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UNIT - I
Energy
Energy is the capacity to do work. It exists in various forms. Energy supplies can be broadly
classified into
1. Conventional energy sources
2. Renewable energy sources
1.Conventional energy sources/supplies:
‘Energy obtained from static stores of energy that remain underground unless released by
human interaction’. Examples are nuclear fuels and fossil fuels of coal, oil and natural gas. Note
that the energy is initially an isolated energy potential, and external action is required to initiate
the supply of energy for practical purposes. Fossil fuels, coal, natural gas reserves are
conventional energy supply sources, so they are termed as “ conventional energy sources” .
Their availability is finite and it takes a very long time to accumulate so they may be termed as
‘non-renewable’ or Brown Energy.
2. Renewable energy sources/supplies:
‘Energy obtained from natural and persistent flows of energy occurring in the immediate
environment’. An obvious example is solar (sunshine) energy, where ‘repetitive’ refers to the
24-hour major period. Note that the energy is already passing through the environment as a
current or flow, irrespective of there being a device to intercept and harness this power. Such
energy may also be called Green Energy or Sustainable Energy.
The above definitions of renewable energy and conventional energy are represented in the
figure 1.1 below
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Figure 1.1 Renewable energy and conventional energy
Table 1.1
Comparison between Renewable energy and Conventional energy
Description Renewable energy supplies (green) Conventional energy supplies (brown)
1. Example Wind, solar, biomass, tidal Coal, oil, gas, radioactive ore
2. Source Natural local environment Concentrated stock
3. Normal state A current or flow of energy. An income Static store of energy. Capital
4. Initial average Static store of energy. Capital Initial Released at ≥100 kW m−2
intensity average intensity
5. Life time of supply Infinite Finite
6. Cost at source Free Increasingly expensive
7.Equipment capital Expensive Moderate without emission control
cost per kW capacity Expensive with emission control
8. Variation and Fluctuating; best controlled by change of Steady, best controlled by adjusting
control load using positive feedforward control source with negative feedback control
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9. Location for use Site- and society-specific General and invariant use
10. Scale Small and moderate scale often Increased scale often improves supply
economic, large scale may present costs, large scale frequently favoured
difficulties
11. Skills Interdisciplinary and varied. Wide Strong links with electrical and
range of skills. mechanical engineering.
12.Context Bias to rural, decentralised industry Bias to urban, centralised industry
13. Dependence Self-sufficient and ‘islanded’ systems Systems dependent on outside inputs
supported
14. Safety Local hazards possible in operation: May be shielded and enclosed to
usually safe when out of action lessen great potential dangers; most
dangerous when faulty
15. Pollution and Usually little environmental harm, Environmental pollution is intrinsic and
Environmental especially at moderate scale Hazards common, especially of air and water.
Damage from excess biomass burning Soil Permanent damage common from
erosion from excessive biofuel use mining and radioactive elements
Large hydro reservoirs disruptive entering the water table.
Compatible with natural ecology Deforestation and ecological
sterilisation from emissions.
16. Aesthetics Visual Local perturbations may be unpopular, Usually utilitarian, with centralisation
impact but usually acceptable if local need is and economy of large scale.
perceived.
Energy and sustainable development
Principles and major issues
Sustainable development can be broadly defined as living, producing and consuming in a
manner that meets the needs of the present without compromising the ability of future
generations to meet their own needs.
It has become a key guiding principle for policy in the 21st century. Worldwide, politicians,
industrialists, environmentalists, economists and theologians affirm that the principle must be
applied at international, national and local level.
Actually applying it in practice and in detail is of course much harder! In the international
context, the word ‘development’ refers to improvement in quality of life, and, especially, standard
of living in the less developed countries of the world.
The aim of sustainable development is for the improvement to be achieved whilst maintaining
the ecological processes on which life depends. The World commission on Environment and
development set up by the United nations released a report following which the concept of
sustainable development became widely accepted.
