Topic 8 Energy Production Flashcards
the law of conservation of energy
“energy cannot be created nor destroyed, only changed from one form to another”
(usually to transfer energy, work must be done, exception: transfer of thermal energy)
sankey diagram
show the flow of energy through a system and identify where energy is lost to the surroundings
fuels:
- are sources of energy
- release energy by changing their chemical or nuclear structure
- in releasing energy their atoms lose Ep and gain Ek (heat)
- an engine or machine is needed if the heat produced is to do work eg. car engine (heat from petrol is used to move the car)
- some heat is always lost to the surroundings (second law of thermodynamics: “it is not possible to convert heat completely into work”)
- this lost energy is known as degraded energy - because this energy is no longer able to perform useful work
specific energy in fuels
the energy liberated per unit mass of fuel consumed
unit: Jkg^–1 (MJkg^–1)
eg. coal = 30 MJkg^–1
uranium = 80 000 000 MJkg^–1
energy density in fuels
the energy liberated per unit volume of fuel consumed
unit: Jm^–3 (MJm^–3)
primary sources definition
has not been transformed or converted before use by a consumer
eg. burning coal to release its chemical potential energy for hearing or using the kinetic energy of the wind to turn a windmill to grind corn.
secondary sources
results from the transformation of a primary source
eg. the electrical energy generated by coal-fired power stations or wind turbines is a secondary source of energy.
non-renewable energy sources definition
energy sources that can be used up because they are used at a greater rate than they are produced
eg. coal, oil, gas, uranium
renewable energy sources definition
energy sources that cannot be used up or are used at a rate that effectively means the sources will NOT run out
ie. rate of production is greater than the rate of usage
eg. hydro, wind, solar, tidal, wave, geothermal
total global fuel use of coal
38%
total global fuel use of coal to produce electrical energy
40%
generating electrical energy: generator
- a conductor is moved relative to a magnetic field,
- then a force is exerted on the electrons in the conductor and a voltage difference will be induced across the conductor.
- If the conductor is part of a circuit a current will flow
fluids typically used in turbines to convert the flow of a fluid into mechanical motion within the generator
- steam
- water
- hot gas
- wind
production and usage of electrical energy measurement unit:
1 kilowatt-hour (kWh) = 3.60 x 10^6 J
a kilowatt-hour is the amount of energy used by a 1kW device in one hour
advantages and disadvantages of fossil fuels
Advantages:
- very high energy density
- easy to transport
- cheap
- can be used directly or heating
- power stations can be built almost anywhere
Disadvantages:
- combustion products produce pollution (e.g. acid rain), “greenhouse” gases
- fuel extraction can damage the environment
- non-renewable
- power stations need large amounts of fuel
how do nuclear power stations generate energy
nuclear fission that releases energy
most common fuel source of nuclear power
uranium-235
splits into barium-141 and krypton-92
how does uranium-235 undergo fission to produce energy
a neutron source such as americium-241 and beryllium-9 is used to initiate the fission process.
if the mass of uranium-235 is large enough (critical mass) then enough neutrons produced by fission will collide with further uranium nuclei to sustain fission before being lost from the surface of the fuel - this is know as a chain reaction
what percentage of uranium is uranium-235 and what percentage does it need to be at to be used to produce power
0.7%
needs to be at around 5% before it can be used in a nuclear reactor
what does a moderator do in nuclear power station
the high energy neutrons must be slowed down so that collisions with U-235 nuclei cause fission to occur.
(collisions between the moderator’s nuclei and the neutrons reduce the kinetic energy of the neutrons from several MeV to just several eV)
makes fission happen
eg. water, graphite
what do control rods do in nuclear power station
the control rods absorb neutrons.
