Sustainable Innovation and Energy Efficiency: Quantile MMQR Insights from the G20 Economies

This study examines the determinants of energy efficiency in G20 economies over the period of 2000–2024 using the method of moments quantile regression (MMQR) to analyze the variation in the impacts of green innovation, green investment, green finance, the strength of energy policy, and trade openness across different levels of energy intensity. The results reveal that these variables do not affect all countries equally; their effects vary with the maturity of institutional and technological structures. Economies with strong regulations benefit more from green innovation and expanded environmental financial instruments, whereas countries with limited ready-made institutions struggle to turn these variables into tangible gains. This study also showed that energy policy was the most stable factor across all levels, while innovation, finance, and investment became more impactful in countries that had made significant progress in energy intensity. This study proposes a differential policy that responds to various institutional readiness levels. Low-intensity energy economies should prioritize strengthening regulatory frameworks and improving energy governance, medium-performing countries should expand green finance opportunities and direct investments toward clean technology, and developed countries should focus on deepening innovation and broadening the base of technology transfer to promote long-term sustainability. Overall, the results confirm that the green shift in the G20 economies requires specialized strategies rather than uniform policies that overlook economic structural differences.