Chapter 10 — ଶକ୍ତି ସମ୍ବଳ

Energy is the capacity to do work, and every activity of human society, from cooking and lighting to running mills, trains and computers, needs a supply of it. The sources from which usable energy is obtained are called energy resources or power resources. Because they are used to drive machines, energy resources are also called power resources, and because coal, oil and gas are dug or pumped from the earth they are often studied under minerals as 'mineral fuels'. The consumption of commercial energy per head is one of the best indicators of a country's level of economic development: a farmer with a bullock uses very little, a city with steel plants, electric trains and air conditioners uses a great deal. India's per capita energy use is still far below the world average, and raising it while protecting the environment is a central problem of the country's planning.

Energy resources are classified in three ways, and a student should be able to place any source in all three.

1. Conventional and non-conventional. Conventional sources are those that have been in use for a long time and on which the bulk of the world's supply still depends: firewood, cattle dung, coal, petroleum, natural gas and electricity generated from water (hydel), coal (thermal) and atomic minerals (nuclear). Non-conventional sources are those that have come into use recently, mostly through new technology: solar energy, wind energy, tidal and wave energy, geothermal energy, biogas and energy from urban waste.

2. Renewable and non-renewable. Renewable sources are those that nature replenishes continuously and that cannot be exhausted by use: sunlight, wind, flowing water, tides, geothermal heat and biomass. Non-renewable sources are those that exist in fixed stocks and are used up once burnt: coal, petroleum, natural gas and uranium. Note that the two classifications do not coincide: hydel power is conventional but renewable; nuclear power is conventional and non-renewable; biogas is non-conventional but renewable.

3. Commercial and non-commercial. Commercial sources are bought and sold in the market: coal, oil, gas and electricity. Non-commercial sources are gathered free by the user, chiefly in villages: firewood, agricultural waste and dried cow dung cakes. In India firewood and dung still provide a large part of the energy used for cooking in rural homes, which causes deforestation, loss of manure and smoke-related disease; replacing them with LPG, biogas and electricity is a national programme.

A further distinction is between primary sources, found in nature (coal, oil, sunlight), and secondary sources, made from a primary one (electricity, petrol, coke). Electricity is the most convenient form of energy because it can be carried by wire, switched on and off and converted to light, heat and motion, and its generation from all the primary sources is the theme of the middle of this chapter.

Coal is the most abundantly available fossil fuel in India and provides a substantial part of the nation's energy requirement. It is used for power generation, for supplying energy to industry, for making coke for the blast furnace and, formerly, for the railways and for domestic use. India is among the three largest coal producers of the world, and coal-fired stations produce roughly seven-tenths of the country's electricity.

Coal is formed from the compression of plant material over millions of years. In the swampy forests of past geological ages, dead trees and plants fell into water and mud, where the absence of oxygen prevented their complete decay. Layer after layer of sediment buried this vegetable matter; the weight, the heat of the earth and the passage of time squeezed out the water and volatile matter and enriched the remainder in carbon. The longer and deeper the burial, the higher the carbon content and the better the coal. Coal is therefore found in a variety of forms depending on the degree of compression, the depth and the time of burial.

Peat is the first stage: decaying plants in swamps, with a low carbon content, high moisture and low heating capacity; it is cut and dried as a poor domestic fuel in a few regions. Lignite or brown coal is a low grade coal, soft, with high moisture content and about 40 to 55 per cent carbon; the principal lignite reserves are at Neyveli in Tamil Nadu, where it is burnt in a large thermal station beside the mine, and in Rajasthan, Gujarat and Jammu and Kashmir. Bituminous coal is coal that has been buried deep and subjected to increased temperature; it has 60 to 80 per cent carbon and is the most popular coal in commercial use. Its coking grade, which softens and fuses on heating into hard porous coke, is of special value in the smelting of iron ore in blast furnaces; India's coking coal is limited to the Jharia field of Jharkhand and a few others. Anthracite is the highest quality hard coal, with over 80 per cent carbon, burning slowly with little smoke; India has almost none, a small quantity occurring in Jammu and Kashmir.

The heating value, ash content and moisture of coal decide its use. Indian coal is generally high in ash (25 to 45 per cent), which lowers its heat value and produces enormous quantities of fly ash at power stations; washing the coal before use reduces this. Because coal is bulky and loses nothing in burning except its energy, it is expensive to transport, so heavy industries and thermal power stations are located as near as possible to the coalfields, which is why the great industrial regions of India, and the thermal stations of Talcher and Ib valley in Odisha, lie beside the coal.

