Renewable Energy Resorces by Omkar Hirawat

8/4/2019 Renewable Energy Resorces by Omkar Hirawat

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Introduction

What is Energy?

Before getting into knowing what are energy sources we must know what energy is.

Energy is the ability to do work. Energy helps in powering business, manufacturing and

transportation of goods and services. There are many different ways in which the abundance

of energy around us can be stored, converted, and amplified for our use. Energy comes in

different forms heat, light, thermal, mechanical, electrical, chemical and nuclear energy. We

all use energy for our daily work like when we walk, jump, eat food, drive car, play,

transportation etc. Energy is stored in different ways and can be transformed from one type to

another.

So, the energy sources from which we gain energy are classified broadly into 2 groups

namely: Renewable and Non-Renewable (Fossil Fuels)

Non-Renewable Sources

Non-Renewable Sources include fossil fuels (Coal, Oil and gas) and Nuclear energy.

They're called fossil fuels because they were formed over millions and millions of years by

the action of heat from the Earth's core and pressure from rock and soil on the remains (or

"fossils") of dead plants and animals. Fossil fuels are relatively easy to use to generate energy

because they only require a simple direct combustion. However, a problem with fossil fuels is

their environmental impact. When used on a larger scale they may deplete from the earthafter some years and also cause the great deal of air pollution. Coal is crushed to a fine dust

and burnt. Oil and gas can be burnt directly. Although very large amount of electricity can be

produced at one place, it has a lot of disadvantages. The major drawback is the pollution

which in turn causes greenhouse effect which may lead to global warming. Also, coal fired

power stations need huge amount of fuel. With the large drawbacks of fossil fuels, scientists

across the world are moving there focus from fossil fuels to Nuclear energy. Non-renewable

energy source is the element uranium, whose atoms we split (through a process called nuclear

fussion) to create heat and ultimately electricity. Most of the nations have started building

nuclear reactors in order to avoid using fossil fuels which contribute to global warming.

Some military ships and submarines even have nuclear power plants for engines. Nuclear

power produces around 11% of the world's energy needs, and produces huge amounts of

energy from small amounts of fuel, without the pollution that you'd get from burning fossil

fuels. Nuclear power is reliable and does not produce smoke or waste but if anything goes

wrong, a nuclear accident can be a major disaster. People all across the globe use theseenergy sources to generate electricity for homes, business, factories and schools. We use this

energy to light bulb, run computer, refrigerators, washing machines and air conditioners etc.

We use energy to run our cars and trucks. Both the gasoline used in our cars, and the diesel

fuel used in our trucks are made from oil. Since, renewable sources are not used on much

wider scale and use of Non-renewable sources cause pollution to the environment and mayextinct if used in a hazardous manner, so the need of the hour is to conserve these resources,


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use them in an efficient manner to minimize the wastage, use of renewable on wide scale and

making this planet a better place to live in.

Renewable Energy sources

Renewable Sources include solar, wind, geothermal, biomass and hydropower. Solar

energy is the energy that we get from the sun. It is the major source of energy among all the

nations. However, there are major drawbacks related to limited production as well as high

costs that don't allow people to use it in a wider scale. Solar energy is responsible for growth

of plants and indirectly, the existence of all animal life. Wind energy is used in large farm

fields where they can use windmills to provide power for the accomplishment of agricultural

tasks has contributed to the growth of civilization. This apart from solar is another clean and

renewable source of energy. The major drawback is that it can be used only in the coastal

regions and can be noisy too. Geothermal energy is the energy stored inside the earth. The

center of the earth has temperature about 6000 degrees F. The heat that is stored inside theearth is used to produce steam, which is then used to drive electrical generators. The main

advantage of it is that it does not cause any pollution and no fuel is needed. However,

hazardous steams and gases may come out from bottom that may cause harm to mankind.

Biomass energy is the enrgy that we get from the organic materials. Biomass is simply the

conversion of stored energy in plants into energy that we can use. Thus, burning wood is a

method of producing biomass energy. "Bioconversion" uses plant and animal wastes to

produce "biofuels" such as methanol, natural gas, and oil. It in turns causes pollution when

you burn them but is relatively cheap and freely available. Hydroelectric energy is the use of

running of water to generate electricity. To trap this energy a dam is built usually in a river orlake and water is allowed to flow through tunnels in the dam to turn the turbines and thus

drive generators. No waste or pollution is caused and power can be generated through out the

year but if the dam is built it may cause the flood in the large area and therefore getting the

suitable site may be difficult. [1]


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Chapter - 1

Renewable energy

Renewable energy is derived from natural processes that are replenished constantly.

In its various forms, it derives directly from the sun, or from heat generated deep within theearth. Included in the definition is electricity and heat generated from solar, wind, ocean,hydropower, biomass, geothermal resources, and bio-fuels and hydrogen derived fromrenewable resources. The share of renewables in electricity generation is around 18%, with15% of global electricity coming from hydroelectricity (including small hydro) and 3% fromnew renewables (like modern biomass, wind, solar, geothermal, and bio-fuels) which aregrowing very rapidly.

Renewable energy replaces conventional fuels in three distinct areas: power generation, hotwater/ space heating, transport fuels.

Power generation-Renewable energy provides 18 percent of total electricitygeneration worldwide. The share electricity generation is around the 15% of global

electricity coming from hydroelectricity and 3% from new renewables.

Heating- Solar hot water makes an important contribution in many countries, most

notably in China, which now has 70 percent of the global total (180 GW). Most of

these systems are installed on multi-family apartment buildings and meet a

requirement of the hot water. Worldwide, total installed solar water heating systems

meet a requirement of the water heating needs of over 85 million households. The use

of biomass for heating continues to grow as well as the direct geothermal for heating

is also growing rapidly. Transport fuels- Renewable bio-fuels or bio-ethanol have contributed to a significant

decline in oil consumption. The 93 billion lit of bio-fuels produced worldwide in 2009

displaced the equivalent of an estimated 68 billion lit of gasoline, equal to about 5

percent of world gasoline production.[2]

1.1 Low-entropy way of using energy

The first law of thermo-dynamics says that the total amount of energy on our planet remainsconstant. The second law states that as forms of energy are expended they become less easilyavailable.

That is entropy: the slow winding down of available energy.

When we burn coal, gas or oil you rapidly convert a relatively easily available, concentrated

source of energy into a much less available form: dispersed exhaust gases. A highly

concentrated energy source, built up over millions of years quickly gone up in smoke!

So, burning fossil fuels is a high-entropy way of using energy.


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Using renewable energy however merely taps into a natural flow of energy, sunlight, moving

water, wind, biological- or geothermal processes. These are part of natural cycles.

Their energy is truly renewable as it remains available to the same degree and is not depleted

any more than it otherwise would by using it. [3]

1.2 Benefits:

1. The advantage of renewable resources includes their inability to produce carbon-

based warming and polluting agents into the atmosphere. The financial cost of its

applications is not always cheap but if the environmental costs of using fossil fuels are

accounted for, renewable energy wins.

2. We can use it repeatedly without depleting it.

3. No contribution to global warming,

4. No polluting emissions

5. Low operating cost [4]


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Chapter - 2

Hydro-energy

Hydro power is considered the largest and most mature application of renewable

energy. The installed capacity worldwide is estimated at 630,000 MW, producing over 20

percent of the worlds electricity. Hydropower is by far the most significant renewable energy

resource of energy exploited to date Hydropower (from hydro meaning water) is energy that

comes from the force of moving water. The fall and movement of water is part of a

continuous natural cycle called the water cycle. Hydropower is called a renewable energy

source because the water on the earth is continuously replenished by precipitation. As long as

the water cycle continues, we wont run out of this energy source.[5]

Energy conversion principals

Hydro-electric energy concern with the efficient and economic conversion of energy

freely available from a supply of water deposited at suitable head by the action of the cycle

of evaporation and rain fall produced by the effect of solar radiation . an essential

requirement is, therefore , that the water should be at suitable height above a lower reference

point to where the water could flow and be discharged. The difference in levels between the

water and the discharged point represent the potential energy that would become available for

used should be allowed to flow between the two levels.

Hence, The power supplied to the turbine , p kW is given by the product of the rate of mass

flow Q (tonns per second) and of net head across the turbine H(net)(meters) correspondindto this flow :

P=9.81Q H(net)

Where is specific mass (tonne per cubic meter) and Q is the volumetric discharge (cubic

meter per second). Power output is, therefore, a function of head and flow[6]

2.1 Hydropower plant

As people discovered centuries ago, the flow of water represents a huge supply of

kinetic energy that can be put to work. Water wheels are useful for generating mechanical

energy to grind grain or saw wood, but they are not practical for generating electricity. Water

wheels are too bulky and slow. Hydroelectric plants are different. They use modern turbine

generators to produce electricity, just as thermal (coal, oil, nuclear) power plants do, except

that they do not produce heat to spin the turbines.

