The concept of integrating the parabolic collectors into the cycle is illustrated in Fig. 6. The temperature level of the solar steam is high enough to be integrated into the high – pressure preheater section and to preheat a part of the boiler feedwater. Thus the preheater’s steam consumption is reduced and the steam remaining in the turbine can be used for an additional power generation. The condensate leaving solar preheater 1 is still at a temperature level to preheat a part of the feedwater in the low pressure preheating section (solar preheater 2). The main part of the feedwater is heated in the preheaters 1 to 4 by extraction steam conventionally.
The integration of external solar generated steam into the water steam cycle of conventional steam power plants is a promising concept to promote renewable energy and as a consequence to reduce the CO2 emissions. The simulation results based on meteorological data of a location in Italy show a power increase following the solar irradiance characteristic nearly without any time delay. This can be managed even with simple control strategies. Since the peak of electricity consumption is usually to be found at noon, the additionally produced power matches very well the electricity demand of industrial countries.
The efficiency factor defined as the ratio of the parabolic trough thermal power output integrated into the cycle and the achievable electrical power increase at the steam turbine’s generator amounts 28% maximum.