2.1.2. Energy
System
Energy is the capacity or capability to do work. All matters
possess energy, because they can all be utilised in some form of energy
conversion process. For example, most substances will burn or vaporise, and the
consequent heat energy can be harnessed within mechanical energy systems that
create motion. The use of energy usually involves transformations between different forms of
energy - a process known as energy conversion. Any conversion between different
energy forms is imperfect in that some of the energy has to be used to
facilitate the conversion process. The converted energy output is lower than
the energy input and this feature is usually described as the conversion
efficiency.
Energy is usually defined as the ability to do work
or the capacity of any system to perform work. Though this is an
anthropocentric and utilitarian perspective of energy, it is a useful
definition for engineering where the aim of machines is to convert energy to
work. As a more general description, energy is a fundamental entity whose
availability and flow are required for all phenomena, natural or artificial. An
understanding of how energy is generated and measured is central to our
decisions concerning the use and conservation of energy. Everything that takes place in the planet is
the expression of flow of energy from one form to another form.
The term energy systems, refers to the interrelated
network of energy sources and stores of energy, connected by conversion,
transmission and distribution process. In
the energy systems, the energy converts from one form to another useable form
of energy.
Framework
The flowchart below depicts the framework for
undertaking projects by the children under the sub-theme of Energy System.
Projects
under the sub-theme ‘energy system’ can go at various spatial scales connected
functionally through the various energy transfer mechanisms. This sub-theme
represented is the study and projects that deal with the energy under transformation or the different aspects of
the system in which the conversion or transmission of energy occurs. During
this conversion, certain amount of energy is lost to the environment, and
cannot be converted to useable forms of energy. Hence, though energy
conservation law states that energy cannot be created or destroyed, but it
converts to un-useable forms, which cannot be used for our purposes. Energy flows take place at all scales, from
the quantum level to the biosphere and cosmos.
At
the children’s level, our aim is to deal with Natural systems such as physical,
chemical and biological processes, the human centric process of generation/harnessing
of energy and its utilization systems. The
energy systems are classified based on the source or the processes.
Source based Energy Systems
·
Renewable Energy Systems (based on renewable energy sources
like solar, wind, biomass etc.)
·
Non-Renewable
Energy Systems ( based on non-renewable energy
sources like coal, oil etc)
Figure
2.1 Energy flow (ABC) and harnessed energy flow (DEF) for renewable and finite
sources of energy
(Ref:
Twidell and Weir. Renewable Energy Resources. ELBS, 2008.
Renewable Energy Systems
Renewable
energy systems are based on the energy sources, which are obtained from the
continuing or repetitive currents of energy
occurring in the natural environment such as Solar energy, wind energy or
biomass energy base systems. Figure 2.2 represents the natural energy current
on earth. Here, we will elaborate a few renewable energy systems.
Solar
Energy Systems
Solar
energy has the greatest potential of all the sources of renewable energy. Only
a small fraction of this form of energy could be sufficient for all energy
requirements of earth. The solar energy can be converted to heat energy or
electricity. In solar thermal energy systems, the solar energy is converted to
heat energy by using an absorber or reflecting surface. This heat energy can
then be used to heat water or air, or to cook food. This heat energy can also
be used for power generation. In case of solar photovoltaic systems, solar
energy falls on solar cell, which directly converts the solar energy to Direct
Current (DC) electricity.
Figure
2.2 Natural energy current on earth, showing renewable energy systems; Units
terawatts (1012 Watts)
(Ref:
Twidell and Weir. Renewable Energy Resources. ELBS, 2008.
Solar
Thermal Energy Systems
Applications
§ Solar
water heating
§ Solar
drying of agricultural and animal products
§ Solar
cookers
§ Solar
distillation
§ Solar
electric power generation
§ Heating
or cooling of residential buildings etc.
Figure 2.3 concentrating type solar cooker
Solar Photovoltaic Energy
Systems
Application
·
Stand
alone systems
¨ Lighting (Solar Lantern, Solar home lighting system,
Solar Street light etc.)
