P3: Energy resources
3.1: Energy demands
In most power stations, water is heated to produce steam, the steam drives a turbine, which is coupled to an electric generator that generates electricity
Most power stations in the UK burn fossil fuels, such as oil, coal, or gas
Fossil fuels are obtained from long-dead biological material
A biofuel is any fuel obtained from living or recently living organisms
Some biofuels can be used in small-scale, gas fired power stations
Biofuels are renewable sources of energy - they can be replaced at the same rate at which they're used up
Biofuels are carbon-neutral - the carbon taken in (as carbon dioxide from the atomsphere by the living organism) can balance the amount released when the biofuel is burnt
Waste vegetable oil, methane, rapeseed plants, ethanol, straw, nutshell, and woodchip are all examples of biofuels
The nuclear fuel used in a nuclear power station is uranium (or plutonium)
The nucleus of a uranium atom is unstable and can split in 2 - this process releases energy
Their are lots of uranium nuclei in the reactor core, so lots of energy can be released - the energy is used to heat water, turning it into steam
3.2: Energy from wind and water
Wind, waves, and the tide are sources of renewable energy
In a wind turbine, the wind passing over the turbine blades at the top of a tall tower makes the turbine rotate and drive a generator
The movement of waves on the sea can be used to drive a floating turbine that turns a generator - the electricity is delivered to the grid system on shore by a cable
At a hydroelectric power station, water is collected in a reservoir at the top of a hill - when the water is allowed to flow back downhill, it turns turbines that are connected to generators at the bottom of the hill
In a pumped storage scheme, the water is then collected in a reservoir at the bottom of the hill and pumped back to the top when demand for electricity is low, so the process can be repeated
At a tidal power station, water from each high tide is trapped behind a barrage - the water is released back into the sea through turbines - the turbines drive generators in the barrage
3.3: Power from the sun and the earth
Electromagnetic radiation from the sun transfers energy to the earth
A solar cell transfers this energy directly into electrical energy - each cell only produces a small amount of electricity, so they are useful to power small devices, such as watches or calculators
Large numbers of solar cells can be joined together to form a solar panel - these can be useful to generate electricity in remote locations where there is no access to a national grid
A solar heating panel uses energy from the sun to heat water that flows through the panel
A solar power tower uses thousands of mirrors to reflect sunlight onto a water tank, which heats the water and produces steam
The steam is used to drive turbines that turn generators, and so produce electricity
Geothermal energy comes from energy released by radioactive substances deep within the earth in volcanic or other suitable locations
This energy heats the surrounding rocks
In a geothermal power station, very deep holes are drilled and cold water is pumped down to the hot rocks
There it is heated and comes back to the surface as steam, which is used to drive turbines
3.4: Energy and the environment
Fossil fuels have some disadvantages
Non-renewable energy resources
Oil and gas will most likely run out in 50 years or so, although coal will last much longer
When they're burned, they release greenhouse gases (like carbon dioxide) - most scientists believe this is causing global warming
Burning coal and oil releases sulfur dioxide, causing acid rain
Nuclear power
Advantages
Doesn't produce greenhouse gases
Transfers much more energy per kg than fossil fuels
Disadvantages
Used fuel rods contain radioactive waste that must be stored safely for centuries
Nuclear power stations are safe in normal use, but an accident can make the surrounding area unsafe for many years
Renewable energy
Advantages
Will never run out and can be produced as fast as they're used
Don't produce greenhouse gases or other dangerous waste
Can be used where connection to the national grid is uneconomical
Disadvantages
Wouldn't currently be able to meet world demand
Most are not available all the time or can be unreliable
Wind, tidal, and hydroelectric schemes can be eyesore and can affect plant and animal life
Solar cells need to cover large areas to produce large amounts of power
3.5: Big energy issues
Different types of power station have different start-up times
A constant amount of electricity is provided by nuclear and coal-fired power stations - this is called the base load demand
The demand for electricity varies at different times during the day, and between summer and winter
This variable demand is met using gas-fired power stations and pumped storage schemes
Renewable energy resources are used when demand is high and the conditions for the resource are suitable
The overall cost of a new power station depends on building costs, fuel costs, maintenance costs, and decommissioning costs