The ability to interconnect with the grid is called Net Metering. Net Metering measures the energy:
Used from MVEA (the grid)
Generated from your renewable system
Your Energy & Renewable System
If your renewable system generates more energy than you use, the excess energy produced is fed into the grid and a credit, called banked use, is applied to your bill.
If you use more energy than your renewable system generates, then the grid will back you up and provide the power you need.
If you are looking for a more detailed explanation of our Net Metering program, read the 20.42 Net Metering Rate (PDF).