**3. Results**

#### *3.1. Environmental Impact of the HBP Technology*

#### 3.1.1. Baseline (Wood Chips)

Figure 3 shows the breakdown of the impact of the HBP technology for the seven investigated impact categories (see Appendix A for absolute values).

**Figure 3.** Main contributions to the cradle-to-grave environmental impact of producing heat and electricity with the HBP technology using wood chips as biomass fuel. The presented breakdown is valid for both functional units. CC = Climate change, PM = Particulate matter, POF = Photochemical ozone formation, AC = Acidification, TE = Terrestrial eutrophication, WRD = Water resource depletion, MFRD = Mineral, fossil, and renewable resource depletion.

The main contributions to the cradle to grave environmental impact are the wood chips used, followed by the maintenance phase and manufacturing phase. The impact of wood chips is made of two components i.e., their transportation and their production. The impact of transporting wood chips (based on the Swiss supply chain assumed by the dataset retrieved from ecoinvent) represents 18–27% of the impact of wood chips for all impact categories, except for photochemical ozone formation (9%) and water depletion (2%). In all impact categories, except water depletion, the impact of the production of wood chips is mainly caused by the production and combustion of diesel and petrol (60–80%) used in power sawing machines, skidders, and chippers. The production of the lubricants used in the three processes mentioned above causes about 2–10% of the impact of wood chips production in all impact categories except for water resource depletion for which it represents 80% of the impact. The water depletion impact of wood chips is mainly due to the fraction of vegetable oils used for lubricating the chains during power sawing activities (in absolute terms, this impact is quite low, see figures in Section 3.1.2 and Section 3.2.2.

The main impact of the manufacturing stage is due to the production of the SOFC system, which contributes to 63–100% of the impacts in this stage (depending on the category). Within the SOFC system, the production of the SOFC stack and the inverter are the main sources of impact. This is mainly due to the large electricity consumption during the manufacturing of the stack (as also highlighted by Rillo et al. [17]) and the manufacturing of chromium steel (mainly caused by the production of ferrochrome [17]).

Concerning the maintenance impacts, the maintenance of the SOFC system contributes to 63–100% of the impact depending on the impact category. The major contributor (95–99%) to the impact of the maintenance of the SOFC system is the replacement of the SOFC stack, which requires the production of a new SOFC stack every five years of operations.

The operation phase is dominated by the operation of the GCU (mainly zinc oxide used and sodium bicarbonate) expect for water depletion whose impact is mainly caused by the water used for the operation of the gasifier. The contribution of direct emissions is negligible in all impact categories. The particulate matter caused by the operation of the HBP technology was only 1% of the total particulate matter impact.

#### 3.1.2. Alternative Scenarios (Wood and *Miscanthus* Pellets)

Figure 4 shows the environmental impact of the baseline scenario in comparison to the alternative scenarios.

**Figure 4.** HBP technology fueled with various biomass fuels (the same graph applies to both 1 MJ heat or 1 kWh electricity). Values are normalized taking as 100% the impacts of the most impacting scenario. CC = Climate change, PM = Particulate matter, POF = Photochemical ozone formation, AC = Acidification, TE = Terrestrial eutrophication, WRD = Water resource depletion, MFRD = Mineral, fossil, and renewable resource depletion. WC = wood chips, WP = wood pellets, MP = *Miscanthus* pellets.

The results show that, in all impact categories, the total life cycle impact is the lowest for the operation with wood chips compared to the other two biomass scenarios (wood pellets and *Miscanthus* pellets). Since the inventories for manufacturing and maintenance are the same, the main difference between the three scenarios is the production of the biomass fuel (wood chips have lower environmental impacts than the two pellets).

The impact of the WC scenario is between 10% and 70% lower than for the WP scenario (with the highest impact difference for water depletion and particulate matter). For water depletion, the impact of wood pellets is almost entirely caused by the electricity consumption of the pellet factory. For particulate matter, the shaving process accounts for about 54% of the impact of producing wood pellets. Shaving is, therefore, the main cause of the significantly higher particulate matter impact in the production of wood pellets compared to wood chips. The impact of shaving is mainly caused by its drying process (87%), which leads to high particulate emissions due to the combustion of industrial wood.

Except for particulate matter and photochemical oxidant formation, the *Miscanthus* scenario presents higher environmental impacts than the wood pellets scenario. The characterized results indicate between 18% and 28% lower impacts for the wood pellets scenario than for the *Miscanthus* scenario in the categories of acidification, climate change, resource depletion (mineral, fossil, and renewables), and terrestrial eutrophication. The particulate matter impact is lower (−27%) in the case of *Miscanthus*

pellets because the shaving process, which was the main source of impact for wood pellets, is not used to produce *Miscanthus* pellets.

The difference in impact is even higher for the water depletion category, which scores 97% lower in the wood pellets scenario than in the *Miscanthus* pellets scenario. The irrigation needed during its cultivation is the main cause of the significantly higher water depletion in the scenario with *Miscanthus* pellets (see Figure 5). Other activities that are an important source of impacts for *Miscanthus* pellets are the electricity for pelleting, the diesel burnt during the harvesting stage and the emissions caused by fertilizing (see Figure 5 for the single contributions in each impact category).

**Figure 5.** Main contributions to the environmental impact of *Miscanthus* pellets supplied to the HBP CHP plant. CC = Climate change, PM = Particulate matter, POF = Photochemical ozone formation, AC = Acidification, TE = Terrestrial eutrophication, WRD = Water resource depletion, MFRD = Mineral, fossil, and renewable resource depletion.

Similar to the baseline case of wood chips, direct emissions have a negligible impact on the operation with wood pellets and *Miscanthus* pellets. This aspect is particularly important in the case of biomass technologies installed in heavily populated areas.

As *Miscanthus* is an energy crop, it is important to assess the impacts due to land use. As for the other impact categories, the selection of the method was based on ILCD recommendations [26]. Accordingly, the carbon deficit caused by land use was assessed using the Soil Organic Matter model of [49]. This model accounts for the changes in soil quality caused by the occupation and transformation of the land. Land occupation generates changes in soil quality which depend on the amount of area occupied and the duration of such an occupation. Land transformation generates changes in soil quality which depend on the extent of changes in land properties and the area affected. In this model, the deficits in soil organic matter content are assessed and expressed by an indicator whose unit is kilograms of carbon deficit. These deficits are caused by the effects of agricultural practices on degradation rates. The changes can also be additions of soil organic matter. For example, these additions can be caused by the application of manure or crop residues. It should be observed that this modelling of land use impacts does not account for the counterfactual effects caused by land use changes modelled in consequential LCAs of bioenergy.

The production of 1 MJ of heat using *Miscanthus* pellets generates a 0.86 kg C deficit. Such an impact is much higher than for 1 MJ of heat generated using wood chips (0.12 kg C deficit) and using wood pellets (0.13 kg C deficit). The reason is that *Miscanthus* is an energy crop. Hence, differently from the feedstock for wood chips and pellets, it requires dedicated cultivation.
