D. Mills*, G. L. Morrison**, and P. Le Lievre***

*School of Physics
University of Sydney
Sydney Australia.

E-mail: d. mills@physics. usyd. edu. au

**School of Mechanical and Manufacturing Engineering
University of New South Wales
Sydney Australia 2052
E-mail: g. morrison@unsw. edu. au

***Solar Heat and Power Pty. Ltd. (SHP)

2 Chifley Square, Sydney NSW 2000, Australia
E-mail: peter@solarheatpower. com

In this paper, the general design philosophy for a large 240 MWe 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) and currently being constructed for a coal fired plant preheating project. In the stand-alone solar plant, the costs of hybrisation with fossil fuel are found to be high, and lower temperature operation seems more cost-effective. The advantage gained by low temperature operation derives from an unusual combination of large low cost low temperature turbines developed for the nuclear industry, and an inexpensive storage concept which suits that particular temperature range. Should both options be applicable, then this may be the most cost-effective solar thermal electricity development path. Comparison of solar electricity cost against a typical 400 MWe coal fired plant in the USA suggests similar cost/performance without green incentives.

Introduction

There has been much emphasis placed in the past on the adaptation of high temperature fossil fuel turbines to solar energy, with an attendant ability to utilise fossil fuel for backup energy. However, there has been a recent shift of interest to 100% solar plants because of the strict incentives that have been set up in countries like Spain, and Germany. Fully renewable operation is also advantageous in tradeable renewables certificates programmes like that of Australia, because the investment in the power block can be repaid at a higher rate.

In the past, it has been usually presumed that primary fossil fuel in large quantities is cheaper than solar heat. We think of solar energy as expensive. Perhaps we should be thinking that the handling of fossil fuel is also expensive. Recent results of a tender in Cyprus for a 120 MW oil fired fossil fuel plant were Turbines: 42.7%;

Boilers: 31.6%; Flue Gas Desulpherisation: 14.1%; Transformers: 11.6%. Boilers and fossil fuel treatment are about 45% of the cost. The cost of 20 years of oil is very similar to the avoided fossil fuel equipment. Perhaps 2/3 of the lifecycle cost of this plant is directly related to either fossil fuel handling or fossil fuel price.

Hybridisation with fossil fuel is used to give solar more reliability in the absence of storage. However, the price paid by a solar system for hybridisation is high, because the solar system must be made compatible in output temperature with the fossil fuel system, and because the actual cost of equipment to handle, combust and dispose of fossil fuel waste is also surprisingly high. A turbine system and storage unit optimally designed for pure solar heat may be very different from that which is designed for a solar/fossil hybrid.