Essentials of Energy Technology E-Book

Jochen Fricke

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2013

Seitenzahl: 735

Beschreibung

An in-depth understanding of energy technology, sources, conversion, storage, transport and conservation is crucial for developing a sustainable and economically viable energy infrastructure. This need, for example, is addressed in university courses with a special focus on the energy mix of renewable and depletable energy resources. Energy makes our lives comfortable, and the existence of amenities such as heaters, cars, warm water, household appliances and electrical light is characteristic for a developed economy. Supplying the industrial or individual energy consumer with energy 24 hours a day is a non-trivial challenge, especially in times where the energy is coming from very diverse resources such as oil, gas, nuclear fuels, wind, sun, or waves. This book gives physics, chemistry, engineering, and materials science students insights in the basics of energy and energy technology. It was developed along a successful course for advanced bachelor or graduate students and is written in a didactic style. The problems and solutions at the end of each chapter are ideal for exams and make self-study easy. Topics covered include energy from fossil and nuclear fuels, renewable sources, energy transport, storage, and conservation.

Leseprobe

Table of Contents

Related Titles

Title Page

Copyright

Acknowledgments

Preface

Abbreviations

Chapter 1: Introduction

1.1 Global Energy Flow

1.2 Natural and Anthropogenic Greenhouse Effect

1.3 Limit to Atmospheric CO2 Concentration

1.4 Potential Remedies

References

Solutions

Chapter 2: Energy Conservation with Thermal Insulation

2.1 Opaque Insulations

2.2 Transparent and Translucent Insulations

References

Solutions

Chapter 3: Thermodynamic Energy Efficiency

3.1 Carnot's Law

3.2 Stirling Engine

3.3 Irreversibilities

3.4 Exergy and Anergy

3.5 Compression Heat Pumps and Air-Conditioning Systems

3.6 Absorption Heat Transformers

3.7 Energy and Exergy Efficiency

References

Solutions

Chapter 4: Fossil Fuel-Fired Energy Converters

4.1 Power Plants

4.2 Internal Combustion Engines

4.3 Thermoelectric Converters (TECs)

4.4 Exotic Energy Converters

4.5 Absorption Cycles

4.6 Condensation Boilers

References

Solutions

Chapter 5: Nuclear Fission Energy and Power Plants

5.1 Binding Energy and Mass Defect

5.2 Fission

5.3 The Multiplication Factor

5.4 Reactor Control

5.5 Neutron Flux

5.6 Reactivity Changes during Power Plant Operation

5.7 Fuel Conversion and Breeding

5.8 Nuclear Reactor Types

5.9 The Fuel Question

5.10 U235 Enrichment

5.11 Spent Fuel

5.12 Reactor Safety and Accidents

References

Solutions

Chapter 6: Hydropower

6.1 Water Runoff from Mountains

6.2 Laminar and Turbulent Flow in Pipes

6.3 Running Water from Oceans

6.4 Ocean Tides

6.5 Ocean Waves

6.6 Ocean Thermal Energy Conversion (OTEC)

6.7 Energy from Osmotic Pressure

References

Solutions

Chapter 7: Wind Power

7.1 Wind Velocity

7.2 Using the Drag

7.3 Using the Lift

7.4 Technical Questions

7.5 Electricity from Wind on Demand

7.6 Small-Scale Wind Energy Conversion

7.7 Alternative Wind Energy Converters

7.8 Wind Energy Concentration

References

Solutions

Chapter 8: Photovoltaics (PV)

