Powering The Nation
A modern developed society like ours makes huge power demands. Most of this power is used in
the form of electricity since this is a very convenient form and easily used to power almost
everything including lighting and heating. Without energy resources our modern way of life would
be crippled. Our dependence on energy resources cannot be underestimated. Many would argue
that the West’s interest in the Middle East has more to do with its oil fields than a moral obligation
to help people in those countries. At present we rely heavily on oil, both as a fuel and for
electricity generation. If used at its present rate world supplies of oil will run out within your
lifetime. This is a serious matter.
Fossil Fuels
Fossil fuels include coal, oil, and gas. They have all been made from the remains of plants and
animals that have been subjected to great pressure in the earth for millions of years. Each one has
the advantage that the energy is very concentrated into a small space. So just a small quantity of
oil can release a large amount of energy when burned. This makes them suitable for supplying
most of our energy needs. They are either burned direct for heating, refined into other fuels..eg
petrol, or used to generate electricity.
Schematic diagram of electricity generation by fossil fuel
Water Turbine Generator
Steam National
Boiler Grid
Coal
Oil
Gas
In electricity generation the fuel is burned to heat water and turn it to steam. The steam passes
over a steam turbine, (a turbine is a device that spins when something flows over it, --in this case
steam). The spinning turbine turns the generator, which makes the electricity. Obviously this
cannot happen instantly and all power stations have a start up time. This is the time it takes for a
power station to go from cold to generating at full power. All fossil fuel power stations have long
start up times. Coal is slowest, then oil, with gas being the fastest. This means that it is not
possible to turn them on and off quickly and so fossil fuel power stations generate continuously
producing a ‘base load’ of electricity 24 hours a day.
There are however serious problems with the burning of fossil fuels.
They cause pollution. In particular, carbon dioxide which contributes to the greenhouse
effect, and in turn global warming, and from coal… sulphur dioxide which dissolves in rain
to form acid rain which kills trees and damages stonework.
They are all non renewable. This means that they will run out and cannot be replaced. Over
the next few years they will become more scarce and more expensive.
Nuclear Power
This uses uranium as a fuel, although this is not burned as a fuel normally is. Energy is released
due to nuclear fission reactions, (see earlier work), inside a nuclear reactor. The heat is used to
make steam which drives the turbines, which drives the generators etc. So apart from the method
of heating the water a nuclear power station is identical to a fossil fuel burning power station. In
terms of start up time nuclear power stations are the slowest of any, so they too run continuously
contributing to the base load for the country.
Schematic diagram of electricity generation by nuclear fuel
Water Turbine Generator
Steam National
Nuclear Grid
Reactor
Uranium
People have mixed feelings about nuclear power. To its advantage it can produce very large
amounts of power putting it on a par with fossil fuel power stations. Also, it produces no pollution
at the time of power production. Nuclear power stations are very clean! When the uranium has
been used up however the fuel rods contain many dangerous and highly radioactive isotopes,
(these are the big bits left over when the uranium nucleus splits in the fission process). This
radioactive waste needs very careful treated and storage. This is what happens at Sellafield, and is
very controversial since people are concerned about the waste leaking in to the environment.
When a nuclear power station reaches the end of its useful life it needs to be decommissioned.
Many of the parts are radioactive and so it has to be taken apart carefully and each piece treated
as nuclear waste. All in all nuclear power is very expensive. On a political note, nuclear power
stations can also produce the high quality plutonium needed to make nuclear weapons, so
although expensive, governments with a nuclear weapons programme have an interest in using
power for electricity generation.
Nuclear power is also non renewable. Once the worlds supply of uranium has been used up there
can be no more.
The search for renewables
Whilst fossil and nuclear fuels do a good job at providing our energy needs, the pollution and
waste they produce together with the fact that they are running out makes it very important that
we look for alternatives that pollute far less and wont run out.
