If you have solar PV you can generate plenty of electricity when the sun is shining. But on overcast days you’ll make less, and you’ll make none at all at night. This generation pattern often doesn’t match up with when households want to use electricity – it’s at night when you want the lights on and to use appliances like a dishwasher or TV.
If your solar panels generate electricity and you don’t use it, it ends up being fed into the National Grid. You may get paid for it, but not as much as you save if you use the power yourself.
This is where battery storage comes in. If you can store the electricity generated during the day, there is less need to consume electricity – e.g. run your washing machine – when the sun is shining and you’ll use more of the power you generate and save money.