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Renewable Energy - (Part - 2) | Environment for UPSC CSE PDF Download

What is Hydropower?

  • Hydropower or water power is power derived from the falling or fast-running water, which may be harnessed for useful purposes. It is then used to turn the turbine, thereby converting the kinetic energy of water into mechanical energy to drive the generator.
  • Hydropower is the cheapest and cleanest energy source, but many environmental and social issues are associated with big dams as seen in projects like Tehri, Narmada, etc. Small hydropower is free from these problems.

Types of hydropower stations

There are three types of hydropower facilities: impoundment, diversion, and pumped storage. Some hydropower plants use dams, and some do not.

  • Impoundment, The most common type of hydroelectric power plant, is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which activates a generator to produce electricity.
  • Diversion A diversion, sometimes called run-of-river facility, channels a portion of a river through a canal or penstock and then flows through a turbine, spinning it, which activates a generator produces electricity. It may not require the use of a dam. 
  • Pumped storage works like a battery, storing the electricity generated by other power sources like solar, wind, and nuclear for later use. When the electricity demand is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir and turns a turbine, generating electricity.

Small Hydro Power (SHP)

Small hydro is defined as any hydropower project which has an installed capacity of less than 25 MW. It is, in most cases, run-of-river, where a dam or barrage is quite small. Usually, just a weir with little or no water is stored. Therefore run-of-river installations do not have the same adverse effect on the local environment as large-scale hydro projects. Small hydropower plants can serve the energy needs of remote rural areas independently. India and China are the major players of the SHP sector, holding the highest number of installed projects.

➤ Small Hydro Potential in India

  • An estimated 5,415 sites of small hydro have been identified with a potential of around 19,750 MW. 
  • River-based projects in the Himalayan states and irrigation canals in other states have massive potential for developing Small Hydro Projects. 
  • According to the XIIth five year plan targets, capacity addition from Small Hydro Projects is targeted at 2.1 GW in 2011-17 period. 
  • The Ministry of New and Renewable Energy is encouraging Small Hydro Projects in public and private sectors. It aims to exploit at least 50% of the current potential in the next 10 years.

Installed capacity

The cumulative installed capacity of Small Hydro Projects amounts to 3726 MW.

Ocean Thermal Energy

➤ What is it?

  • Large amounts of solar energy are stored in the oceans and seas. On average, the 60 million square kilometres of the tropical seas absorb solar radiation equivalent to the heat content of 245 billion barrels of oil. The process of harnessing this energy is called OTEC (ocean thermal energy conversion). It uses the temperature differences between the ocean's surface and the depths of about 1000m to operate a heat engine, which produces electric power.

➤ Wave energy

  • Waves result from the wind's interaction with the sea's surface and represent a transfer of energy from the wind to the sea. The first wave energy, project with a capacity of 150MW, has been set up at Vizhinjam near Trivandrum.

➤ Tidal energy

  • Energy can be extracted from tides by creating a reservoir or basin behind a barrage and then passing tidal waters through turbines to generate electricity. A major tidal wave power project costing of Rs.5000 crores, is proposed to be set up in the Hanthal Creek in the Gulf of Kutch in Gujarat.

➤ Biomass

  • Biomass is a renewable energy resource derived from the carbonaceous waste of various human and natural activities. It is derived from numerous sources, including the by-products from the timber industry, crops, grassy and woody plants, residues from agriculture or forestry, oil-rich algae, and the organic component of municipal, industrial wastes. 
  • Biomass is a good substitute for conventional fossil fuels for heating and energy generation purposes. Burning biomass releases about the same amount of carbon dioxide as burning fossil fuels. However, fossil fuels release carbon dioxide captured by photosynthesis over its formative years.
  • On the other hand, Biomass releases carbon dioxide that is largely balanced by the carbon dioxide captured in its own growth (depending on how much energy was used to grow, harvest, and process the fuel). Hence, Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Chemical processes like gasification, combustion and pyrolysis convert biomass to useful products, combustion being the most common.
  • Each of the technologies mentioned produces a major calorific end product and a mixture of by-products. The processing method is selected based on feedstocks' nature and origin, their physiochemical state and application spectrum of fuel products derived from it.

Anaerobic Digestion/Biomethanation

Biomethanation, or methanogenesis, is a scientific process whereby anaerobic microorganisms in an anaerobic environment decompose biodegradable matter producing methane-rich biogas and effluent. The three functions that take place sequentially are hydrolysis, acidogenosis and methanogenesis.


