Heliostat Optical Error Inspection with Polarimetric Imaging Drone

TL;DR

This paper introduces a polarimetric imaging drone system that significantly improves the contrast and accuracy of heliostat mirror edge detection in CSP fields, enabling fast, non-intrusive, autonomous inspection during operation.

Contribution

The study develops a novel polarimetric imaging method integrated on UAVs, enhancing contrast for heliostat inspection and demonstrating its effectiveness through field tests.

Findings

Enhanced edge detection success rate in challenging scenarios

Improved imaging contrast with polarimetric method

Feasibility of real-time autonomous heliostat inspection

Abstract

On a Concentrated Solar Power (CSP) field, optical errors have significant impacts on the collection efficiency of heliostats. Fast, cost-effective, labor-efficient, and non-intrusive autonomous field inspection remains a challenge. Approaches using imaging drone, i.e., Unmanned Aerial Vehicle (UAV) system integrated with high resolution visible imaging sensors, have been developed to address these challenges; however, these approaches are often limited by insufficient imaging contrast. Here we report a polarimetry-based method with a polarization imaging system integrated on UAV to enhance imaging contrast for in-situ detection of heliostat mirrors without interrupting field operation. We developed an optical model for skylight polarization pattern to simulate the polarization images of heliostat mirrors and obtained optimized waypoints for polarimetric imaging drone flight path to capture images with enhanced contrast. The polarimetric imaging-based method improved the success rate of edge detections in scenarios which were challenging for mirror edge detection with conventional imaging sensors. We have performed field tests to achieve significantly enhanced heliostat edge detection success rate and investigate the feasibility of integrating polarimetric imaging method with existing imaging-based heliostat inspection methods, i.e., Polarimetric Imaging Heliostat Inspection Method (PIHIM). Our preliminary field test results suggest that the PIHIM hold the promise to enable sufficient imaging contrast for real-time autonomous imaging and detection of heliostat field, thus suitable for non-interruptive fast CSP field inspection during its operation.