Renewable Energy

Renewable Energy

Renewable energy is a energy that is generated from natural resources that are continuously replenished. This includes sunlight, geothermal heat, wind, tides and various forms of biomass. This energy cannot be exhausted and is is constantly renewed.

Why do we need renewable source of energy

• To reduce pollutants, greenhouse gases and toxins that are by-products of non-renewable sources of energy;
• The use of alternative energy sources can help preserve the delicate ecological balance of the earth, and help conserve the non-renewable energy sources like fossil fuels; and
• Renewable sources are inexhaustible.

What renewable energy comprises of

• Solar energy - energy generated from the Sun
• Hydel energy - energy derived from water biomass - energy from firewood, animal dung, biodegradable waste and crop residues when it is burnt.
• Geothermal energy - energy from hot dry rocks, magma, hot water springs, natural geysers etc.
• Ocean thermal - energy from waves and also from tidle waves.
• Co-generation - producing two forms of energy from one fuel.
• Fuel cells - fuel cells are also being used as cleaner energy source

Sun - The Ultimate Source of Energy

The sun has been providing us heat and light for billions of years and it is expected that it will continue to do so for billions of years to come. All plants get their energy from the sun and all animals get their energy mainly from the plants.

Solar Grid to harness Solar Energy

The ways to produce electricity from sunlight

• Photovoltaic Electricity - uses photovoltaic cells that absorb the direct sunlight to generate electricity.
• Solar Thermal Electricity - uses a solar collector that has mirrored surface which reflects the sunlight onto a receiver that heats up a liquid. This heated up liquid is used to make steam that produces electricity.

Photovoltaic Electricity

Solar panels attached aluminium mounting system. Photovoltaic (PV) cells are made up of at least two semiconductor layers - a positive charge and a negative charge. As a PV cell is exposed to sunlight, photons are reflected, pass right through, or absorbed by the solar cell. When enough photons are absorbed by the negative layer of the photovoltaic cell, electrons are freed from the negative semiconductor material. These freed electrons migrate to the positive layer creating a voltage differential. When the two layers are connected to an external load, the electrons flow through the circuit creating electricity. The power generated - Direct Current (DC) is converted to Alternate Current (AC) with the use of inverter.

Concentrated Solar Power (CSP) or Thermal Technology

It utilized focused sunlight and convert it into high temperature heat. The heat is then channeled through a conventional generator to produce electricity. Solar collector captures and concentrate sunlight to heat a fluid which in turn generates electricity. There are several variations in the shape of the collectors. The most commonly used are the parabolic through. Parabolic through power plants use a curved, mirrored trough which reflects the direct solar radiation onto a glass tube containing a fluid and fluid gets heated owing to the concentrated solar radiation and the hot steam generated is used to rotate the turbine to generate electricity. Commonly used fluid are synthetic oil, molten salt and pressurized steam. The power generated - Direct Current (DC) is converted to Alternate Current (AC) with the use of inverters.

Potential of Solar Energy in India and it's installed capacity

India has the potential to generate 35 MW/km2 using solar voltaic and solar thermal energy. Solar energy of about 5000 trillion kWh per year is incident over India's land area with most parts receiving 4-7 kWh per sq. m per day. Hence both technology routes (solar thermal and solar photovoltaic) for conversion of solar radiation into heat and electricity can effectively be harnessed providing huge scalability for solar power in India (Specially in high solar radiation area : Rajasthan, Gujarat, Laddakh, Andhra Pradesh, Maharashtra & Madhya Pradesh)

The current installed capacity of solar grid connected power reached 37.627 GW as of 31st March, 2020. A major initiative called 'The National Solar Mission' was formed by Govt of India and its state govt. One of the main features of the mission is to make India a global leader in solar energy and the mission envisages an installed solar generation capacity of 100 GW by 2022.

International Solar Alliance

International Solar Alliance (ISA) is launched at the CoP21 Climate Conference in Paris as a special platform for mutual cooperation among 121 solar resources rich countries lying fully or partially between Tropic of Cancer and Tropic of Capricorn. The alliance is dedicated to address special energy needs of ISA member countries. International Agency for Solar Policy and Application (IASPA) will be the formal name of International Solar Alliance. The ISA secretariat will be set up in National Institute of Solar Energy, Gurugram (India).

