Energy Production Flashcards
primary energy
energy found in nature that has not yet been subject to processing of any kind
examples of primary energy
- energy stored in fuels (crude oil, coal, natural gas)
- solar energy, wind energy
secondary energy
primary energy that has been processed or exploited
specific energy
- ES
- amount of energy that can be extracted from a unit mass of fuel
- Jkg-1
energy density
- ED
- amount of energy that can be extracted from a unit volume of fuel
- Jm-3
non-renewable sources of energy
- finite sources being depleted much faster than they can be produced and so will run out
- e.g. fossil fuels, nuclear fuels
renewable sources of energy
- solar, wind, wave energy
- tidal energy
- are indefinitely available
fossil fuels
produced by decomposition of buried animal and plant matter under combined action of high pressure of material on top and bacteria
coal-burning power plant
How does a coal-burning power plant work?
- burning coal produces energy
- powers boilers that turns water into steam
- pressurized steam forces turbine to turn
- turbine makes coils of generator rotate in a magnetic field
- electricity created by electromagnetic induction
- cold water condenses steam into liquid to be used again
sankey diagram
- arrow block diagram representing energy flow
- width of arrow proportional to amount of energy being transferred
efficiency equation
e = useful power/input power
pros and cons of fossil fuel power plants and natural gas power plants
Fossil fuel power plants
- reasonably efficient: 35%
- contribute greenhouse gases to atmosphere
Natural as power plants
- more efficient: 60%
- smaller greenhouse gas emissions
Advantages of fossil fuels
- relatively cheap while they last
- high power output (high energy density)
- variety of engines and devices use them directly and easily
- extensive distribution network is in place
fossil fuel disadvantages
- will run out
- pollute the environment
- contribute to greenhouse effect by releasing greenhouse gases into atmosphere
nuclear reactor
machine in which nuclear fission reactions take place producing energy
What are the two types of fission reactor?
- pressurised water reaction (PWR)
- gas cooled reactor
pressurised water reactor
gas cooled reactor
What is the fuel of a nuclear reactor?
uranium-235
chain reaction
self-sustaining reaction
What is required for the chain reaction to get going?
- critical mass of uranium-235 must be present
- otherwise neutrons escape without causing further reactions
Describe fission
- neutrons produced can be used to collide with other nuclei in reactor
- produces more fission, energy and neutrons
moderator
- uranium-235 cannot capture neutrons at speed from fission
- slowing of neutrons through collisions with moderator
- material surrounding fuel rods
fuel rods
tubes containing uranium
What materials is the moderator usually?
graphite or water
heat exchanger
- when neutrons collide with moderator, transfer energy to moderator
- extracts heat from moderator
- uses cold water that circulates in pipes throughout the moderator
- water turned into steam at high temperature and pressure
- steam is used to turn turbines producing energy
control rods
- absorb neutrons when too many neutrons are present so decrease rate of reaction
- if rate of reaction needs to be increased, remove control rods
advantages of nuclear power
- high power output
- large reserves of nuclear fuels
- does not produce greenhouse gases
disadvantages of nuclear power
- radioactive waste products difficult to dispose of
- major public health hazard if something goes wrong
- problems associated with uranium mining
- possibility of producing materials for nuclear weapons
advantages of solar power
- free
- inexhaustible
- clean
disadvantages of solar power
- works during day only
- affected by cloudy weather
- low power output
- requires large areas
- initial costs high
solar panels
- sunlight used to heat water for heating house
- blackened surface below glass collects sunlight, glass protects but coated to reduce reflection
- tend to be bulky and cover too much space
photovoltaic cells
- converts sunlight directly into direct current
- 30% efficiency
- sunlight releases electrons and creates potential difference across cell
advantages of hydroelectric power
- ‘free’
- inexhaustible
- clean
disadvantages of hydroelectric power
- very dependent on location
- requires drastic changes to environment
- initial costs high
pumped storage system
water that flows to lower heights is pumped back to its original height using generators of plant as motors
advantages of wind power
- ‘free’
- inexhaustible
- clean
disadvantages of wind power
- dependent on local wind conditions
- aesthetic problems
- noise problems
energy balance
energy input to earth must be equal to energy output because temperature constant
What are the drawbacks of energy balance model?
- zero-dimensional model
- interactions between surface and atmosphere ignored - e.g. latent heat flows
enhanced greenhouse effect
additional warming due to increased quantities of greenhouse gases in atmosphere due to human activity
absolute meaning
Kelvin
how do bodies radiate energy?
- energy radiated through electromagnetic waves
- created by oscillating electric charges in atoms of body
emissivity
- ratio of power radiated per unit area by an object to the power radiated per unit area by a black body
- between 0 and 1
black body
- perfect radiator and absorber
- e = 1
- e.g. charcoal (black and dull surface)
Wein’s law graph: increase temperature
- peak of curve occurs at lower wavelengths
- height of peak increases
Weins law graph: same temperature, different emissivities
- height of curve decreases as emissivity decreases
- otherwise identical
intensity
power of radiation received per unit area
area of a sphere
4*pi*d2
albedo
ratio of power of radiation scattered from the body to the total power incident on the body
high albedo example
snow
low albedo example
charcoal
what factors vary the albedo of the earth?
- time of year (many clouds = increase albedo)
- latitude (more snow = increase albedo)
- desert land (high albedo)
- forest (low albedo)
- water (low albedo)
show solar constant
show average incident intensity
energy flow diagram of greenhouse effect
greenhouse effect
warming of the Earth caused by infrared radiation emitted by the Earth’s surface which is absorbed by various gases in the Earth’s atmosphere and then partly re-radiated towards the surface
greenhouse gases
- water vapor
- carbon dioxide
- methane
- nitrous oxide
natural sources of greenhouse gases
- water vapor
- carbon dioxide
- methane
- nitrous oxide
- evaporation of water from oceans, rivers and lakes
- forest fires, volcanic eruptions, evaporation of ocean water
- wetlands, oceans, lakes and rivers, termites
- forests, oceans, soil and grasslands
anthropogenic sources of greenhouse gases
- water vapor
- carbon dioxide
- methane
- nitrous oxide
- irrigation
- burning fossil fuels in power plants and cars, burning forests
- flooded rice fields, farm animals, processing of coal, natural gas and oil, burning biomass
- burning fossil fuels, manufacturing cement, fertilisers, deforestation
Why do greenhouse gases absorb infrared radiation?
resonance
explain resonance
- the natural frequency of oscillation of the bonds within molecules of the gas is in infrared region
- if driving frequency from radiation emitted from the Earth is equal to natural frequency of molecule resonance occurs
- amplitude of molecular vibration increases, temperature increases
enhanced greenhouse effect
greenhouse effect caused by human activities
what are the three possible explanations for global warming?
- changes in composition of greenhouse gases in atmosphere
- change in intensity of radiation emitted by the sun linked to increased solar flare activity
- cyclical changes in the earth’s orbit and volcanic activity
what happens to the albedo of the earth as temperature rises?
- albedo decreases
- snow and ice melts, increasing area of oceans which have lower albedo than snow
