Solar Energy Engineering. Processes and Systems

815 Pages·2014·17.44 MB·English

by  Soteris A. Kalogirou (Auth.)

Solar Energy Engineering
Processes and Systems
Second Edition
Soteris A. Kalogirou
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Second edition 2014
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Preface
The origin and continuation of humankind is based on solar energy. The most basic processes sup-
porting life on earth, such as photosynthesis and the rain cycle, are driven by the solar energy. From the
very beginning of its history, the humankind realized that a good use of solar energy is in humankind’s
benefit. Despite this, only recently, during the last 40 years, has the solar energy been harnessed with
specialized equipment and used as an alternative source of energy, mainly because it is free and does
not harm the environment.
The original idea for writing this book came after a number of my review papers were published in
the journal Progress in Energy and Combustion Science. The purpose of this book is to give under-
graduate and postgraduate students and engineers a resource on the basic principles and applications of
solar energy systems and processes. The book can be used as part of a complete two-semester junior or
senior engineering course on solar thermal systems. In the first semester, the general chapters can be
taught in courses such as introduction to solar energy or introduction to renewable sources of energy.
This can be done by selecting only the descriptive parts of the various chapters and omitting most of
the mathematical details, which can be included in the course for more advanced students. The
prerequisites for the second part are, at least, introductory courses in thermodynamics and heat
transfer. The book can also be used as a reference guide to the practicing engineers who want to
understand how solar systems operate and how to design the systems. Because the book includes
a number of solved examples, it can also be used for a self-study. The international system of units (SI)
is used exclusively in the book.
The material presented in this book covers a large variety of technologies for the conversion of
solar energy to provide hot water, heating, cooling, drying, desalination, and electricity. In the
introductory chapter, the book provides a review of energy-related environmental problems and the
state of the climate. It also gives a short historical introduction to solar energy, giving some details of
the early applications. It concludes with a review of renewable energy technologies not covered in the
book.
Chapter 2 gives an analysis of solar geometry, the way to calculate shading effects, and the basic
principles of solar radiation-heat transfer. It concludes with a review of the solar radiation-measuring
instruments and the way to construct a typical meteorological year.
Solar collectors are the main components of any solar system, so in Chapter 3, after a review of the
various types of collectors, the optical and thermal analyses of both flat-plate and concentrating
collectors are given. The analysis for flat-plate collectors includes both water- and air-type systems,
whereas the analysis for concentrating collectors includes the compound parabolic and the parabolic
trough collectors. The chapter also includes the second-law analysis of solar thermal systems.
Chapter 4 deals with the experimental methods to determine the performance of solar collectors.
The chapter outlines the various tests required to determine the thermal efficiency of solar collectors. It
also includes the methods required to determine the collector incidence-angle modifier, the collector
time constant, and the acceptance angle for concentrating collectors. The dynamic test method is also
presented. A review of European standards used for this purpose is given, as well as quality test
methods and details of the Solar Keymark certification scheme. Finally, the chapter describes the
characteristics of data acquisition systems.
xv
xvi Preface
Chapter 5 discusses solar water-heating systems. Both passive and active systems are described, as
well as the characteristics and thermal analysis of heat storage systems for both water and air systems.
The module and array design methods and the characteristics of differential thermostats are then
described. Finally, methods to calculate the hot-water demand are given, as are international standards
used to evaluate the solar water-heater performance. The chapter also includes simple system models
and practical considerations for the setup of solar water-heating systems.
Chapter 6 deals with solar space-heating and cooling systems. Initially, methods to estimate the
thermal load of buildings are given. Then, some general features of passive space design are presented,
followed by the active system design. Active systems include both water-based and air-based systems.
The solar cooling systems described include both adsorption and absorption systems. The latter
include the lithium bromide–water and ammonia-water systems. Finally, the characteristics for solar
cooling with absorption refrigeration systems are given.
Industrial process heat systems are described in Chapter 7. First, the general design considerations
are given, in which solar industrial air and water systems are examined. Subsequently, the charac-
teristics of solar steam generation methods are presented, followed by solar chemistry applications,
which include reforming of fuels and fuel cells. The chapter also includes a description of active and
passive solar dryers and greenhouses.
