Abstract

Iran with 300 sunny days in more than two thirds of its land is among the countries with high potential of solar energy. Nevertheless, to date no research has been conducted on status of solar exergy in Iran. In this study, in order to expand the perception of solar energy quality and to compensate the lack of research on solar radiation exergy in Iran, long term meteorological and solar data of eight capital provinces of Iran with five different climatic conditions are utilized. These properly distributed stations include Urmia, Bushehr, Isfahan, Ilam, Kerman, Mashhad, Zahedan and Zanjan. The monthly average daily solar radiation exergy on a horizontal surface for each station is obtained first, then it is recognized that the ratio of exergy to energy is almost independent of the month, the climatic condition and the geographical location; thus, can be considered 0.87 for the whole Iran. For predicting the solar exergy at every station, five empirical models with linear, quadratic, cubic, exponential and power functional forms, all dependent only on relative sunshine duration, are calibrated. Then, eight statistical indicators are utilized to evaluate the performance of the established models for every capital province. The best models recognized for Urmia, Bushehr, Isfahan, Ilam, Kerman, Mashhad, Zahedan and Zanjan have cubic, power, exponential, exponential, linear, quadratic, power and cubic functional forms, respectively. These models are simple and easy to apply and can be also utilized for other places with similar climatic classification and conditions.

Highlights

  • Solar energy is considered a clean source for energy supply to generate electricity and heat, because it does not produce any pollutants and does not endanger the environment

  • The results show that Isfahan in February, March, May, June and September, Zahedan in January, April and November, Kerman in October and December and Mashhad in July and August have the highest monthly average relative sunshine duration values compared with those of other stations at the same months, indicating that these stations enjoy from more sunny hours and sunny days at these months

  • The results show that in all of the stations the maximum monthly average daily solar exergy and the maximum monthly average daily solar radiation occur in June or July, and the minimum monthly average daily solar exergy and minimum monthly average daily solar radiation occur either in November or in December

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Summary

Introduction

Solar energy is considered a clean source for energy supply to generate electricity and heat, because it does not produce any pollutants and does not endanger the environment. It has the highest energy level among all renewable sources. One of the most important information about solar energy is the monthly average daily solar radiation. Many studies have been carried out on the monthly average daily solar radiation measurement, prediction and model development or establishment. Some studies goes back to almost 100 years ago, by which efforts were made to know the important parameters affecting the solar radiation arriving on the earth (Angstrom, 1924)

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