SOLAR
How to Size an Off-Grid Solar System
Preliminary method for sizing panels and batteries for a fully off-grid system.
An off-grid system needs enough panels to generate your daily usage and enough battery to carry you through days without sun. The math is daily use divided by sun hours and by discharge.
THE SHORT ANSWER
How do you size an off-grid solar system?
Divide daily kWh by (sun hours × system efficiency) for the array, then size the battery with daily use × days ÷ depth of discharge. 30 kWh/day at 4.5 sun hrs and 80% efficiency needs about 8.3 kW, or 21 panels of 400 W.
Find your daily usage
Total the kWh you use each day, ideally from an energy meter or a careful estimate of loads.
Size the panel array
Divide daily kWh by the peak sun hours and by the system efficiency after losses. That gives the array size in kW.
- Daily kWh
- Peak sun hours
- System losses
- Panel rating
Size the battery bank
Multiply daily use by the days of autonomy and divide by the usable depth of discharge. That gives the battery capacity in kWh.
This is a preliminary estimate
Use the Off-Grid Solar System Size Calculator for planning, but a real install needs professional design, inspection, permitting and, if grid-tied, interconnection. These figures are not a design.