8.1 Diodes and Solar Cells

8.2 Transport Phenomena, Isc and Uoc

8.3 Temperature Effects

8.4 Equivalent Circuit

8.5 Absorption Process and Transitions

8.6 Advanced Solar Cells

8.7 Si Production and Energy Amortization

8.8 Other Solar Materials

8.9 From Solar Cells to Modules

8.10 Future Prospects for Photovoltaics

8.11 Wet Solar Cells

References

Solutions

Chapter 9: Solar Space and Hot Water Heating

9.1 Solar Radiation

9.2 Flat Plate Collectors

9.3 Evacuated Thermal Collectors

9.4 Compound Parabolic Concentrator (CPC)

9.5 Solar Thermal Heating Systems

References

Solutions

Chapter 10: Electricity and Fuels from Solar Heat

10.1 Concentration of Solar Radiation

10.2 Solar Troughs

10.3 Fresnel Systems

10.4 Solar Dish and Solar Tower

10.5 Solar Thermic Power Plants

10.6 Solar Fuels

References

Solutions

Chapter 11: Biomass Energy

11.1 Growth of Biomass

11.2 Direct Use of Solid Biomass

11.3 Biogas

11.4 Biofuel

11.5 Hydrothermal Carbonization of Biomass

References

Solutions

Chapter 12: Geothermal Energy

12.1 The Origin of Geothermal Energy

12.2 Geothermal Anomalies

12.3 Geothermal Power Plants

12.4 Hot Dry Rock

References

Solutions

Chapter 13: Energy Storage

13.1 Mechanical Energy Storage

13.2 Electric Energy Storage

13.3 Electrochemical Energy Storage

13.4 Chemical Energy Storage

13.5 Thermal Energy Storage

References

Solutions

Chapter 14: Energy Transport

14.1 Mechanical Energy Transport

14.2 Transporting Electricity

14.3 Heat Transport

References

Solutions

Chapter 15: Fuel Cells

15.1 General Considerations

15.2 Polymer Electrolyte Membrane Fuel Cell (PEMFC)

15.3 Solid Oxide Fuel Cell (SOFC)

15.4 Other Fuel Cells

References

Solutions

Chapter 16: Nuclear Fusion Energy

16.1 Introduction

16.2 Fuel for Fusion

16.3 Break-Even and the Lawson Criterion

16.4 Magnetic Confinement Fusion (MCF)

16.5 International Thermonuclear Experimental Reactor (ITER)

16.6 Inertial Confinement Fusion (ICF)

16.7 The National Ignition Facility (NIF)

References

Solutions

Index

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The Authors

Prof. Dr. Jochen Fricke

ZAE Bayern & Physikalisches Institut der

Universität Würzburg

Am Hubland

97074 Würzburg

Germany

Prof. Dr. Walter L. Borst

Texas Tech University

Physics Department

11 Science Building

Lubbock TX 79409

USA

Image credits for the cover illustration:

1) Solar Flare: http://solarsystem.nasa.gov/multimedia/gallery/PIA03149.jpg

2) Turbine: © Imaginis/fotolia.com

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.

© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-33416-2

Acknowledgments

We wish to thank our wives, Ursula Fricke and Zwanette Borst, for their patience during the time we were busy writing this book. We also hope for a secure and safe energy future for our children and grandchildren, and all persons on earth.

Preface

Back in 1980, two young physics professors – one (JF) in Würzburg, the other (WLB) in Carbondale, Illinois – authored the German textbook ENERGIE, which was published by R. Oldenbourg Verlag, München Wien. The book gave a thorough survey of energy-related physics and technology, described the energy situation, discussed global energy problems, and highlighted energy research and development. A second 600-page edition, published in 1984, was also sold out soon. For the next three decades, our professional obligations kept us from writing a revised version of this successful textbook.

Now, more than a quarter of a century later, we both are retired physics professors, but still teaching at our universities. We have taken a new initiative. As energy problems during recent decades have become global and more urgent, we have written a new book, this time in English. We have attempted a more compact treatment, as students today probably would despair of a 600-page book. The new textbook treats the basic physics of present energy technology and its consequences and discusses ideas of future interest. This new book also contains many new problems and their solutions.

We discuss quantitatively and qualitatively the physics and technology of all energy sources of present and likely future interest. The book can be used as textbook for advanced undergraduate and beginning graduate students. A physics background will be helpful. The mathematical level is mostly algebra, but also includes calculus.

General readers with a technical background should also be able to benefit from reading parts of the book. There is sufficient narrative in the text to understand the basic ideas without working through all the formulas and numbers. We hope that in this way the book will serve as a survey of all important energy sources and be useful to a broader audience.

The reader will notice that one of our concerns in the book is the anthropogenic greenhouse effect that results from the burning of fossil fuels. It is very likely that this effect could change our world beyond recognition and threaten terrestrial life in many parts of the globe, unless changes in energy production and use are made.