¨
Water
Pump, Health clinics
¨
Power
for mobile towers (Telecommunications)
¨
Consumer
Electronics (Calculator, watches)
·
Off-grid
systems
¨ Remote Village Electrification
·
Grid-connected
systems
¨ Direct Connection with the utility grid
·
Hybrid
systems
¨ Coupled with Diesel generator / Wind systems/ Biomass
gasification systems etc.
Figure 2.4 Schematic diagram
of a solar photovoltaic system
Wind Energy Conversion
Systems
“Windmills
have fascinated us for centuries and will continue to do so. Like campfires or
falling water, they’re mesmerizing; indeed, entrancing.”
Since
early recorded history, people have been harnessing the energy of the wind.
Wind energy was used to propel boats along the Nile River as early as 5000
B.C. The first windmills were developed
to automate the tasks of grain-grinding and water-pumping and the
earliest-known design is the vertical axis system developed in Persia about
500-900 A.D. The first use was apparently water pumping. Vertical-axis
windmills were also used in China, which is often claimed as their birthplace.
While the belief that the windmill was invented in China more than 2000 years
ago is widespread and may be correct, the earliest actual documentation of a
Chinese windmill was in 1219 A.D. by the Chinese statesman Yehlu Chhu-Tshai.
Here also, the primary applications were apparently grain grinding and water
pumping. The first windmills to appear in Western Europe
were of the horizontal-axis configuration. In 1390, the Dutch set out to refine
the tower mill design, which had appeared somewhat earlier along the
Mediterranean Sea.
Wind
is the result of horizontal differences in air pressure. Air flows from areas
of higher pressure to lower pressure.
Differences in
air pressure are caused by uneven heating of the Earth's surface. Therefore, we
can say that the wind energy is derived from sun (solar energy).
Wind
energy conversion systems are classified in two ways- Horizontal axis wind turbine
and Vertical axis wind turbine. This classification is based on the rotational
axis of turbine. Most of the present application of wind energy systems are
horizontal axis wind turbine, as efficiency of these systems are high in
compare to vertical axis wind turbine.
The available power in the wind depends on the wind speed. The relation can be
written in the following way
Where,
P is the available power, r
is the air density (can be considered as 1.12 kg/m3, however, this
value varies with temperature and pressure of the place), A is called swept
area and V is the wind speed. In the following Figure 2.5, you will be able to
understand the meaning of swept area. So, if we know the wind speed of a place
and the swept area, we will be able to calculate the power available from the
wind. Wind speed is measured by the instrument called Anemometer. Here, power
output varies with cube of the wind speed. So wind speed is the most important
parameter in the above relation. Or, a place with higher wind speed, the power
output will be also higher. Figure 2.6 represents a wind energy conversion
system.
Figure 2.5 Swept area
of blades in a wind energy conversion system
Figure 2.6 Wind
Energy Conversion System
Hydro Energy Systems
It
is the largest source of renewable energy in the world accounting for 6% of
worldwide energy supply or about 15% of the world’s electricity. In India, it
accounts 24% of electricity. The kinetic
energy contained in falling water is converted to electricity with the help of
hydro-electric power plants and the power thus obtained is hydro-electric power
or simply hydro-power. The first recorded use of water power was a clock built
around 250 BC. The first use of moving water to produce electricity was a
waterwheel on the Fox River in Wisconsin (USA)
in 1882. The history of hydropower generation in India goes back more than 100
years. It’s first hydropower station was a small 130 kW facility commissioned
in 1897 at Sidrapong near Darjeeling in west Bengal.
A
hydropower resource can be measured according to the amount of available power,
or energy per unit time. The power of a given situation is a function of the
hydraulic head and rate of flow or discharge. When dealing with water in a
reservoir, the head is the height of the water level in the reservoir relative
to its height after it is released. Each unit of water therefore can produce a
quantity of work equal to its weight times the head. The amount of energy E
released by lowering an object of mass m by a height h in a
gravitational field is: E = mgh; where g is the
acceleration due to the gravity. The energy available to hydroelectric dams is
the energy that can be liberated by lowering water in a controlled way. In
these situations, the power is related to the mass flow rate.