Coal in India occurs in rock series of two main geological ages: the Gondwana coal, a little over 200 million years old, and the Tertiary coal, only about 55 million years old. The Gondwana coalfields hold about 98 per cent of India's reserves and almost all its coking coal.

The Gondwana coalfields lie in the river valleys of the peninsula. The most important are in the Damodar valley of Jharkhand and West Bengal: Jharia, the storehouse of the best coking coal in the country, Bokaro, Giridih, Karanpura and Raniganj, the oldest coalfield in India, worked since 1774. The Godavari valley has the Singareni fields of Telangana; the Mahanadi valley has Talcher in Odisha and Korba, Hasdeo and Mand-Raigarh in Chhattisgarh; the Son valley has Singrauli on the Madhya Pradesh–Uttar Pradesh border and Umaria and Sohagpur; the Wardha valley has the fields of Chandrapur and Yavatmal in Maharashtra; and the Ib valley of Odisha and the Pench–Kanhan valley of Madhya Pradesh are others. Jharkhand, Odisha, Chhattisgarh, West Bengal, Madhya Pradesh, Telangana and Maharashtra are the major producing states, and Odisha, Chhattisgarh and Jharkhand together hold more than half of the country's reserves.

Tertiary coal occurs in the north-eastern states of Meghalaya (Cherrapunji, Darangiri), Assam (Makum, Ledo, Margherita in the Upper Assam fields), Arunachal Pradesh and Nagaland, and in Jammu and Kashmir. Tertiary coal has high sulphur and low ash and is used locally.

Odisha holds about a quarter of India's coal reserves, mostly in two fields. The Talcher coalfield in Angul district, in the Brahmani valley, is one of the largest in India by reserves, with thick seams close to the surface worked by huge open-cast mines at Bharatpur, Ananta, Jagannath, Lingaraj, Hingula, Balram and Kaniha under Mahanadi Coalfields Limited (MCL), a subsidiary of Coal India. The Ib valley coalfield in Jharsuguda and Sundargarh districts, along the Ib river, is worked at Lakhanpur, Belpahar, Samaleswari, Lajkura and Orient. Both fields are non-coking, high-ash power coal, and MCL is one of the largest coal producers among all Coal India subsidiaries. The coal goes by rail and merry-go-round conveyor to the super thermal power stations at Talcher and Kaniha, to the Ib valley stations at Banharpali, to the captive plants of the aluminium and steel complexes at Angul, Jharsuguda and Kalinganagar, and by rail to Paradip port for the coastal power stations of southern India. Coal India's other subsidiaries are Bharat Coking Coal (Jharia), Central Coalfields (Ranchi), Eastern Coalfields (Raniganj), Western Coalfields (Nagpur), South Eastern Coalfields (Bilaspur) and Northern Coalfields (Singrauli), and Neyveli Lignite Corporation is separate.

Petroleum (from the Latin petra, rock, and oleum, oil) or mineral oil is the next major energy source in India after coal. It provides fuel for heat and lighting, lubricants for machinery and raw materials for a number of manufacturing industries. Petroleum refineries act as a 'nodal industry' for synthetic textiles, fertilisers and numerous chemical industries, because naphtha, ethylene and other by-products of refining are their raw materials. Because transport by road, air and sea runs almost entirely on petroleum products, oil is often called 'liquid gold', and a country's dependence on imported oil is a matter of strategic concern.

Petroleum was formed from the remains of tiny marine plants and animals that were buried in the mud of shallow seas millions of years ago and, under pressure and heat and in the absence of oxygen, were slowly converted into liquid hydrocarbons. Most of the petroleum occurrences in India are therefore associated with anticlines and fault traps in the rock formations of the Tertiary age. In regions of folding, anticlines or domes, the oil is trapped in the crest of the up-fold; the oil-bearing layer is a porous limestone or sandstone through which oil may flow, sealed above by an impermeable layer that stops it escaping. Petroleum is also found in fault traps between porous and non-porous rocks. Gas, being lighter, usually occurs above the oil, and water below it.