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There is unevenness of economic development and population growth. This is bringing stress
on the planet's natural resources. These pressures are severe enough to threaten the survival
of some regional populations Changes in lifestyle, especially regarding production and
consumption will be forced on populations by ecological and economic pressures. The pain of
such changes can be eased by foresight, planning and political will.
Energy resources exemplify these issues. World energy use increased more than 10 fold over
the 20 th century predominantly due to fossil fuels. In the 21 st century further increases in the
world energy consumption can be expected aggravated by gross inefficiencies in all the
countries. There is an overriding need for efficient generation and use of energy.
Fossil fuels are not formed at any significant rate and thus, present stocks of coal,oil and gas
are ultimately finite. The reserve lifetime of a resource may be defined as the known accessible
amount divided by the rate of present use. By this definition lifetime of oil and gas resources is
usually only a few decades; whereas lifetime for coal is few centuries. Present patterns of
consumption and growth are not sustainable in the longer term.
Moreover, it is emissions from fossil fuel and nuclear fuel that determine the limitations.
Increasing concentration of CO2 in the atmosphere is such an example. Therefore, on account
of
1. Finite nature of fossil and nuclear fuel materials
2. The harm of emissions
3. Ecological sustainability
it is essential to expand renewable energy supplies and use energy more efficiently.
If the price of energy includes the cost of both obtaining fuel and paying for the damage from
emissions, renewable energy supplies become cheaper for society than traditional fossil
fuels.renewable energy supplies are much more compatible with sustainable development than
are fossil fuels and nuclear fuels. The national energy plans include increased harnessing of
renewable energy, increased efficiency of end use, reduction in pollution and consideration of
lifestyle.
Simple Numerical Model
A simple numerical model describing the need for commercial and noncommercial energy
resources can be given by
R = EN --------------------------------------(1)
R = total energy requirement for a population of N people
E = per capita energy use averaged over one year.The unit of E is power which is energy per
unit time.
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Significant use of non commercial energy ( burning of fuel wood, passive solar heating) may
occur but is absent from company statistics. In terms of total commercial energy use, the
average per capita value of power that is E can be found as below.
Electric power per capita ( in Watt) =
[ average energy per capita in kwh/year] X 0.11408
Where, 1 kWh / year = 1000 Watt / (365 X 24) = 0.11408
Per capita energy use averaged over one year is closely related to provision of food and
manufactured goods.
Electric energy per capita is the electrical energy consumed in kWh per person per year.
It is the total consumption of electrical energy consumed in one year expressed in kwh divided
by the population size. It can be expressed in Watt-hour also.
Examples: For the year 2019
Country Total consumption in Population size Avg. Elect. Avg. power per
GWh/year Energy per capita in W
capita in kWh
China 7225500 1427647000 5061 577
USA 3989566 328200000 12155 1387
India 1547000 1384660000 1117 127
France 449422 66980000 6709 765
Central 140 4745190 30 3.42
Africa
Zambia 13097 17861030 733 84
Standard of living relates in a complex and ill-defined way to E ( Per capita power). If S
represents a crude measure of standard of living (per capita gross national product) then
S = fE ----------------------------------------- (2)
Where f indicates efficiency of transforming energy into wealth.
S does not increase uniformly as E increases S may even decrease for large E. Waste of
energy leads to a lower value of f .
Substituting E = S/f in equation (1) we have
R = SN/ f -------------------------------------- (3)
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If energy efficiency increases S can increase while R decreases.
Global Resources
In a modern society with an appropriate lifestyle E = 2000 Watt per person.
Is this possible from Renewable energy?
Each Sq. m. of earth’s habitable surface is accessible to an average energy flux from all
renewable sources of about 500 Watt as an overall estimated value.
Energy flux for an area of 10mX10m is 500Watt X 10 X 10 = 50000 Watt. If efficiency of
conversion is 4% then we get 2000 Watt from an area of 100 Sq. m. by assuming suitable
methods are available.
