The addition of a battery to your system can greatly increase the amount of solar power you can use and hence reduce the amount you need to buy from the grid. Some electricity suppliers also allow you to charge your battery overnight at an off-peak rate and this can produce reductions in your electricity bill in winter.  

However, you should consider how big a battery to buy and financial return. Obtain a separate quote from installers for a battery rather than let it be rolled into a quote for panels plus battery. If you do get a quote, it could be about £5,000 for a 10kWh battery.