Feyza Akarslan

*Department of Textile Engineering, Engineering and Architectural Faculty, Süleyman Demirel University, Isparta Turkey* 

### **1. Introduction**

20 Modeling and Optimization of Renewable Energy Systems

Sodha, M.S., Dang, A., Bansal, P.K., Sharma, S.B., 1985. An analytical and experimental

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study of open sun drying and a cabinet type drier. *Energy Conversion &* 

based desiccants for solar crop drying applications. *Renewable Energy, Vol.*19, pp.

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designing dryers operated by flat plate solar collectors. *Renewable Energy*, Vol.26.

Improvements in quality of life and rapid industrialization in many countries are increasing energy demand significantly, and the potential future gap between energy supply and demand is predicted to be large. Interest in sustainable development and growth has also grown in recent years, motivating the development of environmental benign energy technologies. Research on applications of solar energy technologies have as a consequence expanded rapidly, exploiting the abundant, free and environmentally characteristics of solar energy. However, widespread acceptance of solar energy technology depends on its competitiveness, considering factors such as efficiency, cost-effectiveness, reliability and availability (Kumar and Rosen, 2011).

Renewable energy sources can be defined as "energy obtained from the continuous or repetitive currents on energy recurring in the natural environment" or as "energy flows which are replenished at the same rate as they are used". All the earth's renewable energy sources are generated from solar radiation, which can be converted directly or indirectly to energy using various technologies. This radiation is perceived as white light since it spans over a wide spectrum of wavelengths, from the short-wave infrared to ultraviolet. Such radiation plays a major role in generating electricity either producing high temperature heat to power an engine mechanical energy which in turn drives an electrical generator or by directly converting it to electricity by means of the photovoltaic

(PV) effect. It is well known that PV is the simplest technology to design and install, however it is still one of the most expensive renewable technologies. But its advantage will always lie in the fact it is environmentally friendly and a non-pollutant low maintenance energy source (Chaar et. al., 2011).

Some solar thermal systems, such as solar water heaters, air heaters, dryers and distillation devices, have advance notably in decades in terms of efficiency and reliability. Efficiencies of these devices typically range from about 40% to 60% for low- and medium-temperature applications (Thirugnanasambandam et al., 2010). Also, the direct conversion of solar energy to electricity has advanced markedly over the last two decades, leading to significantly reduced prices of photovoltaic modules, and applications have increased especially due to the availability of incentives in many parts of the world (Branker and Pearce, 2010). However, the efficiency of mono crystalline silicon based module is still

Photovoltaic Systems and Applications 23

Moreover, such variety in technology is needed to enhance the deployment of solar energy for a greener and cleaner environment. Devices such as space PV cell technology were also described and the progress in this field is expanding. In addition, the applications of PV

Fig. 1. Behavior of light shining on a solar cell: (1) Reflection and absorption at top contact. (2) Reflection at cell surface. (3) Desired absorption. (4) Reflection from rear out of cell. (5)

The photovoltaic phenomenon has been recognized since 1839, when French physicist Edmond Becquerel was able to generate electricity by illuminating a metal electrode in a weak electrolyte solution. The photovoltaic effect in solids was first studied in 1876 by Adam and Day, who made a solar cell from selenium that had an efficiency of 1–2%. The photovoltaic effect was explained by Albert Einstein in 1904 via his photon theory. A significant breakthrough related to modern electronics was the discovery of a process to produce pure crystalline silicon by Polish scientist Jan Czochralski in 1916. The efficiency of first generation silicon cells was about 6%, which is considerable lower than that of contemporary solar cells (about 14–20%). Early efforts to make photovoltaic cells a viable method of electricity generation for terrestrial applications were unsuccessful due to the high device costs. The ''energy crises'' of 1970s spurred a new found of initiatives in many countries to make photovoltaic systems affordable, especially for off-grid applications. The significant reductions in the prices of photovoltaic cells in more recent years has rejuvenated interest in the technology, e.g., the annual growth since 2000 in the production of PV system has exceeded 40% and present total installed capacity worldwide has reached about 22 GW

Absorption after reflection. (6) Absorption in rear contact (Chaar et al., 2011).

installations are described.