November 2012

Jochen Fricke

Walter L. Borst

Würzburg (Germany)

Lubbock (USA)

Abbreviations

ABB

Asea Brown Boveri

AC

air conditioner

ADS

accelerator-driven system

AFC

alkaline fuel cell

AFR

air–fuel ratio

AFUE

annual fuel utilization efficiency

AGR

advanced gas-cooled reactor

AM

air mass

aMDEA

activated methyldiethanolamine

AMTEC

alkali metal thermal energy converter

a-Si

amorphous silicon

ATP

adenosine triphosphate

BMR

basal metabolic rate

BSCO

BiSrCaCuO

BSF

back surface field

BTL

biomass to liquid

BTU

British Thermal Unit

BWR

boiling water reactor

CAES

compressed air energy storage

CANDU

CANadian Deuterium Uranium

CCS

carbon capture and storage

CFL

compact fluorescent lamps

CIGS

copper-indium-gallium-selenide

COP

coefficient of performance

CPC

compound parabolic concentrator

c-Si

crystalline silicon

CSP

concentrating solar power

CVD

chemical vapor deposition

DIN

Deutsche Industrie Norm

DLR

Deutsches Zentrum für Luft- und Raumfahrt

DMFC

direct methanol fuel cell

EDLC

electric double layer capacitor

EMEC

European Marine Energy Center

EPR

European Pressurized Reactor

EPS

expanded polystyrene

ETH

Eidgenössische Technische Hochschule

EVA

ethyl–vinyl acetate

FAME

fatty acid methyl ester

FFV

flexible fuel vehicle

FIT

feed-in-tariff

GWP

global warming potential

HDR

hot-dry-rock

HP

heat pump

HTC

heat transmission coefficient

HVDC

high-voltage direct current

IAEA

International Atomic Energy Agency

ICF

inertial confinement fusion

IEA

International Energy Agency

IGCC

integrated gasification combined cycle

IR

infrared

ITER

International Thermonuclear Experimental Reactor

JET

Joint European Torus

KART

Kumatori accelerator-driven reactor test

LED

light-emitting diode

LIFE

laser inertial fusion energy

LLNL

Lawrence Livermore National Laboratory

LMFBR

liquid metal fast breeder reactor

MBE

molecular beam epitaxy

MCF

magnetic confinement fusion

MCFC

molten carbonate fuel cell

MEA

methylethanolamine

MEGAPIE

megawatt pilot experiment

MHD

magneto-hydro-dynamic

MOX

mixed oxide

mpp

maximal power point

MSR

molten salt reactor

MYRRHA

multipurpose hybrid research reactor for high-tech applications

NADPH

2

nicotinamide adenine dinucleotide phosphate

NIF

National Ignition Facility

NREL

National Renewable Energy Laboratory

ORC

organic Rankine cycle

OTEC

ocean thermal energy converter

OWC

oscillating water column

PAFC

phosphoric acid fuel cell

PBMR

pebble bed modular reactor

PCM

phase change material

PE

polyethylene

PEM

polymer electrolyte membrane

PEMFC

polymer electrolyte membrane fuel cell

PET

poly(ethylene terephthalate)

PHWR

pressurized heavy water-moderated and -cooled reactor

PIUS

process-inherent ultimately safe

PMMA

poly(methyl methacrylate)

PV

photovoltaics

PVDF

poly(vinylidene fluoride)

