Net Metering is the process of selling unused solar energy to your Utility. The amount of energy produced by a solar array is largely beyond the control of the array owner, and there may be times when a solar PV system produces more power than is needed. In these circumstances, the excess power is exported to the utility grid. The utility monitors the amount of energy exported to the grid and credits the customer.
Seasonal variations in energy production and demand may generate excess energy in a given month, while in other months your demand is exceeding solar production. Some states allow customers to carry over excess energy from month to month, which also enables them to more easily be a net-zero consumer. Other states require the net-excess generation to be paid out monthly, usually at a fraction of the retail rate.