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. Solar PV panels produce raw DC electric power when exposed to sunlight, and an inverter can convert this DC power into conventional AC power, which is the type of electricity used in your home appliances. Grid Tied solar PV systems send the electric energy to the grid connection in the building, and out to the power grid; energy that is sent out this way is measured on the meter-base supplied by the local electricity company and credited on the electricity bill against the cost of the energy that is consumed; this is known as net-metering. Off Grid solar PV systems do not have a connection to a power grid, and instead use batteries to store energy produced from the solar panels.