Derivation of an index for evaluating economics of cogeneration systems and its applications

In this paper, a simple index for evaluating the economics of cogeneration systems (CGS) is first derived. Second, various strategies to improve the economics of a CGS is generally discussed. Finally, the impacts of the change in various factors determining the economics of a CGS are investigated, by taking a CGS composed of gas turbines and a waste heat boiler for district heating and cooling as an example. It has been shown that the index derived makes it possible to easily evaluate not only the economic feasibility of the CGS, but also the degree of the impacts of improvement in the following economic and technological factors on its economics: (i) rise of the unit selling price of electricity and heat, (ii) decrease of the fuel cost, (iii) reduction in the annual cost rate for the construction cost of the CGS, (iv) increase in the capacity factor of the CGS, (v) improvements in efficiencies of generating power and heat, and (vi) decrease in the construction cost of the CGS.