# Solar Energy

## E hhxi E hxo

Where m is the mass flow rate and x is mass concentration of LiBr in the solution. The first law of thermodynamics yields the energy balance of each component of the absorption system as follows E m.h i - E hh o EQ - EQo W 0 6.70 An overall energy balance of the system requires that the sum of the generator, evaporator, condenser, and absorber heat transfer must be 0. If the absorption system model assumes that the system is in a steady state and that the pump work and environmental heat losses...

## Ann applications in solar energy Systems

Artificial neural networks have been used by the author in the field of solar energy, for modeling the heat-up response of a solar steam generating plant (Kalogirou et al., 1998), the estimation of a parabolic trough collector intercept factor (Kalogirou et al., 1996), the estimation of a parabolic trough collector local concentration ratio (Kalogirou, 1996a), the design of a solar steam generation system (Kalogirou, 1996b), the performance prediction of a thermosiphon solar water heater...

## Integraltype

Integral-type, natural circulation, solar energy dryers are also called direct passive solar energy dryers. In this system, the crop is placed in a drying chamber, FIGURE 7.15 Schematic diagram of an integral-type passive solar dryer. FIGURE 7.15 Schematic diagram of an integral-type passive solar dryer. which is made with transparent walls therefore, the necessary heat is obtained by the direct absorption of solar radiation at the product, from the internal surfaces of the chamber, and by...

## Insolation On Tilted Surfaces

The amount of insolation on a terrestrial surface at a given location and time depends on the orientation and slope of the surface. In the case of flat-plate collectors installed at a certain fixed angle, system designers need to have data about the solar radiation on the surface of the collector. Most measured data, however, are for either normal incidence or horizontal. Therefore, it is often necessary to convert these data to radiation on tilted surfaces. Based on these data, a reasonable...

## Water Demand and Consumption

Humanity is dependent on rivers, lakes, and underground water reservoirs for freshwater requirements in domestic life, agriculture, and industry. However, rapid industrial growth and a worldwide population explosion has resulted in a large escalation of demand for freshwater, both for household needs and for crops to produce adequate quantities of food. Added to this is the problem of the pollution of rivers and lakes by industrial wastes and the large amounts of sewage discharge. On a global...

## Solar Dryers

Solar drying is another very important application of solar energy. Solar dryers use air collectors to collect solar energy. Solar dryers are used primarily by the agricultural industry. The purpose of drying an agricultural product is to reduce its moisture content to a level that prevents its deterioration. In drying, two processes take place One is a heat transfer to the product using energy from the heating source, and the other is a mass transfer of moisture from the interior of the...

## 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...

## Solar Energy References

Smithsonian Inst. Mish. Coll. Publ. No. 3530 98 5 . Abbot, C.G., December 27, 1938. Solar distilling apparatus. U.S. Patent No. 2,141.330. Abu-Zour, A., Riffat, S., 2006. Environmental and economic impact of a new type of solar louver thermal collector. Int. J. Low Carbon Technol. 1 3 , 217-227. Anderson, B., 1977. Solar Energy Fundamentals in Building Design. McGraw-Hill, New York. Baldacci, A., Burgassi, P.D., Dickson, M.H., Fanelli, M., 1998. Non-electric...

## Solar Power Paris Expositions

As was seen in Chapter 1, Section 1.5, solar thermal power systems were among the very first applications of solar energy. During the 18th century, solar furnaces capable of melting iron, copper, and other metals were constructed of polished iron, glass lenses, and mirrors. The furnaces were in use throughout Europe and the Middle East. The most notable examples are the solar furnace built by the well-known French chemist Lavoisier in 1774, various concentrators built by the French naturalist...

## Reforming of Fuels

Solar energy is essentially unlimited and its utilization does not create ecological problems. However, solar radiation reaching the earth is intermittent and not distributed evenly. There is thus a need to collect and store solar energy and transport it from the sunny uninhabited regions, such as deserts, to industrialized populated regions, where great quantities of energy are needed. An effective way to achieve this process is by the thermochemical conversion of solar energy into chemical...

## Parabolic Trough Collector Systems

Details of this type of collector are given in Chapter 3, Section 3.2.1. As was seen in Chapter 3, parabolic trough collectors are the most mature solar technology to generate heat at temperatures up to 400 C for solar thermal electricity generation or process heat applications. The biggest application of this type of system is the nine southern California power plants known as solar electric generating systems SEGS , which have a total installed capacity of 354 MWe Kearney and Price, 1992 ....

## Parabola construction

To achieve cost-effectiveness in mass production, the collector structure must feature not only a high stiffness-to-weight ratio, to keep the material content to a minimum, but also be amenable to low-labor manufacturing processes. A number of structural concepts have been proposed, such as steel framework structures with central torque tubes or double V trusses and fiberglass Kalogirou et al., 1994b . A recent development in this type of collectors is the design and manufacture of the...

## Renewable Energy Technologies

Renewable energy technologies produce marketable energy by converting natural phenomena into useful forms of energy. These technologies use the sun's energy and its direct and indirect effects on the earth (solar radiation, wind, falling water, and various plants i.e., biomass), gravitational forces (tides), and the heat of the earth's core (geothermal) as the resources from which energy is produced. These resources have massive energy potential however, they are generally diffused and not...

