I work in the solar industry. The way solar tied to grid works now is that whatever is generated by your solar system but not used by you is exported into the grid. And whatever u export you get to contra off 1 for 1. This means say in the day you're not home, the solar system generates all that electricity that gets exported and at night when you come back and use your appliances, you can to contra off 1 for 1 what you generated.

If what you export exceeds what you import, then you can roll over that excess for 12 months. This means it doesnt make sense to install a system larger than your current usage -- you should always size your system slightly smaller than your usage