Free Engineering Tool
Off-Grid System Sizing Calculator
Enter your loads and site conditions to get a first-pass PV array, inverter and battery size — then match the result against models in our catalog.
This calculator sizes an off-grid system with three formulas: PV array watts = daily energy × 1.3 ÷ peak sun hours; inverter watts = simultaneous peak load × 1.25; battery capacity = daily energy ÷ depth of discharge × days of autonomy ÷ system voltage. All three are the same formulas worked through in our off-grid sizing guides.
Matching models from our catalog
Smallest catalog models that meet the numbers above at the selected system voltage.
Fill in the fields above to see a recommended system.
How the three numbers are calculated
PV array
daily energy (Wh) × 1.3 ÷ peak sun hours The 1.3 factor covers conversion, wiring and battery round-trip losses. Peak sun hours is the daily equivalent of full-strength sunlight, not hours of daylight.
Inverter
simultaneous peak load (W) × 1.25 Sized on the load that runs at the same time, never the daily total. Motor starting surge is a separate check — see our surge power guide.
Battery bank
daily energy (Wh) ÷ depth of discharge × days of autonomy ÷ voltage Depth of discharge is how much of the battery is safely usable: about 50% for flooded lead-acid, 55% for AGM / gel and 85% for LiFePO4.
Work through the numbers in detail
Sizing calculator — FAQ
Does this calculator replace an engineering review?
No. It returns a first-pass estimate from the standard derating and depth-of-discharge figures. Motor starting surge, cable and fuse sizing, MPPT input limits, string voltage and destination-market compliance all sit outside it — send us your load audit and our engineers will review the sizing free of charge.
Why does the calculator ask for two different power numbers?
Daily energy and peak load size different parts of the system. The array and battery follow daily energy, because both work on energy over time. The inverter follows the simultaneous peak load, because it has to supply that many watts at once.
What is depth of discharge?
Depth of discharge is the share of a battery's capacity that can safely be used before recharging. Drawing a lead-acid bank below about 50% shortens its life sharply; a LiFePO4 bank tolerates roughly 85%. This is why the same daily energy needs a larger nominal capacity in lead-acid than in lithium.
Does this work for hybrid or grid-tie systems?
The formulas here are for off-grid systems with a battery bank. A grid-tie system has no autonomy requirement and a hybrid system adds export and grid-charging rules, so both are sized differently. Our sizing guides cover the off-grid case; contact us for the others.
Want our engineers to check your sizing?
Send your load audit and target market — we will review it and recommend models, free of charge.