Renewable
Sources of Energy or Non-conventional Sources of Energy
Renewable energy sources are also called
non-conventional energy sources that are continuously replenished by natural
processes. For example, solar energy, wind energy, bio-energy, hydropower etc.,
are some of the examples of renewable energy sources.
A renewable energy system converts the energy
found in sunlight, wind, falling-water, sea waves, geothermal heat, or biomass
into a form, we can use such as heat or electricity. Most of the rmewable
energy comes either directly or indirectly from sun and wind and can never be
exhausted, and therefore they are called renewable. They are available in
unlimited amount in nature and develop in a relatively short period of time.
However, most of the world's energy sources are derived from
conventional sources-fossilfuels such as coal, oil and natural gases. These
fuels are often termed non-renewable energy sources.Although, the available
quantity of these fuels are extremely large, they are nevertheless finites
andso will in principle 'run out at some time in the future.
Renewable energy sources are essentially flows of energy,
whereas the fossil and nuclear fuels are, in essence, stocks of energy
Solar
Energy
Solar energy is the most readily available and free source of
energy since prehistoric times. It is mated that solar energy equivalent to
over 15,000 times the world's annual commercial energy spion reaches the earth
every year
I receive solar energy in the region of 5 to 7 kwh/m² for 300 to
330 days in a year. This is sufficient to set up 20MW solar power plant per
square kilometre land area.Solar energy can be utilized through two different
routes, as solar thermal route and solar electric (solar photovoltaic) routes.
Solar thermal route uses the sun's heat to produce hot water or air for cooking
food, drying materials etc. Solar photovoltaic uses sun's heat to produce
electricity for lighting homes and buildings, running motors, pumps, electric
appliances etc.
Solar
Water Heaters
Most of the solar water heating systems have two main parts: a
solar collector and a storage tank. The most common collector is called a
flat-plate collector (Fig.1). It consists of a thin, flat, rectangular box
with a transparent cover that faces the sun, mounted on the roof of building or
home. Small tubes run through the box and carry the fluid - either water or
other fluid, such as an antifreeze solution - to be heated. The tubes are
attached to an absorber plate, which is painted with special coatings to absorb
the heat. The heat builds up in the collector is then passed through the fluid,
which is passing through the tubes.
Fig1 : Solar Flat
Plate Collector
The last water is collected in an insulated storage tank. It is
similar to water heater, but larger in size. In case of systems that use
fluids, heat is passed from hot fluid to the water stored in the tank through a
coil of tubes.
Solar water heating systems can be either active or passive
systems. The active systems which are most common, rely on pumps to move the
liquid between the collector and the storage tank. The passive systems rely on
gravity and the tendency for water to naturally circulate as it is heated. A
few industrial application of solar water heaters are listed below:
·
Hotels: Bathing, kitchen, washing, laundry
applications
·
Dairies: Ghee (clarified butter) production,
cleaning and sterilizing, pasteurization
·
Textiles: Bleaching, boiling, printing,
dyeing, curing, ageing and finishing
· Breweries & Distilleries: Bottle washing,
wort preparation, boiler feed heating
·
Chemical/Bulk drugs units: Fermentation of
mixes, boiler feed applications
·
Electroplating/galvanizing units Heating of
plating baths, cleaning, decreasing application
· Pulp and paper industries: Boiler feed
applications, soaking of pulp.
Solar
Cooker
Solar cooker is a device in which solar energy is used for
cooking, and thus saving fossil fuels, fuel wood and electrical energy to a
large extent. However, it can only be considered as a supplementary
cooking fuel and it cannot replace the fossil fuel totally. It
is a simple cooking unit, ideal for domestic cooking during most of the year
except during the monsoon season, cloudy days and winter months .
Box
Type Solar Cookers: The box type solar cookers with a single
reflecting mirror are the most popular in India. These cookers have proved
immensely popular in rural areas where women spend considerable time for
collecting firewood. A family size solar cooker is sufficient for 4 to 5
members and saves about 3 to 4 cylinders of LPG every year. The life of this
cooker is upto 15 years. It is cheap and easily available in the market it
costs around Rs.1000.
