Green and Sustainable Energy: Emerging Technologies, Global Trends, and Future Directions — A Comprehensive Review (2020–2025)

The global energy landscape is undergoing an unprecedented transformation driven by the urgent need to decarbonize economies, achieve climate targets set under the Paris Agreement, and fulfill Sustainable Development Goal 7 (SDG 7) on affordable and clean energy. This comprehensive review synthesizes peer-reviewed literature, intergovernmental reports, and policy documents published primarily between 2020 and 2025 to evaluate the current state, emerging innovations, and future directions of green and sustainable energy technologies. The review covers: solar photovoltaics (PV) and concentrated solar power (CSP), wind energy (onshore and offshore), green hydrogen production and storage, advanced energy storage systems, smart grid infrastructure, bioenergy, geothermal and ocean energy, and carbon capture, utilization, and storage (CCUS). Key findings indicate that the levelized cost of energy (LCOE) for solar PV and onshore wind has fallen by more than 85% over the past decade, making renewables the cheapest source of new electricity generation in most markets. Perovskite solar cells have achieved certified efficiencies exceeding 26%. Green hydrogen is emerging as a critical energy carrier for hard-to-abate sectors. Lithium-ion battery costs have declined to approximately USD 115/kWh in 2024. AI and machine learning are increasingly integrated into energy forecasting and grid management. Despite these advances, significant challenges remain: grid stability, rare earth material constraints, and persistent energy poverty in developing nations. This review highlights the necessity of integrated policy frameworks, international cooperation, and technology transfer to accelerate the sustainable energy transition.