Renewable Energy E-Book
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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
In the years since the publication of the first edition of this book, the world has undergone drastic changes in terms of energy sources. This is reflected in the expansion of this second edition from 20 to 26 chapters. The most dramatic occurrence was the Tsunami which struck Japan in March of 2011 and set off a reactor catastrophe at the nuclear power plants in Fukushima. On the other hand fossil fuel technology drives the climate change to a threatening level. So, renewable energy sources are essential for the 21st century. The increasing number of wind power plants, solar collectors and photovoltaic installations demonstrates perceptibly that many innovations for tapping renewable energy sources have matured: very few other technologies have developed so dynamically in the past years.
Nearly all the chapters were written by professionals in the respective fields. That makes this book an especially valuable and reliable source of information. The second edition is extended by several new chapters such as tidal power stations, the Desertec project, thermography of buildings and more. Furthermore, the critical debate about current first generation bio-fuels is carefully reflected, and the book presents promising solutions that do not trade in food for fuel.
The editors are experienced journalists and illustrate the text with simple diagrams and information boxes, printed in full-color throughout.
A valuable resource for applied physicists, engineers in power technology, engineers, and anyone interested in natural sciences.
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Seitenzahl: 551
Veröffentlichungsjahr: 2013
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Contents
Foreword
Preface
First-hand Information
Renewable Energy Sources – a Survey
The European Union – ambitious Goals
Wind Energy is booming internationally
Successful Energy Policies in Germany
The Current Situation
Potential and Limits
Water Power
Land-based Wind Energy
Biomass
Solar Energy
Geothermal Energy
The Window of Opportunity
Offshore and the Open Field
Scenarios for Ecologically Optimized Development
Renewable Energy on a Worldwide Scale
Summary
References
About the Authors
A Tailwind for Sustainable Technology
Three-bladed Turbines with High Tip-Speed Ratio
From Grid-connected to Grid-supporting Wind Power Plants
Lightweight Construction, Intelligent Installations, and Reliability
Wind Energy in the Updraft – Offshore Plants
Grid Integration in Spite of Varying Power Outputs
Economic Feasibility
Nature Conservation and Public Acceptance
Ecological and Economical Expediency
Summary
References and Links
About the Authors
Flowing Energy
River and Storage Hydroelectric Plants
Large-scale Hydroelectric Plants
Small-scale Hydroelectric Plants
Large Dams and their Consequences
Summary
References
About the Author
How the Sun gets into the Power Plant
The Principle
The Concentration of Light
Concentrating Collectors
Heat-Engine Processes
Parabolic-Trough Power Plants
Central Receiver Systems
Dish-Stirling Systems
Cost Effectiveness
Technical Improvements
The Lowest CO2 Emissions
Summary
References
About the Author
Solar Cells – an Overview
Harvest factors are still too low
Area-dependent and Area-independent Costs
Thin Films for Glass Facades
Highest Power Outputs
Organic, Polymer, Dye and Biological Solar Cells
Suggestions for Planning a Solar Installation
Summary
References
About the Author
Solar Cells from Ribbon Silicon
The State of the Art
Thin-Film Solar Cells
Ribbon Silicon
Crystal Defects and Defect Engineering
Strategies for Cost Reduction
Efficiencies
Summary
References
About the Author
Low-priced Modules for Solar Construction
CIS – an Ideal Material
Glass Coating instead of Wafer Technology
Ten Years of Industrial Experience
Solar Architecture using CIS Solar Modules
Summary
References
About the Author
On the Path towards Power-Grid Parity
The best Energy Balance and Lowest Costs
A simple Coating Procedure
A new Coating Process
Summary
References and Links
About the Authors
Energy from the Depths
Geothermal Energy is Still Exotic, but has High Growth Rates
Geothermal Energy Sources
Hot and Deep
Reservoir Engineering
The Geothermal Laboratory in Gross Schönebeck
Need for Further Research
Outlook
Summary
Acknowledgments
References
About the Author
Green Opportunity or Danger?
Ethanol from Cellulose
Genetic Technology for Biofuels
Summary
References
Twists and Turns around Biofuels
The Rational Basis – the Carbon Cycle
A Critical Discussion of Several Criteria
Conclusions
Summary
References
About the Author
Concentrated Green Energy
A Renewable Resource
Production Methods
Production of Chemical Energy Carriers from Microalgae
Biodiesel and Kerosene Substitutes
Bioethanol
Biogas and Hydrogen
Conclusions
Summary
References
About the Authors
Synthetic Fuels from the Biomass
Obstacles to the Use of the Biomass
The Karlsruhe bioliq® Process
The Current State of Development
Costs and Development Potential
Acknowledgments
References
Summary
About the Authors
Electric Power from Hot Air
Operating Principles
The Test Installation in Manzanares
Large Power Plants
The Mildura Project
Outlook
Summary
References
About the Authors
Sun, Moon and Earth as Power Source
Physical Principles
Concepts for Tidal-Stream Installations
Challenges
Case Study: The Technology of Voith Hydro
Installation, Retrieval and Maintenance
First Results
Conclusions
Summary
References
About the Authors
Energy Reserves from the Oceans
The Formation and Propagation of “Gravity Waves”
The Basic Technology for Exploiting Wave Energy
Today’s Standard Technology: the OWC
Existing OWC Projects
Technological and Economic Questions
Other Technologies for the Exploitation of Wave Energy
Can Wave Energy Soon Be Commercially Exploited?
How Expensive Would Wave Energy Be?
Conclusions
Summary
References
About the Author
Salty vs. Fresh Water
Summary
References
About the Author
Power from the Desert
The Increasing Demand for Electric Power and Water
Available Resources and Technologies
Solar-Thermal Power as a Key Element
Technological and Economic Questions
Power Transmission over HVDC Lines
Cost-Effective Power from Sustainable Energy Sources
An Alternative to Climate Change and Nuclear Power
Summary
References
About the Author
Hydrogen: An Alternative to Fossil Fuels?
Properties of Hydrogen
The Present-day Production of Hydrogen
The New Scenario for Hydrogen
Hydrogen in the Gas Tank
The Hydrogen Infrastructure: A Roadblock?