Solar
Electricity Generation
Solar
Photovoltaic (PV): Photovoltaic is the technical term for solar electricity
Photo mcare "light" and voltaic means "electric". PV cells
are usually made of silicos, as element that naturally releases electrons when
exposed to light. Amount of electrons released from silicon cells directly
related to the intensity of light incident on it. The silicon cells is covered
with a grid of metal that directs the electrons to flow in a path to create an
electric current. This current is guided into a wire that is connected to a
battery or DC appliance. Typically, one cell produces about 3,5 of govest
Individual cells are connected together to form a solar panel or module,
capable of producing 3 to 110 Watts power. Panels can be connected together in
series and parallel to make a solar array (Fig 2), which can produce any
amount of Wattage as space will allow. Modules are usually designed to supply
electricity at 12 Volts. PV modules are rated by their peak Watt output at
solar noon on a clear day.
fig 2. Solar Photovoltaic
Array
Applications of PV
Systems: The PV systems are
generally used for the chimerical buildings outdoor (street) lighting rural and
village lighting etc. Solar electric power systems can offer independence from
the utility and offer protection during extended power failures Solar PV syste
are very economical especially in the hilly and far flung areas where
conventional grid power supply will be expensive to reach.
PV tracking system is an alternative to the fixed, stationary PV
panels PV tracking systems are mounted and provided with tracking mechanisms to
follow the sus as it moves through the sky. These tracking systems run entirely
on their own power and can increase output by 40% Back-up systems are necessary
since PV systems only generate electricity when the sun isshining. The two most
common methods of backing up solar electric systems are connecting the system
to the utility grid or storing excess electricity in batteries for use at night
or on cloudy days.
Performance: The performance of a
solar cell is measured in terms of its efficiency at converting sunlight into
electricity. Only sunlight of certain energy will work efficiently to create
electricity, and1.58Environmental Engineering & Disaster Management) much
of it is reflected or absorbed by the material that make up the cell. Because
of this, a typical commercial solar cell has an efficiency of 15% only about
one-sixth of the sunlight striking the cell generates electricity. Low
efficiencies mean that larger arrays are needed and higher investment costs.
The first solar cells, built in the 1950s, had efficiencies of less than 4%.
Solar Water Pumps: In solar water
pumping system, the pump is driven by motor run by solar electricity instead of
conventional electricity drawn from utility grid. A SPV water pumping system
consists of a photovoltaic array mounted on a stand and a motor-pump set
compatible with the photovoltaic array. It converts the solar energy into
electricity, which is used for running the motorpump set. The pumping system draws water from the open well,
bore well, stream, pond, canal etc.
Wind
Energy
Basically the conversion of kinetic energy of the wind into
electrical energy. When solar radiation enters the earth's atmosphere,
different regions of the atmosphere are heated to different degrees because of
earth curvature. This heating is higher at the equator and lowest at the poles.
Since air tends to flow from warmer to cooler regions, this causes what we call
winds, and it is these airflows that are harnessed in windmills and wind
turbines to produce power.
Wind power is not a new development as this power, in the form
of traditional windmills for grinding corn, pumping water, sailing ships - have
been used for centuries. Now wind power is harnessed to generate electricity in
a larger scale with better technology.
Fig. 3 : Wind
Turbine Configuration
Wind Energy Technology: The basic example of
energy conversion device is the wind turbine. Although various designs and
configurations exist, these turbines are generally grouped intotwo types:
(1)
Vertical-axis wind
turbines, in which the axis of rotation is vertical with respect to the
ground (and roughly perpendicular to the wind stream).
(2)
Horizontal-axis
turbines, in which the axis of rotation is horizontal with respect to
theground (and roughly parallel to the wind stream.)
Illustrates the two types of turbines and typical subsystems for
an electricity generation application. The subsystems include a blade or rotor,
which converts the energy to the wind to rotational shaft energy, a drive
train, usually including a gearbox and a generator, a lower that supports the
rotor and drive train, and other equipment, including controls, electrical
cables, ground support equipment and interconnection equipment.
