Most people don’t need batteries for their solar system if they’re already connected to the grid. It is an option, but currently most of the back-up batteries are still big and bulky, expensive, and need to be replaced every 5-10 years. There are, however, ongoing efforts to make batteries more financially sound. There are already some batteries that work well in the commercial projects that help shave demand and increase the savings. Since each project is customized, your building’s specific electricity usage profile would dictate if a battery back-up would be a financially viable solution.