## Suntracking Concentrating Collectors

Energy delivery temperatures can be increased by decreasing the area from which the heat losses occur. Temperatures far above those attainable by flat-plate collectors can be reached if a large amount of solar radiation is concentrated on a relatively small collection area. This is done by interposing an optical device between the source of radiation and the energy-absorbing surface. Concentrating collectors exhibit certain advantages over the conventional flat-plate type Kalogirou et al.,...

## Challenges In Absorption Refrigeration

Heat Conversion Systems. CRC Press, Boca Raton, FL. Ameel, T.A., Gee, K.G., Wood, B.D., 1995. Performance predictions of alternative, low cost absorbents for open-cycle absorption solar cooling. Sol. Energy 54 2 , 65-73. Argiriou, A., 1997. Ground cooling. In Santamouris, M., Asimakopoulos, D. Eds. Passive Cooling of Buildings. James and James, London, pp. 360-403. ASHRAE, 1997. Handbook of Fundamentals. ASHRAE, Atlanta. ASHRAE, 1992. Cooling and Heating Load...

## Photovoltaics

Becquerel discovered the photovoltaic effect in selenium in 1839. The conversion efficiency of the new silicon cells, developed in 1958, was 11 , although the cost was prohibitively high 1000 W . The first practical application of solar cells was in space, where cost was not a barrier, since no other source of power is available. Research in the 1960s resulted in the discovery of other photovoltaic materials such as gallium arsenide GaAs . These could operate at higher temperatures than silicon...

## Thermosiphon Systems

Thermosiphon systems, shown schematically in Figure 5.1, heat potable water or transfer fluid and use natural convection to transport it from the collector to storage. The thermosiphoning effect occurs because the density of water drops with the increase of the temperature. Therefore, by the action of solar radiation absorbed, the water in the collector is heated and thus expands, becoming less dense, and rises through the collector into the top of the storage tank. There it is FIGURE 5.1...

## Direct Circulation Systems

A schematic diagram of a direct circulation system is shown in Figure 5.9. In this system, a pump is used to circulate potable water from storage to the collectors when there is enough available solar energy to increase its temperature and then return the heated water to the storage tank until it is needed. Because a pump is used to circulate the water, the collectors can be mounted either above or below the storage tank. Direct circulation systems often use a single storage tank equipped with...

## Indirect Water Heating Systems

A schematic diagram of indirect water heating systems is shown in Figure 5.11. In this system, a heat transfer fluid is circulated through the closed collector loop to a heat exchanger, where its heat is transferred to the potable water. The most commonly used heat transfer fluids are water-ethylene glycol solutions, although other heat transfer fluids such as silicone oils and refrigerants can be used. When fluids that are non-potable or toxic are used, double-wall heat exchangers should be...

## Air Water Heating Systems

Air systems are indirect water heating systems because air, circulated through air collectors and via ductworks, is directed to an air-to-water heat exchanger. In the heat exchanger, heat is transferred to the potable water, which is also circulated through the heat exchanger and returned to the storage tank. Figure 5.14 shows a schematic diagram of a double storage tank system. This type of system is used most often because air systems are generally used for preheating domestic hot water and...

## Liquid System Thermal Storage

Two types of water storage for liquid systems are available pressurized and unpressurized. Other differentiations include the use of an external or internal Cold water supply Cold water supply Immersed coil heat exchanger Tube bundle heat exchanger FIGuRE 5.16 pressurized storage with internal heat exchanger. heat exchanger and single or multiple tank configurations. Water may be stored in copper, galvanized metal, or concrete tanks. Whatever storage vessel is selected, however, this should be...

Generally, the cost of water produced in solar distillation systems depends on the total capital investment to build the plant, the maintenance requirements, and the amount of water produced. No energy is required to operate the solar stills unless pumps are used to transfer the water from the sea. Therefore, the major share of the water cost in solar distillation is that of amortization of the capital cost. The production rate is proportional to the area of the solar still, which means that...

## Lithiumwater absorption systems

The LiBr-H2O system operates at a generator temperature in the range of 70-95 C, with water used as a coolant in the absorber and condenser, and has a COP higher than the NH3-H2O systems. The COP of this system is between 0.6 and 0.8. A disadvantage of the LiBr-H2O systems is that their evaporator cannot operate at temperatures much below 5 C, since the refrigerant is water vapor. Commercially available absorption chillers for air-conditioning applications usually operate with a solution of...

## Solar Angles

The earth makes one rotation about its axis every 24 h and completes a revolution about the sun in a period of approximately 365.25 days. This revolution is not circular but follows an ellipse with the sun at one of the foci, as shown in Figure 2.3. The eccentricity, e, of the earth's orbit is very small, equal to 0.01673. Therefore, the orbit of the earth round the sun is almost circular. The sun-earth distance, R, at perihelion shortest distance, at January 3 and aphelion longest distance, at...

## Concentrating collector acceptance angle

Another test required for the concentrating collectors is the determination of the collector acceptance angle, which characterizes the effect of errors in the tracking mechanism angular orientation. This can be found with the tracking mechanism disengaged and by measuring the efficiency at various out-of-focus angles as the sun is traveling over the collector plane. An example is shown in Figure 4.8, where the angle of incidence measured from the normal to the tracking axis i.e., out-of-focus...

## Windows Sunspaces

The direct gain system is the simplest way of achieving passive heating. In this system, sunlight enters through windows or skylights and is absorbed by the inside surfaces of the building. In a direct gain system, thermal collection, dissipation, storage, and transfer of energy take place within the habitable space. This is the most effective of all passive concepts from the point of view of energy collection and simplicity. Additionally, this system allows the use of sun for lighting daylight...

