Buying a solar energy system is like buying any other product: in order to make an educated purchase, you’ve got to understand a bit of the lingo. So let's review net metering "a concept that lies at the very center of how and why solar energy can make financial sense".
To begin, what you buy from your utility is best thought of as an electric current. The AC current flows from the point of generation, along the grid and to the final point of use - say a flat screen TV. A meter measures the amount of electricity that flows into your house and, at the end of each month, you pay your utility for each kilowatt-hour used. In a conventional setup, the flow of electricity is uni-directional. That is, it only flows from the grid to your home.
In a net-metering arrangement, the flow of electricity is bi-directional. The DC current generated by your solar panels flows into the inverter, where it’s converted into usable AC current. Any of the AC power that’s not consumed flows back into the grid, running the meter backward. This portion of electricity that flows into the grid is sometimes referred to as net excess generation, or NEG. Many states require utilities to purchase any NEG from you, usually at the going retail rate for electricity. In this way, solar panels drive value by enabling you to offset monthly electricity charges