**2. Photovoltaic systems** 

(Kumar and Rosen, 2011).

around 20% and the cost of production of PV power remains considerably higher than the cost of generating solar thermal heat (Liou, 2010). The efficiency of photovoltaic cells or modules is measured under controlled conditions (solar irradiance 1000 W/m2, cell temperature 25 oC, air mass 1.5), although the nominal operating cell temperature (NOCT) in actual applications is much higher than the reference cell temperature 25 oC; the higher NOCT is considered a major cause of reduced efficiency and electrical power output of photovoltaic modules (Garcia and Balenzategui, 2004). To enhance and possibly maximize the output of photovoltaic modules, the heat generated in the module can be extracted by passing a heat recovery fluid (water, oil, glycol, air) under and/or over the module (Tonui and Tripanagnostopoulos, 2007).

Photovoltaic conversion is the direct conversion of sunlight into electricity without any heat engine to interfere. Photovoltaic devices are rugged and simple in design requiring very little maintenance and their biggest advantage being their construction as stand-alone systems to give outputs from microwatts to megawatts. Hence they are used for power source, water pumping, remote buildings, solar home systems, communications, satellites and space vehicles, reverse osmosis plants, and for even megawatt scale power plants. With such a vast array of applications, the demand for photovoltaics is increasing every year (Parida et al., 2011)

PV history starts in 1839, when Alexandre-Edmund Becquerel observed that ''electrical currents arose from certain light induced chemical reactions" and similar effects were observed by other scientists in a solid (selenium) several decades later. But it was not till the late 1940s when the development of the first solid state devices paved the way in the industry for the first silicon solar cell to be developed with an efficiency of 6%. The development of the first silicon solar cell was fundamental in the initiation of solar technologies as it represented the power conversion unit of a PV system but with practical implications. These Si cells are not used separately rather they are assembled into modules. Presently, various types of solar cells on industrially available, however, the strive for research and development is continuing to expand and improve this energy collector (Chaar et al., 2011).

The growth of such technology depends on materials and structure development; however the goal will always be maximum power at minimum cost. In any structure, solar cells, which are connected in series and in parallel in order to form the desired voltage and current levels, remain the basic semiconductor components of a PV panel. To maximize the power rating of a solar cell which ensures the highest efficiency, hence designed to raise the desired absorption and absorption after reflection (Fig. 1).

This chapter will briefly describe the principles and history of photovoltaic (PV) energy systems and will explore in details the various available technologies while reflecting on the advancement of each technology and its advantages and disadvantages and photovoltaic applications. Included are discussions of the status, development and applications of various PV and solar thermal technologies. This chapter is a full review on the development of existing photovoltaic (PV) technology. It highlights the four major current types of PV: crystalline, thin film, compound and nanotechnology. The aim of continuous development of PV technology is not only to improve the efficiency of the cells but also to reduce production cost of the modules, hence make it more feasible for various applications.

around 20% and the cost of production of PV power remains considerably higher than the cost of generating solar thermal heat (Liou, 2010). The efficiency of photovoltaic cells or modules is measured under controlled conditions (solar irradiance 1000 W/m2, cell temperature 25 oC, air mass 1.5), although the nominal operating cell temperature (NOCT) in actual applications is much higher than the reference cell temperature 25 oC; the higher NOCT is considered a major cause of reduced efficiency and electrical power output of photovoltaic modules (Garcia and Balenzategui, 2004). To enhance and possibly maximize the output of photovoltaic modules, the heat generated in the module can be extracted by passing a heat recovery fluid (water, oil, glycol, air) under and/or over the module (Tonui

Photovoltaic conversion is the direct conversion of sunlight into electricity without any heat engine to interfere. Photovoltaic devices are rugged and simple in design requiring very little maintenance and their biggest advantage being their construction as stand-alone systems to give outputs from microwatts to megawatts. Hence they are used for power source, water pumping, remote buildings, solar home systems, communications, satellites and space vehicles, reverse osmosis plants, and for even megawatt scale power plants. With such a vast array of applications, the demand for photovoltaics is increasing every year

PV history starts in 1839, when Alexandre-Edmund Becquerel observed that ''electrical currents arose from certain light induced chemical reactions" and similar effects were observed by other scientists in a solid (selenium) several decades later. But it was not till the late 1940s when the development of the first solid state devices paved the way in the industry for the first silicon solar cell to be developed with an efficiency of 6%. The development of the first silicon solar cell was fundamental in the initiation of solar technologies as it represented the power conversion unit of a PV system but with practical implications. These Si cells are not used separately rather they are assembled into modules. Presently, various types of solar cells on industrially available, however, the strive for research and development is continuing to expand and improve this energy collector (Chaar