2.1.1 Head and flow

The amount of electricity that can be generated at a hydro plant is determined by

two factors: head and flow. Head is how far the water drops. It is the distance from the


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highest level of the dammed water to the point where it goes through the power-producing

turbine.

Flow is how much water moves through the systemthe more water that moves through a

system, the higher the flow. Generally, a high-head plant needs less water flow than a low-

head plant to produce the same amount of electricity

2.1.2 Storing energy

One of the biggest advantages of a hydropower plant is its ability to store energy. The

water in a reservoir is, after all, stored energy. Water can be stored in a reservoir and released

when needed for electricity production. During the day when people use more electricity,

water can flow through a plant to generate electricity. Then, during the night when people use

less electricity, water can be held back in the reservoir. Storage also makes it possible to save

water from winter rains for summer generating power, or to save water from wet years for

generating electricity during dry years.

2.1.3 How its work

Water from a river is diverted and a lake is created by building a large dam. This water

is allowed to fall from the lake behind the dam into the power plant. This water is directed to

several turbines with blades that are pushed by the force of the water (think of a water wheel

turned on it's side). The turbine turns a shaft which is connected to the generator. The

electrical charge created is collected and transformers convert it into useable electricity. This

power is sent out over the power grid. Power lines carry it to all the cities and towns.

Transformers in each town convert the power into different kinds of electricity for different

uses: some for factories and some for homes. Power is there ready for you to use whenever

you flip the switch!

Fig. :- 2.1 conventional impoundment dam


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Hydro plants are more energy efficient than most thermal power plants, too. That means they

waste less energy to produce electricity. In thermal power plants, a lot of energy is lost as

heat. Hydro plants are about 95 percent efficient at converting the kinetic energy of the

moving water into electricity.

2.1.4 Pumped storage system

Some hydro plants use pumped storage systems. A pumped storage system operates

much as a public fountain does. The same water is used again and again. At a pumped storage

hydro plant, flowing water is used to make electricity and then stored in a lower pool.

Depending on how much electricity is needed, the water may be pumped back to an upper

pool. Pumping water to the upper pool requires electricity so hydro plants usually use

pumped storage systems only when there is peak demand for electricity.

Pumped hydro is the most reliable energy storage system used. Coal and nuclear power plantshave no energy storage systems. They must turn to gas and oil-fired generators when people

demand lots of electricity. They also have no way to store any extra energy they might

produce during normal generating periods. [7]

2.2 Turbines

There are two main types of hydro turbines: impulse and reaction. The type of hydropower

turbine selected for a project is based on the height of standing water referred to as "head"

and the flow, or volume of water, at the site.

Fig.2.2 types of tubines


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2.2.1 Impulse Turbines

The impulse turbine generally uses the velocity of the water to move the runner anddischarges to atmospheric pressure. The water stream hits each bucket on the runner. There isno suction on the down side of the turbine, and the water flows out the bottom of the turbinehousing after hitting the runner. An impulse turbine is generally suitable for high head, low

flow applications.

1. PeltonA pelton wheel has one or more free jets discharging water into an aerated space and

impinging on the buckets of a runner. Draft tubes are not required for impulse turbine since

the runner must be located above the maximum tail water to permit operation at atmospheric

pressure.

2. Cross-FlowA cross-flow turbine is drum-shaped and uses an elongated, rectangular-section

nozzle directed against curved vanes on a cylindrically shaped runner. It resembles a "squirrel

cage" blower. The cross-flow turbine allows the water to flow through the blades twice. The

first pass is when the water flows from the outside of the blades to the inside; the second pass

is from the inside back out. A guide vane at the entrance to the turbine directs the flow to a

limited portion of the runner. The cross-flow was developed to accommodate larger water

flows and lower heads than the Pelton.

2.2.2 Reaction turbine

A reaction turbine develops power from the combined action of pressure and moving

water. The runner is placed directly in the water stream flowing over the blades rather than

striking each individually. Reaction turbines are generally used for sites with lower head and

higher flows than compared with the impulse turbines.

Propeller

A propeller turbine generally has a runner with three to six blades in which the water contacts

all of the blades constantly. Picture a boat propeller running in a pipe. Through the pipe, the

pressure is constant; if it isn't, the runner would be out of balance. The pitch of the blades

may be fixed or adjustable. The major components besides the runner are a scroll case,

wicket gates, and a draft tube. There are several different types of propeller turbines:

Bulb turbine

The turbine and generator are a sealed unit placed directly in the water stream.

Straflo

The generator is attached directly to the perimeter of the turbine.

Tube turbine

The penstock bends just before or after the runner, allowing a straight line connection to

the generator.


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Kaplan

Both the blades and the wicket gates are adjustable, allowing for a wider range of operation

Francis

A Francis turbine has a runner with fixed buckets (vanes), usually nine or more. Water isintroduced just above the runner and all around it and then falls through, causing it to spin.

Besides the runner, the other major components are the scroll case, wicket gates, and draft

tube [8]

2.3 Economics of hydropower

Hydropower is the cheapest way to generate electricity today. No other energy source,

renewable or non-renewable, can match it. Today, it costs about one cent per kWh (kilowatt-

hour) to produce electricity at a typical hydro plant. In comparison, it costs coal plants about

four cents per kWh and nuclear plants about two cents per kWh to generate electricity.

2.3.1 Hydropower and Environment

Hydropower dams can cause several environmental problems, even though they burnno fuel. Damming rivers may permanently alter river systems and wildlife habitats. Fish, forone, may no longer be able to swim upstream. Hydro plant operations may also affect waterquality by churning up dissolved metals that may have been deposited by industry long ago.Hydropower operations may increase silting, change water temperatures, and lower the levels

of dissolved oxygen. Some of these problems can be managed by constructing fish ladders,dredging the silt, and carefully regulating plant operations.

Hydropower has advantages, too. Hydropowers fuel supply (flowing water) is clean

and is renewed yearly by snow and rainfall. Furthermore, hydro plants do not emit pollutantsinto the air because they burn no fuel. With growing concern over greenhouse gas emissionsand increased demand for electricity, hydropower may become more important in the future.Hydropower facilities offer a range of additional benefits. Many dams are used to control

flooding and regulate water supply, and reservoirs provide lakes for recreational purposes,

such as boating and fishing. [7]


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2.4 Tidal energy

The tides rise and fall in eternal cycles. The waters of the oceans are in constantmotion. We can use some of the oceans energy. Tidal energy is the most promising source ofocean energy for today and the near future. Tides are changes in the level of the oceans

caused by the rotation of the earth and the gravitational pull of the moon and sun. Near shorewater levels can vary up to 40 feet, depending on the season and local factors. Only about 20locations have good inlets and a large enough tidal rangeabout 10 feetto produce energyeconomically.

Tidal energy plants capture the energy in the changing tides. A low dam, called a

barrage, is built across an inlet. The barrage has one-way gates (sluices) that allow the

incoming flood tide to pass into the inlet. When the tide turns, the water flows out of the inlet

through huge turbines built into the barrage, producing electricity. The oldest and largest tidal

plantLa Rance in Francehas been successfully producing electricity since 1968.

Fig.2.3 -: the way of producing tidal energy

Today, the electricity from tidal plants costs more than from conventional powerplants. It is very expensive and takes a long time to build the barrages, which can be severalmiles long. Also, tidal plants produce electricity less than half of the time. The seasons andcycles of the moon affect the leveland the energyof the tides. The tides are verypredictable, but not controllable.

On the other hand, the fuel is free and non-polluting, and the plants are easy tomaintain. Only two operators are needed to run the La Rance plant at night and on weekends.And the plants should run for a hundred years with little up-keep. Tidal power is a renewableenergy source. The plants do affect the environment, though they produce no air pollution.

During construction, there are major short-term changes to the ecology of the inlet. Once the


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plants go into operation, there can be long-term changes to water levels and currents. Theplants in operation have reported no major environmental problems. [9]

2.5 Wave energy

There is also tremendous energy in waves. Waves are caused by the wind blowingover the surface of the ocean. In many areas of the world, the wind blows with enoughconsistency and force to provide continuous waves. The west coasts of the United States andEurope and the coasts of Japan and New Zealand are good sites for harnessing wave energy.There are several ways to harness wave energy. The motion of the waves can be used to pushand pull air through a pipe. The air spins a turbine in the pipe, producing electricity. InNorway, a demonstration tower built into a cliff produces electricity for about four cents akWh using this method. The wail of the fast-spinning turbines, however, can be heard formiles.

