Solar Array Size Calculator — Daily Energy, Sun Hours & Panel Count

Design inputs

Results

Solar sizing method

The minimum array power is based on daily energy divided by peak sun hours, array derating, and charge-path efficiency. The design margin is then applied before rounding up to a whole panel count.

The controller-current estimate is a planning value based on installed PV wattage, controller efficiency, and nominal battery voltage. It does not replace PV string-voltage/current compatibility checks, cold-weather Voc calculations, conductor ampacity, overcurrent protection, or controller manufacturer limits.

From daily energy demand to array size

The calculation first determines how much solar energy must be harvested to deliver the requested daily load energy after charge-path losses. It then divides by peak sun hours and array derate to estimate minimum array power, adds design margin, and rounds up to a whole panel count.

Peak sun hours compress a variable solar day into equivalent full-power hours. Seasonal weather, orientation, shading, temperature, soiling, battery acceptance, clipping, and site-specific irradiance still require a more detailed production model.

Equations used by this calculator

Required harvest

E_PV = E_load / η_charge

The array must produce extra energy to cover charge-path losses.

Minimum array power

P_min = E_PV / (PSH · derate)

Peak sun hours and aggregate derate convert daily energy to array nameplate power.

Controller current screen

I_ctrl ≈ P_array η_ctrl / V_bank

Installed array power is converted to an approximate battery-side controller current.

Assumptions behind the sizing figure

Assumptions

Daily energy demand is represented by a single average target.
Peak sun hours and derate are aggregate design inputs supplied by the user.
Panel modules are assumed identical and panel count is rounded up to the next whole module.

Limitations

Does not perform PV string voltage/current compatibility, cold-Voc checks, conductor sizing, protection, rapid-shutdown, or structural mounting design.
Does not replace location-specific hourly or seasonal production simulation.

Worked example

5 kWh/day off-grid load

Use 5,000 Wh/day, 5 peak sun hours, 0.80 array derate, 0.92 charge efficiency, 20% design margin, 400 W panels, and a 48 V battery bank.

Required array harvest is about 5.43 kWh/day.
Minimum array power is about 1.36 kW; with 20% margin it becomes about 1.63 kW.
Rounding up to whole 400 W modules gives five panels, or a 2.0 kW installed array.

Result: The example estimates about 7.36 kWh/day under the entered resource assumptions and about a 50.5 A controller recommendation after the current margin.

Solar Array Size Calculator FAQ

What are peak sun hours?

Peak sun hours are the daily solar irradiation expressed as an equivalent number of hours at 1,000 W/m². They are not the same as daylight hours.

Why does panel count exceed recommended array wattage?

Panels are discrete products, so the calculator rounds up to a whole number of the entered panel wattage.

Is the controller-current result enough to choose an MPPT controller?

No. Controller selection also requires PV string open-circuit voltage, short-circuit current, temperature corrections, manufacturer limits, and applicable code requirements.

Validation checks

These cases confirm the sizing scales linearly where it should.

More sun

Case: Increase peak sun hours with all else unchanged.

Expected: Required array wattage should decrease.

More daily energy

Case: Double the daily energy target.

Expected: Minimum and recommended array power should approximately double before panel-count rounding.

Where this calculation comes from

Sizing logic is shared with the DIY Power System Designer, which carries the fuller battery, controller, and seasonal-irradiance workflow.

Open the source workbench →Read calculation and source methodology →