**10. Parametric effects on PV module efficiency**

The electrical efficiency of photovoltaic modules is influenced by module construction and climatic parameters, with the primary parameters being solar irradiance, packing factor and module temperature. PV cell efficiency increases with solar irradiance, as the greater number of photons associated with higher solar irradiance creates more electron–hole pairs and consequently more current in the photovoltaic cell. The packing factor of a PV, defined as the fraction of absorber area occupied by the photovoltaic cells, significantly affects electrical output. A higher packing factor increases the electrical output per unit collector area, but also increases the module temperature. PV efficiency decreases as PV temperature increases, mainly because a higher cell temperature decreases the voltage significantly (even though it increases current by a very small amount).

Many correlations have been developed for the cell temperature (Tc) as a function of climatic parameters (solar radiation, ambient air temperature, wind speed, etc.). Also, numerous correlations are available to calculate the influence of cell temperature on the efficiency of a PV cell (*<sup>c</sup>* ), but in most practical applications the following linear relation for the cell efficiency can be used without incurring significant loss in accuracy (Skoplaki and Palyvos, 2009):

Tezuka et al. (2002) proposed a new method for estimating the amount of CO2-emission reduction in the case where the carbon-tax revenue is used as the subsidy to promote PVsystem installations and concluded that the amount of CO2-emission reduction increases by advertising the PV system with subsidy policy even under the same tax-rate and the CO2 payback time of the PV system reduces by half if the GDP is assumed not to change after the introduction of carbon taxation. Krauter et al.(2004) examined a CO2 comprehensive balance within the life-cycle of a photovoltaic energy system and found that the actual effect of the PV system in terms of net reduction of carbon dioxide is the difference between the sum of electrical yield related to the local grid and the value for recycling and the sum of the production requirements and the transport emissions. Fthenakis and Kima (2007) studied solar- and nuclear-electricity-generation technologies' entire lifecycle of energy production; carbon dioxide and other gases emitted during the extraction, processing, and disposal of associated materials and determined the greenhouse gas (GHG) emissions, namely, CO2, CH4, N2O, and chlorofluorocarbons due to materials and energy flows throughout all stages of the life of commercial technologies for solar–electric and nuclear-power generation. Kannan et al. (2006) performed life cycle assessment (LCA) and life cycle cost analysis for a distributed 2.7kWpgrid-connected monocrystalline solar PV system operating in Singapore and provided various energy payback time (EPBT) analyses of the solar PV system with reference to a fuel oil-fired steam turbine and their greenhouse gas (GHG) emissions and costs are also compared revealing that GHG emission from electricity generation from the solar PV system is less than one-fourth that from an oil-fired steam turbine plant and onehalf that from a gas-fired combined cycle plant. Tsoutsos et al. (2005) presented an overview of an Environmental Impact Assessment for central solar systems, to estimate the magnitude of potential environmental impacts and proposed appropriate mitigation measures, can play a significant role to proper project design and to a subsequent project public acceptance.

The electrical efficiency of photovoltaic modules is influenced by module construction and climatic parameters, with the primary parameters being solar irradiance, packing factor and module temperature. PV cell efficiency increases with solar irradiance, as the greater number of photons associated with higher solar irradiance creates more electron–hole pairs and consequently more current in the photovoltaic cell. The packing factor of a PV, defined as the fraction of absorber area occupied by the photovoltaic cells, significantly affects electrical output. A higher packing factor increases the electrical output per unit collector area, but also increases the module temperature. PV efficiency decreases as PV temperature increases, mainly because a higher cell temperature decreases the voltage significantly (even

Many correlations have been developed for the cell temperature (Tc) as a function of climatic parameters (solar radiation, ambient air temperature, wind speed, etc.). Also, numerous correlations are available to calculate the influence of cell temperature on the efficiency of a

efficiency can be used without incurring significant loss in accuracy (Skoplaki and Palyvos,

*<sup>c</sup>* ), but in most practical applications the following linear relation for the cell

**9. Environmental aspects** 

**10. Parametric effects on PV module efficiency** 

though it increases current by a very small amount).