Objectives

• to force down prices by driving demand;
• to bring standardization in solar technologies
• to foster research and development

Wind Energy

Wind energy is the kinetic energy associated with the movement of atmospheric air. Wind turbines transform the energy in the wind into mechanical power, further converting to electric power to generate electricity. Five nations - Germany, USA, Denmark, Spain and India account for 80% of the world's installed wind energy capacity.

Wind Energy

Wind farm

• Onshore wind farms : operate one land, where the wind tends to be the strongest. The turbines of a onshore wind farms are less expensive and easier to set up, mantain and operate than offshore turbines.
• Offshore wind farms : Construction of wind farms in large bodies of water to generate electricity. Offshore wind farms are more expensive than onshore wind farms of the same nominal power.

Wind Farm

Working of wind turbines

Wind turbines convert the kinetic energy in the wind into mechanical energy. This mechanical power can be used for specific tasks ( such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity. Most turbines have three aerodynamically designed blades. The energy in the wind turns two or three propeller-like blades around a rotor that is connected to the main shaft , which spins a generator to create electricity. Wind turbines are mounted on a tower to capture the most energy. At 100 ft or more above ground, they can take advantage of faster and less turbulent wind.

Main factors that determine the electricity production

• Wind speed - stronger wind produce more energy. Wind turbine generates energy at a speed of 4-25 metres/sec.
• Blade radius - the larger the radius of blades, the more the energy produced. Doubling the blade radius can result in four times more power.
• Air density - Heavier air exerts more lift on a rotor. Air sensory is a function of altitude, temperature and pressure and lighter air so they are less productive turbine locations. The dense heavy air near sea level drives rotors faster and thus relatively more effective.
• Wind turbines can be of horizontal axis design and vertical axis design.

Potential of wind energy in India and it's installed capacity

The National Institute of Wind Energy (NIWE) has recently launched Wind Energy Resource Map of India at 100 m above ground level (AGL) on online Geographic Information System platform.

The wind energy potential in the country at 100 m AGL is over 302 GW. Gujarat has the maximum potential followed by Karnataka, Maharashtra, Andhra Pradesh according to the resource map.

Wind power generation capacity in India has significantly increased in recent years. As of 29 February 2020 the total installed wind power capacity was 37.669 GW, the fourth largest installed wind power capacity in the world. Wind power capacity is mainly spread across the Southern, Western and Northern regions.

World Wind Energy Association

WWEA is an international non-profit association embracing the wind sector worldwide, with  more than 600 members in around 100 countries. WWEA works for the promotion and worldwide deployment of wind energy technology.

• WWEA provides a platform for the communication of all wind energy actors worldwide.
• WWEA advises and influences national governments and international organisations.
• WWEA enhances international technology transfer.

WWEA Working Principles

• Wind energy shall serve as one cornerstone and a driving force for the immediate application of a world energy system driven by renewable energies to completely substitute fossil and nuclear sources.
• Global dissemination of grid-connected and stand-alone wind energy solutions should rely on experience gained from the most successful implementation strategies, based on favorable legal, political and social framework conditions as initiated by national associations. Local and rural communities and people should be involved and should benefit directly.
• WWEA shall stimulate and support the foundation of national and regional wind energy associations and encourage national governments to set ambitious targets and political frameworks for priority strategies in favour of a fast and sustainable development of all renewable energies.
• WWEA organises together with continental, national and regional wind energy associations World Wind Energy Conferences and further international events for mobilising a wide range of the different wind energy applications.
• WWEA plays an active role in the World Council for Renewable Energies and cooperates with further international renewable energy organisations in order to work for a full substitution of all polluting and hazardous waste causing energies.

Ocean Thermal Energy

Large amount of solar energy is stored in the oceans and seas. On an average, the 60 mill square km of the tropical seas absorb solar radiation equivalent to the content of 245 bill barrels of oil.The process of harnessing this energy is called OTEC (Ocean Thermal Energy Conversion). It uses the temperature differences between the surface of the ocean and the depth of about 1000 m to operate a heat engine, which produce electric produces electric power.

OTEC working Flowchart

Wave Energy

Waves result from the interaction of the wind with the surface of the sea and represent a transfer of energy from the wind to the sea.

The first wave energy, project with a capacity of 150 MW has been set up at Vizhinjam near Trivandrum.

