Solar Battery Sizing Calculator

Required Capacity starts from Backup Energy Needed -- your Daily Energy Usage scaled down to an hourly rate and multiplied by Backup Duration -- and then inflates that figure to account for two real-world losses: Depth of Discharge, because most battery chemistries cannot be safely drained to 0% without damaging cycle life, and Inverter Efficiency, because some of the battery's stored DC energy is lost converting to usable AC power. Both losses work the same mathematical direction: a lower Depth of Discharge or a lower Inverter Efficiency both mean more raw battery capacity has to be installed to deliver the same usable backup energy, so Required Capacity rises as either number falls. Required Amp-Hours converts that same energy figure into a current-based unit by dividing by Battery Voltage, which is why raising system voltage lowers the amp-hour figure even though it does not change Required Capacity in kWh at all -- a 48V system needs proportionally fewer amp-hours than a 12V system to store the identical amount of energy, which is one practical reason larger backup systems typically run at higher nominal voltages.

The 13.5 kWh Batteries Needed figure benchmarks against one common residential battery unit size purely for intuition; it does not represent a specific product recommendation, and other battery products come in materially different capacities. This calculator also assumes a flat, constant load during the backup period -- a real household's demand varies hour to hour, so a home with a large intermittent load (like AC or well-pump start-up current) may need more capacity than this average-usage estimate suggests.