For the majority of households between 5 and 6KW of battery is sufficient to significantly increase the Grid Electricity independence / Self Sufficiency (with EESS). In other terms that battery works hard and therefore quickly returns investment. The battery is being charged by the solar and used by the house.
A second battery for most households barely generates any additional solar savings; therefore, we do not recommend it. The benefit can be illustrated in the proposal document and explained by our staff.
Increasing compacity to between 9kw and 17kw of battery storage to be force charged in winter utilising a cheaper overnight tariff is an option for some households though the usage is still limited so the payback period is much longer. The potential other risk is that the overnight tariff differential reduces or disappears.