How is the utility grid like a backup "battery" for a Solar Home?

When you're producing more electricity than you're consuming, you're sending electricity back into the utility grid.  Your electric meter spins backwards, saving you money on your electric bill.
 
When you're not using the solar energy that your system is harvesting during the daytime, you're giving it back to the utility company as a credit towards your electric bill.
 
The utility grid is kind of like your "battery," because you use electricity from the utility company to power your home at night when it's dark.

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