Solar system sizer

Size the kWp of a residential or commercial PV system from energy use, sun hours and real-world losses. Get panel count, inverter, battery, roof space, string layout and payback.

Project

Residential Commercial

Grid-tied Hybrid (with battery) Off-grid

Switching project type loads typical defaults for that kind of site.

Energy use

I know my kWh I know my bill

Average monthly use (kWh)From your bill, ideally a 12-month average Electricity rate (per kWh)All-in rate on your bill Currency Daytime share of use (%)Portion used while the sun is up. Homes ≈ 30–45%, offices/shops ≈ 60–80%

Sizing target

Location (annual avg. peak sun hours) Sizing strategy Offset target (%)100% = produce what you use over a year Budget cap (kWp)0 = no cap. Also useful for net-metering limits (PH: 100 kW)

Panels and roof

Panel rating (W) Panel area (m²)e.g. 2278 × 1134 mm ≈ 2.58 m² Layout spacing factor1.1–1.2 flush roof mount; 1.4–2.0 tilted rows on flat roofs Usable roof area (m²)0 = not checked

System losses

Temperature loss (%)Tropics 8–12%, temperate 4–7% Inverter efficiency (%) Soiling / dust (%) DC + AC wiring (%) Mismatch + degradation (%)Year-1 LID and panel tolerance Shading (%)

Performance ratio (PR): —. Typical well-built systems land between 0.75 and 0.82.

Inverter

DC/AC ratio1.1–1.3 is typical; higher clips more at noon

Cost and payback

Installed PV cost (per Wp)Panels, inverter, mounting, labor Export credit (per kWh)What the utility pays for surplus; PH net metering ≈ generation charge

String check (optional)

Check modules per string against the inverter

Panel Voc (V) Panel Vmp (V) Voc temp. coefficient (%/°C) Pmax temp. coefficient (%/°C)Used for Vmp at high heat Record low temperature (°C) Record high ambient (°C)Cell temp assumed +25 °C above this Inverter max DC voltage (V) MPPT range min (V) MPPT range max (V)