And Where will the Hydrogen Come From?
Summary
References
About the Author
Heat on Call
The Thermodynamics of Energy Storage
Aquifers as Seasonal Storage Systems
Aquifer Reservoirs for Energy Management – Reichstag and Neubrandenburg
Storage in a Field of Downhole Heat Exchangers
Example: The Max-Planck Campus in Golm
Hot-Water Storage
Solar-Assisted Local Networks
Gravel-Water Storage Systems
Summary
References and Links
About the Authors
Taming the Flame
Applications of Fuel Cells
Fuel Cells for Road Vehicles
Fuel Cells for Stationary, Decentral Energy Production
The PEMFC
The High-Temperature PEM
The Phosphoric Acid Fuel Cell (PAFC)
The Molten Carbonate Fuel Cell (MCFC)
The Solid-Oxide Fuel Cell (SOFC)
Micro-Fuel Cells
Outlook
Summary
References
About the Author
Electric Automobiles
Drive-Motor Power and Battery Capacity
Battery Management System
Lithium-ion Batteries
Principle
Battery Types and Characteristics
Operating Lifetimes
Operating Parameters
Safety
Conclusions
Summary
References and Links
About the Author
Cooling with the Heat of the Sun
Closed Systems
Open Systems
Summary
About the Author
A Super Climate in the Greenhouse
Summary
About the Author
An Exceptional Sustainability Concept
The Heat Supply
CO2 Balance
Summary
About the Authors
The Allure of Multicolored Images
The Goals of Building Thermography
Methods
Examples of Thermal Bridges
Hidden Structures made Visible
View Factor and Thermal Time Constants
Consequences
Summary
References
About the Authors
Subject Index
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The Editors
Roland Wengenmayr
Frankfurt/Main, Germany
Thomas Bührke
Schwetzingen, Germany
German edition and additional articles translated by:
Prof. William Brewer
Foreword
Today, it is generally recognized that human activities are significantly changing the composition of the earth’s atmosphere and are thus provoking the imminent threat of catastrophic climate change. Critical concentration changes are those of carbon dioxide (CO2), laughing gas (dinitrogen monoxide, N2O) and methane (CH4). The present-day concentration of CO2 is above 380 ppm (parts per million), far more than the maximum CO2 concentration of about 290 ppm observed for the last 800,000 years. The most recent reports of the World Climate Council, the Intergovernmental Panel on Climate Change (IPCC) and the COP-16 meeting in Cancun in December, 2010 demonstrate that the world is beginning to face the technological and political challenges posed by the requirement to reduce the emissions of these gases by 80 % within the next few decades. The nuclear power plant catastrophe in Fukushima on March 11th, 2011 showed in a drastic way that nuclear power is not the correct path to CO2-free power production. Germany made a reversal of policy as a result, which has attracted attention worldwide. In the coming years, we shall certainly be trailblazers in the global transformation of our energy system in the direction of one hundred percent renewable sources.
This ambitious goal can be achieved only through substantial progress in the two main areas that affect this issue: Rapid growth of energy production from renewable sources, and increased energy efficiency, especially of buildings which cause a large portion of our total energy needs. Unfortunately, these two concrete, positive goals are still being neglected in the international climate negotiations.
This book presents a comprehensive treatment of these critical objectives. The 26 chapters of this greatly expanded 2nd English edition have been written by experts in their respective fields, covering the most important issues and technologies needed to reach these dual goals. This volume provides an excellent, concise overview of this important area for interested general readers, combined with interesting details on each topic for the specialists.
The topics addressed include photovoltaics, solar-thermal energy, geothermal energy, energy from wind, waves, tides, osmosis, conventional hydroelectric power, biogenic energy, hydrogen technology with fuel cells, building efficiency and solar cooling. The very topical question of how automobile mobility can be combined with sustainable energies is discussed in a chapter on electric vehicles. The treatment of biogenic energy sources has been expanded in additional chapters.
In each chapter, the detailed discussion and references to the current literature enable the reader to form his or her own opinion concerning the feasibility and potential of these various technologies. The volume appears to be well suited for generally interested readers, but may also be used profitably in advanced graduate classes on renewable energy. It seems especially well suited to assist students who are in the process of selecting an inspiring, relevant topic for their studies and later for their thesis research.
Eicke R. Weber,Director,ISE Institute for Solar Energy Systems,Freiburg, Germany
Preface
This book gives a comprehensive overview of the development of renewable energy sources, which are essential for substituting fossil fuels and nuclear energy, and thus in securing a healthy future for our earth.
A variety of energy resources have been discussed by experts from each of the fields to provide the readers with an insight into the state of the art of sustainable energies and their economic potential.
Most important is that:
The good news is that already at the end of 2010, worldwide annual power generation by wind plants and solar cells exceeded the output of all the nuclear power plants in the USA and France combined. However, representatives of the conventional power industry frequently argue that solar conversion is unreliable because the sun doesn’t always shine. We give them an emphatic answer: “No, at night of course not, but who needs more energy at night when there is already more low-cost power available than we can use?” An important point is that solar cells – seen from a worldwide perspective – can make an essential contribution in the midday and afternoon periods, when power consumption is highest. Wind, however, fluctuates more, but with more digitally-regulated power distribution and rapidly developing storage facilities, these fluctuations can be minimized, and already today, wind parks are important contributors to the global power balance.
Today, the nuclear and petroleum industries take the growing competition from wind and solar energy very seriously. In the USA, one is made aware of this by their alarmingly accelerating lobbyist activities in Washington, opposing support of the development of sustainable energies. We in the democratic countries should use our voting power to elect those parties and politicians who understand the necessities of our times and thus the opportunities of sustainable energies, and who support and work towards their further development and implementation.
This book offers a good choice of topics to all its interested readers who want to inform themselves more thoroughly, and in addition to all those who want to work in one of the many branches of sustainable energy development and deployment. It represents an important contribution towards advancing their urgently needed implementation and thereby avoiding a threatening catastrophe brought on by unwise energy policy.
