AQA GCSE Physics 4.1 Β· Year 10 Β· Foundation & Higher
Renewable Energy Sources
Solar, wind, hydroelectric, tidal, geothermal and biomass β advantages, disadvantages and reliability
π Describe how solar panels and solar cells transfer energy from the Sun into useful forms
π¨ Explain how wind turbines generate electricity and identify their limitations
π§ Describe hydroelectric and tidal power stations and compare their reliability
π Explain how geothermal energy is extracted and where it can be used
πΏ Describe how biomass stores energy and the environmental considerations involved
βοΈ Compare renewable sources using advantages, disadvantages and reliability to evaluate energy choices
βοΈ Solar Energy
Renewable energy source: A source of energy that will not run out because it is continuously replenished by natural processes.
Solar energy harnesses energy transferred by electromagnetic radiation from the Sun. There are two main technologies:
Solar cells (photovoltaic cells): Absorb light and directly convert it into electrical energy. Used in calculators, satellites, and solar farms.
Solar panels (thermal collectors): Absorb light and transfer thermal energy to water flowing through pipes, providing hot water for homes.
Useful energy output (J) = Efficiency Γ Total energy input (J)
Solar cells transfer light energy β electrical energy. Solar thermal panels transfer light energy β thermal energy.
Advantages:
No fuel costs once installed
No greenhouse gas emissions during operation
Low maintenance β no moving parts in solar cells
Can be used in remote locations
Disadvantages:
Only generates electricity during daylight β unreliable at night or in cloudy weather
High initial installation cost
Large land area needed for solar farms
Energy storage (batteries) required to cover periods without sunlight
Reliability: Intermittent β output depends on time of day, season, cloud cover and latitude. The UK receives relatively low solar irradiance compared to equatorial regions, making solar less reliable here than in sunnier countries.
Property
Value / Note
Energy source
Electromagnetic radiation from Sun
Output type
Electrical (cells) / Thermal (panels)
COβ emissions (operation)
Zero
Reliability
Intermittent (weather/day dependent)
π¨ Wind Energy
Wind turbines convert the kinetic energy of moving air into electrical energy. Wind causes turbine blades to rotate, which drives a generator.
Kinetic energy (J) = Β½ Γ m Γ vΒ²
The power output of a wind turbine is strongly dependent on wind speed β doubling wind speed gives eight times the power (since P β vΒ³). This makes wind energy highly variable.
Onshore wind farms are cheaper to build and maintain. Offshore wind farms benefit from stronger, more consistent winds but are more expensive to construct and maintain.
Advantages:
No fuel costs and zero operational emissions
Can coexist with farmland (onshore)
Technology is well established and improving rapidly
UK has one of the best wind resources in Europe
Disadvantages:
Intermittent β no electricity generated in calm conditions
Visual impact on landscape; noise pollution
Can harm birds and bats
Offshore maintenance is expensive and challenging
Backup generation or storage needed for calm periods
Reliability: Intermittent. Wind speed is unpredictable, though offshore winds tend to be more consistent. A fleet of turbines spread geographically reduces variability across the national grid.
Power β vΒ³ β small increases in wind speed produce large increases in power output.
π§ Hydroelectric & Tidal Power
Hydroelectric Power (HEP)
Water stored in a high reservoir has gravitational potential energy. When released, it flows downhill through turbines, converting gravitational potential energy β kinetic energy β electrical energy.
Gravitational potential energy: Ep = m Γ g Γ h
where g = 10 N/kg, h = height (m)
Advantages: Highly reliable and controllable β output can be increased or decreased almost instantly by adjusting flow. Can act as a large-scale energy store (pumped-storage). Zero operational emissions.
Disadvantages: Requires flooding valleys, which destroys habitats and displaces communities. High construction costs. Dependent on sufficient rainfall (long-term droughts reduce output).
Tidal Power
Tidal barrages trap water at high tide and release it at low tide through turbines. Tidal stream generators use underwater turbines in tidal currents.
Advantages: Highly predictable β tides are governed by the Moon's gravity, making timing and magnitude known years in advance. Zero fuel costs and emissions.
Disadvantages: Very high construction costs. Disrupts estuarine ecosystems. Only generates electricity during tidal flow (~10 hours per day for a barrage). Limited to coastal locations with large tidal ranges.
HEP is highly reliable and dispatchable. Tidal is predictable but only generates during tidal flow. Both are far more reliable than solar or wind.
Source
Reliability
Controllable?
Hydroelectric
High (rainfall dependent)
Yes β instantly
Tidal
Predictable but intermittent
Partly
Wind
Intermittent
No
Solar
Intermittent
No
π Geothermal Energy
Geothermal energy comes from heat stored inside the Earth. This heat originates from two sources: the residual heat from Earth's formation and the decay of radioactive isotopes in rocks.
In geothermal power stations, cold water is pumped deep underground, heated by hot rocks, and returns as steam. The steam drives a turbine connected to a generator.
