Multicrystalline panels use crystalline silicon, a basic semiconductor material.They are expensive but highly efficient and are often more cost-effective in the long run. Multicrystalline panels are typically 15-18% efficient, meaning that for every unit of solar energy that hits the cell, the panel can convert 15-18% of this energy into electricity. Multicrystalline photovoltaic solar cells may be preferable when roof space is a limiting factor