PV cell (

2009):

$$\eta\_c = \eta\_{ref} \left[ 1 - \beta\_{ref} \left( T\_c - T\_{ref} \right) \right] \tag{1}$$

where *ref* is the efficiency of the photovoltaic cell at temperature Tref. The temperature coefficient *ref* is mainly determined by the cell material, which usually is provided by the manufacturer, and on the Tref, and can be written as (Agarwal and Garg, 1994):

$$\mathcal{J}\_{ref} = \frac{1}{\left(T\_0 - T\_{ref}\right)}\tag{2}$$

Here *To* is the maximum temperature at which the efficiency of the PV cells decreases to zero. For a crystalline Si cell this temperature is about 270° C (Kumar and Rosen, 2011). A range of values of *ref* are suggested for silicon based PV technologies.


aThe reference temperature for each case is 25° C.

Table 1. Temperature coefficients for various PV Technologies.

#### **11. Applications**

The increasing efficiency, lowering cost and minimal pollution are the boons of the photovoltaic systems that have led to a wide range of their application.

#### **11.1 Building integrated photovoltaic systems**

The PV system is composed of a number of individual PV modules that can be connected either in series (to increase the dc output voltage up to the desired value) to form a string. Then, multiple strings are connected in parallel to increase the output current. The possibility of using multiple strings ensures the PV system modularity, which is one of the most important features of the PV technology. The arrangement of the PV modules in strings also allows for using different solutions for the dc/ac conversion. Available solutions include the centralised inverter, collecting the dc output from the whole array of PV modules, string inverters (with one inverter for each string) or module-integrated inverters (with a mono inverter for each PV module). The centralised inverter is a solution most suitable for PV systems with rated power indicatively above 20kW, connected to the supply system through a three-phase inverter. The other solutions are typical of residential installations, where the power is usually not higher than 5–10kW and the inverters are mono-phase. The adoption of module-integrated inverters requires the installation of a relatively high number of inverters, each one with its protections, directly on the field, paying attention to the fact that the inverters have to withstand different climatic conditions. Yet, the adoption of module-integrated inverters allows for individual and independent control of the mono inverters, with possibility of minimising the losses due to different

Photovoltaic Systems and Applications 43

as a 100% solar powered desalination system for any location and quality of brackish water and found that the mono effect solar stills for small scale plants is more viable to use in remote area, where the land value is negligible as solar stills are easy to install and maintained and can be fabricated with locally available materials (Parida et al., 2011). El-Sayed modeled desalination by spiral-wound RO membrane modules driven by solar to power photovoltaic converter panels with the purpose of revealing the economic potential of the combination. Weiner et al. (2001) presented the designing, erection and operation process of a stand-alone desalination plant powered by both solar photovoltaic and wind

A trade-off study in the field of space solar arrays and concentration that defines the parameters to evaluate whether a given concept (cell type, concentrator) becomes appropriate as two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays and thermal and optical behaviors are analysed. Seboldt et al. a developed a new design for an Earth-orbiting Solar Power Satellite (SPS) called "European Sail Tower SPS" featuring an extremely lightweight and large tower-like orbital system with the capability to supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves (Parida et al., 2011). Girish (2006) studied the possibility of nighttime photovoltaic power generation in planetary bodies like moon using reflected light energy flux from nearby planetary objects

Bond et al. (2007) described current experience and trials in East Timor with solar photovoltaic (PV) technology by introduction of solar home systems (SHS). Posorski et al. (2003) proposed SolarHomeSystems (SHS) that are commercially disseminated and used

Pande et al. (2003) designed and developed a Solar Photovoltaic operated (PV) pump drip irrigation system for growing orchards in arid region considering different design parameters like pump size, water requirements, the diurnal variation in the pressure of the pump due to change in irradiance and pressure compensation in the drippers. Meah et al. (2008) discussed some policies to make solar photovoltaic water pumping (SPVWP) system an appropriate technology for the respective application region as it has proved its aspects technically, economically, and environmentally in developed countries. Short et al. (2003) investigated some of the issues involved in solar water pumping projects, described the positive and negative effects that they can have on the community and proposed an entirely new type of pump, considering the steps that could be taken to ensure future sustainability. Badescu (2003) analyzed the operation of a complex time dependent solar water pumping system consisting of four basic units: a PV array, a battery, a DC motor, and a centrifugal

based on latest low-intensity low-illumination (LILT) solar cell technology.

them cost efficiently to substitute kerosene and dry cell batteries to reduce

GHG emissions and thus make a significant contribution to climate protection.

energy.

