P8.2 - Energy Resources and power transmission

What is an energy resource?

A large store of energy that can be used to generate electricity and heat homes and businesses

How is electricity generated from any energy resource?

A turbine is turned which spins a generator to generate electricity

How do fossil fuels generate electricity?

Fossil fuels are combusted to heat water → steam produced → steam turns turbine → turbine spins generator → electricity transferred to National Grid [DRAW: fuel → boiler → steam → turbine → generator → grid]

How does nuclear fuel generate electricity?

Nuclear fission heats water → steam turns turbine → generator produces electricity; same process as fossil fuels but no combustion

How does geothermal energy generate electricity?

Hot rocks underground heat water → steam turns turbine → generator produces electricity; cold water pumped down and returns as steam

How does hydroelectric power generate electricity?

Water stored at height in a reservoir; gravitational PE converted to KE as water falls → turns turbine → generator produces electricity [DRAW: reservoir → pipe → turbine → generator]

How does wind generate electricity?

Wind turns wind turbines directly to generate electricity; no steam or water needed

How do tidal generators work?

Movement of water due to tides turns turbines directly to generate electricity

How do water waves generate electricity?

Moving water from waves turns turbines directly to generate electricity

How does solar generate electricity?

Solar cells use light to generate electricity directly; solar panels use thermal radiation to heat water for domestic use

What is a renewable energy resource?

An energy source replenished at a faster rate than it is being used — it will not run out

Examples of renewable energy resources

Wind; solar; tidal; hydroelectric; bio-fuel; geothermal; water waves

What is a non-renewable energy resource?

One that is used faster than it is replenished — it will eventually run out

Examples of non-renewable energy resources

Fossil fuels (coal, oil, natural gas); nuclear fuel

Three main uses of energy resources

Transport; electricity generation; heating

How is transport mostly powered?

Majority of vehicles run on petroleum products (petrol, diesel, kerosene) — fossil fuels; a growing number of vehicles are now powered by electricity

Advantage of electric vehicles

Produce no carbon emissions at point of use; can use renewable energy sources to charge

Disadvantage of electric vehicles

When charging it is connected to the National Grid which is currently a mix of renewable and non-renewable sources; charging takes time

Can vehicles be powered by biofuel?

Yes — biofuel is a renewable resource; however whether biofuels are truly carbon neutral is controversial

How is heating provided in most homes?

Most homes in cold countries use central heating systems burning gas (non-renewable); some geothermally active countries (e.g. Iceland) can heat homes using geothermal energy

Advantages of fossil fuels

Reliable; can produce large amounts of energy on demand at any time; well-established technology

Disadvantages of fossil fuels

Produce significant greenhouse gases; polluting; non-renewable — will run out

Advantages of nuclear power

Reliable; produces no greenhouse gas emissions during operation; large amount of energy from small amount of fuel

Disadvantages of nuclear power

Produces radioactive waste that can take thousands of years to decay; very expensive to build and decommission

Advantages of bio-fuels

CO₂ produced when burned is absorbed by plants when growing so considered carbon neutral; renewable

Disadvantages of bio-fuels

Takes up a lot of land; requires resources (water, fertiliser) that are needed for food production

Advantages of wind power

Produces no greenhouse gases during operation; renewable; relatively cheap to run

Disadvantages of wind power

Not reliable — depends on wind; turbines can be noisy and unsightly; cannot produce energy on demand

Advantages of hydroelectric power

Reliable; can produce large amounts of energy quickly; can start quickly to meet demand; no greenhouse gas emissions during operation

Disadvantages of hydroelectric power

Constructing flooding can displace people and wildlife; damages habitats; limited suitable locations

Advantages of tidal power

Reliable and predictable (tides are consistent); no greenhouse gas emissions; renewable

Disadvantages of tidal power

Very few suitable locations; expensive to build; environmental harm to aquatic habitats

Advantages of geothermal energy

Reliable; no greenhouse gas emissions; energy available around the clock; renewable

Disadvantages of geothermal energy

Limited to regions with volcanic activity; expensive to drill; not widely available

Advantages of solar power

No greenhouse gas emissions during operation; renewable; good for producing energy to return to National Grid

Disadvantages of solar power

Not reliable — only works when sunny; solar farms can take up lots of land; cannot produce energy on demand at night

What is the Greenhouse Effect?

Global warming caused by increased concentration of greenhouse gases (mainly CO₂ and methane) in the atmosphere trapping heat [DRAW: sun rays hitting Earth → some infrared reflected back → greenhouse gases trap infrared → Earth warms]

How does the Greenhouse Effect work step by step?