The oil fields of India are in three regions. (1) Mumbai High, an offshore field about 160 km north-west of Mumbai in the Arabian Sea, discovered in 1974 and worked from platforms like Sagar Samrat, produces about 63 per cent of India's crude oil; Bassein and Panna-Mukta are neighbouring offshore fields. (2) Gujarat, around the Gulf of Khambhat, with the fields of Ankleshwar, Kalol, Mehsana, Nawagam, Kosamba, Lunej and Cambay, produces about 18 per cent. (3) Assam, the oldest oil producing region of India, with Digboi (where oil was first struck in 1867 and the first refinery built in 1901), Naharkatiya, Moran-Hugrijan, Rudrasagar, Lakwa and Geleki in the Brahmaputra valley, produces about 16 per cent. Newer finds are in the Krishna–Godavari basin of Andhra Pradesh (both onshore and deep offshore), the Cauvery basin of Tamil Nadu, Barmer in Rajasthan (Mangala, one of the largest onshore fields found in recent decades) and the Cachar area of Assam. Exploration and production are done chiefly by the Oil and Natural Gas Corporation (ONGC), set up in 1956, and Oil India Limited, with private companies since the 1990s. Despite these fields India produces only about a fifth of the crude oil it consumes and imports the rest, chiefly from West Asia, making crude oil the largest item of the country's import bill.

Crude oil as it comes from the well is a thick, dark mixture of hydrocarbons that cannot be used as it is. It must be refined, that is, separated by fractional distillation into petrol, diesel, kerosene, aviation fuel, LPG, naphtha, lubricants, bitumen and petroleum coke. A refinery is therefore as essential as the oil field, and its location follows one of two principles: near the oil field (Digboi, Ankleshwar) or near the market and the port through which imported crude arrives (Mumbai, Kochi, Chennai, Paradip).

India has about two dozen refineries. The oldest is Digboi in Assam (1901); the others in Assam are Guwahati (Noonmati), Bongaigaon and Numaligarh. Bihar has Barauni, fed by pipeline from Assam. Gujarat has Koyali near Vadodara, and the giant private refineries at Jamnagar (the largest refining complex in the world) and Vadinar. Maharashtra has two at Mumbai (Trombay). Uttar Pradesh has Mathura, Haryana has Panipat, Punjab has Bathinda, Madhya Pradesh has Bina, Karnataka has Mangaluru, Kerala has Kochi, Tamil Nadu has Chennai (Manali) and Nagapattinam, Andhra Pradesh has Visakhapatnam, West Bengal has Haldia and Odisha has Paradip. The Paradip refinery of the Indian Oil Corporation, commissioned in 2016, is one of the most modern in the country; it receives imported crude through a single-point mooring in the Bay of Bengal, supplies petrol and diesel to eastern India through the Paradip–Haldia–Durgapur and Paradip–Hyderabad pipelines, and has a petrochemical complex attached. The refinery has made Paradip a growth centre of Odisha's coast.

Pipelines are the cheapest and safest means of moving crude oil, refined products and natural gas over land, and their network in India has grown rapidly. The major ones are: the Naharkatiya–Noonmati–Barauni crude oil pipeline of the north-east; the Salaya–Koyali–Mathura crude pipeline from the Gujarat coast to the Mathura refinery, later extended to Panipat and Jalandhar; the Mumbai High–Mumbai–Ankleshwar–Koyali pipeline; the Hazira–Vijaipur–Jagdishpur (HVJ) gas pipeline, 1,700 km long, which carries gas from the western offshore fields across Gujarat, Madhya Pradesh and Rajasthan to the fertiliser plants and power stations of Uttar Pradesh; the Kandla–Bhatinda product line; and the Paradip–Haldia–Durgapur product line. The Jagdishpur–Haldia–Bokaro–Dhamra gas pipeline ('Urja Ganga') is bringing natural gas to Odisha and the eastern states. Pipelines are laid once at high cost but then move fuel continuously at low running cost without loss, and they are safe from the accidents and pilferage of road and rail transport.

Natural gas is an important clean energy resource found in association with or without petroleum. It consists mainly of methane with smaller amounts of ethane, propane and butane. Because it is a gas it burns completely and cleanly, leaving no ash and producing much less carbon dioxide than coal or oil for the same heat; it is therefore considered an environment-friendly fuel. It is used as a source of energy in power stations and industry, as a domestic fuel (piped natural gas, PNG), as vehicle fuel in the form of compressed natural gas (CNG), which is replacing petrol and diesel in the buses, taxis and autos of Delhi, Mumbai and other cities to reduce air pollution, and as an industrial raw material in the petrochemical and fertiliser industries, where it supplies the hydrogen for making ammonia and urea. The liquefied petroleum gas (LPG) used in kitchens is a related product obtained from both natural gas and refining.