## Using A Solar Simulator

In countries with unsuitable weather conditions, the indoor testing of solar collectors with the use of a solar simulator is preferred. Solar simulators are generally of two types those that use a point source of radiation mounted well away from the collector and those with large area multiple lamps mounted close to the collector. In both cases, special care should be taken to reproduce the spectral properties of the natural solar radiation. The simulator characteristics required are also...

## Pebble bed storage size correction

For the development of the -chart of Figure 11.6, a standard storage capacity of 0.25 cubic meters of pebbles per square meter of collector area was considered, which corresponds to 350 kJ m2- C for typical void fractions and rock properties. Although the performance of air-based systems is not as sensitive to the storage capacity as in liquid-based systems, other storage capacities can be used by modifying the factor X by a storage size correction factor, Xc X, as given by Klein et al., 1977...

## T-s Diagram Of Regenerative Rankine Cycle

Or h4. h3 - turbine h3 - h4 3151 - 0.8 3151 - 2787 2860 kJ kg. At point 5, P5 13 bar and T5 390 C. From superheated steam tables, h5 3238 kJ kg and s5 7.212 kJ kg-K. At point 6, s6 s5 7.212 kJ kg-K. From the problem definition, P6 0.16 bar. From steam tables, s6f 0.772 kJ kg-K and s6g 7.985 kJ kg-K. Therefore, at this point, we have a wet vapor and its dryness fraction is s - sf _ 7.212 - G.772 7.9S5 - G.772 At a pressure of 0.16 bar, hf 232 kJ kg and hfg 2369 kJ kg therefore, h6 hf xhfg 232...

## References

Handbook of Systems and Equipment. ASHRAE, Atlanta, GA. ASHRAE, 2007. Handbook of HVAC Applications. ASHRAE, Atlanta, GA. Charters, W.W.S., de Forest, L., Dixon, C.W.S., Taylor, L.E., 1980. Design and performance of some solar booster heat pumps. In ANZ Solar Energy Society Annual Conference, Melbourne, Australia. Close, D.J., 1962. The performance of solar water heaters with natural circulation. Solar Energy 6 1 , 33-40. Duff, W.S., 1996. Advanced Solar Domestic Hot Water...

## The Multi Stage Flash MSF Process

The MSF process is composed of a series of elements, called stages. In each stage, condensing steam is used to pre-heat the seawater feed. By fractionating the overall temperature differential between the warm source and seawater into a large number of stages, the system approaches ideal total latent heat recovery. Operation of this system requires pressure gradients in the plant. The principle of operation is shown in Figure 8.4. Current commercial installations are designed with 10-30 stages...

## Power Tower Systems

As was explained in Chapter 3, Section 3.2.4, power towers or central receiver systems use thousands of individual sun-tracking mirrors, called heliostats, to reflect solar energy onto a receiver located atop a tall tower. The receiver collects the sun's heat in a heat transfer fluid molten salt that flows through the receiver. This is then passed optionally to storage and finally to a power conversion system, which converts the thermal energy into electricity and supplies it to the grid....

## Semiconductors

To understand the photovoltaic effect, some basic theory about semiconductors and their use as photovoltaic energy conversion devices needs to be given as well as information on p-n junctions. These are explained in the following sections. As is well known, atoms consists of the nucleus and electrons that orbit the nucleus. According to quantum mechanics, electrons of an isolated atom can have only specific discrete or quantized energy levels. In elements that have electrons in multiple...

## Incidence ANGLE

The solar incidence angle, 9, is the angle between the sun's rays and the normal on a surface. For a horizontal plane, the incidence angle, 9, and the zenith angle, are the same. The angles shown in Figure 2.9 are related to the basic angles, shown in Figure 2.5, with the following general expression for the angle of incidence Kreith and Kreider, 1978 Duffie and Beckman, 1991 cos 9 sin L sin 6 cos 3 - cos L sin 6 sin 3 cos Zs cos L cos 6 cos h cos 3 sin L cos 6 cos h sin 3 cos Zs cos 6 sin h...

## Dish Systems

As was seen in Chapter 3, Section 3.2.3, dish systems use dish-shaped parabolic mirrors as reflectors to concentrate and focus the sun's rays onto a receiver, which is mounted above the dish at the dish focal point. The receiver absorbs the energy and converts it into thermal energy. This can be used directly as heat or can support chemical processes, but its most common application is in power generation. The thermal energy can be either transported to a central generator for conversion or...

## Exploded View Of A Flat Plate Collector And Absorbed Details

Copyright METEOTEST Bern, Switzerland FIGURE 2.30 Annual total solar irradiation on horizontal surface for Europe. Source Meteonorm database of Meteotest www.Meteonorm.com . Copyright METEOTEST Bern, Switzerland FIGURE 2.30 Annual total solar irradiation on horizontal surface for Europe. Source Meteonorm database of Meteotest www.Meteonorm.com . Global radiation, annual mean 1981-2000 www.meteonorm.com Copyright METEOTEST Bern, Switzerland FIGURE 2.31 Annual total solar irradiation on...

