Hydroelectric Power

OCR

GCSE

Hydroelectric power systems harness the gravitational potential energy of water stored at elevation, converting it into kinetic energy to drive turbines and electrical generators. This renewable energy source is critical for grid stability due to its rapid start-up time and ability to function as a pumped storage system for load balancing. Candidates must demonstrate proficiency in calculating energy transfers using standard formulae, analyzing efficiency losses, and evaluating the socio-environmental impacts of reservoir construction, including habitat displacement and carbon footprints associated with infrastructure.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

What You Need to Demonstrate

Key skills and knowledge for this topic

Award 1 mark for identifying the initial energy store as Gravitational Potential Energy (GPE) of water at height
Credit responses that describe the transfer pathway: GPE → Kinetic Energy (water/turbine) → Kinetic Energy (generator) → Electrical Energy
Award 1 mark for explaining pumped storage: water is pumped to a higher reservoir during periods of low demand/excess electricity
Credit specific environmental impacts such as 'flooding of valleys', 'release of methane from rotting vegetation', or 'disruption of aquatic habitats'
Award 1 mark for stating that hydroelectric stations have a short start-up time allowing them to meet surges in demand

Example Examiner Feedback

Real feedback patterns examiners use when marking

"You correctly identified the renewable nature, but you must specify 'no carbon emissions' rather than just 'no pollution'"
"Good calculation of energy, but remember to divide by time in seconds to find the Power in Watts"
"You mentioned it is expensive—clarify whether you mean building the dam (expensive) or running it (cheap)"
"Excellent description of the energy transfer; to improve, explicitly mention the kinetic energy of the turbine blades"

Marking Points

Key points examiners look for in your answers

Award 1 mark for identifying the initial energy store as Gravitational Potential Energy (GPE) of water at height
Credit responses that describe the transfer pathway: GPE → Kinetic Energy (water/turbine) → Kinetic Energy (generator) → Electrical Energy
Award 1 mark for explaining pumped storage: water is pumped to a higher reservoir during periods of low demand/excess electricity
Credit specific environmental impacts such as 'flooding of valleys', 'release of methane from rotting vegetation', or 'disruption of aquatic habitats'
Award 1 mark for stating that hydroelectric stations have a short start-up time allowing them to meet surges in demand

Examiner Tips

Expert advice for maximising your marks

💡When asked about 'pumped storage', focus on the timing: water is pumped up when demand is low (and electricity is cheap) and released when demand is high
💡Use precise terminology for costs: distinguish between 'high capital/commissioning costs' and 'low running/marginal costs'
💡In calculation questions involving dams, you may need to calculate the mass of water using Density = Mass/Volume before using E = mgh

Common Mistakes

Pitfalls to avoid in your exam answers

Stating that hydroelectric power is 'free' without clarifying that this refers to zero fuel costs, not zero capital/construction costs
Failing to mention the intermediate Kinetic Energy store of the turbine when describing the energy transfer sequence
Confusing reliability with renewability; students often argue it is reliable 'because it is renewable', rather than because it can be controlled unlike wind or solar
neglecting to convert time from minutes or hours into seconds when calculating Power (P = E/t)

Key Terminology

Essential terms to know

Energy transfers (GPE to Kinetic to Electrical)

Pumped storage and grid load balancing

Renewability and reliability factors

Environmental and geographical impact analysis

Likely Command Words

How questions on this topic are typically asked

State

Describe

Explain

Calculate

Evaluate

Compare

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