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 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 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 948,000 million tons (2008), and the world natural gas reserves are 178.3 trillion m3 (2009). The current production rate is equal to 87.4 million barrels per day for oil, 21.9 million tons per day for coal and 9.05 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 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 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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