Storage you must buy is larger than the energy you will use. Batteries should not be drained to empty: depth of discharge (DoD) might be 80–90% for lithium and ~50% for lead-acid. Inverter and round-trip losses mean you also divide by efficiency (often ~90%).
Required nameplate kWh = (daily kWh × days of autonomy) ÷ (DoD × efficiency). Number of batteries is that energy divided by each unit’s usable kWh (nameplate × DoD × efficiency).
Read daily kWh from your utility bill (kWh per month ÷ days). This is battery math only—it does not size solar panels.
Cooling tons are not the same as stored kWh—use the AC ton calculator for the air conditioner. Household hot water is sized on the water heater size calculator.
How this calculation works
kWh_bank = (kWh/day × days) / (DoD × eff). Batteries = ceil(energy need ÷ usable kWh per battery).