*3.2. External Cost of Recycling*

We found that the total external cost of PV EoL management is about USD 5.7/m2. The PV recycling process makes up the majority of the external costs (USD 4.08/m2) since the environmental impacts associated with the processing of PV waste have a greater environmental impact than the sum of both the impacts of transportation (USD 0.73/m2) and landfilling (USD 0.36/m2). In fact, both transpiration and landfilling combined only make up 19% of the total external cost of PV EoL management. Various reasons cause this contrast. First off, the landfilling value is low because the positive impact of recovered energy from landfill incineration is factored into the total. This energy recovered offsets some of the negative externality costs of landfilling. The recycling process uses different chemicals such as HNO3 and Ca(OH)2, which are particularly harmful for the environment. Both the transportation and recycling processes require the input of diesel fuel, however, because the recycling process requires other chemical inputs as well, it acquires a higher external cost. This relationship can be seen in Figure 4 below.

**Figure 4.** External costs of solar photovoltaic (PV) recycling.

The emissions associated with acidification, ecotoxicity and particulate matter (PM) impacts have the greatest external cost. Particularly, acidification-related emissions dominate the recycling and transportation steps of c-Si PVs' EoL phases. About 75% of acidifying emissions of the recycling process are released to the environment during the sieving and acid leaching of c-Si modules to separate the content of the materials of the silicon wafer and during the filtration, electrolysis, and neutralization processes to extract copper, metallurgical grade silicon and silver materials from the silicon wafer [20]. The acidifying emissions of transportation are due to the upstream emissions of diesel fuel extraction in refineries [20]. Figure 4 also shows that the external cost of landfilling is dominated by the particulate matter (PM) emissions. These PMs are released during the incinerations of polymer-based materials such as cables used in the balance-of-system of PV modules and encapsulant materials (Ethylene Vinyl Acetate (EVA)). Note that another reason that acidification and particulate matters dominate the external cost of c-Si PV's EoL management is that these two impact categories are priced with the

highest externality cost according to x and y sources, with USD 341.80 kg PM2.5-eq and USD 64.47 per kg of SO2, for particulate matter and acidification impacts, respectively.

The second highest external cost contributor to the recycling process and transportation steps of c-Si PV's EoL management was found to be the freshwater ecotoxicity (Ecotox.,F). This is important to note because the cost value associated with freshwater ecotoxicity is on the lower end of the damage cost values shown in Table 1, which indicates that the number of ecotoxic emissions is greater than other emissions during the EoL management of PVs. Similar to particulate matter impacts, the incinerations of polymer-based materials are found to be the reasons for the harmful ecotoxic emissions to freshwater. The incineration process does not involve direct emissions to water. Rabl et al. explain that the air emissions from incinerators end up in water bodies due to the wet or dry deposition of aerosols [34]. Among the ecotoxic emissions from incinerators, the impact of mercury, lead and chromium was found to be dominant [34].


**Table 1.** Damage cost of different impact categories.

The net external cost of disposal was found to be the lowest. In fact, the external cost of the landfilling process is very similar to transportation; however, the negative cost (avoided impacts) due to heat generation in the incineration creates credit values, which resulted in a lower external cost during the landfilling.