Wind Power
The basic method is to erect a wind turbine and generator at the top of a
mast or tower. Electricity is generated when the wind blows. It is clean,
non polluting, has a very fast start up time and relatively cheap to install.
The wind carries with it enormous amounts of energy. Unfortunately this
energy is spread across large areas of countryside, and wind turbines can
only extract the energy from the area swept out by the turbine blades.
This means that wind power can never match fossil and nuclear fuels for
the quantity of power. It is certainly useful in generating power on small
scale, say for a single remote farmhouse, but will struggle to generate for
a whole city. One way around this is to cover a whole hill side with dozens
of turbines creating what is known as a wind farm. This will generate
useful amounts of power, but the environmentalists say that it is noisy
and spoils the view of the countryside.
Wind power is also intermittent and doesn’t generate when there is no
wind. For small scale projects this can be overcome by having the turbines
charge batteries whilst windy, so that the batteries can be used at times
when it is calm.
Hydroelectric Power
Here water flowing down hill spins a water turbine which drives the generator. This can generate
large amounts of power and again can match the power output of fossil fuel stations. One very big
advantage is that the start up time is very fast… often about one minute rather than hours for a
fossil fuel station. There are different ways hydroelectric power can be implemented.
Natural lakes: Where there is a lake high in the mountains pipes can carry the water
down to a turbine. Often this is not an alternative because there are no
suitable lakes or because they are too remote and there would be huge
technical problems getting the cable away from the site which is probably
very remote.
Artificial Dam: An alternative is to build a dam across the end of an enclosed valley. The
turbine and generators are built into the wall of the dam. Once the valley
has flooded the water flows through the wall of the dam turning the
turbine. This arrangement is not always popular with environmentalists
who object to the flooding of the valley with loss of habitat for plants and
animals.
Pumped Storage: In this version a lake high in the hills is connected to a lake low down.
The pipes connecting the two lakes run through the turbine and
generator. The difference here is that the generators and turbine can run
in reverse, operating as a pump to return the water from the bottom lake
back to the top lake so it can be used again. Since machines are never
100% efficient it obviously takes more energy to pump the water up than
you get back when the water returns to the bottom. Remember however
that fossil fuel plants must generate continuously, and during the night
they are generating more than is needed. It is this spare electricity that is
used to pump the water back up. This ability to ‘save and store’ energy
that would otherwise be wasted, together with a very fast start up time
makes this a very environmentally friendly option.
Solar Power
There are many different ways that this can be used.
Passive Solar Heating: By having excellent insulation, and south facing windows in a home,
the sun can significantly reduce the need for additional heating.
Solar Panels: These are roof mounted panels that have pipes snaking through
them. The pipes are oil filled. As the oil warms up it circulates around
the system passing its heat to the household water supply. In this
way less fuel needs to be used to fully heat up the household hot
water. The pipes are usually painted black to absorb the heat better
and placed in front of a reflective surface.
Solar Volatic Cells: These convert sunlight direct into
electricity…eg the solar cells on
the front of many calculators. They
are however very expensive and do
not generate on a large scale. They
are only suitable for very small
scale projects eg calculators,
remote weather stations, and
parking meters, (look out along
Wigan Lane near the hospital !)
Solar Furnace: This is probably the only way
solar energy can be used on a
large scale. Large arrays of
mirrors, covering areas similar
to football fields track the sun
and reflect the heat all to one
spot. At this focus the heat
boils water to make steam
which drives the turbine etc.
This can produce large
amounts of power but is
probably only possible in
countries with almost continual sunshine.
Tidal Power
In many ways this is similar to hydroelectric power. Here a river estuary is dammed off. As
the tide comes in water is allowed to flow through the dam, Then as the tide turns the water
is trapped behind the dam and only allowed to return to the sea side of the dam after
flowing through the turbines which are in the wall of the dam. This system can generate
large amounts of power, it is renewable and causes no pollution. It is however very
expensive to build and is unpopular with environmentalists because it results in mud flats
which used to be exposed at low tide allowing wild birds to feed, becoming permanently
flooded. Here the energy comes from the gravitational attraction of the moon and sun,
(mostly the moon).
