Commercial Solar System Design Calculator

Array size from commercial electricity consumption.

Annual electricity usage (kWh)

Peak sun hours (PSH)

System efficiency (derate)

Panel wattage (W)

DC:AC ratio

Installed cost ($/W DC)

Tab to move between fields

Required system size (kW DC)

82.19

Number of panels206

Actual DC capacity (kW)82.4

Inverter capacity (kW AC)68.67

Roof area needed (sq ft)6,209

Est. annual production (kWh)120,304

Solar offset (%)100.3%

Estimated system cost ($)$90,411.00

How to Use This Calculator

Enter your annual electricity usage in kWh from utility bills.
Set peak sun hours for your location (NREL data; US range 3-7 PSH).
Enter panel wattage, system derate factor, and DC:AC ratio.
Input installed cost per watt DC before incentives.
Review the required system size in kW DC, panel count, roof area needed, and estimated annual production.

How the result changes with Peak sun hours (PSH)

Annual electricity usage (kWh): Total annual electricity consumption from utility bills.
Peak sun hours (PSH): Average daily peak-sun-hours for your location (NREL data). US range: 3–7.
System efficiency (derate): Overall DC-to-AC derate factor including inverter, wiring, soiling, and temperature losses.
Panel wattage (W): STC rated wattage per module. Commercial panels are typically 370–550 W.
DC:AC ratio: DC array size / inverter AC capacity. 1.1–1.3 is typical for commercial.
Installed cost ($/W DC): Total installed cost per watt DC before incentives.

Required system size (kW DC): Minimum DC array capacity to offset your annual consumption.
Number of panels: Modules required at selected wattage.
Actual DC capacity (kW): True DC capacity from whole-panel count.
Inverter capacity (kW AC): Required inverter AC capacity based on DC:AC ratio.
Roof area needed (sq ft): Approximate flat-roof area including row spacing for tilt racks.
Est. annual production (kWh): Expected year-1 energy production.
Solar offset (%): Percentage of annual consumption covered by solar.
Estimated system cost ($): Pre-incentive installed cost.

Identify Input Parameters
4 parameters
Annual electricity usage (kWh) = 120000, Peak sun hours (PSH) = 5, System efficiency (derate) = 0.8, Panel wattage (W) = 400 = 6 input(s) provided
Calculate Required system size
Required system size = annualKWh / (peakSunHours * 365 * systemEfficiency)
82.19 = 82.19
Calculate Number of panels
Number of panels = ceil(systemSizeW / panelWatts)
206 = 206
Calculate Actual DC capacity
Actual DC capacity = (panelCount * panelWatts) / 1000
82.4 = 82.4