If you are selecting a solar panel based on the degradation rate, I’m here to tell you something. It’s not a degradation rate at all. What you are reading is a promise. It’s a warranty figure used to determine the maximum rate a solar panel can degrade before you have a claim against the manufacturer.
Don’t get me started about warranty lunacy in the industry.
The vital thing to know is that a degradation rate you see on a spec sheet, something you heard in an advertisement, or something your slick salesperson told you is not something that is set in stone. Two solar panels with wildly different warranted rates may actually turn out to be the same. In fact, the lesser option may outperform the seemingly better option. You will not know until the future happens.
Sure, there are manufacturing techniques that build on history and research. These techniques should improve the degradation rate over time. But at what cost? Would you pay twice as much for a panel that promises to be 4% better in 10 years or 8% better in 25 years? Keeping in mind that this is just a guess, is it worth it?
Check out this video where I discuss the essential issues and questions:
One last thing. How are you going to PROVE it? Serious question. Think about 15 years down the road, you suspect a panel is underperforming. That panel is going to cost less to replace than it would to go through the effort of proving you have a valid warranty claim. Even warranties that cover parts, labor, and shipping don’t cover the cost of diagnosis. Imagine trying to find a solar contractor to explore your hunch that a panel isn’t working well. Are they going to spend hours of analysis looking at it on the monitoring app? Are they going to roll a truck to your house?
I assure you, you will not be successful at proving a degradation warranty claim well down the road. If you have a massive and obvious failure, sure – you might have an easy claim. But agonizing over the minute differences in degradation rates between panels is a fool’s errand. You will never win.