Our cells by the watt come from larger pieces of chipped and broken monocrystalline AND polycrystalline silicon cells. Monocrystalline cells are the most efficient as they use a single, very pure crystal of silicon in each cell. These cells are best when solar surface area is restricted or when highly efficient panels are required. Polycrystalline cells are generally slightly less efficient than monocrystalline cells, and correspondingly, are slightly less expensive. Polycrystalline cells are often the most cost-effective option for large solar panels and arrays.