Prospect PV simulator electrical simulation

In this document

This document describes the electrical simulation stage of the Prospect PV simulator. It explains how the effective GTI values from the optical simulation are converted into AC power output at the inverter terminals, including all electrical losses along the way.

Overview

The electrical simulation follows directly after the optical simulation in the Prospect PV simulation chain. It takes the spectrally corrected cell GTI (GTI_eff) produced by the optical stage and converts it into AC power output, tracking all electrical losses from the PV cell through to the inverter output.

This stage uses the same core models as the Argus PV simulator — De Soto's single diode model for cell I-V curve generation and the Sandia inverter model for DC/AC conversion — implemented with computational optimizations that make them practical for the Prospect simulator's high-throughput, portfolio-scale use case. The key optimization is a pre-computed I-V curve lookup table with bilinear interpolation, which avoids recalculating the Lambert W function for every cell at every time step while preserving accuracy across the full range of operating conditions.

The Prospect simulator models partial shading at the string level with bypass diode logic, capturing the non-linear losses caused by shading of individual sub-modules. The final output of this stage — AC power at the inverter terminals — is then adjusted for AC and transformer losses and post-processing factors (snow, technical availability) to produce the final energy yield.

Processes included in this stage

The following processes are applied sequentially during the Prospect simulator electrical simulation:

Cell temperature calculation (NOCT-based thermal model)
Single diode model and I-V curve generation (De Soto, with lookup table and bilinear interpolation)
PV field simulation — string aggregation with bypass and blocking diodes
DC losses (mismatch and cabling, combined factor)
Inverter DC/AC conversion (Sandia inverter model, MPP tracking)
AC and transformer losses
Post-processing losses (snow, technical availability)

Electrical simulation

Cell temperature

Cell temperature is calculated from air temperature and the effective GTI using the NOCT_MODEFF_WS model — a NOCT-based thermal model extended with a wind speed correction term.

The effective NOCT combines the module's nominal operating cell temperature with a mounting type correction (moduleNOCT + mountingNOCTcorrection). The module efficiency term is estimated from the module's nominal power, physical dimensions, and a cell-to-module area ratio of 0.95.

The effective GTI input accounts for shading (horizon, near-shading, and self-shading), soiling, angular losses, and spectral correction. For bifacial modules, front and rear irradiance contributions are combined.

Note: The Prospect simulator uses a static NOCT-based temperature model, while the Argus PV simulator uses a transient weighted moving-average thermal correction model. The NOCT approach is well suited to the representative-day, percentile-aggregated input structure of the Prospect simulator.

Single diode model and I-V curve generation

De Soto's single diode model generates current-voltage (I-V) curves for each PV cell from five reference parameters — modified ideality factor, diode saturation current, photocurrent, series resistance, and shunt resistance — adjusted to the actual cell GTI and temperature.

An I-V curve for any given GTI and temperature is reconstructed by bilinear interpolation of the four nearest curves in the lookup table. The table uses adaptive sampling — more sample points are placed around the knee of the I-V curve — and supports a configurable number of points per curve.

For full details on the single diode model, see PV conversion model.

PV field simulation — string aggregation

The simulator iterates over all strings in the field. For each string, cells are classified as fully lit, fully shaded, or partially shaded based on the direct shadow and diffuse shading information from the optical stage.

String I-V curves for all strings connected to one inverter are then combined at constant voltage, with blocking diodes applied, to produce the total I-V curve at the inverter input.

DC losses

DC mismatch and cabling losses are applied as a combined multiplicative factor to the maximum power point of the inverter input I-V curve before it is passed to the inverter model. Both loss percentages are user-configurable simulation parameters.

Inverter DC/AC conversion

The Sandia (SAM/SNL) inverter model converts the DC maximum power point to AC output power as a function of DC voltage and DC power. Strings are assigned to inverters automatically. The last string on each inverter may contain fewer modules than the others.

For full details on the Sandia inverter model, see Inverter model.

AC and transformer losses

AC transformer and cabling losses are applied as percentage reductions to the AC output after inverter conversion.

Post-processing losses

Two additional loss factors are applied after the electrical simulation to produce the final AC output:

Snow losses — applied as a percentage reduction.
Technical availability — applied as a percentage reduction.

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