Topic 8: Energy, power and climate change Flashcards
How is thermal energy converted to work?
In principle, thermal energy can be completely converted to work in a single process, but the continuous conversion of this energy into work implies the use of machines that are continuously repeating their actions in a fixed cycle. Any cyclical process must involve the transfer of some energy from the system to the surroundings that is no longer available to perform useful work.
Explain what is meant by degraded energy.
Energy that is unavailable to a system because it has been transferred to the surroundings.
What happens to energy that is transferred to the surroundings?
It is no longer available to do work.
What is a Sankey diagram?
A diagram used to represent energy conversions.
In what direction should the main arrow in a Sankey diagram be drawn?
From left to right.
What does the main arrow in a Sankey diagram represent?
The energy changes taking place.
What does the width of the arrow in a Sankey diagram represent?
The power or energy involved at a given stage.
What does the arrow drawn up or down in a Sankey diagram represent?
Degraded energy.
Outline the principle mechanisms involved in the production of electrical power. (5)
- A fuel is used to release thermal energy 2. Thermal energy is used to boil water to make steam 3. Steam is used to turn turbines 4. Motion of the turbines is used to generate electrical energy by rotating coils in a magnetic field 5. Transformers alter the potential difference
Identify different world energy sources.
In most instances, the Sun is the prime energy source for world energy. Other cases: - gravitational energy of the Sun and the Moon - nuclear energy stored within atoms - the Earth’s internal heat energy
What are six renewable energy sources?
- hydroelectric
- photovoltaic cells
- active solar heaters
- wind
- biofuels
- geothermal
What are four non-renewable energy sources?
- oil
- natural gas
- coal
- nuclear
Which four energy sources emit carbon dioxide?
- coal
- natural gas
- oil
- biofuels
Define: renewable energy source
Energy that comes from resources which are naturally replenished on a human time scale
Define: non-renewable energy source
A resource that cannot be replaced when it is used up.
Define: energy density
energy density = (energy released by fuel) / (mass of fuel consumed)
What is the standard index measurement for energy density?
J kg-1
Discuss how choice of fuel is influenced by its energy density.
When the fuel needs to be transported: the greater the mass of fuel that needs to be transported, the greater the cost.
What is the energy density of coal?
3.3 X 107 J kg-1
What is the energy density of oil?
4.2 X 107 J kg-1
What is the energy density of natural gas?
5.4 X 107 J kg-1
What was the world’s proportional energy consumption of oil in 2003?
38%
What was the world’s proportional energy consumption of natural gas in 2003?
24%
What was the world’s proportional energy consumption of coal in 2003?
24%
What was the world’s proportional energy consumption of nuclear in 2003?
6%
What was the world’s proportional energy consumption of other resources in 2003?
8%
Advantages of nuclear power.
- Extremely high energy density – a great deal of energy is released from a very small mass of uranium
- Reserves of uranium are large compared to oil
- Do not produce carbon dioxide
Disadvantages of nuclear power.
- Process produces radioactive nuclear waste that is currently just stored
- Larger possible risk if anything should go wrong
- Non-renewable (but should last a long time)
Advantages of wind energy
- Very clean production – no harmful chemical by-products
- Renewable source of energy
- Source of energy is free
Disadvantages of wind energy.
- Source of energy is unreliable – could be a day without wind
- Low energy density – a very large area would be need to be covered for a significant amount of energy
- Some consider large wind generators to spoil the countryside because they are ugly and produce a lot of noise
Advantages of water energy.
- Very clean production – no harmful chemical by-products
- Renewable source of energy
- Source of energy is free
Disadvantages of water energy
- It has been difficult to scale up the designs for wave machines to produce large amounts of electricity.
- Tidal barrages destroy the habitat of estuary species, including wading birds.
- Construction of dam will involve land being buried under water and the rotting vegetation underwater releases methane, which is a greenhouse gas.
Advatages of solar power
- Very clean production – no harmful chemical by-products
- Renewable source of energy
- Source of energy is free
Disadvantages of solar power.
- Can only be utilised during the day
- Source of energy is unreliable – could be a cloudy day
- Low energy density – a very large area would be needed for a significant amount of energy
Outline the historical and geographical reasons for the widespread use of fossil fuels.
- Industrial Revolution in Western Europe in the late 18th and 19th Centuries involved the development of large-scale manufacturing industries and the introduction of the factory as a place of work
- Machines were designed and built, replacing manual labour
- The industrial growth of towns and regions in the UK started a process that spread throughout the world
- As the industrial revolution spread, the rate of energy usage increased and industry tended to develop near to existing deposits of fossil fuels
- Once factories were established, people seeking work would tend to migrate towards the cities
- In addition, infrastructure was created to allow coal and other fossil fuels to be transported as the higher rates of energy usage demanded the use of fuels with a high energy density
- This encouraged the growth of industries located near the raw materials
Discuss the energy density of fossil fuels with respect to the demands of power stations.
Higher rates of energy usage demanded the use of fuels with a high energy density.
Calculate the rate of fuel consumption by a 500 MW coal power station.
- Electrical power supply:
- = 500MW = 5 X 108 J s-1<span><span></span></span>
-
<span></span>Power released from fuel
- = (5 X 108) / (efficiency)
- = (5 X 108 ) / (0.35)
- = 1.43 X 109 J s-1
- Rate of consumption of coal
- = (1.32 X 109) / (energy density) kg s-1
- = (1.43 X 109) / (3.3 X 107) kg s-1
- = 43.3 kg s-1
- = 43.3 X 60 X 60 kg hr-1
- = 1.56 X 105 kg hr-1
- = 160 tonnes hr-1
Calculate the rate of fuel consumption by a 500 MW oil power station.
- Electrical power supply
- = 500 MW = 5 X 108 J s-1
- Power released from fuel
- = (5 X 108) / (efficiency)
- = (5 X 108) / 0.38
- = (1.32 X 109) J s-1
- Rate of consumption of coal
- = (1.32 X 109) / (energy density) kg s-1
- = (1.32 X 109) / (4.2 X 107) kg s-1
- = 31.4 kg s-1
- = 31.4 X 60 X 60 kg hr-1
- = 1.13 X 105 kg hr-1
- = 113 tonnes hr-1
Calculate the rate of fuel consumption by a 500 MW natural gas power station.
- Electrical power supply
- = 500 MW = 5 X 108 J s-1
- Power released from fuel
- = (5 X 108) / efficiency
- = (5 X 108) / 0.45
- = (1.11 X 109) J s-1
- Rate of consumption of coal
- = (1.11 X 109) / energy density kg s-1
- = (1.11 X 109) / (5.4 X 107) kg s-1
- = 20.6 kg s-1
- = 20.6 X 60 X 60 kg hr-1
- = 7.40 X 104 kg hr-1
- = 74 tonnes hr-1
Advantages of fossil fuels (5)
- Very high energy density – a great deal of energy is released from a small mass of fossil fuel
- Fossil fuels are relatively easy to transport
- Still cheap when compared to other sources of energy
- Can be built anywhere with good transport links and water availability
- Can be used directly in the home to provide heating
Disadvantages of fossil fuels (5)
- Combustion products can produce pollution, notably acid rain
- Combustion products contain greenhouse gases
- Extraction of fossil fuels can damage the environment
- Non-renewable
- Coal-fired power stations need large amounts of fuel