**11.3 Space** 

**11.4 Solar home systems** 

**11.5 Pumps** 

pump.

electrical behavior of the modules (that is, the mismatching of the current/voltage characteristics) and may bring some benefits in increasing the system availability, since the occurrence of an inverter failure affects only a mono module and the relatively low failure rate of the inverter may prevail over the increase of the number of inverters installed with respect to the other solutions (Andrei et al., 2007).

Building-integrated photovoltaic (BIPV) systems incorporate photovoltaic properties into building materials such as roofing, siding, and glass and thus offer advantages in cost and appearance as they are substituted for conventional materials in new construction. Moreover the BIPV installations are architecturally more appealing than roof-mounted PV structures. Yoo et al. (2002) proposed a building design to have the PV modules shade the building in summer, so as to reduce cooling loads, while at the same time allowing solar energy to enter the building during the heating season to provide daylight and conducted an analysis of the system performance, evaluation of the system efficiency and the power output. Bakos et al. (2003) described the installation, technical characteristics, operation and economic evaluation of a grid-connected building integrated photovoltaic system (BIPV) and the technical and economical factors were examined using a computerized renewable energy technologies (RETs) assessment tool. Xu et al. (2008) developed and evaluated the performance of an Active Building Envelope (ABE) systems, a new enclosure technology with the ability to regulate their temperature (cooling or heating) by interacting with the sun which integrates photovoltaic (PV) and thermoelectric (TE) Technologies. Chow et al. (2003) described effectiveness of cooling by means of a natural ventilating air stream numerically based on two cooling options with an air gap between the PV panels and the external facade: (i) an open air gap with mixed convective heat transfer, and (ii) a solar chimney with buoyancy induced vertical flow and found that effective cooling of a PV panel can increase the electricity output of the solar cells. Wong et al. (2008) proposed semi-transparent PV top light material for residential application with 50% radiation transmission rate contributing to a maximum of 5.3% reduction in heating and cooling energy consumption when compared with a standard BIPV roof. Cheng et al. (2005) developed an empirical approach for evaluating the annual solar tilted planes irradiation with inclinations from 0 to 90◦ and azimuths from 0 to 90◦ on building envelopes for BIPV applications in Taiwan. Ruther et al. (2008) studied the behavior of grid connected, building integrated photovoltaic(BIPV) solar energy conversion in the urban environment of a metropolitan area in a Brazilian state capital, aiming at maximizing the benefits of the distributed nature of PV generation. Jardim et al. (2008) Studied the behaviour of grid-connected, building integrated photovoltaic solar energy conversion in the built environment of ametropolitan area in Brazilian state capital, aiming at maximising the benefits of the distributed nature of PV generation.

#### **11.2 Desalination plant**

Lamei et al. (2008) discussed electricity price at which solar energy can be considered economical to be used for RO (Reverse Osmosis) desalination that is independent of RO plant capacity and proposed an equation to estimate the unit production costs of RO desalination plants that can be used to calculate unit production costs for desalinated water using photovoltaic (PV) solar energy based on current and future PV module prices. A simple mono-effect solar still plant with a capacity of 5.8m3 per day for the treatment of reject brine obtained from Sadous PV-powered RO desalination plant that can be configured as a 100% solar powered desalination system for any location and quality of brackish water and found that the mono effect solar stills for small scale plants is more viable to use in remote area, where the land value is negligible as solar stills are easy to install and maintained and can be fabricated with locally available materials (Parida et al., 2011). El-Sayed modeled desalination by spiral-wound RO membrane modules driven by solar to power photovoltaic converter panels with the purpose of revealing the economic potential of the combination. Weiner et al. (2001) presented the designing, erection and operation process of a stand-alone desalination plant powered by both solar photovoltaic and wind energy.

