**3. Results**

This section presents the results of the LCA study completed to the mid-point level.

#### *3.1. Manufacturing Process of the VIPV*

The results of the analysis of the manufacturing phase [*kg CO*2*eq*] demonstrate the impact before the operation starts. The manufacturing process VIPV shows similar results to other PV systems. The most dominant contributor to this phase is the Solar-Grade Process. It is responsible for 444.30 kg CO2 eq, a third of total emissions. The process of integration of the cells into the panel emits 235.24 kg CO2 eq. The calculated total amount of emissions during the manufacturing process is 1143.12 kg CO2 eq (see Figure 4).

#### *3.2. Operation Phase of the VIPV*

The on-board generation of electricity was simulated based on the assumptions on degradation, system losses, and shadowing factor, as previously described in Section 2.4. While driving the EV, the batteries will discharge and will recharge again using the on-board PV modules. The degree of VIPV's impact was expected to vary with the usage patterns: different daily driving distances have different depths of discharge corresponding to daily driving durations. In this study, all incoming irradiance during the day is used, assuming energy is being collected energy and the battery is being charged, even if not driving. The results of the energy flow model are shown in Table 7.



For the reference scenario of 8 years operation and a shadowing factor of 30%, the VIPV contribution is 3738.116 kWh. Prolonged operation of 12 years generates 5526.702 kWh in total.

#### *3.3. Comparison to the Emissions of the Grid Charge*

For the same amount of energy, if the grid would be used, 1630 kg CO2-eq for 8 years and 2267 kgCO2-eq for 12 years were calculated. The losses appearing due to grid distribution were not calculated, because the emission factor is already based on an energy consumption perspective.

Main findings of the comparison with grid electricity show: VIPV can improve the carbon footprint for the reference case of an average shadowing factor of 30% and 8 years of operation time. For the functional unit of 1 kWh of on-board generated PV electricity, the emission factor of 0.357 kgCO2-eq/kWh is calculated for the reference case. In comparison, the average grid emissions for the operation time are expected to be 0.435 kgCO2-eq/kWh.

Considering the data quality of the LCA, reduction of emissions of the functional unit for the reference case compared to the grid is about 18%. The holistic view of the results for the reference case shows 3738 kWh VIPV contribution. For the functional unit of 1 kWh of on-board generated PV electricity, the emission factor of 0.357 kgCO2eq/kWh is calculated. In comparison, the average grid emissions for the operation time are expected to be 0.435 kgCO2eq/kWh. Compared to the estimated grid average, about 18% less emissions per kWh are caused by VIPV. Projected contribution of VIPV was replaced by grid charging to find out in which operation year VIPV have fewer emissions than the grid and thus calculate the "ecological break-even point". In the previously described reference case, this point is achieved in the year 2022. That means that after 6.5 years of operation, the ecological impact of VIPV equals the impact of the grid charge. However, an increasing shadowing factor of mobile application causes a significant growth of emissions per kWh.

## *3.4. Sensitivity Analysis*

The results of the study are wide-ranging. The variations mainly arise from system operating assumptions (e.g., solar irradiation, system lifetime, shadowing factors) and technology improvements (e.g., electricity consumption for manufacturing processes). In this section some adjustments of the reference case (8 years of operation, 0.7% degradation, and 30% shadowing factor) are considered.

PV-generated power is an essential variable for the reduction in emissions. By increasing the shadowing factor, emissions per kWh grow significantly. An emission factor of 0.357 kgCO2-eq/kWh is calculated for the reference case. The increased shadowing factor of 40% results in 0.435 kgCO2-eq/kWh, which equals the average emissions of the future grid electricity. As shown in Figure 5, the ecological benefit over the grid charge disappears completely when the shadowing factor reaches 40%.

**Figure 5.** Emissions depending on the shadowing factor.

Sensitivities show that if the VIPV is used for a prolonged life of 12 years, the emission factor of the produced electricity decreases to 0.221 kgCO2-eq/kWh. A reduction of 38% (0.136 kgCO2-eq/kWh) compared to the reference case of 8 years is noted. The average grid mix emissions of prolonged use decrease to 0.409 kgCO2-eq/kWh. Comparable results can be achieved with a shadow factor of 55% or an average annual VIPV generation of about 260 kWh/a. Lifetime extension of the vehicle operation will automatically result in a reduction of the emissions per produced kWh of the VIPV. Figure 6 demonstrates the potential of the longer operation phase for different shadowing factors.

