This is a way to maximise the benefit of your battery – charging it during the night with cheaper off-peak electricity from the national grid and then using that cheaper electricity during the day. This is particularly useful in the winter months when there is much less solar energy.
The key to this is finding the right tariff. Economy 7 tariffs provide different day and night–time rates, but some suppliers are withdrawing them. The likely replacements are time of use tariffs, or TOUs. As opposed to a flat rate model, the TOUs charge a dynamic hourly price that is responsive to supply and demand of energy. You will need a smart meter to be able to access this kind of tariff. For more information, visit the Energy Saving Trust’s website. It lists some providers, but will need to do your own research into what tariffs are currently available.