ECEg-4242
Renewable Energy Systems
Lecture 2
Renewable Energy Resources and
Energy Conversion Techniques
department of Electrical &
Computer Engineering
Collage of Technology
Bonga University
Akililu Getahun
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Introduction
• Energy is closely link with key contemporary global challenges the world
faces:
i. social development and poverty alleviation
ii. environmental degradation and climate change and food security
and is therefore a defining issue of our time.
• Climate change engages the energy sector particularly closely because
energy is central both to the problem and to its resolution.
• Energy-related emissions (including energy used in transportation) account
for over two thirds of anthropogenic greenhouse gas (ghg) emissions and
contribute well over 80% of worldwide emissions of CO2.
• Also one third of the global emissions of methane, the second largest
source of ghgs, mainly from natural gas production; transportation; and coal
production.
• Energy contributes a small share of global emissions of N2O, the third
largest source, principally from biomass burning.
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Introduction …
• But energy is also a key driver of social and economic development. A
world without energy would be incapable of development, sustainable.
• Energy systems are therefore a necessity, and to be compatible with
sustainable development
• Therefore, Energy system should be designed to meet the WEC criteria,
encapsulated in the three “3A’s” accessibility (to affordable energy);
acceptability (of the energy sources used, particularly in environmental
terms); and availability (how secure and reliable are those sources?)
How to reduce climate change?
➢To reduce climate change we have to look at ;
✓ what drives greenhouse emissions from the energy sector;
✓what policies have been introduced to restrain those emissions;
and
✓how effective those policies have been.
➢Unbalanced energy policies undermine sustainable development
➢Measures that have to be taken to reduce climate change
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Energy Resources
• Energy resources – or rather occurrences – are the stocks (e.g., oil,
coal, uranium) and flows (e.g., wind, sunshine, falling water) of energy
offered by nature. Stocks, by definition, are exhaustible, and any
resource consumption will reduce the size of the concerned stock.
• Flows, in turn, are indefinitely available as long as their utilization does
not exceed the rate at which nature provides them
• Conventional and non conventional or renewable and non renewable
resources
Useful Energy
The application of useful energy provides energy services such as a
moving vehicle (mobility), a warm room (thermal comfort), process heat
(for materials manufacturing), or light (illumination).
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Energy resource: Reserves and Resources
• In order to avoid misunderstandings, the terms “reserves” and
“resources” are defined here:
• Reserves: that part of the total resources, which are documented in
detail and can be recovered economically by using current technology.
• Resources: that part of the total resources, which are proved but at
present not economically recoverable, geologically indicated, or which
for some other reasons cannot be assigned to the reserves.
• Total resources: reserves plus resources. It is to be noted that the
reserves are not included in the resources
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World energy consumption
• The world demand for oil and gas is increasing significantly each year –
China and India
• The present global energy consumption is 16TW
• IEA forecast that by 2030 demand for energy will be some 60% more
than it is now
• The last 50 year increment is stimulated due to cheap of fossil fuel and
industrialization in USA, Europe and Japan
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What is the problem? Finite resource
• Difficult to determine precise figure on ultimate availability
of fossil fuel
• Fossil fuel reserve only lasts from 100-160 years
• Future exploration will be expensive
• Only limited number of today technology will survive the
21 st century due to limited reserve of conventional energy
carrier . This fact is sufficient reason to switch our present
energy supply to non fossil and non nuclear energy source
Renewable energy source
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Kyoto Protocol
• Kyoto Protocol is a protocol to the United Nations
Framework Convention on Climate Change (UNFCCC or
FCCC) that set binding obligations on the industrialized
countries to reduce their emissions of greenhouse gases
• Kyoto protocol signed 1997 aims at reducing green house
gas emission in the period of 2008- 2012 to 5.2 % below
those of 1990
• Assignment ( review Kyoto protocol )
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Conversion technique
➢ Solar, Wind, Hydro, Bio ...
➢ Depending upon the type of RES, the conversion technique
to electrical energy differs.
➢ Some conversion takes easy step and other conversion takes
series of steps.
Solar energy to electrical energy conversion can take place the
technical term for solar electric.
