Describe how a Savonius rotor extracts energy from the wind.

A Savonius rotor has curved scoops, and drag on the hollow side of each scoop pushes the rotor round. The rotor turns slowly but with high starting torque.

How does a Darrieus rotor differ from a Savonius rotor?

A Darrieus rotor has aerofoil blades that generate lift, so it spins faster and more efficiently. A Savonius rotor relies on drag and turns slowly.

Why is a Darrieus turbine often unable to start by itself?

A Darrieus rotor produces little torque when stationary, because its aerofoils only generate useful lift once moving. Many designs need a motor or a small Savonius rotor to start them.

CCEA A-Level Environmental Technology 3930

Fossil Fuels

Topic overview Coal, oil and gas in modern society Reserves, lifespan and accessibility Fossil fuel combustion and the IPCC evidence Carbon trading schemes Fossil fuel demand, emerging economies and fuel security Environmental impacts of fossil fuel use

Global Action on Energy Conservation and Climate Change

Topic overview Sustainable development and climate agreements Emissions and energy efficiency targets for 2020 Renewable energy and demand reduction in policy Nuclear power as an alternative

Macrogeneration

Topic overview Conservation of energy and the simple generator Thermal power stations and steam turbines Direct and indirect renewable electricity Electricity transmission through the National Grid Smart grids and interconnectors Combined heat and power

Microgeneration

Topic overview Microgeneration technologies Benefits of home and community microgeneration The heat pump cycle and coefficient of performance Air source and ground source heat pumps

Energy From Wind

Topic overview Horizontal and vertical axis wind turbines Kinetic energy, wind power and the Betz limit Power curves, rated output and energy losses Swept area, blade length and turbine mass Air density, hub height and turbine siting Power control, yawing and survival speed Choosing a location for a commercial wind farm

Energy From the Sun

Topic overview Solar radiation, tracking and concentrating solar power Flat plate and evacuated tube collectors Sizing a domestic solar thermal system Photovoltaic cells and semiconductor wafers Types of photovoltaic module compared Planning regulations and solar incentives Passive solar design in new and existing buildings

Energy From Biomass

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Energy Storage

Topic overview Intermittency and reliability of renewable supply Why renewable energy needs storing Pumped hydro and compressed air energy storage Where energy storage is most beneficial

Plastics for the Future

Topic overview Crude oil as a fuel and a feedstock Refinery gases and the making of polymers Persistent plastic waste and the Great Pacific Garbage Patch Toxic gases from incinerating plastics Biodegradable, photodegradable and compostable plastics Testing photodegradable plastic against polythene Bio-derived polyethylene and a sustainable plastics future

Renewable Energy Investigations

Topic overview Desktop research on renewable energy technologies Choosing an investigation and its variables Apparatus and risk assessment for energy practicals Accuracy and reliability of energy measurements Presenting and analysing energy data Evaluating a method and site-based recommendations

Sustainable Development

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Waste Management

Topic overview Landfill dependence and the landfill tax Waste types, priority waste streams and EU directives The waste management hierarchy Recycling at a Materials Recovery Facility Landfill decomposition, methane and leachate Engineered landfill: dry tomb and bioreactor designs

Waste to Energy Technologies

Topic overview Embodied energy Incineration with energy recovery Digester design: solids content, residence time and staging Stages of anaerobic digestion and biogas CHP Composting and catering waste

Land Contamination and Remediation

Topic overview Contaminated land, risk and traditional remediation Bioremediation principles and bioreactor systems Micro-organisms that degrade named pollutants Bioremediation benefits and genetically engineered microbes Phytoremediation of metals and other elements Phytoextraction with Indian mustard and alpine pennycress Biohydrometallurgy and phytomining of ores

Hydrogen Fuel Cells

Topic overview Hydrogen as a fuel: properties and storage Hydrogen production: steam reforming, electrolysis and photocatalysis How a fuel cell works and the PEM cell Alkaline, phosphoric acid, molten carbonate and solid oxide fuel cells Fuel cell applications and the challenges of hydrogen

Transport System Challenges

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Energy Performance of Buildings

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Emerging Technologies

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Sustainable Urban and Rural Communities

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The Code for Sustainable Homes

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Energy From Wind

Horizontal and vertical axis wind turbines

3 things to know
AS 1

Overview

Horizontal and vertical axis designs, Savonius and Darrieus rotors, upwind and downwind turbines, and the nacelle, gearbox, hub, blades, anemometer, wind vane, brake, transformer, tower and foundation.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Evaluation

Give three advantages of a vertical axis wind turbine over a horizontal axis design.

Key term

What is the main difference between a horizontal axis and a vertical axis wind turbine?

Process

Why does a vertical axis wind turbine not need a yaw mechanism?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the main difference between a horizontal axis and a vertical axis wind turbine?
Model answer
A horizontal axis wind turbine has its main rotor shaft parallel to the ground and pointing into the wind. A vertical axis wind turbine has its shaft standing upright, at right angles to the ground.
2
Why does a vertical axis wind turbine not need a yaw mechanism?
Model answer
A vertical axis turbine accepts wind from any direction without turning. The rotor works the same whichever way the wind blows.
3
Describe how a Savonius rotor extracts energy from the wind.
Model answer
A Savonius rotor has curved scoops, and drag on the hollow side of each scoop pushes the rotor round. The rotor turns slowly but with high starting torque.
4
How does a Darrieus rotor differ from a Savonius rotor?
Model answer
A Darrieus rotor has aerofoil blades that generate lift, so it spins faster and more efficiently. A Savonius rotor relies on drag and turns slowly.
5
Why is a Darrieus turbine often unable to start by itself?
Model answer
A Darrieus rotor produces little torque when stationary, because its aerofoils only generate useful lift once moving. Many designs need a motor or a small Savonius rotor to start them.
6
Give three advantages of a vertical axis wind turbine over a horizontal axis design.
Model answer
A vertical axis turbine needs no yaw system because it accepts wind from any direction. The gearbox and generator can sit at ground level, which makes maintenance easier. A vertical axis turbine also copes better with turbulent, gusty winds such as those around buildings.

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Fossil Fuels

Global Action on Energy Conservation and Climate Change

Macrogeneration

Microgeneration

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