You don't need to install a battery for your solar panels to work, but a battery can help you get the most out of the energy your panels are generating.
Solar panels will create energy when there is daylight and you can use this solar electricity instead of buying it from your energy supplier. However, these panels don't work at night time (when you tend to use the most energy). So, what happens then?
If you don't have a battery, you'll switch back to using energy from the national grid - which will cost you money. If you have a battery installed, you can use any extra energy stored in the battery at night time. This reduces your reliance on the grid for electricity.
Want to use solar energy at night? Install a battery.