Wave Power
Like the wind, waves carry tremendous energy but it is very spread out. This together with
the unpredictable nature of waves in stormy conditions make this a very difficult form of
energy to extract. There are two main methods.
Oscillating Air Column: This is a structure built on the shore. When waves enter and move
up and down they push the air in and out of the top of the
structure. This moving air turns a turbine. Being built on the shore
this might be more resistant to winter storms but it only extracts
energy from a small section of waves.
Salter’s Ducks Here huge floats are strung across an estuary. The bobbing up and
down motion is used to turn the generator. Although this tries to
extract energy from a wide area of waves this is very difficult to
engineer, likely to be destroyed in winter storms, and is a hazard to
shipping.
A recent attempt to build a wave generator ended in disaster. The construction sank whilst
being towed out to sea. Wave power is proving to be one of the most difficult forms of
energy to harness.
Biomass
When organic waste is digested by bacteria methane gas is released as a waste product. This
gas can be collected and used as a fuel. Usually this is only suitable for small to medium
scale projects. Examples include…
Sewage Farm: The ‘sludge’ from the sewage is piped to a digester tank. The
methane produced is stored and used to power an engine which
drives a generator. This system is used at Leigh Waste Water
Treatment works, where enough electricity is made to power the
whole plant with some to spare which is sold to the National Grid.
Landfill: Organic waste rotting in a landfill site would also produce methane.
This could build up in the ground to dangerous level. To avoid this
and to make use of the methane pipes are laid in the ground to
collect the methane. Again this could be used to make electricity or
burned as a fuel to provide heating for local residents.
Remote Village: Small villages, especially in under developed countries can use this
to generate electricity for the village. The system will take any
organic waste including stalks from last years crop and animal
manure. This has the added advantage that otherwise harmful waste
is disposed of. Once the digestion process has stopped what is left
is harmless and can be spread on the fields to help fertilise next
years crop.
Growing wood as a fuel is sometimes referred to under the heading of biomass. Provided
the forest is properly managed with a controlled programme of planting and harvesting it
is possible to farm trees for use as a fuel in a way that can be considered renewable.
Geothermal
The interior of the earth is very hot. In some places these hot rocks come close enough to
the surface to allow their heat energy to be extracted. Bore holes are drilled, down which
cold water can be pumped. The water heats up and returns to the surface under pressure via
a second bore hole at a temperature above 100 0C. When the pressure is reduced the water
turns to steam which drives a turbine etc.
This is a non polluting, renewable resource. The scale of production depends on the local
geology. In this country there are only small experimental plants in Cornwall, however in
Iceland geothermal energy makes a significant contribution to the national energy
requirements.
The origin of the heat within the earth is thought to be due to radioactive decay.
Hot,
superheated Turbine Generator
Cold Water water Steam National
Grid
Hot Rocks
Origins of the Energy
It is worth considering where all this energy comes from. It is the sun’s energy that causes
the weather patterns on the earth, and hence causes the wind, and waves. The sun also
makes plants grow, so in fact the energy of the sun is responsible for…
fossil fuels
biomass
solar
wind power
hydroelectric power
wave power
Resources that do not have the origin of the energy in the sun’s heat are therefore…
tidal power
geothermal power
nuclear power.
Task:
Read through the above text. As you do, highlight or underline the text according to the
following…
Blue: Description of the energy resource
Red: Disadvantages
Green: Advantages.
Then compile a table in the following format for each energy resource. Wind power has been done
for you.
Energy Resource Advantages Disadvantages
Renewable Noisy
Wind Power Non polluting Spoils view of countryside
Relatively cheap to install Relatively small amounts of
electricity
Only generates when wind blows