Solar radiation models. Part 1: A review

WOS: 000220662800008Solar energy occupies one of the most important places among the various possible alternative energy sources. In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. In other words, a reasonably accurate knowledge of the availability of the solar resource at any place is required by solar engineers, architects, agriculturists, and hydrologists in many applications of solar energy such as solar furnaces, concentrating collectors, and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of the present study is to review solar radiation models available in the literature for both Turkey in general and some of the provinces. In this regard, a total of 41 models developed between 1983-2002 was given. Of this, 15 models were for the whole of Turkey, while the remainder were for some of Turkey's provinces such as Antalya, Elazig, Gebze, Istanbul, Izmir Konya and Trabzon. It may be concluded that the models investigated predict the solar radiation reasonably well for the projections

Determination of Weibull parameters for wind energy analysis of Izmir, Turkey

WOS: 000175450900003In this study, the two Weibull parameters of the wind speed distribution function, the shape parameter k (dimensionless) and the scale parameter c (m s(-1)), were computed from the wind speed data for Izmir. Wind data, consisting of hourly wind speed records over a 5-year period, 1995-1999, were measured in the Solar/Wind-Meteorological Station of the Solar Energy Institute at Ege University. Based on the experimental data, it was found that the numerical values of both Weibull parameters (k and c) for Izmir vary over a wide range. The yearly values of k range from 1.378 to 1.634 with a mean value of 1.552, while those of c are in the range of 2.956-3.444 with a mean value of 3.222. The average seasonal Weibull distributions for Izmir are also given. The wind speed distributions are represented by Weibull distribution and also by Rayleigh distribution, with a special case of the Weibull distribution for k = 2. As a result, the Weibull distribution is found to be suitable to represent the actual probability of wind speed data for Izmir (at annual average wind speeds up to 3 m s(-1)). Copyright (C) 2002 John Wiley Sons, Ltd

Comparison of the diffuse fraction of daily and monthly global radiation for Izmir, Turkey

WOS: 000183312900002In this study, empirical correlations were developed to establish a relationship between the daily diffuse fraction (K-d) and the daily clearness index (K-T) for the city of Izmir in Turkey. Hourly global and diffuse radiation measurements on a horizontal surface were performed in the Solar-Meteorological Station of the Solar Energy Institute in Ege University over a 5 year period from 1994 to 1998. The present models were then compared to the 16 models available in the literature in terms of the widely used statistical indicators, namely, correlation coefficient (R-2), main percentage error (MPE), main bias error (MBE), root main square error (RMSE), and the t-statistic (t-stat) combining the last 2 errors. It may be concluded that the present models predict the values of Kd as a function of KT for Izmir better than other available models, while all the models tested appear to be location-independent models for diffuse radiation predictions, at least for Izmir

Solar radiation models. Part 2: Comparison and developing new models

WOS: 000220662800009Solar engineers, architects, agriculturists, and hydrologists in many applications of solar energy require a reasonably accurate knowledge about the availability of solar resources at any place. For this purpose, in the past, several empirical models have been developed in order to estimate the solar radiation around the world. The main objective of the present study is twofold, namely: (1) to compare some existing models used for estimating the monthly average daily global solar radiation on a horizontal surface (H) for Turkey's big cities such as Istanbul, Ankara and Izmir which cover approximately 30% of the population of Turkey, and (2) to develop some empirical models for these cities. Experimental data for Izmir were measured in the Solar-Meteorological Station of the Solar Energy Institute at Ege University. The present models were then compared with the 25 models, of which 12 were given in Part I of this study (defined as national models), while the remainder (called international models), presented here, and used for calculating H. The main percentage error (MPE), the root mean square error (RMSE), the main bias error (MBE) and the t-statistic (t-stat) methods were used for evaluating the performance of the models studied. It may be concluded that the present models predict the values of H for the three big cities better than other available models

Exergetic assessment of direct-expansion solar-assisted heat pump systems: Review and modeling

Although the idea of using a solar collector as the evaporator in the traditional heat pump cycle was first proposed in the year 1955, studies on the subject began in the late 70s. One of the keystones for obtaining sustainable development is also the use of exergy analysis. In this regard, the main objectives in doing the present study are twofold, namely (i) to review studies on direct-expansion solar-assisted heat pump systems (DX-SAHPs) and (ii) to present a mathematical model along with an illustrative example, which is used for heating an office space in Solar Energy Institute of Ege University, Izmir, Turkey, by floor heating with a DX-SAHP system. The system uses a 4 m2 bare flat-plate collector as the evaporator, while the working fluid is chosen to be R-22. Water is heated by the heat pump and heat is delivered to the office space by floor heating. Exergy equations for the system are derived, while exergy calculations are made. The exergy efficiency values for the individual components of the DX-SAHP system are found to range from 10.74% to 88.87%. It is expected that this study will be very beneficial to everyone involved or interested in the exergetic design, analysis and performance assessment of DX-SAHPs. © 2007 Elsevier Ltd. All rights reserved.Fundamental Research Fund of Shandong University Ege ÜniversitesiThe authors would like to thank Ege University Research Fund for their financial support. -