## Thermal Analysis of Compound Parabolic Collectors

The instantaneous efficiency, r , of a CPC is defined as the useful energy gain divided by the incident radiation on the aperture plane that is, In Eq. 3.85 , Gt is the total incident radiation on the aperture plane. The useful energy, Qu, is given by an equation similar to Eq. 3.60 , using the concept of absorbed radiation as Qu Fr SAa - ArUL T - Ta 3.86 The absorbed radiation, S, is obtained from Duffie and Beckman, 1991 S GB,CPCTc,BTCPC,Ba B GD,CPCTc,D TCPC,Da D GG,CPCTc,G TCPC,GaG tc...

## Collector Thermal Efficiency

The collector performance test is performed under steady-state conditions, with steady radiant energy falling on the collector surface, a steady fluid flow rate, and constant wind speed and ambient temperature. When a constant inlet fluid temperature is supplied to the collector, it is possible to maintain a constant outlet fluid temperature from the collector. In this case, the useful energy gain from the collector is calculated from From Chapter 3, we have seen that the useful energy...

## Horizontal ns axis with ew tracking

For a plane rotated about a horizontal north-south axis with continuous adjustment to minimize the angle of incidence, 9 can be obtained from Kreith and Kreider, 1978 Duffie and Beckman, 1991 cos 9 sin2 a cos2 6 sin2 h 2.28a or from this equation Meinel and Meinel, 1976 cos 9 cos cos h cos 6 sin2 h 2.28b The basic geometry of this configuration is shown in Figure 2.10d. The greatest advantage of this arrangement is that very small shadowing effects are encountered when more than one collector...

## Solar azimuth angle z

The solar azimuth angle, z, is the angle of the sun's rays measured in the horizontal plane from due south true south for the Northern Hemisphere or due north for the Southern Hemisphere westward is designated as positive. The mathematical expression for the solar azimuth angle is This equation is correct, provided that ASHRAE, 1975 cos h gt tan 6 tan L . If not, it means that the sun is behind the E-W line, as shown in Figure 2.4, and the azimuth angle for the morning hours is tc z and for the...

## Intentional Thermal Mass Effects

To make the best use of thermal mass, the building should be designed with this objective in mind. Intentional use of the thermal mass can be either passive or active. Passive solar heating is a common application that utilizes the thermal mass of the building to provide warmth when no solar energy is available. Passive cooling applies the same principles to limit the temperature rise during the day. The spaces can be naturally ventilated overnight to absorb surplus heat from the building mass....

## Qu AcFr[GtTa UlT Ta

This is the same as Eq. 3.31 , with the difference that the inlet fluid temperature T replaces the average plate temperature Tp with the use of the FR. In Eq. 3.60 , the temperature of the inlet fluid, T, depends on the characteristics of the complete solar heating system and the hot water demand or heat demand of the building. However, FR is affected only by the solar collector characteristics, the fluid type, and the fluid flow rate through the collector. FIGURE 3.29 Collector flow factor as...

## Thermal Analysis Of Solar Power Plants

Thermal solar power plants are similar to the conventional ones with the exception that a field of concentrating solar collectors replaces the conventional steam boiler. In hybrid plants, a conventional boiler is also present, operating on conventional fuel, usually natural gas, whenever there is a need. Therefore, the thermal analysis of solar power plants is similar to that of any other plant and the same thermodynamic relations are applied. The analysis is greatly facilitated by drafting the...

## Process Selection

During the design stage of a renewable energy-powered desalination system, the designer must select a process suitable for that particular application. The factors that should be considered for such a selection are the following Kalogirou, 2005 1. The suitability of the process for renewable energy application. 2. The effectiveness of the process with respect to energy consumption. 3. The amount of freshwater required in a particular application, in combination with the range of applicability...

## Concentrating Collectors

As we have seen in Section 3.2, concentrating collectors work by interposing an optical device between the source of radiation and the energy-absorbing surface. Therefore, for concentrating collectors, both optical and thermal analyses are required. In this book, only two types of concentrating collectors are analyzed compound parabolic and parabolic trough collectors. Initially, the concentration ratio and its theoretical maximum value are defined. The concentration ratio C is defined as the...

The main factor affecting the power output from a PV system is the absorbed solar radiation, S, on the PV surface. As was seen in Chapter 3, S depends on the incident radiation, air mass, and incident angle. As in the case of thermal collectors, when radiation data on the plane of the PV are unknown, it is necessary to estimate the absorbed solar radiation using the horizontal data and information on incidence angle. As in thermal collectors, the absorbed solar radiation includes the beam,...

## Solar Cooling With Absorption Refrigeration

The greatest disadvantage of a solar heating system is that a large number of collectors need to be shaded or disconnected during summertime to reduce overheating. A way to avoid this problem and increase the viability of the solar system is to employ a combination of space heating and cooling and domestic hot water production system. This is economically viable when the same collectors are used for both space heating and cooling. Flat-plate solar collectors are commonly used in solar space...

## Differential temperature controller

One of the most important components of an active solar energy system is the temperature controller because a faulty control is usually the cause of poor system performance. In general, control systems should be as simple as possible and should use reliable controllers, which are available nowadays. One of the critical parameters that need to be decided by the designer of the solar system is where to locate the collector, storage, over-temperature, and freezing-temperature sensors. The use of...

## Cpc Evacuated Tube

FIGURE 3.7 schematic diagram of an evacuated tube collector. influences, such as condensation and moisture, cause early deterioration of internal materials, resulting in reduced performance and system failure. Evacuated heat pipe solar collectors tubes operate differently than the other collectors available on the market. These solar collectors consist of a heat pipe inside a vacuum-sealed tube, as shown in Figure 3.7. In an actual installation, many tubes are connected to the same manifold as...

