1.2. Non-renewable energy sources
A. Coal
Coal is a sedimentary rock. The majority of coal was formed during the Carboniferous Period, because it
provided ideal conditions for coal formation. When it burns, it releases more carbon dioxide than when we burn oil
or natural gas. China is the world top coal producer (49% of the world).
Coal is formed when peat is altered physically and chemically. Peat is an
accumulation of partially decayed that is unique to natural areas called
peatlands. Time increases its energetic power. Peat must be buried by
sediment. Burial compacts the peat; the deposit becomes more and more
carbon-rich. The stages of this trend proceed from plant debris through
peat, lignite, bituminous coal to anthracite coal. As a result, the type of
coal depends upon the carbon composition and the duration of time of the
coal formation. Peat is the coal with less carbon content and produces a little heat, while anthracite coal is the most
carbon-rich, producing 2 to 3 times more heat than peat. If coal has a lower quantity of carbon, it produces less
carbon dioxide, but it has more sulfur, nitrogen … producing the most dangerous and toxic fumes. Coal is extracted
from the ground by coal mining, either by underground mining or by open pit mining extraction.
Forty percent of electricity is produced in thermal power stations that use coal as fuel because it’s cheaper
and has high heat content. It’s used to heat houses and buildings too.
ADVANTAGES
Coal energy is an affordable energy source because of coal’s stable price compared to other fuel sources.
It is easy to burn.
Coal produces high energy upon combustion.
DISADVANTAGES
The extraction in underground mining is very dangerous because mines can collapse, and the methane
released by the coal formation is toxic and flammable. Open pit mining extraction causes an important
and whatever that is found in the terrain. It also contaminates a lot of water and dangerous chemical
substances and dust are released into the environment.
Burning coal produces more pollution than burning oil or gas, although modern power stations pollute less
than older ones. The burning of these fossil fuels always produces carbon dioxide which means the
greenhouse effect is increasing; burning fossils fuels also leads to atmospheric pollution: it produces
harmful gases, such as sulphur dioxide and nitrogen dioxide which can cause acid rain.
Supplies are limited.
As fossil fuels run out, they become more difficult and expensive to extract.
B. Petroleum
Petroleum or crude oil is a mixture of hydrocarbons found within the Earth crust formed from fossilised organic
material in a process that takes millions of years to complete. It is considered a fossil fuel, meaning, a combustible
originated from the remains of life forms that existed long time ago; mainly zooplankton. These accumulate in the
bottom of seas and lakes in absence of oxygen; otherwise, they would decompose. Then, a layer of sedimentary
rock, referred to as cap rock, forms above them (it is essential that it is impermeable), creating the pressure and
temperature required. As time passes, the organic matter present undergoes a series of changes which result in the
formation of oil; this oil accumulates in a permeable layer of rock. Sometimes, oil escapes and biodegrades before it
can be extracted. Partially biodegraded oil sometimes accumulate in the form of sand, referred to as oil sand. If this
sand is mixed with hot water, we can obtain oil from it.
The process by which this liquid is extracted is called oil drilling. The crude oil obtained is a mixture of different
hydrocarbons which can be separated in a process referred to as fractional distillation; all of them have different
properties (and therefore different uses). Fractional distillation requires a fractional distillation tower, which consists
of different compartments in a vertical scale. Between them, there are openings through which gases can ascend.
The bottom of this tower is hot; each room’s temperature decreases as you move upwards. Since each component
liquefies at a different temperature and thus, in a different compartment, all the components of oil can be separated
from one another. The products obtained include:
Petrol gas: used mainly for heating, cooking and to make
plastics.
Petrol, also known as gasoline.
Naphtha: used chiefly as a solvent.
Kerosene: fuel for airplanes and tractors; it is also
employed as a starting point for making other products.
Diesel fuel: used for heating and fuelling; like kerosene,
we can use it to obtain new products.
Lubricating oil: used to prevent engines from wearing
down due to friction
Fuel oil: used as a fuel by certain ships and factories. Residuals: they include all sorts of substances, such as
ADVANTAGES
It has a very high energy density.
Technologies for extracting oil from the ground are very well developed and can be exploited. Deposits can
be reached in different geological conditions (at great depths of the continental shelf seas and oceans in
special climate conditions).
Oil extraction is relatively low cost and with a much reduced physical and technical effort (like the
extraction of coal, for example).
Due to its liquid form, it is easy to transport, and store; its management is relatively easy.
It has broad areas of application, from the chemical, transport and finishing industries and is used as an
energy resource in power plants.
DISADVANTAGES
Oil spills can occur.
The burning of these fossil fuels always produces carbon dioxide which means the greenhouse effect is
increasing; burning fossils fuels also leads to atmospheric pollution: it produces harmful gases, such as
sulphur dioxide and nitrogen dioxide which can cause acid rain.
Supplies are limited.
As fossil fuels run out, they become more difficult and more expensive to extract.
C. Natural gas
Natural gas is a fossil fuel formed when microorganisms, sea plants and animals died over 300 million years
ago. Layers of dead sea plants, animals, sand, mud, and other debris built up over time and the pressure and heat
from the earth turned them into petroleum and natural gas. The natural gas would get trapped in pockets of
underground rocks.