All together, it is a pleasure to read this book; it deserves a special place on every bookshelf, with its excellent form and content. It will have a lasting value in recording the current state of the rapid developments of sustainable energies.
Karl W. Böer,Distinguished Professor of Physics and Solar Energy, emeritusUniversity of Delaware
First-hand Information
In the four years since the publication of the first edition of this book, the world has undergone drastic changes in terms of energy. This is reflected in the expansion of this second edition to nearly 30 chapters. The most dramatic occurrence was the terrible Tsunami which struck Japan in March of 2011 and set off a reactor catastrophe at the nuclear power plants in Fukushima. In Germany, the government reacted by deciding to phase out nuclear power completely by 2022. Nevertheless, the ambitious German goals for reducing the emissions of greenhouse gases were retained. Renewable energy sources will therefore have to play an increasing role in the coming years.
Nearly four hundred thousand jobs have been created in Germany in the field of sustainable energy, many of them in the area of wind energy. However, the German photovoltaic industry is in crisis, in part because Chinese solarmodule producers can now manufacture and market their products at a lower price. In 2012, the U. S. Deparment of Commerce posted anti-dumping duties on solar cells from China. This conflict illustrates what basically is good news for the world as a whole, since the increased competition will rapidly lower the costs of solar power.
This book of course is not restricted to only the German perspective. In particular, it introduces a variety of technologies which can help the world to make use of sustainable energies. From a technical point of view, this field is extremely dynamic. This can be seen by again looking at the example of photovoltaic power: Since the first edition, the established technologies based on silicon have encountered increasing competition from thin-film module manufacturers, whose products save on energy and resources. Accordingly, Nikolaus Meyer completely revised his chapter on chalcopyrite (CIS) solar cells. The chapter by Michael Harr, Dieter Bonnet and Karl-Heinz Fischer on the promising cadmium telluride (CdTe) thin-film solar cells is completely new in this edition.
The biofuels industry, on the other hand, has developed an image problem. Aside from the competition for arable land with food-producing agriculture (the ‘food or fuel’ controversy), the first generation of biofuels has also been pilloried because of its poor CO2 balance. Gerhard Kreysa gives an extensive analysis of the contribution that can be made by biofuels to the world’s energy supply in a reasonable and sustainable way. Nicolaus Dahmen and his collaborators introduce their environmentally friendly bioliq® process from the Karlsruhe Institute of Technology, which is on the threshold of commercialization and has aroused interest internationally. Carola Griehl’s research team looks forward to a future powered by biofuels produced from algae.
Electric power from renewable sources requires intelligent distribution and storage. An exciting international example is the DESERTEC project, which envisions a supply of power to Europe from the sunny regions of North Africa. Franz Trieb from the German Aeronautics and Space Research Center was involved in the DESERTEC feasibility study and presents its results in detail here, in particular the win-win situation for both producers and consumers. The large solar thermal plants can meet the rapidly growing power needs of the North African population, for example for supplying potable water by desalination of seawater.
Nearly all the chapters were written by professionals in the respective fields. That makes this book an especially valuable and reliable source of information. It can be readily understood by those with a general educational background. Only a very few chapters include a small amount of mathematics. We have left these formulas intentionally for those readers who want to delve more deeply into the material; these few short passages can be skipped over without losing the thread of information. Extensive reference lists and web links (updated shortly before printing) offer numerous opportunities to access further material on these topics.
All the numbers and facts have been carefully checked, which is not to be taken for granted. Unfortunately, there is much misinformation and misleading folklore in circulation regarding sustainable energies. This book is therefore intended to provide a reliable and solid source of information, so that it can also be used as a reference work. Its readers will be able to enter into informed discussions and make competent decisions about these important topics.
We thank all of the authors for their excellent cooperation, William Brewer for his careful translation, and the publishers for this beautifully designed and colorful book. In particular, we want to express our heartfelt thanks to Ulrike Fuchs of Wiley-VCH Berlin for her active support and her patience with us. Without her, this wonderful book would never have been completed.
Thomas Bührke and Roland Wengenmayr
Schwetzingen and Frankfurt am Main, Germany
August 2012
This large photovoltaic roof installation, above the Munich Fairgrounds building, has a nominal power output of about 1 MWel. (Photo: Shell Solar).
The Development of Renewable Energy Carriers
Renewable Energy Sources – a Survey
BY HARALD KOHL | WOLFHART DÜRRSCHMIDT
Renewable energy sources have developed into a global success story. How great is their contribution at present in Germany, in the European Union and in the world? How strong is their potential for expansion? A progress report on the balance of innovation.
Renewable energy has become a success story in Germany, in Europe, the USA and Asia. Current laws, directives, data, reports, studies etc. can be found on the web site on renewable energies of the German Federal Ministry for the Environment [1].
The European Union – ambitious Goals
Let us first take a look at developments within the European Union: On June 25, 2009, Directive 2009/28/EG of the European Parliament and the Council for the Advancement of Renewable Energies in the EU took effect [2]. The binding goal of this directive is to increase the proportion of renewable energy use relative to the overall energy consumption in the EU from ca. 8.5 % in the year 2005 to 20 % by the year 2020. The fraction used in transportation is to be at least 10 % in all the member states by 2020. This includes not only biofuels, but also electric transportation using power from renewable sources. A binding goal was set for each member state for the fraction of sustainable energy in the total energy consumption (electric power, heating/cooling and transportation), depending on the starting value in that country. For Germany, this goal is 18 % by 2020, while for the neighboring countries, it is: Belgium, 13 %; Denmark, 30 %; France, 23 %; Luxemburg, 11 %; the Netherlands, 14 %; Austria, 34 %; Poland, 15 %; and for the Czech Republic, 13 %.
The member states can choose for themselves which means they employ to reach these goals. The development of renewable energy sources for electric power generation has been particularly successful in those member states which, like Germany, have given priority and a grid feed-in premium to power from these sources, analogous to the German Renewable Energy Act (EEG). Twenty of the EU countries have in the meantime adopted such laws to promote the use of power from renewable sources; worldwide, 50 countries have done so [3,4].
