We have a 12 panel array which is feeding into our  Pylontech US3000 battery. 
On a good day like today our battery is 90% full the panels are producing 2.97kwh. As our usage is low at this time, 2pm, the energy produced by the panels is being fed into the grid. 
we are just about to go onto a new tariff paying 44p/kwh   
A new Pylontech US5000 battery will cost £1400. 
Is an additional battery worth investing in? Not sure how to work it out. We are currently producing between 1/3 and ½ of our daily usage   This obviously goes down considerably in winter months between 1-3kWh depending on the weather.
All our hot water at this time of year is coming from the panels via a solar iboost to an immersion heater 
Summary, half our production on a sunny day is being fed to the grid. What can I do? How many batteries would I need.