Solar panel count calculator
Enter the array size you want and the panel you are considering. The calculator returns how many panels, the nominal array size, the roof area with walkways, and the expected output in your city on an average day, in the worst month and over a year.
Inputs
kWp
From the sizing calculator or an installer's design.
W
From the datasheet (Pmax at STC).
m²
Length × width from the datasheet. 550 W ≈ 2.28 × 1.13 m.
%
Walkways, edge clearance, clamps.
Solar yield from Global Solar Atlas.
%
Shading, off-optimum orientation, soiling beyond the model. 5–15% typical.
ResultsLagos
Panels
—
rounded up
Nominal array
—
kWp actually installed
Roof area
—
m² including spacing
Average day
—
kWh at the inverter
Worst month
—
kWh per day
Per year
—
kWh
Formulas and assumptions
Panels = ceil(Target_kWp × 1000 ÷ Panel_W)
Nominal_kWp = Panels × Panel_W ÷ 1000
Roof_m² = Panels × Panel_area × (1 + spacing)
Daily_kWh = Nominal_kWp × PVOUT_day × (1 − site_losses)
Annual_kWh = Nominal_kWp × PVOUT_year × (1 − site_losses)
Nominal_kWp = Panels × Panel_W ÷ 1000
Roof_m² = Panels × Panel_area × (1 + spacing)
Daily_kWh = Nominal_kWp × PVOUT_day × (1 − site_losses)
Annual_kWh = Nominal_kWp × PVOUT_year × (1 − site_losses)
PVOUT already includes temperature, soiling, wiring and inverter losses for a typical system; the extra site-loss field is for your roof's specific problems.
What this is
An estimate from stated formulas and typical values, for planning and for checking quotations. It is not an engineering design, does not replace a load audit and site survey by a qualified installer, and does not account for shading, roof orientation, cable losses or local standards. ZEUS is not an engineering firm.