Installation of a wind-energy plant at the offshore wind energy park Alpha Ventus, which started operation in the North Sea in 2009 (photo: alpha ventus).
As an interim result, by 2010 the following proportions of renewable energy were used in the EU: for electricity, about 20 %; for heating/cooling, around 13 %; and for road transportation, around 4 %. Electric power generating plants, especially those using wind power, solar energy and bioenergy, have made clear progress. In the future, they will most likely maintain their head start. In this process, not only are technical progress and cost efficiency relevant, but also the establishment of organizational structures which take into account all the criteria of sustainability. Systems analysis and optimization, participation and acceptance by affected citizens, accompanying ecological research, environmental and nature protection as well as resource conservation are all becoming increasingly important. In order to reach the goals for renewable energy of 10 % of transportation and 20 % of the total energy consumption by 2020, the fraction of electric power from renewable sources must be around one-third of the total by then. A finely-meshed monitoring system was established, based on regular reports by the member states and the EU Commission [4–6].
Wind Energy is booming internationally
Especially the example of wind energy demonstrates that the rate of success can vary considerably even with comparable starting conditions. The environmental and energy-policy framework is decisive here. In particular, the German Renewable Energy Act (EEG), with its power feed-in and repayment regulations that encourage investments in renewable energy, along with similar legislation in Spain, has had considerable effect in comparison to other countries. Germany and Spain had an installed wind power of around 50,000 MW in 2010, more than half of that in the EU as a whole (with ca. 94,000 MW) [4, 7].
TAB. 1WORLDWIDE INSTALLED WIND POWER IN MW; YEAR 2010
Source: [10]. The values are in part preliminary due to rounding errors, shutdown of plants, and differing statistical methods, leading to deviations from national statistics.
But not only in the EU, also in China, India and the USA, the market for wind power plants is booming (Table 1). In the past few decades, a whole new branch of engineering technology has developed. Megawatt installations are now predominant. German and Danish firms are among the leaders in this field. About three-fourths of the wind power plants manufactured in Germany are now exported. Germany has acquired a similar prominence in solar power generation, both in photovoltaics and in solar thermal technology.
Successful Energy Policies in Germany
The German example in particular shows how the efforts of individual protagonists, support via suitable instruments (research and development, Renewable Energy Act, Heat Energy Input Act, assistance for entering the market, etc.) as well as cooperation between scientific institutions and innovative industrial firms in the area of renewable energy sources can lead to the growth of a whole new high-tech industry. Today, this industry is an economically successful global player. The Technical University in Berlin analyzed these developments over the past decades in a research project funded by the German Federal Ministry for the Environment [8,9]. Let us look at the developments in Germany more closely:
Renewable energy use has increased apace in Germany in the past years. In the year 2011, 20 % of the power from German grids came from renewable energy sources, nearly seven times as much as even in 1990 [4]. This was initially due to the successful development of wind energy, but in the meantime, there are important contributions from bioenergy and photovoltaics. With an overall energy input of 46.5 terawatt-hours (TWh) in 2011, wind power has clearly outdistanced the traditionally available hydroelectric power (which contributed 19.5 TWh in 2011). Electric power production from bioenergy sources (including the biogenic portion of burned waste) moved up to second place in 2011 at around 37 TWh. Photovoltaic power generation also caught up rapidly, and in 2011, it already contributed 3 % of the overall power production, at 19 TWh. It has thus increased by a factor of 300 since the year 2000. Geothermal power production still plays only a minor role. Figure 1 shows the rapid development dynamics of electric power production from renewable energy sources in Germany. In the first half of 2011, the fraction of the total electric power supplied by renewable sources had already increased to around 20 % [1].
Germany has thus exceeded the goal for the proportion of energy supplied from renewable sources set by the Federal government only a few years ago – at that time, 12.5 % was the aim for the year 2010. This represents a great success for all those involved. The new resolution of the government for the ‘Energy Turnaround’ (Energiewende), enacted on June 6, 2011, sets even more ambitious goals for the future use of renewable energy sources in Germany. For electric power, these new goals were already anchored in the amended EEG as of summer 2011 [1]. Its details are set out in the section ‘Goals for Renewable Energy in Germany’ on p. 11.
The Current Situation
Figure 2 (left) shows the distribution of the primary energy usage in Germany in the year 2010. It should not be surprising that fossil fuels still dominate the energy supply, providing together 89.1 % of the total [4]. Renewable energy sources had already attained a fraction of 10.9 % of the overall primary energy consumption by 2010. The right-hand part of Fig. 2 shows the origin of primary energy from renewable sources in the year 2010. Over two-thirds (71 %) of these renewable energy carriers are derived from the biomass. Wind energy contributes 13.4 %, water power 7.2 %, solar energy 6.3 % and geothermal energy 2.1 % (Figure 2).
The reason for the strong growth of renewable energy supplies in Germany is to be found mainly in political decisions. In the past twenty years, a public legal and economic framework was set up which has given renewable energy sources the chance to establish themselves on the market, in spite of their relatively high delivered power costs. Aside from various support programs and the market introduction program of the Federal government, the relevant laws were in particular the Power Feed-In Law (SEG) in 1990 and the Renewable Energy Act (EEG) in 2000, which gave the development of renewable energy sources an initial boost. The principle is straightforward: Power generated from renewable sources is given priority and a minimum price is guaranteed for power fed into the grid from these sources. On the basis of regular reports on the effectiveness of the EEG, the law is adjusted to the current situation as needed; most recently this was done in the summer of 2011 [1].
The prices paid for renewable-source power are scaled according to the source and other particular requirements of the individual energy carriers. They are graded regressively, i.e. they decrease from year to year. This is intended to force the renewable energy technologies to reduce their costs and to become competitive on the energy market in the medium term. The renewable energy technologies can accomplish this only through temporary subsidies, such as were given in the past to other energy technologies, e.g. nuclear energy. The renewable energy technologies will become strong pillars of the energy supply in the course of the 21st century only if they can demonstrate that they operate reliably in practice and are economically viable. To this end, each technology must go down the long road of research and development, past the pilot and demonstration plant stages, and finally become competitive on the energy market. This process requires public subsidies as well as a step-by-step inclusion of economic performance.