Fig 2.4 -: schematic dig. of wave energy setup

Another way to produce energy is to bend or focus the waves into a narrow channel,increasing their power and size. The waves then can be channeled into a catch basin, like tidalplants, or used directly to spin turbines. There arent any big commercial wave energy plants,

but there are a few small ones. There are wave-energy devices that power the lights andwhistles on buoys. Small, on-shore sites have the best potential for the immediate future,especially if they can also be used to protect beaches and harbors. They could produceenough energy to power local communities. Japan, which must import almost all of its fuel,has an active wave-energy program.[10]


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Chapter- 3

Wind energy

Wind is simply air in motion. It is caused by the uneven heating of the earths surface by

radiant energy from the sun. Since the earths surface is made of very different types of landand water, it absorbs the suns energy at different rates. Water usually does not heat or coolas quickly as land because of its physical properties. An ideal situation for the formation oflocal wind is an area where land and water meet. During the day, the air above the land heatsup more quickly than the air above water. The warm air over the land expands, becomes lessdense and rises. The heavier, denser, cool air over the water flows in to take its place,creating wind. In the same way, the atmospheric winds that circle the earth are createdbecause the land near the equator is heated more by the sun than land near the North andSouth Poles. Today, people use wind energy to make electricity. Wind is called a renewableenergy source because the wind will blow as long as the sun shines. [11]

3.1 Wind speed

It is important in many cases to know how fast the wind is blowing. Wind speed canbe measured using a wind gauge or anemometer. One type of anemometer is a device withthree arms that spin on top of a shaft. Each arm has a cup on its end. The cups catch the windand spin the shaft. The harder the wind blows, the faster the shaft spins. A device insidecounts the number of spins per minute and converts that figure into mphmiles per hour. Adisplay on the anemometer shows the speed of the wind. Good wind speed data is critical todetermining the economic feasibility of a wind project. Prime sites have average wind speedsgreater than 7.5 metres/sec (27 km/hr).

3.2 Wind turbineLike old-fashioned windmills, todays wind turbines use blades to capture the winds

kinetic energy. Wind turbines work because they slow down the speed of the wind. When thewind blows, it pushes against the blades of the wind turbine, making them spin. They power agenerator to produce electricity.Most wind turbines have the same basic parts: blades, shafts, gears, a generator, and a cable.(Some turbines do not have gearboxes.) These parts work together to convert the winds

energy into electricity.

Fig. 3.1 -: wind mill


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1. The wind blows and pushes against the blades on top of the tower, making them spin.2. The turbine blades are connected to a low-speed drive shaft. When the blades spin, the shaftturns. The shaft is connected to a gearbox. The gears in the gearbox increase the speed of thespinning motion on a high-speed drive shaft.3. The high-speed drive shaft is connected to a generator. As the shaft turns inside the

generator, it produces electricity.4. The electricity is sent through a cable down the turbine tower to a transmission line.The amount of electricity that a turbine produces depends on its size and the speed of thewind. Wind turbines come in many different sizes. A small turbine may power one home.Large wind turbines can produce enough electricity to power up to 1,000 homes. Largeturbines are sometimes grouped together to provide power to the electricity grid. The grid isthe network of power lines connected together across the entire country.

Wind turbine components

Blades: Most wind turbines have three blades, though there are some with two blades. Blades

are generally 30 to 50 meters (100 to 165 feet) long, with the most common sizes around 40meters (130 feet). Longer blades are being designed and tested. Blade weights vary,depending on the design and materialsa 40 meter LMGlasfiber blade for a 1.5 MW turbine weighs 5,780 kg (6.4 tons) and one for a 2.0 MWturbine weighs 6,290 kg (6.9 tons).

Controller: There is a controller in the nacelle and one at the base of the turbine. Thecontroller monitors the condition of the turbine and controls the turbine movement.

Gearbox: Many wind turbines have a gearbox that increases the rotational speed of the shaft.A low-speed shaft feeds into the gearbox and a high-speed shaft feeds from the gearbox intothe generator. Some turbines use direct drive generators that are capable of producingelectricity at a lower rotational speed. Theseturbines do not require a gearbox.

Fig. 3.2 -: turbine components


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Generators: Wind turbines typically have a single AC generator that converts the mechanicalenergy from the wind turbines rotation into electrical energy. Clipper Windpower uses a

different design that features four DC generators.

Nacelles: The nacelle houses the main components of the wind turbine, such as the controller,

gearbox, generator, and shafts.

Rotor: The rotor includes both the blades and the hub (the component to which the blades areattached).

Towers: Towers are usually tubular steel towers 60 to 80 meters (about 195 to 260 feet) highthat consist of three sections of varying heights. (There are some towers with heights around100 meters (330 feet)).[12]

3.3 Wind farmsWind power plants, or wind farms, are clusters of wind turbines used to produce

electricity. A wind farm usually has dozens of wind turbines scattered over a large area.Choosing the location of a wind farm is known as siting a wind farm. The wind speed anddirection must be studied to determine where to put the turbines. As a rule, wind speedincreases with height, as well as over open areas with no windbreaks. Turbines are usuallybuilt in rows facing into the prevailing wind. Placing turbines too far apart wastes space. Ifturbines are too close together, they block each others wind. The site must have strong,steady winds. Scientists measure the winds in an area for several years before choosing a site.The best sites for wind farms are on hilltops, on the open plains, through mountain passes,and near the coasts of oceans or large lakes. The wind blows stronger and steadier over waterthan over land. There are no obstacles on the water to block the wind. There is a lot of wind

energy available offshore. Offshore wind farms are built in the shallow waters off the coast ofmajor lakes and oceans. Offshore turbines produce more electricity than turbines on land, butthey cost more to build and operate. Underwater construction is difficult and expensive. Thecables that carry the electricity must be buried deep under the water.

Fig. 3.3 -: wind farm


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Wind ProductionEvery year, wind produces only a small amount of the electricity this country uses,

but the amount is growing every year. One reason wind farms dont produce more electricityis that they can only run when the wind is blowing at certain speeds. In most places withwind farms, the wind is only optimum for producing electricity about three-fourths of the

time. (That means most turbines run 18 hours out of 24.) Wind energy offers manyadvantages, which explains why it's the fastest-growing energy source in the world. Researchefforts are aimed at addressing the challenges to greater use of wind energy.[13]

3.4 Advantages

Wind energy is fueled by the wind, so it's a clean fuel source. Wind energy doesn't

pollute the air like power plants that rely on combustion of fossil fuels, such as coal or

natural gas.

Wind turbines don't produce atmospheric emissions that cause acid rain or greenhouse

gasses. Wind energy relies on the renewable power of the wind, which can't be used up.

Wind is actually a form of solar energy; winds are caused by the heating of the

atmosphere by the sun, the rotation of the earth, and the earth's surface irregularities.

Wind energy is one of the lowest-priced renewable energy technologies available

today, costing between 4 and 6 cents per kilowatt-hour, depending upon the wind

resource and project financing of the particular project.

Wind turbines can be built on farms or ranches, thus benefiting the economy in rural

areas, where most of the best wind sites are found. Farmers and ranchers can continue

to work the land because the wind turbines use only a fraction of the land. Wind

power plant owners make rent payments to the farmer or rancher for the use of the

land.

3.5 Challenges

Wind power must compete with conventional generation sources on a cost basis.

Depending on how energetic a wind site is, the wind farm may or may not be cost

competitive.

Even though the cost of wind power has decreased dramatically in the past 10 years,

the technology requires a higher initial investment than fossil-fueled generators. Good wind sites are often located in remote locations, far from cities where the

electricity is needed. Transmission lines must be built to bring the electricity from the

wind farm to the city.

Wind resource development may compete with other uses for the land and those

alternative uses may be more highly valued than electricity generation.

Although wind power plants have relatively little impact on the environment

compared to other conventional power plants, there is some concern over the noise

produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have

been killed by flying into the rotors. Most of these problems have been resolved or


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greatly reduced through technological development or by properly siting wind

plants.[14]

Wind power is not the perfect answer to our electricity needs, but it is a valuable part of thesolution. It is called a renewable energy source because the wind will blow as long as the sunshines.


