Batteries are an interesting technology. Only about 1% of solar systems are coming with batteries these days and they are mostly in situations where someone is operating off the utility grid. The reason batteries aren’t needed is there is something called Net Energy Metering which allows you to push energy back into the grid in the middle of the day when you don’t need it, and you get credit for it. Then at night when you need it, you use the credits you’ve received. This resets on a yearly basis so often times customers will gain credits during the summer, which they use in the winter. So because of this program, the utility acts as a battery. Not only that, but if you are on a time of use schedule, and you push energy back into the grid in the middle of the day, you may be able to push 1 unit of energy into the grid, then at night pull 1.5 to 2 units off because of the change in cost of energy. It’s a great deal!