Renewable Energy - (Part - 1) | Environment for UPSC CSE PDF Download

Renewable Energy

Renewable energy is energy obtained from resources that are naturally replenished on a human timescale. Typical renewable resources include sunlight, wind, rain, tides, waves and geothermal heat. The term often includes biomass, although the carbon-neutral status of some biomass sources is subject to debate.

• Renewable energy sources are generally cleaner than fossil fuels, available locally and can reduce air, water and soil pollution when deployed appropriately.
• Some renewable technologies may cause local environmental impacts (land use, habitat disturbance) and certain biomass uses contribute to indoor air pollution when combusted in inefficient appliances.
• Renewable energy broadly reduces dependence on imported fuels and improves energy security when integrated into the electricity mix.

Major categories of renewable energy

• Solar energy - energy from sunlight, converted either directly to electricity or to heat.
• Hydel energy - energy derived from moving or stored water (small, large and pumped storage hydropower).
• Biomass - energy from organic material such as firewood, animal dung, biodegradable waste and crop residues; includes bioenergy and biopower.
• Geothermal energy - heat from the Earth's interior obtained from hot rocks, hot water springs, geysers and engineered geothermal systems.
• Ocean energy - energy from tides, waves and ocean thermal gradients.
• Wind energy - kinetic energy of moving air converted to electricity by turbines.
• Co-generation - simultaneous production of two useful forms of energy (typically electricity and heat) from one fuel or process.
• Fuel cells - electrochemical devices that convert chemical energy (for example hydrogen) into electricity with high efficiency and low emissions.

Primary and secondary energy sources

• Primary sources are naturally available energy flows such as solar, wind and geothermal.
• Secondary sources are forms produced by conversion of primary sources, for example electricity generated from coal, oil or natural gas. Electricity itself is a secondary energy carrier widely used across sectors.

Installed capacity and national targets (India)

• The Government of India set an overall renewable energy capacity target of 175 GW by 2022, comprising 100 GW solar, 60 GW wind, 10 GW biopower and 5 GW small hydropower.
• As of April 2016 the total installed renewable capacity in India was approximately 42,800 MW. The sectoral ownership distribution at that time was roughly 39% State sector, 31% Private sector and 29% Central sector.

India receives abundant solar radiation over much of the country, making solar power a key option for large-scale and distributed generation. Electricity from sunlight can be produced by two principal routes: direct conversion to electricity using photovoltaic devices, and conversion to heat followed by electricity generation using solar-thermal systems.

Photovoltaic (PV) electricity

• PV systems use solar cells-semiconductor devices with a p-n junction-to convert incident photons into electrical current via the photovoltaic effect.
• A typical PV cell has a negative (n-type) and a positive (p-type) semiconductor layer. When sunlight strikes the cell, photons are absorbed and free charge carriers (electrons and holes) are generated.
• These carriers are separated by the internal electric field at the p-n junction, creating a voltage. When the cell is connected to an external load, current flows and electrical power is delivered.
• PV modules produce direct current (DC); inverters convert DC to alternating current (AC) for grid connection or AC loads.
• PV systems range from small rooftop installations to utility-scale solar parks; they require siting, tilt and orientation optimisation, and consideration of shading, soiling and temperature effects.

Concentrated Solar Power (CSP) / Solar-thermal electricity

• CSP systems use mirrors or reflectors to concentrate sunlight onto a receiver to produce high-temperature heat.
• The heat is used to generate steam that drives a conventional turbine-generator to produce electricity; CSP therefore couples solar collection with a conventional thermal power block.
• Common collector geometries include parabolic troughs, linear Fresnel, solar towers and parabolic dishes. Parabolic troughs are widely used and concentrate radiation onto a receiver tube containing a heat transfer fluid.
• Typical heat transfer fluids include synthetic oils, molten salts and pressurised steam. Molten salt storage can provide thermal energy storage for several hours, improving dispatchability.

Potential of solar energy in India

• Estimates indicate a technical potential in India of around 35 MW per km² for solar PV/thermal deployment under typical conditions.
• Solar radiation incident over India is very large - roughly 5,000 trillion kWh per year is incident on the land area, with most regions receiving about 4-7 kWh/m²/day.
• States with very high solar insolation include Rajasthan, northern Gujarat, parts of the Ladakh region, and areas in Andhra Pradesh, Maharashtra and Madhya Pradesh.

Installed capacity and national initiatives

• Grid-connected solar capacity in India crossed 10,000 MW (10 GW) as of 2017 according to MNRE estimates.
• The National Solar Mission (part of the National Action Plan on Climate Change) aims to scale up solar deployment and envisaged an installed solar generation capacity target of 100 GW by 2022 (revised target under various notifications).