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Chapter-4

Bio-fuels

Bio-fuels derived from plant-based feed-stocks, such as corn and sugarcane, are

considered renewable and are an environmentally clean energy source, and they havepotential to significantly decrease fossil fuel consumption. Bio-ethanol and biodiesel can be

used in the form of a gasoline/diesel blend. Besides, biogas which is produced at most

biological treatment plants has been considered as one of the most important renewable

energy sources. Anaerobic biotechnology has been reported as a sustainable alternative to

current disposal strategies because the volume of the organic waste is reduced and stabilized,

a residue (compost) that can be used for soil conditioning is produced, and energy in the form

of methane is recovered Bio-fuels is an alternative fuel for diesel engines that is gaining

attention of the world. Its primary advantages are that it is one of the most renewable fuels

currently available and it is also non-toxic and biodegradable. It can also be used directly in

most diesel engines without requiring extensive engine modifications.

Types of bio-fuels

Bio-methane(bio-gas)

Bio-diesel

Bio-ethanol

4.1 Bio-methane

The bio-methane (or bio-natural gas) extracted from biomass can replace fossil-based

natural gas. It can in this way abate the emissions from green house gases, and thus achieve

an important contribution to a sustainable and environmentally friendly energy\economy.

CO2 emissions resulting from the burning of fossil-based energy sources are known to be a

primary cause of global warming. Natural energy sources like bio-methane release only as

much CO2 as is absorbed from the atmosphere by plants as they mature. Thereby, the ideal

circumstances of climate-neutral energy consumption become conceivable. The utilization of

agricultural waste by biogas generation can make a further contribution to climate protection.

The fermentation of liquid manure and the subsequent output in the field reduces the potential

of global warming. This positive consequence is unique to biogas production. It is for this

reason that biogas and bio-methane can be seen as having a more positive influence on the

global climate balance than other forms of biomass currently in use.


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4.2 Bio-diesel

Biodiesel is an alternative fuel for diesel engines that is gaining attention of world theafter reaching a considerable level of success in Europe. Its primary advantages are that it isone of the most renewable fuels currently available and it is also nontoxic and biodegradable.

It can also be used directly in most diesel engines without requiring extensive enginemodifications. In simple terms, biodiesel is a renewable fuel manufactured from methanoland vegetable oil, animal fats, and recycled cooking fats. It usually made from soybean oil, itis renewable because we can grow more plants in a short time to make more bio-diesel. Bio-diesel works in engines as diesel fuel. It is a better fuel, though it is more expensive. Burningbiodiesel dose not produced as much air pollution as burning petroleum fuels. This means theair is cleaner and healthier to breathe when biodiesel is used. Biodiesel is non-toxic , it is notdangerous to people or the environment and it is safe to handle .if the biodiesel spills , it isbiodegradable, it breaks down quickly into harm less substance. Biodiesel can be used insteadof diesel fuel or it can be mixed with diesel fuel. It is usually mixed with diesel fuel as twopercent (B2), five percent (B5) or 20 percent (B20) biodiesel blends. Pure biodiesel is called

B100. That means it is 100 percent biodiesel.Biodiesel contains no sulphur, so it can reduce sulfur levels in the nations diesel. If

you remove sulfur from petroleum based diesel fuel it losses it lubrication. Adding only oneor two percent biodiesel can restore the lubricating properties of diesel fuel when the sulfur sremoved this the most important characteristic of biodiesel

Vegetable and biodieselNow we can start to deal with biodiesel. As we know, biodiesel is derived from

vegetable oils. The major components of vegetable oils are triglycerides. Triglycerides areesters of glycerol with long-chain acids, commonly called fatty acids. In the formation of

esters from acids and alcohols, an ester can react with another alcohol. In that case, the newalcohol is derived from the original ester is formed and the new ester is derived from theoriginal alcohol. Thus, an ethyl ester can react with methanol to form a methyl ester andethanol. This process is called transesterification.

The transesterification reaction


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Transesterification is extremely important for biodiesel. Biodiesel as it is defined today isobtained by transesterifying the triglycerides with methanol. Methanol is the preferredalcohol for obtaining biodiesel because it is the cheapest (and most available) alcohol (whereR-is corresponding to CH3).

Why are vegetable oils transesterified to produce biodiesel?Vegetable oil methyl esters have lower viscosities (resistance to flow of a liquid) than

the parent vegetable oils (think of honey or syrup, which have high viscosities and flow withdifficulty, vs. water or milk, which have low viscosities and flow easily). Compared to theviscosities of the parent vegetable oils, the viscosities of vegetable oil methyl esters are muchcloser to that of petrodiesel. High viscosity causes operational problems in a diesel enginesuch as poor quality fuel injection and the formation of deposits.

Batch process for mfg. of bio-diesel

Feed-stocks Used in Biodiesel Production

The primary raw materials used in the production of biodiesel are vegetable oils, animalfats, and recycled greases. These materials contain triglycerides, free fatty acids, and othercontaminants depending on the degree of pretreatment they have received prior to delivery.Since biodiesel is a mono-alkyl fatty acid ester, the primary alcohol used to form the ester isthe other major feedstock. Most processes for making biodiesel use a catalyst to initiate theesterification reaction. The catalyst is required because the alcohol is sparingly soluble in theoil phase. The catalyst promotes an increase in solubility to allow the reaction to proceed at a

reasonable rate. The most common catalysts used are strong mineral bases such as sodiumhydroxide and potassium hydroxide. After the reaction, the base catalyst must be neutralizedwith a strong mineral acid.

Typical proportions for the chemicals used to make biodiesel are:Reactants Fat or oil (e.g. 100 kg soybean oil)Primary alcohol (e.g. 10 kg methanol)Catalyst Mineral base (e.g. 0.3 kg sodium hydroxide)

Neutralizer Mineral acid (e.g. 0.25 kg sulfuric acid)

Fats and Oils: Choice of the fats or oils to be used in producing biodiesel is an economic

decision. With respect to process chemistry, the greatest difference among the choices of fatsand oils is the amount of free fatty acids that are associated with the triglycerides. Othercontaminants, such as colour and odour bodies can reduce the value of the glycerin produced,and reduce the public acceptance of the fuel if the colour and odour persist in the fuel.

Alcohol: The most commonly used primary alcohol used in biodiesel production is methanol,although other alcohols, such as ethanol, isopropanol, and butyl, can be used. A key qualityfactor for the primary alcohol is the water content. Water interferes with transesterificationreactions and can result in poor yields and high levels of soap, free fatty acids, andtriglycerides in the final fuel. Unfortunately, all the lower alcohols are hygroscopic and arecapable of absorbing water from the air. Other issues such as cost of the alcohol, the amount

of alcohol needed for the reaction, the ease of recovering and recycling the alcohol, fuel taxcredits, and global warming issues influence the choice of alcohol. A base catalyzed process


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typically uses an operating mole ratio of 6:1 mole of alcohol rather than the 3:1 ratio requiredby the reaction. The reason for using extra alcohol is that it drives the reaction closer to the99.7% yield we need to meet the total glycerol standard for fuel grade biodiesel. The unusedalcohol must be recovered and recycled back into the process to minimize operating costs andenvironmental impacts. Methanol is considerably easier to recover than the ethanol. Ethanol

forms an azeotrope with water so it is expensive to purify the ethanol during recovery. If thewater is not removed it will interfere with the reactions. Methanol recycles easier because itdoesnt form an azeotrope.

Catalysts and Neutralizers:Catalysts may either be base, acid, or enzyme materials. The most commonly used

catalyst materials for converting triglycerides to biodiesel are sodium hydroxide, potassiumhydroxide, and sodium methoxide. The catalyst is required because the alcohol is sparinglysoluble in the oil phase. The catalyst promotes an increase in solubility to allow the reactionto proceed at a reasonable rate. Most base catalyst systems use vegetable oils as a feedstock.

Neutralizers are used to remove the base catalyst from the product biodiesel and glycerol.

If you are using a base catalyst, the neutralizer is typically an acid, and vice-versa. If thebiodiesel is being washed, the neutralizer can be added to the wash water. While hydrochloricacid is a common choice to neutralize base catalysts, as mentioned earlier, if phosphoric acidis used, the resulting salt has value as a chemical fertilizer.

