While there are numerous types of solar panels, the 2 most commonly utilized for residential installations are categorized as mono-crystalline and poly-crystalline. The main difference is really in the manufacturing process but there are some visible distinctions. The cells in the mono-crystalline panels are typically black in color and square with rounded corners. The cells in the poly-crystalline panels are of a light or darker blue hue with an inconsistent uniformity. The mono-crystalline panels are slightly more efficient than the poly-crystalline ones and thus a solar array would probably have fewer panels but typically carry a higher price tag. Which type of panel is best for your roof is determined on a case-by-case study.