Volume 7 geothermal energy 7 01 – geothermal energy – introduction Volume 7 geothermal energy 7 01 – geothermal energy – introduction Volume 7 geothermal energy 7 01 – geothermal energy – introduction Volume 7 geothermal energy 7 01 – geothermal energy – introduction Volume 7 geothermal energy 7 01 – geothermal energy – introduction Volume 7 geothermal energy 7 01 – geothermal energy – introduction
7.01 Geothermal Energy – Introduction TI Sigfusson, Innovation Center, Reykjavik, Iceland © 2012 Elsevier Ltd All rights reserved This volume is dedicated to geothermal energy, one of the most fundamental energy sources that characterizes the environment and influences the lifestyle of humans The volume is the product of a team of experts from a number of corners of the world It should reflect the increased awareness and status of the subject as a viable alternative to the use of hydrocarbons, which, in turn, will help mitigate climate change Enormous amounts of heat are stored within planet Earth This heat originates from the original formation of the planet and from radioactive decay of minerals, most likely partly accreted from space as well as solar energy absorbed at the surface Built on the Greek language roots for the words ‘earth’ and ‘heat’ – geo and thermos, respectively – this energy is commonly called geothermal energy The Earth’s internal heat naturally flows to the surface by conduction and is subsequently replenished by radioactive decay of minerals There is a net surface loss of this energy at a rate of about 14 TW The energy flow out of the Earth’s crust gives rise to temperature gradients, which are highest near plate boundaries Combined with fluids naturally occurring inside the crust, these gradients form the conductive mechanism that drives the geothermal energy source Fluid flows in the form of magmatic conduits and hydrothermal circulation characterize the overall energy stream of the geothermal scenario In daily use, most geothermal energy is converted into electricity, with over 10 TW online in about 25 countries Some of it is used directly for district heating, in spas, or in various industrial processes The first use of this energy source can be traced back to Paleolithic times – the earliest being reported in the Qin Dynasty in China in the third century BC Some twenty-two centuries later, in Lardarello in Italy at the beginning of the nineteenth century, the industrial application of geothermal energy began Although geothermal energy is very reliable and in most cases environmentally friendly, it has historically been limited to the tectonic plate boundaries In scientific analysis, geothermal energy is generally counted as sustainable, primarily because any projected heat extraction is small compared to the Earth’s heat content This, on the other hand, has to be monitored closely in some local situations where an accelerated pace of harnessing could result in overexploitation Unlike most other sustainable energy sources, which originate from the Sun or the Moon, the roots of geothermal energy are derived from heat generated from nuclear processes within the Earth Theoretically, the Earth’s geothermal resources are more than adequate for supplying the energy needs of modern society, although only a very small fraction may be profitably exploited given present state-of-the-art technology Recent findings point to increasing potential of geothermal energy exploitation as a viable method for mitigating global warming, because only a relatively small proportion of greenhouse gases are emitted per energy unit during conversion This volume of Comprehensive Renewable Energy is devoted to geothermal energy It will help reflect recent technological advances that have dramatically expanded the range and size of viable resources It should be able to function as a general reference for anyone wanting to study the connectivity of the subject, which requires knowledge of physics, thermodynamics, chemistry, and geology as well as material engineering Together, these span the world of geothermal exploitation Energy cannot be created – geothermal energy utilization is about energy conversion It is about converting the heat energy of the Earth to useful sources of energy in many forms, from heat to electric current Endless engineering possibilities exist to convert this energy further for other possible applications and innovations The approach of the volume is very much like the approach of anyone wanting to make a geothermal system work We study the hot rock close to the surface, for which we need sufficient permeability or porosity of the rock as well as sufficient quantity – and quality – of water or steam, which are the natural energy-carrying substances for energy transfer from the Earth Alternatively, we can choose to inject water from external reservoirs or even use a third energy-carrying substance and create binary systems All these aspects form the subject of the narrative ahead of us The volume starts with a thorough investigation into the physical and chemical nature of the resource The first chapter describes physical and chemical methodologies in order to create and present a thorough picture of the origins of geothermal energy The reader will then be able to assess geothermal energy resources, their distribution around the planet, and ways to assess and utilize them Considerable effort is put into reservoir physics, exploitation techniques, and extraction methods, along with subsequent materials degradation and wear This brings us to the important aspect of materials and engineering solutions for optimizing efficiency and longevity of any infrastructure associated with the harnessing of geothermal energy Power plants are studied, as well as common use of geothermal energy for other purposes The most straightforward use of geothermal steam is to connect it directly to a flash turbine When the primary geothermal fluid has a low temperature, the so-called binary power generating system can be used This is often based on the Rankine cycle, with geothermal fluid as the heating source and a low-boiling-point medium as working fluid When adopting the low-boiling-point medium as the working fluid, the system can generate electric power from a low-temperature source The economics of geothermal energy utilization are also analyzed to give a comprehensive overview of the subject It is here that some of the best qualities of the geothermal resource come clearly into view Utilization can include space heating, encompassing district heating systems; greenhouse and covered ground heating; aquaculture pond and raceway heating; agricultural drying; a Comprehensive Renewable Energy, Volume doi:10.1016/B978-0-08-087872-0.00701-0 Geothermal Energy – Introduction multitude of industrial applications; and finally bathing, swimming pools, and spa heating In arctic areas, snow melting is carried out by geothermal means The possibility of space cooling exists where geothermal resources are present in warm climates, such as in the tropics This last point is a good example of how thermal physics can be utilized in order to make geothermal energy conversion so wide ranging and colorful Last but not least, this volume contains important considerations about geothermal energy as an investment opportunity A chapter dealing with this subject analyzes the driving forces behind international investment in geothermal electricity projects It addresses the important factor of a generally higher investment risk (e.g., in the exploration phase) than in the traditional energy sector, which in turn means that relatively few investors are attracted On the other hand, returns can be better, as the authors point out Although it covers the subject from a different angle, this chapter fits into the overall content of this volume When looking toward the future, it seems obvious that geothermal energy holds many promises in terms of humanity’s increased technological skills as well as increased awareness of the need for greater use of renewable energy sources One of the ways explored intensively at present is deep drilling, which is a way to get closer to the warmer part of the ground – closer to the magma chambers, in some cases Recent studies in the United States point toward a possible 10-fold increase in the proportion of geothermal energy in the energy portfolio of the country by the middle of the century This would mean that geothermal energy could account for 10% of the total energy use If this proves feasible, geothermal energy would become one of the most important energy sources in the world It is in this spirit that this volume is written at the onset of a century that will celebrate renewable energy As volume editor, I want to thank the authors for their contributions and express my sincere hope that the contents will help shed light on the subject and reveal the interconnectivity of the various disciplines affected by the heat of the Earth ... the proportion of geothermal energy in the energy portfolio of the country by the middle of the century This would mean that geothermal energy could account for 10% of the total energy use If this...2 Geothermal Energy – Introduction multitude of industrial applications; and finally bathing, swimming pools, and spa heating In arctic areas, snow melting is carried out by geothermal. .. geothermal energy would become one of the most important energy sources in the world It is in this spirit that this volume is written at the onset of a century that will celebrate renewable energy