Photovoltaic (PV) systems are central to global decarbonization, but their assessed environmental impacts vary due to inconsistencies in life cycle assessment (LCA) methodologies. These differences hinder comparability and the development of a transparent sustainability framework. To address this issue, this review systematically synthesizes PV LCA studies across five continents. The analysis highlights variations in system boundaries, functional units, data quality, and regulatory frameworks, revealing that methodological coherence is strongly shaped by regional policy and data infrastructure. Europe, supported by stringent regulations and localized inventories, demonstrates high methodological alignment. In contrast, Africa and Latin America face major data gaps, with over 90 % of studies relying on non local inventories, creating uncertainty in the results. Building on these findings, this study proposes key harmonization strategies, including enhanced transparency, the adoption of standardized guidelines such as IEA PVPS Task 12, and the targeted development of regional life cycle inventory databases. These measures provide policymakers, industry, and researchers with a practical framework to strengthen the reliability and comparability of PV sustainability assessments, supporting solar energy's role in a low carbon future. Future research should prioritize the expansion of localized datasets and the integration of dynamic LCA approaches to capture rapid technological evolution and circular economy principles