THE SG4 BIG DISH

Introduction       Documentation     Background

 

The Australian National University campus is home to the “SG4” prototype 500m2 Big Dish Solar concentrator.   SG4 is the world’s biggest solar dish.

The design of SG4 is a systematic optimisation for cost effective mass production for utility scale power systems. It has achieved best practice optical performance with identical mirror panels and no time consuming individual alignment of mirrors.

Construction of the prototype on the ANU campus began in the first quarter of 2008. The first on sun test was carried out on 29 June 2009.

This sequence of photo’s covers the construction process from groundbreaking to on sun operation:

 

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 The Design

The mission was to design a large-area solar dish to produce energy at minimum installed cost, when mass produced on a large scale. Additional  requirements included minimising technical risk and maximising reliability. Being attractive to investors, ease of operator training and applicability to a range of energy conversion options, were considered. The design process followed rigorous systems-design principles and carefully considered the interactions between the key subsystems of structure, mirrors, receiver, foundation, and actuation, as each was developed in parallel.

Whereas the previous SG3 400m2 dish design relied on assembly of accurate prefabricated spaceframe components to produce the required accurate paraboloid, the SG4 design instead relies on a very accurate re-useable jig, to provide the accuracy of the frame supporting the optical surface. Novel fabrication techniques have been employed to form the frame on this jig in a manner that can be rapid and cost-effective.  A key element of this is the on-site production of roll-formed structural sections from steel coil stock.

Mirrors were identified as a key driver for the design. A Glass on Metal laminate approach using thin low iron back silvered glass mirrors can be a durable and effective. For dish mirrors, forming  multilayered cored panels provides a stiff panel design needed for optical quality and means that there is an opportunity to leverage this to a contribution to the overall dish structure. Such an integrated approach is key to a cost optimized outcome.

Features

  • A large aperture, Altitude Azimuth tracking dish
  • Engineered for mass production for sites requiring tens or hundreds of units
  • Formed on an accurate jig
  • Front surface of frame made from compliant sections roll formed on site
  • Space-frame based on circular pipe with simple welded joins
  • Identical spherical mirror panels glued to frame with no post installation alignment
  • Mirror panels contribute to dish structural integrity

Specifications

  • Aperture 494m2
  • Focal length 13.4m
  • Average diameter 25m
  • Average rim angle 50.1o
  • Mirror reflectivity 93.5%
  • Number of mirrors 380
  • Mirror size 1165mm x 1165mm
  • Total mass of dish 19.1t
  • Total mass of base and supports 7.3t
  • Concentration ratio at 95% capture 2,000x
  • Peak optical concentration 14,000x

Presentations

Many presentations at conferences and forums have been given over the period of design, construction and testing of the SG4 dish. These presentations overlapped in content to a considerable degree as different audiences were addressed at different times. They frequently included background material on the Concentrating Solar Thermal industry and other issues.  Here the power point slides used at 4 events at key times during the process are provided:

  1. A talk given at the Australian Academy of Science in April 2009 gave an update on construction progress in the context of the discussion on the future role of CSP. Lovegrove_AcademyOfSciience_April09 . A transcript of the talk can also be found on the Academy’s website  (add link).
  2. A talk at the SolarPACES conference in Berlin in 2009, provided a complete presentation on the SG4 project ending with the first optical tests. Lovegrove_BigDish_SolarPACES_Berlin09
  3. Similar ground was covered, with additional context on the CSP industry in a presentation to ‘Beyond Zero Emissions’ a Melbourne based think tank. They recorded the presentation and produced a transcript and downloadable slides and audio recording: http://bze.org.au/dr-keith-lovegrove-unveiling-new-big-dish-091207/with the slides also repeated at http://www.slideshare.net/beyondzeroemissions/dr-keith-lovegrove-unveiling-the-new-big-dish
  4. Two years later, a talk at the SolarPACES conference in Granada in 2011 provided results of performance tests with the first steam generating receiver. Lovegrove_BigDish_SolarPACES_Granada2011

 Videos

Jose Zapata recorded some time lapse photo sequences of some of the key steps in the construction of the dish, that have been converted to video and placed on you-tube.

This one records lifting of the dish frame off the assembly jig:

This one shows lifting it and mounting it to the base frame after the base frame had been constructed on the same location where the jig previously stood:

Subsequently, testing the Azimuth rotation of the completed dish and base frame assembly:

Early tests with the monotube boiler receiver fitted, with the steam released from a valve at the back of the receiver:

Awards

The innovations and achievements in the SG4 project have been recognised by two awards: