Freeform solar concentrator with a highly asymmetric acceptance cone

Brian Wheelwright, J Roger P Angel, Blake Coughenour, Kimberly Hammer

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

A solar concentrator with a highly asymmetric acceptance cone is investigated. Concentrating photovoltaic systems require dual-axis sun tracking to maintain nominal concentration throughout the day. In addition to collecting direct rays from the solar disk, which subtends ∼0.53 degrees, concentrating optics must allow for in-field tracking errors due to mechanical misalignment of the module, wind loading, and control loop biases. The angular range over which the concentrator maintains <90% of on-axis throughput is defined as the optical acceptance angle. Concentrators with substantial rotational symmetry likewise exhibit rotationally symmetric acceptance angles. In the field, this is sometimes a poor match with azimuth-elevation trackers, which have inherently asymmetric tracking performance. Pedestal-mounted trackers with low torsional stiffness about the vertical axis have better elevation tracking than azimuthal tracking. Conversely, trackers which rotate on large-footprint circular tracks are often limited by elevation tracking performance. We show that a line-focus concentrator, composed of a parabolic trough primary reflector and freeform refractive secondary, can be tailored to have a highly asymmetric acceptance angle. The design is suitable for a tracker with excellent tracking accuracy in the elevation direction, and poor accuracy in the azimuthal direction. In the 1000X design given, when trough optical errors (2mrad rms slope deviation) are accounted for, the azimuthal acceptance angle is +/-1.65°, while the elevation acceptance angle is only +/-0.29°. This acceptance angle does not include the angular width of the sun, which consumes nearly all of the elevation tolerance at this concentration level. By decreasing the average concentration, the elevation acceptance angle can be increased. This is well-suited for a pedestal alt-azimuth tracker with a low cost slew bearing (without anti-backlash features).

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSPIE
Volume9175
ISBN (Print)9781628412024
DOIs
StatePublished - 2014
EventHigh and Low Concentrator Systems for Solar Energy Applications IX - San Diego, United States
Duration: Aug 19 2014Aug 20 2014

Other

OtherHigh and Low Concentrator Systems for Solar Energy Applications IX
CountryUnited States
CitySan Diego
Period8/19/148/20/14

Keywords

  • acceptance angle
  • CPV
  • Solar concentration
  • tracking

ASJC Scopus subject areas

  • Applied Mathematics
  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Fingerprint Dive into the research topics of 'Freeform solar concentrator with a highly asymmetric acceptance cone'. Together they form a unique fingerprint.

  • Cite this

    Wheelwright, B., Angel, J. R. P., Coughenour, B., & Hammer, K. (2014). Freeform solar concentrator with a highly asymmetric acceptance cone. In Proceedings of SPIE - The International Society for Optical Engineering (Vol. 9175). [917505] SPIE. https://doi.org/10.1117/12.2060754