Sun emits radiation → Earth absorbs and re-emits as infrared → greenhouse gases in atmosphere absorb infrared → re-emit it back toward Earth → Earth's average temperature rises; higher concentration of greenhouse gases = higher average temperature

Main greenhouse gases

Carbon dioxide (CO₂) — from burning fossil fuels; methane (CH₄) — from livestock and landfill

Consequences of global warming

Rising sea levels (melting ice caps) flooding low-lying countries; extinction of species due to habitat loss; migration of humans from uninhabitable areas; spread of disease in warmer climates; loss of habitat (e.g. glaciers melting)

Trends in UK energy use over past 30 years

Fossil fuel use dropped from 75% to 55%; renewable energy use increased from 2% to 35%; coal use has dropped dramatically and been replaced largely by natural gas

Why has coal been replaced by natural gas?

Out of the 3 fossil fuels, coal produces the most carbon dioxide while natural gas produces the least; gas is not a solution but is a step in the right direction

What balanced approach is needed to reduce carbon emissions?

Combination of carbon-neutral energy technologies + public support + government policy; more nuclear power stations; new generation of nuclear power stations in development; moving away from coal; political, social, ethical and economic considerations all involved

What is the National Grid?

A system of cables and transformers linking power stations to consumers (houses, factories and buildings) across the UK

What two types of transformer does the National Grid use?

Step-up transformers which increase the voltage and decrease the current for transmission; step-down transformers which decrease the voltage and increase the current for domestic use [DRAW: power station → step-up transformer → transmission lines → step-down transformer → homes]

Why is electricity transmitted at high voltage across the National Grid?

High voltage means lower current for the same power (P = VI); lower current means less energy lost as heat in the cables → more efficient transmission

Relationship between current and energy loss in cables

Lower current → less heating effect in cables → less energy wasted; this is why high voltage/low current is used for transmission

What is direct current (DC)?

Current that flows continuously in one direction only; potential difference across circuit is fixed positive or negative; produced by cells and batteries

What is alternating current (AC)?

Current that constantly changes direction, going back and forth around a circuit; potential difference alternates between positive and negative

UK mains electricity frequency and potential difference

Frequency: 50 Hz; potential difference: 230 V

What graph shape represents DC?

Flat horizontal line (constant current in one direction) [DRAW: current vs time graph — flat straight line]

What graph shape represents AC?

Sinusoidal wave (current alternates between positive and negative) [DRAW: current vs time graph — sine wave oscillating above and below zero]

What are the three wires in a mains cable?

Live wire (brown); neutral wire (blue); earth wire (green and yellow stripes)

Function of the live wire

Carries alternating potential difference from the supply (230 V); most dangerous wire — can cause electrocution even if not directly touching it

Function of the neutral wire

Completes the circuit; at approximately 0 V; much less dangerous than the live wire

Function of the earth wire

Safety wire — only carries current if appliance develops a fault; provides low resistance path to earth; large current flows → blows fuse → cuts off electricity supply → appliance safe to touch

Voltages of the three wires

Live: 230 V; Neutral: 0 V; Earth: 0 V (only carries current in a fault)

Why is the live wire dangerous even when a switch is open?

It is always at 230 V relative to earth; touching it completes a circuit through your body to earth even when device is off

Why is the earth wire a safety device?

If a fault connects the live wire to the metal casing → current flows through earth wire → very large current → blows fuse → electricity cut off → safe to touch

What is a transformer?

A device that changes the potential difference (voltage) of an alternating current electricity supply

Structure of a transformer

Primary coil + secondary coil wound around an iron core; iron core is easily magnetised [DRAW: transformer diagram — primary coil, iron core, secondary coil]

How does a transformer work?

AC in primary coil → continuously changing current → changing magnetic field in iron core → changing magnetic field cuts through secondary coil → induces alternating potential difference in secondary coil → AC flows if circuit is complete

What is a step-up transformer?

Has more turns on the secondary coil than primary; increases voltage and decreases current; used at power stations before National Grid transmission

What is a step-down transformer?

Has more turns on the primary coil than secondary; decreases voltage and increases current; used before electricity reaches homes (e.g. 230 V for domestic use)

Transformer equation (turns ratio)

Vₚ/Vₛ = nₚ/nₛ where Vₚ = primary voltage, Vₛ = secondary voltage, nₚ = primary turns, nₛ = secondary turns

Transformer equation (ideal — power in = power out)

Vₚ × Iₚ = Vₛ × Iₛ where I = current; an ideal transformer is 100% efficient

Why are real transformers not 100% efficient?

Due to the law of conservation of energy — some energy is always lost (e.g. as heat in coils); they can increase voltage but cannot increase power output

Why does a step-up transformer increase efficiency of the National Grid?

Increases voltage → decreases current → less energy lost as heat in transmission cables → more energy reaches consumers