Potential and Limits
Often, the potential of the various technologies which exploit renewable energy sources is regarded with skepticism. Can renewable energies really make a decisive contribution towards satiating the increasing worldwide appetite for energy? Are there not physical, technical, ecological and infra-structural barriers to their increasing use?
Fundamentally, their potential is enormous. Most of the renewable energy resources are fed directly or indirectly from solar sources, and the sun supplies a continuous energy flux of over 1.3 kW/m2 at the surface of the earth. Geothermal energy makes use of the heat from within the earth, which is fed by kinetic energy from the early stages of the earth’s history and by radioactive decay processes (see the chapter “Energy from the Depths” in this book).
These energy sources are, however, far from being readily usable. Conversion processes, limited efficiencies and the required size of installations give rise to technical restrictions. In addition, there are limits due to the infrastructure, for example the local character of geothemal sources, limited transport radius for biogenic fuels, the availability of land and competition for its use. Not least, the limited availability and reliability of the energy supplies from fluctuating sources play a significant role. Furthermore, renewable energy sources should be ecologically compatible. Their requirements for land, potential damage to water sources and the protection of species, the landscape and the oceans set additional limits. All this means that the natural, global supply of potential renewable energy resources and the technically feasible energy production from each source differ widely (Figure 3).
In spite of these limitations, a widespread supply of renewable energies is possible. In order for it to be reliable and stable, it must be composed of the broadest possible mix of different renewable energy sources. In principle, water and wind power, use of the biomass, solar energy and geothermal heat can together meet all of the demands. Germany is a good example of this. Although it is not located in the sunny South, and has only limited resources in the areas of hydroelectric and geothermal power, nevertheless renewable energy sources can in the long term supply all of Germany’s energy requirements. Estimates put this contribution at around 800 TWh for electrical energy, 900 TWh for heat, and 90 TWh for fuels [4,11]. This corresponds to about 130 % of the current electric power consumption and 70 % of the current requirement for heating energy. With improved energy efficiency and a reasonable usage of power for heating and cooling as well as for transportation, the energy requirements in Germany can be met completely on the basis of renewable energy sources over the long term.
ABB. 3NATURAL SUPPLY AND AVAILABILITY
The natural supply of renewable energies in relation to the current world energy consumption (black cube, normalized to 1). Small cubes: The fraction of each energy source that is technically, economically and ecologically exploitable. Yellow-green: solar radiation onto the continents; blue: wind; green: biomass; red: geothermal heat; violet: ocean/wave energy; dark blue: water power (source: [11]).
Water Power
Water is historically one of the oldest energy sources. Today, hydroelectric power in Germany comprises only a small contribution, which has remained stable for decades: 3 to 4 % of the electric power comes from storage and flowing water power plants. Its potential is rather limited in Germany, in contrast to the countries in the Alps such as Austria and Switzerland. In the future, it will therefore be possible to develop it further only to a limited extent. In 2010, the roughly 7000 large and small plants delivered about 20 TWh of energy, 90 % of this in Bavaria and Baden-Württemberg. The worldwide potential for hydroelectric power is considerably greater: nearly 16 % of the power generated in 2010 came from hydroelectric plants [12,13]. Thus, water power – considered globally – is ahead of nuclear power. So far, it is the only renewable energy source which contributes on a large scale to the world’s requirements for electrical energy. The other types of renewable energy sources contributed around 3 % to global electricity generation in 2010 [12,13]. In particular, ‘large-scale water power’ is significant. An example is the Chinese Three Gorge Project, which generates more than 18 GW of electric power, corresponding to about 14 nuclear power plant blocks (see the chapter “Flowing Energy”).
In Germany, the so-called ‘small-scale’ water power still has limited possibilities for further development. New construction and modernization of this type of water power plants with output power under 1 MW however has ecological limits, since it makes use of small rivers and streams and it can affect their ecosystems. Synergetic effects can be expected when existing hydroelectric installations are modernized with transverse construction (dams) to increase their power generation capacities and at the same time to improve their hydro-ecological impacts. This development potential in Germany is estimated to imply an increase from currently 20 TWh up to 25 TWh per year.
The advantages of water power are obvious: The energy is normally available all the time, and water power plants have very long operating lifetimes. Furthermore, water turbines are extremely efficient, and can convert up to 90 % of the kinetic energy of the flowing water into electric power. By comparison: Modern natural gas combi-power plants have efficiencies of 60 %, and light-water reactors have only about 33 % efficiency.
ABB. 4WIND POWER INSTALLATIONS IN GERMANY
The development of wind energy e.g. in Germany from 1990 to 2011. The bars show the total number of wind power plants installed each year (accumulated); the blue curve gives the total installed generating capacity (right axis) (source: [14]).
Land-based Wind Energy
In Germany, the use of wind power (48.9 TWh) had clearly outstripped that of water power (18.8 TWh) by the year 2011. Modern wind energy plants attain efficiencies of up to 50 %. In 2011, plants yielding a wind power of about 2,000 MW were newly installed, bringing the total to 22,930 wind plants with an overall output power of 29,000 MW, generating about 7.6 % of the overall power consumed [14]. In the meantime, the so-called repowering is gaining momentum: Old plants are being replaced by more modern and more efficient installations. Thus, in 2011, 170 old plants with a nominal output power of 123 MW were replaced by 95 new ones with an overall output power of 238 MW [14].
In 2011, about 900 new plants were installed in Germany, with a total generating capacity of 2,000 MW; thus about 2.24 MW per installation. Given a long-term renewable potential wind power of 80,000 MW on land in Germany, and an average installed output power of 2.5 MW per plant, it would require 32,000 plants to realize the full potential of wind energy. At present, about 22,300 plants, each with an average power output of 1.3 MW, are in operation. Within the limitations of acceptance, citizen participation, questions of noise pollution, and the interests of nature and landscape conservation, it will be important in the coming years, in the course of authorization proceedings and land planning, to set up more efficient wind plants on higher towers (greater power yields!) at suitable locations.
