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

Prof. Dr. M. M. El-Kassaby

Renewable Energy

Renewable Energy –Prof. Mohamed 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).


Solar Energy


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


Solar Map

المشارق ” • برب أقسم فال تعالى الله قال “ رقم اية لقادرون أنا سورة 40والمغارب

المعارج.مشارق” • يستضعفون كانوا الذين القوم وأورثنا

كلمة وتمت فيها باركنا التى ومغاربها االرضصبروا بما اسرائيل بنى على الحسنى ربككانوا وما وقومه فرعون يصنع كان ما ودمرنا

رقم“ اية االعراف 137يعرشون سورة


• - سائح” الف رمسيس وجه على تتعامد الشمسفى الشمس تعامد ظاهرة امس فجر شاهدوا

قدس داخل الثانى رمسيس الملك معبدالفلكية الظاهرة هذه استمرت وقد االقداس

لمدة الظاهرة 18النادرة هذه وتحدث دقيقةفى عام كل و 22مرتين “22فبراير أكتوبر

االهرام • 2000-10-23جريدة


• 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

الشمس must be known. The orbit and ,مسارrotation occur about axes at an angle of about 23½° to one another. Figure 2.5 shows this relationship.



• 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.



• 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.



• 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.



• 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.


• 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.





• 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.




• 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.




• References

• Principles of solar Engineering, by Frank Kreith and Jan F. Kreider, Mac Graw Hill


• CALCULATION OF RADIATION INTERCEPTED BY SURFACES-BEAM COMPONENT



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.


Where:

L = the latitude angle.


Energy ConversionThe 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.



Thermal ConversionThermal 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.


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.


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.


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.


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.


Photovoltaic ConversionThe 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


Biological ConversionBiological conversion of solar energy by means

of photosynthesis الضوئى is a naturalالتمثيلprocess 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.


Wind PowerThe 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.


Solar Energy Conversion by OceansAlmost 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.


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.


Thermal storageWhy we need thermal storage?


Storage MaterialsSensible-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.



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.


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.



Sensible-Heat Storage-SolidsSensible-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.


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.



Latent-Heat StorageLatent-heat exchanges are involved in all

changes of phase-solid-solid, solid-liquid, solid-gas, liquid-gas, etc. Phase changes involving gases should generally be avoided in solar systems, since the large volume of gas involved precludes compact storage. Of the many substances undergoing phase changes at useful temperatures, all corrosive, combustible, expensive, and toxic materials are usually eliminated from consideration.



Phase-Change StoragePhase-change storage containers must be

carefully designed to account for poor heat-transfer properties of the media, possible corrosion, and leakage. If a volume change is associated with the phase change (30 percent is typical), the container must be capable of accommodating the change.

No general rules can be stated for shaping these storage containers other than that they must have a small cross section and large area normal to the direction of motion of the solid-liquid interface


SOLAR WATER HEATINGSolar water heating represents a low -

temperature use of solar energy in a mechanically simple system. Since most hot-water loads are quite uniform on a monthly basis, this solar application has a particularly high load factor and therefore can be quite cost-effective. From a thermodynamic viewpoint the best match of collection temperature to use temperature dictates use of a no concentrating collection device. Flat-plate liquid collectors are normally used in conjunction with aqueous storage.


Thermo siphon SystemsThe natural tendency of a less dense fluid to

rise above a more dense fluid can be used in a simple solar water heater to cause fluid motion through a collector. The density difference is created within the solar collector where heat is added to the liquid. This collection concept is called a thermo siphon. Figure 6.8 shows schematically the major components of such a system.



Since the driving force in a thermo siphon system is only a small density difference and not a pump, larger-than-normal plumbing fixtures must be used to reduce pipe friction losses. In general, one pipe size larger than would be used with a pump system is satisfactory. Under no conditions should piping smaller than 1/2-in national pipe thread (NPT) be used. Most commercial thermo siphons use 1-in NPT pipe.

The flow rate through a thermosiphon system is about 1 gal/ft2 • hr (40 liters/m2 • hr) in bright sun. Isometric views of Israeli and Australian thermo siphon heaters are shown in Fig. 6.9.



Optimum Tilt Angle


Where:

L = the latitude angle.


• For any period of time starting with day number N3 and ending with N4, the optimum tilt angle can be expressed as:

• Where N is the day number in the year starting from January first.





The highest position for January and December

The second position for February and November

The third position for march and October

The fourth position for April and September

The last position for may to end of august


Solar Air-Heating System





Passive Solar Heating System


Solar desalination



Intermediate Temperature Collector

(operating temperature in the range 367-439 K) Reasons for using Concentrating

Collectors

Three reasons are commonly cited for using concentrators:

1. To increase energy delivery temperatures in order to achieve a thermodynamic match between temperature level and task.


2. To improve thermal efficiency by reducing the heat-loss area relative to the receiver area. There would also be a reduction in transient effects, since the thermal mass is usually much smaller than for a flat-plate collector.

3. To reduce cost by replacing an expensive receiver by a less expensive reflecting or refracting area.


The CPC Collector (Concentrating Parabolic Collector)


Parabolic Troughs


Fresnel Lens Collectors


Central Receiver System


Hydro-power




Wind Energy


Small wind turbines have a maximum rated output of 100 kW. Such a wind turbine has a

blade diameter of 20 meters.

Almost all large wind turbines have three rotor blades, while the small wind turbines have a

variety of structural shapes.

The largest wind turbines in the market (2005) have a rotor diameter of 126 meters and rated outputs of up to 5000 kW, alternatively 5 MW.


للتوسع والطاقة الكهرباء وزارة خطةعام حتى المتجددة الطاقة 2010فى




Minister of electricity cited plans for generating 850 megawatts from the wind farm in Al-Zafarana by 2010.

Al-Zafarana currently provides 145 megawatts and work is underway to add 205 megawatts.

As for solar power, the Minister said that work on the first solar electricity plant in el-Korimat is in progress.

El Korimat is expected to generate 150 megawatts by 2008.

Documents

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