Low cost solar array design

In this paper, the general design philosophy for a large pure solar storage plant is discussed. The proposed stand alone plant design will use the same low cost Compact Linear Fresnel Reflector (CLFR) array system previously reported (Mills et al, 2003; Hu et al, 2003) as is being constructed for a coal fired plant preheating project of 35 MWe integrated with a coal-fired plant. This current coal saver project has been now been re­estimated to be 40 MWe. The project, being built for Macquarie Generation, is composed of three stages; a proving array of 1100 m2, an intermediate array of 20236 m2, and a final array of 134909 m2. After stage 3 is built, it will be the largest solar electricity plant built since the last LS3 parabolic trough field built in California in 1990, and will provide a solar electricity capacity about 3 times the current PV capacity of Australia. The kWh cost of the first plant is expected to be similar to, or below, current

wind technology in Australia.

The array system is linear like a parabolic trough collector, but it has many advantages over troughs which allow significant cost reductions, such as a long focal length with allows elastically bent flat standard glass reflector to be used.

Fig. 1. The Stage 1 array and tower line produced by SHP at the Liddell power plant site.

The array technology used in this project is of the Linear Fresnel type and was originally developed at the University of Sydney (Mills and Morrison,1999). It is called the Compact Linear Fresnel Reflector (CLFR) technology. In this approach, ground level reflector rows aim solar beam radiation at a downward facing receiver mounted on multiple elevated parallel tower lines. The technology is innovative in that it allows reflectors to have choice of two receivers so that a configuration can be chosen which offers minimal mutual blocking of adjacent reflectors and minimum ground usage. However, there are also many
supporting engineering innovations in the commercial product, including highly rigid space frame mirror supports with 360° roatation capability, long horizontal direct steam generation cavity receivers, and array fine tracking control electronics. The design of the CLFR array design incorporates high volume production elements to reduce engineering cost.

The authors have previously described some of the cost advantages of the CLFR array system (Mills et al, 2003) of the current trough technology, but have not discussed the general issue of overall stand-alone solar plant design. The traditional approach to the design of a line focus solar plant is to use a parabolic trough system to the supply of heat at between 320°C and 400°C to the main boiler and superheater of a conventional turbogenerator (NREL, 2003). Some higher cost trough designs utilise fossil fuel in off — solar hours, not only to increase the plant capacity factor, but to lower the overall cost of delivered energy. The present CLFR design can also be straightforwardly adapted in this direction. However, in trough and CLFR systems, thermal losses can rise rapidly with array operating temperature, partially cancelling out improvements in thermal conversion efficiency. In addition, the traditional path of using a superheated turbine requires more highly efficient and durable selective coatings, thicker-walled tubing for steam pressure containment, and the use of oil instead of water as a heat transfer fluid if operating above the water triple point.