🌱 Final Exam Revision

Green Energy
Study Hub

Master every section — from solar panels to nuclear reactors — with flip cards and self-testing MCQs.

7
Topics
60+
Flip Cards
56
MCQs
Developed by tutor Warren Tam

What Is Green Energy?

Energy sources that generate power with little or no environmental damage — especially low greenhouse gas emissions and minimal pollution.

☀️
Solar
Sunlight → Electricity / Heat
💨
Wind
Kinetic air energy → Electricity
💧
Hydro
Moving water → Electricity (≥85% efficient)
🌋
Geothermal
Earth's heat → Electricity / Heating
🌿
Biomass
Organic matter → Heat / Power
⚛️
Nuclear
~12 g CO₂/kWh (like wind)
🏠
Heat Pumps
COP 2.5–4.5 × more efficient

Test Your Foundations

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☀️ Solar Energy

Energy from sunlight converted into electricity (PV) or heat (solar thermal). Panels use the photoelectric effect to move electrons through silicon semiconductors.

Key Concepts — Click to Flip
🔆
Photovoltaic (PV)
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Solar
Converts sunlight directly into DC electricity when photons strike a semiconductor (usually silicon) and displace electrons, creating a current.
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Inverter
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Solar
Converts DC electricity (from panels) into AC electricity required for household appliances and grid connection.
🪞
CSP — Concentrated Solar Power
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Solar
Uses mirrors (heliostats or parabolic troughs) to focus sunlight, producing heat (400–1000°C) to create steam and drive turbines.
🧂
Molten Salt Storage
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CSP
CSP plants store thermal energy in hot molten salt tanks, enabling electricity generation hours after sunset — unlike PV panels.
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Net Metering
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Grid
System by which households export surplus solar electricity back to the grid, receiving credit or payment in return.
📊
Typical Panel Efficiency
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Performance
Residential solar panels convert about 15–23% of incident sunlight into electricity. High heat actually reduces efficiency.
Solar MCQs
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💨 Wind Energy

Converts kinetic energy of moving air into electricity via turbines. Think of a wind turbine as a fan in reverse — wind moves the blades to make electricity.

Key Concepts — Click to Flip
🌀
HAWT
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Wind
Horizontal-Axis Wind Turbine — blades spin around a horizontal axis, facing directly into the wind. Most efficient and common design worldwide. Requires yaw system to track wind direction.
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VAWT
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Wind
Vertical-Axis Wind Turbine — rotor spins around a vertical shaft, accepting wind from any direction. Better for urban/turbulent conditions, easier maintenance.
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Offshore Wind
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Wind
Turbines installed in seas/oceans. Stronger, more consistent winds than onshore. Types: fixed-bottom (shallow) and floating (deep water). Less visual conflict.
⚙️
Nacelle
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Wind
Housing at the top of a wind turbine tower containing the generator and gearbox — the main mechanical and electrical components that convert rotational energy to electricity.
💧
Wind Pumping
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Applications
Mechanical use of wind energy to pump water for agriculture and irrigation. Traditional windmills use this principle. Can lift hundreds of litres per hour.
🔀
Wind-Solar Hybrid
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Emerging
Combined wind and solar farms increase overall energy efficiency and reliability, as wind is often stronger at night/winter when solar is weak.
Wind MCQs
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💧 Hydropower

Electricity from moving water. Water at height has potential energy; as it flows downward it becomes kinetic energy, spinning turbines. Often above 85% efficient.

Hydropower Formula

P = ρ g h Q

P = Power (W)  |  ρ = Water density (1000 kg/m³)  |  g = 9.81 m/s²  |  h = Head height (m)  |  Q = Flow rate (m³/s)

Key Concepts — Click to Flip
🏗️
Reservoir (Dam) Hydropower
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Hydro
Water stored behind a dam is released in a controlled way to spin turbines. Uses gravitational potential energy P=ρghQ. Reliable and can meet peak demand.
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Run-of-River
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Hydro
Uses natural river flow with minimal storage. Lower head height so depends on flow rate. Smaller environmental impact but output varies with seasons and rainfall.
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Pumped Storage
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Hydro
Two reservoirs at different heights. Excess grid electricity pumps water uphill. Water released later generates electricity. Mainly energy storage, not a primary source.
🌊
Tidal Hydropower
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Hydro
Driven by gravitational forces of Moon and Sun. Types: Tidal barrage (dam across estuary) and tidal stream (underwater turbines). Extremely predictable output.
🏡
Micro/Pico Hydro
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Hydro
Small-scale: micro up to 100 kW, pico under 5 kW. Used for remote homes and off-grid communities. Minimal environmental footprint.
⬆️
Head Height (h)
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Physics
Vertical distance between reservoir surface and turbine. Higher head → more potential energy E=mgh → more power. Taller dams produce significantly more power.
Hydro MCQs
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🌋 Geothermal Energy

Heat from inside the Earth — from radioactive decay, magma movement, and leftover planetary heat. Works 24/7, unlike solar or wind.