PWR

pressurized water reactor

QDSL

quantum dot superlattice

RBMK

Reaktor Bolschoi Moschtschnosti Kanalny

RF

radiative forcing

RFS

redox flow system

RME

rapeseed methyl ester

RPV

reactor pressure vessel

SAD

Subcritical Assembly Dubna

SCR

Selective Catalytic reaction

SEER

seasonal energy efficiency ratio

SEGS

Solar Electric Generating System

SL

superlattice

SMES

superconducting magnetic energy storage

SOFC

solid oxide fuel cell

SWU

separation work unit

TEC

thermoelectric converter

TFTR

Tokamak Fusion Test Reactor

THTR

thorium high-temperature reactor

TiNOx

titanium-nitrite-oxide

TISES

Texas Instrument Solar Energy System

TMI

Three Mile Island

TNT

trinitrotoluene

Tokamak

Toroidalánaya kameras magnitnymi katushkami

TRADE

Triga accelerator-driven experiment

TS

temperature–entropy

TSR

tip speed ratio

VRFS

vanadium-redox flow system

VIG

vacuum-insulated glazing

VIP

vacuum insulation panel

WCD

World Commission on Dams

WEC

wind energy converter

WIPP

Waste Isolation Pilot Plant

XPS

extruded polystyrine

YBCO

YBaCuO

ZAE Bayern

Bayerische Zentrum für Angewandte Energieforschung

ZEBRA

Zeolite Battery Research Africa

Chapter 1

Introduction

1.1 Global Energy Flow

The global demand for primary energy has grown enormously during the past decades. It is now about 5.0 · 1020 J per year or 16 TW (Figure 1.1). Most of this energy is dissipated as waste heat. As the solar power reaching the Earth (insolation) is 170 000 TW, we recognize that, on a global scale, the heat dissipation caused by human activities is about 10 000 times smaller than the solar input. However, inside cities, the anthropogenic heat dissipation and the solar input can become comparable. This leads to a warmer microclimate.

Figure 1.1 Present global energy flow in Watt. The numbers in parentheses are relative to the solar input. About 80% of our primary energy is provided by fossil fuels, about 10% by biomass, and 6% by nuclear reactors. The contributions from photovoltaics, solar thermal, wind, geothermal, and tides are not shown, as each of them still amount to <1% of the primary energy demand.

(Source: Adapted from [1].)

1.2 Natural and Anthropogenic Greenhouse Effect

A much more severe and global problem associated with the flow of energy is the anthropogenic emission of greenhouse gases. Most important among these is carbon dioxide (CO2) released by burning of fossil carbon (Table 1.1). The average dwell time of CO2 in the atmosphere is about 120 years. CO2 is a natural constituent of the atmosphere together with water vapor, the latter being the dominant greenhouse gas. These gases interact with a thermal radiation of 1.1 · 1017 W or about 220 W/m2 from the Earth (Figures 1.1 and 1.2). Their molecules either have a permanent electric dipole moment, as with H2O, or are vibrationally excited, as in the case of CO2 and CH4, another greenhouse gas.

Table 1.1 The amount of CO2 emitted per thermal kilowatt hour depends strongly on the atomic carbon/hydrogen ratio of the fossil fuel (1 kg of C is oxidized into 3.7 kg CO2).

Figure 1.2 Hypothetical atmosphere of the Earth without infrared-active trace gases assumed in the left half of the figure. About two-thirds of the incoming solar radiation is absorbed at the surface of the Earth (with an albedo or reflectivity of 0.35), reemitted as thermal radiation, and completely given off into space. The resulting temperature would be about 18 °C below zero, preventing life as we know it. Greenhouse gases present in the real atmosphere are added in the right half of the figure. They absorb part of the outgoing thermal radiation and send it back to Earth. This greenhouse effect provides life-supporting temperatures of +15 °C. The most important greenhouse gas is H2O with typically 1–2% by weight, followed by CO2, CH4, NOx, and so on.

These gases thus reduce the radiative heat transfer from the Earth into space, raising the global mean temperature from −18 to +15 °C, a precondition for a habitable Earth. A stable mean temperature requires a balance between solar input and thermal output (Figure 1.3).

Figure 1.3 Normalized solar radiation input and thermal radiation at 300 K as a function of wavelength. The solar blackbody spectrum at 6000 K is modified by absorption in the Earth's atmosphere.

It is important to answer the question why the concentration of CO2 is of any consequence. After all, the concentration of water vapor is about 100 times larger. Figure 1.4 shows that some of the absorption bands of CO2 coincide with “windows” in the H2O spectrum. Thus, a relatively small amount of CO2 can reduce the thermal flow, that would otherwise escape into space through these windows. The effect of the other greenhouse gases on the thermal flow into space is characterized by the global warming potential (GWP). For example, CH4 has a GWP ≈ 25, indicating that one molecule of CH4 is 25 times more effective than one molecule of CO2.

Figure 1.4 Relative spectral absorption of water vapor and carbon dioxide in the atmosphere. A value of 1 means a saturated absorption or complete opaqueness, 0 indicates a “window” for radiative escape. One sees, for example, that CO2 drastically reduces the escape of thermal radiation in the H2O-window of 4–5 µm. Note that the three CO2-absorption bands shown are saturated only in their center but not in the flanks. Therefore, a further increase in CO2 in the atmosphere can definitely enhance the greenhouse effect.

(Source: Adapted from [2].)

