Renewable Energy

Renewable Energy Renewable Energy –Prof. Mohamed El-Kassaby Prof. Dr. M. M. El-Kassaby

The energy production in Egypt through the year 2005 was 100996 GWh. 73.9% of the total production was produced from thermal power station. 12.5 % was produced through the hydro station (Aswan Dam, Aswan reservoir, Esna and Nagh-hamady( 0.5% produced by wind (Zahfarana station). Prof. Dr. M. M. El-Kassaby

Solar Energy Prof. Dr. M. M. El-Kassaby

AVAILABILITY OF SOLAR ENERGY The mean extraterrestrial irradiance normal to the solar beam on the outer fringes of the earth's atmosphere is approximately 1.35 kW/m2. The earth and its atmosphere receive continuously 1.7X 1017 W of radiation from the sun. A world population of 10 billion with a total power need per person of 10 kW would require about 1011 kW of energy. It is thus apparent that if the irradiance on only 1 percent of the earth's surface could be converted into useful energy with 10 percent efficiency, solar energy could provide the energy needs of all the people on earth Prof. Dr. M. M. El-Kassaby

Solar Map • قال الله تعالى ” فلا أقسم برب المشارق والمغارب أنا لقادرون“ اية رقم 40 سورة المعارج. • ”وأورثنا القوم الذين كانوا يستضعفون مشارق الارض ومغاربها التى باركنا فيها وتمت كلمة ربك الحسنى على بنى اسرائيل بما صبروا ودمرنا ما كان يصنع فرعون وقومه وما كانوا يعرشون“ اية رقم 137 سورة الاعراف Prof. Dr. M. M. El-Kassaby

” الشمس تتعامد على وجه رمسيس- الف سائح شاهدوا فجر امس ظاهرة تعامد الشمس فى معبد الملك رمسيس الثانى داخل قدس الاقداس وقد استمرت هذه الظاهرة الفلكية النادرة لمدة 18 دقيقة وتحدث هذه الظاهرة مرتين كل عام فى 22 فبراير و22 أكتوبر“ • جريدة الاهرام 23-10-2000 Prof. Dr. M. M. El-Kassaby

Solar Motion—Altitude and Azimuth Angles • Since all motion is relative, it is convenient to call the earth fixed and to describe the sun's virtual motion in a coordinate system fixed to the earth with its origin at the site of interest. This approach is used throughout the analysis. To understand the geometry of the sun's motion, the relationship of the earth's axis of rotation to the plane of its orbit, the ecliptic مسار الشمس, must be known. The orbit and rotation occur about axes at an angle of about 23½° to one another. Figure 2.5 shows this relationship. Prof. Dr. M. M. El-Kassaby

Prof. Dr. M. M. El-Kassaby

the location of the sun can be specified by two angles, as shown in Fig. 2.6. The solar altitude angle α, is measured from the local horizontal plane upward to the center of the sun. It is measured between a line collinear with the sun's rays and the horizontal plane. The azimuth angle as, is measured in the horizontal plane between a due south line and the projection of the site-to-sun line on the horizontal plane as shown. The sign convention used for azimuth angle is positive east of south and negative west of south. A less convenient angle used by some solar engineers is the zenith angle z, which is the complement of the altitude angle α. Prof. Dr. M. M. El-Kassaby

Solar altitude and azimuth angles are not fundamental angles, however; they must be related to the fundamental angular quantities -hour angle, latitude, and solar declination - all of which will be described in turn. The three angles are shown in Fig. 2.7. • The solar hour angle hs is equal to 15° times the number of hours from local solar noon. Again, values east of due south, that is, morning values, are positive; values west, negative. The numerical value of 15°/hr is based upon the nominal time (24 hr) required for the sun to move around the earth (360°) once. Prof. Dr. M. M. El-Kassaby

The declination of the sun δs is the angle between the sun's rays and the zenith direction (directly overhead) at noon on the earth's equator as shown in Fig. 2.7. Stated another way, it has the same numerical value as the latitude at which the sun is directly overhead at noon on a given day. The tropics of Cancer (23½ °N) and Capricorn (23 ½ °S) are at the extreme latitudes where the sun is overhead at least once a year as shown in Fig. 2.5. The Arctic and Antarctic circles are defined as those latitudes above which the sun does not rise above the horizon plane at least once per year. They are located, respectively, at 66 ½ °N and 66 ½ ° S. Prof. Dr. M. M. El-Kassaby