Solar desalination systems are examined in Chapter 8. The chapter initially analyzes the relation of
water and energy as well as water demand and consumption and the relation of energy and desali-
nation. Subsequently, the exergy analysis of the desalination processes is presented, followed by
a review of the direct and indirect desalination systems. The chapter also includes a review of the
renewable energy desalination systems and parameters to consider in the selection of a desalination
process.
Although the book deals mainly with solar thermal systems, photovoltaics are also examined in
Chapter 9. First the general characteristics of semiconductors are given, followed by photovoltaic
panels and related equipment. Then, a review of possible applications and methods to design photo-
voltaic (PV) systems are presented. Finally, the chapter examines the concentrating PVand the hybrid
photovoltaic/thermal (PV/T) systems.
Chapter 10 deals with solar thermal power systems. First, the general design considerations are
given, followed by the presentation of the three basic technologies: the parabolic trough, the power
tower, and the dish systems. This is followed by the thermal analysis of the basic cycles of solar
thermal power plants. Finally, solar ponds, which are a form of large solar collector and storage system
that can be used for solar power generation, are examined.
In Chapter 11, methods for designing and modeling solar energy systems are presented. These
include the f-chart method and program, the utilizability method, the F, f-chart method, and the
unutilizability method. The chapter also includes a description of the various programs that can be
used for the modeling and simulation of solar energy systems and a short description of the artificial
intelligence techniques used in renewable energy systems modeling, performance prediction, and
control. The chapter concludes with an analysis of the limitations of simulations.
No design of a solar system is complete unless it includes an economic analysis. This is the subject
of the final chapter of the book. It includes a description of life cycle analysis and the time value of
money. Life cycle analysis is then presented through a series of examples, which include system
optimization and payback time estimation. Subsequently, the P1, P2 method is presented, and the
chapter concludes with an analysis of the uncertainties in economic analysis.
Preface xvii
The appendices include nomenclature, a list of definitions, various sun diagrams, data for terrestrial
spectral irradiation, thermophysical properties of materials, curve fits for saturated water and steam,
equations for the CPC curves, meteorological data for various locations, and tables of present worth
factors.
The material presented in this book is based on more than 25 years of experience in the field and
well-established sources of information. The main sources are first-class journals of the field, such as
Solar Energy and Renewable Energy; the proceedings of major biannual conferences in the field, such
as ISES, Eurosun, and World Renewable Energy Congress; and reports from various societies. A
number of international (ISO) standards were also used, especially with respect to collector perfor-
mance evaluation (Chapter 4) and complete system testing (Chapter 5).
In many examples presented in this book, the use of a spreadsheet program is suggested. This is
beneficial because variations in the input parameters of the examples can be tried quickly. It is,
therefore, recommended that students try to construct the necessary spreadsheet files required for this
purpose.
Finally, I would like to thank my familydmy wife Rena, my son Andreas, and my daughter
Annadfor the patience they have shown during the lengthy period required to write this book.
Soteris Kalogirou
Cyprus University of Technology
Preface to Second Edition
The new edition of the book incorporates a number of modifications. These include the correction of
various small mistakes and typos identified since the first edition was published. In Chapter 1 there is
an update on Section 1.4 on the state of climate, which now refers to the year 2011. The section on
wind energy (1.6.1) is modified and now includes only a brief historical introduction into wind energy
and wind systems technology, as a new chapter is included in the second revision on wind energy
systems. The following sections are also updated and now include more information. These are
Section 1.6.2 on biomass, Section 1.6.3 on geothermal energy, which now includes also details on
ground-coupled heat pumps, Section 1.6.4 on hydrogen, which now gives more details on electrolysis,
and Section 1.6.5 on ocean energy, which is enhanced considerably.
In Chapter 2 the sections on thermal radiation (2.3.2) and radiation exchange between surfaces
(2.3.4) are improved. In Section 2.3.9 more details are added on the solar radiation measuring
equipment. Additionally a new Section 2.4.3 is added, describing in detail TMY type 3. Some of the
charts in this chapter are improved and the ones that the reader can use to get useful data are now
printed larger in landscape mode to be more visible. This applies also to other charts in other chapters.
