Solar PV Workspace

What This Solar PV Calculator Solves

This photovoltaic power calculator estimates the real-world electrical output of a solar array from a small set of design inputs: the number of modules, each module's nameplate STC rating, the plane-of-array irradiance, the cell temperature, the module's temperature coefficient, the inverter efficiency, and the local peak sun hours. It returns DC power before the inverter, AC power delivered to the load or grid, estimated daily energy yield in kWh, and an overall system efficiency metric. It is a first-pass sizing and yield-estimate tool, not a full bankable energy model.

Governing Equations

Module nameplate ratings are specified at Standard Test Conditions (STC): 1000 W/m² irradiance, 25 °C cell temperature, and AM1.5 spectrum. Real operation rarely matches STC, so the DC power is corrected for actual irradiance and cell temperature:

P_dc = N · P_mod · (G / G_stc) · (1 + γ · (T_cell − 25))

where N is the number of modules, P_mod is the STC rating in watts, G is the plane-of-array irradiance in W/m², G_stc = 1000 W/m², γ is the power temperature coefficient (typically around −0.0035 per °C for crystalline silicon), and T_cell is the cell temperature in °C.

AC power after the inverter is:

P_ac = P_dc · η_inv

Daily energy yield is approximated by multiplying AC power by the site's peak sun hours (PSH), which represent the equivalent number of hours at 1000 W/m²:

E_daily = P_ac · PSH

The system efficiency compares delivered AC power to the array nameplate:

η_sys = P_ac / (N · P_mod)

Calculation Method

The calculator follows a standard PV yield sequence:

1. Scale the array nameplate power from module count and STC rating.
2. Apply the irradiance ratio G / G_stc.
3. Apply the linear temperature correction using γ and (T_cell − 25).
4. Multiply by inverter efficiency to obtain AC power.
5. Multiply AC power by peak sun hours for daily energy.
6. Divide AC power by nameplate power for system efficiency.

Input Parameters

Panel count (N) scales the array linearly. Errors in panel count propagate directly to all downstream outputs.

Module STC power (P_mod) is the nameplate rating in watts at 1000 W/m² and 25 °C. Using a nameplate from a different module family than the one installed is a common modelling mistake.

Irradiance (G) is the plane-of-array irradiance actually received by the modules, not the horizontal global irradiance. Tilt and azimuth substantially change this value.

Cell temperature (T_cell) is the operating cell temperature, typically 20–35 °C above ambient in full sun. Using ambient temperature instead of cell temperature underestimates the thermal derating.

Temperature coefficient (γ) is negative for silicon modules (around −0.3 to −0.45 %/°C of P_max). It must be entered in consistent fractional units, not as a percentage.

Inverter efficiency (η_inv) is typically 94–98 % for modern string and central inverters at rated load; part-load efficiency is lower.

Peak sun hours (PSH) is a site- specific daily energy resource metric, not simply the number of daylight hours.

Engineering Interpretation

The performance ratio (PR) is the ratio of actual AC energy to the irradiance-scaled nameplate energy. It is a compact health metric for a PV plant: a well-designed, clean, well-ventilated system in a temperate climate typically achieves PR in the 0.75–0.85 range. Values below that range suggest soiling, shading, thermal problems, inverter clipping, or mismatch. Note that the DC/AC power and daily energy computed here are first-order estimates and are not a substitute for a full yield assessment using time-series irradiance and temperature data.

Units and Conversion

The calculator uses irradiance in W/m², power in W or kW, energy in kWh, temperature in °C, and efficiency as a dimensionless fraction. Useful conversions include 1 kW = 1000 W, 1 MWh = 1000 kWh, and 1 %/°C = 0.01/°C for temperature coefficients. Because P_dc is linear in both irradiance and (1 + γ·ΔT), a unit slip in γ — for example, entering −0.35 instead of −0.0035 — produces a physically impossible result.

General Case vs. Simplified Case

This tool computes a single operating-point estimate from steady inputs. A full PV yield model would integrate time-series irradiance and cell temperature, apply the one-diode or Sandia model of the module, account for IAM (incidence angle modifier) losses, soiling, shading, mismatch, DC and AC wiring losses, inverter part-load efficiency and clipping, transformer losses, and availability. This workspace intentionally covers the dominant first-order effects only.

Assumptions and Limitations

• Irradiance and cell temperature are treated as constant steady-state values.
• The temperature correction is linear in ΔT, using a single coefficient.
• No soiling, shading, mismatch, or wiring losses are included.
• Inverter efficiency is assumed constant, independent of load.
• Peak sun hours are treated as an equivalent full-power duration.
• Module degradation, ageing, and spectral effects are not modelled.
• No MPPT, string sizing, or code-compliance check is performed.

Practical Engineering Use

This solar PV calculator is useful during early system design and quick feasibility studies: estimating array output for a given roof area, comparing module choices in a hot climate where temperature derating matters, sanity-checking an installer's production estimate, or evaluating how much daily energy a target load requires in kWh. It is not a substitute for a full PVsyst, SAM, or equivalent yield study, nor for electrical code compliance, structural verification of the mounting system, or utility interconnection requirements.