This study develops empirical models in order to estimate the monthly average daily global solar radiation on a horizontal surface (H). The seven big cities considered in the model have 33.4% of Turkey's population and are as follows: Izmir in the Aegean Sea, Samsun in the Black Sea, Ankara in the Central Anatolia, Van in the East Anatolia, Istanbul in the Marmara, Antalya in the Mediterranen Sea, and Urfa in the Southeast Anatolia Region of Turkey. The developed models were analyzed using the seven statistical analyzing methods such as the mean percentage error (MPE), mean absulate percentage error (MAPE), sum of squares of relative error (SSRE), relative standard error (RSE), mean bias error (MBE), root mean square error (RMSE) and correlation coefficient (R). It may be concluded that the present models estimate the values of H, reasonably well for the cities studied and possibly elsewhere with similar climatic conditions.
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INTRODUCTIONTurkey's geographic location has several advantages for extensive use of most of the renewable energy sources, as shown in Fig. 1. It is on the humid and warm climatic belt, which includes most of Europe, the near east and western Asia. A typical Mediterranean climate is predominant at most of its coastal areas, whereas the climate at the interior part between the mountains that are a part of the Alpine Himalayan mountain belt is dry with typical steppe vegetation. This is mainly because the country is surrounded by seas at three sides: the Black sea at the north, the Marmara sea and Aegean sea to the west and the Mediterranean sea to the south. Although solar energy is the most important renewable energy source, it has not yet become widely commercial, even in nations with high solar potential such as Turkey. In the early 1960s, solar energy was realized as an alternative energy in Turkey, while the mid1970s, solar thermal utilization technologies began gaining high attention of universities, the government and the industry and have been developed at an increasing speed. Residential and industrial consumption of solar energy in Turkey started in 1986 and 1988, respectively. Solar energy use accounted for 129 kilo tons of oil equivalent (ktoe) in 2000 and is projected to be 431 ktoe and 828 ktoe in 2010 and 2020, respectively. There are limited applications, and most of them are inefficient, both in terms of energy use and economical benefits. The economical feasibility of a solar energy system is mainly determined by its initial cost and long term efficiency. The cost of the conventional energy replaced by solar means is, of course, another important parameter. Therefore, in the use of solar energy systems, careful consideration is vital to determine the system capacity for optimum useful energy collection at the installation site. Clean, domestic and renewable energy is commonly accepted as the key for future life, not only for Turkey but also for the world. All nations, regardless of their degree of development, are trying to develop and apply technologies th...