Learning outcomes

By the end of this unit you should be able to:

  • explain the principles that underlie the ability of wave power to deliver useable energy;

  • outline the technologies that are used to harness the power of waves;

  • discuss the positive and negative aspects of wave energy in relation to natural and human aspects of the environment.


Author(s): The Open University

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Introduction

Energy from sources other than fossil or nuclear fuels is to a large extent free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. Many alternative sources of energy have been used in simple ways for millennia, e.g. wind and water mills, sails, wood burning – but only in the last two centuries has their potential begun to be exploited on an industrial scale. Except
Author(s): The Open University

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Figures

Figure 1a Cour
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3 Summary

Power output from wind turbines is proportional to the area swept by their blades, and to the cube of wind speed. The narrow range of useable wind speeds restricts the areas where wind energy can be exploited.

Wind power has great potential, but has three main drawbacks. Output depends on intermittent wind speeds, irregular distribution of suitable wind speeds, and occupancy of large areas of land.


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2 The future of wind energy

A great advantage of using wind energy is that, unlike power generation from combustion of fossil fuels, it produces no gas emissions. Even a small 750 kW wind turbine operating with wind speeds just above that of turbine cut-off would reduce annual emissions to the atmosphere by 1200 t of carbon dioxide, 6.9 t of sulphur dioxide and 4.3 t of nitrogen dioxide, compared with the equivalent power output from coal-fired generators. Nevertheless, wind turbines and their infrastructures are substa
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1 Wind energy

Wind energy was the fastest growing power source at the start of the 21st century, yet wind-driven mills and pumps, and nautical sails for transport were, along with waterwheels, the first mechanical devices to power industrial production. The advantages of harnessing wind energy are obvious; it is free, clean and widely available (but see later). Although a favoured source of ‘green’ energy, the increasing deployment of wind turbines where they are most efficient, on hilltops and coasts,
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Learning outcomes

By the end of this unit you should be able to:

  • explain the principles that underlie the ability of various natural phenomena to deliver wind energy;

  • outline the technologies that are used to harness the power of the wind;

  • discuss the positive and negative aspects of wind energy in relation to natural and human aspects of the environment.


Author(s): The Open University

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Introduction

Energy from sources other than fossil or nuclear fuels is to a large extent free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. Many alternative sources of energy have been used in simple ways for millennia, e.g. wind and water mills, sails, wood burning – but only in the last two centuries has their potential begun to be exploited on an industrial scale. Except
Author(s): The Open University

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Acknowledgements

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Author(s): The Open University

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6 Summary

Solar power is an immense source of directly useable energy and ultimately creates other energy resources: biomass, wind, hydropower and wave energy.

Most of the Earth's surface receives sufficient solar energy to permit low-grade heating of water and buildings, although there are large variations with latitude and season. At low latitudes, simple mirror devices can concentrate solar energy sufficiently for cooking and even for driving steam turbines.

The energy of light shifts el
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5 Biomass conversion of solar energy

Photosynthesis in the geological past was responsible for all fossil fuel reserves, but its products are buried about 2000 times more slowly than we use them at present. The total carbon content of all biomass growing on land is estimated to be 5.6 × 1014 kg and, as Figure 10 shows, about one-fifth of this mass is renewed each year. Figure 6 shows how modern plant biomass is distributed across the continents. Clearly, biological conversion of solar energy to a chemical form in com
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1 Solar energy

The Sun will radiate energy until it ceases thermonuclear fusion, in around 5 billion years. The solar power that enters the Earth's system is 1.1 × 105TW (0.3 × 105 TW to atmospheric heating and 0.8 × 105 TW absorbed at the surface – Figure 1). This is equivalent to a global e
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References

Sheldon, P. (2005) Earth’s Physical Resources: An Introduction (Book 1 of S278 Earth’s Physical Resources: Origin, Use and Environmental Impact), The Open University, Milton Keynes
Smith, S. (2005) Water: The Vital Resource (Book 3 of S278 Earth’s Physical Resources: Origin, Use and Environmental Impact), The Open University, Milton Keynes

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7 The pros and cons, and future of geothermal energy

Geothermal energy is renewable but the fluids emit gases such as CO2, H2S, SO2, H2, CH4 and N2 when used for electricity generation. However, geothermal power plants are usually sited in areas of natural geothermal activity, where such emissions occur anyway. Other potential pollutants are various ions dissolved in the geothermal fluids, but these are almost always returned to the reservoir when the spent fluids are re-injected
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3 Hot dry rock (HDR) fields

Heat flow through some parts of the continental crust can be well above normal locally because the underlying rocks contain abnormally high concentrations of uranium, thorium and potassium, which generate considerable heat. To add significantly to surface heat flow and thereby create high-temperature anomalies at shallow depths requires a large volume of such radioactive rocks. This condition is satisfied by some, but not all, granitic igneous intrusions, whose original magma became ch
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2 High- to medium-enthalpy steam fields

When the geothermal gradient heats water above the temperature at which it boils at atmospheric pressure, at a depth accessible to drilling, conditions can favour using natural geothermal steam to generate electricity. Typically, the pressure can be several tens to hundreds of times that of the atmosphere. Even at 200 °C, high pressure can ensure that much of the fluid in a geothermally heated aquifer remains in the liquid state. Author(s): The Open University

1 Geothermal energy

Although energy from the Earth's interior that flows though the surface is on average very low — about a thousand times less than the solar energy that falls on the surface — it is sufficiently abundant worldwide to make it locally worth exploiting. The top 3 km of the Earth's crust stores an estimated 4.3 × 107 EJ of thermal energy by virtue of the temperature of rocks and their thermal capacity. Because global consumption of energy during 2002 was 451 EJ heat stored within t
Author(s): The Open University

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Learning outcomes

By the end of this unit you should be able to:

  • explain the principles that underlie the ability of geothermal energy to deliver useable energy;

  • outline the technologies that are used to harness the power of geothermal energy;

  • discuss the positive and negative aspects of geothermal energy in relation to natural and human aspects of the environment.


Author(s): The Open University

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Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Introduction

Energy from sources other than fossil and nuclear fuels is to a large extent free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. And many alternative sources of energy have been used in simple ways for millennia, e.g. wind and water mills, sails, wood burning — but only in the last two centuries has their potential begun to be exploited on an industrial scale. Ex
Author(s): The Open University

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Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Acknowledgements

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence.

Author(s): The Open University

License information
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Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share