This will permit the total number of plants to be limited, while at the same time increasing the overall yield: 32,000 plants on land, each with 2.5 MW output power, operating 2,500 full-power hours per year, would deliver a total of 200 TWh of electrical energy; that is about one-third of the current demand. This would be possible by making use of suitable sites on the seacoasts, but also in the interior by employing tower heights of over 100 m.A smaller portion of this potential could also be realized by installing smaller modern plants, taking the above criteria into account. A roughly equal potential of 200 TWh per year could in addition be realized by offshore wind plants in the Baltic and North Seas, so that simply by exploiting the available wind energy in Germany, in the long term, two-thirds of the current electric energy demand (of about 600 TWh/year) could be provided.
On windy days, the yield of wind energy in certain regions of Germany already exceeds the demand; on the other hand, on quiet days, other power sources have to compensate for the variable output of wind power plants. This applies increasingly also to photovoltaic plants, while in contrast, hydroelectric plants and the biomass have a ‘builtin’ storage capacity and can thus be independently regulated to meet demand. The future energy supply system will have to be able to deal with the fluctuating supply of power by means of rapidly controllable, decentral power plants (CHP, natural gas or gas produced using renewable energy), energy storage reservoirs, power management, etc. This new orientation of power system optimization based on supply security and making use of control engineering, information and communications technology can be considered to be a major challenge for the coming years [15,16].
ABB. 6WORLD PRODUCTION OF RENEWABLE ELECTRIC POWER
The fractions of electric power produced from various energy sources in 2008 (sources: [4,18]).
Biomass
The utilization of energy from the biomass is often underestimated. At present, biogenic heating fuels are being rediscovered in Germany. Wood, biowastes, liquid manure and other materials originating from plants and animals can be used for heating and also for electric power generation. The combination of the two uses is particularly efficient. In Germany, currently 90 % of the renewable heat energy originates from biofuels, mainly from wood burning – but increasingly also from wood waste, wood-chip and pellet heating and biogas plants, as well as the biogenic component of waste. Its contribution to electric power generation is also increasing: in 2011, it was 6 % of the overall German demand, corresponding to 37 TWh.
Biofuels are available around the clock and can be utilized in power plants like any other fuel. Biogenic vehicle fuels, as mentioned above, are getting renewable energy carriers rolling as suppliers for transportation.
Biogenic fuels, however, have come under massive public criticism, because they are not always produced under ecologically and socially acceptable conditions. In the worst case, they can even yield a poorer climate balance than fossil fuels. They thus require a detailed critical analysis and optimization process for each product, as is discussed in detail in the chapter “Biofuels: Green Opportunity or Danger?”.
Solar Energy
Solar energy is the renewable energy source par excellence. Its simplest form is the use of solar heat from collectors, increasingly employed for household warm water heating and for public spaces such as sports halls and swimming pools. More than 15 million square meters of collectors were installed on German rooftops as of 2011 [14].
Solar thermal power generation has meanwhile also made the transition to commercial applications on a large scale (see also the chapter “How the Sun gets into the Power Plant”). Parabolic trough collectors, solar towers or paraboloid dish reflector installations can produce temperatures of over 1000 °C, which with the aid of gas or steam turbines can be converted into electric power. These technologies could in the medium term contribute appreciably to the electric power supply. They are however efficient only in locations with a high level of insolation, such as in the whole Mediterranean region. Germany would thus have to import solar power from solar thermal plants via the common power grid, which initially could be laid out on a European basis; in the long term, North African countries could supply solar power via a ring transmission line around the Mediterranean Sea (see also the chapter “Power from the Desert”) [11,16,17].
The most immediate and technologically attractive use of solar energy is certainly photovoltaic conversion. The market for photovoltaic installations currently shows the most dynamic growth: Between 2000 (76 MW) and 2011 (25,039 MW), the installed peak power capacity increased in Germany by a factor of more than 300. This corresponds to a growth rate of 72 % per year during the past decade [4]. New production techniques at the same time offer the chance to produce solar cells considerably more cheaply and with less energy investment, and thus to allow a breakthrough onto the market (see the chapters “Solar Cells – An Overview”, “Solar Cells from Ribbon Silicon”, “Low-priced Modules for Solar Construction”, and “On the Path towards Power-Grid Parity”).
Geothermal Energy
The renewable energy resource which at present is the least developed is geothermal heat. Deep-well geothermal energy makes use either of hot water from the depths of the earth, or it utilizes hydraulic stimulation to inject water into hot, dry rock strata (hot-dry rock process), with wells of up to 5 km deep (see the chapter “Energy from the Depths”). At temperatures over 100 °C, electric power can also be produced – in Germany for example at the Neustadt-Glewe site in Mecklenburg-Vorpommern. Favorable regions with high thermal gradients are in particular the North German Plain, the North Alpine Molasse Basin, and the Upper Rhine Graben.
Geothermal heat has the advantage that it is available around the clock. Nevertheless, the use of geothermal heat and power production is still in its infancy. Especially the exploitation of deep-well geothermal energy is technically challenging and still requires intense research and development. Near-surface geothermal energy is more highly developed; heat pumps have long been in use.
The exploitation of deep-well and near-surface geothermal heat more than tripled in the decade from 2000 (1.7 TWh) to 2010 (5.6 TWh). If and when it becomes possible to utilize geothermal energy on a major scale, then its constancy and reliability will make a considerable contribution to the overall energy supply. Its long-term potential in Germany is estimated to be 90 TWh/year for electric power generation and 300 TWh/year for heating.
The Window of Opportunity
How will energy supplies in Germany develop in the future? Will all the renewable energy source options play a role, and if so, to what extent? The resolution of the federal government on June 6, 2011 contains the following elements for an energy turnaround in Germany:
An exit strategy for nuclear power in Germany by the end of 2022;
Continuous development of the use of renewable energy sources;
Modernization and further development of the electric power grid;
Energy conservation and an increase in efficiency in all areas concerning energy;
Attaining the challenging climate protection goals and thereby a clear-cut reduction in the consumption of fossil fuels.