In Chapter 3, the section on flat-plate collectors is improved by adding more details on selective
coatings, and transpired solar collectors are added in the air collectors category. New types of
asymmetric CPC designs are now given in Section 3.1.2. A new Section 3.3.5 is added on the thermal
analysis of serpentine collectors and a new Section 3.3.6 is added on the heat losses from unglazed
collectors. Section 3.4 on thermal analysis of air collectors is improved and now includes analysis of
air collectors where the air flows between the absorbing plate and the glass cover. In Section 3.6.4, on
thermal analysis of parabolic trough collectors, a new section is added on the use of vacuum in annulus
space.
In Chapter 4 a new Section 4.6 has been added on efficiency parameter conversion and there is
a new Section 4.7: Assessment of Uncertainty in Solar Collector Testing. The listing of the various
international standards is updated as well as the description and current status of the various standards.
In Chapter 5, Section 5.1.1 on thermosiphon systems analysis is improved. The same applies for
Section 5.1.2 on integrated collector storage systems, where a method to reduce night thermal losses is
given. In Section 5.4.2 the array shading analysis, and pipe and duct losses are improved and a section
on partially shaded collectors is added. The status of the various international standards in Section 5.7
is updated. Finally, two new exercises are given.
In Chapter 6, Section 6.2.1 on building construction is modified and now includes a section on
phase-change materials. Section 6.2.3 on thermal insulation is improved and expanded by adding the
characteristics of insulating materials and advantages and disadvantages of external and internal
insulation.
In Chapter 7, Section 7.3.2 on fuel cells is clarified and diagrams of the various fuel cell types are
added. Section 7.4 on solar dryers is improved by adding some more details on the various types of
dryers and general remarks concerning the drying process.
Chapter 8 is modified by adding more analysis of desalination systems. Particularly, a diagram of
a single-slope solar still is now given as well as the design equations for Section 8.4.1 the multi-stage
flash process, Section 8.4.2 the multiple-effect boiling process, Section 8.4.3 the vapor compression
process, and Section 8.4.4 reverse osmosis.
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xx Preface to Second Edition
Chapter 9 is restructured considerably. In particular, Section 9.2.2 on types of PV technology,
Section 9.3.2 on inverters, Section 9.3.4 on peak power trackers and Section 9.4.5 on types of
applications are improved by adding new data. In the latter a new section is added on building-
integrated photovoltaics (BIPV). A new Section 9.6 on tilt and yield is added describing fixed tilt,
trackers, shading and tilting versus spacing considerations. Section 9.7 on concentrating PV is updated
and in Section 9.8 hybrid PV/T systems, two sections on the design of water- and air-heat recovery
have been added as well as a section on water and air-heating BIPV/T systems.
In Chapter 10, Section 10.2 on parabolic trough collector systems and 10.3 on power tower systems
are modified by adding details of new systems installed. A new Section 10.6 on solar updraft tower
systems is added, which includes the initial steps and first demonstration plants and the thermal
analysis. Additionally, Section 10.7 on solar ponds is improved by adding a new section on methods of
heat extraction, description of two experimental solar ponds and the last section on applications is
improved adding some cost figures.
In Chapter 11, a new Section 11.1.4 is added describing the f-chart method modification used for
the design of thermosiphon solar water-heating systems. Section 11.5.1 is modified by adding details
of TRNSYS 17 and TESS and STEC libraries. Chapter 12 has almost no modification from the first
edition.
Finally in this second edition a new chapter is added on wind energy systems. This chapter begins
with an analysis of the wind characteristics, the one-dimensional model of wind turbines, a survey of
the characteristics of wind turbines, economic issues, and wind energy exploitation problems.
Many thanks are given to people who communicated to me various mistakes and typos found in the
first edition of the book. Special thanks are given to Benjamin Figgis for his help on Chapter 9 and also
to Vassilis Belessiotis and Emanuel Mathioulakis for reviewing the section on uncertainty analysis in
solar collector testing and George Florides for reviewing the section on ground-coupled heat pumps.
Soteris Kalogirou
Cyprus University of Technology
CHAPTER
Introduction
1
1.1 General introduction to renewable energy technologies
The sun is the only star of our solar system located at its center. The earth and other planets orbit
the sun. Energy from the sun in the form of solar radiation supports almost all life on earth via
photosynthesis and drives the earth’s climate and weather.