In this process, waste is directly burned in excess air (oxygen) at high temperatures (about 800°C), liberating heat energy, inert gases and ash. Combustion results in a transfer of 65–80% of the organic matter's heat content to hot air, steam, and hot water. The steam generated, in turn, can be used in steam turbines to generate power.


  • Pyrolysis is a process of chemical decomposition of organic matter brought about by heat. In this process, the organic material is heated in the absence of air until the molecules thermally break down to become a gas comprising smaller molecules (known collectively as syngas). 
  • Gasification can also occur due to partial combustion of organic matter in the presence of a restricted quantity of oxygen or air. The gas so produced is known as producer gas. The gases produced by pyrolysis mainly comprise carbon monoxide (25%), hydrogen and hydrocarbons (15%), and carbon dioxide and nitrogen (60%). The next step is to 'clean' the syngas or producer gas. Thereafter, the gas is burned in internal combustion (IC) engine generator sets or turbines to produce electricity.


  • Cogeneration is producing two forms of energy from one fuel. One form of energy must always be heated, and the other may be electricity or mechanical energy. In a conventional power plant, fuel is burnt in a boiler to generate high-pressure steam. This steam is used to drive a turbine, which drives an alternator through a steam turbine to produce electric power. The exhaust steam is generally condensed to water which goes back to the boiler.
  • As the low-pressure steam has a large quantum of heat lost in the process of condensing, the efficiency of conventional power plants is only around 35%. In a cogeneration plant, the low-pressure exhaust steam coming out of the turbine is not condensed but used for heating purposes in factories or houses. 
  • Thus, it is very high-efficiency levels, in the range of 75%–90%, can be reached. Since cogeneration can meet both power and heat needs, it has other advantages and significant cost savings for the plant and reduces emissions of pollutants due to reduced fuel consumption.
  • Even at conservative estimates, the potential of power generation from cogeneration in India is more than 20,000 MW. Since India is the largest producer of sugar in the world, bagasse-based cogeneration is being promoted.
  • Thus, cogeneration's potential lies in facilities with joint requirements of heat and electricity, primarily sugar and rice mills, distilleries, petrochemical sector and industries such as fertilizers, steel, chemical, cement, pulp and paper, and aluminium.

Potential in India

  • Biomass energy is one of the most important energy sources forming 32% of the country's total primary energy usage with more than 70% of the Indian population dependent on it for its energy needs. 
  • The current biomass availability is estimated at 450-500 million tonnes annually translating to a potential of around 18000 MW. 
  • Besides, about 5000 M W additional power could be generated through bagasse based cogeneration in the country's 550 Sugar mills 
  • It attracts over Rs 600 crore in investments annually creating rural employment of more than 10 million working days while generating more than 5000 million electricity units.

Installed capacity in India

  • Approximately over 300 biomass power and cogeneration projects aggregating 3700 MW have been installed in the country for feeding power to the grid. Also, 30 biomass power projects aggregating about 350MW are under different stages of implementation. 
  • Andhra Pradesh, Tamil Nadu, Karnataka, Maharashtra and Uttar Pradesh are the leading states in implementing bagasse cogeneration projects. 
  • In the biomass power projects, Andhra Pradesh, Chhattisgarh, Maharashtra, Madhya Pradesh, Gujarat and Tamil Nadu have taken a leadership position. 
  • The Government plans to meet 20% of the countries diesel requirements by 2020 using biodiesel. Potential biodiesel production sources have been identified in wild plants such as jatropha curcas, neem, mahua, karanj, Simarouba (exotic tree). 
  • Several incentive schemes have been introduced to rehabilitate wastelands through the cultivation of Jatropha.
  • Central Finance Assistance (CFA) is provided by the Ministry of New and Renewable Energy (MNRE) in capital subsidy and financial incentives to India's biomass energy projects.

Waste to Energy

  • Waste-to-energy can divert waste from landfills and generate clean power without the emission of harmful greenhouse gas. This significantly reduces the volume of waste that needs to be disposed of and can generate power Pyrolysis and gasification are emerging technologies apart from the common incineration and biomethanation.