Process

The simplest method for producing alcohol esters is to use a batch or stirred tank reactor.Alcohol to triglyceride ratios from 4:1 to 20:1 (mole:mole) have been reported, with a 6:1ratio most common. The reactor may be sealed or equipped with a reflux condenser. The

operating temperature is usually about 65C, although temperatures from 25C to 85C havebeen reported. The most commonly used catalyst is sodium hydroxide, with potassiumhydroxide also used. Typical catalyst loadings range from 0.3 % to about 1.5%. Thoroughmixing is necessary at the beginning of the reaction to bring the oil, catalyst and alcohol intointimate contact. Towards the end of the reaction, less mixing can help increase the

Fig. 4.1- Batch process


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extent of reaction by allowing the inhibitory product, glycerol, to phase separate from theester oil phase. Completions of 85% to 94 % are reported. Some groups use a two-stepreaction, with glycerol removal between steps, to increase the final reaction extent to 95+percent. Higher temperatures and higher alcohol:oil ratios also can enhance the percentcompletion. Typical reaction times range from 20 minutes to more than one hour. Fig. shows

a process flow diagram for a typical batch system. The oil is first charged to the system,followed by the catalyst and methanol. The system is agitated during the reaction time. Thenagitation is stopped. In some processes, the reaction mixture is allowed to settle in the reactorto give an initial separation of the esters and glycerol. In other processes the reaction mixtureis pumped into a settling vessel, or is separated using a centrifuge. The alcohol is removedfrom both the glycerol and ester stream using an evaporator or a flash unit. The esters areneutralized, washed gently using warm, slightly acid water to remove residual methanol andsalts, and then dried. The finished biodiesel is then transferred to storage. The glycerol streamis neutralized and washed with soft water. The glycerol is than sent to the glycerol refiningsection.[15,16,17]

Biodiesel offers full blending potential with conventional diesel, a high octane number givingimproved combustion in compression ignition engines, and low emissions of sulphur andparticulates. Biodiesel is the fastest growing biofuel but from a lower base than ethanol.Global production passed from 2.1 bnl in 2004 to 3.9 bnl in 2005 and it can be increase upto20 bnl in 2015.


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4.3 Bio-ethanol

Ethanol is one of the most important renewable fuels contributing to the reduction of

negative environmental impacts generated by the worldwide utilization of fossil fuels.

Ethanol has been described as one of the most exotic synthetic oxygen-containing organicchemicals because of its unique combination of properties as a solvent, a germicide, an

antifreeze, a fuel, a depressant and especially of its versatility as a chemical intermediate for

other organic chemicals. Since the energy crisis of the 1970, the development of low-cost,

sustainable and renewable energy sources such as ethanol has been a major focus in scientific

research. Biologically produced ethanol represents such a renewable fuel with various

environmental and socio-economic merits, which is already being used in significant

quantities in different countries. According to F.O. Licht data, in 2008 total world

production of ethanol was about 40700 million litres, of which 73% were used as vehicles

fuel, 17% for production of beverages and 10% for other industry needs.

Since ethanol contains 34.7% oxygen (against 0% in gasoline), it generates full

combustion resulting in less generation of harmful carbon mono-oxide. Ethanol has a higher

detonating resistance than gasoline resulting in higher compression ratio. It has got higher

Research Octane Number (RON) 108 against gasoline (from 88 to 98). It also helps in

boosting agriculture sector and more economic opportunities for rural India and reducing

country's dependency on fuel imports. Subsequently, the Government had decided on

9.10.2007 to make 5% blending of ethanol with petrol mandatory with immediate effect and

optional blending of 10% ethanol with petrol from October 2007 and thereafter mandatory

blending from October 2008.

An increasing number of spark ignition, 4-stroke internal combustion engines useethanol blends worldwide. Environmental concerns as well as the need for renewable energy

sources have driven the government to encourage the use of ethanol blends. The reality is that

the majority of the engines that use low percentage ethanol blends are designed to run on

gasoline. The objective of this research was to determine the effect of ethanol blending on the

performance and emissions of internal combustion engines that are calibrated to run on 100%

gasoline. Experimental tests were performed on an engine using pure gasoline, 10% ethanol

and 20% ethanol blends. The results of the study show that 10% ethanol blends can be used

in internal combustion engines without any negative drawbacks. The fuel conversion

efficiency remains the same, while CO emissions are greatly reduced. 20% ethanol blendsdecrease the fuel conversion efficiency and brake power of an engine, but still reduces CO

emissions.

Fermentation processes from any material that contains sugar can derive ethanol. The

many and varied raw materials used in the manufacture of ethanol via fermentation are

conveniently classified under three types of agricultural raw materials: sugar, starches, and

cellulose materials. Sugars (from sugar cane, sugar beets, molasses, fruits) can be converted

to ethanol directly. Starches (from grains, potatoes, root crops) must first be hydrolyzed to

fermentable sugars by the action of enzymes from malt or molds. Cellulose from wood,

agricultural residues, waste sulfite liquor from pulp and paper mills) must likewise be


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converted to sugars, generally by the action of mineral acids. Once simple sugars are formed,

enzymes from yeast can readily ferment them to ethanol.

4.3.1 Ethanol from sugarcane molasses

Molasses differs from other feedstocks for alcohol production such as corn andpotatoes in that these plant products contain carbohydrate stored as starch. As a result, thesefeedstocks must be pre-treated by cooking and enzymatic action to hydrolyze starch intofermentable sugars. In contrast, the carbohydrates in molasses are already in the form ofsugars and need no pretreatment.

Basic sugar chemistry

The simplest form of sugar is glucose, It has the formula C6H12O6 and is made up ofmolecules with a single ring structure (Figure 1). Very slight rearrangements of the atoms inthe molecule can give other sugars with distinctly different properties.

For instance, if the end groups are rotated it becomes galactose, which is not readilyfermentable by normal yeasts (Figure 2). Alternatively, by rearranging the ring structure, itbecomes the fermentable fructose. There are many other simple sugars, but only glucose andfructose will be considered here. Glucose does not exist extensively in the free state in nature.It is mostly polymerized as starch or cellulose, in which long chains of glucose units areformed. Glucose also exists in combination with fructose to form the disaccharide (two sugarmolecules) or common table sugar. Sucrose is the principal sugar contained in molasses andis readily fermentable either directly, or as its glucose and fructose components.

Blackstrap molasses production

In the production of cane sugar, the cane is crushed in a mill to squeeze out the juice.The juice is heated, clarified by filtration and the addition of lime (to remove cane fibers andsludge) and then evaporated to concentrate the sugar and cause it to crystallize. The syrupcontaining the crystals is then centrifuged to separate the crystals and the syrup residue(which still has a high content of sugar). The residue is referred to as .A molasses.. It isevaporated and centrifuged again to recover more crystalline sugar; and the syrup residue isnow referred to as .B molasses.. The process may be repeated to yield more sugar and a .Cmolasses. as residue. Sugar mills normally evaporate and centrifuge a maximum of three

times, but the number of treatments will depend on marketplace economics.


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When sugar prices are high, a fourth processing may be practiced with production of a.D molasses., which has lost most of its available crystallizable sugar. On the other hand,when sugar prices are low, the .A molasses. may be sold directly. Repeated evaporation andcentrifugation decreases the sugar content of molasses and increases the viscosity andconcentration of salts and other impurities. The result is thick, viscous, brown liquid which is

very heavy. The concentration of molasses is normally measured in degrees Brix. The Brixscale is the same as the Balling scale, which is a measure of what the sugar content of a liquidwould be if all the dissolved and suspended solids were sugar. Expressed another way, it isthe sugar content of a sugar solution with the same specific gravity as the sample.

Fermentation of molassesPre-treatments

Blackstrap molasses at 80o Brix will not ferment without dilution as the sugars andsalts exert a very high osmotic pressure. It is therefore necessary to dilute the molasses tobelow 25o Brix. Yeast will not start fermenting rapidly above this point; and contaminationmay develop before the yeast become established since molasses is laden with contaminating

bacteria. When diluting molasses, it must be remembered that the Brix scale measures on aweight % basis and all calculations must be based on weight and not volume. 80o Brixmolasses has a specific gravity of 1.416, therefore a gallon weighs about 11.8 lbs and a toncontains about 169.5 gallons. When the molasses is diluted to 25o Brix the sugar content isonly about 14.3% (Calculated: 25 x 46/80 = 14.3). This is only sufficient to yield 7-8% v/v ofethanol in the fermented beer. Distilleries generally need a higher final ethanol content toeconomize on energy for distillation; but the fermentation cannot begin at a much higher Brixwithout running into problems of slow starts and bacterial contamination. Some distilleriesovercome this problem by diluting the first portion of molasses going into the fermenter toabout 18o Brix, which allows the yeast to get established very rapidly. When the Brix readingin the fermenter is down to about 12o Brix, molasses diluted to around 35o Brix is added.This allows beer ethanol levels of around 10% to be attained. This procedure is the first steptoward what is known as incremental feeding.