Energy transferred = m Γ c Γ ΞT
where c = specific heat capacity (J/kgΒ°C), ΞT = temperature change (Β°C)
Advantages:
Continuous, reliable output β not weather dependent
Very low carbon emissions during operation
Small surface footprint compared to wind or solar farms
Can also provide direct heating for homes and industry
Disadvantages:
Only economically viable in volcanically active regions (Iceland, New Zealand, parts of USA)
High drilling costs
Can release trapped gases (HβS) from underground
Risk of inducing minor earthquakes (induced seismicity)
Reliability: Excellent β geothermal provides a constant baseload. It is one of the most reliable renewable sources available. However, its use in the UK is very limited due to the geology not being favourable (though deep geothermal projects exist in Cornwall).
Geothermal energy ultimately comes from radioactive decay within the Earth β making it a long-term, reliable but geographically limited resource.
πΏ Biomass Energy
Biomass refers to biological material (wood, crops, animal waste) that stores chemical energy originally transferred from the Sun via photosynthesis. Burning biomass releases this energy as heat, which can generate steam to drive turbines.
Chemical energy (fuel) β Thermal energy β Kinetic energy β Electrical energy
Biomass can also be converted into biogas (methane-rich gas from decomposing organic matter) or biofuels for transport.
Advantages:
Can be used on demand β controllable and dispatchable, unlike solar or wind
Carbon neutral in theory: COβ released equals COβ absorbed during plant growth
Can use waste materials (agricultural residues, food waste)
Compatible with existing power station infrastructure
Disadvantages:
Not truly carbon neutral: energy used in growing, harvesting and transporting biomass adds emissions
Land use conflicts β growing energy crops may displace food production or natural habitats
Air pollution from combustion (particulates, NOβ, SOβ)
Deforestation risk if not sustainably managed
Reliability: High β biomass fuel can be stored and burned when needed, giving it an advantage over intermittent renewables. However, sustainability depends on responsible land management.
Biomass is dispatchable (controllable output) but its environmental credentials depend heavily on how it is produced and sourced.
Renewable Source
Energy Transfer
Reliability
Dispatchable?
Solar
Light β Electrical/Thermal
Low (intermittent)
No
Wind
Kinetic β Electrical
LowβMedium
No
Hydroelectric
GPE β KE β Electrical
High
Yes
Tidal
KE β Electrical
Medium (predictable)
Partly
Geothermal
Thermal β KE β Electrical
Very High
Yes
Biomass
Chemical β Thermal β Electrical
High
Yes
Example 1 β Efficiency of a Solar Cell A solar cell receives 500 J of light energy from the Sun. It transfers 75 J as useful electrical energy. Calculate the efficiency of the solar cell and suggest what happens to the remaining energy.
1Write the efficiency equation: Efficiency = (Useful energy output Γ· Total energy input) Γ 100%
4Account for remaining energy: Remaining = 500 β 75 = 425 J This is dissipated as thermal energy (heating the solar cell) and reflected light β wasted to the surroundings.
Efficiency = 15%. The remaining 425 J is wasted as thermal energy and reflected light.
Example 2 β Gravitational Potential Energy in Hydroelectric Power A hydroelectric reservoir holds water at a height of 80 m above the turbines. Calculate the gravitational potential energy stored in 5000 kg of water. (g = 10 N/kg)
1Write the equation: Ep = m Γ g Γ h
2Identify values: m = 5000 kg, g = 10 N/kg, h = 80 m
3Calculate: Ep = 5000 Γ 10 Γ 80
4Ep = 4 000 000 J = 4 MJ
Gravitational potential energy = 4 000 000 J (4 MJ)
Example 3 β Comparing Renewable Sources A town needs a reliable electricity supply year-round. Evaluate whether solar power or hydroelectric power is the better choice, giving reasons based on reliability and controllability.
1Consider solar power: Solar is intermittent β only generates during daylight and when skies are clear. Output drops to zero at night and is significantly reduced in winter, especially in the UK. Solar cannot be controlled β you cannot increase output on demand.
2Consider hydroelectric power: Hydroelectric is highly reliable β water stored in reservoirs can be released at any time. Output is controllable and can respond to demand within seconds. The only limitation is prolonged drought reducing reservoir levels.
3Evaluate for a year-round reliable supply: Hydroelectric is far better suited to providing a reliable, year-round supply because it is dispatchable. Solar would require large and expensive battery storage systems to bridge overnight and winter gaps.
Hydroelectric power is the better choice for year-round reliability because it is controllable and dispatchable. Solar is intermittent and cannot meet demand at night or during prolonged overcast periods without costly storage.
Example 4 β Biomass Carbon Neutrality A student claims that burning wood chip biomass is carbon neutral. Explain why this claim may not be entirely accurate, referring to the carbon cycle.
1Explain the carbon neutral argument: Plants absorb COβ from the atmosphere during photosynthesis, storing carbon in their biomass. When burned, this carbon is released back as COβ. In theory, the COβ released equals the COβ previously absorbed, making it carbon neutral.