**Figure 6.** Emissions of "prolonged use" scenario.

Based on findings of the sensitivity analyses, the highest potential for emission reduction can be confirmed for a "green" electricity scenario, where renewable electricity is used for the manufacturing process. The emission factor of 0.831 kgCO2/kWh for the electricity mix of China used for the simulation of the reference case is based on the GaBi Education Database from 2017. With the increasing share of renewable energy in the electricity mix, lower GWP impact will arise from the production phase of the VIPV. Using green electricity has the potential to be almost carbon-free, as is the case for today's hydropower. For "green" electricity, assumptions of hydro plants with average emissions of 0.003 kgCO2-eq/kWh were used to cover the energy need of the manufacturing phase in China [15]. As illustrated in Figure 7, the emissions decrease from 0.357 to 0.230 kgCO2-eq/kWh for the shadowing factor of 30%.

**Figure 7.** Emissions of "green manufacturing" scenario.

#### **4. Discussion and Conclusions**

The study reports the unique observation that placing a PV system on-board of an existing StreetScooter can improve the carbon footprint of the generated electricity for the reference case of an average shadowing factor of 30% and 8 years of operation time. The ecological benefits of PV-powered light utility vehicles are confirmed for the reference case of the StreetScooter. Yet, the results of the LCA show that viability is heavily dependent on the vehicle's deployment region and usage scenario. Main findings of the comparison to the grid electricity show: VIPV can improve the carbon footprint for the reference case of an average shadowing factor of 30% and 8 years of operation time. For the functional unit of 1 kWh of on-board generated PV electricity, the emission factor of 0.357 kgCO2-eq/kWh is calculated. In comparison, the average grid emissions for the operation time are expected to be 0.435 kgCO2-eq/kWh. Considering the data quality of the LCA, reduction of emissions of the functional unit for the reference case compared to the grid is about 18%. By increasing the shadowing factor, emissions per kWh grow significantly. The ecological benefit to the grid charge disappears completely when the shadowing factor reaches 40%. However, if the operation time is prolonged to 12 years, the shadowing factor can reach 55%, having similar emissions to grid charge. For the reference case with 30% shadowing, a reduction of 38% compared to 8 years in use can be noted. For this case, 0.221 kgCO2-eq/kWh is estimated for the functional unit.

One of the key challenges of this work was finding an appropriate vehicle usage model to reproduce the ratio of using solar power and performance assessment of Maximum Power Point Tracker (MPPT) algorithms for VIPV. Tests with radiation sensors investigating shading and reflection conditions are suggested. Numeric simulation of VIPV output test drives with irradiance profiles of routes should include di fferent vehicle usage times, e ffects of panel position and movement. Additionally, it is necessary to address the electrical and technical issues.

For the recycling process, no established and reliable routes were found. As to the knowledge of the author, no study provides details on the LCI with the input and output of every process stage. However, if material depletion is considered, recycling is crucial, and further research should include recyclability options. Since second use is an important issue, the mounting structure, removable, and lightweight, must become a priority for research. Furthermore, a scenario of VIPV connection to the public grid while parking during weekends, in which the surplus of unused electricity can be fed into the grid, seems to be realistic. Vehicle2Grid (V2G) concepts can be very profitable, but first, the dependence on the state of charge (SOC) of the battery including an ageing model of the battery with charging and discharging losses should be analyzed. Enhanced communication and cooperation between automotive companies and PV players can contribute to the positive image of vehicle integrated photovoltaic systems in order to achieve the goal to change the image of VIPV. Likewise, international methods for evaluating the reduction of emissions of PV-powered vehicles can help to communicate the created value for the di fferent driving and charging behaviors. To contribute to the growth of the VIPV market, governments willing to achieve emission goals must support the standardization of the technology. To solve this problem, international methods of evaluating added value on the reduction of grid power and ecological benefits are required.

**Author Contributions:** Conceptualization O.K., K.D.; methodology O.K., J.M.; software, validation, investigation, resources, data curation and writing—original draft preparation O.K.; writing—review and editing A.R., J.M., K.D.; visualization, O.K.; supervision J.M., A.R., project administration K.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Federal Ministry for Economic Affairs and Energy in the framework of the STREET project (grant: DB001618).

**Acknowledgments:** This work is based on the Master's thesis by Olga Kanz at the Hochschule Köln 2019. The authors appreciate the support of the research group of IEA Photovoltaic Power System Programme Task 17, which focuses on possible contributions of photovoltaic technologies to transport and support from Toshio Hirota and Keichi Komoto. Costs for publishing are covered by Forschungszentrum Jülich GmbH.

**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
