spots, delamination, wiring failures, and plain old glass breakage. For some details about this, you can read our article on solar panel lifespans.

Quality testing standards and solar panel longevity

Fortunately, there are industry standards in place to help ensure that modern solar panels last as long as possible. One of the most important standards is IEC 61215, which includes a long set of quality testing standards that manufacturers must put their solar panels through in order to receive certification.

These tests include a wide range of things that simulate the real world conditions that a solar panel will experience in more than two decades of operation, including thermal cycles, wet weather, hail testing (which involves shooting ice balls at the panel), intense light, and applying weight to the front and back of the panel.

There are 19 tests in total. You can read the specification here. Any panel for home use in the United States should have this certification. You can check the manufacturer’s datasheet to be certain.