Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See Terms and Conditions. Figure 1 Copyr
Figures
4 Groundwater movement Groundwater flows underground in response to elevation differences (downwards) and pressure differences (from areas of high pressure to areas of low pressure). Near the water table, this means that groundwater usually flows ‘downhill’, i.e. from a higher level to a lower level, just as it would on the surface. The difference in energy between two points that are l metres apart horizontally on a sloping water table is determined by the difference in height (h) between them (<
Introduction Many people have the impression that underground water occupies vast caverns, such as those in the Derbyshire Peak District, flowing from one cavern to another along underground rivers. This is a common misconception: underground caverns are fairly rare, but huge quantities of water exist underground, within rocks. This is because many rocks contain pores, spaces that come in all shapes and sizes. In sediments, and consequently sedimentary rocks, there are often pores between grains which can
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
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1 Wave energy The energy carried by ocean waves derives from a proportion of the wind energy transferred to the ocean surface by frictional drag. So, ultimately it stems from the proportion of incoming solar energy that drives air movement. Just how much energy is carried by a single wave depends on the wind speed and the area of ocean surface that it crosses; wave height, wavelength, and therefore wave energy, are functions of the distance or fetch over which the wind blows. Not surprisingly the ma
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.
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
Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See Terms and Conditions. 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.
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
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,
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.
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
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):
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
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
2 Solar thermal energy Solar heating of trapped air, water and solids has been used for centuries, but modern architectural design can enhance all three effects for space heating, hot water supply and heat storage. Such passive solar heating relies on short-wave radiation being absorbed by materials so that they heat up and then slowly re-emit long-wave radiation. The most obvious example is inside a greenhouse, where solar radiation that passes through the glass heats the inside air to temperatures well abo
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
References
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