## Example

The system described in Example 11.15 is heated by a hybrid collector-passive storage system. The solar collector is air type with an area equal to 30 m2, FR ja n 0.65, FRUL 4.95 W m2- C, and t 0.91. In this case, the room temperature is 20 C. Estimate the solar fraction for December and the auxiliary energy required. UA h Tb - Ta A_cFRUL T - Ta AcFr Ta 197.3 18.3 - 11.1 30 X 4.95 20 - 11.1 From Example 11.15, A -0.888, B -0.615, and C 0.521. From Eq. 11.34 , Similarly, d 0.603. From Eq. 11.100...

## Materials Processing

Solar energy material processing involves affecting the chemical conversion of materials by their direct exposure to concentrated solar energy. For this purpose, we use solar furnaces made of high-concentration, hence, high-temperature, collectors of the parabolic dish or heliostat type. Solar energy can also assist in the processing of energy-intensive, high-temperature materials, as in the production of solar aluminum, the manufacture of which is one of the most energy-intensive processes. It...

## Thermal Analysis Of Flatplate Collectors

In this section, the thermal analysis of the collectors is presented. The two major types of collectors, flat plate and concentrating, are examined separately. The basic parameter to consider is the collector thermal efficiency. This is defined as the ratio of the useful energy delivered to the energy incident on the collector aperture. The incident solar flux consists of direct and diffuse radiation. While flat-plate collectors can collect both, concentrating collectors can utilize direct...

## Building Heat Transfer

The design of space heating or cooling systems for a building requires the determination of the building thermal resistance. Heat is transferred in building components by all modes conduction, convection, and radiation. In an electrical analogy, the rate of heat transfer through each building component can be obtained from Q _ total UA X ATota 6.28 ATtotal total temperature difference between inside and outside air K . totai total thermal resistance across the building element, YRi m2-K W . A...

## Characteristics of a thermal storage wall

A thermal storage wall is essentially a high-capacitance solar collector directly coupled to the room. Absorbed solar radiation reaches the room either by conduction through the wall to the inside wall surface from which it is convected and radiated into the room or by the hot air flowing though the air gap. The wall loses energy to the environment by conduction, convection, and radiation through the glazing covers. A thermal storage wall is shown diagrammatically in Figure 6.4. Depending on...

## A Brief HiStory Of Solar Energy

Solar energy is the oldest energy source ever used. The sun was adored by many ancient civilizations as a powerful god. The first known practical application was in drying for preserving food Kalogirou, 2004 . Probably the oldest large-scale application known to us is the burning of the Roman fleet in the bay of Syracuse by Archimedes, the Greek mathematician and philosopher 287-212 B.C. . Scientists discussed this event for centuries. From 100 B.C. to 1100 A.D., authors made reference to this...

## Solar Ponds

Salt gradient lakes, which exhibit an increase in temperature with depth, occur naturally. A salt gradient solar pond is a body of saline water in which the salt concentration increases with depth, from a very low value at the surface to near saturation at the depth of usually 1-2 m Tabor, 1981 . The density gradient inhibits free convection, and the result is that solar radiation is trapped in the lower region. Solar ponds are wide-surfaced collectors in which the basic concept is to heat a...

## Polar ns axis with ew tracking

For a plane rotated about a north-south axis parallel to the earth's axis, with continuous adjustment, 9 is equal to FIGuRE 2.13 Daily variation of solar flux tilted N-S axis with tilt adjusted daily. FIGuRE 2.13 Daily variation of solar flux tilted N-S axis with tilt adjusted daily. FiGuRE 2.14 Daily variation of solar flux polar N-S axis with E-w tracking. FiGuRE 2.14 Daily variation of solar flux polar N-S axis with E-w tracking. This configuration is shown in Figure 2.10b. As can be seen,...

## Ammoniawater absorption systems

Contrary to compression refrigeration machines, which need high-quality electric energy to run, ammonia-water absorption refrigeration machines use low-quality thermal energy. Moreover, because the temperature of the heat source does not usually need to be so high 80-170 C , the waste heat from many processes can be used to power absorption refrigeration machines. In addition, an ammonia-water refrigeration system uses natural substances, which do not cause ozone depletion as working fluids....

## Classification of Solar Distillation Systems

On the basis of various modifications and modes of operation introduced in conventional solar stills, solar distillation systems are classified as passive or active. In active solar stills, an extra-thermal energy by external equipment is fed into the basin of a passive solar still for faster evaporation. The external equipment may be a collector-concentrator panel, waste thermal energy from any industrial plant, or a conventional boiler. If no such external equipment is FIGURE 8.2 Common...

## Integrated Collector Storage Systems

Integrated collector storage ICS systems use the hot water storage as part of the collector, i.e., the surface of the storage tank is used also as the collector FIGURE 5.4 Mantle heat exchanger concept. absorber. As in all other systems, to improve stratification, the hot water is drawn from the top of the tank and cold make-up water enters the bottom of the tank on the opposite side. Usually, the storage tank surface is selectively coated to minimize heat loss. The main disadvantage of the ICS...

## The Heat Balance Method

The heat balance method is able to provide dynamic simulations of the building load. It is the foundation for all calculation methods that can be used to estimate the heating and cooling loads. Since all energy flows in each zone must be balanced, a set of energy balance equations for the zone air and the interior and exterior surfaces of each wall, roof, and floor must be solved simultaneously. The energy balance method combines various equations, such as equations for transient conduction...