Taking a population density of 500 persons per Sq. km, and per capita power as 2000 Watt per
person total demand is 2000 X 500 = 1000000 Watts or 1000 kW for an area of 1 Sq. km.
Supposing that we get 2000 Watt for an area of 100 sq. m. ( 4 % efficiency) from this area of 1
sq. km. we get 20,000kW. But 5% of this energy obtainable from 1 sq. km habitable area is
sufficient for 500 people.
Above calculation shows renewable energy supplies can provide a satisfactory standard of
living, but only if the technical methods and institutional frameworks exist to extract use and
store the energy.
Energy Sources
There are five ultimate sources of useful energy.
1. The Sun
2. The motion and gravitational potential energy of the Sun, Moon and Earth
3. Geothermal energy from cooling, chemical reactions and radioactive decay in the earth.
4. Human induced nuclear reactions
5. Chemical reactions from mineral sources
Sun is the most significant source of energy to earth. Finite energy supplies are derived from
Sun’s energy ( Fossil fuels), Geothermal energy (hot rocks), nuclear reactions and chemical
reactions. Chemical reactions are minor but useful for primary batteries (Dry cells).
Environmental Energy
The flows of energy passing continuously as renewable energy through the earth can be shown
as in the diagram below.
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Natural energy currents on earth showing renewable energy system (Global Data)
Environmental energy flows occurring in a particular region are of practical interest. The system
has to be matched to particular environmental energy flow. Occurring in a region or location.
Primary Supply to End use
Energy available in the environment has to be channelled and transformed into an “ end use”
form of energy. All energy systems can be visualised as a series of pipes or circuits through
which the energy currents are channelled and transformed to become useful in domestic,
industrial and agricultural circumstances.
Let us consider an example of energy flow from primary resources to end use for Austria in the
year 2000 with a population of 8.1 million people as per the IEA data available:
The primary energy supplies are crude oil, oil products, coal, fossil gas, biomass and hydro.
The end uses are Transportation, Industry, Residential and others. The percentage share of
different primary energy forms are :
Petroleum - 42% , Gas - 23%, Hydro - 13 %, Coal - 12 % , Biomass - 10% total to 1200 PJ .
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The dependence on petroleum fuel is higher and they are imported fuels. It is observed by the
IEA that use of biomass and hydro power are higher in Austria than other countries. The share
of different end use energy was found to be transportation and industry both 30 % , Residential
28% and others 12 %. The share of energy in transportation is high and is dependent on
imported fuels. So, the Government of Austria encourages use of biofuels. The heat produced
from generation of electricity from thermal plants is used for district heating and residential
purposes. The end use energy total to 970 PJ. Losses are more in transforming the energy
from primary resources to end use form is more. The population of Austria has grown by 10 %
from 1970 to 2000 whereas , the energy use has increased by 50 % during the same period.
The flow of energy through channels or networks at national level can be shown with the help of
SANKEY diagrams or Spaghetti diagrams.
Spaghetti diagram / SANKEY DIAGRAM Energy Flow Austria 2000
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Energy Planning
1. Analyse energy systems completely
Energy systems must be analysed from supply to end use without separating the supply.
Supplies are not well matched to end use as precise needs for energy are not available.
Energy losses and uneconomic operations frequently occur.
Heating for residential purposes would be more efficient and cost effective from direct
heat production with local distribution rather than converting it into electricity and then
use electricity for heat production.
2. Efficiency of Energy system
System efficiency is defined as the ratio of useful energy output from a process to the
total energy input. In electric lighting systems, energy is produced from conventional
thermal generation.
