Off Grid Solar Calculator

Size a complete off-grid solar system including array, battery and inverter.

About Off Grid Solar Calculator

Off-grid systems must be sized for the worst month rather than the annual average, which makes them substantially larger than grid-tied systems for the same load. The consequence is a large summer surplus that cannot be exported. That structural over-sizing is why off-grid systems cost far more per kWh delivered than grid-connected ones, and why load reduction pays back so strongly.

Formula

Off Grid Solar

Array = daily kWh ÷ (worst-month sun hours × derate); battery = daily kWh × autonomy ÷ DoD

worst-month sun hours: Design basis for off-grid, unlike grid-tied which uses annual average
autonomy: Days the battery must carry the load with no generation

Worked example

With the default values below, Off Grid Solar Calculator returns Array Size Required of 5.714. Change any input above and every figure here is recalculated in your browser.

Inputs used

Daily energy consumptionminimum 0 kWh: 8 kWh
Worst-month peak sun hoursaccepts 0.1–12 h: 2 h
Days of autonomyaccepts 0.5–14 days: 3 days
Depth of dischargeaccepts 0–100 %: 50 %
System lossesaccepts 0–100 %: 30 %
Peak loadminimum 0.01 kW: 3 kW

Results

Array Size Required: 5.714 kW
Battery Capacity Required: 48.000 kWh
Inverter Rating Required: 3.750 kW
Panels at 430 W Each: 14
Summer Surplus Over Requirement: 120.0%

Step by step

1Values used
2Off Grid Solar
3Array Size Required= 5.714 kW
4Battery Capacity Required= 48.000 kWh
5Inverter Rating Required= 3.750 kW
6Panels at 430 W Each= 14
7Summer Surplus Over Requirement= 120.0

Assumptions and limits

The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Off Grid Solar calculated?

Array = daily kWh ÷ (worst-month sun hours × derate); battery = daily kWh × autonomy ÷ DoD Off-grid systems must be sized for the worst month rather than the annual average, which makes them substantially larger than grid-tied systems for the same load. The consequence is a large summer surplus that cannot be exported.

Why does Off Grid Solar matter?

That structural over-sizing is why off-grid systems cost far more per kWh delivered than grid-connected ones, and why load reduction pays back so strongly.

What values do I need to enter?

This calculator takes 6 inputs: Daily energy consumption, Worst-month peak sun hours, Days of autonomy, Depth of discharge, System losses, Peak load. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.