Thermo-ecological cost analysis of cogeneration and polygeneration energy systems - Case study for thermal conversion of biomass

The aim of the paper is the thermo-ecological cost analysis of cogeneration and polygeneration energy systems. Within the paper biomass-fired CHP plants and their integration with thermal conversion of biomass units are investigated. In order to estimate the environmental effects of integration, the allocation of the thermo-ecological cost between different products is required. Some of the allocation methods have their origins in economic cost allocation, others in energy, emission or exergy analysis. Within this paper four different methods are investigated: avoided production in national energy system, avoided production in single-product processes, and physical and exergetic allocation. When applied to cogeneration technology, the avoided production in national energy system can give misleading results, mainly due to the nature of the thermo-ecological cost. In polygeneration energy systems, the avoided production in separate processes method can also lead to wrong conclusions due to the assumptions concerning reference efficiencies. At the end, the exergetic allocation method is proposed as a suitable way to allocate the thermo-ecological cost in cogeneration and polygeneration energy systems. Additionally, positive environmental effects of integration can be observed.