• Energy Research

As there is currently a lack of reliable guidance for investors to make the most sustainable choice when it comes to different renewable heating technologies for residential buildings, this contribution presents a methodological approach for a comprehensive comparison, while also addressing data requirements. A focus point of the methodology development and the sustainability assessment lies on the integration of a dynamic electricity mix to account for the continuous decarbonization in an energy grid that is more and more based on renewables. Its influence on the final environmental impact results of the presented exemplary system combining a solar thermal collector and an air source heat pump is assessed. The results indicate a significant influence of the electricity mix on the carbon footprint (- 48%) of the provided heat. The resource use is only slightly changed (+ 3%).

To mitigate the effects of climate change, the massive deployment of renewable energies is a key challenge in the near future. While for wind power plants, repowering is common practice to increase the energy yield, the early replacement of old photovoltaic (PV) modules with newer, more efficient ones is receiving less attention in industry, politics and research. In recent years, significant technological improvements have led to a reduction of energy and material use in the production as well as to an increase in PV system efficiencies. To assess the ecological implications of PV repowering, a life cycle assessment has been performed for a 3 kWp rooftop silicon PV plant and for a 1.07 MWp open field silicon PV plant for the two reference-production years of 2004 and 2020. The earliest and the optimum points in time, at which a premature replacement can be ecologically beneficial have been calculated for the indicators Climate change, Ecotoxicity, freshwater, Land use and Resource use, minerals and metals. Three scenarios, that differ regarding the respective repowering goal and the end-of-life treatment, have been analyzed. The calculated optimum repowering time for the investigated PV plants lies between 15 and 21 years on average, while it varies significantly between scenarios as well as impact indicators. The results show that a dedicated recycling as well as a repowering above the initial peak power are crucial in making repowering a sustainable option. Moreover, our calculation approach can be used to assess further technological variations at different reference years by using life cycle impact assessment results. It must be noted, these results are based on the technological progress achieved between 2004 and 2020. As it cannot be assumed that the technological progress of the last two decades can be projected into the future to the same extent, assumptions will have to be adapted for calculations for future time periods.

The environmental footprint of photovoltaic electricity is usually assessed using nominated power or life cycle energy output. If performance degradation is considered, a linear reduction in lifetime energy output is assumed. However, research has shown that the decrease in energy output over time does not necessarily follow a linear degradation pattern but can vary at different points in the module’s lifetime. Further, photovoltaic modules follow different degradation patterns in different climate zones. In this study, we address the influence of different degradation aspects on the greenhouse gas (GHG) emissions of PV electricity. Firstly, we apply different non-linear degradation scenarios to evaluate the GHG emissions and show that the differences in GHG emissions in comparison to a linear degradation can be up to 6.0%. Secondly, we use the ERA5 dataset generated by the ECMWF to calculate location-dependent degradation rates and apply them to estimate the location-specific GHG emissions. Due to the reduction in lifetime energy output, there is a direct correlation between the calculated degradation rate and GHG emissions. Thirdly, we assess the impact of climate change on degradation rates and on the respective GHG emissions of photovoltaic electricity using different climate change scenarios. In a best-case scenario, the GHG emissions are estimated to increase by around 5% until the year 2100 and by around 105% by 2100 for a worst-case scenario.

A product made from virgin raw materials that ends up in a landfill presents a linear supply chain model. Today's photovoltaic (PV) industry is still largely based on this model. With the increasing volume of production, the raw materials required for it, and consequently the volume of waste, the application of circular economy principles in the PV sector can significantly increase its environmental efficiency. This study analyzes the impact of circularity on the supply chain of PV silicon used for PV module production. Four scenarios based on the combination of technological pathways and circularity options are created. Their evaluation is carried out by the methodologies of Material Circularity Indicator (MCI) and Life Cycle Assessment (LCA). The State-of-art case of the PV polysilicon supply chain corresponds to the MCI score of 0.54. Closed-loop circularity solutions provide the MCI score of 0.80 presenting the potential for a circular economy approach in the industry. LCA results show the reduction of environmental impact by 12% with improved circularity. The study presents the benefits of potential circularity options within the supply chain as well as the impact of technological development on the polysilicon demand.

Abstract Life Cycle Assessments (LCA) of single-crystalline silicon (sc-Si) photovoltaic (PV) systems often disregard novel module designs (e.g. glass-glass modules) and the fast pace of improvements in production. This study closes this research gap by comparing the environmental impacts of sc-Si glass-backsheet and glass-glass modules produced in China, Germany and the European Union (EU), using current inventory data. Results show lower potential environmental impacts for glass-glass compared to glass-backsheet modules and lower impacts for production in the EU and Germany compared to China for most impact categories. Concerning climate change, glass-backsheet (glass-glass) modules produced in China, Germany or the EU are linked to emissions of 810 (750), 580 (520) and 480 (420) kg CO2-eq/kWp, respectively. This corresponds to CO2-eq emission reductions of 30% for German and 40% for European production compared to Chinese production, and 8–12.5% reduction in glass-glass compared to glass-backsheet modules. Carbon intensity of produced electricity, excluding balance of system (BOS), amounts to 13–30 g CO2-eq/kWh, depending on production location and electricity yield calculation method. A warranty-based yield calculation method shows the influence of different lifetime electricity yields of glass-glass and glass-backsheet modules on the potential environmental impacts. This study identifies module efficiency, energy requirements, silicon consumption and carbon-intensity of electricity during production as significant levers for future reductions of environmental impacts. It emphasizes the importance of up-to-date inventories and current modelling of electricity mixes for representative LCA results of PV modules. Lastly, this paper argues that more differentiated methodological guidelines are needed to incentivize the development of sustainable module designs.

The large-scale deployment of photovoltaics (PV) is a central pillar in decarbonizing energy systems and reaching climate goals. Although PV is inherently associated to environmental awareness, it is not immune to reputational risks nor exempt of a responsibility for transparency and sustainability leadership. So far, advances in the PV industry have mainly been shaped by cost-reduction targets. We identified in previous works 16 topics where the PV sector comes short in addressing the United Nations Sustainable Development Goal 12 (SDG 12) “Ensure sustainable consumption and production patterns”. In this paper, practical approaches to address each of these sustainability gaps are proposed. The best-practices identified cover all aspects of sustainability as defined by SDG 12–from resource use and hazardous substances through corporate reporting and risk assessment to due diligence and waste management. Insights on methodological needs to improve sustainability assessment and accounting in PV are also provided. The compiled list of actions needed, although not intended to be exhaustive, constitutes a starting point for stakeholders to raise their ambitions and achieve more sustainability in PV value chains.

PV waste management will gain relevance proportionally to the amounts of waste that are expected to arise with the phasing-out of old installations in the upcoming years and decades. The Life Cycle Assessment (LCA) methodology is used here to analyze the environmental performance of photovoltaic systems and the waste management methods that have been developed recently. Several LCA studies have already been performed for PV technologies, but in most cases these do not include the end of life stage, thus there is still uncertainty about the impacts of recycling on the environmental footprint of PV electricity. The present study offers a more detailed analysis of different end-of-life approaches for the main photovoltaic technologies that are found on the market. The results from the analysis demonstrate that recycling has the potential to improve the environmental profile of PV electricity but at the same time there is room for further improvements in developing dedicated recycling technologies.