About 74% of the sun’s mass is hydrogen, 25% is helium, and the rest is made up of trace quantities
of heavier elements. The sun has a surface temperature of approximately 5500 K, giving it a white
color, which, because of atmospheric scattering, appears yellow. The sun generates its energy by
nuclear fusion of hydrogen nuclei to helium. Sunlight is the main source of energy to the surface of the
earth that can be harnessed via a variety of natural and synthetic processes. The most important is
photosynthesis, used by plants to capture the energy of solar radiation and convert it to chemical form.
Generally, photosynthesis is the synthesis of glucose from sunlight, carbon dioxide, and water, with
oxygen as a waste product. It is arguably the most important known biochemical pathway, and nearly
all life on earth depends on it.
Basically all the forms of energy in the world as we know it are solar in origin. Oil, coal, natural
gas, and wood were originally produced by photosynthetic processes, followed by complex chemical
reactions in which decaying vegetation was subjected to very high temperatures and pressures over a
long period of time. Even the energy of the wind and tide has a solar origin, since they are caused by
differences in temperature in various regions of the earth.
Since prehistory, the sun has dried and preserved humankind’s food. It has also evaporated seawater
to yield salt. Since humans began to reason, they have recognized the sun as a motive power behind
every natural phenomenon. This is why many of the prehistoric tribes considered the sun as a god.
Many scripts of ancient Egypt say that the Great Pyramid, one of humankind’s greatest engineering
achievements, was built as a stairway to the sun (Anderson, 1977).
From prehistoric times, people realized that a good use of solar energy is beneficial. The Greek
historian Xenophon in his “memorabilia” records some of the teachings of the Greek philosopher
Socrates (470–399 BC) regarding the correct orientation of dwellings to have houses that were cool in
summer and warm in winter.
The greatest advantage of solar energy compared with other forms of energy is that it is
clean and can be supplied without environmental pollution. Over the past century, fossil fuels
provided most of our energy, because these were much cheaper and more convenient than en-
ergy from alternative energy sources, and until recently, environmental pollution has been of
little concern.
Solar Energy Engineering. http://dx.doi.org/10.1016/B978-0-12-397270-5.00001-7 1
Copyright Ó 2014 Elsevier Inc. All rights reserved.
2 CHAPTER 1 Introduction
Twelve autumn days of 1973, after the Egyptian army stormed across the Suez Canal on October
12, changed the economic relation of fuel and energy as, for the first time, an international crisis was
created over the threat of the “oil weapon” being used as part of Arab strategy. Both the price and the
political weapon issues were quickly materialized when the six Gulf members of the Organization of
Petroleum Exporting Countries (OPEC) met in Kuwait and abandoned the idea of holding any more
price consultations with the oil companies, announcing at the same time that they were raising the
price of their crude oil by 70%.
The rapid increase in oil demand occurred mainly because increasing quantities of oil, produced at
very low cost, became available during the 1950s and 1960s from the Middle East and North Africa.
For the consuming countries, imported oil was cheap compared with indigenously produced energy
from solid fuels.
The proven world oil reserves are equal to 1341 billion barrels (2009), the world coal reserves are
3
948,000 million tons (2008), and the world natural gas reserves are 178.3 trillion m (2009). The
current production rate is equal to 87.4 million barrels per day for oil, 21.9 million tons per day for coal
3
and 9.05 billion m per day for natural gas. Therefore, the main problem is that proven reserves of oil
and gas, at current rates of consumption, would be adequate to meet demand for only another 42 and
54 years, respectively. The reserves for coal are in a better situation; they would be adequate for at least
the next 120 years.
If we try to see the implications of these limited reserves, we are faced with a situation in which the
price of fuels will accelerate as the reserves are decreased. Considering that the price of oil has become
firmly established as the price leader for all fuel prices, the conclusion is that energy prices will in-
crease continuously over the next decades. In addition, there is growing concern about the environ-
mental pollution caused by burning fossil fuels. This issue is examined in Section 1.3.