Wave Energy Plant 

Tidal Energy

Energy can be extracted from tides by creating a reservoir or basin behind a barrage and then passing tidal waters through turbines in the barrage to generate electricity.

A major tidal wave power project costing of Rs 5k crores, proposed to be set up in the Hanthal Creek in the Gulf of Kutch in Gujarat.

Tidal Energy

Biomass

Energy from biomass is the oldest fuel used by human’s .Our ancestors burned wood to keep the cave warm. Biomass is a renewable energy resource derived from plants and animal waste. The energy from biomass (biomass conversion) is released on burning or breaking the chemical bonds of organic molecules formed during photosynthesis. Thus biomass represents an indirect form of solar energy. Biomass fuels can be used directly or they can be transformed into more convenient form and then used.

Biomass Plant

Sources of BioMass

It is derived from numerous sources, including the by-products from the timber industry, agricultural crops and their by products, raw material from the forest, major parts of household waste and wood.

Biomass can be burnt directly as a source for cooking, heating, lighting, generating steam, for industrial use for producing electricity.

• can be used to generate gaseous fuels (gasification).
• can be converted into alcohol (liquid biofuels) by distillation.

Methane and biogas can be produced from urban wastes in landfills and sewage at waste water treatment plants. In some facilities, manure from livestock and other organic waste is converted by microorganisms in specially designed digestion chamber to form methane(CH4), which is burned to produce electricity, used in fuel cell, or used as fuel for vehicles. Molasses obtained from sugarcane is fermented to produce ethanol, that can be used in automobiles.

Bagasse as biofuel

Indian sugar mills are rapidly turning to bagasse, the leftover of cane after it is crushed and its juice extracted, to generate electricity. This is mainly being done to clean up the environment, cut down power costs and earn additional revenue. According to current estimates, about 3500 MW of power can be generated from bagasse in the existing 430 sugar mills in the country. Around 270 MW of power has already been commissioned and more is under construction.

Biogas plant

The biogas plant consists of two components: 

A digester (or fermentation tank) and a gas holder. The digester is a cube-shaped or cylindrical waterproof container with an inlet into which the fermentable mixture is introduced in the form of liquid slurry. The gas holder is normally an airproof steel container that, by floating like a ball on the fermentation mix, cuts off air to the digester (anaerobiosis) and collects the gas generated. In one of the most widely used designs, the gas holder is equipped with a gas outlet, while the digester is provided with an overflow pipe to lead the sludge out into a drainage pit.
Any biodegradable (that which can be decomposed by bacteria) substance can be fermented anaerobically (in absence of oxygen) by methane-producing (methanogenic) bacteria. Cow dung or faeces are collected and put in a biogas digester or fermenter (a large vessel in which fermentation can take place). A series of chemical reactions occur in the presence of methanogenic bacteria (CH4 generating bacteria) leading to the production of CH4 and CO2.

Methanogenesis is a microbial process, involving many complex, and differently interacting species, but most notably, the methane-producing bacteria. The biogas process is shown below in figure 30.3, and consists of three stages; hydrolysis, acidification and methane formation.

Petro-crops (Plants)

Petroleum and wood are chief energy resources from time immemorial, but they have been overused and not being replenished fast enough. This is cause for concern. There is a need for alternative energy providing sources that can be regenerated. Recent researches suggest that hydrocarbon producing plants can become alternative energy sources, which can be inexhaustible and ideal for liquid fuel. These plants called petroplants/petrocrops can be grown on land which are unfit for agriculture and not covered with forests. The most critical step in bioenergy production is the selection of plant species that produce substances from which useful products can be extracted in an economically viable way.

Many such promising species belong to the families Asclepiadaceae, Asteraceae, Anacardiaceae Euphorbiaceae, Convolvulaceae, Caprifoliaceae, Lamiaceae, and Moraceae. Jatropa Curcas is an important petro plant.

Jatropa Curcas : A fuel plant

Potential of Biomass Energy in India

India has a potential of about 18 GW of energy from Biomass. Currently, about 32% of total primary energy used in India is derived from Biomass. More than 70% of the country’s population depends upon biomass for its energy needs. India has ~5+ GW capacity biomass powered plants: 83% are grid connected while the remaining 17% are off-grid plants. The off- grid plants are divided between co-generation plants that do not utilize bagasse, biomass gasifiers for rural applications and biomass gasifiers for thermal applications in industry. Around 70 Co-generation projects are under implementation with surplus capacity aggregating to 800 MW.

