Solar panel degradation and how to slow it down

Although solar panels are sturdy and reliable, they don’t last forever — nothing does. Over the years panels tend to gradually lose their efficiency. This process is called solar panel degradation. How fast they lose their power, how long warranties last and what to do to prolong the lifespan of your solar system — here in this article.

Solar panels last for more than 25 years

There is little that can happen to a solar panel. An estimated lifespan of solar panels is 25-30 years and even more. The truth is, the panels could sit on your roof for decades, slowly aging and losing power, but eventually people just replace them with newer models — sometimes for aesthetic reasons.

What makes solar panels so long-lasting and durable is the absence of moving parts. A solar panel is like a sandwich. Solar cells in the middle are encapsulated in EVA (ethylene vinyl acetate). A 6-7 mm layer of tempered glass protects them on the front side. The backsheet is made from a durable polymer-based material to prevent water, soil, and things like that from entering the panel from the back. The aluminum frame keeps everything together and protects against impact and weather.

Before putting solar panels on the market, manufacturers test them for performance and endurance. The panels withstand extreme weather conditions well: only 0.1% of 50,000 solar panel systems were damaged or seriously affected by extreme winds or hurricanes between 2009 and 2013, according to National Renewable Energy Laboratory (NREL). The panels are also made to endure hail balls falling at 23 m/s or wind of at least 140 mph.

It doesn't mean that they are invincible though. Harsh weather, extreme temperatures and ultraviolet are the reasons why solar panels degrade until eventually they produce little energy.

Solar panels degrade by 0.5-0.8% every year

The sun is what makes PV modules function and it’s also the cause of their eventual demise. Ultraviolet radiation makes slow work of them.

Panels lose around 1-3% of efficiency right after the installation as they become exposed to the sun for the first time. It’s called a Light Induced Degradation or LID.

From the second year in service, the degradation slows down. The average degradation rate of solar panels is close to 0.8% with a median value of 0.5%, according to NREL.

Heat shortens the life of a solar panel

The panels installed in dry, hot, desert places where ultraviolet radiation is especially harsh show the highest rates of degradation. Solar panels lose almost 1% of efficiency every year in these conditions. Northern parts of the USA show the lowest degradation rates due to the moderate climate. However, northern states aren’t the sunniest which means less energy is produced.

High voltage wears solar cells out

A process called Potential Induced Degradation or PID can occur in solar systems with voltages above 600 V when combined with high heat and humidity. Dirt and glass cracks can speed up the PID. The power losses from PID can account for 1-10% of the module’s rated output over its lifetime.

Corrosion may find a way inside a panel

Solar panels are made to be resistant to corrosion but only to a certain extent. When the climate is humid and panels are exposed to moisture for a long time, the components may start to rust. Corrosion affects metal connectors, the frame, and other exposed parts. This compromises the electrical connectivity and structural integrity and leads to the end of solar panel’s lifetime.

Degradation rates are different across solar panels. The main factors that affect it are the area where panels are installed, the year of manufacture and the brand.

Check warranties that brands offer

Here is a list of brands whose panels age the slowest:

- Sunpower Maxeon — 0.2% degradation rate
- Panasonic — 0.25% degradation rate
- REC — 0.25% degradation rate
- LG Solar — 0.3% degradation rate
- Hanwha Q CELLS — 0.4% degradation rate

Solar panels get two types of warranties: one for product and one for performance. The product warranty protects the material against defects in material, environmental and workmanship issues. It lasts between 10 and 25 years, depending on the brand. The highest it gets is 40 years with some of SunPower's solar panels.

The performance warranty guarantees that the panels will produce a certain amount of power for a specified number of years. Most solar panels have 25-year output warranties, but some manufacturers go further and offer three decades. Bifacial panels mostly receive a 30-year production warranty.

Output coverage often comes in two shapes. A standard tiered warranty specifies that the module will retain at least 90% of its rated output after 10 years and at least 80% after 25 years. A linear performance warranty shows that power output is expected to decrease by a fixed degradation rate. The datasheet often includes solar panel degradation curve.

Keep your solar panels clean and safe

Solar panels are a relatively carefree investment. Simple maintenance is going to prolong their lifespan.

Regular check-ups by an electrician will prevent potential damage to panels. Trying to fix problems with panels by yourself is dangerous for you. You also risk breaking panels and voiding the warranty for them. Consult with the manufacturer about the best ways to keep your panels safe and efficient.

Cleaning panels will keep production numbers high. How often you should do it depends on the area where you live and how your system is installed.

When panels are on the ground, it’s best to clean them at least once a year. The rain takes care of the rooftop panels but eventually, they’ll still need a proper cleaning. The monitoring system lets you know when it’s time for a scrub — if the production of panels dropped, the dirt or fallen leaves are the most obvious reason.

Solar panels don’t like thick layers of snow on them — not only does it lowers the amount of sunlight they are able to receive at a given time, it might increase the degradation rate. If snow doesn’t slide off the panels, you have to clean them yourself or call for a special service.

Solar panels don’t stop after 25 years

Solar panels do not just break right after 25 years have passed and the warranty has run out. The output of panels will go down little by little but they'll still produce energy. You don’t have to immediately remove them from the roof: keep them checked, keep them clean and they will keep doing their job for many more years.

While solar panels themselves last for a long time, other components of the system might want a replacement much sooner. An inverter, for example, lasts for 10-15 years and the lifespan of some models can exceed 20 years. Solar charge controllers also work reliably for 15 years on average. The life of a battery highly depends on maintenance. It might serve you for a decade or it may die after several months.

So is the investment worth it? Or to be more precise, would solar panels bring in more money in 25 years than their initial cost plus installation cost plus all the parts of the system plus this degradation rate? The answer is “yes” in almost any case.

The average solar payback time in the USA is around 8.5 years. After that, all that solar panels bring in is pure profit. You could say that a solar panel system pays for itself 2-3 times during its lifespan.

Most of the time it’s not even a question about how much energy your solar panels produce, but rather how much electricity costs in the state. In our recent article, we demonstrate how an investment in solar panels can be justified even in (and sometimes especially in) cloudy states where on paper you end up with less free electricity — come check it out!