1.1 Various energy sources can be used to generate
the electricity we need. There are advantages and
disadvantages of using each energy source..
Electricity is distributed via the National Grid.
1.1.1 In some power stations an energy
source is used to heat water. The
steam produced drives a turbine that
is coupled to an electrical generator.
Energy sources include fossil fuels
which are burnt to heat water or air,
uranium and plutonium, when energy
from nuclear fission is used to heat
water and biofuels that can be burnt
to heat water. Water and wind can be
used to drive turbines directly.
22.214.171.124 The main nuclear fuels are uranium and plutonium. These
are radioactive metals. Nuclear fuels are not burnt to
release energy. Instead, nuclear fission reactions
release heat energy. The rest of the process of
generating electricity is then identical to the process
using fossil fuels. Unlike fossil fuels, nuclear fuels do not
produce carbon dioxide or sulfur dioxide. There are
disadvantages however: nuclear fuels are
non-renewable energy resources; risk of large amounts
of radioactive material released into the environment and
nuclear waste remains radioactive and is hazardous to
health for thousands of years and must be stored safely.
126.96.36.199.1 The wind is produced as a result of convection currents in the
atmosphere, which are driven by heat energy from the sun. Wind
turbines use the wind to drive turbines directly. They have huge
blades mounted on a tall tower. The blades are connected to a
'nacelle', or housing, which contains gears linked to a generator.
As the wind blows, it transfers some of its kinetic energy to the
blades, which turn and drive the generator. Several wind turbines
may be grouped together in windy locations to form wind farms.
Wind is a renewable energy resource and there are no fuel costs.
No harmful polluting gases are produced. However wind farms are
noisy and may spoil the view for people living near them. The
amount of electricity generated depends on the strength of the
wind. If there is no wind, there is no electricity.
188.8.131.52.1.1 Water can be used to drive turbines directly. Machines use the kinetic energy in the
movement of waves to drive electricity generators. Huge amounts of water move in and
out of river mouths each day. A tidal barrage is a barrier built over a river estuary to
make use of the kinetic energy in the moving water. Hydroelectric power stations use
the kinetic energy in moving water. The water high up behind the dam contains
gravitational potential energy which is transferred to kinetic energy. Water is a
renewable resource with no fuel costs and no harmful polluting gases produced.
Barrages and HEP stations are reliable and easily switched on. It is difficult to design
wave machines producing large amounts of electricity. Tidal barrages destroy the
habitat of estuary species. Hydroelectricity dams flood farmland pushing people from
their homes. The rotting vegetation underwater releases methane, a greenhouse gas.
184.108.40.206.1.1.1 Hot water and steam from deep underground can be used to
drive turbines; geothermal energy. Several types of rock contain
radioactive substances such as uranium. Radioactive decay of
these substances releases heat energy, which warms up the
rocks. In volcanic areas, the rocks may heat water so that it
rises to the surface naturally as hot water and steam. Here the
steam can be used to drive turbines and electricity generators. In
some places, the rocks are hot, but no hot water or steam rises
to the surface. Deep wells can be drilled down to the hot rocks
and cold water pumped down. The water runs through
fractures in the rocks and is heated up. It returns to the surface
as hot water and steam, where its energy can be used to drive
turbines and electricity generators. Geothermal energy is a
renewable energy resource with no fuel costs. No harmful
polluting gases are produced. Most parts of the world do not
have suitable areas where geothermal energy can be exploited.
220.127.116.11.18.104.22.168 Solar cells are devices that convert light energy directly into electrical energy. Solar panels use heat energy from the Sun
to heat up water. You may see small solar cells in calculators. Larger arrays of solar cells are used to power road signs in
remote areas, and even larger arrays are used to power satellites in orbit around Earth. Solar energy is a renewable
energy resource and there are no fuel costs. No harmful polluting gases are produced. Solar cells provide electricity in
remote locations. Solar cells are expensive and inefficient, so the cost of their electricity is high. They do not work at night.
22.214.171.124.126.96.36.199.1 Using different energy resources has different
effects on the environment. These effects include the
release of substances into the atmosphere, the
production of waste materials, noise and visual
pollution and the destruction of wildlife habitats.
188.8.131.52.184.108.40.206.1.1 Carbon capture and storage is a rapidly evolving technology. To prevent carbon dioxide
building up in the atmosphere we can catch and store it. Some of the best natural
containers are old oil and gas fields, such as those under the North Sea.
2 P1.4.2 The National Grid
2.1 Electricity is distributed
from power stations to
consumers along the
2.1.1 Electricity is transferred from power stations to consumers through the wires and cables of the National Grid.
When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. To
reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage.
220.127.116.11 Transformers are used in the National Grid. A transformer is an electrical device
that changes the voltage of an alternating current (ac) supply, such as the mains
electrical supply. A transformer that increases the voltage is a step-up transformer
and one which decreases the voltage is a step-down transformer.
18.104.22.168.1 Power stations produce electricity at 25,000 V. Step-up transformers change the voltage to the very
values needed to transmit electricity through the National Grid power lines. Electricity is sent through
these at 400,000 V, 275,000 V or 132,000 V. This reduces energy losses during transmission but the
voltages would be dangerous in homes. Step-down transformers are used locally to reduce the voltage
to safe levels. The voltage of household electricity is about 230 V.
22.214.171.124.1.1 Electricity from a power station goes to step-up
transformers, high voltage transmission lines,
step-down transformers and then to consumers.