The sun’s energy has been used by both nature and humankind throughout time in thousands of
ways, from growing food to drying clothes; it has also been deliberately harnessed to perform a
number of other jobs. Solar energy is used to heat and cool buildings (both actively and passively), heat
water for domestic and industrial uses, heat swimming pools, power refrigerators, operate engines and
pumps, desalinate water for drinking purposes, generate electricity, for chemistry applications, and
many more operations. The objective of this book is to present various types of systems used to harness
solar energy, their engineering details, and ways to design them, together with some examples and case
studies.
1.2 Energy demand and renewable energy
Many alternative energy sources can be used instead of fossil fuels. The decision as to what type of
energy source should be utilized in each case must be made on the basis of economic, environmental,
and safety considerations. Because of the desirable environmental and safety aspects it is widely
believed that solar energy should be utilized instead of other alternative energy forms because it can be
provided sustainably without harming the environment.
If the world economy expands to meet the expectations of countries around the globe, energy
demand is likely to increase, even if laborious efforts are made to increase the energy use efficiency. It
is now generally believed that renewable energy technologies can meet much of the growing demand
at prices that are equal to or lower than those usually forecast for conventional energy. By the middle of
1.2 Energy demand and renewable energy 3
the twenty-first century, renewable sources of energy could account for three-fifths of the world’s
1
electricity market and two-fifths of the market for fuels used directly. Moreover, making a transition
to a renewable energy-intensive economy would provide environmental and other benefits not
measured in standard economic terms. It is envisaged that by 2050 global carbon dioxide (CO2)
emissions would be reduced to 75% of their levels in 1985, provided that energy efficiency and re-
newables are widely adopted. In addition, such benefits could be achieved at no additional cost,
because renewable energy is expected to be competitive with conventional energy (Johanson et al.,
1993).
This promising outlook for renewables reflects impressive technical gains made during the past two
decades as renewable energy systems benefited from developments in electronics, biotechnology,
material sciences, and in other areas. For example, fuel cells developed originally for the space pro-
gram opened the door to the use of hydrogen as a non-polluting fuel for transportation.
Moreover, because the size of most renewable energy equipment is small, renewable energy
technologies can advance at a faster pace than conventional technologies. While large energy facilities
require extensive construction in the field, most renewable energy equipment can be constructed in
factories, where it is easier to apply modern manufacturing techniques that facilitate cost reduction.
This is a decisive parameter that the renewable energy industry must consider in an attempt to reduce
cost and increase the reliability of manufactured goods. The small scale of the equipment also makes
the time required from initial design to operation short; therefore, any improvements can be easily
identified and incorporated quickly into modified designs or processes.
According to the renewable energy-intensive scenario, the contribution of intermittent
renewables by the middle of this century could be as high as 30% (Johanson et al., 1993). A high
rate of penetration by intermittent renewables without energy storage would be facilitated by
emphasis on advanced natural gas-fired turbine power-generating systems. Such power-generating
systemsdcharacterized by low capital cost, high thermodynamic efficiency, and the flexibility to
vary electrical output quickly in response to changes in the output of intermittent power-generating
systemsdwould make it possible to backup the intermittent renewables at low cost, with little, if
any, need for energy storage.
The key elements of a renewable energy-intensive future are likely to have the following key
characteristics (Johanson et al., 1993):
1. There would be a diversity of energy sources, the relative abundance of which would vary from
region to region. For example, electricity could be provided by various combinations of
hydroelectric power, intermittent renewable power sources (wind, solar thermal electric, and
2
photovoltaic (PV)), biomass, and geothermal sources. Fuels could be provided by methanol,
ethanol, hydrogen, and methane (biogas) derived from biomass, supplemented with hydrogen
derived electrolytically from intermittent renewables.
1
This is according to a renewable energy-intensive scenario that would satisfy energy demands associated with an eightfold
increase in economic output for the world by the middle of the twenty-first century. In the scenario considered, world energy
demand continues to grow in spite of a rapid increase in energy efficiency.
2
The term biomass refers to any plant matter used directly as fuel or converted into fluid fuel or electricity. Biomass can be
produced from a wide variety of sources such as wastes of agricultural and forest product operations as well as wood,
sugarcane, and other plants grown specifically as energy crops.