To determine the performance level of solar panels, several essential methods can be utilized. Understanding panel specifications, 2. Solar panels are graded into categories A, B, C, and D based on their quality, and the cost differences between these grades can be significant. Grade A panels, for instance, are the highest quality, while Grade D panels are typically considered low-grade materials with limited usability. The cost gap is also very large. So what kind of solar panel is called A grade, and what kind of solar panel is called D grade? Here is a brief. How to tell the grading of solar panels? 1.