CO2 and other noncondensing greenhouse gases together account for about 25% of the terrestrial greenhouse effect. Atmospheric modeling [3] shows that these gases via feedback processes provide the necessary infrared absorption to sustain the present levels of water vapor and clouds, which make up the remaining 75% of the terrestrial greenhouse effect. (Without CO2 and the other noncondensing greenhouse gases, the atmospheric water vapor would condense. The terrestrial greenhouse would collapse within a few decades, sending Earth into an ice-bound state.)

In summary, the natural greenhouse effect determined the climate on the Earth in the past and supported the development of life. About 150 years of anthropogenic activities, however, accompanied by the burning of coal, oil, and natural gas, have led to a drastic increase in the concentration of greenhouse gases in the atmosphere. This is causing an additional, human-related reduction in the thermal radiation transfer to space. The imbalance, also called radiative forcing, is about 1 W/m2 today [4]. This is only a 0.5% contribution to the total radiative heat transfer from the Earth. Furthermore, the large thermal mass of the oceans has stored large amounts of heat. Nonetheless, a global warming of about 0.8 K since 1870 and 0.6 K since about 1960 is observed.

The main culprit for the warming of the Earth is anthropogenic CO2. Its concentration in the atmosphere rose from a preindustrial value of 280 to about 390 ppm in the year 2010 (Figure 1.5).

Figure 1.5 The concentration of CO2 in the atmosphere at present is increasing by nearly two parts per million by volume per year (ppmv) and was about 390 ppmv in 2010. The oscillations on the continuous rise are about 6.5 ppmv peak-to-peak and are caused by annual variations in bioactivity and oxidation of biomass. Photosynthesis in summer causes a relative minimum in September/October, while oxidation of biomass in winter leads to a relative maximum in May. The preindustrial value was 280 ppmv.

(Source: Adapted from Mauna Loa, Hawaii.)

In order to put the anthropogenic influence on our climate in perspective, we have to look at the history of CO2. The CO2 concentration during the past 400 000 years fluctuated between about 180 and 280 ppm, and never exceeded 300 ppm. A higher CO2 concentration was always accompanied by warmer temperatures and vice versa. The increase to 390 ppm thus is rather dramatic. The retreat of mountain glaciers and the north polar ice sheet appear to be manifestations of the problem.

Problem 1.1

A warmer atmosphere can hold more moisture [5] and thus more torrential rains can be expected. Calculate the relative increase in water vapor pressure for an atmosphere at 20 °C, assuming a temperature increase of 1 K. The exponential dependence of vapor pressure on temperature is p(T) = p0 · exp[−ΔE/(kB · T)]. (In order to find ΔE, start with the mass specific heat of vaporization, then find the molar mass of water and the number of water molecules per mole.)

We should mention here that aerosols in the atmosphere are responsible for a negative radiative forcing. Combustion caused by humans has increased the amount of atmospheric aerosols substantially. The interaction between these aerosols and solar radiation leads to a direct cooling of the atmosphere. In addition, aerosols enhance the condensation of moisture and modify the optical properties of clouds. The sign of this indirect aerosol effect – whether positive or negative – is still uncertain. A third indirect aerosol effect involves the change of biochemical cycles [6]. All three effects may have reduced global warming substantially. Anticipating future worldwide installations of scrubbing devices, much higher CO2 mitigation costs could result than previously thought.

1.3 Limit to Atmospheric CO2 Concentration

In order to prevent catastrophic climate changes in the future, causing, for example, a rise in sea level of several meters, the CO2 concentration in the atmosphere will have to be limited. The actual limit is the subject of much discussion at present.

As an example, let us consider a maximum tolerable CO2 concentration of 560 ppm, that is, twice the preindustrial value. From the known global annual use of fossil fuels and the measured CO2 increase in the atmosphere, one can obtain the following estimate [7]: For each 4 Gt of burned carbon, the CO2 concentration in the atmosphere increases by 1 ppm. (If about one-half of the emitted CO2 were not absorbed in the ocean and by forests, the parts per million increase would be about twice as high). This amount of carbon corresponds to 4 · (12 + 32)/12 Gt = 14.7 Gt of CO2.

A limit of 560 ppm would “allow” an increase in CO2 concentration of (560 − 390) ppm = 170 ppm. This corresponds to a maximum total CO2 emission of 170 ppm · 14.7 Gt/ppm = 2500 Gt. If we assume the present annual global CO2 emission of 35 Gt to be constant in the future, we find a time span of about 70 years for “allowed” CO2 emissions. After that, any CO2 emission would have to stop. If we limit the CO2 concentration to 450 ppm, as many scientists suggest, the time span would shrink dramatically.