Potential of waste-to-energy

  • There is an estimated potential of about 225 M W from all sewage and about 1460 MW from Municipal Solid Waste (MSW) in India totalling around 1700 MW of power. 
  • There is current potential to recover 1,300 MW of power from industrial wastes, projected to increase to 2,000 MW by 2017. 
  • The total installed capacity of grid-interactive power from Waste to energy is 99.08 MW of grid power and about 115.07 MW of off-grid power. 
  • MNR E is actively promoting the generation of energy from waste by providing incentives and subsidies on projects

Major Constraints Faced by the Indian Waste to Energy Sector

  • Choice of technology - Waste-to-Energy is still a new concept in India. Most of the proven and commercial technologies in respect of urban wastes are required to be imported; 
  • High costs - The projects' costs, especially based on biomethanation technology, are high as critical equipment for a project is required to be imported. 
  • Improper segregation - India lacks a source-separated waste stream due to the low compliance of Municipal Solid Waste (MSW) Rules 2000 by the Municipal Corporations/ Urban Local Bodies. The organic waste is mixed with other types of waste. Hence, the operations of the waste to energy techniques are hindered, and a lack of smoothness causes short-lived attempts. 
  • Lack of policy support - Lack of conducive policy guidelines from State Governments regarding allotment of land, a supply of garbage and power purchase/evacuation facilities.

Geothermal Energy

What is it?

Geothermal energy is heat derived within the sub-surface of the earth. Water and/or steam carry the geothermal energy to the Earth's surface. Depending on its characteristics, geothermal energy can be used for heating and cooling purposes or be harnessed to generate clean electricity.

➤ How is it captured?

  • Geothermal systems can be found in regions with a normal or slightly above normal geothermal gradient (gradual temperature change is known as the geothermal gradient, which expresses the increase in temperature with depth in the earth's crust. The average geothermal gradient is about 2.5-3 °C/100 m.) and especially in regions around plate margins where the geothermal gradients may be significantly higher than the average value.
  • The most common current way of capturing geothermal sources' energy is to tap into naturally occurring "hydrothermal convection" systems where cooler water seeps into the earth's crust, is heated up and then rises to the surface. When heated water is forced to the surface, it is relatively easy to capture that steam and drive electric generators.

➤ Potential in India

  • India has the potential for producing around 10,600 MW of power from geothermal resources. Although India was among the earliest countries to begin geothermal projects since the 1970s, there are no operational geothermal plants in India.
  • 340 hot springs were identified across India. These have been grouped and termed as different geothermal provinces based on their occurrence in specific geotectonic regions, geological and structural regions such as orogenic belt regions, structural grabens, deep fault zones, and active volcanic regions etc.

➤ Orogenic regions

  • Himalayan geothermal province 
  • Naga-Lushai geothermal province 
  • A Andaman-Nicobar Islands geothermal province

➤ Non-orogenic regions

  • Cambay graben, 
  • Son-Narmada-Tapigraben, 
  • West coast, 
  • Damodar valley, 
  • Mahanadi valley, 
  • Godavari valley etc

➤ Potential Sites

  • Puga Valley ( J&K) 
  • Tattapani (Chhattisgarh) 
  • Godavari Basin Manikaran (Himachal Pradesh) 
  • Bakreshwar (West Bengal) 
  • Tuwa (Gujarat) 
  • Unai (Maharashtra) 
  • Jalgaon (Maharashtra)

Recent Developments

In 2013, India's first geothermal power plant was announced to be set up in Chhattisgarh. The plant would be set up at Tattapani in the Balrampur district. Satellites like the IRS-1 have played an important role, through infrared photographs, in locating geothermal areas.


➤ High generation costs

  • Most costs relating to geothermal power plants are incurred due to resource exploration and plant construction.

➤ Drilling costs

  • Although the cost of generating geothermal electricity has decreased by 25 per cent during the last two decades, exploration and drilling remain expensive and risky. Because rocks in geothermal areas are tough and hot, developers must frequently replace drilling equipment.

➤ Transmission barrier

  • Geothermal power plants must be located near specific areas near a reservoir because it is not practical to transport steam or hot water over distances greater than two miles. 
  • Since many of the best geothermal resources are located in rural areas, developers may be limited by their ability to supply electricity to the grid. New power lines are expensive to construct and difficult to site. 
  • Many existing transmission lines are operating near capacity and may not transmit electricity without significant upgrades. Consequently, any significant increase in the number of geothermal power plants will be limited by the plants' ability to connect, upgrade or build new lines to access the power grid and whether the grid can deliver additional power to the market.

➤ Accessibility

  • Some areas may have sufficient hot rocks to supply hot water to a power station, but many are located in harsh areas or high up in the mountains. This curbs the accessibility of geothermal resources adding on to the costs of development.

➤ Execution challenges

  • Harmful radioactive gases can escape from deep within the earth through the holes drilled by the constructors. The plant must be able to contain any leaked gases and ensure safe disposal of the same.

Fuel Cells

What are fuel cells?

Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly and efficiently into electricity (DC) and heat, thus doing away with combustion. The most suitable fuel for such cells is hydrogen or a mixture of compounds containing hydrogen. A fuel cell consists of an electrolyte sandwiched between two electrodes. Oxygen passes over one electrode and hydrogen over the other, and they react electrochemically to generate electricity, water, and heat.

➤ Fuel cells for automobile transport

  • Compared to vehicles powered by the internal combustion engine, fuel-cell-powered vehicles have very high energy conversion efficiency, near-zero pollution, CO2 and water vapour are the only emissions. Fuel-cell-powered EVs (electric vehicles) score over battery-operated EVs in increased efficiency and easier and faster refuelling.
  • In India, diesel-run buses are a major means of transport, and these emit significant quantities of SPM and SO2. Thus, fuel-cell-powered buses and electric vehicles could be introduced with relative ease to dramatically reduce urban air pollution and positively impact urban air quality.

➤ Fuel cells for power generation

  • Conventional large-scale power plants use non-renewable fuels with significant adverse ecological and environmental impacts. Fuel cell systems are excellent candidates for small-scale decentralized power generation.
  • Fuel cells can supply combined heat and power to commercial buildings, hospitals, airports and military installation at remote locations. Fuel cells have efficiency levels up to 55% as compared to 35% of conventional power plants. The emissions are significantly lower (CO2 and water vapour being the only emissions). Fuel cell systems are modular (i.e. additional capacity can be added whenever required with relative ease) and set up wherever power is required.


The high initial cost is the biggest hurdle in the widespread commercialization of fuel cells.


REN21 is the global renewable energy policy multi-stakeholder network that connects a wide range of key actors from:

  • Governments 
  • International organizations 
  • Industry associations 
  • Science and academia as well as civil society

To facilitate knowledge exchange, policy development and joint action towards a rapid global transition to renewable energy. REN21 promotes renewable energy to meet the needs of both industrialized and developing countries driven by climate change, energy security, development and poverty alleviation.

REN21 is an international non-profit association and committed to the following objectives:

  • Providing policy-relevant information and research-based analysis on renewable energy to decision-makers, multipliers and the public to catalyze policy change 
  • Offering a platform for interconnection between multi-stakeholder actors working in the renewable energy field worldwide and identifying barriers and working to bridge existing gaps to increase the largescale deployment of renewable energy worldwide.

Efficient use of renewable energy would reduce our dependence on non-renewable sources of energy, make us energy self-sufficient and make our environment cleaner. As more green power sources are developed - displacing conventional generation - the overall environmental impacts associated with electricity generation will be significantly reduced.

The document Renewable Energy - (Part - 2) | Environment for UPSC CSE is a part of the UPSC Course Environment for UPSC CSE.
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FAQs on Renewable Energy - (Part - 2) - Environment for UPSC CSE

1. What is hydropower?
Ans. Hydropower is a form of renewable energy that harnesses the energy of flowing or falling water to generate electricity. It involves the use of dams or other structures to capture the energy of water and convert it into mechanical energy, which is then used to turn turbines and generate electricity.
2. How does hydropower work?
Ans. Hydropower works by using the force of flowing or falling water to spin turbines, which are connected to generators that produce electricity. This is achieved by constructing a dam on a river or other water source, creating a reservoir that stores water. When water is released from the reservoir, it flows through turbines, causing them to rotate and generate electricity.
3. What are the advantages of hydropower?
Ans. Hydropower offers several advantages as a renewable energy source. Firstly, it is a clean and environmentally friendly option, as it does not produce air pollution or greenhouse gas emissions during operation. Additionally, hydropower provides a reliable and consistent source of electricity, as water flow can be controlled to meet demand. It also helps in water management, flood control, and irrigation for agricultural purposes.
4. Are there any limitations or drawbacks to hydropower?
Ans. While hydropower has many benefits, it also has some limitations. One drawback is the environmental impact caused by the construction of dams and reservoirs, which can disrupt ecosystems and alter natural water flow patterns. There may also be challenges associated with the relocation of communities and ecosystems due to dam construction. Additionally, hydropower generation can be affected by droughts, reducing its reliability during periods of low water availability.
5. What is the global significance of hydropower?
Ans. Hydropower holds significant global importance as a renewable energy source. It is currently the largest source of renewable electricity worldwide, accounting for a substantial portion of the global energy mix. Many countries heavily rely on hydropower to meet their electricity needs, particularly in regions with abundant water resources. Its contribution to mitigating climate change and reducing reliance on fossil fuels makes it a crucial component of sustainable energy systems.
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