Modeling Optimization Renewable Energy Systems ITO12

Modeling Optimization Renewable Energy Systems ITO12

(Parte 1 de 7)

Edited by Arzu Şencan Şahin

Edited by Arzu Şencan Şahin

Modeling and Optimization of Renewable Energy Systems Edited by Arzu Şencan Şahin

Published by InTech Janeza Trdine 9, 51000 Rijeka, Croatia

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Modeling and Optimization of Renewable Energy Systems, Edited by Arzu Şencan Şahin ISBN 978-953-51-0600-5

Contents

Preface IX

Chapter 1 Solar-Energy Drying Systems 1 Feyza Akarslan

Chapter 2 Photovoltaic Systems and Applications 21 Feyza Akarslan

Chapter 3 A New Adaptive Method for Distribution

System Protection Considering Distributed Generation Units Using Simulated Annealing Method 53 Hamidreza Akhondi and Mostafa Saifali

Chapter 4 Exergoeconomic Analysis and

Optimization of Solar Thermal Power Plants 65 Ali Baghernejad and Mahmood Yaghoubi

Chapter 5 Optimization of

Renewable Energy Systems: The Case of Desalination 89 Karim Bourouni

Chapter 6 Heat Transfer Modeling of the Ground Heat Exchangers for the Ground-Coupled Heat Pump Systems 117 Yi Man, Ping Cui and Zhaohong Fang

Chapter 7 Promoting and Improving Renewable

Energy Projects Through Local Capacity Development 147 Rafael Escobar, David Vilar, Enrique Velo, Laia Ferrer-Martí and Bruno Domenech

Chapter 8 Utilization of Permanent

Grassland for Biogas Production 171 Pavel Fuksa, Josef Hakl, Zuzana Hrevušová, Jaromír Šantrůček, Ilona Gerndtová and Jan Habart

VI Contents

Chapter 9 Globalization of the Natural Gas

Market on Natural Gas Prices in Electric Power Generation and Energy Development 197 Thomas J. Hammons

Chapter 10 An Analysis of the Effect of Renewable Energies on Spanish

Electricity Market Efficiency 239 Blanca Moreno and María Teresa García-Álvarez

Chapter 1 Modernization and Intensification of Nitric Acid Plants 259

Marcin Wilk, Andrzej Kruszewski, Marcin Potempa, Romuald Jancewicz, Jacek Mendelewski, Paweł Sławiński, Marek Inger and Jan Nieścioruk

Chapter 12 Optimal Design of an Hybrid Wind-Diesel

System with Compressed Air Energy Storage for Canadian Remote Areas 269 Younes Rafic, Basbous Tammam and Ilinca Adrian

Preface

Energy needs are continuously increasing and the demand for electrical power continues to grow rapidly. The world energy market has to date depended almost entirely on nonrenewable, but low cost, fossil fuels.

Renewable energy is the inevitable choice for sustainable economic growth, for the harmonious coexistence of human and environment as well as for the sustainable development. As we learn how to economically harness the renewable energy sources, they will get cheaper and cheaper while fossil fuels get more and more expensive. A wind, solar or geothermal power plant may be more expensive to build now than a fossil power plant, but the future cost of fuel will be zero. In addition, the effects of the pollution fossil fuels produce become more and more destructive. The cost of controlling these pollutants is growing every day.

Arzu Şencan Şahin

Süleyman Demirel University,

Technology Faculty, Energy System Engineering, Isparta, Turkey

Solar-Energy Drying Systems

Feyza Akarslan

Department of Textile Engineering, Engineering and Architectural Faculty,

Süleyman Demirel Univercity, Isparta Turkey

1. Introduction

Energy is important for the existence and development of humankind and is a key issue in international politics, the economy, military preparedness, and diplomacy. To reduce the impact of conventional energy sources on the environment, much attention should be paid to the development of new energy and renewable energy resources. Solar energy, which is environment friendly, is renewable and can serve as a sustainable energy source. Hence, it will certainly become an important part of the future energy structure with the increasingly drying up of the terrestrial fossil fuel. However, the lower energy density and seasonal doing with geographical dependence are the major challenges in identifying suitable applications using solar energy as the heat source. Consequently, exploring high efficiency solar energy concentration technology is necessary and realistic (Xie et al., 2011).