#### **11.3 Space**

42 Modeling and Optimization of Renewable Energy Systems

electrical behavior of the modules (that is, the mismatching of the current/voltage characteristics) and may bring some benefits in increasing the system availability, since the occurrence of an inverter failure affects only a mono module and the relatively low failure rate of the inverter may prevail over the increase of the number of inverters installed with

Building-integrated photovoltaic (BIPV) systems incorporate photovoltaic properties into building materials such as roofing, siding, and glass and thus offer advantages in cost and appearance as they are substituted for conventional materials in new construction. Moreover the BIPV installations are architecturally more appealing than roof-mounted PV structures. Yoo et al. (2002) proposed a building design to have the PV modules shade the building in summer, so as to reduce cooling loads, while at the same time allowing solar energy to enter the building during the heating season to provide daylight and conducted an analysis of the system performance, evaluation of the system efficiency and the power output. Bakos et al. (2003) described the installation, technical characteristics, operation and economic evaluation of a grid-connected building integrated photovoltaic system (BIPV) and the technical and economical factors were examined using a computerized renewable energy technologies (RETs) assessment tool. Xu et al. (2008) developed and evaluated the performance of an Active Building Envelope (ABE) systems, a new enclosure technology with the ability to regulate their temperature (cooling or heating) by interacting with the sun which integrates photovoltaic (PV) and thermoelectric (TE) Technologies. Chow et al. (2003) described effectiveness of cooling by means of a natural ventilating air stream numerically based on two cooling options with an air gap between the PV panels and the external facade: (i) an open air gap with mixed convective heat transfer, and (ii) a solar chimney with buoyancy induced vertical flow and found that effective cooling of a PV panel can increase the electricity output of the solar cells. Wong et al. (2008) proposed semi-transparent PV top light material for residential application with 50% radiation transmission rate contributing to a maximum of 5.3% reduction in heating and cooling energy consumption when compared with a standard BIPV roof. Cheng et al. (2005) developed an empirical approach for evaluating the annual solar tilted planes irradiation with inclinations from 0 to 90◦ and azimuths from 0 to 90◦ on building envelopes for BIPV applications in Taiwan. Ruther et al. (2008) studied the behavior of grid connected, building integrated photovoltaic(BIPV) solar energy conversion in the urban environment of a metropolitan area in a Brazilian state capital, aiming at maximizing the benefits of the distributed nature of PV generation. Jardim et al. (2008) Studied the behaviour of grid-connected, building integrated photovoltaic solar energy conversion in the built environment of ametropolitan area in Brazilian state capital,

aiming at maximising the benefits of the distributed nature of PV generation.

Lamei et al. (2008) discussed electricity price at which solar energy can be considered economical to be used for RO (Reverse Osmosis) desalination that is independent of RO plant capacity and proposed an equation to estimate the unit production costs of RO desalination plants that can be used to calculate unit production costs for desalinated water using photovoltaic (PV) solar energy based on current and future PV module prices. A simple mono-effect solar still plant with a capacity of 5.8m3 per day for the treatment of reject brine obtained from Sadous PV-powered RO desalination plant that can be configured

**11.2 Desalination plant** 

respect to the other solutions (Andrei et al., 2007).

A trade-off study in the field of space solar arrays and concentration that defines the parameters to evaluate whether a given concept (cell type, concentrator) becomes appropriate as two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays and thermal and optical behaviors are analysed. Seboldt et al. a developed a new design for an Earth-orbiting Solar Power Satellite (SPS) called "European Sail Tower SPS" featuring an extremely lightweight and large tower-like orbital system with the capability to supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves (Parida et al., 2011). Girish (2006) studied the possibility of nighttime photovoltaic power generation in planetary bodies like moon using reflected light energy flux from nearby planetary objects based on latest low-intensity low-illumination (LILT) solar cell technology.

