CO2 mitigation through the use of hybrid solar-combined cycles

Abstract

The integration of a solar collector field generating steam into a conventional combined cycle in order to partially replace the fossil fuel required by the latter results in a substantial reduction in greenhouse gases, in an increase in the return on investments associated with the solar field and in an almost complete elimination of the need for solar energy storage. This paper discusses the design of such an integrated hybrid solar-fossil combined cycle with maximum daily and nightly power outputs of 88 MWe and 58 MWe, respectively. This cycle is currently being evaluated from a technical and economic risk feasibility standpoint for possible implementation as a pilot plant in Tunisia. This paper outlines pertinent design considerations utilized in the thermoeconomic optimization approach employed for developing the hybrid combined cycle proposed here. The approach shows that there are several advantages to this type of design when compared with a purely solar steam cycle or any of the several other hybrid solar concepts which exist today. In addition to these advantages, the design presented revolves around the definition of a number of degrees of freedom which allow the solar energy part of the cycle to be highly integrated into the conventional part. A discussion of them is given. Finally, from an environmental standpoint, the obvious advantage of this type of cycle is that due to the substitution of fossil fuel, there is a marked mitigation in CO2 and NOx emissions when compared to a conventional cycle and to other hybrid concepts. Pertinent results for these reductions are presented.