Solar energy is free, environmentally clean, and therefore is recognized as one of the most promising alternative energy recourses options. In near future, the large-scale introduction of solar energy systems, directly converting solar radiation into heat, can be looked forward. However, solar energy is intermittent by its nature; there is no sun at night. Its total available value is seasonal and is dependent on the meteorological conditions of the location. Unreliability is the biggest retarding factor for extensive solar energy utilization. Of course, reliability of solar energy can be increased by storing its portion when it is in excess of the load and using the stored energy whenever needed. (Bal et al., 2010).

Solar drying is a potential decentralized thermal application of solar energy particularly in developing countries (Sharma et al., 2009). However, so far, there has been very little field penetration of solar drying technology. In the initial phase of dissemination, identification of suitable areas for using solar dryers would be extremely helpful towards their market penetration.

Solar drying is often differentiated from “sun drying” by the use of equipment to collect the sun’s radiation in order to harness the radiative energy for drying applications. Sun drying is a common farming and agricultural process in many countries, particularly where the outdoor temperature reaches 30 °C or higher. In many parts of South East Asia, spice s and herbs are routinely dried. However, weather conditions often preclude the use of sun drying

Modeling and Optimization of Renewable Energy Systems because of spoilage due to rehydration during unexpected rainy days. Furthermore, any direct exposure to the sun during high temperature days might cause case hardening, where a hard shell develops on the outside of the agricultural products, trapping moisture inside. Therefore, the employment of solar dryer taps on the freely available sun energy while ensuring good product quality via judicious control of the radiative heat. Solar energy has been used throughout the world to dry products. Such is the diversity of solar dryers that commonly solar-dried products include grains, fruits, meat, vegetables and fish. A typical solar dryer improves upon the traditional open-air sun system in five important ways (Sharma et al., 2009):

It is faster. Matetrials can be dried in a shorter period of time. Solar dryers enhance drying times in two ways. Firstly, the translucent, or transparent, glazing over the collection area traps heat inside the dryer, raising the temperature of the air. Secondly, the flexibility of enlarging the solar collection area allows for greater collection of the sun’s energy.

It is more efficient. Since materials can be dried more quickly, less will be lost to spoilage immediately after harvest. This is especially true of products that require immediate drying such as freshly harvested grain with high moisture content. In this way, a larger percentage of product will be available for human consumption. Also, less of the harvest will be lost to marauding animals and insects since the products are in safely enclosed compartments.It is hygienic. Since materials are dried in a controlled environment, they are less likely to be contaminated by pests, and can be stored with less likelihood of the growth of toxic fungi.It is healthier. Drying materials at optimum temperatures and in a shorter amount of time enables them to retain more of their nutritional value such as vitamin C. An added bonus is that products will look better, which enhances their marketability and hence provides better financial returns for the farmers.It is cheap. Using freely available solar energy instead of conventional fuels to dry products, or using a cheap supplementary supply of solar heat, so reducing conventional fuel demand can result in significant cost savings.

2. Classification of drying systems

All drying systems can be classifed primarily according to their operating temperature ranges into two main groups of high temperature dryers and low temperature dryers. However, dryers are more commonly classifed broadly according to their heating sources into fossil fuel dryers (more commonly known as conventional dryers) and solar-energy dryers. Strictly, all practically-realised designs of high temperature dryers are fossil fuel powered, while the low temperature dryers are either fossil fuel or solar-energy based systems (Ekechukwu and Norton, 1999).