The energy efficiencies with different types of lamps are
i) Incandescent lamp:
Generation efficiency = 30%, Distribution efficiency = 90%, Incandescent bulb 4
to 5 %, overall efficiency is 0.3X0.9X0.005 = 1,5% (approximately) .
ii) CFL lamp
The CFL lamp efficiency is 22%. Therefore overall efficiency will be
0.3X0.9X0.22 = 6% (approximately)
Instead of conventional power generation, if combined cycle heat power generation is
used for electricity generation then efficiency of generation will be put at 85% the overall
efficiency of lighting with CFL bulb would be 0.85 X 0.9X 0.22= 16 to 17 %.
The advantages of efficient systems are
i) less fuel is required
ii) Smaller generation capacity for the same end use
iii) less per unit emission cost
iv) Equipment last longer
The total life cycle cost of the more efficient systems will be less than conventional
systems but it has higher per unit capital cost.
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Scientific Principles of Renewable Energy
The nature of renewable energy supplies and finite energy supplies are different. As a
consequence efficient use of renewable energy requires correct application of certain
principles.
1. Energy currents
The renewable energy flux must already be present in the local environment; it is not a
good practice to try to create this energy current. Bio- gas production should be
contemplated as a by product of the animal industry and not vice -versa.
For setting up biomass energy stations biomass must exist locally as transportation of
huge biomass results in inefficiency. This means the local environment must be
monitored and analysed over a long period to establish what energy flows are present. .
2. Dynamic Characteristics
End use requirements of energy vary with time say Electricity demand on a power
network. If power is provided from a finite source input can be adjusted in response to
demand and saving in fuel can be obtained. However, in a renewable energy system
end use and natural supply both vary uncontrollably. Renewable energy sources must
be matched dynamically. Wind resource is variable , tidal resource can be predicted and
solar energy is predictable in some regions and in some it is a variable.
3. Quality of Supply
The quality of an energy supply or store may be defined as the proportion of an energy
source that can be converted into mechanical work. Electrical energy has high quality
as 95% is converted into mechanical work through an electric motor. The quality of
nuclear or fossil fuel or biomass fuel in a single stage thermal power station is
moderately low. Only 33% of the calorific value appears as mechanical work. If the fuel
is used in a combined cycle power plant the quality is improved to 50%. It is possible to
analyse such factors in terms of the thermodynamic variable energy defined here as the
“theoretical maximum amount of work obtainable” at a particular environmental
temperature from an energy source.
In view of the quality of the supply renewable energy supply systems divide into three
broad divisions based upon the type of output or force it produces.
i) Mechanical supplies: Resources such as hydro, wind and tidal power give
Mechanical energy output. This mechanical energy is transformed into electricity.
The proportion of the power extracted from the environment is determined by
the mechanics of the process linked to variability of the source.
Examples:Wind (Kinetic energy) == Mechanical energy through wind turbine(35%)
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Hydro (Potential energy) == mechanical through hydel turbine (75%)
Wave (Kinetic energy) == mechanical energy through turbine (50%)
Tidal (Force) == mechanical energy (75%)
ii) Heat supplies: Renewable energy sources such as biomass combustion, solar
thermal collectors give heat energy output. Heat is extracted as mechanical work
and hence electricity. The quality of the supplies can be estimated using II law of
Thermodynamics and Carnot’s theorem. But in practice mechanical output
produced will be half of Carnot’s criteria. In thermal power plants with boiler fed
steam engines maximum realisable quality of supply will be 35%.
iii) Photon Processes: Solar energy is transformed into electricity by solar photovoltaic.
cells other Photon processes maybe photosynthesis, Biomass, food, photochemistry
Photons in sunlight of one frequency may be transformed into mechanical work via
. electricity with high efficiency using a matched solar cell. In practice the broadband
frequencies in the solar spectrum makes matching difficult and proton conversion
efficiencies of 20 to 30% are considered good.