Wind
Energy in India
India has been considered as one of the most promising countries
for wind power development,with an estimated potential of 20,000 MW. Total
installed capacity of wind electric generators in theworld as on Sept. 2001 is
23270 MW, and India-1426 MW top the list of countries. Thus, India ranksfifth
in the world in wind power generation.
There are 39 wind potential stations in Tamil Nadu, 36 in
Gujarat, 30 in Andhra Pradesh, 27 in Maharshtra, 26 in Karnataka, 16 in Kerala,
8 in Lakshadweep, 8 in Rajasthan, 7 in Madhya Pradesh, 7 in Orissa, 2 in West
Bengal, 1 in Andaman Nicobar and 1 in Uttar Pradesh. Out of 208 suitable
stations 7 stations have shown wind power density more than 500 Watts/m²
Applications of Wind
Energy
·
Utility interconnected wind turbines generate
power which is synchronous with the grid and are used to reduce utility bills
by displacing the utility power used in the household and by selling the excess
power back to the electric company. Wind turbines for remote homes (off the
grid) generate DC current for battery charging.
·
Wind turbines for remote water pumping
generate 3 phase AC current suitable for driving an electrical submersible pump
directly. Wind turbines suitable for residential or village scale wind power
range from 500 Watts to 50 kilowatts.
Merits of Wind Energy
(i)
Non-polluting and environment friendly source
of energy
(ii)
Renewable and sustainable source of energy,
available free of cost.
(iii)
Power generation is cheaper as there is no
shortage of input cost and recursion expenses are almost nil,
Limitations of Wind
Energy
(i) It has low energy density.
(ii) It is generally favorable in geographic locations which are
away from cities.
(iii) It is variables unsteady, irregular, intermittent, erotic
and sometimes dangerous.
(iv) The appearance of windmills on the landscape and their
continual whirling and whistlingcan be irritating.
Bio
Energy
The main and important source of bio energy is biomass. Biomass
is a renewable energy resource derived from the carbonaceous waste of various
human and natural activities. It is derived from numerous sources, including
the by-products from the wood industry, agricultural crops, raw material from
the forests, household wastes etc.
Biomass does not add carbon dioxide to the atmosphere as it
absorbs the same amount of carbon in growing as it releases when consumed as a
fuel. Its advantage is that it can be used to generate electricity with the
same equipment that is now being used for burning fossil fuels. Biomass is an
important source of energy and the most important fuel worldwide after coal,
oil and natural gas. Bio-energy, in the form of biogas, which is derived from
biomass, is expected to become one of the key energy resources for global
sustainable development. Biomass offers higher energy efficiency through form
of biogas than by direct burning (See chart).
Applications of Bio
Energy
Bio energy is being used for cooking, mechanical applications,
pumping, power generation etc.
Some of the devices used are Biogas plant/ gasifier/burner,
gasifier engine pump sets, Stirling engine pump sets, producer gas/ biogas
based engine generator sets etc.
Biogas
Plants: Biogas is a clean and efficient fuel, generated from cow-dung,
human waste or any kind of biological materials derived through anaerobic
fermentation process. The biogas consists of 60% methane with rest mainly
carbon dioxide. Biogas is a safe fuel for cooking and lighting. By product is
usable as high-grade manure.
Atypical biogas plant has the following components:
1.A digester: In which the slurry
(dung mixed with water) is fermented.
2. Inlet tank: For mixing the feed
and letting it into the digester.
3.Gas holder: It is a dome shape
collector in which the generated gas is collected. 4. Outlet tank: To remove
spent slurry.
5.Distribution
pipelines: To transport the gas into the kitchen.
6. Manure pit: To store the spent slurry.
Biomass fuels account for about one-third of the total fuel used
in the country. It is the most important fuel used in over 90% of the rural
households and about 15% of the urban households. Using only local resources,
namely cattle waste and other organic wastes, energy and manure are derived.
Thus the biogas plants are the cheap sources of energy in rural areas. The
types of biogas plant designs popular are: floating drum type, fixed dome-type
and bag-type portable digester.