2Identify reasons the claim is not fully accurate: Growing, harvesting, processing and transporting biomass all require energy, often from fossil fuels, releasing additional COβ. This means the total carbon footprint exceeds the COβ re-absorbed by new plant growth.
3Consider time scales: A tree may take 50β100 years to re-absorb the COβ released when it is burned. In the short term, burning biomass adds net COβ to the atmosphere.
4Consider land use: If forests are cleared and not replanted, the carbon sink is permanently lost, making it far from carbon neutral.
Biomass is only approximately carbon neutral if new plants replace those burned at the same rate. Emissions from transport, harvesting and processing, plus time lags in carbon reabsorption, mean it is not truly carbon neutral in practice.
Question 1. Which of the following renewable energy sources is MOST reliable and can be dispatched on demand?
Question 2. A wind turbine generates 200 J of electrical energy from 800 J of kinetic energy in the wind. What is its efficiency?
Question 3. Which statement about tidal power is correct?
Question 4. Calculate the gravitational potential energy stored in 2000 kg of water at a height of 50 m above a turbine. (g = 10 N/kg)
Question 5. Which of the following is a disadvantage of geothermal energy?
Challenge 1 β Extended Calculation A hydroelectric power station has a reservoir containing 2 Γ 10β· kg of water at a height of 120 m above the turbines. The turbines have an efficiency of 80%. (a) Calculate the total gravitational potential energy stored in the reservoir. (g = 10 N/kg) (b) Calculate the useful electrical energy output if all the water flows through the turbines.
(a) Ep = m Γ g Γ h = 2 Γ 10β· Γ 10 Γ 120 = 2.4 Γ 10ΒΉβ° J
(b) Useful output = Efficiency Γ Input = 0.80 Γ 2.4 Γ 10ΒΉβ° = 1.92 Γ 10ΒΉβ° J
Challenge 2 β Evaluation Question A coastal town is considering building either an offshore wind farm or a tidal barrage to supply electricity. The town needs a consistent electricity supply. Evaluate both options, considering reliability, environmental impact and cost. Conclude which is the more suitable choice for this town. (6 marks)
Offshore wind: Generates electricity when wind blows β intermittent, unpredictable. Strong offshore winds give reasonable capacity factor. Zero operational emissions. High construction and maintenance cost offshore. Can affect seabirds. Requires backup or storage for calm periods.
Tidal barrage: Predictable output β tides known years in advance. However, only generates ~10 hours/day as water flows through turbines. Very high construction cost. Significant disruption to estuary ecosystem (fish migration, mudflat habitats). Zero operational emissions. Long operational lifespan.
Conclusion: For a town needing consistent supply, the tidal barrage offers more predictability β energy output times are known in advance and can be planned around. However, the environmental impact on the estuary and very high cost are serious concerns. A balanced answer may conclude that offshore wind combined with grid storage is better overall, or that the tidal barrage is preferred if the tidal range is large enough to justify cost, with appropriate mitigation for ecosystem impact. Credit any well-reasoned conclusion supported by evidence.
Challenge 3 β Biomass Calculation A biomass power station burns 500 kg of wood. The wood releases 9000 J/kg of energy. The station operates at 35% efficiency. (a) Calculate the total energy released by burning the wood. (b) Calculate the useful electrical energy output. (c) State one reason why biomass is described as 'approximately' but not 'truly' carbon neutral.
(a) Total energy = 500 Γ 9000 = 4 500 000 J = 4.5 MJ
(b) Useful electrical energy = 0.35 Γ 4 500 000 = 1 575 000 J = 1.575 MJ
(c) Any one of: fossil fuels are used in harvesting/transporting biomass adding extra COβ; newly planted trees take many years to reabsorb the COβ released; land may not be replanted, permanently removing the carbon sink.
Challenge 4 β Comparing All Sources The table below shows data for four renewable energy sources. Use the data to answer the questions.
Source
Capacity Factor (%)
COβ (g/kWh)
Cost per kWh (p)
Solar
11
20
5
Wind (offshore)
40
7
8
Hydroelectric
45
4
6
Biomass
80
230
9
(a) Which source has the highest capacity factor? What does this tell you about its reliability?
(b) Despite being renewable, which source produces the most COβ per kWh? Explain why.
(c) Suggest why solar has the lowest capacity factor in the UK.
(a) Biomass has the highest capacity factor (80%). This means it generates electricity 80% of the time at full capacity β making it the most reliable source in the table, as it can be controlled and operated on demand.
(b) Biomass produces the most COβ (230 g/kWh). Although the plants absorb COβ when growing, burning releases it quickly. Additional emissions from harvesting, processing and transporting the fuel add to the total. It is therefore not truly carbon neutral in practice.
(c) The UK has limited hours of strong sunlight β particularly in winter when days are short and the Sun is low in the sky. Frequent cloud cover further reduces output, giving solar a very low capacity factor of around 11% in the UK.