Given photovoltaics' (PVs) constant improvements in terms of material usage and energy efficiency, this paper provides a timely update on their life-cycle energy and environmental performance. Single-crystalline Si (sc-Si), multi-crystalline Si (mc-Si), cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) systems are analysed, considering the actual country of production and adapting the input electricity mix accordingly. Energy pay-back time (EPBT) results for fixed-tilt ground mounted installations range from 0.5 years for CdTe PV at high-irradiation (2300 kWh/(m 2¨y r)) to 2.8 years for sc-Si PV at low-irradiation (1000 kWh/(m 2¨y r)), with corresponding quality-adjusted energy return on investment (EROI PE-eq ) values ranging from over 60 to~10. Global warming potential (GWP) per kWh el averages out at~30 g (CO 2 -eq), with lower values (down to~10 g) for CdTe PV at high irradiation, and up to~80 g for Chinese sc-Si PV at low irradiation. In general, results point to CdTe PV as the best performing technology from an environmental life-cycle perspective, also showing a remarkable improvement for current production modules in comparison with previous generations. Finally, we determined that one-axis tracking installations can improve the environmental profile of PV systems by approximately 10% for most impact metrics.

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This paper provides a comprehensive assessment of the current life-cycle sustainability status of crystalline-based photovoltaic (PV) systems. Specifically, singlecrystalline Si (sc-Si) and multicrystalline Si (mc-Si) PV systems are analyzed in terms of their environmental and energy performance, providing breakdown contributions and comparisons with estimates published 6 years ago. Results clearly show the significant environmental improvement in the sc-Si PV system production-mainly at the wafer stage-for which the impacts have been reduced by up to 50% in terms of carbon emissions and 42% in terms of acid gas emissions. The life-cycle cumulative energy demand is estimated to be approximately 48% lower (for sc-Si) and 24% lower (for mc-Si) than previously reported estimates. Energy payback times of currently installed systems range from 1.3 (for c-Si PV) and 1.5 years (mc-Si PV) for fixed-tilt ground-mounted installations at low irradiation (1000 kWh/m 2 /year), to 0.6 years at high irradiation (2300 kWh/m 2 /year). The resulting energy returns on investmentexpressed in terms of primary energy-range from 22 (at low irradiation) to 52 (at high irradiation) for sc-Si PV systems and from 21 to 47 for mc-Si PV systems. Furthermore, we examine the effects of cleaner electricity grids and grid efficiency improvements on these environmental and energy indicators.

Perovskite photovoltaics reached record efficiencies in the laboratory, and if sustainably commercialized, they would accelerate a green energy transition. This article presents the development of life cycle inventory material and energy databases of four most promising single-junction and three tandem scalable perovskite systems with assumptions regarding scalable production validated by industry experts. We conducted comprehensive "ex ante" life cycle analysis (LCA) and net energy analysis, analyzing their cumulative energy demand, global warming potential profiles, energy payback times, and energy return on investment (EROI). LCA contribution analysis elucidates the most impactful material and process choices. It shows that solutionbased perovskite manufacturing would have lower environmental impact than vaporbased methods, and that roll-to-roll (RtR) printing offers the lowest impact. Among material choices, MoOx/Al has lower impact than Ag, and fluorine-tin-oxide lower than indium-tin-oxide. Furthermore, we compare perovskites with commercial crystalline-silicon and thin-film PV, accounting for the most recent developments in crystalline-Si wafer production and differences in life expectancies and efficiencies. It is shown that perovskite systems produced with RtR manufacturing could reach in only 12 years of life, the same EROI as that of single-crystalline-Si PV lasting 30 years. This work lays a foundation for sustainability investigations of perovskite large-scale deployment.

For new technologies, such as perovskite solar cells (PSC), life cycle analysis (LCA) offers a fundamental framework for examining potential environmental, energy and health impacts and mitigation options before large-scale commercialization and for guiding improvements in development and production that further reduce their environmental footprint. However, credible LCA studies require actual process-based material, energy and emissions data, which may not exist before the technologies are commercially produced. Thus, the perovskite LCA literature is based on linear extrapolations of laboratory data. In this paper we critically reviewed the PSC LCA literature, explain the reasoning for a wide divergence of results, and determined which data apply to scalable industrial production, materials and processes. Our investigation probed into the formulation of each layer of a PSC device, and its potential for industrial scale fabrication. We found that electricity use is the main contributor to reported LCA results, explaining the large difference, ranging from 7.78 kWh to 1460 kWh m −2 , among various studies. Subsequently, we identified and discuss methodological errors in some of these estimates. In terms of life-cycle toxicity most of the reviewed LCA studies do not attribute any major overall toxicity impact to the presence of lead in the PSC devices. We also reviewed and critiqued studies describing 'worst-case' scenarios of accidental release of lead into the environment, and, in spite of statements in those studies, we found them to be inconclusive. Finally, we discussed end-of-life (EoL) management options for resource recovery and for minimizing environmental impacts.

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