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PlantPredict

Models & Algorithms

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Summary

This section provides technical documentation of the physical and empirical models that form PlantPredict’s prediction engine. Each page describes a specific model or algorithm used to simulate solar PV system performance, from solar resource assessment through grid-delivered power including optional battery energy storage.

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Purpose and Scope

The Models & Algorithms section documents the calculation methods used in PlantPredict Version 12 to predict energy production from utility-scale solar photovoltaic systems. These models translate solar physics and electrical engineering principles into quantitative predictions of system performance under varying environmental and operational conditions. The prediction engine is organized into five main stages that correspond to the physical energy conversion process:

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Stage 1: Irradiance Calculation

From solar resource characterization (sun position, horizontal irradiance components, and system geometry) to effective plane-of-array irradiance:
  • sun Position & Extraterrestrial Irradiance: Solar position algorithm, sunrise/sunset times, extraterrestrial irradiance, and correction
  • Horizontal Irradiance Data Processing: Weather data quality control and, if needed, diffuse-direct
  • System Geometry: Fixed-tilt and single-axis tracker orientations, including tracking algorithm (true tracking, backtracking, or terrain-aware backtracking)
  • Models: Converting horizontal irradiance components to plane-of-array irradiance, including 3D transposition
  • Shading Models: Horizon shading, sky diffuse shading, ground-reflected shading, direct beam shading (geometric, legacy 3D, or detailed 3D scene), and electrical shading effects
  • Plane-of-Array Irradiance: Soiling, incidence angle modifiers, spectral corrections, and bifacial irradiance gain

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Stage 2: Photovoltaic Conversion

From plane-of-array irradiance to module-level DC electrical power:
  • Cell Temperature: Thermal models for cell temperature estimation (Heat Balance, Sandia, NOCT-SAM, or measured surface temperature)
  • DC System Losses: Mismatch, module quality, LID, and DC health losses applied to effective irradiance
  • DC Performance Models: Single diode model, recombination models, and temperature coefficients
  • Degradation: Time-dependent power reduction due to module aging, applied to DC power or AC energy depending on model selection

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Stage 3: DC–AC Conversion

From module-level DC power to inverter-level AC power:
  • Inverter Models: Temperature derating, DC field aggregation, operating regions, and efficiency

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Stage 4: AC Collection and Interconnection

From inverter-level AC power to grid-delivered energy:
  • AC Losses: MV/HV transformer losses, AC collection, transmission, availability, and grid limits

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Stage 5: Energy Storage

Optional battery energy storage system integrated with PV:
  • Dispatch Algorithms: LGIA excess, energy available, and custom dispatch modes
  • Battery State: State of charge tracking and degradation modeling
  • ESS Losses: Round-trip efficiency, inverter, transformer, and HVAC losses
  • PV+Storage Integration: Combined power flow through HV equipment to grid

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Documentation Structure

Each model page follows a consistent structure:
  • Title: Clear, descriptive model name
  • Summary: Concise description of the model purpose and outputs
  • Inputs: Table listing all input parameters with symbols, units, and descriptions
  • Outputs: Table listing all output parameters with symbols, units, and descriptions
  • Detailed Description: Complete mathematical description of the model, including equations and algorithmic steps
  • References: Academic and technical references for the model
Overview pages within each stage provide navigation and describe the relationships between models within that section. The Prediction Model Flow page provides a complete walkthrough of the calculation sequence.

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Version 12 Focus

This documentation describes models as implemented in PlantPredict Version 12. Where Version 12 differs from previous versions, those differences are explicitly noted. New features in Version 12 include:
  • Site-Level 3D Scene Shading: Polygon clipping algorithm for fast, accurate shade calculations across entire site
  • Terrain-Aware Backtracking (TABT): Optimization of tracker angles accounting for local terrain slopes
  • 3D Transposition: Bay-to-bay (tracking systems) or rack-to-rack (fixed-tilt systems) irradiance variations in 3D scene calculations
  • Enhanced Bifacial Modeling: Improved rear-surface irradiance calculations with view factors
  • Quadratic AC Collection Losses: Load-dependent AC collection system losses
  • Battery Energy Storage: Dispatch algorithms, degradation modeling, and PV+storage integration

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Conventions

All models in this documentation follow consistent conventions for units, angles, and coordinate systems. Key conventions include:
  • Azimuth angles: Measured clockwise from north (0° = North, 90° = East, 180° = South, 270° = West)
  • Tilt angles: Measured from horizontal (0° = horizontal, 90° = vertical)
  • Zenith angles: Measured from vertical (0° = overhead, 90° = horizon)
  • Irradiance units: W/m² unless otherwise specified
  • Temperature: Celsius unless otherwise specified
  • Pressure: hPa (hectopascals) unless otherwise specified