#### **11.4 Solar home systems**

Bond et al. (2007) described current experience and trials in East Timor with solar photovoltaic (PV) technology by introduction of solar home systems (SHS). Posorski et al. (2003) proposed SolarHomeSystems (SHS) that are commercially disseminated and used them cost efficiently to substitute kerosene and dry cell batteries to reduce

GHG emissions and thus make a significant contribution to climate protection.

#### **11.5 Pumps**

Pande et al. (2003) designed and developed a Solar Photovoltaic operated (PV) pump drip irrigation system for growing orchards in arid region considering different design parameters like pump size, water requirements, the diurnal variation in the pressure of the pump due to change in irradiance and pressure compensation in the drippers. Meah et al. (2008) discussed some policies to make solar photovoltaic water pumping (SPVWP) system an appropriate technology for the respective application region as it has proved its aspects technically, economically, and environmentally in developed countries. Short et al. (2003) investigated some of the issues involved in solar water pumping projects, described the positive and negative effects that they can have on the community and proposed an entirely new type of pump, considering the steps that could be taken to ensure future sustainability. Badescu (2003) analyzed the operation of a complex time dependent solar water pumping system consisting of four basic units: a PV array, a battery, a DC motor, and a centrifugal pump.

Photovoltaic Systems and Applications 45

Hegazy (2000) compared the performances of four commonly used PV/T air collector configurations (Fig. 16). In the four designs, the air flow passage is located above the absorber (model I), below the absorber (model II) and on both sides of the absorber, in a mono- pass (model III) or double-pass (model IV) mode. Numerical solutions of the energy balances indicate that the electrical and thermal outputs for models II–IV are similar and superior to that for model I, and that the pumping power needed is lowest for model III and

Tonui and Tripanagnostopoulos (2007) improved PV/T air collectors by enhancing heat extraction. They addressed some inherent shortcomings of PV/T air collectors, such as the low density, volumetric heat capacity and thermal conductivity of air, by using a thin suspended flat metallic sheet between the absorber surface and back plate and/or by using fins on the back plate of the air duct (Fig. 17). They report energy efficiencies of 30%, 28% and 25%, respectively, for finned, suspended metallic plate and normal air heaters. The choice of particular design depends on location, especially latitude. The use of finned systems is advantageous for higher latitudes where higher heat gains are needed in winter, whereas the PV/T system with a suspended metallic sheet is usually preferable for low

second lowest for model IV.

latitude or tropical countries.

Fig. 16. Various PV/T models (Hegazy, 2000).

## **11.6 Photovoltaic and thermal (PV/T) collector technology**

Chow et al. (2007) described an experimental study of a centralized photovoltaic and hot water collector wall system that can serve as a water pre-heating system using collectors mounted at vertical facades preferring natural water circulation over forced circulation and the thermal efficiency was found 38.9% at zero reduced temperature, and the corresponding electricity conversion efficiency was 8.56%. He et al. (2006) proposed the hybrid photovoltaic and thermal (PV/T) collector technology using water as the coolant as a solution for improving the energy performance. Vokas et al. (2006) studied a photovoltaic– thermal system for domestic heating and cooling concluding that the system can cover a remarkable percentage of the domestic heating and cooling demands. Chow et al. (2006) presented a photovoltaic-thermosyphon collector for residential applications with rectangular flow channels and discussed the energy performance.

The merits of photovoltaic technology relative to other power generation technologies include noiseless, relatively environmentally benign, proven, long life (e.g., 20–30 years for crystalline silicon modules) and low maintenance. However, several factors limit the efficiency of photovoltaic module, e.g., 20% or less for crystalline Si and 12% or less for amorphous Si. In particular, the efficiency of PV devices decreases as temperature increases and PV cells utilize only a part of solar spectrum (less than 1.11 m for c-Si) for electricity generation. Even the total energy collected in the solar spectrum less than 1.11 m is not converted into electricity, due to the band gap restriction of silicon (1.12 eV) (Helden et al., 2004). Therefore, much of the collected solar energy in a PV module elevates the temperature of its cells. This absorbed heat needs to be extracted to maintain a high electrical output. This requirement creates an opportunity, as the extracted heat can be utilized for many low- and medium-temperature applications.

