Solar panels can either be polycrystalline or monocrystalline, both of which are silicone based. The basic scientific principle is based on the photovoltaic effect. This effect allows photons from the Sun to dislodge electrons from a material and then transfer those electrons through wires which can be used to perform work. Solar PV systems use silicone wafers called solar cells to convert sunlight into electricity. The solar cells consist of one or two layers of a semi-conducting material. When sunlight shines on the solar cell it creates an electric field across the layers causing electricity to flow. The greater the intensity of the sunlight, the greater the flow of electricity. Solar cells are referred to in terms of the amount of energy they generate in full sunlight, measured in electric power, Watts or Kilowatts. The solar cells are wired together to make solar panels, conventionally having either 60 or 72 cells.