Energy Generation
- You need to know about the main ways of generating electricity:
- The equipment involved
- The advantages and disadvantages
- Calculate power obtained for different setups
- These revision notes cover:
- Nuclear Power
- Burning Fossil Fuels
- Wind Electricity Generators
- Hydroelectric Power
- Solar Power
Nuclear Power
Control Rods & Moderators:
- In a nuclear reactor, a chain reaction is required to keep the reactor running
- When the reactor is producing energy at the correct rate, two factors must be controlled:
- The number of free neutrons in the reactor
- The energy of the free neutrons
- To do this, nuclear reactors contain control rods and moderators
The overall purpose of a nuclear reactor is to collect the heat energy produced from nuclear reactions
Control Rods:
Purpose of a control rod: To absorb neutrons
- Control rods are made of a material which absorb neutrons without becoming dangerously unstable themselves
- The number of neutrons absorbed is controlled by varying the depth of the control rods in the fuel rods
- Lowering the rods further decreases the rate of fission, as more neutrons are absorbed
- Raising the rods increases the rate of fission, as fewer neutrons are absorbed
- This is adjusted automatically so that exactly one fission neutron produced by each fission event goes on to cause another fission
- In the event the nuclear reactor needs to shut down, the control rods can be lowered all the way so no reaction can take place
Moderator:
The purpose of a moderator: To slow down neutrons
- The moderator is a material that surrounds the fuel rods and control rods inside the reactor core
- The fast-moving neutrons produced by the fission reactions slow down by colliding with the molecules of the moderator, causing them to lose some momentum
- The neutrons are slowed down so that they are in thermal equilibrium with the moderator, hence the term ‘thermal neutron’
- This ensures neutrons can react efficiently with the uranium fuel
Shielding:
- The entire nuclear reactor is surrounded by shielding materials
- The purpose of shielding is to absorb hazardous radiation
- The daughter nuclei formed during fission, and the neutrons emitted, are radioactive
- The reactor is surrounded by a steel and concrete wall that can be nearly 2 metres thick
- This absorbs the emissions from the reactions
- It ensures that the environment around the reactor is safe
Shielding metals in a nuclear reactor
Advantages & Disadvantages of Nuclear Power
- Advantages of using nuclear power include:
- Extensive reserves of fissionable materials
- Increasingly refine technology available
- No greenhouse gases produced
- A large amount of power is produced
- Disadvantages of using nuclear power include:
- Hazardous radioactive waste materials produced
- Dangerous if the power plant goes significantly wrong
- Danger of misuse of nuclear material
- Problems with mining fuel
Burning Fossil Fuels
- Fossil fuels, such as coal and oil, are used to produce energy on-demand when energy is needed
- This is done by burning the materials when the energy is required
- When fossil fuels are burned, it is used to heat water
- This water is heated until it becomes steam
- Steam is forced around the system and this turns a turbine
- The turbine spins and is connected to a generator which generates electricity
- This electricity is carried out of the system by electrical lines
- The steam within the turbine will cool and condense and then be pumped back into the boiler to repeat the process
Diagram of a Fossil fuel based Reactor. The overall purpose of the reactor is to collect the heat energy produced from burning fossil fuels
- The approximate efficiency of fossil-fuel based power plants is approximately 40%
- Energy is lost to heat within exhaust gases, heat loss in the condenser process and friction within the system
Advantages & Disadvantages of Fossil Fuels
- Advantages of using fossil fuel based power plants include:
- Extensive infrastructure in place
- High energy density of fuel
- Available energy at any time
- Well-known and developed technology
- Disadvantages of using fossil fuel based power plants include:
- Produces greenhouse gases
- Unsustainable (non-renewable)
- Produces pollution
Wind Electricity Generators
- Wind generators can be principally horizontally or vertically aligned
- The majority of modern designs use horizontally aligned designs
The two main designs of wind generators: horizontal and vertical alignment
- The approximate efficiency of wind generators is approximately 30%
- Energy is lost to aerodynamic limits, losses transferring the electricity to the grid and friction within the system
Advantages & Disadvantages of Wind Power
- Advantages of using wind-powered generators include:
- Clean (non-polluting) energy generation
- Freely available
- Is always sustainable and will never run out
- Disadvantages of using wind-powered generators include:
- Not consistent energy production
- Needs favourable local conditions to be placed in windy locations
- Can be visually unappealing
Hydroelectric Power
- Hydroelectric power using water stored at a height h, that mass of water m, is allowed to flow through turbines being pulled down by the acceleration due to gravity g
- The falling water has stored gravitational potential energy which is released when falling and used to spin turbines that generate electricity
- Energy can be stored for later use by pumping water back up to a higher location to be released to a lower location and spinning the turbines again when needed
- The approximate efficiency of hydroelectric power generation is approximately 90%
- Energy is lost to friction and other resistive forces
- The approximate maximum power that can be generated from a hydroelectric generator can be estimated by considering the rate of change of potential energy of the water falling through the turbines
A hydroelectric power generation station. In off-peak hours water can be pumped back to the higher reservoir.
Advantages & Disadvantages of Hydroelectric Power
- Advantages of using hydroelectric generators include:
- Clean (non-polluting) energy generation
- Is sustainable
- Can be stored for when needed
- Disadvantages of using hydroelectric generators include:
- Large areas and changes to the environment are needed
- It relies on suitable locations
- A large initial investment is required