The growth of such technology depends on materials and structure development; however the goal will always be maximum power at minimum cost. In any structure, solar cells, which are connected in series and in parallel in order to form the desired voltage and current levels, remain the basic semiconductor components of a PV panel. To maximize the power rating of a solar cell which ensures the highest efficiency, hence designed to raise the

This chapter will briefly describe the principles and history of photovoltaic (PV) energy systems and will explore in details the various available technologies while reflecting on the advancement of each technology and its advantages and disadvantages and photovoltaic applications. Included are discussions of the status, development and applications of various PV and solar thermal technologies. This chapter is a full review on the development of existing photovoltaic (PV) technology. It highlights the four major current types of PV: crystalline, thin film, compound and nanotechnology. The aim of continuous development of PV technology is not only to improve the efficiency of the cells but also to reduce production cost of the modules, hence make it more feasible for various applications.

desired absorption and absorption after reflection (Fig. 1).

and Tripanagnostopoulos, 2007).

(Parida et al., 2011)

et al., 2011).

Moreover, such variety in technology is needed to enhance the deployment of solar energy for a greener and cleaner environment. Devices such as space PV cell technology were also described and the progress in this field is expanding. In addition, the applications of PV installations are described.

Fig. 1. Behavior of light shining on a solar cell: (1) Reflection and absorption at top contact. (2) Reflection at cell surface. (3) Desired absorption. (4) Reflection from rear out of cell. (5) Absorption after reflection. (6) Absorption in rear contact (Chaar et al., 2011).

#### **2. Photovoltaic systems**

The photovoltaic phenomenon has been recognized since 1839, when French physicist Edmond Becquerel was able to generate electricity by illuminating a metal electrode in a weak electrolyte solution. The photovoltaic effect in solids was first studied in 1876 by Adam and Day, who made a solar cell from selenium that had an efficiency of 1–2%. The photovoltaic effect was explained by Albert Einstein in 1904 via his photon theory. A significant breakthrough related to modern electronics was the discovery of a process to produce pure crystalline silicon by Polish scientist Jan Czochralski in 1916. The efficiency of first generation silicon cells was about 6%, which is considerable lower than that of contemporary solar cells (about 14–20%). Early efforts to make photovoltaic cells a viable method of electricity generation for terrestrial applications were unsuccessful due to the high device costs. The ''energy crises'' of 1970s spurred a new found of initiatives in many countries to make photovoltaic systems affordable, especially for off-grid applications. The significant reductions in the prices of photovoltaic cells in more recent years has rejuvenated interest in the technology, e.g., the annual growth since 2000 in the production of PV system has exceeded 40% and present total installed capacity worldwide has reached about 22 GW (Kumar and Rosen, 2011).

Photovoltaic Systems and Applications 25

through most of the latter half of the last century, other cell types have been developed that compete either in terms of reduced cost of production (solar cells based on the use of multicrystalline Si or Si ribbon, and the thin-film cells based on the use of amorphous Si, CdTe, or CIGS) or in terms of improved efficiencies (solar cells based on the use of the III-V compounds). The market share of the different cell types during 2006 are given in Fig. 3.

Fig. 3. Market share for various photovoltaic cell technologies in 2006.

**3.1.1 Mono (single)-crystalline photovoltaic cells/panels** 

The first generation of PV technologies is made of crystalline structure which uses silicon (Si) to produce the solar cells that are combined to make PV modules. However, this technology is not obsolete rather it is constantly being developed to improve its capability and efficiency. Mono-crystalline, multi-crystalline, and emitter wrap through (EWT) are cells under the umbrella of silicon crystalline structures and are discussed in the following

This type of cell is the most commonly used, constitutes about 80% of the market recently and will continue to the leader until amore efficient and cost effective PV technology is developed. It essentially uses crystalline Si p–n junctions. Due to the silicon material, currently attempts to enhance the efficiency are limited by the amount of energy produced by the photons since it decreases at higher wavelengths. Moreover, radiation with longer wavelengths leads to thermal dissipation and essentially causes the cell to heat up hence reducing its efficiency. The maximum efficiency of mono-crystalline silicon solar cell has reached around 23% under STC, but the highest recorded was 24.7% (under STC). Due to combination of solar cell resistance, solar radiation reflection and metal contacts available on the top side, self losses are generated. After Si ingot is manufactured to a diameter between 10 to 15 cm, it is then cut in wafers of 0.3mm thick to form a solar cell of approximately 35mA of current per cm2 area with a voltage of 0.55V at full illumination. For some other

**3.1 Silicon crystalline structure** 

sections.