The goal is a transition to a secure energy supply based for the most part on renewable energy sources in the long term. The basis for such a transition was already laid down in the past decade, with a renewable electric power fraction of 20 %, and 12 % of the overall energy supply in 2011. The upcoming system transformation will require continuing strong commitment and efforts.
The fact that the development of renewable energy sources is already leading to a number of positive results, including economic effects, is shown by its achievements up to the year 2011:
Reduction of greenhouse gas emissions by 130 million tons;
Avoided environmental damage worth about 10 billion € (especially climate damage at an average value of 80 €/ton of CO
2
);
Reduced imports of energy carriers: ca. 6.5 billion €;
Investments: 22.9 billion €;
Employment: 381,600 jobs;
Increase of regional added value.
If all the relevant quantities are considered (systems-analytical cost-benefit effects, distribution effects, macroeconomic effects), the benefits today already outweigh the costs. Nevertheless, support will still be necessary in the foreseeable future, since these quantities are related in a complex way [4,19,20]. In the course of the cost regression for subsidies of the various technologies making use of renewable energy sources, and the expected cost increases for fossil energy carriers due to their limited supplies and harmful effects on the climate, the beneficial aspects of renewable energy sources will presumably become more and more apparent [16].
Offshore and the Open Field
The next major step in the modification of the energy systems in Germany will be the start-up of offshore wind energy. Along the German seacoasts and within the ‘exclusive economic zone’ (EEZ), which extends out to a distance of 200 nautical miles (370km) from the coastline, a potential power-generating capacity of up to 25 GW of electric power output is predicted by the year 2020.
Such offshore wind installations will have to be built far from the coastline in water depths of up to 60 m. This is particularly true of the North Sea, which has strong winds. In the shallow water near the coasts, there are no suitable sites due to nature conservation areas, traditional exploitation rights such as gravel production, restricted military zones and ship traffic. Plants in deeper water, however, require a more complex technology and are more expensive. The high-power sea cables for transmitting the power to the coast over distances of 30 to 80 km will also drive up the investment costs.
However, the offshore installations far from the coast have a considerable advantage: The wind from the free water surface is stronger and steadier. This compensates to some extent for the higher costs of these wind parks. To be sure, the individual plants must deliver high power outputs. Only when they achieve an output power capacity of at least 5 MWel can they be economically operated under such conditions. A pioneering role in this development is being played by the wind park Alpha Ventus, which stands in water 30 m deep and 45 km in front of the coast of the island of Borkum: On August 12, 2009, the first 5 MW wind energy plants started delivering power, and in the meantime, all 12 plants are in operation [21]. The Fino offshore platforms perform useful services for the development of offshore wind parks. The Fino Research Initiative in the North and Baltic Seas is financed by an Offshore Trust, founded by commercial firms, nonprofit organizations and power-grid operators, and supported by the Federal Ministry for the Environment [22].
Scenarios for Ecologically Optimized Development
Just how the proportion of renewable energy sources within the energy mix in Germany will evolve in reality cannot of course be precisely predicted. However, model calculations make it clear which paths this evolution might take under plausible assumptions. The Institute for Technical Thermodynamics at the DLR in Stuttgart carried out a comprehensive study in 2004, analyzing various scenarios [23]. They took into account technical developments, economic feasibility, supply security and ecological and social compatibility. This study illustrates the essential trends. A series of other studies on ecological optimization and accompanying research has looked into various individual renewable energy technologies.
Figure 5 gives the distribution of power generation in Germany according to the type of power plant and the energy source within the long-term scenarios 2011 of the “Lead Study 2011” [16]. These scenarios aim at an economically acceptable increase in the use of renewable energy sources, but also take ecological factors into account. For over twelve years, the Federal Ministry for the Environment has issued such scenarios for the development of renewable energy sources. These scenarios have considered development paths which are ecologically optimized and are designed around sustainability criteria. They consider the dynamics of technical and economic developments and the interactions of the whole energy system in view of increasing contributions from renewable energy sources.
The so-called “Lead Study 2011” [16] took into account the energy turnaround package of the Federal government, in which nuclear energy is to be phased out by 2022. All of its assumptions agree precisely with the Resolution of June 6th, 2011, and they still represent a very felicitous summary of the development of renewable energy technologies, of other energy carriers, and of the necessary transformation of the overall energy system. This study also shows clearly that the required reductions in greenhouse gas emissions by 2020 and 2050 can in fact be accomplished: Half of the reductions through the continued development of renewable energy sources, and the other half through reduced energy consumption, improved energy efficiency and the reduction of the consumption of fossil energy carriers, in spite of the phasingout of nuclear power.
Renewable Energy on a Worldwide Scale
Figure 6 shows the contributions of various energy carriers to worldwide electric power generation in 2008. Fossil fuels were predominant, at 68 % of the total, while renewable energy sources already supplied 18.5 %, and nuclear energy 13.5 %. In the areas of heating and transportation, biogenic fuels in particular supply an appreciable fraction, which however must be critically examined in terms of its real sustainability.
Renewable energy sources can also play the leading role in the long-term global energy supply [12,13,24]. However, their further development alone will not achieve this goal. Thus, Figure 7 shows the parallel increase of the world’s population and of the global energy demand from 1971 to 2008 [18]. Without an energy turnaround on a global scale, reversing these trends will not be possible. We can reach the goal of a global energy supply with a high proportion of energy from renewable sources on a long-term basis only if we make additional strong efforts. One of these concerns improved energy efficiency and access to energy. In addition, worldwide population growth must be slowed considerably.
Summary
By the year 2011, already 12,5 % of the final energy consumption in Germany was supplied from renewable energy sources; for electrical energy, the proportion was 20,3 %, while for heating, it was 11 %, and for vehicle fuels, around 5.5 %. In the first half of 2012, its contribution to electric power generation had already risen to ca. 25 %. The German Federal government, with its resolutions of June 6th, 2011, intends (in the energy turnaround – Energiewende) to secure a continuous further development, which satisfies all of the ecological, economic and social criteria of sustainability. In Germany, a productive industrial sector with nearly 400,000 employees has developed around the exploitation of renewable energy sources. The goals enacted by the government are ambitious: at least 35 % of electric power to come from renewable sources by 2020 at the latest, and at least 80 % by 2050 at the latest; 18 % of the overall energy consumption by 2020, and 60 % by 2050. This national strategy is embedded in an EU Directive for the advancement of renewable energy sources. For global energy supplies, also, renewable sources must assume the predominant role. Successes within the EU and in other countries can serve as examples. Worldwide, 18.5 % of the electric power was generated from renewable sources.
