An alternative case can be made for a design which minimises array thermal losses using low temperature (200°C — 300°C) saturated steam Rankine cycle turbines. Although some effort has been made to look at low temperature trough systems using small organic rankine cycle turbines (NREL, 2002), in this temperature range, higher efficiency demands a large turbine. The array cost of the CLFR is low enough that the added cost of fossil hybridisation is relatively high. For low cost and reliability, one needs a proven system stripped of expensive fossil fuel equipment.

Such systems exist. The nuclear power industry has spent many years and huge sums developing non-fossil fuel turbines which, at about 31-33%, are more efficient than smaller organic rankine cycle plants. These turbines operate from wet steam, using steam separators to dry out the steam before entering the turbine, and they use special turbine blade design. No superheating stage is required, so the solar array needs only meet the main boiler operating temperature, which in the case of the VVET is only 250°C. If one were to design a turbine type to to suit a large solar direct steam generation array like the CLFR, it would be something close to the VVER design, although there might be a case for operating in the range 300°C — 350°C to increase thermodynamic efficiency. Operation at 250°C allows significantly lower array losses than operation at 450-500°C as proposed for advanced trough systems (NREL, 2003) and allows the use of a wider variety of air stable selective coatings on the receiver. Steam pipes are also substantially cheaper at the lower temperature range.

However, the smallest nuclear turbines one can obtain are of about 240 MWe peak capacity, which would lead to a solar plant larger than any yet built. The low temperature turbine costs used in the paper are based upon approximate estimates (VVER, 2003) supplied by JSC “Atomstroyexport” (Russia). The supply of a 240 MWe VVER steam turbine and steam separator and control equipment of about US$18
million for a single turbine, well below high temperature turbine cost. It is conservatively assumed in this paper that an additional 1/3 will be added to the turbogenerator price to cover delivery and installation. Several sites have been found in Australia with excellent solar radiation and grid access. The most attractive of these has enough spare grid capacity for a 240 MWe installation.