PlantPredict simulates the electricity production from a photovoltaic power plant. This document outlines the PlantPredict’s algorithmic capabilities. The formal software architecture, graphical user interface, and implementation details are not contained in this document.
At a top level, as illustrated in Figure 1, the input to PlantPredict consists of a time series of environmental
inputs such as irradiance, temperature, and a static power plant using a nested hierarchy of subassemblies to create
a representation of a photovoltaic power plant. A set of model choices, simulation settings, and controls allow
the user to combine the weather and power plant model into an executed prediction.
The output of the tool can be compared to the monitoring points in the actual power plant (irradiance, array current & voltage, power meter) to benchmark the tool performance against actual generation.
Figure 1. PlantPredict Overview
Power Plant Characteristics
From a modeling perspective, a solar power plant is comprised of the following hierarchy of building blocks, as shown in Figure 2. A set of photovoltaic modules is electrically connected in series to obtain the desired DC system voltage. The strings are then connected in parallel through a hierarchy of wire harnesses and combiners to achieve the desired current rating appropriate for the DC input to the inverters.
The parallel aggregation of harnesses into combiner boxes and DC inputs to the inverter terminal will be treated monolithically by the simulation engine; i.e. I(V) curves of the individual modules will be scaled in parallel and series to generate the “effective” I(V) curve seen by the inverter, with allowances made for module mismatch and DC health losses. Physically, the matrix of modules are arranged in tables and rows into DC Fields surrounding a Power Conversion Station housing one or more inverters, collectively referred to as an Array.
Figure 2. Power Plant Nomenclature
The inverters attempt to bias the DC Fields at the optimum maximum power point, and transform the DC current into a low-voltage 3-phase AC current which is then transformed to a medium voltage (MV) by an adjacent transformer. The output of several Arrays are daisy-chained through underground AC cabling to a photovoltaic combining switchgear, collectively referred to as a Block, which aggregate the current into larger conductors suitable for underground or above-ground conductors for transmission to the on-site substation.
At the System onsite substation, a further high-voltage (HV) transformer steps the voltage up to the grid voltage, the actual point of interconnection (POI). The overall energy conversion process is shown in Figure 3