Calculation for diluting the molasses


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Nutrient use in molasses fermentationIn blackstrap fermentations it may be necessary to add some nitrogen and phosphorus

to obtain optimum results. Nitrogen should not be in the form of ammonium sulfate as it willadd to the scaling problem by forming calcium sulfate. Likewise, liquid ammonia isundesirable as it tends to raise the pH and encourage bacterial contamination unless it is

counteracted with acid additions. (Some plants using liquid ammonia either use sulfuric acidto balance the pH, which introduces the undesirable sulfate anion, or use phosphoric acid,which generally introduces more phosphate than necessary. Urea may be used to supplynitrogen in molasses fermentations for fuel ethanol production, but its use for beveragealcohol production should be approached with caution. Urea usage may lead to theproduction of carcinogenic ethyl carbamate, which is unacceptable in alcoholic beverages. Ifphosphorus is deficient in the molasses, diammonium phosphate may be added with acorresponding reduction in urea or other nitrogenous nutrient. Generally, blackstrap molassesrequires no other added nutrients for fermentation.

Microorganism contamination of molasses

The most employed microorganism is Saccharomyces cerevisiae due to its capabilityto hydrolyze cane sucrose into glucose and fructose, two easily assimilable hexoses. Aerationis an important factor for growth and ethanol production by S. cerevisiae. Although thismicroorganism has the ability to grow under anaerobic conditions, small amounts of oxygenare needed for the synthesis of substances like fatty acids and sterols. The oxygen may besupplied through the addition to the medium of some chemicals like urea hydrogen peroxide(carbamide peroxide), which also contributes to the reduction of bacterial contaminants.Other yeasts, as Schizosaccharomyces pombe, present the additional advantage of toleratinghigh osmotic pressures (high amounts of salts) and high solids content. Among bacteria, themost promising microorganism is Zymomonas mobilis, which has a low energy efficiencyresulting in a higher ethanol yield (up to 97% of theoretical maximum).[19]

The fermentation unit aims at producing a beer at 9% (vol.) ethanol. Fermentationoperates in a continuous mode and comprises two successive steps :

(1)the pre-fermentation of a fraction of the molasses, to produce the required amount ofyeasts for fermentation,

(2)and, the fermentation itself, aiming at converting the sugars into ethanol by means ofthe yeasts. The fermentation process lasts for 72-76 hours.

The sample was fermented to different pH values between 1.0 and 8.0 to obtain maximum

yield of bio-ethanol by adding lime or sulphuric acid. The samples were kept in anaerobiccondition for a period of 3-4 days and the fermented solution was analyzed for every 12 hintervals. The test shows that the bio-ethanol concentration gradually increases along with theincrease in pH and reaches a maximum percentage of bio-ethanol production when pH isequal to 4 and later it starts declining due to the lesser activity of yeast. The temp. ismaintained in between 35-40 0C because ethanol production reaches maximum value at thistemperature. Further increasing in temperature reduces the percentage of ethanol productionand it is mainly due to the denature of the yeast cells.[18]

The fermentation is carried out in absence of oxygen in fermentation process thecarbon dioxide produced pushes out air and automatically creates an anaerobic atmosphere.The reaction being exothermic thus it not required external heating provision.

In a first stage the Sucrose (disaccharide) is converted to glucose or fructose(monosaccharides) by the ation of enzymes through the following hydrolysis reaction:


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C12H22O11 + H2O 2C6H12O6Sucrose Water Glucose

Then Ethanol is produced by the fermentation of these monosaccharide sugars according to

the following reaction:

C6H12O6 2C2H5OH + 2CO2

Glucose Ethanol

The reaction is exothermic and liberates 1200 kJ/kg of ethanol.

Fig. 4.2- flow sheet for production of ethanol

Distillation

The distillation unit aims at producing a hydrated ethanol at up to 93% (vol.). The unique

distillation column operates at low temperature and in vacuum, in order to avoid possible

clogging problems. As opposed to the corn process, the stillage is sent directly, as such, to the

pre-concentration unit, without a clarification/separation stage. The distillation is coupled, in

terms of energy use, to the pre-concentration unit, in order to reduce the global energy

consumption. Hence, the distillation column is heated by direct injection of the steam

produced in the first evaporator effect of the pre-concentration unit.


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Pre-concentration

The pre-concentration unit aims at concentrating the produced stillage by evaporation.

The evaporation is realized in a double-effect counter current unit, each effect comprising a

group evaporator-separator with forced recirculation. The second effect is heated by steam

coming from the boiler, and the evaporation steam, in turn, heats the first effect. The

evaporation steam of the first effect (as it was mentioned previously) provides the heat for the

distillation stage by direct injection. The net consumption of plant steam in pre-concentration,

and hence the concentration of dry matter at the exit, depends directly on the quantity of

steam necessary at the distillation stage (therefore indirectly also on the ethanol concentration

of the fermented mash).

Dehydration

The dehydration of the hydrated ethanol (93% vol.) coming from the distillation unit

is done by means of molecular sieves with regeneration by difference of pressure. Thedehydration stage may not coupled with the distillation stage, in which case, the production

of fuel-ethanol is not dependent upon the operating discontinuities of the distillation unit,

themselves related to the availability of the feedstock. The hydrated ethanol is overheated

prior to dehydration, in order to avoid any risk of condensation in the adsorbers. The

dehydration stage is performed in vapour phase, in a cyclical and sequential way : adsorption,

desorption. The alternation of cycles makes the production of anhydrous ethanol

continuous.[20]

The bio-ethanol demand will grow very fast till 2015. Indian demand of fossil fuels amounts

to 4.0 EJ (diesel,83%; gasoline, 17%). India imported 90 millions tones of crude oil and

imports will continue to increase fast causing a significant burden on the balance of trade and

energy security. Wide scale introduction of bio-ethanol as fuel for automotive will improve

the diversity of Indian energy supply.


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Chapter- 5

Solar energy

In today's climate of growing energy needs and increasing environmental concern,

alternatives to the use of non-renewable and polluting fossil fuels have to be investigated.One such alternative is solar energy. Solar energy is quite simply the energy produceddirectly by the sun and collected elsewhere, normally the Earth. The sun creates its energythrough a thermonuclear process that converts about 650,000,000 tons of hydrogen to heliumevery second. The process creates heat and electromagnetic radiation. The heat remains in thesun and is instrumental in maintaining the thermonuclear reaction. The electromagneticradiation (including visible light, infra-red light, and ultra-violet radiation) streams out intospace in all directions. Only a very small fraction of the total radiation produced reaches theEarth. The radiation that does reach the Earth is the indirect source of nearly every type ofenergy used today. Even fossil fuels owe their origins to the sun; they were once living plantsand animals whose life was dependent upon the sun. Much of the world's required energy canbe supplied directly by solar power. More still can be provided indirectly. The practicality ofdoing so will be examined, as well as the benefits and drawbacks. In addition, the uses solarenergy is currently applied to will be noted. Due to the nature of solar energy, twocomponents are required to have a functional solar energy generator. These two componentsare a collector and a storage unit. The collector simply collects the radiation that falls on itand converts a fraction of it to other forms of energy (either electricity and heat or heatalone). The storage unit is required because of the non-constant nature of solar energy; atcertain times only a very small amount of radiation will be received. At night or during heavycloud cover, for example, the amount of energy produced by the collector will be quite small.The storage unit can hold the excess energy produced during the periods of maximum

productivity, and release it when the productivity drops. In practice, a backup power supply isusually added, too, for the situations when the amount of energy required is greater than bothwhat is being produced and what is stored in the container. Methods of collecting and storingsolar energy vary depending on the uses planned for the solar generator. In general, there arethree types of collectors and many forms of storage units.

The three types of collectors are flat-plate collectors, focusing collectors, and passivecollectors. Flat-plate collectors are the more commonly used type of collector today. They arearrays of solar panels arranged in a simple plane. Focusing collectors are essentially flat-plane collectors with optical devices arranged to maximize the radiation falling on the focusof the collector. These are currently used only in a few scattered areas. Solar furnaces areexamples of this type of collector. Passive collectors are completely different from the other

two types of collectors. The passive collectors absorb radiation and convert it to heatnaturally, without being designed and built to do so.[21]

5.1 Flat plate collectors

The Photovoltaics

The word Photovoltaic is a combination of the Greek word for Light and the name ofthe physicist Allesandro Volta. It identifies the direct conversion of sunlight into energy bymeans of solar cells. The conversion process is based on the photoelectric effect discoveredby Alexander Bequerel in 1839. The photoelectric effect describes the release of positive andnegative charge carriers in a solid state when light strikes its surface.Photovoltaics offer the

ability to generate electricity in a clean, quiet and reliable way. Photovoltaic systems arecomprised of photovoltaic cells, devices that convert light energy directly into electricity.