Gas occurs in the same Tertiary sedimentary basins as oil. Large reserves of natural gas have been discovered in the Krishna–Godavari basin, both onshore in the delta and in the deep waters off the Andhra coast, which is now the biggest gas field of India. Along the west coast the reserves of Mumbai High and the allied fields (Bassein, Tapti) are supplemented by finds in the Gulf of Khambhat and Hazira in Gujarat. The Andaman and Nicobar islands are also important areas with large reserves of natural gas, so far unexploited. Smaller quantities come from Assam, Tripura, Rajasthan (Jaisalmer) and Tamil Nadu (Cauvery basin), and coal-bed methane is being tapped from the coalfields of Jharkhand and West Bengal.

The 1,700 km long Hazira–Vijaipur–Jagdishpur (HVJ) cross-country gas pipeline links Mumbai High and Bassein with the fertiliser, power and industrial complexes of western and northern India. This artery provided an impetus to India's gas production, and the power and fertiliser industries are its key users. Since gas cannot be moved except by pipeline (or by ship after liquefaction into LNG at very low temperature), India's gas network has been expanded by GAIL (Gas Authority of India Limited), and imported LNG is received at terminals at Dahej, Hazira, Dabhol, Kochi and Ennore. The Pradhan Mantri Urja Ganga pipeline from Jagdishpur through Bihar and Jharkhand to Haldia, Bokaro and Dhamra in Odisha, with an LNG terminal at Dhamra port, is bringing piped gas to the fertiliser plant at Talcher (being revived to make urea from coal gas) and to the industries and cities of Odisha. City gas networks are being laid in Bhubaneswar and Cuttack. Natural gas is thus the bridge fuel between the coal age and the age of renewable energy.

Electricity has such a wide range of applications in today's world that its per capita consumption is considered as an index of development. It is the most convenient form of energy: it can be sent hundreds of kilometres by wire, switched on instantly and turned into light, heat, motion or sound. Electricity is generated mainly in three ways: by running water, which drives hydro turbines to generate hydel electricity; by burning fuels such as coal, petroleum and natural gas to drive turbines to produce thermal power; and by the fission of atomic minerals to produce nuclear power. Of these, thermal power is the largest source in India, providing about seven-tenths of all electricity generated, and coal is the fuel of most of it.

In a thermal power station the fuel is burnt in a boiler to turn water into high-pressure steam; the steam drives a turbine coupled to a generator, and the spent steam is condensed with cooling water and returned to the boiler. A station therefore needs three things: fuel, large quantities of water and a site for ash disposal. Because coal is bulky and expensive to carry, the largest stations are built at the pit head of the coalfields; because they need water, they are placed on a river or reservoir. The thermal stations are run by the central National Thermal Power Corporation (NTPC), by the state electricity boards and generation companies, and increasingly by private companies and by the captive plants of steel and aluminium works.

The major thermal stations of India include Singrauli, Rihand and Obra (Uttar Pradesh), Korba (Chhattisgarh), Ramagundam (Telangana), Vindhyachal (Madhya Pradesh), Farakka and Kolaghat (West Bengal), Chandrapur (Maharashtra), Neyveli (Tamil Nadu, on lignite), Mundra (Gujarat), Dadri (gas), and Kahalgaon (Bihar). Odisha has two of NTPC's largest: the Talcher Super Thermal Power Station at Kaniha in Angul district, one of the biggest in the country, and the older Talcher Thermal Power Station, both burning Talcher coal and drawing water from the Brahmani and the Samal barrage; the Ib Thermal Power Station at Banharpali in Jharsuguda, on the Ib valley coal and the Hirakud reservoir; and the huge captive plants of NALCO at Angul, Vedanta at Jharsuguda, and the steel plants at Kalinganagar and Rourkela. Talcher–Angul–Jharsuguda is one of the largest concentrations of thermal generation in India, and much of its output is sent by high-voltage lines to the southern grid.

Thermal power has the advantages of quick construction, steady output in all seasons and location near the load, but its disadvantages are heavy: it consumes a non-renewable fuel, produces fly ash, sulphur dioxide, nitrogen oxides and carbon dioxide, pollutes rivers with hot water and ash slurry, and its running cost rises with the price of coal. The ash ponds and grey air of Talcher are the local price of the electricity the state sells.