Problem 1.2

Calculate the remaining time span for a maximal CO2 concentration of 450 ppm. Assume that the global CO2 output due to human activities is kept at 35 Gt per year.

This type of estimate suggests how strongly the CO2 emission has to be reduced in the near future. As a reduction of the anthropogenic CO2 emission remains rather elusive, some concerned scientists have proposed geoengineering, the intentional large-scale alteration of the climate system [8]. The proposals include light shades positioned in space, ocean fertilization, aerosol injection into the stratosphere, and cloud brightening with saltwater droplets.

Considering the CO2 problem, we find that the discussion about “peak oil production or consumption” can be misleading. The carbon limit resulting from the above CO2 emission limit is 2500 · (12/44) Gt ≈ 680 Gt. Releasing this amount would severely worsen the greenhouse problem, but this amount is small compared to the still available fossil carbon resources. It seems that we will not be able to consume these resources.

On the other hand, we note that there are no energy or electricity sources that are entirely CO2-free. Even if a power plant emits no CO2 during operation, this greenhouse gas is emitted during construction of the plant. Thus electricity and thermal energy even from nuclear reactors and renewable sources are not CO2-free, but they have a low CO2 “footprint.” Perhaps in the far future, nonfossil energy systems will provide the energy needed for constructing power plants without a CO2 footprint.

Problem 1.3

Which reactions generate heat in a coal-fired power plant and in a nuclear reactor?

1.4 Potential Remedies

A compulsory lower CO2 production will be extremely difficult to accomplish in the next few decades if we keep in mind the magnitude of 13 TW of power produced from fossil fuels. In the following, we discuss some possible measures for reducing the emission of CO2 in the near term:

Energy conservation

Rational energy production and use

Carbon capture and storage (

CCS

)

Nuclear energy

Renewable energies.

1.4.1 Energy Conservation

A most efficient way to conserve energy is the thermal insulation of buildings. This especially applies to heating in cold climates and cooling in hot climates. Here, consumption could be reduced by a factor of 3 or more if existing houses were converted into low or ultra-low-energy houses. Many new houses in Germany are “passive houses,” where the demand for heating is below 30 kWh per m2 of living space and year. In Germany, 20 cm thick conventional fiber or foam insulation is the insulation standard for walls at the present time. In the United States, similar measures could be applied to a greater extent. Quite independent of this, much energy could be saved with more efficient and smaller cars.

Problem 1.4

A rather heavy car of mass m = 2000 kg stops every 0.5 km in city traffic and then accelerates again to v = 50 km/h. Calculate the extra number N of liters of diesel fuel (volume specific enthalpy h = 40 MJ/l) needed for this over a distance = 100 km. Assume an engine efficiency of η = 0.35. If the fuel mileage of the car is 7 l per 100 km or about 34 miles per gallon (mpg) during steady highway driving, what is it during city driving? Comment on alternatives to obtain a better fuel mileage.

1.4.2 Rational Energy Production and Use

Gas-fired, combined-cycle power plants employing gas and steam turbines in combination can achieve efficiencies of 60% for the generation of electricity. Fossil energy can be converted into electricity plus useful heat with efficiencies of over 80% if the power plant is connected to a district heating system. In the near future, coal-fired power plants with steam temperatures of 700 °C and efficiencies around 50% are feasible.

Another area with a large potential for higher energy efficiency is refrigeration. Refrigerators manufactured with an innovative insulation technology, using VIPs (vacuum insulation panels) with a nearly 10-fold improved insulation capability, consume 40–60% less electricity than conventionally insulated systems.

Replacing incandescent light bulbs by compact fluorescent lamps (CFL) and light-emitting diodes (LEDs) reduces the electricity demand for lighting by about a factor of 5.

1.4.3 Carbon Capture and Storage (CCS)

The extraction of CO2 from flue gases is being tested worldwide in pilot plants [9, 10]. The CO2 is absorbed at low temperatures in an amine solution and desorbed at higher temperatures for compression and storage, for example, in saline aquifers. Another technique, the oxifuel process, uses oxygen for combustion instead of air. This renders an extraction unnecessary but requires the separation of nitrogen and oxygen. The attitude of “not in my backyard” characterizes the difficulties of finding suitable underground storage sites for CO2. However, as 80% of our primary energy supply is still provided by fossil resources, carbon capture and storage (CCSs) seems a must.

