All solar panels lose a small amount of performance every year. Exposure to direct sunlight puts physical wear-and-tear on any material — think of lawn furniture, decking or shingles. The performance degradation of solar panels is expected and is very slight, only one-half of one percent per year. The panels are warranted to produce at least 80% of their rated power at year 25. In fact, they will continue producing power long after that, just a little bit less each year.