4. Dispersed vs centralised energy
There is a big difference in energy flux densities of renewable energy supplies and finite
energy supplies at the initial transformation. Solar energy commonly arrives at about 1 Kilowatt
per metre square wind energy at 10 metre per second. But finite supplies like boiler tubes in
gas furnaces transfer hundred Kilowatt per metre square and in nuclear reactor first wall heat
exchanger must transmit several megawatt per metre square.
Apart from major loads such as metal refineries, energy flux density required at the end uses is
much less than what finite resources can provide. For most of the other applications end use
requirements of renewable energy and finite sources are similar. Thus, we can summarise finite
energy is easily produced centrally and is expensive to distribute. Renewable energy is most
easily produced in dispersed locations and is expensive to concentrate and make it centralised.
As a consequence of the dispersed nature of renewable energy, its use in the rural areas lead
to development and economic growth. In an urban location renewable energy does not give
economic competitiveness.
5. Complex systems
Renewable energy supplies are linked to the natural environment. Efficient use of renewable
energy sources requires all the main disciplines say plant physiology to electronic control
engineering.
Examples: energy from integrated farming, animal and plant wastes may be used to generate
Methane Gas, liquid and solid fuels and whole systems integrated with fertiliser production and
nutrient cycling. This type of system is required to cut across all disciplinary boundaries. ( not
just electrical engineering to harness energy )
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6. Situation dependence
Renewable energy systems cannot be applied universally. It depends on the load environment
to supply the energy and suitability of the society to accept the energy. It is required to conduct
a survey of domestic, industrial and agricultural needs of the local community. Particular
renewable energy supplies can be matched with the end uses subject to economic constraints.
Solar energy systems in Southern Italy are different from those in Northern Italy. Bio fuels may
be suitable for farmers in Missouri not not in New England. The consequence of “ situation
dependence” of renewable energy is that national and international plans on energy can not be
made. A suitable scale for planning renewable energy might be taken as 250 km. However, the
present day large urban and industrialised societies are not well suited for such flexible and
variable energy supply.
Technical Implications
1. Prospecting the environment
Monitoring of the data at the site in question is required. The data recorded must be
useful in analysing the dynamic characteristics of the energy system planned.The
official meteorological data are always different from the energy generating sites.The
methods of recording and analysing are not ideal for energy prospecting. It will only
serve as basic data. Wind velocities may be monitored for several months at a
particular prospective generating site and comparing data from the nearest
meteorological base station. Data unrelated to meteorological measurements
Is difficult to obtain- flow of biomass and waste materials.
Forecasting of renewable energy supplies requires specialized methods and equipment
That demands finance and man power.
2. End use requirements and efficiency
Energy generation should always follow assessment of energy end use requirements.
In electrical energy systems the end use requirement is called the load. The size and
characteristics of the Load will greatly affect the type of generating supply. The uses of
energy for heat generation and transport are generally large and are associated with energy
storage. inclusion of these requirements in the analysis can improve Energy Efficiency.
Money spent in energy conservation and improvements in end use efficiency gives long term
benefit than money spent on enhancing generation and supply capacity.
3. Matching supply and Demand
After estimating the dynamic characteristics of end use demands and renewable energy supply
options, the total demand and supply have to be brought together.
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i) The maximum amount of environmental energy must be utilised within the capability of
intercepting devices and system components. The main benefit is in reduction in size of the
generating equipment,
ii) Negative feedback control: The block diagram of negative feedback control is shown
below.
Negative feedback control
This type of control is not suitable for renewable energy supplies. Negative feedback from load
to source results in waste of harnessable energy. It calls for the under utilisation of the
equipment. This is because flow of renewable energy can not be stopped, In case of finite
sources negative feedback is beneficial as it saves fuel.
iii) The end use requirements and properties are not always the same as renewable energy
supply. Then it is required to have storage. But storage devices are expensive. In order to get
low life cycle costs of energy it should be incorporated at the earlier stages of planning.
iv) To overcome difficulties in matching the renewable energy supplies to end use one approach
is to connect to an energy network. Here the renewable energy supply is embedded in a grid
network which has inputs from finite sources having feedback control.
