The origin and continuation of humankind is based on solar energy. The most basic processes supporting life on earth, such as photosynthesis and the rain cycle, are driven by solar energy. From the very beginning of its history humankind realized that a good use of solar energy is in humankind's benefit. Despite this, only recently, during the last 40 years, has 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 undergraduate 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 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 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 xiii 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.
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 characteristics of solar steam generation methods are presented, followed by solar chemistry applications, which include reforming of fuels and solar 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 desalination. 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 photovoltaic (PV) systems are presented. Finally, the chapter examines the concentrating PV and 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 /-chart method and program, the utilizability method, the $, /-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.
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 performance 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 family—my wife Rena, my son Andreas, and my daughter Anna—for the patience they have shown during the lengthy period required to write this book.
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 as 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 energy from alternative energy sources, and until recently, environmental pollution has been of little concern.
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 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 1200 billion barrels (2005) and the world natural gas reserves are 180 trillion m3 (2004). The current production rate is equal to 80 million barrels per day for oil and 7.36 billion m3 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 41 and 67 years, respectively (Goswami, 2007). The reserves for coal are in a better situation; they would be adequate for at least the next 230 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 increase continuously over the next decades. In addition, there is growing concern about the environmental 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.
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