Surface Temperature (0C)
Thermal gradient (0C/km)
60 - 95
புதன், 11 ஜூலை, 2012
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.
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
§ 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
· 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
Electrification Remote Village
· 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
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
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 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. India
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
and Iceland ,
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. New Zealand
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:
· Son-Narmada-Tapi (SONATA)
· Bakreswar province
· The Barren island
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)
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
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 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 (
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.
220.127.116.11. Model Project
Project I. Evaluate the energy efficiency of different chullahs in a village
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.
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.
· 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.
· 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)
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.
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.
Binoculars, Magnifying glasses, microscope, notebook, pen/pencil etc
· 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.
Understanding and appreciating the energy transactions in the natural ecosystems.
18.104.22.168. 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.
இடுகையிட்டது TNSF தமிழ்நாடு அறிவியல் இயக்கம் நேரம் 7/11/2012