Key Concepts — Click to Flip
💨
Dry Steam System
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Geothermal
Steam from underground reservoir is piped directly to drive turbines. Simplest and oldest type of geothermal system. Requires high-temperature steam reservoirs.
💦
Flash Steam System
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Geothermal
High-pressure hot water is brought to the surface and allowed to "flash" (rapidly vaporize) into steam to drive turbines. Most common geothermal power plant type.
🔁
Binary Cycle System
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Geothermal
Moderately hot water heats a secondary fluid with a lower boiling point (binary fluid) that vaporizes to drive the turbine. Works at lower temperatures.
🗺️
Ring of Fire
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Geography
Pacific tectonic plate boundary where volcanic/seismic activity brings heat close to surface. Countries: USA, Indonesia, Philippines, New Zealand, Japan use geothermal heavily.
🇮🇸
Iceland
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Geography
Geothermal heat supplies heating to almost 90% of Iceland's homes due to abundant volcanic activity. Exemplary model of geothermal utilisation.
🇬🇧
UK Geothermal
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UK Context
UK has limited geothermal electricity (far from plate boundaries). Instead, ground source heat pumps are common as shallow ground stays at stable temperature year-round.
Geothermal MCQs
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🌿 Biomass Energy

Energy from organic materials — plants, wood, agricultural waste, food scraps. Plants store solar energy via photosynthesis; biomass releases it.

Key Concepts — Click to Flip
🔥
Combustion
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Biomass Process
Biomass (wood chips, pellets) burned to produce heat → steam → turbines → electricity. Most common method. Used in district heating and power plants like Drax.
🦠
Anaerobic Digestion
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Biomass Process
Microorganisms break down organic waste without oxygen, producing biogas (mostly methane). Used on farms and wastewater plants. Methane can be burned for energy.
🌫️
Gasification
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Biomass Process
Biomass is heated with limited oxygen to produce "syngas" (synthetic gas) that can power engines or turbines. More efficient than simple combustion.
🏭
Drax Power Station
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UK
North Yorkshire — largest biomass plant in the UK. Originally a coal plant, converted to burn wood pellets. Generates a significant portion of UK biomass electricity.
📈
UK Biomass Share
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UK Stats
Biomass provides about 10–12% of UK total energy demand and ~14% of electricity generation. Second-largest renewable electricity source after wind in the UK.
🌾
Energy Crops
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Biomass Source
Fast-growing plants like switchgrass or willow grown specifically for biomass energy. Considered renewable if replanted sustainably and part of the carbon cycle.
Biomass MCQs
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⚛️ Nuclear Energy

Energy released by splitting heavy atomic nuclei (fission). ~12 g CO₂/kWh life-cycle — similar to wind — making it a low-carbon energy source.

Einstein's Mass-Energy Equivalence

E = mc²

Tiny mass converts into enormous energy during nuclear fission

Key Concepts — Click to Flip
💥
Nuclear Fission
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Nuclear
Splitting of a heavy nucleus (Uranium-235) when struck by a neutron. Produces energy, fission fragments (Barium, Krypton), and 2–3 new neutrons that continue the chain reaction.
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Control Rods
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Nuclear
Made of boron/cadmium — absorb neutrons to control the chain reaction rate. Inserting rods slows reaction; withdrawing increases it. SCRAM = rapid full insertion for emergency shutdown.
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Moderator
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Nuclear
Substance (water, heavy water, graphite) that slows fast neutrons to "thermal" speeds so they can be absorbed by Uranium-235. Also a safety feature — if water turns to steam, reaction slows (negative void coefficient).
🏗️
SMR
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Nuclear Types
Small Modular Reactor: 50–300+ MW, factory-built modules aiming for faster, cheaper, repeatable builds. Part of UK's Advanced Nuclear Framework alongside AMRs and MMRs (micro-nuclear).
🇬🇧
UK Nuclear Fleet
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UK
As of 2026: 5 operating sites with 9 reactors (8 AGR + 1 PWR at Sizewell B) = ~5.9 GW total capacity. Hinkley Point C (new PWR) under construction, expected ~2030.
PWR vs AGR
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Reactor Types
PWR (Pressurised Water Reactor): most common globally, high-pressure water coolant. AGR (Advanced Gas-cooled Reactor): historic UK specialty, uses gas cooling and graphite moderation.
Nuclear MCQs
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🏠 Heat Pumps

A device that transfers heat from one place to another using electricity and a refrigeration cycle. Think of it as a reversible air conditioner.

Coefficient of Performance

COP = Heat Output ÷ Electrical Input

Typical COP: 2.5–4.5  |  Gas boiler equivalent: ~0.9  |  Electric heater: 1.0

Key Concepts — Click to Flip
💨
ASHP — Air Source
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Heat Pump
Extracts heat from outdoor air (even when cold). Subtypes: air-to-air (warm air) and air-to-water (radiators/underfloor). Lower installation cost, good for UK climate. Efficiency drops in very cold weather.
🌍
GSHP — Ground Source
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Heat Pump
Extracts heat from stable ground temperature year-round via horizontal loops or vertical boreholes. Very high efficiency and consistent performance. Higher installation cost, needs land or drilling.
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The Refrigeration Cycle
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Physics
1. Evaporation — refrigerant absorbs heat → gas. 2. Compression — pressure/temp rises. 3. Condensation — heat released indoors → liquid. 4. Expansion — pressure drops, cools. Repeat.
📉
Why UK Bills Can Rise
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Economics
UK electricity costs ~27p/kWh vs gas ~7p/kWh. Even at COP 3, heat cost = 9p/kWh vs gas boiler ~7.8p/kWh. Poor insulation/small radiators can drop COP to 2 → 13.5p/kWh heat.
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COP Changes with Temperature
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Performance
COP is not fixed. 10°C outside → COP ≈ 4. –5°C outside → COP ≈ 2.5. Best at mild outdoor temperatures with underfloor heating (low flow temp 35–45°C) in well-insulated homes.
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Hybrid Heat Pump
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Heat Pump
Combines a heat pump with a gas boiler. Heat pump runs most of the time; boiler kicks in during extreme cold. Easier fossil fuel transition but still relies partly on gas.
Heat Pump MCQs
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