Adding battery storage is optional, but we generally recommend it to ensure that you're making the most of your system.
By storing the energy your home generates during the day, you'll reduce your need to pay for energy from the grid after dark, which could significantly increase the savings your new system delivers. However, this does vary depending on how much electricity you generate, and when you use it most.
Your engineer will be able to offer advice based on your personal circumstances during their design process.