The way home generation works is: while you are at away at work during the day, your house is gathering midday solar energy and feeding it into the grid. Then, when you return home and at night, you are sucking the energy back from the grid. It’s like a daily deposit and withdrawal from a bank.
This is pretty good. But it’s not as good as being more “off grid” and using as much of the charge you create in-house. (In short: the value you get from feeding into the grid is less than the cost of taking from it, the power you get from the grid isn’t as clean as your pure solar energy, and there are efficiency losses.)
The eventual answer is to have a battery system like the Tesla Powerwall* at home alongside your solar system to gather the juice by day and squeeze it out again by night, with minimal transfer with the utility.
So is it worth getting a battery system now? The short answer is no, not yet, but yes, eventually. This is because battery prices are falling quickly. At the moment they are still just too expensive for the ROI to work out.
It’s definitely possible to add a battery later to your system. I was told to give it a couple of years as economies of scale kick in, and then reconsider.
* Incidentally, the Tesla Powerwall is fancy looking but not the most respected battery system out there. It’s expensive, has Apple-like proprietary interconnects, and I’m told doesn’t contain all the components needed, so while it looks sexy on its own, it will be surrounded by other devices that wreck that look.