(by lowering the rods into, or raising them out of, the reactor ore the fission reaction can be controlled. an uncontrolled chain reaction is like totally bad - it’s a nuclear bomb)
control the rate of fission
eg. cadmium
what does a heat exchanger do in nuclear power station
water heated by the fission reactions enters the heat exchanger and its thermal energy is transferred to cold water in a seperate circuit to convert it into steam to drive the turbines
energy flow diagram of nuclear power generator
Ek of fission products ––> thermal energy of water ––> Ek of turbines ––> Ek of generator ––> electrical energy
advantages and disadvantages of nuclear power
advantage:
- uranium has a very high specific energy (need 10x more coal)
- relatively large reserves of uranium
- no greenhouse gases are produced during energy production
disadvantage:
- radioactive waste is produced (safe storage is needed)
- high risk if things go wrong (radioactive contamination)
- non-renewable (but uranium reserves will last a long time)
safety issues with nuclear power
- the reactor core needs to be constantly cooled, otherwise a thermal meltdown may occur causing an explosion that sends radioactive material over a wide area
- nuclear reactors produce radioactive waste which must be stored for a long time (millions of years)
- uranium mining is hazardous
- transportation of both uranium and the radioactive waste is hazardous
- the by-products of nuclear power (eg. plutonium-239) can be used to make nuclear weapons
why can’t we perform nuclear fusion right now
include maintaining:
- the very high temperatures required so that the nuclei have enough energy to overcome their electrostatic repulsion and combine
- the magnetic field needed to contain the plasma
- the plasma at a high enough density ie. at high pressure, so nuclei are close together to increase the chance of collision between them
energy flow diagram of wind power generator
Ek of wind ––> Ek of turbines (blades) ––> Ek of generator ––> electrical energy
advantages and disadvantages of wind power
advantages:
- “clean” - no harmful by-products eg. CO2
- renewable
- free source of energy
disadvantages:
- some consider wind turbines visually undesirable
- often need to be build far from population centres
- unreliable (dependant on amount of wind)
- low energy density so wind turbines need to be large and numerous
energy flow diagram of wind power from sun
solar energy of sun ––> thermal energy of land and atmosphere ––> Ek of air molecules (wind)
hydroelectric power generation uses
gravitational potential energy of water. this water is stored in one of three ways:
- in a lake using a dam
- by capturing water at high tide and releasing it a low tide
- **by pumping water from a low to high reservoir when energy demands are low (pumped storage)
energy flow diagram of hydroelectric power generator
Ep of water ––> Ek of water ––> Ek of turbines ––> Ek of generator ––> electrical energy
energy losses of hydroelectric power due to:
- friction and turbulence of water in the penstock
- friction in the turbines and generator
- electrical heating losses due to resistance of wiring
pumped storage hydroelectric systems
- when demand for electricity is high, water is allowed to run from the upper to the lower reservoir, through the turbines, and electrical energy is generated
- when demand for electricity is low, the turbines operate in reverse (using electrical energy which is cheap at this time) to pump water back up from the lower to the higher reservoir
pumped storage systems can meet a rapid increase in demand for electrical energy by releasing large volume of water through the turbines
advantages and disadvantages of hydroelectric power
advantage:
- “clean” - no harmful by-products eg. CO2
- renewable
- free source of energy
disadvantage:
- only available in areas where suitable bodies of water exist
- building dams involves land being covered in water
solar power can be used in ___ ways:
two ways: photovoltaic cell and solar hearing panel
how does photovoltaic cell work
- converts solar energy to electrical energy (using photoelectric effect)
- only produce small voltage so only used for electrical devices that do not need much energy eg. TV, radio, lighting, phone charger
- for higher VOLTAGES connect in SERIES
- for higher CURRENTS connect in PARALLEL
how does solar hearing panel work
- converts solar energy to thermal energy (in water)
- water in black copper pipes is heated by the sun
- used to provide hot water for domestic use (it uses the most energy to heat water)
the average amount of solar energy falling on the outer edge of the Earth’s atmosphere ____ __________ _________ ____ _____ ____ is approximately:
the average amount of solar energy falling on the outer edge of the Earth’s atmosphere at right angles to the Sun’s rays is approximately:
1400W m^–2
why does only half of the average amount of solar energy falling on the outer edge of the Earth’s atmosphere at right angles to the Sun’s rays reach the earth’s surface?
- the atmosphere itself absorbs solar radiation
- clouds reflect solar radiation
- during different seasons the angle at which the Sun’s rays are incident on different parts of the Earth vary; the shallower the angle, the more the energy is spread out
advantages and disadvantages of solar power
advantages:
- “clean” - no harmful by-products eg. CO2
- renewable
- free source of energy
disadvantages:
- only available during the day (when energy demand is low)
- unreliable (dependant on the amount of cloud cover)
- low energy density (large area needed)
- seasonal variations in sunlight
