Net metering simply allows a solar system to export excess electricity production (that cannot be used by the home/building) to the grid. Ameren keeps track of the kilowatt hours (kWh) exported to the grid in a “kWh bank” similar to roll-over minutes in a cell phone plan. At night or on a cloudy day, when electricity is imported from the grid, there is no cost for the electricity up to the balance of the kWh bank. Ameren charges you only for the net amount of the electricity you consume.