Biomass potential of the world

The world production of biomass is estimated at 146 billion metric tons a year, mostly wild plant growth. Biomass accounts for 35% of primary energy consumption in developing countries, raising the world total to 14% of primary energy consumption. In the future, biomass has the potential to provide a cost-effective and sustainable supply of energy, while at the same time aiding countries in meeting their greenhouse gas reduction targets. By the year 2050, it is estimated that 90% of the world population will live in developing countries.

Co-generation

Co-generation is producing two forms of energy from one fuel. One of the forms of energy must always be heat 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 system is used to drive a turbine, which in turn drives an alternator steam turbine to produce electric power. The exhaust system is generally condensed to water which goes back to the boiler. As the low pressure steam has a large quantum of heat which is lost in the process of condensing, the efficiency of conventional power plant is only around 35%. In a co-generation plant, the low pressure exhaust steam coming out of the turbine is not condensed, but used for heating purposes in factories or houses and thus very high efficiency level, in the range of 75% to 95%, can be reached. Since co-generation can meet both power and heat needs, it has other advantage as well as in the form of significant cost savings for the plant and reduction in emission of pollutants due to reduce fuel consumption.

Potential in India and it's installed capacity

Biomass energy is one of the most important sources of energy forming 32% of total primary energy usage in the country with more than 70% of India's population dependent on it for energy needs.

The current availability of biomass is estimated at about 450-500 mill tonnes annually translating to a potential of around 18000 MW.

In addition, about MW power could be generated through bagasse based co-generation in the country's 550 sugar mills.

Approximately over 300 biomass power and co-generation projects aggerating 3700 MW have been installed in the country for feeding power to the grid. Also, 30 biomass power projects aggregating about 350 MW are under different stages of implementation.

The government plans to meet 20% of the countries diesel requirement by 2020 using bio-diesel. Potential sources of bio-diesel production have been identified in wild plants such as jatropha curcas, neem, mahua, karanj, simarouba (exotic tree) etc.

Geothermal Energy

Geothermal generation first to sing of geothermal energy of the vast reserver of heat stored in the earth's inner core. Below the earth's crust, there is a layer of hot and molten rock called 'magma'. Heat is continually produced there, mostly from the decay of naturally radioactive materials is Uranium and Potassium.

Thermal Energy emit from the Earth surface

How is it captured

Geothermal system can be found in regions with a normal or slightly above normal geothermal gradiant (gradual change in temperature is known as the geothermal gradiant, which expresses the increase in temperature with depth in the earth's crust. The average geothermal gradiant is about 2.5-3 ℃/100 m.) and especially in regions around plate margins where the geothermal gradiants may be significantly higher than the average value.

The most current way of capturing the energy from geothermal sources 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 use it to drive electric generators.

Fuel Cells

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

Hydrogen Fuel Engine

Fuel cells for automobile transport

Compared to vehicles powered by the internal combustion engine, fuel cell powered vehicles have very high energy conversion efficiency, and near-zero pollution, CO2 and water vapour being the only emissions. Fuel-cell- powered EV's (electronic vehicles) score over battery operated EV's  in terms of 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 to make a positive impact on urban air quality.

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 when ever required with relative ease) and can be set up where ever power is required.

REN21

REN21 is the global renewable energy policy multi-stake-holder network that connects a wide range of key actors form -

• Governments
• International organisation
• 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 that are driven by climate change, energy security, development and poverty allevation.

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 catalyses policy change.
• Offering a platform for interconnection between multi-stakeholders actors working in the renewable energy field worldwide and identifying barriers as well as working to bridge existing gaps to increase the large-scale deployment of renewable energy worldwide.

International Renewable Energy Agency (IRENA)

IRENA has 150 member nations with Headquarters in Abu Dhabi.

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

IRENA promotes the widespread adoption and sustainable use of all forms of renewable energy, including bioenergy, geothermal, hydro-power, ocean, solar and wind energy the pursuit of sustainable development, energy access, energy security and low-carbon economic growth and prosperity.

IRENA Official Logo

Conclusion

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.