Natural gas in its pure form is odourless (the "rotten egg" odour is added for safety). It is a combination of
several gases like propane, butane …, but primarily made up of methane.
Natural gas is used for energy consumption as one of the main heating fuel. It is also an essential raw
ADVANTAGES
As compared to petroleum or coal, natural gas causes less damage to the environment. It is made up of
methane and results in less carbon emissions.
Easy storage and transport.
Residential use: natural gas can be piped into homes for heating and cooking purposes.
It is relatively abundant compared to other fossil fuels, it burns more cleanly and is easy to distribute.
DISADVANTAGES
Toxic and flammable: leaks of natural gas are tremendously dangerous. Such leaks may cause explosions or
fire. When inhaled, the gas is highly toxic.
Damage to environment: burning of natural gas also releases carbon dioxide, carbon monoxide and other
carbon compounds that are greenhouse gases that cause global warming and climate change.
Non-renewable.
Expensive installation: the infrastructure for natural gas production and distribution is expensive.
When used as a fuel in vehicles, it provides less mileage than gasoline.
D. Nuclear power
Nuclear energy uses the energy released during nuclear reactions (certain chemical elements, for example uranium,
can be broken down by nuclear fission) to heat water to produce steam and this steam drives turbines, which
produce electricity. Although nuclear energy is used to produce electric power in nuclear plants, it also has other
uses such as medical applications.
ADVANTAGES
It is an alternative to fossil fuels such as coal or oil. Nuclear energy avoids the problem of global warming,
which is believed to have a more important influence on global climate change. This would improve the
quality of the air we breathe with all that this implies in the decrease of disease and the improvement of
the quality of life.
It is one of the cheapest sources of electricity production.
DISADVANTAGES
Irresponsible decisions can produce accidents in nuclear plants but, even worse, it can be used for military
purpose like during the second world war where the U.S. used two nuclear bombs.
It produces dangerous waste that stays radioactive for thousands of years.
There is a risk of radiation leaks or explosions.
It is extremely expensive first to build nuclear power stations, and then later demolish them when they are
no longer needed.
1.3. Renewable energy sources
A. Biomass-energy
Biomass is biological material derived from living, or recently living organisms. The energy of biomass is
extracted from three sources:
Wood is the largest energy source of biomass: it can be plant matter grown as a crop in a special plantation,
Waste energy is the second largest source of biomass energy. The main contributors are: municipal solid
waste and manufacturing waste.
Alcohol fuel is the third largest contributor and is derived mainly from corn.
Biomass can be burned to produce energy (electricity or hot water) or converted into a liquid fuel called
biofuel; one type of biofuel is biodiesel, which is used in cars.
Biomass is renewable; we continue to make waste products, plants and trees continue to die and the cycle
continues. This ensures that the sources contributing to biomass are always available.
ADVANTAGES
Biomass can be used for fuels, power production and products that would otherwise be made from fossil
fuels.
It can be used to generate electricity with the same equipment or power plants that are now burning fossil
fuels.
Biomass fuel generally tends to be cheap.
Using biomass sources places less demand on the Earth's resources.
The use of biomass energy has the potential to greatly reduce greenhouse gas emissions.
DISADVANTAGES
Large areas of land are needed to grow biofuel crops, which paradoxically can cause deforestation
problems, because trees are cut down to make space for the crop. The amount of energy produced is quite
small, so large amounts of biomass are needed.
B. Geothermal energy
We call geothermal energy as thermal energy produced and stored inside the Earth. The Earth's internal
heat is thermal energy generated from radioactive decay and continual heat loss from Earth's
formation. The geothermal gradient, which is the difference in temperature between the core and its surface, drives
a continuous conduction of thermal energy in the form of heat .
From hot springs, geothermal energy has been used for bathing since the Paleolithic times and for heating
since ancient Roman times, but it is now better known for electricity generation.
ADVANTAGES
DISADVANTAGES
The availability of geothermal energy that is capable of feeding geothermal power stations is limited. This
intense energy source is often only available in countries where geothermal activity is at its peak, mainly
tectonic/volcanic regions such as Iceland.
A significant investment is often required prior to building a geothermal power station. Geological surveys
have to be undertaken to ensure the location is suitable for geothermal electricity production before any
potential installation work can go ahead.
Geothermal power stations have the potential to release harmful gases into the air. Toxic gases exist deep
beneath the ground in various regions and can sometimes be released via the infrastructure used by
geothermal power stations.
As geothermal energy is trapped beneath our feet, we cannot extract, store and transport this energy
source to other countries as we do with fossil fuels such as oil, coal and gas.
Geothermal power stations, as with many other power station designs, can be unsightly and provide visual
pollution.
C. Tidal energy
Tidal energy uses the movements of seawater during the rise and fall of the tides (caused by the
gravitational pull of the Moon and the Sun) to make the turbines of tidal generators move, and produce electricity.
