Solar Panel Degradation

As regular readers know, I have tracked the battery degradation of my EVs since purchasing a Nissan Leaf in 2011. Recently, Mark from The Tesla Life asked me how much my solar panels have degraded. I said, they are still producing and I haven't noticed any degradation, but that's not a very analytical answer.

We have production data on both of our solar PV systems going back to the day they were installed. So let's dig into the data and see what it shows.

Our older PV system was installed in 2007 and our newer one in 2015. But how do we go about comparing the results from then to now? Any given day can have weather, cloud shading, wildfire smoke, or other impacts; maybe the panels were dirty, pollen-covered, etc. 

To smooth over some of this, we'll be looking at annual solar production numbers and I'll note any special circumstances that apply to that year. 

Here's the chart of production for our two systems. You can see that production is generally flat for both of them until 2022.

Generally speaking, solar panels degrade about 0.5% per year. Using this rule-of-thumb, our 2007 panels production should be about 92% of their original capacity.

Let's look at the Mr. Sun system since it's older and the degradation is more likely to be visible. 2008 was our first full year of production. We'll use this as our baseline. The 2009 and 2010 years are lower. This could be the degradation we're looking for. I cleaned the panels in the spring of 2012 and production quickly returned to 2008 levels. So that was not degradation.

2016 has a similar dip and then 2017 returns to normal production. 

2021 was surprising in that it was our best production year ever. I would expect some degradation in a 14-year-old system that would prevent it from having its best year ever at that age.  

In 2022, there were more than a dozen wildfires in Oregon. This had a noticeable impact on our solar production. 

In 2023, our production was even lower than 2022 because the solar panels were offline during June and July while we had a new roof was installed.

So there you have it. The degradation signal is lost in the noise of production interference. I guess that's good news since the degradation is not large and obvious. Hopefully, 2024 will be a year where we keep the panels on the roof, no inverters go down, and the sky is not darkened for weeks by wildfires.