International Solar Alliance (ISA)

• The International Solar Alliance was launched at the COP21 climate conference in Paris on 30 November as a platform for cooperation among solar-resource-rich countries lying fully or partially between the Tropic of Cancer and the Tropic of Capricorn.
• ISA focuses on scaling up deployment of solar energy, mobilising finance, encouraging technology standards and supporting member countries' energy needs.
• The document refers to a formal name International Agency for Solar Policy and Application (IASPA) and locates the ISA Secretariat at the National Institute of Solar Energy, Gurgaon.
• Objectives of the ISA include reducing costs through aggregate demand, promoting standardisation of solar technologies and fostering research and development.
• Additional initiatives mentioned include the IESS 2047 (India Energy Security Scenarios 2047) calculator to explore future energy scenarios.
• The Prime Minister referred to countries between the two tropics as "Surya Putra" (also called "Sunshine Countries"), inviting them to join the alliance.

Luminescent Solar Concentrators (LSCs)

A luminescent solar concentrator (LSC) is a device that traps solar radiation over a large area in a thin sheet and guides re-emitted light to photovoltaic cells mounted at the sheet edges. The sheet is typically a polymer such as polymethylmethacrylate (PMMA) doped with luminescent species (organic dyes, quantum dots or rare-earth complexes).

• Need for LSCs: LSCs aim to replace large areas of expensive solar cells with a cheaper collector material, reducing module cost (£/W) and levelised cost of energy (£/kWh). LSCs collect both direct and diffuse light and therefore do not require sun-tracking, making them attractive for building-integrated photovoltaics (BIPV) and cloudier climates.
• Ideal properties of LSC materials: broad absorption across the solar spectrum, near-unity quantum yield (efficient emission), a large Stokes shift (separation between absorption and emission spectra) to reduce re-absorption losses, and long-term photochemical stability.
• Challenges: achieving high optical efficiency close to theoretical limits, minimising re-absorption and scattering losses, developing stable luminescent materials and scalable manufacturing processes.

The International Renewable Energy Agency (IRENA) is an intergovernmental organisation that supports countries in their transition to a sustainable energy future. IRENA functions as a platform for international cooperation and a repository of policy, technology, resource and financial knowledge on renewable energy.

• IRENA promotes the adoption and sustainable use of renewable energy forms including bioenergy, geothermal, hydropower, ocean, solar and wind energy.
• IRENA has about 150 member nations and its headquarters is located in Abu Dhabi.
• Its roles include providing policy advice, capacity building, data and analysis, and facilitating international collaboration on renewable deployment and finance.

Wind energy is the kinetic energy of moving air in the atmosphere. Wind turbines convert this kinetic energy into mechanical power and then into electricity via a generator. Wind power is deployed in onshore and offshore wind farms and is a major global renewable source.

Wind farms: onshore and offshore

• Onshore wind farms are located on land. They tend to be less expensive to install and maintain and benefit from easier grid connection and logistics.
• Offshore wind farms are sited in bodies of water. Offshore sites usually have higher and more consistent wind speeds, but construction and operation costs are higher than for onshore projects.

Working of wind turbines

Wind turbines capture wind energy using aerodynamically designed blades that rotate a hub connected to a main shaft. The main shaft drives a generator to produce electricity. Modern utility turbines generally have three blades and are mounted on tall towers to access stronger, less turbulent winds.

• Three key variables that determine turbine power output:
• Wind speed: power available in wind rises with the cube of wind speed; typical operational wind speed range for generation is about 4-25 m/s.
• Blade radius (swept area): a larger rotor sweeps more area and captures more energy; doubling the blade radius increases swept area and can increase power by a factor of four (area ∝ radius²).
• Air density: denser air (at lower altitude and lower temperature) increases aerodynamic forces and available power.

Types of wind turbine designs

• Horizontal-axis turbines have two or three blades and rotate about an axis parallel to the ground. They are the dominant design for electricity generation and are sited on towers to access higher wind speeds.
• Vertical-axis turbines rotate about an axis perpendicular to the ground. They have advantages in certain low-height or turbulent sites and can have high torque at low speeds, but they are generally less efficient for large-scale electricity generation and do not benefit from high wind speeds at elevated hub heights.

Potential of wind energy in India

• The National Institute of Wind Energy (NIWE) launched a Wind Energy Resource Map at 100 metres above ground level (AGL) on an online GIS platform.
• The wind energy potential in India at 100 m AGL is estimated to be over 302 GW.
• According to the resource map, Gujarat has the maximum potential, followed by Karnataka, Maharashtra and Andhra Pradesh.