A tidal stream generator makes use of the kinetic energy or movements of masses of water to make
turbines move and create electric energy. Tidal stream generators are the cheapest and the least ecologically
damaging among the main forms of tidal power generation.
A tidal barrage uses the potential energy of water, i.e. the difference in height between high and low tides. It takes
place in some specific dams (a barrage). At high tide, sea water is stored behind the dam and at low tide, the dam is
opened; the water drives turbines, which generate electricity.
ADVANTAGES
It is an inexhaustible source of energy.
Tidal energy is environmentally friendly and does not produce greenhouse gases (heat- trapping gases).
As 71% of Earth’s surface is covered by water, there is scope to generate this energy on large scale.
We can predict the rise and fall of tides as they follow cyclic fashion. Tides are more predictable than wind
energy and solar power
Efficiency of tidal power is far greater than coal, solar or wind energy. Its efficiency is around 80%.
Although cost of construction of tidal power is high, maintenance costs are relatively low.
Tidal Energy does not require any kind of fuel to run.
The life of a tidal energy power plant is very long.
DISADVANTAGES
Tidal barrages (large structures containing electrical generators, which are built across a bay or cove where
the tide goes in and out) have to be built in large coves (indentation in the coastline) and this infrastructure
has a considerable environmental impact.
Intensity of sea waves is unpredictable and there can be damage to power generation units.
Influences aquatic life adversely and can disrupt migration of fish.
Frozen sea, straight shorelines, low tidal rise or fall are some of the obstructions.
Usually the places where tidal energy is produced are far away from the places where it is consumed.
This transmission is expensive and difficult.
D. Wind power
Wind energy uses the movement of the wind to turn the paddles of a wind turbine. A generator then
transforms the kinetic energy into electrical energy. A wind farm is a group of wind turbines in the same location
used for production of electricity. A large wind farm may consist of several hundred individual wind turbines
distributed over an extended area, but the land between the turbines may be used for agricultural or other
purposes. A wind farm may also be located offshore.
ADVANTAGES
Wind power, as an alternative to fossil fuels, is plentiful, renewable, widely distributed and clean.
DISADVANTAGES
Wind farms have to be built in very windy areas (they depend on meteorological conditions so the amount
of energy produced is variable and difficult to store) and they take up a lot of land, because the turbines are
large and we need a lot of them.
The turbines are not always very attractive and also they make a lot of noise and this can disturb the people
who live near them.
They also interfere with some migratory routes (some old turbines did kill lots of birds, but new ones are
designed to avoid this).
E. Solar energy
Solar energy is energy derived from the Sun's radiation. It is the technology used to harness the sun's
energy and make it useable. This energy is in the form of solar radiation, which makes the production of solar
electricity possible.
Photovoltaic (PV) solar cells directly convert sunlight into electricity. The simplest cells are used to operate
wristwatches and calculators, and more complicated systems are used to light houses. PV cells are combined into
modules called arrays; the number of arrays used determines the amount of electricity produced. For example, a
large number of arrays would be needed to generate electricity for a power plant. A power plant can also use
a concentrating solar power system where sunlight is focused with mirrors to create a high-intensity heat source to
PV panels are being used increasingly, both in the city and in remote locations, to produce electricity for
households, schools and communities, and to supply power for equipment such as telecommunication and water
pumps. Solar technologies use the sun's energy to provide heat, light, hot water, electricity, and even cooling, for
homes, businesses, and industry.
ADVANTAGES
Solar energy is a clean and renewable energy source.
Once a solar panel is installed, solar energy can be produced free of charge.
Solar energy will last forever whereas it is estimated that the world’s oil reserves will last for 30 to 40 years.
Solar energy causes no pollution.
Solar cells make absolutely no noise at all.
Very little maintenance is needed to keep solar cells running.
In the long term, there can be a high return on investment due to the amount of free energy a solar panel
can produce; it is estimated that the average household will see 50% of their energy coming in from solar
panels.
DISADVANTAGES
Solar panels can be expensive to install resulting in a time-lag of many years for savings on energy bills to
match initial investments.
Electricity generation depends entirely on a region´s exposure to sunlight.
Solar power stations do not match the power output of similar sized conventional power stations; they can
also be very expensive to build.
Solar power is used to charge batteries so that solar powered devices can be used at night. The batteries
can often be large and heavy, taking up space and needing to be replaced from time to time.
F. Hydroelectric energy
Hydroelectric power stations use the potential energy of water moving
downhill from a reservoir (so it changes into kinetic energy) to turn the turbines
of a generator and produce electricity.
ADVANTAGES
It is a clean energy source, without waste products.
It is easy to store. The water stored in reservoirs situated at altitude
permits the regulation of the flow of the river.
DISADVANTAGES
To construct a reservoir, we must build a dam and flood a valley, and the inhabitants of the villages in the
valley have to move away (and flooding river valleys changes the natural environment too: loss of
productive soil and fauna due to the flooding of their habitat; they also cause a decrease in the flow of the
rivers and streams below the dam and alter the quality of the waters).
There are very few places appropriate for a hydroelectric power station: there must be abundant rainfall,
and the shape of the land must be suitable to build a high dam.