## Water Systems

Many variaties of systems can be used for both solar space heating and domestic hot water production. The basic configurations are similar to the solar water heating systems outlined in Sections 5.2.1 and 5.2.2. When used for both space and hot water production and because solar-heated water can be added to storage at the same time that hot water is removed from storage to meet building loads, the system allows independent control of the solar collector-storage and storage-auxiliary-load loops....

## Heat pump Systems

Active solar energy systems can also be combined with heat pumps for domestic water heating or space heating. In residential heating, the solar energy system can be used in parallel with a heat pump, which supplies auxiliary energy when the sun is not available. Additionally, for domestic water systems requiring high water temperatures, a heat pump can be placed in series with the solar storage tank. A heat pump is a device that pumps heat from a low-temperature source to a higher-temperature...

## Natural ventilation

One way of achieving comfort is by direct evaporation of sweat with air movement through ventilation openings. In many parts of the earth, in some months of the year, local cooling of a building can be achieved with natural ventilation. This is achieved by allowing air that is colder than the building to enter the building. Doing so removes some of the heat stored in the building. The reduction of cooling load varies from 40 to 90 . The lower number applies in warm, humid areas and the larger...

## Declination

As shown in Figure 2.3 the earth axis of rotation the polar axis is always inclined at an angle of 23.45 from the ecliptic axis, which is normal to the ecliptic plane. The ecliptic plane is the plane of orbit of the earth around the sun. As the earth rotates around the sun it is as if the polar axis is moving with respect to the sun. The solar declination is the angular distance of the sun's rays north or south of the equator, north declination designated as positive. As shown in Figure 2.5 it...

## Thermodynamic analysis

Compared to an ordinary cooling cycle, the basic idea of an absorption system is to avoid compression work by using a suitable working pair. The working pair consists of a refrigerant and a solution that can absorb the refrigerant. A more detailed schematic of the LiBr-water absorption system is shown in Figure 6.23 FIGURE 6.24 Pressure-temperature diagram of a single effect, LiBr-water absorption cycle. FIGURE 6.24 Pressure-temperature diagram of a single effect, LiBr-water absorption cycle....

## Direct Collection Systems

Among the non-conventional methods to desalinate brackish water or seawater is solar distillation. This process requires a comparatively simple technology and can be operated by unskilled workers. Also, due to the low maintenance requirement, it can be used anywhere with a smaller number of problems. A representative example of the direct collection system is the typical solar still, which uses the greenhouse effect to evaporate salty water. It consists of a basin in which a constant amount of...

## Solarrelated air conditioning

Some components of systems installed for the purpose of heating a building can also be used to cool it but without the direct use of solar energy. Examples of these systems can be heat pumps, rock bed regenerators, and alternative cooling technologies or passive systems. Heat pumps were examined in Section 6.3.5. The other two methods are briefly introduced here. Rock bed regenerator. Rock bed or pebble bed storage units of solar air heating systems can be night-cooled during summer to store...

## Heat Extraction Rate and Room Temperature

The cooling equipment, in an ideal case, must remove heat energy from the space's air at a rate equal to the cooling load. In this way, the space air temperature will remain constant. However, this is seldom true. Therefore, a transfer function has been devised to describe the process. The room air transfer function is P q ,e-i6 - qc,e- 6 g t - tr,e- 6 6.17 p , g transfer function coefficients ASHRAE, 1992 . qc cooling load at various times W . t room temperature used for cooling load...

## Indirect Collection Systems

The operating principle of indirect collection systems involves the implementation of two separate subsystems a renewable energy collection system solar collector, PV, wind turbine, etc. and a plant for transforming the collected energy to freshwater. Some examples employing renewable energy to power desalination plants are presented in this section a more extensive review is presented in Section 8.5. The plant subsystem is based on one of the following two operating principles Phase-change...

## Solar Detoxification

Another field of solar chemistry applications is solar photochemistry. Solar photochemical processes make use of the spectral characteristics of the incoming solar radiation to effect selective catalytic transformations, which find application in the detoxification of air and water and the processing of fine chemical commodities. Solar detoxification achieves photocatalytic treatment of non-biodegradable persistent chlorinated water contaminants typically found in chemical production processes....

## Load Heat Exchanger Size Correction

The size of the load heat exchanger strongly affects the performance of the solar energy system. This is because the rate of heat transfer across the load heat exchanger directly influences the temperature of the storage tank, which consequently affects the collector inlet temperature. As the heat exchanger used to heat the building air is reduced in size, the storage tank temperature must increase to supply the same amount of heat energy, resulting in higher collector inlet temperatures and...

## General Remarks

The -chart design method is used to quickly estimate the long-term performance of solar energy systems of standard configurations. The input data needed are the monthly average radiation and temperature, the monthly load required to heat a building and its service water, and the collector performance parameters obtained from standard collector tests. A number of assumptions are made for the development of the -chart method. The main ones include assumptions that the systems are well built,...

## Active Systems

In active systems, water or a heat transfer fluid is pumped through the collectors. These are usually more expensive and a little less efficient than passive systems, particularly if antifreeze measures are required. Additionally, active systems are more difficult to retrofit in houses, especially where there is no basement, because space is required for the additional equipment, such as the hot water cylinder. Five types of systems belong in this category direct circulation systems, indirect...

