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Distant Observer

Tool Quickly Identifies Costly Flaws in Concentrating Solar Power (CSP) Fields

National Renewable Energy Laboratory

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Technology Marketing Summary

As we pursue efforts to lower the capital and installation costs of parabolic trough solar collectors, it is essential to maintain high optical performance. The Distant Observer (DO) tool, developed by engineers at the National Renewable Energy Laboratory (NREL), is a fast and highly accurate tool that provides complete characterization of the performance of the optical components which include the mirror panels and thermal receiver. This tool is very useful for testing both prototype and operational modules.

Description

The Distant Observer is an optical measurement tool for parabolic solar collectors that measures reflector slope error, absorber position error and the combined errors, as seen in Figure 1. Reflector slope errors occur for many reasons including imperfection in structural frame design, manufacturing and assembly. Absorber position error can be caused by poor structural design, poor installation, sag from the absorber weight, or change in the structure over time. If not properly monitored and fixed they may result into a significant loss of energy generation. The collector performance metrics, the intercept factor, can be readily derived to accurately capture solar plant power performance by measuring the reflector slope error and absorber position error.

The DO requires the minimal equipment and setup for fast and accurate field measurements. A digital camera is used to collect the reflected image of the absorber in the collector. The camera can be set up on the ground using a camera tripod, a truck, and a lift; it also can be mounted to a drone to fly over the solar field, as seen in Figure 2. After acquiring photograph images of the test module at specific and different camera locations, a sophisticated software will be used to post-process the images and derive the optical error over the reflector surface. The reflector slope error combining the impact of the absorber position error is illustrated in Figure 3. 

The DO combines hardware and software capable of acquiring data within both laboratory or field environments and analyzing the results. The DO software provides a user-friendly interface that allows for easily performing complex image analysis operations resulting in a complete description of the optical metrology of the linear concentrating system. 

Advantages

Flexible

  • Any collector angle
  • Stationary or Rotating collector
  • Ground-based camera or drone-driven camera

Thorough

  • Surface profile
  • Absorber position
  • Gravitational effects

Fast

  • 2 seconds per collector using drone-driven camera
  • Capable of full-plant characterization

Accurate

  • Slope error uncertainty: less than +0.5mrad
Benefits
  • Assists in the design of parabolic troughs
  • Easily scalable to measure full solar fields
  • Allows plant operators to quickly spot errors
  • Keeps plant operating at maximum efficiency
  • Reduces plant operating costs
  • Minimal equipment and setup required 
Applications and Industries

Concentrated Solar Power (CSP)

Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL SWR 12-09DevelopmentAvailable08/07/201508/07/2015

Contact NREL About This Technology

To: Doreen Molk<doreen.molk@nrel.gov>