1.4.4 Nuclear Energy

Worldwide, 437 nuclear reactors with a total installed power of about 390 GW were operating in 31 countries as of December 2011 [11]. They provide roughly 2600 TWh per year of base-load electricity. This corresponds to about 12% of the global annual electricity production of 22 000 TWh [12]. At present, 63 nuclear reactors with a total electric power output of 65 GW are under construction in 15 countries.

The reactors under development, so-called generation IV reactors, have improved safety features and higher efficiencies and they produce less radioactive waste than conventional reactors. For example, the European Union had been supporting a $400-million-a-year international effort to develop such reactors before the Fukushima reactor disaster [13]. The thorium high-temperature reactor (THTR) in Germany, operated in the 1980s and decommissioned in 1989, already had characteristics of a Gen IV reactor. The molten salt reactor (MSR) developed and operated in the 1960s at Oak Ridge National Laboratory in Tennessee used thorium fuel and had improved safety features compared to light water reactors, that is, a low pressure and a core that cools down and solidifies by itself.

After Fukushima, several countries have decided to phase out nuclear reactors, while others adhere to their commitment for more nuclear power. The German government announced in May 2011 that it would shut down all 17 German reactors. Italian voters opted for a non-nuclear future. On the other hand, South Korea announced plans in November 2012 to add 17 reactors to its 20 existing reactors by 2030 and to begin research and development on next-generation reactors. South Korean companies are preparing to build four reactors in the United Arab Emirates. China has 14 operating reactors and 27 reactors under construction. However, after Fukushima, it suspended approvals for new reactor construction. Vietnam, Turkey, Bangladesh, and Belarus are planning their first nuclear reactors with imports from abraod, primarily Russia. In the United States, the Nuclear Regulatory Commission granted the first construction permits for new reactors since 1978. The price tag for a new reactor is about $10 billion today compared to about $2 billion then and may pose an impediment [13].

In many countries, the commitment to nuclear power is strong. Largely unresolved is the storage or burial of the spent fuel in many parts of the world. Positive exceptions are Switzerland, Sweden, and Finland.

1.4.5 Renewable Energies

Hydroelectricity with 1000 GW installed power delivers about 3500 TWh per year or 16% of base-load electricity [12]. It has risen since 1965 at a rate of about 50 TWh/a, and has potential for further growth. In many countries, however, the growth is being slowed by environmental concerns. Base-load electricity from biomass amounts to about 400 TWh (2%). Wind energy with 240 GW installed power in 2011 provides a comparable but fluctuating output [12]. Geothermal sources with an output of 11 GW deliver 70 TWh (0.3%) of base load. Nearly 70 GW (fluctuating) from photovoltaics provided an amount of 70 TWh (0.3%) in 2011 [12]. Investments especially in wind turbines and photovoltaic and solar–thermal power plants are rising steeply today. With increasing installed power, the fluctuating electricity output of wind turbines and photovoltaic installations will pose problems for the stability of the electrical grid. Supply and demand have to be balanced on time scales ranging from seconds to months.

Energy storage facilities such as pumped water storage and electrochemical batteries are scarce. Highly dynamic power plants will have to cover the required loads in times of calm wind or overcast sky. Related to this is the search for suitable “smart grids.” These are intended to switch on and off electricity-consuming devices such as refrigerators and batteries of electric cars, depending on the availability from the grid.

If one considers the long times necessary for changes to our energy system and the yet very low worldwide electricity production from renewable sources, it is difficult to assess the impact of these in the future. In the very long term, that is, a century and beyond, solar, wind, and nuclear energy are likely to dominate our electricity supply.

Problem 1.5

The delivery of electricity from hydroelectric and photovoltaic installations differs fundamentally. Please state the difference.

