*2.4. Benefits*

The benefit cost data were found by adding the monetized energy recovered from the incineration disposal process and the cost payback from the materials recovered during the recycling process

$$\text{Berefits of PV recyccling} = \text{B}\_{\text{R,c}} + \text{B}\_{\text{R,m.}} \tag{6}$$

Recovery yield was included within the scope of this paper because it is an important aspect when evaluating the success of the cost-saving measures of using non-virgin materials. Although the recycling process requires high up-front investment costs, money can be saved in the purchasing of new materials. This is because many of these materials are saved after the recycling process and can be sold to manufacturers or, in the case of First Solar, with its identity as both a manufacturing and recycling facility, processed again as recycled feed (First Solar's Module Collection and Recycling Program). The beneficiary of the recovered products depends on whether there is a closed-loop vs. open-loop process. In an open-loop process, materials are sold to external processing facilities, and in a closed-loop process, the materials are sent to make more of the same product they had been pre-recycled.

In this work the percent yields of recovered materials were taken from the literature [20]. Using these numbers, the cost of the recovered materials per m<sup>2</sup> were found. Recovery cost tables can be found in the Supplementary Information tables (Tables S5 and S6).

#### **3. Results**

#### *3.1. Private Cost of Recycling*

The total EoL cost of 1 m2 of c-Si PV module was found to be USD 6.72/m2 (Figure 3). Of the three cost components of PV EoL management, the transportation-associated cost was found to be the highest (USD 3.36/m2) while the cost of the recycling process (the cost of consumed materials, electricity or the investment for the recycling facilities) was found to be the most insignificant (USD 0.25/m2).

The main reason for the high transportation cost can be attributed to the long distance of transportation required in the end-of-use of PV panels. Figure 3 also shows each transportation step and its cost in carrying them with a truck, as referred to in the FRELP method. The costs of each transportation step correlate directly with the distance between facilities. As can be derived from Figure 3, the long distances from deployment locations to PV recycling facilities are the main drivers of the high cost due to transportation in the EoL of PVs (an average of 400 km away from the collection points [20]). The table containing these distances can be found in Supplementary Information Table S3 (note that the cost of transportation is linearly proportional with traveled distances).

The disposal cost of c-Si PV waste is made up of the tipping fees for four materials such as contaminated glass, fly ash, liquid waste and sludge (Figure 3) in landfills. The landfilling associated cost can be attributed to the high cost of tipping fees for the sludge treatment that consists of hazardous materials. The recycling of 1 m2 of c-Si PV resulted in the generation of 0.70 kg of sludge, which equals approximately 90% of the total landfilling cost of c-Si PV's EoL management. For every 1000 kg of PV panels processed, 374.4 kg of waste is produced [20].

**Figure 3.** The end of life (EoL) management (private) cost of EoL of 1 m2 of c-Si PV.

The total cost of the investment and processing for recycling has a minor impact on the private cost of c-Si PV's EoL management. In the FRELP recycling method, diesel fuel, electricity, nitric acid (HNO3), water, and calcium hydroxide (Ca(OH)2) were consumed during the recycling process of c-Si PV modules. Figure 3 also shows the cost breakdown of these process inputs. As seen, the electricity consumed is the most expensive cost component of the PV recycling process, with a value of 12 cents/kWh. Electricity is only used in the recycling process, totaling 1.55 KWh. The electricity is consumed in multiple steps during recycling such as during disassembly of the module, glass separation, and PV sandwich cutting. The second-largest cost component of the recycling process can be contributed to the chemicals required. The FRELP method utilizes 0.1 kg of nitric acid per 1 m2 during the acid leaching process. Another chemical utilized during the FRELP method is calcium hydroxide, which is needed for the neutralization step of PV dismantling. This step is necessary because of the need to neutralize the nitric acid used in the acid leaching step beforehand. A total of 0.5 kg of calcium hydroxide per 1 m2 is used, making it the largest amount of material required for the direct PV dismantling process, disregarding water. We found the impact of the investment cost for the instruments required for the recycling of c-Si PV panels is insignificant (¢1.1/m2). The most outstanding cost component among the eight pieces of the instruments required for the FRELP process was found in the cartesian robot system, making up ¢0.6/m2. Note that the instruments used in PV recycling can process about 8 million kg of PV waste annually and they can be used for long period of time (approximately 20 years) [20]. Therefore, their impact on processing 1 m2 of the PV module was found to be very limited.

Faircloth et al. [33] also calculated the processing cost of the FRELP method as USD 0.03 per kg PV waste, which equals USD 0.48 per m2 of PV waste, assuming that the FRELP recycling facility operates in Thailand. The difference (24 cents per m2) between the processing cost of our and Faircloth et al.'s [33] results can be attributed to the differences in the cost of materials (acids, diesel fuel, water etc.) and electricity in the US and Thailand which are required for the FRELP process, as well as differences in methods of recycling. Similarly, we compared the disposal cost of the unrecovered materials from the recycling of PV waste with Faircloth et al.'s values [33]. However, the high cost of transportation was not identified in the literature. The reason could be the difference in the modeling approaches on transportation distances. Faircloth et al [33] assumed the total distance of travel as 100 km while Latunnusa et al [20] reported the overall distance of travel as 850 km. The type of fuel used

is another factor which could cause discrepancies between different papers about PV transportation. However, diesel fuel is used by both this paper and Faircloth et al. [33].
