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
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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
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
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
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
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):
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
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.
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
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 Nuclear power generation results from fission of uranium isotopes when bombarded by neutrons. Conventional burner reactors require relatively scarce uranium-235, whereas fast breeder reactors (which have not yet been developed on any significant scale) would exploit more abundant uranium-238. In the early 21st century over 400 nuclear — mainly burner — reactors produced 16% of global electricity demand. The UK played a leading role in nuclear power developments during the 1950
4.5 Geological criteria for safe radioactive waste disposal Even in the best of circumstances, containers such as the one shown in Figure 19 will survive for only 100–1000 years, although the glass itself may inhibit the migration of radioactive isotopes for a further 1000 years. So, in view of the long decay times (Author(s):
4.4 Radioactive waste disposal Most fission products from nuclear reactors are solid at ordinary temperatures. They cluster around atomic mass numbers 90 and 140 (see, for example, Equation 2). From the point of view of waste disposal, the problem is that most of them are highly radioactive. The common radioactive isotopes produced in nuclea
