Conventional power plants for the generation of electrical energy such as combined cycle power plants can be operated in combination with renewable energy sources in order to reduce the CO2 emissions for a given electric power production. When renewable energy sources such as wind or solar energy are available and made to contribute to the electrical power production, a fossil fuel fired combined cycle power plant can be operated at part-load and still produce the full electric power. However, the efficiency of a combined cycle power plant during its part load operation is typically less than its efficiency at full load. The specific CO2-emissions at part-load operation of the combined cycle power plant are then increased, and the reduction in CO2 emissions due to the implementation of renewable energy sources is again diminished.
DE19627425 discusses a combined cycle power plant, where feed water of the water-steam cycle of the steam turbine is led into a solar steam generator and the resulting solar steam is added to steam generated by the heat recovery steam generator of the power plant. The mixture of the two steam flows is superheated for use in the steam turbine. During operation using the solar steam generator only, preheated feedwater is led into the solar generator and the steam generated there is led directly to the steam turbine.
US Patent number US2009/0235634 discusses a system that allows extending the turndown range of a turbomachine during partload operation. The turndown range is defined there as the loading range of the machine, within which the machine operates while maintaining emissions compliance. The extension of the partload operation turndown range is realized by the use of a heat source external to the turbomachine, such as solar heat, for the preheating of inlet air to the compressor of the turbomachine. The preheating of the inlet air results in a higher temperature of the air exiting the compressor and entering the combustion chamber. Effectively, less fuel is then needed to reach a necessary firing temperature of the gas turbine.
GB2449181 discusses a power plant comprising a gas turbine and a solar hybrid cycle, where heat provided to air after the gas turbine compressor and prior to the combustion process is supplied by direct solar heat. The heating of the air is realized by direct heat transfer from solar radiation to the air generating high air temperatures above 350° C. The concept allows for higher temperatures at which energy is extracted from the thermodynamic cycle of the gas and steam turbines yielding a higher power output and greater cycle efficiency.