Method: Solar array size is estimated from daily electricity use ÷ peak sun hours, with the entered system-loss allowance applied. Battery storage is sized from daily electricity use × backup days. The calculation also allows for usable battery depth, battery efficiency and inverter conversion losses. Lithium batteries are calculated using a 90% usable depth and approximately 95% battery efficiency. Lead-acid batteries use a 50% usable depth and approximately 85% battery efficiency. Inverter sizing uses the entered maximum simultaneous load with a 25% design margin and rounds up to a practical standard inverter size. This calculator provides preliminary system sizing. Motor starting loads, seasonal solar variation, prolonged cloudy weather, battery temperature, charging limits and equipment manufacturer requirements should be checked for final design.