Having a back-up battery at your home is a wise decision to make. But here is a disclaimer, back-up batteries can be really expensive. Nevertheless, these are worth investing for because they will save you large sum of costs in the future and you would not have a problem with energy supply when the main grid supply runs out or when the solar panels cannot provide energy during the night.
Back-up batteries enable you to have a continuous supply at the time you need it the most, and in case you are in a solar powered system, that is during the night. How does a back-up battery work? Solar panels convert the sunlight into solar energy for your day consumption. Depending on how much you consume in the day, the excess energy solar panels convert will be transmitted to these back-up batteries for storage and for future use. You do not have to connect to the main grid to have your supply of energy during the night. The back-up batteries will do that for you. It is very cost-efficient because you still use the solar energy your solar panels converted in the day thus, you do not outsource from the main grid system.
Furthermore, back-up batteries save you from running out of energy supply especially when the main grid runs out of its supply on its own. Thus, you achieve energy independence. Having back-up batteries in your household is very important especially when you cannot live a day without energy supply. It may be a bit pricey to buy at first, but you will soon realise that it is a good return on investment because of the tons of money you will get to save from harnessing your own energy supply for your household.