## Steam Generation Methods

The steam-flash system is shown schematically in Figure 7.5. In this system, water, pressurized to prevent boiling, is circulated through the collector and flashed across a throttling valve into a flash vessel. Treated feedwater input maintains the level in the flash vessel and the sub cooled liquid is recirculated through the collector. The in situ boiling concept, shown in Figure 7.6, uses a similar system configuration with no flash valve. Sub cooled water is heated to boiling and steam...

## Solar water heater performance evaluation

Many test procedures have been proposed by various organizations to determine the thermal performance of solar water heaters. Testing of the complete system may serve a number of purposes. The main one is the prediction of the system's long-term thermal performance. System testing may also be used as a diagnostic tool to identify failure and causes of failure in system performance. other purposes include the determination of the change in performance as a result of operation under different...

## General regression neural network architecture

Another type of architecture is general regression neural networks GRNNs , which are known for their ability to train quickly on sparse data sets. In numerous tests, it was found that a GRNN responds much better than back-propagation to many types of problems, although this is not a rule. It is especially useful for continuous function approximation. A GRNN can have multidimensional input, and it will fit multidimensional surfaces through data. GRNNs work by measuring how far a given sample...

## Mixedmode TYPE

Mixed-mode, natural circulation, solar energy dryers combine the features of the integral-type and the distributed-type natural circulation solar energy dryers. In this case, the combined action of solar radiation incident directly on the product to be dried and the air heated in a solar air collector provide the necessary heat required for the drying process. A mixed-mode, natural circulation solar energy dryer has the same structural characteristics as the distributed type, i.e., a solar air...

## 2880 Kj Of Solar Energy

Repeat Example 4.2 by considering the system to have a fully mixed storage tank of 100 L and no load. The initial storage tank temperature at the beginning of the day is 40 C and the environmental temperature at the area where the storage tank is located is equal to the ambient air temperature. The tank UA value is 12 W C. Calculate the useful energy collected over the day. By using Eq. 5.34 , the new storage tank temperature can be considered as the collector inlet. This is correct for the...

## Degree Day Method

Frequently, in energy calculations, simpler methods are required. One such simple method, which can give comparatively accurate results, is the degree day method. This method is used to predict the seasonal energy consumption. Each degree that the average outdoor air temperature falls below a balance temperature, Tb, of 18.3 C 65 F represents a degree day. The number of degree days in a day is obtained approximately by the difference of Tb and the average outdoor air temperature, Tav, defined...

## Cell Temperature

As was seen in Section 9.1.3, the performance of the solar cell depends on the cell temperature. This temperature can be determined by an energy balance and considering that the absorbed solar energy that is not converted to electricity is converted to heat, which is dissipated to the environment. Generally, when operating solar cells at elevated temperatures, their efficiency is lowered. In cases where this heat dissipation is not possible, as in building integrated photovoltaics and...

## Desalination Processes

Desalination can be achieved using a number of techniques. Industrial desalination technologies either use phase change or involve semipermeable membranes to separate the solvent or some solutes. Therefore, desalination techniques may be classified into the following categories phase change or thermal processes and membrane or single-phase processes. All processes require a chemical pre-treatment of raw seawater to avoid scaling, foaming, corrosion, biological growth, and fouling and also...

## Black box correlation procedures

ISO 9459-2 is applicable to solar-only systems and solar preheat systems. The performance test for solar-only systems is a black box procedure, which produces a family of input-output characteristics for a system. The test results may be used directly with daily mean values of local solar irradiation, ambient air temperature, and cold-water temperature data to predict annual system performance. The results of tests performed in accordance with ISO 9459-2 permit performance predictions for a...

## Biological and artificial neurons

A biological neuron is shown in Figure 11.15. In the brain, coded information flows using electrochemical media, the so-called neurotransmitters from the synapses toward the axon. The axon of each neuron transmits information to a number of other neurons. The neuron receives information at the synapses from a large number of other neurons. It is estimated that each neuron may receive stimuli from as many as 10,000 other neurons. Groups of neurons are organized into subsystems, and the...

## Air System Thermal Storage

The most common storage media for air collectors are rocks. Other possible media include PCM, water, and the inherent building mass. Gravel is widely used as a storage medium because it is abundant and relatively inexpensive. In cases where large interior temperature swings can be tolerated, the inherent structure of the building may be sufficient for thermal storage. Loads requiring no storage are usually the most cost-effective applications of air collectors, and heated air from the...

## Review Of Renewable Energy Desalination Systems

Renewable energy systems offer alternative solutions to decrease the dependence on fossil fuels. The total worldwide renewable energy desalination installations amount to capacities of less than 1 of that of conventional fossil-fueled desalination plants Delyannis, 2003 . This is mainly due to the high capital and maintenance costs required by renewable energy, making these desalination plants non-competitive with conventional fuel desalination plants. Solar desalination plants coupled with...

## Genopt and trnopt programs

When simulation models are used to simulate and design a system, it is usually not easy to determine the parameter values that lead to optimal system performance. This is sometimes due to time constraints, since it is time consuming for a user to change the input values, run the simulation, interpret the new results, and guess how to change the input for the next trial. Sometimes time is not a problem, but due to the complexity of the system analyzed, the user is just not capable of...

## Ga applications in solar energy systems

Genetic algorithms were used by the author in a number of optimization problems the optimal design of flat-plate solar collectors (Kalogirou, 2003c), predicting the optimal sizing coefficient of photovoltaic supply systems (Mellit and Kalogirou, 2006a), and the optimum selection of the fenestration openings in buildings (Kalogirou, 2007). They have also been used to optimize solar energy systems, in combination with TRNSYS and ANNs (Kalogirou, 2004a). In this, the system is modeled using the...

