2.2.1. Unit Processes, Data, and Assumptions

This study assesses the small scale configuration of the HBP technology, which has a nominal electricity output of the SOFC of 199 kW. Its main characteristics during the average lifetime (assumed 18 years) are reported in Table 2.



For the foreground system, data on the gasifier and the GCU were collected from the industrial partners involved in the H2020 HiEff-BioPower project. For the SOFC, secondary data based on the scientific literature [17] were used due to the unavailability of specific primary data. The background data were largely based on the ecoinvent database (version 3.4). For unavailable data, assumptions were made based on literature (see the following sub-sections for details regarding each phase of the life cycle).

As the system provides two different products (and functional units), it was necessary to determine an allocation key to partition the overall impact to the two functional units. Allocation by physical causality was not applied under the absence of a representative mathematical model (to model the causality relationships) [36–38]. Among the possible remaining allocation methods, the exergy key was chosen because it can represent both quantity and quality of both functional outputs, and is common practice for CHPs (e.g., ecoinvent uses such key [39] and is recommended by RED II [40]). Table 2 shows the biomass input, intermediate performance indicators, and energy outputs in terms of their exergy and economic values. The exergetic outputs expressed in percentage reported in Table 2 represent also the allocation factors used for the baseline calculations. The economic values are based on three years (2015–2017) average prices for medium size industries without VAT, in Germany, retrieved from Eurostat [41]. The prices were 0.079 € per kWh of industrial electricity and 0.0086 € per MJ of industrial heat.