Biomass Briquetting: Biomass Briquetting
is the process in which the loose agro-waste densifying into a solidified
biomass of high density, which can be conveniently used as a fuel. Briquette is
also termed as "Bio-coal". It is pollution free and eco-friendly. Some
of the agricultural and forestry residues can be briquetted after suitable
pre-treatment. A list of commonly used biomass materials that can be briquetted
are given below:
ComCob, JuteStick, Sawdust, PineNeedle, Bagasse, CoffeeSpent,
Tamarind, CoffeeHuskAlmondShell, Groundnutshells, CoirPith, BagascePith,
Barleystraw, Tobaccodust, RiceHusk, DeoiledBran.
Advantages of Biomass
Briquetting
Some of advantages of biomass briquetting are high calorific
value with low ash content, absence of polluting gases like sulphur, phosphorus
fumes and fly ash- which eliminate the need for pollution control equipment,
complete combustion, ease of handling, transportation and storage - because of
uniform size and convenient lengths.
Applications of
Biomass Briquetting
Biomass briquettes can replace almost all conventional fuels
like coal, firewood and lignite inalmost all general applications like heating,
steam generation etc. It can be used directly as fuel tead of coal in the
traditional chulhas and furnaces or in the gasifier. Gasifier converts solid
fuel into a more convenient to use gaseous form of fuel called producer gas.
Biomass
Gasifiers
Biomass gasifiers are the devices which can convert the solid
biomass such as wood waste, agricultural residues etc. into a combustible gas
mixture which normally called as producer gas. The conversion efficiency of the
gasification process is in the range of 60%-70%. The producer gas consists of
mainly carbon-monoxide, hydrogen, nitrogen gas and methane, and has a lower
calorific value (1000-1200 kcal/Nm'),
Gasification of biomass and using it in place of conventional
direct burning devices will result savings of atleast 50% in fuel consumption.
The gas has been found suitable for combustion in the internal combustion
engines for the production of power.
Applications
Water
Pumping and Electricity Generation: Using biomass gas, it is possible to operate
a diesel engine on dual fuel mode-part diesel and part biomass gas. Diesel
substitution of the order of 75 to 80% can be obtained at nominal loads. The
mechanical energy thus derived can be used either for energizing a water pump
set for irrigational purpose or for coupling with an alternator for
electricalpower generation-3.5 KW-10 MW
Heat
generation: A few of the devices, to which gasifier could be retrofitted,
are dryers-for drying tea, flower, spices, kilns for baking tiles or potteries,
furnaces for melting non-ferrous metals,boilers for process steam, etc.
Direct combustion of biomass has been recognized as an
importantroute for generation of power by utilization of vast amounts of
agricultural residues, agro-industrial residues and forest wastes. Gasifiers
can be used for power generation and available upto a capacity 500 kW. The
Government of India through MNES and IREDA is implementing power-generating
system based on biomass combustion as well as biomass gasification.
High
Efficiency Wood Burning Stoves: These stoves save more than 50% fuel
woodconsumption. They reduce drudgery of women saving time in cooking and fuel
collection andconsequent health hazards. They also help in saving firewood
leading to conservation of forestsThey also create employment opportunities for
people in the rural areas.
Bio
fuels: Unlike other renewable energy sources, biomass can be
converted directly into liquid fuels biofuels-for our transportation needs
(cars, trucks, buses, aeroplanes, and trains). The two most common types of
biofuels are ethanol and biodiesel.
Ethanol is an alcohol, similar to that used in beer and wine. It
is made by fermenting any biomass high in carbohydrates (starches, sugars, or
cellulases) through a process similar to brewing beer. Ethanol is mostly used
as a fuel additive to cut down a vehicle's carbon monoxide and other smog
causing emissions. Flexible-fuel vehicles, which run on mixtures of gasoline
and up to 85% ethanol, are now available:
Biodiesel, produced by plants such as rapeseed (canola),
sunflowers and soybeans, can be extracted and refined into fuel, which can be
burned in diesel engines and buses. Biodiesel can also made by combining
alcohol with vegetable oil, or recycled cooking greases. It can be used as an
additive to reduce vehicle emissions (typically 20%) or in its pure form as a
renewable alternative fuel for diesel engines.
