Very few installations use batteries. Right now in the Bay Area, almost everyone is using net energy metering (NEM). You get a bill once per year, and they ba

Very few installations use batteries. Right now in the Bay Area, almost everyone is using net energy metering (NEM). You get a bill once per year, and they balance out your usage vs generation, and any extra usage is charged. There is a minimum you have to pay each year, so most installers aim for 85-95% of your usage to be generated by your system. As other folks have stated, it's not advantageous to sell back to the grid given the low price - as such, very very few people actually sell back to the grid, and instead make a small purchase each year, and mostly at off-peak rates.