HOW TO USE IT
How to use the Off-Grid Solar System Size Calculator
- 1
Find your daily usage: Total the kWh you use each day, ideally from an energy meter or a careful estimate of loads.
- 2
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.
- 3
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.
- 4
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.
THE MATH
Off-grid size calculation method
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.Divide daily kWh by the peak sun hours and by the system efficiency after losses. That gives the array size in kW.
PRACTICAL EXAMPLE
Worked example for Off-grid size
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.
FAQ
Frequently asked questions
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.
What should I verify before using the result?
Oversize the array slightly and keep a few days of battery autonomy. The sun is rarely on schedule.
Is this a final quote or design?
No. Use it as a planning estimate, then confirm measurements, local rates, product requirements, permits and jobsite conditions before bidding or building.