Hydro-electricity or hydel power is generated by the force of falling or fast-flowing water turning a turbine. Water stored behind a dam is led through pipes (penstocks) to turbines in a powerhouse at a lower level; the head, that is the height through which the water falls, and the quantity of water together decide the power produced. Hydel power is renewable, because the river keeps flowing; clean, because nothing is burnt; and cheap to run, because the fuel is free, though the dam is costly to build. Its disadvantages are that it depends on rainfall and so varies with the season, that the reservoir submerges forests, farms and villages and displaces people, and that the best sites are often far from the cities that need the power.

India has large hydel potential in the Himalayan rivers, the Western Ghats and the peninsular rivers, of which only about a quarter has been developed. The multi-purpose river valley projects built after Independence combined power with irrigation, flood control and navigation. The famous ones are the Bhakra Nangal project on the Sutlej (Punjab–Himachal), Damodar Valley (Jharkhand–West Bengal), Kopili (Assam), Tehri on the Bhagirathi (Uttarakhand), Nagarjuna Sagar and Srisailam on the Krishna, Sardar Sarovar on the Narmada, Koyna in Maharashtra, Sharavati and Kali in Karnataka, Idukki in Kerala, Mettur in Tamil Nadu and Salal and Baglihar on the Chenab. The National Hydroelectric Power Corporation (NHPC) builds the central projects and the states build their own.

Odisha, with its hilly plateau and heavy monsoon rivers, is well placed for hydel power, and its projects are managed by the Odisha Hydro Power Corporation (OHPC). The Hirakud dam on the Mahanadi near Sambalpur, completed in 1957 as the first major multi-purpose project of independent India and one of the longest earthen dams in the world (about 26 km with its dykes), has powerhouses at Burla and Chiplima; the Balimela project on the Sileru in Malkangiri, shared with Andhra Pradesh; the Upper Kolab project in Koraput; the Upper Indravati project in Kalahandi–Nabarangpur, which diverts the Indravati into the Mahanadi basin and is the state's largest hydel plant; the Rengali dam on the Brahmani in Angul; the Machkund project on the Odisha–Andhra border, the oldest of them (1955); and smaller stations at Mukhiguda and Potteru. Together they give Odisha about 2,000 MW, though the share of hydel in the state's total has fallen as thermal capacity has grown. In a good monsoon the reservoirs also irrigate the Sambalpur, Bargarh and Koraput plains and hold back floods on the Mahanadi.

Nuclear energy is obtained by altering the structure of atoms. When the nucleus of a heavy atom such as uranium-235 is split (fission) by a neutron, it releases an enormous amount of heat and further neutrons which split more nuclei in a chain reaction. In a nuclear reactor this chain reaction is controlled, the heat is used to make steam, and the steam drives a turbine and generator exactly as in a thermal station. The great advantage is the concentration of energy: one kilogram of uranium yields as much energy as about 3,000 tonnes of coal, and a reactor produces no smoke, ash or carbon dioxide. The disadvantages are the danger of accidents (Chernobyl 1986, Fukushima 2011), the problem of storing radioactive waste for thousands of years, the very high cost of building and decommissioning plants and the link with nuclear weapons.

The atomic minerals are uranium and thorium. Uranium is mined at Jaduguda in Singhbhum district of Jharkhand (with Narwapahar and Turamdih), the only working uranium mines of India for decades, and is found in the Aravalli rocks of Rajasthan, in Nalgonda (Telangana), Cuddapah (Andhra Pradesh) and Domiasiat in Meghalaya. Thorium is obtained from monazite sand on the beaches of Kerala (Chavara), Tamil Nadu (Manavalakurichi) and Odisha (Chhatrapur in Ganjam, where Indian Rare Earths Limited separates monazite, ilmenite and zircon), and India has the largest thorium reserves in the world. Because uranium is scarce and thorium plentiful, India follows a three-stage programme: natural-uranium reactors first, then fast breeder reactors, and finally thorium-based reactors.

The Atomic Energy Commission (1948) and the Department of Atomic Energy, founded under Homi J. Bhabha, run the programme, and the Nuclear Power Corporation of India operates the stations. The nuclear power stations of India are Tarapur in Maharashtra (the first, 1969), Rawatbhata near Kota in Rajasthan, Kalpakkam near Chennai in Tamil Nadu (where the fast breeder reactor is also being built), Narora in Uttar Pradesh, Kakrapar in Gujarat, Kaiga in Karnataka and Kudankulam in Tamil Nadu, the largest, built with Russian collaboration. Odisha has no nuclear power station, but its thorium sands at Chhatrapur are a resource for the third stage of the programme. Nuclear power provides only about three per cent of India's electricity today; heavy water plants at Talcher (now closed), Kota, Thal and Manuguru, and the Bhabha Atomic Research Centre at Trombay support the industry.

