For our customers, YouSolar designs the solar array’s size, location, and orientation and specifies the solar panel power. We also provide the panel-level STEP™ Micro-converter, which is integral to the performance of the PowerBloc, but we do not recommend a particular panel or install the solar array.

Many customers ask us what solar panels to buy for their projects. We suggest buying a quality panel from a well-known brand but not trying to compare specifications and degradation rates in detail.

We often hear from customers that “Our installer recommends a [REC/Silfab/QCells/Fill-in-the-Blank] panel. He (or she) says it is the best on the market.” That may be so, but it may also be because the installer buys that particular panel in bulk and wants and needs to use it. But an installer who wants to stay in business will only recommend panels he has not seen fail. So, there is some value in the recommendation.

Solar installers do not have any data on panel performance, nor do they have any control over the conditions under which the panels perform. Panel degradation is now guaranteed for 25 years. How many installers have been in business that long?

So, to better advise our customers, we read a 2022 paper on module degradation by Sandia, NREL, and the University of Central Florida. (You can read a summary of the paper on Sandia’s website.) The paper represents the best science available, but it is a tedious read, and the data is difficult to interpret.

Even though prices of solar panels have declined precipitously in the past 40 years, the quality has not suffered. The long useful life of solar panels, which is 25+ years, is astounding.

Here are our takeaways from the study

• The specifications of efficiency and degradation by panel manufacturers bracket a value, but the range may not be a distribution.
• Manufacturers change raw materials and processes continually. Based on that, a 25-year degradation warranty is only the manufacturer’s “educated guess.”
• Solar panel quality has not changed in 40 years, and its useful life of 25 or more years is astounding.
• Assume a 0.6% degradation per year and buy a quality panel from a manufacturer who will cover workmanship problems because it is next to impossible to determine performance specifications accurately.

Solar panels are incredibly reliable and high-performing. Buy a quality panel from a brand-name manufacturer. Assume a 0.6% degradation per year. If looks are important, then make them part of your purchase decision. It is o.k.