Where
Q is the rate of flow or discharge (m3/s), r is
the density of the water (kg/m3), g is the acceleration due to
gravity (m/s2), h is the head or height (m) and h
is the efficiency of the system. The power generated is represented by the
above equation can be simplified by considering the efficiency of 80% and the acceleration
of gravity, of 9.81 m/s2 to
P (kW) = 7.84 x H (m) x Q
(m3/s)
Figure
2.7 Photographs of Pico Hydro power
Geothermal
Energy Source base systems
Human
utilized geothermal energy systems for a variety of uses for a long time. The
Romans used geothermally heated water in their bathhouses for centuries. They
also used water to treat illnesses and warm homes. In Iceland and New Zealand ,
many people cooked their food using geothermal heat base systems. Some North
American native tribes also used geothermal vents for both space comfort and
cooking. Most of these early uses of the Earth's heat were through the
exploitation of geothermal vents. The first modern geothermal power plants were
built in Lardello, Italy (1904). They were destroyed in World War II and
rebuilt again. Today after 90 years, the Lardello field is still functional.
Geothermal
energy i.e., Heat from the Earth is a proven resource for direct heat
and power generation. Average
geothermal heat flow at the earth’s surface is only 0.06 W/m2, with a temperature gradient
<30 0C (which is much lower than other renewable energy intensity
on the earth’s surface). However, at some locations, this temperature gradient
is higher, indicating significant geothermal resource. The reasons for the
geothermal energy sources is based on
·
Natural cooling and friction
from the core
·
Radioactive
decay of elements
·
Chemical
reactions inside the earth surface
Geothermal Heat Source are classified into following
three sections
·
Natural
Hydrothermal circulation (Water
percolates to deep aquifers to be heated to dry steam, vapor/liquid mixture, or
hot water. Emissions of each type are observed in nature).
·
Hot
igneous systems (Heat associated
form semi-molten magma that solidifies lava).
·
Dry
rock fracturing (Poorly conducting
dry rock, e.g., granite, stores heat over millions of years with a
subsequent increase in temperature).
Power generating capacity of Indian geothermal
provinces
Indian has 400 medium to high temperature geothermal springs, clustered in seven provinces. The most
promising provinces are:
·
The Himalaya
·
Cambay
·
Son-Narmada-Tapi
(SONATA)
·
The Godavari
·
Bakreswar
province
·
The
Barren island
Province
|
Surface Temperature (0C)
|
Reservoir
Temperature (0C)
|
Heat Flow
(mW/m2)
|
Thermal gradient (0C/km)
|
>90
|
260
|
468
|
100
|
|
Cambay
|
40-90
|
150-175
|
80-93
|
70
|
West coast
|
46-72
|
102-137
|
75-129
|
47-59
|
SONATA
|
60 - 95
|
105-217
|
120-290
|
60-90
|
50-60
|
175-215
|
93-104
|
60
|
Figure
2.8 Dry Steam Electrical Power Generation through geothermal energy source
(ref: Twidell and Weir)
Biomass
energy based systems
A
wide variety of conversion technologies are available for converting biomass
based energy sources to high grade fuel.
Each biomass resource like wood, cow dung, vegetable waste can be
converted in many ways to provide a wide spectrum of useful products. Figure
2.9 represents the various conversion processes of biomass. Biomass conversion
can be performed in various ways
·
Direct combustion (such as
firewood burned in traditional chulha etc.)
