TAHA Engineering Toolsby TAHA Knowledge Lab

Energy & Renewables

Solar Panel Output Estimator

Estimated DC and AC output of solar panels at a given sun and temperature, or their daily energy from peak sun hours.

Inputs

Calculate from
Sunlight of irradiance G falls on a tilted panel; DC power passes to an inverter that gives AC power.G W/m²T(cell) = T(amb) + (NOCT − 20) ÷ 800 × GP(DC)Inverterη(inv)P(AC)P(DC) = N × P(STC) × G/1000 × [1 + γ(T(cell) − 25)] × (1 − L(DC))
Output falls in steps from the rating: weaker sun (G ÷ 1000), hotter cells (1 + γ(T(cell) − 25), with γ negative), DC losses, then the inverter efficiency. Real output is an estimate, not a guarantee. Diagram not to scale.

1000 W/m² is the standard test value (bright sun facing the panel).

Nominal operating cell temperature from the data sheet, typically about 40–48 °C.

Negative, from the data sheet (often about −0.3 to −0.45 %/°C for crystalline panels).

Shows clipping when the DC power is more than the inverter can deliver.

Result

AC output power (after the inverter)
344.71
DC output power (at the panels)
359.073
Cell temperature
60
Temperature factor
0.8775
Working
T_cell = T_amb + (NOCT − 20) ÷ 800 × G = 35 + 25 ÷ 800 × 800 = 60 °C Temperature factor = 1 + γ (T_cell − 25) = 1 + -0.35/100 × 35 = 0.8775 P_DC = 1 × 550 W × 0.8 × 0.8775 × 0.93 = 359.07 W P_AC = P_DC × 0.96 = 344.71 W

The panels give about 359.073 W DC, or 344.71 W AC after the inverter, at these conditions.

  • Estimated output, not guaranteed generation.

Educational estimate — check the assumptions below.

About this calculator

A solar panel’s rating (W at STC) is measured at 1000 W/m² of sun and a cell temperature of 25 °C. In real use the sun is weaker, the cells are hotter — which lowers output — and some energy is lost in dust, wiring and the inverter. This calculator estimates the DC output at the panels and the AC output after the inverter, either at a moment or as daily energy from peak sun hours.

All results are estimates for the values entered, not guaranteed generation.

Formula

Tcell = Tamb + (NOCT − 20) ÷ 800 × G    PDC = N × PSTC × (G ÷ 1000) × [1 + γ (Tcell − 25)] × (1 − LDC)

PAC = min(PDC × ηinv, AC limit)    EDC = N × PSTC × PSH × [1 + γ (T̄cell − 25)] × (1 − LDC)    EAC = EDC × ηinv

G = irradiance on the panel (W/m²), NOCT = nominal operating cell temperature (°C), γ = power temperature coefficient (negative, per °C), LDC = DC losses, PSH = peak sun hours, T̄cell = average cell temperature during sunny hours.

Worked example

  • One 550 W panel at 800 W/m², 35 °C air, NOCT 45 °C, γ −0.35 %/°C, DC losses 7%, inverter 96%: Tcell = 35 + 25 ÷ 800 × 800 = 60 °C; factor 1 − 0.0035 × 35 = 0.8775 → PDC = 359.1 W, PAC = 344.7 W.
  • Daily: 5.5 peak sun hours at an average cell temperature of 50 °C → factor 0.9125 → EDC = 2.567 kWh, EAC = 2.464 kWh/day.

Assumptions and limitations

  • Estimated output only, not guaranteed generation.
  • Output is taken as proportional to irradiance, with a linear temperature correction from the data-sheet coefficient. Low-light efficiency, angle of incidence and spectrum are not modelled.
  • The NOCT method estimates cell temperature for an open-rack mounting with light wind; roof-mounted panels with little air gap run hotter.
  • The daily estimate uses one average cell temperature and ignores shading, clipping during the day, AC cable losses and ageing.

References

  • IEC 61215 / IEC 61853 — module rating and NOCT (nominal operating cell temperature) conditions.
  • Dobos, A. P. (2014), PVWatts Version 5 Manual, NREL/TP-6A20-62641 (temperature correction and default losses).