Generating Electricity
This lesson covers how electricity is generated from different energy resources, and how it is distributed through the National Grid, as required by the Edexcel GCSE Physics specification (1PH0), Topic 3: Conservation of Energy. You need to understand the basic principles of generators, how different power stations work, and why transformers are used.
The Basic Principle: Generators
Most power stations — whether they use fossil fuels, nuclear fuel, or renewable sources — generate electricity using the same basic principle:
A generator converts kinetic energy into electrical energy by rotating a coil of wire (or a magnet) inside a magnetic field. This changing magnetic field induces (creates) a voltage across the coil.
You do not need to know the details of electromagnetic induction at this stage, but you should understand the basic idea:
- A magnet or coil of wire rotates.
- This creates a changing magnetic field.
- The changing magnetic field induces a voltage (and therefore a current if the circuit is complete).
How a Fossil Fuel Power Station Works
The majority of electricity is still generated in power stations that burn fossil fuels. The energy transfer chain is:
flowchart LR
A["Chemical Store\n(fuel)"] -->|"Burning"| B["Thermal Store\n(steam)"]
B -->|"Steam turns turbine"| C["Kinetic Store\n(turbine)"]
C -->|"Turbine drives generator"| D["Electrical energy\n(to National Grid)"]
Step by Step
- Fuel is burned in a furnace → releases thermal energy (from the chemical store of the fuel).
- Thermal energy heats water in a boiler → water turns to high-pressure steam.
- Steam flows over the blades of a turbine → turbine rotates (thermal → kinetic energy).
- The turbine is connected to a generator → generator converts kinetic energy to electrical energy.
- Electricity is sent to the National Grid for distribution.
- Steam is cooled in cooling towers → condenses back to water → recycled to the boiler.
Efficiency
- A typical fossil fuel power station is about 35–40% efficient.
- The main energy losses are through the cooling towers (waste thermal energy) and friction in the turbines.
Nuclear Power Stations
Nuclear power stations work on the same principle, but the heat comes from nuclear fission rather than burning fuel.
How Nuclear Fission Works (Simplified)
- Atoms of uranium-235 (or plutonium-239) are split apart in a controlled chain reaction.
- Each fission event releases a large amount of thermal energy.
- This thermal energy heats water to produce steam.
- From this point, the process is the same as a fossil fuel station: steam → turbine → generator → electricity.
Key Differences from Fossil Fuel Stations
| Feature | Fossil Fuel Station | Nuclear Station |
|---|
| Energy source | Chemical (burning fuel) | Nuclear (fission) |
| CO₂ emissions | High | Very low (during operation) |
| Waste | CO₂, SO₂, particulates | Radioactive waste |
| Fuel amount needed | Large | Very small (high energy density) |
| Response time | Fast (gas), moderate (coal) | Slow (takes time to start/stop) |
Renewable Electricity Generation
Wind Turbines
- The wind turns the blades of the turbine.
- The blades are connected to a generator via a gearbox.
- The generator converts kinetic energy of the blades into electrical energy.
- Energy chain: kinetic store (wind) → kinetic store (blades) → electrical energy.
Solar Panels (Photovoltaic Cells)
- Solar panels do not use turbines or generators.
- Photovoltaic (PV) cells convert light energy directly into electrical energy.
- Each cell produces a small voltage — many cells are connected together to form a panel.
- Energy chain: radiation (light from the Sun) → electrical energy.
Hydroelectric Power
- Water is stored behind a dam at height — it has gravitational potential energy.
- Water is allowed to flow downhill through pipes.
- The flowing water turns a turbine at the bottom, which drives a generator.
- Energy chain: gravitational potential store → kinetic store (water) → kinetic store (turbine) → electrical energy.
- Pumped storage: during times of low demand, electricity is used to pump water back up to the reservoir. During peak demand, the water is released to generate electricity quickly.
Tidal Power
- A tidal barrage (dam) is built across an estuary.
- As the tide comes in and goes out, water flows through turbines in the barrage.
- The turbines drive generators.
- Energy chain: kinetic store (tidal water) → kinetic store (turbine) → electrical energy.
Geothermal Power
- In volcanic regions, heat from the Earth's interior is close to the surface.
- Water is pumped down into hot underground rocks.
- The water turns to steam and rises to the surface.
- The steam turns turbines → generators → electricity.
- Energy chain: thermal store (underground rocks) → kinetic store (steam/turbine) → electrical energy.
The National Grid
The National Grid is the system of cables, pylons, and transformers that distributes electricity from power stations to homes and businesses across the UK.
Why We Need Transformers
Electricity is transmitted at very high voltages (up to 400,000 V) through the National Grid. This is because:
P=I×V
For a given power (P), increasing the voltage (V) means the current (I) is reduced.
Why does reducing the current matter?
Energy is lost as heat in the cables. The power lost is given by:
Plost=I2R
Where R is the resistance of the cables. By reducing the current, the power lost as heat is greatly reduced (because of the I² relationship).
Step-Up and Step-Down Transformers
| Transformer | What It Does | Where It Is Used |
|---|
| Step-up transformer | Increases voltage (decreases current) | At the power station — steps voltage up to 400,000 V for transmission |
| Step-down transformer | Decreases voltage (increases current) | Near homes/businesses — steps voltage down to 230 V for safe domestic use |
flowchart LR
A["Power Station\n25,000 V"] -->|"Step-up\ntransformer"| B["National Grid\n400,000 V"]
B -->|"Step-down\ntransformer"| C["Homes\n230 V"]
Key Points About the National Grid
- High voltage + low current = less energy lost as heat in the cables.
- The cables still have some resistance, so there is always some energy loss.
- Thicker cables have lower resistance and reduce energy loss further, but they are heavier and more expensive.
- The system is a compromise between efficiency, cost, and safety.