References

1. Romer, R.H. (1976) Energy – An Introduction to Physics, W.H. Freeman and Company, San Francisco, CA.

2. Schlegel, M. and Deutscher, W. (1985) Promet – Meteorologische Fortbildung, 4/1985.

3. Lacis, A.A., Schmidt, G.A., Rind, D., and Ruedy, R.A. (2010) Science, 330, 356.

4. Trenberth, K.E. and Fasullo, J.T. (2009) Bull. Am. Meteorol. Soc., 90, 311.

5. Wentz, F.J., Ricciardulli, L., Hilburn, K., and Mears, C. (2007) Science, 317, 2.

6. Mahowald, N. (2011) Science, 334, 794.

7. Huntingford, C.C. and Lowe, J.J. (2007) Science, 316, 829.

8. Blackstock, J.J. and Long, J.C.S. (2010) Science, 327, 527.

9. Manning, L.R., Eric Russell, J., Padovan, J.C., Chait, B.T., Popowicz, A., Manning, R.S., and Manning, J.M. (2009) Science, 325, 1641–1658.

10. (2011) BWK, 63(3), 25–27.

11. Weßelmann, C. (2012) BWK, 64(7+8), 31.

12. Bloche, K., Witt, J., Kaltschmitt, M., and Janczik, S. (2012) BWK, 64(5), 5.

13. Normile, D. (2012) Science, 335, 1166.

Solutions

Solution 1.1 dp/dT = p0 · exp[−ΔE/(kB · T)](+ΔE/kB · T2) = p(T) · (+ΔE/kB · T2); dp/p0 = dT · ΔE/(kB · T02). With kB = 1.38 · 10−23 J/K, heat of vaporization of one molecule ΔE = 7 · 10−20 J, ΔT = 1 K and T0 = 293 K, we obtain dp/p0 ≈ 0.06 or 6% for the increase in water vapor pressure.

Solution 1.2 t(450) = (450 − 390) ppm · (14.7 Gt/ppm)/(35 Gt/a) ≈ 25 years.

Solution 1.3 The two heat-generating reactions are, respectively, C + O2 → CO2 and U235 + n(thermal) → fission products + 2.3 n(fast).

Solution 1.4 The extra number N of liters of fuel needed in the stop-and-go traffic of city driving is N = 2 · · (m · v2/2)/(η · h) = 2 · 100 · 2000 · (502/3.62)/(2 · 0.35 · 40 · 106) l ≈ 2.8 l. This means a fuel consumption of 9.8 l per 100 km or 24 mpg in the city for this heavy car compared to 7 l per 100 km or 34 mpg on the highway. Comment: Driving a smaller car would save energy. Regenerative breaking with an electric motor/generator combination would save even more energy.

Solution 1.5 Hydroelectricity is base-load electricity; photovoltaics provides fluctuating electricity with capacity factors between 10 and 20%, depending on the number of sunshine hours.

Chapter 2

Energy Conservation with Thermal Insulation

How can we reduce our energy consumption? In many countries substantial public resources are devoted to developing energy-saving technologies. As a result, people have choices. Policies to influence these include subsidies for installing solar thermal or solar photovoltaic collectors, information about the efficiency of appliances, education about energy conserving room temperature settings in summer and winter, and laws and regulations concerning energy use in new homes [1].

One of the most urgent tasks is a reduction in the heating and cooling requirements for buildings. In the United States buildings use 40% of the primary energy and more than 70% of all electricity [2]. In Germany more than 20 million houses and apartments are in need of renovation. Their energy requirement for heating alone is nearly 200 kWh per year and square meter of living space. This corresponds to about 20 liter of heating oil or 20 m3 of natural gas.

We describe here in detail the characteristics of various thermal insulations and how they can be used to conserve energy. This is one of the easiest and most cost-effective ways to reduce energy consumption. However, our emphasis on thermal insulation in this chapter should not detract from other important and often more challenging ways to conserve energy. We address many of these throughout this book.

2.1 Opaque Insulations

One of the most efficient ways for saving energy is to wrap the opaque parts of buildings with a thick layer of insulation and to install modern windows. Possible materials for thermal insulation are shown in Figure 2.1. At present, fiber and foam insulations dominate. Some environmentalists prefer cork, woodchips, straw, or paper clippings.

Conventional insulation suppresses convection because of small pore dimensions in the sub-millimeter range. This type of insulation does, however, experience heat losses by conduction through the gas and the lightweight solid fiber or foam skeleton. The other significant heat loss is via thermal radiation. More recently, the installation of flat vacuum insulation panels (s) [3, 4] in refrigerators and buildings has been on the increase. In these new systems gas conduction is greatly suppressed.