A systematic review of scale-up methods in prospective life cycle assessment of emerging solar energy technologies

The accelerating development of solar energy technologies requires forward-looking environmental assessment approaches capable of addressing technological immaturity, uncertain scale-up pathways, and evolving background systems. Prospective life cycle assessment (pLCA) has emerged as a key framework for such analyses, yet methodological practices particularly regarding technology scale-up modelling, validation, and alignment with technology maturity remain fragmented and inconsistently applied. This study presents a systematic methodological review of 39 peer-reviewed pLCA studies published between 2011 and 2026, focusing on photovoltaic (PV), concentrated solar power (CSP), and concentrated solar thermal (CST) technologies. Following the PRISMA 2020 protocol, the review examines how different foreground scale-up modelling approaches (empirical, engineering-based, learning-curve, and hybrid) are applied across Technology Readiness Levels (TRLs), and how these choices interact with prospective background assumptions, including future electricity systems and assessment time horizons. The results show that low-TRL solar technologies are predominantly assessed using laboratory-based extrapolations with limited validation, while higher-TRL systems increasingly employ physically grounded models combined with scenario-conditioned backgrounds. Across technologies, validation and benchmarking practices are uneven, and substantial heterogeneity in functional units, system boundaries, impact assessment methods, and background electricity assumptions constrains interpretability particularly for low-TRL studies where the primary objective is often design guidance rather than cross-technology comparison or policy support. This review advances a goal-dependent, TRL-sensitive perspective on pLCA practice. By explicitly mapping scale-up strategies, validation approaches, and modelling assumptions to technology maturity, it provides diagnostic guidance to support transparent, credible, and context-appropriate application of pLCA in the assessment of emerging solar energy technologies.