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Because the source of light is usually the sun, they are often called solar cells. The wordphotovoltaic comes from photo, meaning light, and voltaic, which refers to producingelectricity. Therefore, the photovoltaic process is producing electricity directly from

sunlight. Photovoltaics are often referred to as PV. We are probably familiar withphotovoltaic cells. Solar-powered toys, calculators, and roadside telephone call boxes all use

solar cells to convert sunlight into electricity.Over 95% of all the solar cells produced worldwide are composed of the

semiconductor material Silicon (Si). As the second most abundant element in earth`s crust,silicon has the advantage, of being available in sufficient quantities, and additionallyprocessing the material does not burden the environment.

One can distinguish three cell types according to the type of crystal: Monocrystalline,polycrystalline and amorphous. To produce a monocrystalline silicon cell, absolutely puresemiconducting material is necessary. Monocrystalline rods are extracted from melted siliconand then sawed into thin plates. This production process guarantees a relatively high level ofefficiency. The production of polycrystalline cells is more cost-efficient. In this process,liquid silicon is poured into blocks that are subsequently sawed into plates. During

solidification of the material, crystal structures of varying sizes are formed, at whose bordersdefects emerge. As a result of this crystal defect, the solar cell is less efficient. If a siliconfilm is deposited on glass or another substrate material, this is a so-called amorphous or thinlayer cell. The layer thickness amounts to less than 1m (thickness of a human hair: 50-100m), so the production costs are lower due to the low material costs. However, the efficiencyof amorphous cells is much lower than that of the other two cell types. Because of this, theyare primarily used in low power equipment (watches, pocket calculators) or as facadeelements.

Material Level of efficiency in % Lab Level of efficiency in % Production

Monocrystalline Silicon approx. 24 14 to17

Polycrystalline Silicon approx. 18 13 to15

Amorphous Silicon approx. 13 5 to7

The majority of solar cells fabricated to date have been based on silicon in monocrystalline orlarge- grain polycrystalline form, the reason is that the silicon it is an elementalsemiconductor with good stability and well balanced properties set of electronic, physical andchemical properties, the same set of strength that have made silicon the preferred material for

microelectronics.

Fig. 5.1-: Polycrystalline silicon cell


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5.1.1 A solar cell

Photovoltaics is the field of technology and research related to the devices which directlyconvert sunlight into electricity. The solar cell is the elementary building block of the

photovoltaic technology. Solar cells are made of semiconductor materials, such as silicon.One of the properties of semiconductors that makes them most useful is that theirconductivity may easily be modified by introducing impurities into their crystal lattice. Forinstance, in the fabrication of a photovoltaic solar cell, silicon, which has four valenceelectrons, is treated to increase its conductivity. On one side of the cell, the impurities, whichare phosphorus atoms with five valence electrons (n-donor), donate weakly bound valenceelectrons to the silicon material, creating excess negative charge carriers. On the other side,atoms of boron with three valence electrons (p-donor) create a greater affinity than silicon toattract electrons. Because the p-type silicon is in intimate contact with the n-type silicon a p-n

junction is established and a diffusion of electrons occurs from the region of high electronconcentration (the n-type side) into the region of low electron concentration (p-type side).

Fig. 5.2 -: construction of solar cell

When the electrons diffuse across the p-n junction, they recombine with holes on the p-typeside. However, the diffusion of carriers does not occur indefinitely, because the imbalance ofcharge immediately on either sides of the junction originates an electric field. This electricfield forms a diode that promotes current to flow in only one direction. At the p-n junction, aninterior electric field is built up which leads to the separation of the charge carriers that arereleased by light. Through metal contacts, an electric charge can be tapped. If the outer circuit

is closed, meaning a consumer is connected, and then direct current flows.


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The usable voltage from solar cells depends on the semiconductor material. In silicon itamounts to approximately 0.5 V. Terminal voltage is only weakly dependent on lightradiation, while the current intensity increases with higher luminosity. A 100 cm silicon cell,for example, reaches a maximum current intensity of approximately 2 A when radiated by

1000 W/m. The output (product of electricity and voltage) of a solar cell is temperaturedependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. Thelevel of efficiency indicates how much of the radiated quantity of light is converted intouseable electrical energy.

To increase their utility, dozens of individual PV cells are interconnected together in asealed, weatherproof package called a module. When two modules are wired together inseries, their voltage is doubled while the current stays constant. When two modules are wiredin parallel, their current is doubled while the voltage stays constant.

Fig. 5.3 -: Photovoltaics cells, modules and array

To achieve the desired voltage and current, modules are wired in series and parallelinto what is called a PV array. The flexibility of the modular PV system allows designers tocreate solar power systems that can meet a wide variety of electrical needs, no matter howlarge or small. They can be connected in both series and parallel electrical arrangements toproduce any required voltage and current combination. There are two main types ofphotovoltaic system. Grid connected systems (on-grid systems) are connected to the grid andinject the electricity into the grid. For this reason, the direct current produced by the solarmodules is converted into a grid-compatible alternating current. However, solar power plantscan also be operated without the grid and are then called autonomous systems (off-gridsystems). More than 90 % of photovoltaic systems worldwide are currently implemented as

grid-connected systems.[22]


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5.1.2 Efficiency of solar cell

The energy of the photon that strikes the cell must be contents in a definite range inorder to allow the transformation from solar energy to electric energy. In fact if the energy istoo low the electrons are not free and the holes do not move. When the photons energy is

more than the required amount, the execs of energy is lost by heating the cell. Because ofthat, the efficiency of a photovoltaic cell is quite low. Efficiency can be defined as:

Pout = Electrical ratio powerPR = Radiation powerUsually efficiency of commercial available solar cell is around 14%-17%. Others restrictionslimit the efficiency.

5.1.3 Capital cost

Solar PV has one of the highest capital costs of all renewable energy sources, but it hasrelatively low operational costs, owing to the low maintenance and repair needs.For a solar PV power plant, the approximate capital cost per MW is approximately Rs. 16crores the precise cost depends on scale. This includes the cost of panels, the balance ofsystems, the cost of land and other support infrastructures.

Table : Break-Up for the Capital Expenses per MW

Component Amount(in Rs crores)

% of total

Solar panel arrays 8 50

Inverter 2 12.5

Balance of system 2 12.5

Installation 1.6 10

Others 2.5 15

5.1.4 Investment of Solar PV in IndiaMany investors see Indias potential in tapping solar energy as even greater than wind,

given that its sunny days are around 93% of the year and can be more easily distributed. Bothequity-based and debt-based investments into solar PV power plants in India are expected toaccelerate dramatically in 2010 owing to the National Solar Mission and similar thrustsprovided by the state governments for solar PV investments. Some prominent examples ofinvestments into solar PV that have taken place until Mar 2010 are provided below:1. Azure Power2. Moser Baer Photovoltaic (for solar PV cell production)3. Titan Solar

4. KPCL5. Clover Solar


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Karnataka Power Corporation Limited (KPCL) has so far invested Rs 120 crore onsetting up two solar PV power plants, 3 MW each in Kolar, Belgaum and Raichur districts. InJun 2010, the solar PV plant located at the Yalesandra village in Kolar district was formallylaunched. The will provide energy to 500 pumpsets of 10 HP each and benefit about 1,000

farmers. While the Belgaum power plant is also operational, the Raichur PV power plant isexpected to become operational before end of 2010. [23]

5.1.5 Useful sectors for investing in PV systems

1. Villages that have no grid connectivity2. Companies that use diesel generator sets as a power backup3. Mobile telecom towers in many parts of India that have little access to the utility grid,

and other stand alone commercial and industrial ventures.

5.1.6 Merits

1. A high growth industry with significant future potential.2. Sunlight is available in sufficient quantities in many regions.3. Technology proven, with low operation and maintenance costs, and scalable.4. Availability of soft loans and government incentives for growth and expansion

5.1.7 Demerits

1. Solar PV systems have high capital costs.2. Owing to high capital costs, the business needs external incentives to be economically

feasible, thus increasing dependence on governmental policies.3. The capital intensive nature of the business might favour larger businesses over

smaller ones.4. The distributed and intermittent nature of solar energy makes it difficult for utilities to

rely on solar PV for their base load.

5.1.8 Threats1. Technology innovation is high, so there are risks of obsolescence.2. Off-peak seasons reduce cash flow.3. Industry is new, so finding skilled workforce could be a problem.

5.1.9 Opportunities1. Opportunities exist all along the solar PV business value chain, not just for powerplants.

2. Entirely new opportunities could open up as the there is high innovation in technologyand the technology could prove to be a disruptive business, especially with reductionsin costs in future.


