Physics L1
Unite 2 : ENERGY
Chapter 2 : Energy Resources
Chapter 2 ENERGY RESOURCES & GENERATING ELECTRICITY
2.1 ENERGY RESOURCES
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Energy resources are large banks of energy that can be transferred into a form that can be
used by society.
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The various energy resources involve different energy transfers, as shown in the table
below:
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Advantages & Disadvantages
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All energy resources have advantages and disadvantages associated with them.
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A renewable energy resource is one that is replenished at a faster rate than the rate at which
it is being used.
As a result of this, renewable energy resources cannot run out.
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A reliable energy resource is one that can produce energy at any time.
Non-reliable resources can only produce energy some of the time (e.g. when it’s windy).
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4.2 GENERATING ELECTRICITY
From Renewable resources
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Generators are the devices that transfer kinetic energy into electrical energy.
Generators can be turned directly, for example, by:
✓ wind turbines
✓ hydroelectric turbines
✓ wave and tidal turbines
When electricity is generated using wave, wind, tidal or hydroelectric power (HEP)
there are two steps:
1. The turbine turns a generator.
2. Electricity is produced.
Pumped storage hydroelectric power station
In a hydroelectric power station water is stored behind a dam in a reservoir. This water has
gravitational potential energy.
➢ the water runs down pipes (potential to kinetic energy) to turn the turbine
➢ the turbine is connected to a generator to produce electricity (kinetic to electrical energy)
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From Non-Renewable resources
Most non-renewable energy resources use fossil fuels (coal, oil and natural gas) to generate
electricity. In fossil fuel generators, the chemical energy of the fuel is burned to release heat
energy.
Power stations
Power stations fuelled by fossil fuels or nuclear fuels are reliable sources of energy, meaning
they can provide power whenever it is needed. However, their start-up times vary according to the
type of fuel used.
This list shows the type of fuel in order of start-up time:
1. gas-fired station (shortest start-up time)
2. oil-fired station
3. coal-fired station
4. nuclear power station (longest start-up time)
➢ Fig.7 is a block diagram that describes each energy
change that happens inside a fossil fuel power station.
Fig .7
A block diagram of the process from fuel input to electricity output
a block diagram should includes the steps of the energy transfer and the component of a power
station.
Block diagrams can be drawn as above or can be drawn as the one below:
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Nuclear power station
The main nuclear fuels are uranium and plutonium. In a nuclear power station nuclear fuel
undergoes a controlled chain reaction in the reactor to produce heat - nuclear to heat energy.
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Heat is used to change water into steam in the boiler.
The steam drives the turbine (heat to kinetic energy)
This drives the generator to produce electricity - kinetic to electrical energy.
Advantages
➢ Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulphur dioxide which
increase the global warming.
➢ 1 kg of nuclear fuel produces millions of times more energy than 1 kg of coal.
➢ A small amount of fuel is needed, when compared with coal or gas.
Disadvantages
➢ Like fossil fuels, nuclear fuels are non-renewable energy resources.
➢ If there is an accident, large amounts of radioactive material could be released into the
environment. Although modern reactor designs are extremely safe.
➢ Nuclear waste remains radioactive and is hazardous to health for thousands of years. It
must be stored safely.
➢ building the power stations is quite expensive
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Nuclear Fission
✓
In a nuclear reactor, a neutron is absorbed into a nucleus (typically uranium-235). This
causes the nucleus to become uranium-236, which is violently unstable.
✓
The entire
nucleus splits into two
large fragments called
'daughter nuclei'. In
addition to the
'daughter' products,
two or three neutrons
also explode out of the
fission reaction and
these can collide with
other uranium nuclei to
cause further fission
reactions. This is
known as a chain
reaction.
✓
The fast moving neutrons carry most of the energy from the reaction with them (99%) but
before the neutrons can collide with fresh uranium nuclei, they need to be slowed down.
✓
This is so that the energy can pass on to other components in the nuclear reactor, which is
used to heat water to drive the turbines that turn the generators.
Rate of energy released
The energy released in nuclear fission is far greater than the energy released in a chemical
reaction, such as burning fuel. This means that the power output of a nuclear power station is large.
The lifetime of a nuclear power station is about 20 years.
The efficiency of the power station doesn’t reach 100% may be due to energy loss as :
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exhaust gases (from combustion)
specific friction e.g. in any machine or between two stated moving parts
transformer losses e.g. (resistive) heat loss in wires
waste heat from condenser system
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