References
[1] German Federal Ministry for the Environment, BMU: Web pages on renewable energy, www.erneuerbare-energien.de/english/renewable_energy/aktuell/3860.php.
[2] EP/ER: Directive of the European Parliament and Council, 2009/28/EG from April 23rd, 2009, for The Advancement of the Use of Energy from Renewable Sources, Official Register of the EU, L140/15 June 2009.
[3] International Feed-In Cooperation, www.feed-in-cooperation.org.
[4] BMU – Renewable Energy in Figures, Brochure, August 2012; available as pdf from www.erneuerbare-energien.de/english/renewable_energy_in_figures/doc/5996.php.
[5] European Commission: Communication 31.1.2011: Renewable Energy: Progressing towards the 2020 target. Available from: bit.ly/TRPt5V.
[6] Eurostat, Statistical Office of the EU, Luxemburg: Online Database. See epp.eurostat.ec.europa.eu/portal/page/portal/energy.
[7] EWEA – Annual Report 2010 of the European Wind Energy Association, 2011. Download: www.ewea.org/index.php?id=11.
[8] E. Bruns et al., Renewable Energies in Germany’s Electricity Market; Springer, Heidelberg 2010.
[9] Agency for Renewable Energies (Eds.): 20 Years of Support for Power from Renewable Energy in Germany, See: www.unendlich-viel-energie.de/en/homepage.html.
[10] Bundesverband Windenergie (BWE), www.windenergie.de (in German); European Wind Energy Association (EWEA), www.ewea.org; Global Wind Energy Council (GWEC), www.gwec.net.
[11] BMU – Renewable Energies – Perspectives for a Renewable Energy Future, Brochure, Heidelberg, 2011; See: www.erneuerbare-energien.de/english/renewable_energy/downloads/doc/44744.php.
[12] International Renewable Energy Agency (IRENA), 2011. www.irena.org.
[13] Renewable Energy Policy Network – REN21: Renewables2011Status Report: www.ren21.net.
[14] German Wind Energy Institute (DEWI): DEWI 2011: Jahresbilanz Windenergie 2010. See: www.dewi.de/dewi/index.php?id=1&L=0.
[15] Fraunhofer Institute for Wind Energy and Energy Systems Technology, IWES2011; See: www.iwes.fraunhofer.de/en.html.
[16] DLR, IWES, IfnE: Long-term scenarios 2011, “Lead Study 2011”, commissioned by the BMU, March 2012. See: www.erneuerbareenergien.de/english/renewable_energy/downloads/doc/48532.php.
[17] Desertec Foundation 2011, See: www.desertec.org.
[18] International Energy Agency (IEA), Renewables Information, Edition 2010. IEA/OECD, Paris 2010.
[19] ISI, GWS, IZES, DIW: Individual and Global Economic Analysis of Costs and Side Effects of the Development of Renewable Energies on the German Electric Power Market, Update 2010. See: www.erneuerbareenergien.de/english/renewable_energy/studies/doc/42455.php.
[20] GWS, DIW, DLR, ISI, ZSW: Short- and Long-Term Effects on the Employment Market of the Development of Renewable Energies in Germany, commissioned by the BMU (Ed.), Feb. 2011, See: www.erneuerbare-energien.de/english/renewable_energy/studies/doc/42455.php.
[21] Alpha Ventus2011, www.alpha-ventus.de/index.php?id=80.
[22] Fino Offshore Platforms 2011. See: www.fino-offshore.de (in German).
[23] Nitsch et al.: Ecologically optimised development of the utilisation of renewable energies, DLR: Stuttgart 2004 (in German). Commissioned by the BMU. See: www.erneuerbare-energien.de/english/renewable_energy/studies/doc/42455.php.
[24] IPCC Special Report on Renewable Energies2011. See: www.ipcc.ch.
The publications of the BMU can be ordered from the Department of Public Relations (Oeffentlichkeitsarbeit) in Berlin or from www.erneuerbare-energien.de.
About the Authors
Harald Kohl studied physics in Heidelberg and carried out his doctoral work at the Max-Planck Institute for Nuclear Physics there. Since 1992, he has worked at the Federal Ministry for the Environment, Natural Conservation and Nuclear Safety (BMU) in Bonn and Berlin. He is currently head of the Division of Public Information.
Wolfhart Dürrschmidt studied physics in Tübingen and earned his doctorate at the Institute for Physical and Theoretical Chemistry there. He is head of the Division of Fundamentals and Strategy for Renewable Energy at the BMU in Berlin.
Addresses:
Dr. Harald Kohl, Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (BMU), Referat K, Stresemannstr. 128–130, 10117 Berlin, Germany.
Dr. Wolfhart Dürrschmidt, BMU, Referatsleiter Kl III 1, Renewable Energies Köthener Str. 2–3, 10963 Berlin, Germany.
Wind Energy
A Tailwind for Sustainable Technology
BY MARTIN KÜHN | TOBIAS KLAUS
In Germany, more than 22,000 wind-energy plants are now online, providing about 10 % of the total power consumption. They have thus outstripped every other sustainable energy form here [1]. The Federal Ministry for the Environment considers a contribution of 25 % by the year 2030 to be possible. What potential does wind energy still hold?
Mankind has been making use of wind power for at least 4000 years. In Mesopotamia, Afghanistan and China, wind-powered water pumps and grinding mills were developed very early, apart from to the use of wind power for sailing ships. In earliest times, windmills utilized a vertical-shaft rotor, which was driven by the drag force acting on the rotor blades by the wind. This design concept, known as a drag device, has a low efficiency, roughly a fourth of that of the aerodynamic rotors described in the following sections [2]. It is still used by the widespread cup anemometers that measure wind velocity.
In Europe from around the 12th
