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Solar panels are amazing things. They cut pollution, save planets, and — by draining its power — move us closer to humanity’s ancient dream of destroying the sun. But they’re not quite perfect. If you happen to buy the cheapest panels you can get your hands on I’m sure you’ll soon find they can be very far from perfect. 

All panels will slowly degrade in output as they age. But, the performance warranties from the high quality panels actually mean something. Crap panels can fall apart after a few years and you’ll have a hard time getting warranty support from a crap panel manufacturer.

Causes Of Solar Panel Degradation

Panels slowly decline in output over the years as tiny cracks develop in the silicon solar cells — known as microcracks — and electrical connections deteriorate. If degradation becomes severe it can lead to a runaway effect where damage begets damage causing panel deterioration to accelerate; rapidly resulting in complete failure. Fingers crossed this won’t happen to any solar panel you purchase within its performance warranty period.

The main contributors to panel deterioration are:

§ Thermal cycling: Materials expand and contract at different rates with temperature changes. This puts joins between different materials under strain and causes slow deterioration. The main temperature change — or thermal cycle — occurs between night and day, but there can be many thermal cycles during a day as the sun goes behind clouds or rain hits panels.

§ Dynamic Mechanical Load: This is a fancy term for flexing caused by wind. While properly clamped panels won’t flex much, it’s still enough to cause damage over time.

§ Humidity: The combination of high heat and humidity found in tropical  can be hard on solar panels. Crap ones can literally fall apart as the glue holding them together gives up the ghost. It can also contribute to a form of electrical deterioration known as PID. This is short for Potential Induced Degradation and is basically caused by naughty electrons going where they’re not supposed to or, more accurately, it’s caused by naughty panels that don’t keep electrons under control.

§ UV damage: This isn’t a serious problem for decent solar panels that have quality UV blockers in the epoxy (glue) that holds them together. But if a manufacturer leaves it out to save a few dollars per unit they will start to turn yellow in the sun and in extreme cases the panel will come apart as its glue is destroyed.

Freezing: If water can enter joints and seals and the temperature falls below freezing, ice expansion can contribute to deterioration.

The Greatest Degradation Is On Day 1

Solar panel performance warranties generally allow for 2-3% degradation in their first year and 0.7% or less each year after. The reason why they allow for extra degradation early on is not because panels degrade rapidly in their first year. It’s because they degrade rapidly in their first few hours.

Light Induced Degradation, or LID, affects most solar panels and reduces their efficiency by 1-3% during the first few hours they are exposed to sunlight.  Science says:

"This is caused by oxygen impurities in crystalline silicon bonding with boron dopant to produce a boron oxygen complex that reduces the minority carrier diffusion length."

This is impossible to avoid with the most common solar cells that are P-type while the more expensive and exclusive N-type cells don’t have this problem.  However, their performance warranties still seem to allow for a similar performance drop early in their lives. This is to make their performance warranties look better as it helps keep the yearly degradation figure low and that is what people are likely to use to compare performance warranties.