The concept of photovoltaic–thermal collectors (PV/T) began in the 1970s and now some companies are marketing such collectors. In PV/T collectors, the photovoltaic cells are integral part of the absorber surface. These collectors are known as hybrid solar collectors due to their inherent ability to generate electricity and heat simultaneously. The working principle of these collectors is similar to flat plate solar collectors, except part of the incident solar radiation is converted into electricity. If the heat transfer fluid (air) is flowing through the flow passage attached with the absorber surface, collectors are categorized as a photovoltaic– thermal air collectors or simply PV/T air heaters (Chow, 2010).

The potential of PV/T collectors has been recognized since 1970 and has received increased attention in the past decade. Compared to using separate solar technologies for heat and electricity, the production of heat and electricity from the same collector surface is often considered more cost effective, requires less space and exhibits significantly lower balanceof-system costs (Zondaga, 2003). The potential of PV/T collectors is large, as many potential users have simultaneous requirements for heat and electricity.

#### **11.7 PV/T air heating collectors**

Significant research has been performed on PV/T collectors over the last four decades, on such topics as design development, numerical simulation, prototype design, experimental testing and testing methodologies for PV/T collectors. In the subsequent sections we describe major investigations on PV/T solar air collectors.

Chow et al. (2007) described an experimental study of a centralized photovoltaic and hot water collector wall system that can serve as a water pre-heating system using collectors mounted at vertical facades preferring natural water circulation over forced circulation and the thermal efficiency was found 38.9% at zero reduced temperature, and the corresponding electricity conversion efficiency was 8.56%. He et al. (2006) proposed the hybrid photovoltaic and thermal (PV/T) collector technology using water as the coolant as a solution for improving the energy performance. Vokas et al. (2006) studied a photovoltaic– thermal system for domestic heating and cooling concluding that the system can cover a remarkable percentage of the domestic heating and cooling demands. Chow et al. (2006) presented a photovoltaic-thermosyphon collector for residential applications with

The merits of photovoltaic technology relative to other power generation technologies include noiseless, relatively environmentally benign, proven, long life (e.g., 20–30 years for crystalline silicon modules) and low maintenance. However, several factors limit the efficiency of photovoltaic module, e.g., 20% or less for crystalline Si and 12% or less for amorphous Si. In particular, the efficiency of PV devices decreases as temperature increases

converted into electricity, due to the band gap restriction of silicon (1.12 eV) (Helden et al., 2004). Therefore, much of the collected solar energy in a PV module elevates the temperature of its cells. This absorbed heat needs to be extracted to maintain a high electrical output. This requirement creates an opportunity, as the extracted heat can be

The concept of photovoltaic–thermal collectors (PV/T) began in the 1970s and now some companies are marketing such collectors. In PV/T collectors, the photovoltaic cells are integral part of the absorber surface. These collectors are known as hybrid solar collectors due to their inherent ability to generate electricity and heat simultaneously. The working principle of these collectors is similar to flat plate solar collectors, except part of the incident solar radiation is converted into electricity. If the heat transfer fluid (air) is flowing through the flow passage attached with the absorber surface, collectors are categorized as a

The potential of PV/T collectors has been recognized since 1970 and has received increased attention in the past decade. Compared to using separate solar technologies for heat and electricity, the production of heat and electricity from the same collector surface is often considered more cost effective, requires less space and exhibits significantly lower balanceof-system costs (Zondaga, 2003). The potential of PV/T collectors is large, as many potential

Significant research has been performed on PV/T collectors over the last four decades, on such topics as design development, numerical simulation, prototype design, experimental testing and testing methodologies for PV/T collectors. In the subsequent sections we

m for c-Si) for electricity

m is not

**11.6 Photovoltaic and thermal (PV/T) collector technology** 

rectangular flow channels and discussed the energy performance.

and PV cells utilize only a part of solar spectrum (less than 1.11

utilized for many low- and medium-temperature applications.

users have simultaneous requirements for heat and electricity.

describe major investigations on PV/T solar air collectors.

