On-grid: Powered exclusively by purchasing electricity services from your local electric utility, from the local power lines.
Off-grid: The system is not connected to the power grid (power lines from the utility company). Power is stored in a bank of batteries that run the loads. Extra power is used for air or water heating.
Grid-tied: The system is directly connected to the power grid. Power is not really stored, instead the grid is used as a “battery.” If the grid experiences a blackout, there is no power for loads--the house is blacked out too. Extra power is sold back to the utility.
Grid-tied plus battery backup: The system is connected to the power grid. Power is stored in a battery bank, so if the grid experiences a blackout the house still has power to run loads. Extra power is sold back to the utility.

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