Life Cycle Assessment of a Low-Metal Organic Solar Cell

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Examensarbete för masterexamen
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2020
Författare
Holm, Minnea
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Recent developments in the field of photovoltaic technology have led to the creation of a new type of thin-film solar cell called organic photovoltaic (OPV). Unlike other thin-film solar cells, it is not dependent on scarce or toxic materials. In addition, OPVs can be produced rapidly and energy efficiently through continuous (roll-to-roll) processing. This gives OPVs an advantage compared to the already established photovoltaic technologies that either require a large amount of energy for their manufacturing or contain scarce and toxic materials. Previous studies have predicted that the energy payback time (EPBT) of OPV cells can be as little as a few days, compared to three to four years for the most common type of solar cell on the market. However, as OPV is under development, the environmental impact and EPBT differs significantly depending on the OPV technology applied. In this study, the environmental impacts and the EPBT of a specific low-metal OPV technology, here called OPV-C, is explored using life cycle assessment. The production is currently on pilot-scale, but it is planned to be scaled up in the near future. The functional unit of the study was 1 m2 active area OPV-C. The results show that the plastic substrate encapsulating the solar cell is responsible for 90% of the cumulative energy demand (CED) (in total 900 MJeq per m2 active area), and it is the largest contributor to all the environmental impact categories considered. This is because the substrate is treated with a thin protective barrier in an energy-intensive sputtering process. The sputtering process uses electrical energy, which is why the electricity mix applied is critical for the final environmental impact. Two scenarios were created, one with a German electricity mix and one with a Swedish electricity mix. These were chosen to show the difference in the results when using electricity with different carbon footprints. The location of the barrier substrate production is unknown, although suppliers has several manufacturing sites in Germany. When a German electricity mix, which has a relatively high carbon footprint, is applied in the sputtering process, the contribution to climate change equals 53 kg CO2 equivalents per m2 active area. If instead a Swedish electricity mix is applied in the sputtering process, the emissions are less than 5 kg CO2 equivalents for the same area. This shows not only the impact of the electricity mix, but also that the overall impact from the sputtering is very large, as nothing but this process was changed between the two scenarios. For calculating the EPBT, a hypothetical scenario of future large-scale electricity production was applied. In this scenario, where 10 years lifetime of the solar cell and an average-world insolation was assumed, the EPBT is 16 months for an OPV-C cell with 5% efficiency, and eight months for an OPV-C cell with 10% efficiency. For the same scenario, the energy return factor (ERF) was 7.6 for a module with 5% efficiency and 15.1 for a module with 10% efficiency, meaning that the OPV-C cell can either return 7.6 or 15.1 times the invested energy throughout its lifetime, depending on the efficiency of the cell.
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Organic solar cells, Organic photovoltaics, OPV, Thin-film, Life cycle assessment
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