Isı Bilimi ve Tekniği Dergisi, 29, 2, 99-108, 2009 J. of Thermal Science and Technology ©2009 TIBTD Printed in Turkey ISSN 1300-3615 99 ESTIMATION OF SOLAR RADIATION FROM ANGSTROMS COEFFICIENTS BY USING GEOGRAPHICAL AND METEOROLOGICAL DATA IN BISHKEK, KYRGYZSTAN İnci TÜRK TOĞRUL Afyon Kocatepe University, Engineering Faculty, Chemical Engineering Department, 03200 Afyon Karahisar; e-mail: itogrul@aku.edu.tr (Geliş Tarihi: 09. 09. 2008, Kabul Tarihi: 25. 05. 2009) Abstract: In this study, the usability of clear sky radiation and Angstrom coefficients depend on geographical and meteorological parameters for predicting monthly mean global solar radiation in Bishkek, Kyrgyzstan were investigated. A multiple linear regression was applied to explain the relationship among Angstrom coefficients and geographical and meteorological data sets which were monthly mean clear sky or extraterrestrial radiation, the ratio of sunshine hours to day length, ambient and soil temperatures, relative humidity, sine of declination angle. Variables in these equations were used to estimate the global solar radiation. Values calculated from models were compared with the meteorological values. Keywords: Clear sky radiation, solar energy estimation, Angstrom coefficient, multiple linear regression, t statistic BİŞKEK, KIRGIZİSTAN’DA COĞRAFİK VE METEOROLOJİK VERİYİ KULLANARAK ANGSTROM KATSAYILARINDAN GÜNEŞ IŞIMASININ HESAPLANMASI Özet: Bu çalışmada, Bişkek, Kırgızistan’da coğrafik ve meteorolojik parametrelere bağlı olarak Angstrom katsayısı ve açık gökyüzü ışımasının kullanılabilirliği araştırıldı. Aylık ortalama açık gökyüzü ışıması veya atmosfer dışı ışıma, güneşlenme süresinin gün uzunluğuna oranı, çevre ve toprak sıcaklıkları, bağıl nem, deklinasyon açısı gibi meteorolojik parametreler ve Angstrom katsayıları arasındaki ilişkiyi açıklamak için çok yönlü lineer regresyon uygulandı. Daha sonra bu eşitliklerdeki değişkenler toplam güneş ışımasını hesaplamada kullanıldı. Modellerden hesaplanan değerler meteorolojik değerlerle mukayese edildi. Anahtar Kelimeler: Açık gökyüzü ışıması, güneş ışımasının hesaplanması, Angstrom katsayısı, çok yönlü lineer regresyon, t- istatistik INTRODUCTION Energy and fresh water are two major commodities furnishing the fundamentals of every human activity for reasonable and good life quality. These two resources are intricately related to each other. In fact, during the early civilizations, water power has been employed as the major energy sources. Solar energy is the most ancient source, and root material for almost all fossil and renewable types. Special devices have been used for benefiting from the solar energy since immemorial and such applications actually date back to before Christ. Energy is a continuous steering power for the social and technological prospective developments. Energy sources are vital and essential ingredients for all human transactions and without them human activities of all kinds will not be progressive at all. On one hand, the energy sources are limited and on the other, the population growth at present average rate 2% inserts extra pressure on additional energy demands. Solar energy is an almost inexhaustible source for future generations. Recent progress in solar and possible future research trends is presented by Şen (2004, 2007). In many applications of solar energy, the most important parameters that are often needed are the average global solar irradiation and its components. Unfortunately, the measurements of this parameter are done only at a few places. For this reason there have been attempts at estimating them from theoretical models. This correlations estimate the amounts of monthly average solar radiation from more readily available meteorological parameters such as the sunshine duration, extraterrestrial radiation. Several empirical models have been developed to calculate global solar radiation using various parameters. Angstrom (1924) developed the earliest model used for estimating global radiation, in which the sunshine duration data and clear sky radiation ( c H ) data were used.