Solar Panel System GuideA polycrystalline solar panel is built from cells that contain many silicon crystals instead of one. That structure lowers the panel's efficiency compared with monocrystalline, which usually means more panel area for a given amount of power. The trade has historically been a lower panel price. Facts here come from EnergySage and the U.S. Department of Energy.
What makes a cell polycrystalline
Both panel types start from silicon. The Department of Energy notes that crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice, and that silicon is by far the most common semiconductor material used in solar cells.
The difference is in the crystal structure. EnergySage explains that polycrystalline panels have many more crystals in each cell, which means less freedom for the electrons to move. Fewer paths for electrons is the direct reason a polycrystalline cell converts a smaller share of sunlight into electricity.
Like all silicon modules, polycrystalline panels are long-lived. The Department of Energy states that modules are expected to last for 25 years or more, still producing more than 80 percent of their original power after this time.
Efficiency and the roof-area trade
EnergySage reports that polycrystalline panels typically have an efficiency of 15 to 17 percent, and that most polycrystalline models top out below 20 percent. For contrast, EnergySage places today's residential monocrystalline panels between 20 and 23 percent.
Lower efficiency per panel means each panel converts less of the sunlight that lands on it. When roof space is tight, that gap can decide how much total power a home can install, since a lower-efficiency panel delivers fewer watts from the same footprint.
The Department of Energy frames efficiency as the percentage of the solar energy shining on a PV device that is converted into usable electricity, which is the yardstick these panel numbers are measured against.
Cost and appearance
The historical case for polycrystalline was price. EnergySage notes that monocrystalline solar panels are more expensive than polycrystalline solar panels when comparing panels alone, and attributes the difference to manufacturing complexity, since polycrystalline uses a simpler process while monocrystalline production must be controlled very carefully.
The two also look different on a roof. EnergySage notes that polycrystalline panels can appear to have a blue hue, while monocrystalline panels are usually black.
EnergySage adds a market caveat worth keeping in view. It says that for a traditional rooftop system, monocrystalline is now the right choice for nearly every homeowner, because panel prices have come down enough that the old cost argument for polycrystalline no longer applies.