The Sun-Path Diagram • In any given day the path of the sun is in a plane tilted at an angle from the horizontal plane equal to (90— L). The isometric sketch of sun paths at the solstices and equinoxes in Fig. 2.9a shows the orbital plane. Figure 2.9b contains both plan and elevation views of this same sun path showing the horizontal and vertical projections of the sun path for the example site at 40°N latitude. Prof. Dr. M. M. El-Kassaby

The projection of the sun's path on the horizontal plane is called a sun-path diagram. Such diagrams are very useful in determining shading phenomena associated with solar collectors, windows, and shading devices. As shown earlier, the solar angles (α, as) depend upon the hour angle, declination, and latitude. Since only two of these variables can be plotted on a two-dimensional graph, the usual method is to prepare a different sun-path diagram for each latitude with variations of hour angle and declination shown for a full year. A typical sun-path diagram is shown in Fig. 2.10 for 30°N latitude. Prof. Dr. M. M. El-Kassaby

EXAMPLE • A solar building with a south-facing collector is sited to the north-northwest of an existing building. Prepare a shadow map showing what months of the year and what part of the day point C at the base of the solar collector will be shaded. Ban and elevation views are shown in Fig. 2.12. Prof. Dr. M. M. El-Kassaby

SOLUTION • The limiting profile angle for shading is 40° and the limiting azimuth angles are 45° and 10° as shown in Fig. 2.12. These values are plotted on the the solar map. (Fig.2.13), shows that point C will be shaded during the following times of day for the periods shown: • Declination Date Time of day -23°27' Dec. 22 8:45 a.m.-12:40 p.m. -20° Jan. 21, Nov. 22 8:55 a.m.-12:35 p.m. -15° Feb. 9, Nov. 3 9:10 a.m.-12:30 p.m. Prof. Dr. M. M. El-Kassaby

References • Principles of solar Engineering, by Frank Kreith and Jan F. Kreider, Mac Graw Hill Prof. Dr. M. M. El-Kassaby

CALCULATION OF RADIATION INTERCEPTED BY SURFACES-BEAM COMPONENT Prof. Dr. M. M. El-Kassaby

Availability of solar and its Map At 30 oN latitude summer day sunny hours could reach 14 hours. winter minimum day sunny hours is 10 hours. Prof. Dr. M. M. El-Kassaby

Where: L = the latitude angle. Prof. Dr. M. M. El-Kassaby

Energy Conversion • The principal methods currently under consideration for solar energy conversion is subdivided into natural and technological collection systems, and these are further subdivided as shown in Fig. 1.4. Each of the methods is described briefly below. Prof. Dr. M. M. El-Kassaby

Thermal Conversion Thermal conversion is a technological scheme that utilizes a familiar phenomenon. When a dark surface is placed in sunshine, it absorbs solar energy and heats up. Solar energy collectors working on this principle consist of a surface facing the sun, which transfers part of the energy it absorbs to a working fluid in contact with it. To reduce heat losses to the atmosphere one or two sheets of glass are usually placed over the absorber surface to improve its efficiency. Prof. Dr. M. M. El-Kassaby

These types of thermal collectors suffer from heat losses due to radiation and convection, which increase rapidly as the temperature of the working fluid increases. Improvements such as the use of selective surfaces, evacuation of the collector to reduce heat losses, and special kinds of glass are used to increase the efficiency of these devices. Prof. Dr. M. M. El-Kassaby

The simple thermal-conversion devices described above are called flat-plate collectors. They are available today for operation over a range of temperatures up to approximately 365 K (200° F). These collectors are suitable mainly for providing hot service water and space heating and possibly are also able to operate absorption-type air-conditioning systems. Prof. Dr. M. M. El-Kassaby

The thermal utilization of solar energy for the purpose of generating low-temperature heat is at the present time technically feasible and economically viable for producing hot water and heating swimming pools, in some parts of the world thermal low-temperature utilization is also economically attractive for heating and cooling buildings. Other applications, such as the production of low-temperature steam, can be expected to become economically feasible soon. Prof. Dr. M. M. El-Kassaby

