SolarSizr

Off-Grid Solar Calculator

Size a complete off-grid system from your daily loads: solar array, battery bank, charge controller and inverter, all in one place.

ApplianceWattsHours/day

How to use this off-grid solar calculator

List the appliances you run each day with their power in watts and how many hours per day they run. Add or remove rows to match your setup, then pick your system voltage, battery type, peak sun hours and days of autonomy. The calculator sizes the four core parts of an off-grid system at once.

  • Solar array — enough panels to refill your daily energy use during your available sun hours.
  • Battery bank — enough storage for your days of autonomy, adjusted for how deeply the battery can be discharged.
  • Charge controller — rated for the array's current with a safety margin.
  • Inverter — rated for your peak simultaneous AC load.

How the sizing works

daily energy (Wh) = sum of (watts × hours) for each appliance
array (W) = daily Wh ÷ peak sun hours ÷ 0.8 (system losses)
battery (Wh) = daily Wh × days of autonomy ÷ depth of discharge
battery (Ah) = battery Wh ÷ system voltage
controller (A) = array W ÷ system voltage × 1.25
inverter (W) = peak simultaneous load × 1.25

The 0.8 factor covers wiring, controller and temperature losses. Depth of discharge is how much of the battery you can safely use, about 80% for lithium and 50% for lead-acid, which is why lead-acid banks are sized larger.

Frequently asked questions

Start from your daily watt-hours (watts × hours per appliance). Array = daily Wh ÷ peak sun hours ÷ 0.8. Battery = daily Wh × days of autonomy ÷ usable depth of discharge. Then size the controller from array watts and the inverter from your peak simultaneous load.
The hours per day when sunlight averages 1000 W/m². Most places get 3 to 6 depending on location and season. Size for your worst usable month.
How long the battery runs your loads with no sun. Two days is a common start; three or more is safer in cloudy climates but needs a bigger battery.
Under ~1 kWh/day, 12V is fine. Roughly 1 to 3 kWh/day, use 24V. Above that, 48V. Higher voltage means less current, so thinner wire and smaller controllers.

More SolarSizr calculators

Once you know your system size, set the panel angle, the wire size, and the charge controller.