Many countries are targeting the rapid and deep decarbonization of their energy supply, with renewable energy technologies playing a key role. Despite increased technology maturity and dramatically decreased costs, the deployment momentum of renewables often lags behind ambitious policy commitments. Accordingly, policymakers must accelerate the development of projects to meet decarbonization goals. However, we currently lack a comprehensive understanding of how long projects of renewable energy take to commission, whether projects are executed faster as technologies mature, and which factors affect the timelines – this knowledge gap affects policymakers and energy researchers providing model-based policy advice alike. To fill this gap, we analyzed global commissioning times between 2005 and 2022, drawing on the data for 12,475 projects using solar photovoltaic (PV), wind onshore, wind offshore, biomass, and run-off-river hydro in 48 countries. We found that average commissioning times have increased substantially over the past two decades for all renewable energy technologies of all project sizes. This finding highlights the need to incorporate up-to-date commissioning times in energy models to generate realistic model-based policy advice. In addition, we identified five categories of factors that affect commissioning timelines, conducted cross-sectional analyses with fixed-effect models, and present implications for policymakers, businesses, and researchers.