Connection to grid network with feedback contro
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These are relatively large scale operations and include an electricity grid for transmission and
distribution. Storage helps in increasing the proportion of renewable energy supply.
(Pumped hydro, Thermal storage)
v) The most efficient way to use renewable energy is to have a range of end uses that can be
switched or adjusted so that the total load equals the supply at any given time.
Feed forward Load control
The end use blocks may be fixed or adjustable. Like, water pumping, water heating (variable
voltage). Here end use load increases with increase in renewable energy supply. This is positive
feedforward control.
4. Control Options
The three possible control options to match renewable energy supply with load are
i) Spill the excess energy
ii) incorporate storage
iii) operate load management control
The above options can be incorporated separately or together. The matching is obtained
between supply and demand by controlling machines, devices etc.
i) Spill Excess energy: Available energy when not used is energy wasted.
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Examples : run of the river hydroelectric plants , shades and bands with passive solar
heating, pitch control of wind turbine blades.
ii) Incorporate storage
The environmental energy available can be stored. example: storing water in a dam for a
hydroelectric plant. The energy can also be stored after transformation in this method store of
energy is treated equivalent to a fuel stored. The control methods are conventional. In large
capacity approximately 10 megawatt hydro storage is used whereas at approximately 10
kilowatt levels flow control devices become expensive. Storage of water for electricity
generation causes environmental damage. In small systems storage after transformation will
gain importance. Electrical energy can be stored in battery or hydrogen production and storage
of hydrogen
Storage before and after transformation of energy
iii) Load control: Parallel arrangements of end uses can be switched and controlled.
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Electronic control of end use
Turbines and generators operate at constant load. Load controller shuts power between users.
This type of control can be applied on small and large capacity loads .It is advantageous when
many varied end users are available locally. The advantages of of load control applied to
renewable energy systems are
a. Environmental energy is harnessed as there are many parallel loads to take it.The
intercepting devices are well utilised.
b. Priorities and requirements for different types of end uses can be incorporated.
c. Storage capacity can be switched to give the benefits of storage at no extra cost.
d. Microprocessor based electronic controllers are suitable which have benefits of low cost,
reliability and extremely fast and accurate operation.
In wind energy generation, wind fluctuates greatly in speed , the wind turbine should
change rotational frequency to maintain optimum output. Electronics based feed forward
control into several parallel loads is most useful without adding mechanical complexity.
Switching of Electrical loads in Wind Energy Generation
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5. Societal Implication
Around the 1950's many countries in the world obtained independence from colonialism.
There is a relation between coal mining and development of industrialised countries. The
increased use of energy sources has led to profound changes in lifestyle.
i). Dispersed living :
Populations grew in response to employment opportunities. Industries are located
around a centralised electrical energy supply grid ( close to high tension towers).
Coal mining and steel production, gas supplies and urban complexes are also linked.
As renewable energy flux density is low it favours dispersed communities. With RE
supplies power flow will be based on . local generation and local demand.
In rural areas approximately 100 people per sq. km. population densities are common.
Acceptance of renewable energy supplies would allow relief from excessive
urbanisation. A further advantage is the increased energy security for a nation having
dispersed systems for energy supply.
ii) Pollution and Environmental impact
Renewable energy is extracted from flows of energy already compatible with the
environment. Environmental pollution occurs if brown energy is used for the materials
and manufacturing of devices used with renewable energy supply. This may be
considered as small over the lifetime of the equipment. Burning of biomass causes air
pollution, further pollution from RE technology depends on the technology and the
circumstances.
iii) The Future.
We can expect changes to occur with wide spread use of renewable energy. Owing to
advancements in technology, standards of living can be expected to rise , especially in
rural and previously less developed sectors. Sustainable nature of renewable energy
should produce greater socio economic stability than has been the case with fossil fuels.
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