The growing consumption of energy has made India increasingly dependent on fossil fuels such as coal, oil and gas, and this dependence brings three dangers. First, scarcity and price: fossil fuels are finite; the rising prices of oil and gas and their potential shortages have raised uncertainties about the security of energy supply in the future, and India already imports most of its oil. Second, environmental damage: the burning of fossil fuels is the largest cause of air pollution and of the greenhouse gases that cause global warming and climate change, which threaten the monsoon, the coasts and agriculture. Third, uneven distribution: coal and oil lie in a few places, and moving them is costly, while the sun and the wind reach every village. There is therefore a pressing need to use renewable energy sources such as solar energy, wind, tide, biomass and energy from waste material. These are called non-conventional sources because their large-scale use is new, and a country like India, which has ample sunshine, long coasts, windy plateaus and huge amounts of animal and farm waste, has every reason to develop them.

India recognised this early. The Ministry of New and Renewable Energy (originally the Department of Non-conventional Energy Sources, 1982) is the only such ministry in the world, and the country has set itself among the most ambitious targets for renewable capacity. Renewable sources have several general advantages: they are inexhaustible, they are clean, they can be installed in small units close to where power is needed (a solar lamp, a village wind pump, a family biogas plant) and so suit the scattered villages of India, and once installed their running cost is very low. Their disadvantages are that the supply is intermittent (no sun at night, no wind on a calm day), the energy is dilute and needs large areas of collectors, the initial cost of the equipment is high, and electricity from them must be stored in batteries or backed by conventional plants until better storage is developed.

The sections that follow take up each source: solar energy, the most promising for India; wind energy, already the largest renewable source of electricity in the country; biogas and biomass, which turn farm and animal waste into fuel and manure; tidal and wave energy of the coast; and geothermal energy of the hot springs. For Odisha, with about 300 sunny days a year, a 480 km coast, the waste of a large cattle population and a mountainous interior, all of these are relevant, and the state's renewable capacity in solar and small hydel is growing.

India is a tropical country and has enormous possibilities of tapping solar energy. Most parts of the country receive bright sunshine for 250 to 300 days a year, and the energy falling on one square metre in a day is enough to run a household's lights and fans if it could all be captured. Solar energy is used in two ways. In solar thermal devices the heat of the sun is used directly: solar water heaters on roofs, solar cookers (a black box with a glass lid and reflector that reaches 100 °C or more), solar driers for crops and fish, solar stills for distilling water, and large mirror fields that concentrate sunlight to raise steam for a turbine. In photovoltaic (PV) technology, solar cells made of silicon convert sunlight directly into electricity; panels of such cells power street lights, water pumps, telephone exchanges, satellites and, increasingly, entire grids.

Solar energy is fast becoming popular in rural and remote areas because it can be produced where it is used, without transmission lines. Solar lanterns, solar home lighting systems and solar pumps for irrigation have reached villages of Odisha's tribal districts that no wire had reached. It is expected that the use of solar energy will minimise the dependence of rural households on firewood and dung cakes, which in turn will contribute to environmental conservation and an adequate supply of manure in agriculture, since dung can go back to the fields. The cost of solar cells has fallen so sharply in recent years that solar electricity from large parks is now cheaper than that from a new coal station.

The largest solar plants of India are in the sunniest, driest regions: the Bhadla solar park in Jodhpur district of Rajasthan, one of the largest in the world, the parks at Pavagada (Karnataka), Kurnool (Andhra Pradesh), Rewa (Madhya Pradesh) and Charanka (Gujarat), and the canal-top panels of Gujarat which also reduce evaporation. India was a founder of the International Solar Alliance (2015), which unites the sunny countries between the tropics. In Odisha solar capacity is growing with parks in Bolangir, Sonepur and Nuapada in the sunny west of the state, floating solar panels planned on the Hirakud and Rengali reservoirs, roof-top systems on government buildings in Bhubaneswar and solar street lights in thousands of villages. The limitation of solar power is that it stops at sunset and weakens in the cloudy monsoon months, so it must be combined with storage batteries, pumped-storage hydel or thermal back-up to supply power at night.