·
Thermo-chemical conversion (
biomass converts to producer gas in gasification systems)
·
Bio-chemical
conversion ( cow dung, vegetable waste to high grade
fuel in anaerobic digestion)
Direct
combustion
Biomass is burnt to
provide heat for cooking, comfort (space heat), crop drying, factory processes
and raising steam for electricity production and transport. Traditional use of
biomass combustion includes (a) cooking with firewood, and (b) commercial and
industrial use for heat and power. A significant proportion of the world’s
population depends on fuel wood or other biomass for cooking, heating and other
domestic uses. Average daily consumption of fuel is about 0.5 – 1 kg of dry
biomass per person, i.e. 10–20MJ/day. The conventional method for cooking
practice is actually inefficient cooking
method, the most common of which is still an open fire. This ‘device’ has a
thermal efficiency of only about 5 - 10%. That is, only about 5-10% of the heat
that could be released by burning of the wood reaches the interior of the
cooking pot. The rest is lost by incomplete combustion of the wood, by wind and
light breezes carrying heat away from the fire, and by radiation losses, etc.
resulting from the mismatch of fire and pot size. Considerable energy is also
wasted in evaporation from uncovered pots and from wet fuel. Smoke (i.e.
unburnt carbon and tars) from fire is the evidence of incomplete combustion.
Figure
2.9 Biofuel production process
Thermo-chemical
conversion
This
process takes into two forms: gasification and liquefaction. Gasification takes
place by heating the biomass with limited oxygen to produce producer gas. The composition of producer gas is CO (20%),
CO2 (12%), H2 (20%), CH4 (2%) and N2
(46%). The calorific value of the producer gas is in the range of 4-5 MJ/kg.
This producer gas can be used for thermal application by direct burning in a
burner or can be used to produce electricity by using a gas engine.
Bio-chemical
conversion
Bio-chemical
conversion takes places in two forms: Anaerobic digestion and fermentation.
Anaerobic digestion involves the microbial digestion of biomass. This process
takes place in bio-gas plants (commonly called Gobar gas plant) and produce
biogas. Biogas is a mixture of 55-65% methane and 30-40 % CO2 , and
rest the impurities. This gas can be produced from the decomposition of animal,
plant and human wastes. The calorific value of the gas is of the order of 20-23
MJ/kg. This gas can be directly used for
cooking or lighting purpose. Even this gas can be used for power generation by
feeding into an engine. Fermentation is the breakdown of complex molecules in
organic compounds under the influence of a ferment such as yeast, bacteria etc.
This is a widely accepted conversion process where, grains, sugra crops
converted into ethanol.
Non-Renewable Energy Systems
Thermal based energy systems
The thermal
power station is a power plant where coal is mainly used as fuel. Here,
water is heated, turns into steam and spins a steam
turbine which drives an electrical generator. After it passes through
the turbine, the steam is condensed in a condenser
and recycled to where it was heated. Natural gas, nuclear fuels are also used
to produce steam in place of coal. A large part of human CO2
emissions comes from fossil fuel based thermal power plants. In case of Nuclear
power plants, this CO2 emission is not there. The average CO2
emission is 0.81 kg/kWh from the coal based power plants of India.
Process based Energy systems
Biological energy systems
(Living Organisms and ecosystems)
A
living organism depends on an external source of energy—radiation from the Sun
in the case of green plants; chemical energy in some form in the case of
animals—to be able to grow and reproduce. Energy from Sun which is stored by
the plants in its body parts passes through a series of users. The mechanism
made to facilitate this energy transfer is the basis of wonder what we call as
life on earth. The energy flow in each of the ecosystem depends on the
complexity of the food chain and food web of the ecosystem.
( this figure needs
to be redrawn or omitted, looks very bad)
Any
animal body including human is a best example of energy system for study.