**11.7 PV/T air heating collectors** 

generation. Even the total energy collected in the solar spectrum less than 1.11

photovoltaic– thermal air collectors or simply PV/T air heaters (Chow, 2010).

Hegazy (2000) compared the performances of four commonly used PV/T air collector configurations (Fig. 16). In the four designs, the air flow passage is located above the absorber (model I), below the absorber (model II) and on both sides of the absorber, in a mono- pass (model III) or double-pass (model IV) mode. Numerical solutions of the energy balances indicate that the electrical and thermal outputs for models II–IV are similar and superior to that for model I, and that the pumping power needed is lowest for model III and second lowest for model IV.

Tonui and Tripanagnostopoulos (2007) improved PV/T air collectors by enhancing heat extraction. They addressed some inherent shortcomings of PV/T air collectors, such as the low density, volumetric heat capacity and thermal conductivity of air, by using a thin suspended flat metallic sheet between the absorber surface and back plate and/or by using fins on the back plate of the air duct (Fig. 17). They report energy efficiencies of 30%, 28% and 25%, respectively, for finned, suspended metallic plate and normal air heaters. The choice of particular design depends on location, especially latitude. The use of finned systems is advantageous for higher latitudes where higher heat gains are needed in winter, whereas the PV/T system with a suspended metallic sheet is usually preferable for low latitude or tropical countries.

Fig. 16. Various PV/T models (Hegazy, 2000).

Photovoltaic Systems and Applications 47

driven thermoelectric devices. Takigawa et al. (2003) developed a new concept of "smart power conditioner" with small storage battery for value-added PV application that has a smoothing function to reduce PV output variation and customer's load fluctuation, and also has the additional function to compensate for the harmonics current and reactive power caused by customer's load. Bechinger et al. (1998) developed self-powered electrochromic windows where a semi-transparent photovoltaic (PV) cell provides the power to activate an electrochromic system deposited on top of the solar cell and showed that dye-sensitized solar cells and EC (electrochromic) cells can be easily combined. Chow et al. (2007) developed an energy model of a PV ventilated window system and conducted the overall performance analysis for different window orientations. Ji et al. (2009) presented a novel photovoltaic/thermal solar-assisted heat pump (PV/TSAHP) system, which can generate electricity and heat energy simultaneously and introduced a mathematical model based on the distributed parameter technique for predicting the dynamic system behavior. Ahmad et al. (2006) presented a small PV power system for hydrogen production using the photovoltaic module connected to the hydrogen

Electricity produced from photovoltaic (PV) systems has a far smaller impact on the environment than traditional methods of electrical generation. During their operation, PV cells need no fuel, give off no atmospheric or water pollutants and require no cooling water. Unlike fossil fuel (coal, oil, and natural gas) fired power plants, PV systems do not contribute to global warming or acid rain. The use of PV systems is not constrained by material or land shortages and the sun is a virtually endless energy source. The cost of PV systems has decreased more than twenty times since the early 1970's, and research continues on several different technologies in an effort to reduce costs to levels acceptable for wide scale use. Current PV cells are reliable and already cost effective in certain applications such as remote power, with stand-alone PV plants built in regions not reached by the utility networks. Besides that, integration of PV systems into buildings in residential areas, where the PV system is also connected to the electricity grid to provide an alternative supply source to the load, is becoming even more attractive. Various alternatives have been designed for building-integrated PV systems, including roof-top, facade and sun-shield systems. Early solutions were aimed at superposing the PV modules onto the building structures. Yet, nowadays an increasing attention is paid to the integration of the PV modules into the structural elements that form the building architecture. Although at present the costs of the PV solutions are still not competitive in comparison to other energy sources, the adoption of buildingintegrated solutions and some incentives provided by national regulations and installation programs could make the investment on PV systems affordable. The future extent of using PV systems will strongly depend upon research to reduce costs and on the value societies place on the negative environmental impacts associated to other forms

The PV module technology and the type of installation affect significantly the performance of the PV systems. Experimental studies aimed at characterizing the electrical behavior of the PV systems are then essential to understand the peculiarities of

electrolyzer with and without maximum power point tracker .

**12. Conclusion** 

of electricity generation.