Biopower: Biopower, or biomass
power, is the use of biomass to generate electricity. There mare six major
types of biopower systems: direct-fired, coffering, gasification, anaerobic
digestion,pyrolysis, and small-modular.
Basics of Environment
Most of the biopower plants in the world use direct-fired
systems. They burn bioenergy feedstocks directly in boiler to produce steam.
This steam drives the turbo-generator. In some industries, the steam is also
used in manufacturing processes or to heat buildings. These are known as
combined heat and power facilities. For example, wood waste is often used to
produce both electricity and steam at paper mills. Many coal-fired power plants
use coffering systems to significantly reduce emissions, especially sulphur
dioxide emissions. Coffering involves using bio energy feedstock as a
supplementary fuelsource in high efficiency boilers.
Gasification systems use high temperatures and an oxygen-starved
environment to convert biomass into a gas (a mixture of hydrogen, carbon
monoxide, and methane). The gas fuels a gas turbine, which runs on an electric
generator for producing power.
The decay of biomass produces methane gas, which can be used as
an energy source. Methane can be produced from biomass through a process called
anaerobic digestion. Anaerobic digestion involves using bacteria to decompose
organic matter in the absence of oxygen. In landfills-scientific waste disposal
site - wells can be drilled to release the methane from the decaying organic
matter. The pipes from each well carry the gas to a central point where it is
filtered and cleaned before burning. Methane can be used as an energy source in
many ways. Most facilities burn it in a boiler to produce steam for electricity
generation or for industrial processes. Two new ways include the use of
microturbines and fuel cells. Microturbines have outputs of 25 to 500 kilowatts.
About the size of a refrigerator, they can be used where there are space
limitations for power production. Methane can also be used as the
"fuel" in a fuel cell. Fuel cells work much like batteries, but never
need recharging, producing electricity as long as there is fuel.
In addition to gas, liquid fuels can be produced from biomass
through a process called pyrolysis. Pyrolysis occurs when biomass is heated in
the absence of oxygen. The biomass then turns into liquid called pyrolysis oil,
which can be burned like petroleum to generate electricity. A biopower system
that uses pyrolysis oil is being commercialized.
Several biopower technologies can be used in small, modular
systems. A small, modular system generates electricity at a capacity of 5
megawatts or less. This system is designed for use at the small town level or
even at the consumer level. For example, some farmers use the waste from their
livestock to provide their farms with electricity. Not only do these systems
provide renewable energy, they also help farmers meet environmental
regulations.
Biomass Cogeneration: Cogeneration
improves viability and profitability of sugar industries. 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 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.
Hydro
Energy
The potential energy of falling water, captured and converted to
mechanical energy by waterwheels, powered the start of the industrial
revolution. Wherever sufficient head, or change in elevation, could be found,
rivers and streams were dammed and mills were built. Water under pressure flows
through a turbine causing it to spin. The turbine is connected to a generator,
which produces electricity. In order to produce enough electricity, a
hydroelectric system requires a location with the following features:
Change in elevation or head: 20 feet @ 100 gal/min=200 Watts.
100 feet head @ 20 gal/min gives the same output.
In India the potential of small hydro power is estimated about
10,000 MW. A total of 183.45 MW small Hydro project have been installed in
India by the end of March 1999. Small Hydro Power projects of 3 MW capacity
have been also installed individually and 148 MW project is under construction.
Small
Hydro Power: Small Hydro Power is a reliable, mature and proven technology.
It is non-polluting, and does not involve setting up of large dams or problems
of deforestation, submergence and rehabilitation. India has an estimated
potential of 10,000 MW.
Hilly regions of India, particularly the Himalayan belts, are
endowed with rich hydel resources with tremendous potential. The MNES has
launched a promotional scheme for portable micro hydel sets for these areas.
These sets are small, compact and light weight. They have almost zero
maintenance cost and can provide electricity/power to small cluster of
villages. They are ideal substitutes for diesel sets run in those areas at high
generation cost.
Micro (upto 100kW) mini hydro (101-1000 kW) schemes can provide
power for farms, hotels,schools and rural communities, and help create local
industry.
