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Most home solar installs are grid-tied. No utility power, no solar power.

It simplifies the system a lot, because the grid provides "instantaneous" load matching for your house. If the inverter is sourcing more current than your house is sinking, the grid will sink it. If the house is sinking more current than your inverter is sourcing, the grid will source it.

When there's a utility outage, you need something else to provide the load matching. Either a local generator, or a battery is common; but either way, it's a lot more expensive.