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5.2 Solar Thermal Electricity

Like solar cells, solar thermal systems, also called concentrated solar power (CSP),use solar energy to produce electricity, but in a different way. Concentrated solar power

systems use lenses or mirrors and tracking systems to focus a large area of sunlight into asmall beam, which heats a liquid. The super-heated liquid is used to make steam to produceelectricity in the same way that coal plants do. Commercial concentrated solar power plantswere first developed in the 1980s, and the 354 MW CSP installation is the largest solar powerplant in the world and is located in the Mojave Desert of California. Other large CSP plantsinclude the Solnova Solar Power Station (150 MW) and the Andasol solar power station (100MW), both in Spain. A wide range of concentrating technologies exists; the most developedare the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and thesolar power tower. Various techniques are used to track the Sun and focus light. In all ofthese systems a working fluid is heated by the concentrated sunlight, and is then used forpower generation or energy storage.

5.2.1 Central receiving system

Central receiver systems(concentrating linear fresnel reflector) contain an array ofFresnel reflectors (heliostats) with two axes of rotation. The common focus is stationary,located on a solar tower (Figure 14b). The two-axis tracking enables a higher concentrationratio and the higher operating temperatures and power conversion efficiency than those of theline focus configuration. However, as the system size increases, the optical efficiency (theratio of sunlight capture to incident sunlight) declines.

Fig 5.4(a) -: central receiving system
http://en.wikipedia.org/wiki/Solnova_Solar_Power_Stationhttp://en.wikipedia.org/wiki/Andasol_solar_power_stationhttp://en.wikipedia.org/wiki/Working_fluidhttp://en.wikipedia.org/wiki/Working_fluidhttp://en.wikipedia.org/wiki/Andasol_solar_power_stationhttp://en.wikipedia.org/wiki/Solnova_Solar_Power_Station


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5.2.2 Line Focus Systems.

In line focus systems, incident sunlight is folded from a plane to a line. In most

cases, the optical configuration is that of a trough tracking the sun from east to west and atarget that rotates accordingly (Figure b).

Fig 5.4(b) -: line focus system

The main inherent advantage of the system is its compatibility with large engines (i.e., steamturbines of hundreds of megawatts). The main inherent disadvantage is the low operatingtemperature, limited to less than 750K by the relatively low concentration and long tubularreceiver configuration.

Lower temperatures reduce the efficiency of the heat transfer to the fluid located in thetubular receiver; this fluid provides the thermal energy to drive electricity generation cycles.

The current systems range from 350 MWe to newer small-scale 1-MWe systems.
http://en.wikipedia.org/wiki/File:Moody_Sunburst.jpghttp://en.wikipedia.org/wiki/File:Moody_Sunburst.jpg


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5.2.3 On-axis Tracking Systems.

On-axis systems, such as parabolic dish concentrators (Figure c), provide the highestoptical efficiency of all the concentrating solar systems. Their main drawback is theconcentrator size, which is limited by practical structural consideration. Recent progress in

the development of small Brayton engines provides the option of using a dish/Brayton systemas an alternative to the dish/Stirling system.

Fig 5.4(c) -: Stirling system

Estimates of large-scale (>50-MW) dish/Stirling facility costs are about $2.5/W (Stoddard etal. 2005), although the current costs, based on several demonstration systems, are three tofour times higher. A recent research indicates that new developments in current areas ofresearch can reduce cost by more than $0.5/W.

Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems

to focus a large area of sunlight into a small beam. The concentrated heat is then used as aheat source for a conventional power plant. Various techniques are used to track the Sun andfocus light (as explained above). In all of these systems a working fluid is heated by theconcentrated sunlight, and is then used for power generation or energy storage.[24]

5.3 Photobiological hydrogen

Photobiological hydrogen technologies use certain photosynthetic microbes thatproduce hydrogen from water in their metabolic activities using light energy. However, it ispossible to modify conditions such that the reducing end of the photosynthetic process is

coupled to a hydrogen-evolving enzyme, as hydrogenase (e.g. in green algae) or nitrogenase(e.g. in cyanobacteria). Photon-tohydrogen conversion efficiency under ideal conditions


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approaches ~10%, and recently 7.5% was obtained in green algal photosynthesis. A majordifficulty is that the algal systems saturate at solar irradiances above ~0.03 suns, where thephoton absorption rate exceeds the rate at which photosynthesis can utilize them, resulting indissipation and loss of the excess photons (up to 95% of absorbed photons as fluorescence orheat). Thus, genetic engineering is required to reduce the size and/or effectiveness of the

lightharvesting antenna chlorophyll pool to allow greater solar conversion efficiencies andhigher photosynthetic productivity.

Another problem concerns the stability of hydrogen evolving enzymes in the presenceof oxygen. Because oxygen is produced along with the hydrogen, the technology mustovercome the limitation of oxygen sensitivity of the hydrogen-evolving enzyme systems.Researchers are addressing this issue by screening for naturally occurring organisms that aremore tolerant of oxygen, and by creating new genetic forms of the organisms that cansustain hydrogen production in the presence of oxygen. Practical applications of biologicalsystems for hydrogen synthesis are still far away since the current understanding of biologicalprocesses is too limited. More fundamental research is required to understand, among others,molecular mechanisms, the structure and functionality of enzyme catalysts, and the kinetics

of biological hydrogen metabolism.[24]

Solar energy has great potential for the future. Solar energy is free, and its supplies areunlimited. It does not pollute or otherwise damage the environment. It cannot be controlled

by any one nation or industry. If we can improve the technology to harness the suns

enormous power, we may never face energy shortages again.


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Chapter-6

Geothermal energy

Geothermal energy is the earths natural heat available inside the earth. This thermal

energy contained in the rock and fluid that filled up fractures and pores in the earths crust Itoriginates from radioactive decay deep within the Earth and can exist in the form of hotwater, steam, or hot dry rocks, can profitably be used for various purposes. It is an enormous,underused heat and power resource that is clean (emits little or no greenhouse gases),reliable (average system availability of 95%), and home-grown (making us less dependenton foreign oil).

Geothermal energy provides an affordable, clean method of generating electricity andproviding thermal energy. Geothermal power plants tap certain high-temperature resources(above 190F) to generate electricity with minimal or no air emission.

Geothermal energy originates from the earths molten interior and the decay ofradioactive materials. Heat is brought near to the surface by deep circulation of groundwaterand by intrusion into the earths crust of magma. On average, the temperature of the earthincreases by about 3 oC for every 100 meters of depth. Eachand every year, more than 10000 TWh of heat energy is conducted from the earths interior to

its surface.

Two challenges for geothermal energy are that resources are difficult to locate andtend to be found in rural areas. The fact that they are found in remote areas constrainsgeneration and direct use development. Geothermal resources range from shallow ground tohot water and rock several miles below the Earth's surface, and even farther down to theextremely hot molten rock called magma. Mile-or-more-deep wells can be drilled intounderground reservoirs to tap steam and very hot water that can be brought to the surface foruse in a variety of applications.

Heat energy from inner Earth

Billions of years ago our planet was a fiery ball of liquid and gas. As the earthcooled, an outer rocky crust formed over the hot interior, which remains hot to this day. Thisrelatively thin crust floats on a massive underlying layer of very hot rock called the mantle.

Some of the mantle rock is actually melted, or molten, forming magma. The heat from themantle continuously transfers up into the crust. Heat is also being generated in the crust bythe natural decay, or breakdown, of radioactive elements.

The crust is broken into enormous slabstectonic platesthat are actually movingvery slowly (at the rate your fingernails grow) over the mantle, separating from, crushinginto, or sliding (sub ducting) under one another.

The edges of these huge plates are often restless with volcanic and earthquakeactivity. At these plate boundaries, and in other places where the crust is thinned or fractured,rising magma can travel up the many cracks and fissures. Sometimes the magma emerges

above ground where we know it as lava. But most of it stays below ground where, overtime, it creates large regions of hot rock.


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Geothermal reservoirs

Rainwater and snowmelt can seep miles underground, where it absorbs heat from the

hot rock. This water can get really hot. It can reach temperatures of 500 F (260C) or higherway above boiling.Sometimes this hot water will work its way back up (hot water is less dense than cold and sotends to rise). If it reaches the surface it can form hot springs, steam vents (fumaroles), mudpots, or geysers. If it gets trapped deep below the surface, it can form a geothermalreservoir of hot water and steam. A geothermal reservoir is an underground area of crackedand porous (permeable) hot rock saturated with hot water. The water and steam from thesesuperheated reservoirs are the geothermal energy resources we use to generate electricity.

Hot locations

The edges of the continents that surround the Pacific Ocean (the Pacific Ring of Fire)are prone to earthquakes and volcanoes and have some of the best geothermal resources inthe world. This includes the western part of North, Central, and South America; Japan; thePhilippines; and Indonesia. Some of the other prime geothermal locations include Iceland,Italy, New

Renewable Energy Resorces by Omkar Hirawat

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