## Energyrelated EnviRonmental Problems

Energy is considered a prime agent in the generation of wealth and a significant factor in economic development. The importance of energy in economic development is recognized universally and historical data verify that there is a strong relationship between the availability of energy and economic activity. Although in the early 1970s, after the oil crisis, the concern was on the cost of energy, during the past two decades the risk and reality of environmental degradation have become more...

## Building construction Thermal Mass Effects

Heat can be stored in the structural materials of the building to reduce the indoor temperature, reduce the cooling load peaks, and shift the time that maximum load occurs. The storage material is referred to as the thermal mass. In winter, during periods of high solar gain, energy is stored in the thermal mass, avoiding overheating. In the late afternoon and evening hours, when energy is needed, heat is released into the building, satisfying part of the heating load. In summer, the thermal...

## Reverse Circulation In Thermosiphon Systems

At night or whenever the collector is cooler than the water in the tank, the direction of the thermosiphon flow reverses, thus cooling the stored water. It should be noted that thermosiphon collector loop circulation is driven by thermal stratification in the collector loop and the section of the tank below the collector flow return level. The major problem in thermosiphon system design is to minimize heat loss due to reverse thermosiphon circulation at night, when the sky temperature is low....

## Desalination Systems Exergy Analysis

Although the first law is an important tool in evaluating the overall performance of a desalination plant, such analysis does not take into account the quality of energy transferred. This is an issue of particular importance when both thermal and mechanical energy are employed, as they are in thermal desalination plants. First-law analysis cannot show where the maximum loss of available energy takes place and would lead to the conclusion that the energy loss to the surroundings and the...

## Pool Heating Systems

Solar pool heating systems require no separate storage tank, because the pool itself serves as storage. In most cases, the pool's filtration pump is used to circulate the water through solar panels or plastic pipes. For daylong operation, no automatic controls are required, because the pool usually operates when the sun is shining. If such controls are employed, they are used to direct the flow of filtered water to the collectors only when solar heat is available. This can also be achieved by a...

## Evaporation heat loss

The following analysis is for a still pool as per ISO TR 12596 1995 1995a . The evaporative heat loss from a still outdoor pool is a function of the wind speed and of the vapor pressure difference between the pool water and the atmosphere, given by qe 5.64 5.96vo3 CPw - Pa 5.18 qe heat loss by evaporation MJ m2-d . Pw saturation water vapor pressure at water temperature, tw kPa . Pa partial water vapor pressure in the air kPa . v0.3 wind speed velocity at a height of 0.3 m above the pool m s ....

## Hourly Utilizability

Utilizability can also be defined as the fraction of incident solar radiation that can be converted into useful heat. It is the fraction utilized by a collector having no optical losses and a heat removal factor of unity i.e., Fr to 1, operating at a fixed inlet to ambient temperature difference. It should be noted that the utilizability of this collector is always less than 1, since thermal losses exist in the collector. The Hottel-Whillier equation Hottel and Whillier, 1955 relates the rate...

## Fuzzy systems applications in solar energy systems

The applications of fuzzy systems in solar applications are much fewer. They concern the design of a fuzzy single-axis tracking mechanism controller (Kalogirou, 2002) and a neuro-fuzzy based model for photovoltaic power supply system (Mellit and Kalogirou, 2006b). In fact, the membership functions shown in Figures 11.24 and 11.25 and the rule basis, given previously, are from the first application, whereas the latter is a hybrid system described in the next section. Hybrid systems are systems...

## Location of Auxiliary Heater

One important consideration concerning the storage tank is the decision as to the best location for the auxiliary heater. This is especially important for solar space-heating systems because larger amounts of auxiliary energy are usually required and storage tank sizes are large. For maximum utilization of the energy supplied by an auxiliary source, the location of this energy input should be at the load, not at the storage tank. The supply of auxiliary energy at the storage tank will...

## Compound Parabolic Collector

,ec n 2 lt e lt 3n 2 - ec 5.16 The two expressions for p 9 are equivalent for the point P in Figure 5.5, where 9 9c -rc 2. The curve is generated by incrementing 9 in radians, calculating p, then calculating the coordinates, X and Y, by X R sin e - p cos e Y -R cos e - p sin e Figure 5.5 shows a full, untruncated curve, which is the mathematical solution for a reflector shape with the maximum possible concentration ratio. The reflector shape shown in Figure 5.5 is not the most practical design...

## Solar industrial Air and Water Systems

The two types of applications employing solar air collectors are the open circuit and the recirculating applications. In the open circuit, heated ambient air is used in industrial applications where, because of contaminants, recirculation of air is not possible. Examples are paint spraying, drying, and supplying fresh air to hospitals. It should be noted that heating outside air is an ideal operation for the collector because it operates very close to ambient temperature, thus more efficiently....

## Wind Energy

Wind is generated by atmospheric pressure differences, driven by solar power. Of the total of 175,000 TW of solar power reaching the earth, about 1200 TW (0.7 ) are used to drive the atmospheric pressure system. This power generates a kinetic energy reservoir of 750 EJ with a turnover time of 7.4 days (Soerensen, 1979). This conversion process takes place mainly in the upper layers of the atmosphere, at around 12 km height (where the jet streams occur). If it is assumed that about 4.6 of the...