2.1 High temperature dryers

High temperature dryers are necessary when very fast drying is desired. They are usually employed when the products require a short exposure to the drying air. Their operating temperatures are such that, if the drying air remains in contact with the product until equilibrium moisture content is reached, serious over drying will occur. Thus, the products are only dried to the required moisture contents and later cooled. High temperature dryers

Solar-Energy Drying Systems are usually classifed into batch dryers and continuous-flow dryers. In batch dryers, the products are dried in a bin and subsequently moved to storage. Thus, they are usually known as batch-in-bin dryers. Continuous-flow dryers are heated columns through which the product flows under gravity and is exposed to heated air while descending. Because of the temperature ranges prevalent in high temperature dryers, most known designs are electricity or fossil-fuel powered. Only a very few practically-realised designs of high temperature drying systems are solar-energy heated (Ekechukwu and Norton, 1999).

2.2 Low temperature dryers

In low temperature drying systems, the moisture content of the product is usually brought in equilibrium with the drying air by constant ventilation. Thus, they do tolerate intermittent or variable heat input. Low temperature drying enables products to be dried in bulk and is most suited also for long term storage systems. Thus, they are usually known as bulk or storage dryers. Their ability to accommodate intermittent heat input makes low temperature drying most appropriate for solar-energy applications. Thus, some conventional dryers and most practically-realised designs of solar-energy dryers are of the low temperature type(Ekechukwu and Norton, 1999).

3. Types of solar driers

Solar-energy drying systems are classified primarily according to their heating modes and the manner in which the solar heat is utilised.

In broad terms, they can be classified into two major groups, namely (Ekechukwu and Norton, 1999):

active solar-energy drying systems (most types of which are often termed hybrid solar dryers); and

passive solar-energy drying systems (conventionally termed natural-circulation solar drying systems).

Three distinct sub-classes of either the active or passive solar drying systems can be identified which vary mainly in the design arrangement of system components and the mode of utilisation of the solar heat, namely (Ekechukwu and Norton, 1999):

Direct (integral) type solar dryers; İndirect (distributed) type solar dryers.

Direct solar dryers have the material to be dried placed in an enclosure, with a transparent cover on it. Heat is generated by absorption of solar radiation on the product itself as well as on the internal surfaces of the drying chamber. In indirect solar dryers, solar radiation is not directly incident on the material to be dried. Air is heated in a solar collector and then ducted to the drying chamber to dry the product. Specialized dryers are normally designed with a specific product in mind and may include hybrid systems where other forms of energy are also used (Sharma et al., 2009). Although indirect dryers are less compact when compared to direct solar dryers, they are generally more efficient. Hybrid solar systems allow for faster rate of drying by using other sources of heat energy to supplement solar heat.

Modeling and Optimization of Renewable Energy Systems

The three modes of drying are: (i) open sun, (i) direct and (ii) indirect in the presence of solar energy. The working principle of these modes mainly depends upon the method of solar-energy collection and its conversion to useful thermal energy.

3.1 Open sun drying (OSD)

Fig. 1 shows the working principle of open sun drying by using solar energy. The short wavelength solar energy falls on the uneven product surface. A part of this energy is reflected back and the remaining part is absorbed by the surface. The absorbed radiation is converted into thermal energy and the temperature of product stars increasing. This result in long wavelength radiation loss from the surface of product to ambient air through moist air. In addition to long wavelength radiation loss there is convective heat loss too due to the blowing wind through moist air over the material surface. Evaporation of moisture takes place in the form of evaporative losses and so the material is dried. Further a part of absorbed thermal energy is conducted into the interior of the product. This causes a rise in temperature and formation of water vapor inside the material and then diffuses towards the surface of the and finally losses thermal energy in the and then diffuses towards the surface of the and finally losses the thermal energy in the form of evaporation. In the initial stages, the moisture removal is rapid since the excess moisture on the surface of the product presents a wet surface to the drying air. Subsequently, drying depends upon the rate at which the moisture within the product moves to the surface by a diffusion process depending upon the type of the product (Sodha, 1985).

(Parte 1 de 7)

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