Achieving universal access to affordable, reliable and clean energy i.e. Sustainable Development Goal 7 remains challenging for large emerging economies facing rising climate risks and institutional constraints. Yet how climate vulnerability and governance quality jointly shape SDG 7 outcomes remains less understood. Here we analyse BRICS countries from 2000-2022 to examine how these factors condition the effectiveness of key SDG 7 drivers, including environmental policy stringency, innovation, financial development, inequality and demographic structure. Using a two-stage empirical framework, we estimate marginal impacts while allowing climate vulnerability and governance quality to act as interactive moderators and simulate four extreme governance-vulnerability stylized regime combinations. We find that strong governance and lower vulnerability substantially amplify the positive effects of finance, innovation and policy stringency on energy access, renewable deployment and efficiency. Under high climate stress and weak governance, these gains diminish or reverse, particularly for electricity generation efficiency and rising energy demand. Country-level results highlight persistent heterogeneity across BRICS economies, with Brazil and China capturing greater benefits from finance and innovation; while India, Russia and South Africa facing persistent constraints in efficiency and clean energy expansion. No single policy lever performs robustly across regimes, indicating that governance strengthening and climate resilience are necessary preconditions for delivering SDG 7 in large emerging economies. Our results show that progress towards SDG 7 is highly conditional on institutional capacity and climate resilience, underscoring the need for differentiated, context-specific energy policies in large emerging economies.