Solar Photovoltaic (PV) :- Photo means “light” and Voltaic means
“electric”
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solar …
➢ PV cells are usually made of silicon, an element that
naturally releases electrons when exposed to light.
➢ A silicon cell has a characteristics of a battery with a power
ranging between 1.5 – 3 watts, typically at 0.58 V and 3.1 A
➢ The cells are connected in series to build up voltage and
constitute a module.
➢ The cells are connected in parallel to build up current and
constitute a module.
➢ The modules are connected in series and parallel to
constitute an array.
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solar…
PV system Components and operation
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Wind
➢ The wind is a free, clean, and inexhaustible energy source.
➢ The energy is contained in the flow of wind, where strong
wind is associated with its speed.
➢ One of the most critical features of wind generation is the
variability of wind. Wind speeds vary with time of day, time
of year, height above ground, and location on the earth’s
surface.
➢ The kinetic energy of the wind is converted to electrical
energy.
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Turbines axis
1. Horizontal-axis turbines, in
which the axis of rotation is
horizontal with respect to the
ground (and roughly parallel to
the wind stream.)
2. Vertical-axis wind turbines, in
which the axis of rotation is
vertical with respect to the
ground (and roughly
perpendicular to the wind
stream),
• Wind energy harvesting
magnitudes relative to the blade
diameter.
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Hydro
➢ Hydropower is another renewable energy source.
➢ The energy is contained in the elevated/falling of water.
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Gilgel Gibe II Tekeze-300MW
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Geothermal Energy
➢ Utilizes the Earth’s inner heated rocks to heat water. This water is turned
to steam then captured to operate steam-powered generators.
➢ The construction cost is by far expensive compared to other forms of
renewable energies.
➢ Steam at high pressure and temperature is used to drive a steam turbine
generator set. Ideal for continuous use once set up.
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Biomass Energy
➢ Biomass energy means the use of
organic matter as source of sustainable
energy.
➢ Biomass is widely used form of renewable energy in
Ethiopia.
➢ If the use of it is properly balanced, it is environment
friendly energy source.
➢ Electrical energy can be generated using steam turbines run
by the biomass energy.
➢ Direct use of heat energy is possible.
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➢ Ocean wave energy conversion
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➢ Wave gun arrangement.
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Comparison of Energy sources
• The chief sources of energy used for the generation of
electrical energy are hydro power, fuels and nuclear energy.
Below is given their comparison in a tabular form :
S. No particular Hydro power Fuels Nuclear
energy
1 Initial cost High Low Highest
2 Running cost Less High Least
3 Reserves Permanent Exhaustible Inexhaustible
4 Cleanliness Cleanest Dirtiest Clean
5 Simplicity Simplest Complex More complex
6 Reliability More
reliable
Less
reliable
More reliable
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Efficiency of Energy Conversion
• It is the ratio of useful energy output to energy input
• Efficiency = Useful Energy Out/Total Energy In
• Greater energy efficiency can reduce energy costs to consumers,
enhance environmental quality, maintain and enhance our standard
of living, increase our freedom and energy security, and promote a
strong economy.
• In all energy conversions, some energy is wasted. However, some
energy conversion processes require a large amount of energy in to
obtain a small amount of energy out. Such conversion processes are
inefficient.
• Since every energy conversion process wastes some energy, the
efficiency ratio for any energy conversion process is less than one
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• Energy efficiency is the amount of useful energy you get from a
system. A perfect, energy-efficient machine would change all the
energy put in it into useful work—an impossible dream.
• In fact, most energy transformations are not very efficient. The
human body is a good example.
• Your body is like a machine, and the fuel for your machine is food.
Food gives you the energy to move, breathe, and think. But your
body isn’t very efficient at converting food into useful work. Your
body is less than five percent efficient most of the time. The rest of
the energy is lost as heat. You can really feel that heat when you
exercise!
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Assignment one
1. What are the main renewable energy sources present in
Ethiopia?
2. Discuss in detail how to cope with our current and future
world energy supply and demand problems.
3. Describe Environmental problems, which appear due to
the energy conversion
4. In your opinion what is the level of energy efficiency in
Ethiopia? What kind of programmes/policies/regulations
could promote greater efficiency in Ethiopia
5. What are some of the barriers to investment in energy
efficiency Ethiopia’s industrial sector?
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