Wind is air in motion, and its kinetic energy has been used for centuries to sail ships, pump water and grind grain. A modern wind turbine is a tall tower carrying a rotor of two or three long blades; the wind turns the blades, which drive a generator in the nacelle at the top, and the electricity is fed to the grid. Turbines are grouped in wind farms of tens or hundreds of machines. A site needs a steady wind of at least 5 to 6 metres per second for most of the year, which is found on coasts, on hill ridges and passes, and on open plateaus. Wind energy is renewable, clean and cheap to run, and turbines use little land (the fields beneath can still be farmed); its disadvantages are that the wind is intermittent and seasonal, that turbines make noise and kill birds, and that the best sites are limited.

India has great potential for wind power, and it was for many years the largest renewable source of electricity in the country. The largest wind farm cluster is located in Tamil Nadu from Nagarcoil to Madurai, where the Aralvaimozhi and Palghat gaps of the Western Ghats funnel the south-west monsoon winds through Kanniyakumari, Tirunelveli and Coimbatore districts; Muppandal near Kanniyakumari is one of the largest wind farms in Asia. Apart from these, Gujarat (the Kachchh and Saurashtra coasts, Jamnagar, Lamba), Maharashtra (Satara, Sangli, Dhule, Ahmednagar), Karnataka (Chitradurga, Gadag, Davangere), Rajasthan (Jaisalmer), Andhra Pradesh (Anantapur, Kurnool) and Kerala (Palakkad) and the Lakshadweep islands have important wind farms. Nagarcoil and Jaisalmer are well known for the effective use of wind energy in the country. India makes its own turbines, and companies of Pune and Chennai are among the world's manufacturers.

Odisha's wind is weaker than that of the peninsular coast, because the Bay of Bengal winds are less steady, but sites have been identified on the coast of Ganjam and Puri and on the ridges of the Eastern Ghats in Koraput and Gajapati, and offshore wind farms off the Odisha coast are under study. Small wind pumps for lifting water are used on the coast. Wind and solar complement each other: the monsoon months that cloud the sun are the windiest, so a hybrid park of both gives steadier power through the year.

Biogas is produced by the decomposition of organic matter, shrubs, farm waste, animal dung and human waste, by bacteria in the absence of air (anaerobic fermentation). The gas is about 60 per cent methane and burns with a clean blue flame. It has a higher thermal efficiency in comparison to kerosene, dung cakes and charcoal, because it burns completely without smoke. A biogas plant consists of a mixing tank, an underground digester of brick or steel into which dung mixed with water is fed, a gas holder (a floating steel drum or a fixed dome) that collects the gas, and an outlet for the digested slurry. The plants are set up at the municipal, cooperative and individual levels; the plants using cattle dung are known in rural India as gobar gas plants. These provide twin benefits to the farmer: energy for cooking and lighting, and the improved quality of manure, since the slurry that comes out is richer in nitrogen than raw dung and free of the weed seeds and flies that dung heaps breed. Biogas also stops the burning of dung cakes, which wastes manure, and reduces the cutting of firewood, and it saves rural women from the smoke of the chulha. A family plant of 2 cubic metres needs the dung of three or four cattle; a community plant serves a whole hamlet.

Biomass in the wider sense includes firewood, crop residues (paddy straw, bagasse of sugarcane, rice husk, groundnut shells), and energy crops. Bagasse is burnt in sugar mills to run their boilers, and rice husk fires small power plants in the rice belts of Odisha and Chhattisgarh. Biomass gasifiers turn wood chips into a gas that runs engines, and ethanol from sugarcane and biodiesel from jatropha or used oil are blended into petrol and diesel. Biomass is renewable if the plants are regrown, and carbon-neutral, since the carbon dioxide released was taken from the air by the plant.

Energy from urban waste is a newer field. The garbage of a city contains organic matter that can be digested to gas, and the rest can be burnt to raise steam; the landfill gas at Okhla in Delhi and the waste-to-energy plants at Delhi, Jabalpur and Hyderabad are examples. Bhubaneswar is installing a waste-to-energy plant at its Bhuasuni dump. Such plants solve two problems at once, the mountain of waste and the demand for power, but the burning of mixed waste must be controlled to avoid toxic smoke. In Odisha's villages the National Biogas programme has installed lakhs of family plants, and community plants in Ganjam and Cuttack districts run dairy cooperatives.

