U.S. Department of Energy

Advanced High Temperature Trough Collector Development

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Solar Millenium's Flagsol SKAL-ET heliotrough underwent prototype testing in a 1-MW loop at the SEGS plant in Kramer Junction, California.

The Solar Millennium Group and its subsidiary Flagsol, under the CSP R&D FOA, are completing work on an advanced parabolic trough collector that uses molten salt as a heat transfer fluid.


Solar Millennium has developed a preliminary design of an advanced geometry parabolic trough collector, designated NTPro. This follows the Flagsol SKAL-ET collector that was prototype-tested at the FPLE SEGS V plant at Kramer Junction, California, in 2002. The collector was selected for the Andasol 1 and 2 plants in Spain, the Kuraymat plant in Egypt, and early Solar Millennium commercial projects in the United States. The NTPro design has three primary goals: higher performance, lower cost, and the potential to operate with a molten salt heat transfer fluid (HTF). Solar Millennium and Flagsol intend to:

  • Complete the final design of selected components of the NTPro collector
  • Construct and test a prototype NTPro-VP1 (oil HTF) collector loop at the SEGS V plant at Kramer Junction, working with FPLE
  • Develop design modifications to the NTPro collector to enable operation with molten salt
  • Modify the prototype NTPro collector loop to accommodate salt HTF
  • Implement a prototype loop test of the NTPro-MS (molten salt HTF) collector.


Solar Millennium is the only awardee in the CSP portfolio currently exploring torque tube collector frames. The design employs counterweights, a large aperture (~6.7m), and fewer drives/foundations. It is being designed to operate with molten salt as the HTF. At the end of this project, Solar Millennium/Flagsol intends to have developed a large-aperture trough with increased efficiency and reduced LCOE for molten salt integration.

Publications, Patents, and Awards

At this time, this project does not have published articles, patents, or awards.

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Quarterly Progress Reports

CSP Program Overview

Learn about other DOE competitive awards for concentrating solar power research that are in progress.