अक्षय उर्जा या नवीकरणीय ऊर्जा में वे सारी उर्जा शामिल हैं जो प्रदूषणकारक नहीं हैं तथा जिनके स्रोत का क्षय नहीं होता, या जिनके स्रोत का पुनः-भरण होता रहता है। सौर ऊर्जा, पवन ऊर्जा, जलविद्युत उर्जा, ज्वार-भाटा से प्राप्त उर्जा, बायोगैस, जैव इंधन आदि नवीनीकरणीय उर्जा के कुछ उदाहरण हैं। भारत में है

Renewable energy is energy from renewable natural resources that are replenished on a human timescale. Mainstream renewable energy options include solar energy, wind power, hydropower, bioenergy and geothermal power. Renewable energy installations can be large or small. They are suited for urban as well as rural areas. Renewable energy is often deployed together with further electrification. This has several benefits: electricity can move heat or objects efficiently, and is clean at the point of consumption. Variable renewable energy sources are those that are not dispatchable due to their fluctuating nature, such as wind power and solar power. In contrast, controllable renewable energy sources include dammed hydroelectricity, bioenergy, or geothermal power. Using renewable energy and energy efficiency technologies is resulting in more energy security, climate change mitigation, and economic benefits.