Abstract
Five metropolitan governments in Southeast Asia faced increasing pressure to expand rooftop solar deployment, yet adoption remained uneven. Previous studies focused mainly on national renewable-energy policies, while the role of city-level policy instruments and paradiplomacy received limited attention. This study examined rooftop-solar policies in Singapore, Jakarta, Kuala Lumpur, Ho Chi Minh City, and Bangkok using comparative case studies and an exploratory city-year panel (2010–2024). The analysis distinguished national policies from city-level regulatory instruments to assess metropolitan governments' contributions to rooftop-solar implementation. The findings revealed heterogeneous policy effects. Singapore demonstrated the strongest procurement-led expansion, whereas Kuala Lumpur and Bangkok remained at earlier implementation stages. Jakarta and Ho Chi Minh City highlighted the difficulty of separating national incentives from local initiatives. The study concluded that urban energy transition in Southeast Asia depended not only on national incentives but also on the regulatory, institutional, and diplomatic capacities of metropolitan governments to implement effective rooftop-solar programmes.