Geothermal
Energy
It is heat of the earth and is defined as naturally occurring
thermal energy found within rock formations and the fluids held within those
formations. Geothermal energy can be exploited only in those particular areas
(hot spots) where geological formation lead to high temperature gradient. Such
high temperature regions found in volcanic eruptions, geysers and bubbling mud
holes. Geothermal energy taken from natural steam, hot water or dry rocks may
be used for electric power generation. space heating, ground water heat pumps,
recreational or health spas, agricultural growth enhancement, agricultural
drying and industrial drying.
Merits of Geothermal
Energy
(i)
Most versatile and least polluting renewable
energy resource.
(ii)
It is relatively inexpensive.
(iii)
Power generation level is higher than solar
and wind.
(iv)
Geothermal power plants could be brought
online more quickly than most other energy sources in case of and extended
national emergency.
Limitations of
Geothermal Energy
(i)
Geothermal hot spots are sparsely distributed
and usually some distance away from the area needing energy.
(ii)
The overall efficiency for power production is
quite low (15% compared to 35-40% of fossil fuel).
(iii)
Air pollution results in case of release of
gases like HS, NH, CO, present in the steam and hot water carrying out of the
geothermal fields.
(iv)
Noise pollution results from the drilling
operations in geothermal fields.
Tidal
and Ocean Energy
Tidal Energy: Tidal electricity
generation involves the construction of a barrage across an estuary to block
the incoming and outgoing tide. The head of water is then used to drive
turbines to generate electricity from the elevated water in the basin as in
hydroelectric dams.
Barrages (dams) can be designed to generate electricity on the
ebb side, or flood side, or both.Tidal range may vary over a wide range
(4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for
economical operation and for sufficient head of water for the turbines.
Ocean Energy: Oceans cover more
than 70% of Earth's surface, making them the world's largest solar collectors.
Ocean energy draws on the energy of ocean waves, tides, or on the thermalenergy
(heat) stored in the ocean. The sun warms the surface water a lot more than the
deep oceanwater, and this temperature difference stores thermal energy.
The ocean contains two types of energy: thermal energy from the
sun's heat and mechanical energy from the tides and waves.
Ocean thermal energy is used for many applications, including
electricity generation. There are three types of electricity conversion
systems: closed-cycle, open-cycle, and hybrid. Closed cycle systems use the
ocean's warm surface water to vaporize a working fluid, which has a low boiling
point, such as ammonia. The vapor expands and turns a turbine. The turbine then
activates a generator to produce electricity. Open-cycle systems actually boil
the seawater by operating at low pressures. This produces steam that passes
through a turbine/generator. The hybrid systems combine both closed-cycle and
open-cycle systems.
Ocean mechanical energy is quite different from ocean thermal
energy, Even though the sun affects all ocean activity, tides are driven
primarily by the gravitational pull of the moon and waves Ocean mechanical
energy is quite different from ocean thermal energy. Even though the sun are
driven primarily by the winds. A barrage is typically used to convert tidal
energy into electricity by forcing the water through turbines, activating a
generator.
India has the World's largest programs for renewable energy.
Several renewable energy technologies have been developed and employed in
villages and cities of India. A Ministry of NonConventional Energy Sources
(MNES) created in 1992 for all matters relating to Non-Conventional Renewable
Energy. Government of India also created Renewable Energy Development Agency
Limited (IREDA) to assist and Bureau of Energy Efficiency 15912. Application of
Non-Conventional and Renewable Energy Sources provide financial assistance in
the form of subsidy and low interest loan for renewable energy projects.
IREDA covers a wide spectrum of financing activities including
those that are connected to energy conservation and energy efficiency. At
present, IREDA's lending is mainly in the following areas:
·
Solar energy technologies, utilization of
solar thermal and solar photovoltaic systems
·
Wind energy setting up grid connected wind
farm projects
·
Small hydro setting up small, mini and micro
hydel projects
·
Bio-energy technologies, biomass based
co-generation projects, biomass gasification, energy from waste and briquetting
projects
·
Hybrid systems
·
Energy efficiency and conservation
