renewable energy

Renewable energy harnesses naturally replenishing sources—sunlight, wind, flowing water, geothermal heat and biomass—to generate power without depleting the resource itself. Its uniqueness lies in the dual promise of meeting growing electricity demand while curbing greenhouse‑gas emissions, a combination that underpins global climate commitments and reshapes energy security for nations ranging from Norway to India. ## Historical Background The first recorded use of renewable forces dates to 3rd‑century BC watermills in the Roman Empire, while windmills appeared in Persia around the 9th century to grind grain. Modern hydroelectric generation began with the 1882 Niagara Falls plant, delivering 50 MW to Buffalo, New York, and demonstrated that kinetic energy of water could be scaled for industrial use. The 1973 oil embargo triggered the first coordinated policy response: the United States established the Solar Energy Research Institute (now NREL) in 1977, and Germany introduced feed‑in tariffs for wind in the early 1990s. The 1992 United Nations Framework Convention on Climate Change (UNFCCC) codified renewable energy as a climate mitigation tool, and the 2015 Paris Agreement set a collective goal of limiting warming to 1.5 °C, cementing renewables at the heart of national energy plans. ## How Renewable Energy Works Solar photovoltaic (PV) modules convert photons into electricity via semiconductor p‑n junctions; commercial silicon cells achieve 15–22 % conversion efficiency, with laboratory‑recorded perovskite cells reaching 29 % as of 2023. Wind turbines extract kinetic energy from moving air using rotor blades attached to a generator; modern 3‑MW onshore turbines operate at a capacity factor of 30–45 % depending on site wind speed. Hydropower exploits the potential energy of water stored behind dams, with the Three Gorges Dam in China delivering 22.5 GW of installed capacity and a capacity factor above 45 %. Biomass power plants combust organic material, releasing roughly 0.5 t CO₂ per MWh—significantly lower than coal’s 0.9 t CO₂ per MWh—while geothermal facilities tap heat from the Earth’s crust, with Iceland generating 25 % of its electricity from geothermal sources as of 2022. ## Global Landscape The International Energy Agency reported 3,200 GW of renewable electricity capacity worldwide at the end of 2023, accounting for 29 % of total generation. China led with 1,200 GW, the United States contributed 400 GW, and the European Union collectively installed 600 GW, driven largely by offshore wind and solar farms. Norway’s grid is powered by 98 % renewable electricity, primarily hydro, making it the world’s most renewable‑dependent nation. India, the third‑largest emitter, reached 177 GW of cumulative renewable capacity by December 2022—87 GW solar, 44 GW wind, 45 GW hydro and 1 GW biomass—and has pledged 450 GW by 2030. A landmark policy announced in May 2024 mandates that all solar modules sold in India from 1 June 2024 must contain domestically manufactured cells, a move aimed at bolstering local supply chains and reducing import dependence. ## India’s Renewable Energy Journey The National Solar Mission, launched in 2008 under the Ministry of New and Renewable Energy (MNRE), set an initial target of 20 GW solar capacity by 2022; a 2015 revision raised the ambition to 100 GW, a milestone the country surpassed in early 2022 with 87 GW operational. The Renewable Purchase Obligation (RPO) introduced in 2015 obliges large consumers to procure a minimum share of renewable electricity, currently fixed at 20 % for the power sector. In 2020, the Electricity Act was amended to facilitate open access for renewable generators, and the 2023 Green Energy Corridor project began constructing 20 GW of high‑capacity transmission lines to alleviate curtailment in solar‑rich states such as Rajasthan and Gujarat. The 2024 solar‑cell mandate, enforced by MNRE and the Ministry of Commerce, imposes a 30 % domestic content requirement for all PV modules entering the Indian market, with penalties of up to ₹10 crore for non‑compliance. ## Significance and Challenges Renewable electricity avoided an estimated 2.5 gigatonnes of CO₂ emissions globally in 2022, according to the IEA, while also reducing water consumption by up to 30 % compared with coal‑fired plants that require extensive cooling‑water withdrawals. In India, shifting 50 % of thermal generation to renewables could cut water‑related pollution in the Ganges basin by an estimated 12 million m³ per year. Nevertheless, intermittency remains a technical hurdle: