Simple PVWatts-style power calculator

One hour, one array. Uses P = G / 1000 x P0 x (1 + gamma x (Tcell - 25)), then lumped losses and a flat inverter efficiency.

Estimate for learning, not a design or a yield guarantee. The cell-temperature rise (25 K at 1000 W/m2) and the 96% inverter efficiency are our placeholders. Replace them with your datasheet and site values.

Array size P0, kWdc (STC) Plane-of-array irradiance, W/m2 (0 to 1,500) Air temperature, deg C Cell temperature rise at 1,000 W/m2, K (placeholder) Power temperature coefficient gamma, % per deg C (datasheet; negative) Lumped losses, % (soiling, wiring, mismatch and so on) Inverter efficiency, % (flat, placeholder) Inverter AC limit, kW (leave blank for none)

Result for one hour

Cell temperature	-
Temperature factor 1 + gamma x (Tcell - 25)	-
DC power before losses, kW	-
DC power after losses, kW	-
AC power, kW	-
Energy in this hour, kWh	-

The formula is the DC form documented for pvlib.pvsystem.pvwatts_dc (pvlib stable docs, checked October 2026). Cell temperature here is air temperature plus the rise scaled by irradiance, which is a simplification. It ignores angle-of-incidence loss, wind and inverter part-load curves.