400m2 Big Dish Solar Concentrator

The ANU 400m2 dish is the world’s largest paraboloidal dish solar concentrator. It is currently operated with a monotube boiler receiver which produces superheated steam at up to 500oC, 4.5MPa. This dish is a prototype of a design that is ultimately intended for use in large scale solar thermal power generation systems, where large arrays of dishes are joined to feed energy to a central power generation plant. The group operates the dish, to obtain experimental data to support investigation into energy conversion processes, to seek design improvements and to support efforts to licence and commercialise the technology. At the end of 2004, the ANU reached agreement with the local company Wizard Information Systems (see www.wizardpower.com.au ) to licence the technology for commercial deployment. During 2005, this working relationship prospered, with Wizard and the ANU team securing a Business ACT Knowledge Fund Collaboration Grant, followed by an AusIndustry Renewable Energy Development Initiative grant later in the year.

Trough Concentrator Thermal Systems

The group operates a trough concentrator test-bed, that consists of a rotating horizontal platform onto which a short horizontal axis tracking trough unit is mounted. This system allows two axis sun-tracking so that short modules of trough systems that would normally be used in a long single axis tracking configuration, to be tested. At present the system has a 3.5m aperture trough system fitted with a prototype ammonia dissociation receiver. Other thermal conversion processes have also been investigated.

3m aperture trough concentrator system during ammonia dissociation experiments.

In 2005, the group collaborated with the CSIRO the National Solar Energy Centre in Newcastle on thermal trough ystem development. The CSIRO commissioned a survey of available trough concentrator and thermal energy conversion systems around the world. This was followed by the their purchase of 130 m2 of trough concentrator mirror modules for their Organic Rnakine Cycle power generation project. The troughs were manufactured at the Solar Thermal Group's workshop, and are an improved version of the units previously developed by the group for the Bruce Hall PV concentrator system. The tracking structure designed in collaboration with CSIRO personnel.

Mirror development

The ANU has developed a new solar reflector technology based on the application of thin, back-silvered, low-iron glass permanently bonded to a thin sheet metal substrate. Figure 6 shows a triangular prototype GOML™ solar reflector element for ANU’s 400 m2 dish.

Techniques have been developed to cost-effectively shape GOML™ base-units into high-performance parabolic as well as paraboloidal solar reflector panels, the latter ones using a structural cored sandwich design. Extensive optical and on-going accelerated-lifetime tests over the past 3 years have proven the technical maturity of this new solar reflector manufacture.

Concentrator characterisation

In the field of solar concentrator characterisation and performance analysis specific expertise has been developed in using videographic 'flux-mapping' of light distributions in the focal regions of solar concentrators (including troughs and dishes), and in the use of close-range photogrammetry to accurately determine the coordinates of concentrator surfaces. This latter technique allows distortions inherent in reflective surfaces to be quantified to a precision high enough to allow computer based ray-tracing algorithms to be employed to predict the ways that sunlight will reflect off the surfaces and concentrate in the focal region.

Efforts are directed in three areas:

1. Photogrametric surface measurement:
   This technique uses multiple photographs taken from different positions to deduce the three dimensional shape of a surface such as the mirror in a solar concentrator. Optical targets are placed on concentrator surfaces and a combination of digital photographic and image analysis techniques are used to achieve this aim.
   
2. Ray tracing for focal region flux prediction:
   Knowledge of real reflector surface shape allows raytrace calculations based on an assumed sun shape to be used to predict the distribution of radiation falling on objects such as receivers of various shapes, placed in the focal region.
   Focal region flux measurement:
   
3. Ultimately concentrator performance must be determined by a direct measurement of focal region flux distribution. This is done by placing a watercooled lambertian (ie uniform diffusely reflecting) white target in the focal region. digital images of the target are recorded and calibrated against a radiometer measurement obtained from a single representative point to deduce the overall distribution.

Theoretical investigations

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