Tidal energy uses the twice-daily rise and fall of the sea caused by the gravitational pull of the moon and sun. Where a narrow inlet, estuary or bay has a large tidal range, a dam with sluice gates can be built across it: during high tide water flows into the inlet and is trapped when the gates close; after the tide falls the trapped water is released to the sea through turbines that generate electricity, and the incoming tide can drive them again. Tidal power is renewable and perfectly predictable, since the tides follow the calendar, but the suitable sites are few and the dam disturbs the estuary's fish and mud flats. In India the Gulf of Khambhat and the Gulf of Kachchh on the Gujarat coast, with tidal ranges of 6 to 11 metres, and the Sundarban region of the Ganga delta in West Bengal provide ideal conditions for tidal energy, and a pilot plant has been set up in the Sundarbans. The Bay of Bengal coast of Odisha has too small a tidal range for such projects. Wave energy, which uses the up-and-down motion of sea waves to compress air or move floats, has been tested at Vizhinjam near Thiruvananthapuram in Kerala, and ocean thermal energy, which uses the temperature difference between warm surface and cold deep water, has been tried off the Tamil Nadu coast; both remain experimental.

Geothermal energy is the heat of the earth's interior. The temperature of the earth rises with depth, and where magma lies close to the surface, or where deep faults let groundwater sink and reheat, hot water and steam rise to the surface as hot springs and geysers. This steam can be tapped to drive turbines, or the hot water can be used directly for heating, greenhouses and drying. Geothermal power is used on a large scale in Iceland, New Zealand, Italy, the Philippines and the United States. India has several hundred hot springs, but only two projects have been set up to harness geothermal energy experimentally: the Parvati valley near Manikaran in Himachal Pradesh and the Puga valley in Ladakh. Other hot spring areas are Tattapani in Chhattisgarh, the Sohana belt of Haryana, the Cambay basin of Gujarat and the Godavari and Mahanadi valleys. Odisha has hot springs at Atri near Khurda, Taptapani in Ganjam, Deulajhari in Angul and Tarabalo in Nayagarh; they are used for bathing and are of religious and tourist interest, and Taptapani and Atri have been surveyed as possible small geothermal sources. Geothermal energy is renewable, clean and available day and night, but it is confined to a few geological sites and the hot water can be corrosive and mineral-laden.

These sources contribute little to India's electricity today, but they show the range of renewable options the country possesses and the direction of research.

Energy is a basic requirement for economic development. Every sector of the national economy, agriculture, industry, transport, commerce and domestic life, needs inputs of energy, and the economic development plans implemented since Independence necessarily required increasing amounts of energy to remain operational. As a result, consumption of energy in all forms has been steadily rising all over the country. But the fossil fuels that supply most of it are finite and polluting, and India imports the greater part of its oil. In this background there is an urgent need to develop a sustainable path of energy development, one that meets the needs of the present without harming the ability of future generations to meet theirs. That path has two sides: the promotion of energy conservation and the increased use of renewable energy sources. Both are needed, because the cheapest and cleanest unit of energy is the one that is not used at all: it is far cheaper to save a megawatt by efficiency than to build a new megawatt of capacity.

Conservation in daily life. As concerned citizens we can do our bit by using public transport instead of individual vehicles, by walking or cycling for short distances, by switching off lights, fans and appliances when not in use, by using LED lamps and BEE star-rated efficient appliances, by using pressure cookers and keeping lids on vessels while cooking, by not over-cooling rooms, by having vehicles serviced and tyres properly inflated, and by getting our electric devices checked regularly. A house designed with cross-ventilation, shade and a light-coloured roof needs less cooling.

Conservation in industry and agriculture. Industry, the largest consumer, can save enormously by modern furnaces, waste-heat recovery, co-generation of steam and power, energy audits and the recycling of metals, which needs a fraction of the energy of primary production. In agriculture, efficient pump sets, drip and sprinkler irrigation and solar pumps cut the diesel and electricity used for lifting water.

Conservation in supply. A large part of India's electricity is lost in transmission, distribution and theft; better lines, transformers and metering save it. Thermal stations can raise efficiency with supercritical boilers, and coal can be washed to reduce ash. The Bureau of Energy Efficiency (2002) sets standards and the star labels, the Energy Conservation Act 2001 gives the legal frame, and the national programmes for LED bulbs and efficient fans have already saved thousands of megawatts. In Odisha, whose industries and power stations consume large amounts of energy, and whose villages still burn firewood, conservation combined with solar, small hydel and biogas is the way to spread the benefit of energy to all without wrecking the land and air of Angul and Jharsuguda. Energy saved is energy produced.