Targets and installed capacity

• Different targets appear in policy documents and announcements; for example, a commonly cited target for wind capacity was 60,000 MW (60 GW) by 2022 as part of broader renewable goals.
• Other long-term targets or ambitions have been expressed as higher numbers (for instance figures around 200,000 MW (200 GW)) in different contexts; these reflect evolving policy aims and planning horizons.
• State-wise installed capacities (indicative): Tamil Nadu - 7,200 MW; Maharashtra - 4,000 MW; Karnataka - 2,700 MW; Rajasthan - 2,700 MW. Several states such as Andhra Pradesh, Madhya Pradesh and Kerala had less than 1,000 MW in earlier records.

National Offshore Wind Energy Policy (2015)

• The policy designates the Ministry of New & Renewable Energy (MNRE) as the nodal ministry for the use of offshore areas within India's Exclusive Economic Zone (EEZ).
• The National Institute of Wind Energy (NIWE) is authorised as the nodal agency for offshore wind development, allocation of offshore blocks and coordination with other ministries and agencies.
• The policy enables offshore wind development in waters up to 200 nautical miles (the EEZ), and aims to create a level playing field for domestic and international investors for offshore projects, research and development.

National Wind Energy Mission (proposed)

• A proposed National Wind Energy Mission seeks to consolidate efforts to meet Plan targets and renewable energy goals under national climate and energy programmes.
• Objectives include precise resource assessment, effective grid integration, technological improvement, strengthening the manufacturing base and maintaining competitiveness in the wind sector.

• Hydropower: uses stored or flowing water to drive turbines. Small hydropower and pumped storage play roles in balancing variable generation and providing ancillary services.
• Biomass and biopower: solid biomass, biogas and liquid biofuels can produce heat, electricity and transport fuels. Sustainable feedstock sourcing, conversion efficiency and emissions control are key considerations.
• Geothermal: provides baseload heat and power where geothermal gradients are favourable; resources include hot springs, steam reservoirs and hot dry rock technologies.
• Ocean energy: includes tidal stream, tidal range, wave energy and ocean thermal energy conversion. These technologies are at different stages of commercial maturity.
• Co-generation: industrial processes (for example sugar mills, pulp and paper) may capture waste heat to generate electricity and improve overall fuel efficiency.
• Fuel cells: devices that convert chemical fuels such as hydrogen into electricity with high electrical efficiency and low local emissions; they are used for stationary, transport and backup power applications.

• Intermittency and variability: solar and wind output vary with weather and diurnal cycles. Solutions include energy storage (batteries, pumped hydro), demand response, diversity across regions and complementary generation portfolios.
• Grid integration: high shares of variable renewables require grid upgrades, flexible generation, improved forecasting and market mechanisms to manage variability.
• Storage and flexibility: large-scale electrical storage, thermal storage (for CSP), and hybrid systems are essential for firming renewable output and enabling dispatchability.
• Land use and environmental impacts: siting must consider ecological sensitivity, land availability and social impacts; distributed rooftop solar and use of degraded lands can reduce conflicts.
• Financing and cost reduction: policies such as auctions, feed-in tariffs (historically), viability gap funding, concessional finance and risk mitigation measures reduce capital costs and attract investment.
• Manufacturing and supply chains: scaling requires domestic manufacturing capability, quality standards and supply chain resilience to secure components (panels, turbines, inverters, storage).
• Socioeconomic aspects: job creation, skill development and inclusive policies are needed to ensure equitable benefits from renewable deployment.
• Biomass indoor pollution: reliance on traditional biomass for cooking causes indoor air pollution; cleaner stoves, transitions to LPG and biogas, and electrification of cooking can reduce health impacts.

• Policy instruments: renewable purchase obligations (RPOs), auctions/tenders, capital incentives, tax benefits, net metering for rooftop solar and public sector procurement are commonly used to accelerate deployment.
• International cooperation: organisations such as IRENA and initiatives like the ISA facilitate technology transfer, finance mobilisation and capacity building.
• Applications: utility-scale power plants, rooftop solar for homes and commercial buildings, BIPV (building-integrated photovoltaics), off-grid and microgrid systems for remote areas, wind farms for grid supply, and hybrid systems combining multiple resources.
• Storage and balancing: pumped hydro is a mature bulk storage technology; battery energy storage systems (BESS) are increasingly deployed for ancillary services, peak shaving and time-shifted energy delivery.
• Cogeneration and industrial use: industries with high process heat demand can improve energy efficiency and reduce fossil fuel use through cogeneration systems and waste-heat recovery.

Renewable energy comprises a diverse set of technologies that can provide clean, local and increasingly cost-competitive energy. Realising the full potential requires integrated planning: robust resource assessment, grid upgrades, storage and flexibility measures, sound policy instruments, investment in manufacturing and R&D, and careful environmental and social management. National and international initiatives - such as sector missions, multilateral agencies and intergovernmental alliances - play an important role in mobilising finance, technology and expertise to scale renewables effectively.