Adenosine triphosphate (ATP) is the immediately usable form of chemical energy
for muscular activity. It is stored in most cells, particularly in muscle
cells. Other forms of chemical energy, such as that available from the foods we
eat, must be transferred into ATP before they can be utilized by the muscle
cells. Since energy is released when ATP is broken down, energy is required to
rebuild or resynthesize ATP. The building blocks of ATP synthesis are the
by-products of its breakdown- adenosine diphosphate (ADP )
and inorganic phosphate (Pi). The energy for ATP resynthesis comes from three
different series of chemical reactions that take place within the body. Two of
the three depend upon the food we eat, whereas the other depends upon a
chemical compound called phosphocreatine. The energy released from any of these
three series of reactions is coupled with the energy needs of the reaction that
resynthesizes ATP. The separate reactions are functionally linked together in
such a way that the energy released by the one is always used by the other.
Chemical energy systems
(battery, fuel cell)
Chemical
energy is the potential of a chemical substance to undergo a transformation
through a chemical reaction or, to transform other chemical substances.
Breaking or making of chemical bonds involves energy, which may be either
absorbed in or evolved from a chemical system. Energy that can be released (or
absorbed) because of a reaction between a set of chemical substances is equal
to the difference between the energy content of the products and the reactants.
Battery is one or more electrochemical cells that convert stored
chemical energy
into electrical energy. Batteries are connected in series, to increase the
voltage. Cells may be either of primary or secondary types. A primary cell is
discarded when its chemical energy is exhausted. A secondary cell can be
recharged. The most common primary cell is the zinc/carbon (Leclanché) as used
in torches, portable radios etc.
Fuel
cells are classified primarily by the kind of electrolyte they employ. This
classification determines the kind of chemical reactions that take place in the
cell, the kind of catalysts required, the temperature range in which the cell
operates, the fuel required, and other factors. These characteristics, in turn,
affect the applications for which these cells are most suitable. There are
several types of fuel cells currently under development, each with its own
advantages, limitations, and potential applications.
Mechanical energy (fly
wheel, compressed air systems)
Mechanical energy is
the sum of potential energy and kinetic
energy present in the components of a mechanical
system. It is the energy associated with the motion and position of an
object. Many modern devices, such as the electric
motor or the steam engine, are used today to convert mechanical
energy into other forms of energy, e.g. electrical
energy, or to convert other forms of energy, like heat, into mechanical
energy. A flywheel is a rotating mechanical device that is used to store rotational
energy. The amount of energy stored in a flywheel is proportional to the
square of its rotational speed. Energy is transferred to a
flywheel by applying torque to it, thereby increasing its rotational speed, and
hence its stored energy. Conversely, a flywheel releases stored energy by
applying torque to a mechanical load, thereby decreasing its rotational speed. Compressed
air is air which is
kept under a certain pressure, usually greater than that of the atmosphere.
Compressed air is regarded as the fourth utility, after electricity, natural
gas and water. However, compressed air is more expensive than the other three
utilities when evaluated on a per unit energy delivered basis.
2.1.1.1.
Model Project
Project
I. Evaluate the energy efficiency of
different chullahs in a village
Introduction
Chullahs
are the major energy system working in the villages for preparation of food. The
issues related to chullah directly linked to the amount of firewood consumed,
time required for cooking and pollution free environment inside the kitchen.
Objectives:
i. To
identify the different types of chullahs in practice in a village.
ii. To
study the differences in structure, location and other details of chullahs.
iii. To
evaluate the relative energy efficiency of the chullahs and to recommends the best
design aspect available in the village of study.
Methodology
·
Identify the different types
of chullahs used in a village.
·
Note
down the different structural aspects of the chullahs with measurements.
·
Draw a
rough picture of each of these chullahs in the note book
·
Classify
the chullahs into different types.
·
Analyse
the differences in the design aspects of each type.
·
Identify
one representative chullah of each type.
·
Cook a
specific amount of food in similar way with similar utensils and same fuel and
record the time taken for cooking and amount of fuel used.
·
Analyse
the result and identify the best and efficient system and try to interpret the
reasons for it.
Expected Outcome:
·
Understanding of the village
cooking energy system
·
Developing scientific awareness
among the children and villagers on energetic of cooking.
