SolarPILOT: A Power Tower Solar Field Layout and Characterization Tool

Michael J. Wagner, Tim Wendelin

Research output: Contribution to journalArticlepeer-review

135 Scopus Citations


This paper develops and demonstrates a new Solar Power tower Integrated Layout and Optimization Tool (SolarPILOT). The tool uses the analytical flux image Hermite series approximation originally implemented in the DELSOL3 software developed by Sandia National Laboratory in the early 1980s. By applying the analytical model to individual heliostat images rather than large groups or zones of heliostats, SolarPILOT can characterize a wide variety of heliostat field layouts. The individual heliostat modeling approach increases computational expense in comparison with DELSOL3, so SolarPILOT implements a number of improvements to the analytical approximation method to improve model accuracy and computational efficiency. This paper discusses several of these methods, including dynamic heliostat grouping to reduce the expense of intercept factor evaluation, approximation of annual productivity with a subset of time steps throughout the year, polygon clipping to accurately calculate inter-heliostat shadowing and blocking, receiver and tower geometry optimization, and a trigonometric image transformation technique that ensures model accuracy for small heliostats. SolarPILOT also integrates a Monte-Carlo ray tracing engine (SolTrace), providing improved receiver optical modeling capability, a user-friendly front end for geometry definition, and side-by-side validation of the analytical algorithms.

Original languageAmerican English
Pages (from-to)185-196
Number of pages12
JournalSolar Energy
StatePublished - 1 Sep 2018

Bibliographical note

Publisher Copyright:
© 2018

NREL Publication Number

  • NREL/JA-5500-66106


  • Heliostat layout
  • Optical characterization
  • Power tower
  • Simulation optimization
  • SolarPILOT


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