Exergy and economic analyses of replacing feedwater heaters in a Rankine cycle with parabolic trough collectors

Fossil fuels are exhaustible and their consumption causes environmental problems. As a result, renewable energy resources, specifically solar energy, should be utilized more to overcome the aforementioned issues. The biggest problem with renewable energy utilization is that their capital cost is very high. To tackle this problem, renewable energies should be coupled with conventional energy systems to lower the initial investment. In this paper, a parabolic trough collector is coupled with a conventional Rankine cycle to increase output power of the system by replacing its closed feedwater heaters. Also, to be able to use the system during the nights, a thermal storage system is added to the cycle. A complete energy, exergy and economic analyses are performed on the system and the results are compared with the base case condition. The results show that by using the proposed system, net generated power of the plant increases by 8.14%. Also, exergy analysis shows that in both cases boiler has the highest rate of exergy destruction. In general, due to huge amount of losses in the collector, exergy efficiency of the system decreases. Finally, economic analysis shows that simple payback time of the system equals to 1.5 years which is very low.