Project
II : Comparison
of Food web of two different natural ecosystems in an area ( this model needs to be
reviewed)
Introduction
Food
chain and food web represents the complexity of energy transaction or energy
flow in an ecosystem. By careful observation and recording, children can
identify various elements of different food chain operating in the area
and construct the functional food web.
Objectives
i. To
identify the food chains of two different natural ecosystems in the area
ii. To
construct the food web of each of these area and study the difference.
iii. To
construct the approximate energy flow diagrams applicable for the ecosystems
under study.
Materials required:
Binoculars,
Magnifying glasses, microscope, notebook, pen/pencil etc
Methodology:
·
Identify the two different
ecosystems of similar special extent for study.
·
Mark the boundaries and make
an approximate manual map of the area depicting the changes of micro ecosystems
of the area.
·
Spend 10 hours per week for
at least two months in each of the area and note down all observations of
organisms.
·
Identify directly or by
taking photos, in the case of soil insects collect a few of them and identify
using the magnifying / microscope.
·
Record all the observation
of eating and being eater with details of time and date.
·
Construct the simple food
chains first later develop in to the working food web of the system.
·
It is estimated that only
less than 7 % of the solar energy is used in photosystheis at each trophic
level of energy transfer ther is similar loss of energy.
·
Construct an approximate
energy flow diagram and appropriate energy pyramid for the two ecosystems under
study.
· Compare
the energy flow scenario between the ecosystems, interpret the result discuss
the energy transaction and its implications.
Expected
Outcome:
Understanding
and appreciating the energy transactions in the natural ecosystems.
2.1.1.2.
Suggestive project idea
i. Using
a solar module, calculate the maximum power output at different solar radiation
and also try to evaluate the power output at different inclination angle of the
solar module.
ii. Try
to make a concentrating type solar cooker and measure the temperature at the
focal point at different solar radiation throughout the day.
iii. Make
a box type solar cooker by using ply-board and cook your food. Note down the
time taken for cooking of different kind of food items.
iv. Measure
the amount of gas output from different kinds of organic waste materials (cow
dung, vegetable waste, food waste, municipal solid waste etc.).
v. Evaluation/estimation
of human energy used for the human activities such as procuring water from the
well, bringing the fodder, ploughing of cattle and estimate the amount of other
conventional energy sources required to substitute them.
vi. Evaluation/estimation
of energy supplied by cattle in the village ecosystem for the traction power,
cow dung as fuel etc and estimates the amount of other conventional energy
sources required to substitute them.
vii. Study
the amount of fuel required to boil water/cook a certain amount of food in
different structured utensils and identify the most energy efficient one.
viii.
Study the components of
energy systems supporting in maintaining a garden and relative roles.
ix. Study
the relative role of different energy systems in development of a green
building.
x. Study
the energy systems involved in the road transport.
xi. Study
the relative energy systems that are in use in operating a boat.
xii. Comparison
of energy usage and energy system contributions in food processing.
xiii.
Compare the heating value of
different biomass (fire wood) by noting the time taken to boil a certain fixed
amount of water and the amount of biomass consumed.
xiv. Try
to note down the different kinds of chullahs in the village (draw the details
and quantify the minor differences). Check the performance of each type and
rank them on the basis of performance.
xv. Write
down the different energy conversion systems in a village. This need to include
the energy source conversion devices, output work and kind of losses and try to
rank them based on the work performance.
xvi. Use
one solar module to charge the battery. During charging, note down the voltage vs.
time and plot the profile. Repeat this experiment during the discharge by connecting
with the battery for different rating of LED lamps.
xvii.
Construct a zero energy
refrigeration system. Measure the inside and outside temperature at different
seasons of the year. Observe the freshness of vegetables kept in the refrigeration system.
xviii.
Record and analyse the room
temperature inside the building with different types of roofs.
xix. Charcoal
production potential of different types of biomass.
xx. Use
two GI sheets and try to make blades of a wind turbine. Now connect the system
with a dynamo motor.
Measure the power output from the system at different wind velocity.