Fig. 17. Cross-sections of (a) a typical PV/T air collector, (b) a PV/T air collector with a suspended plate, and (c) a PV/T air collector with fins. Air flow is perpendicular to the page in all cases. (Tonui and Tripanagnostopoulos, 2007 )

The use of a CPC with a double-pass PV/T air heater was examined by Othman et al. (2005). In the considered design, the bottom surface of the absorber has vertical fins (Fig. 18). Electricity production from the PV/T air collector was observed to depend significantly on the air flow rate and to decreases with increasing air temperature. The latter result implies that the air temperature should be maintained at a lower value to generate more electrical energy. These observations are in line with the results reported by Garg and Adhikari (1999) for PV/T air collectors using CPCs.

Fig. 18. Double pass PV/T air heater with CPC and fins (Othman et al., 2005).

#### **11.8 Other applications**

Mpagalile et al. (2006) fabricated a novel, batch operated oil press, powered by solar PV system designed to suit small-scale oil processors in developing countries with the press providing an opportunity for the processor to use different oilseeds and volumes of the materials being processed by either changing the size of the chamber or adjusting the screw rod to reduce the volume of the upper chamber and for pressing the materials at low or high pressure depending on the expression efficiency required. Xi et al. (2007) presented the development and applications of two solar-driven thermoelectric technologies (i.e., solar-driven refrigeration and solar-driven thermoelectric power generation) and the currently existing drawbacks of the solar-based thermoelectric technology as well as methods to improve and evaluate the performance of the solar-

Fig. 17. Cross-sections of (a) a typical PV/T air collector, (b) a PV/T air collector with a suspended plate, and (c) a PV/T air collector with fins. Air flow is perpendicular to the page

Fig. 18. Double pass PV/T air heater with CPC and fins (Othman et al., 2005).

Mpagalile et al. (2006) fabricated a novel, batch operated oil press, powered by solar PV system designed to suit small-scale oil processors in developing countries with the press providing an opportunity for the processor to use different oilseeds and volumes of the materials being processed by either changing the size of the chamber or adjusting the screw rod to reduce the volume of the upper chamber and for pressing the materials at low or high pressure depending on the expression efficiency required. Xi et al. (2007) presented the development and applications of two solar-driven thermoelectric technologies (i.e., solar-driven refrigeration and solar-driven thermoelectric power generation) and the currently existing drawbacks of the solar-based thermoelectric technology as well as methods to improve and evaluate the performance of the solar-

The use of a CPC with a double-pass PV/T air heater was examined by Othman et al. (2005). In the considered design, the bottom surface of the absorber has vertical fins (Fig. 18). Electricity production from the PV/T air collector was observed to depend significantly on the air flow rate and to decreases with increasing air temperature. The latter result implies that the air temperature should be maintained at a lower value to generate more electrical energy. These observations are in line with the results reported by Garg and Adhikari (1999)

in all cases. (Tonui and Tripanagnostopoulos, 2007 )

for PV/T air collectors using CPCs.

**11.8 Other applications** 

driven thermoelectric devices. Takigawa et al. (2003) developed a new concept of "smart power conditioner" with small storage battery for value-added PV application that has a smoothing function to reduce PV output variation and customer's load fluctuation, and also has the additional function to compensate for the harmonics current and reactive power caused by customer's load. Bechinger et al. (1998) developed self-powered electrochromic windows where a semi-transparent photovoltaic (PV) cell provides the power to activate an electrochromic system deposited on top of the solar cell and showed that dye-sensitized solar cells and EC (electrochromic) cells can be easily combined. Chow et al. (2007) developed an energy model of a PV ventilated window system and conducted the overall performance analysis for different window orientations. Ji et al. (2009) presented a novel photovoltaic/thermal solar-assisted heat pump (PV/TSAHP) system, which can generate electricity and heat energy simultaneously and introduced a mathematical model based on the distributed parameter technique for predicting the dynamic system behavior. Ahmad et al. (2006) presented a small PV power system for hydrogen production using the photovoltaic module connected to the hydrogen electrolyzer with and without maximum power point tracker .