The generation of higher working temperatures as needed, for example, to operate a conventional steam engine requires the use of focusing devices in connection with a basic absorber-receiver. Operating temperatures as high as 4000 K (6740° F) have been achieved in the Odeillo solar furnace in France, and the generation of steam to operate pumps for irrigation purposes has also proved technologically feasible. Prof. Dr. M. M. El-Kassaby

Photovoltaic Conversion • The conversion of solar radiation into electrical energy by means of solar cells has been developed as a part of satellite and space-travel technology. The theoretical efficiency of solar cells is about 24 percent, and in practice efficiencies as high as 15 percent have been achieved with silicon photovoltaic devices Prof. Dr. M. M. El-Kassaby

Biological Conversion • Biological conversion of solar energy by means of photosynthesis التمثيل الضوئىis a natural process that has been studied by scientists for many decades. This form of solar energy utilization has been of the greatest importance by far to the human race. It provides a small but vital part of our energy consumption in the form of food and for thousands of years has served our ancestors in the form of wood as the only source of heat. Last, but not least, it is this process that in the course of millions of years produced our fossil fuels, which currently provide most of our energy. Prof. Dr. M. M. El-Kassaby

Wind Power The utilization of wind power has been widespread since medieval times. Windmills were used in rural United States to power irrigation pumps and drive small electric generators used to charge batteries that provided electricity during the last century. A windmill or wind turbine converts the kinetic energy of moving air into mechanical motion, usually in the form of a rotating shaft. This mechanical motion can be used to drive a pump or to generate electric power. Prof. Dr. M. M. El-Kassaby

Solar Energy Conversion by Oceans Almost 71 percent of the world's surface is covered by oceans. Oceans serve as a tremendous storehouse of solar energy because of the temperature differences produced by the sun as well as the kinetic energy stored in the waves. There are a number of places in the ocean where temperature differences of the order of 20-25 K exist at depths of less than 1000 m, and these temperature differences could be used to operate low-pressure heat engines. Prof. Dr. M. M. El-Kassaby

The second method of utilizing the storage capacity of the oceans for energy generation is through ocean waves. This approach is being developed in Japan and the United Kingdom, where prototype installations are presently being built. Cost estimates and projections in areas of the world favorable for this type of solar energy utilization method look encouraging. Although the applicability of ocean wave conversion will be limited to relatively few places, it may be one of the more important ways of providing power to some energy-poor nations of northern Europe. Prof. Dr. M. M. El-Kassaby

Thermal storage Why we need thermal storage? Prof. Dr. M. M. El-Kassaby

Storage Materials Sensible-Heat Storage-Liquids The most common medium for storing sensible heat for use with low- and medium-temperature solar systems is water. Water is cheap and abundant and has a number of particularly desirable properties. Table 5.2 lists advantages and disadvantages of aqueous storage of thermal energy. Prof. Dr. M. M. El-Kassaby

Water is the standard storage medium for solar-heating and -cooling systems for buildings today. For these systems, useful energy can be stored below the boiling point of water (without pressurization). The storage of water at temperatures above its normal boiling point requires expensive pressure vessels and is rarely cost-effective. Prof. Dr. M. M. El-Kassaby

Other liquids can be used for thermal storage above 100°C without a pressure vessel. Such liquids are usually organic chemicals with lower density and specific heat than water and with higher flammability. It is possible, however, to store substantial amounts of energy per unit volume, because higher temperatures may be utilized. The thermal properties of a number of common organic liquids with particularly high specific heats are given in Table 5.3. Prof. Dr. M. M. El-Kassaby

Sensible-Heat Storage-Solids • Sensible-heat storage in solids is advantageous for some applications. For example, thermal energy from an air collector can be stored in a bed of solid material for later heating of a building, or steam can be condensed in a particle bed and the heat removed later by a counter flow of air. Storage beds formed from uniformly sized particles of solid storage medium can act as both a storage medium and heat exchanger, thereby saving the cost of a separate heat exchanger. Prof. Dr. M. M. El-Kassaby

Solid-phase storage has an advantage over liquid storage in the size of the maximum allowable storage temperature excursion. Since most solid storage media do not melt readily, they are suited for use with high-temperature, concentrating collectors. Care must be taken to avoid thermal fracturing, however, since this could induce an overall particle size reduction and result in bed constriction. Prof. Dr. M. M. El-Kassaby

Renewable Energy