Optimal photovoltaic panel tilt angle determination for different climate zones of Turkey

Technology is rapidly evolving in the world and major transformations are also undergoing in terms of consumption habits. The products that are placed on the market in order to make life easier are directing people to more comfort. In the progress of getting used to this comfort, the most of the devices used in daily life need electrical energy. Most of the electrical energy needs are met by conventional energy sources. However, the reasons such as; the limited reserves of energy resources, the vast majority of these resources in certain regions and their effects on the environment have forced the countries to shift from conventional sources to different energy sources. At this point, renewable energy sources are important options for more sensitive to the environment. Important research and development processes are carried out in many renewable energy sources such as solar, wind, biomass, geothermal, wave and hydro energy. A similar situation can be seen especially in the last 5 years in Turkey. Turkey meets its energy needs from abroad and this situation occupies a big place in the national economy. In order to reduce dependency in energy, especially in regions which have a potential in renewable energy, wind and solar energy investments have accelerated. Government grants have contributed to this situiaton. Solar energy investments have been one of the areas that have been revitalized by the government's incentives. Turkey has a good solar energy potential and in recent years, many solar power plants have been commissioned or the constructions are ongoing in the Central Anatolia and Southeastern Anatolia Regions. In addition to that, the government continues its actions for YEKA projects. Existing solar power plants are mostly composed of fixed-angle systems. With the field measurements, an optimal panel inclination angle is determined annually. This means that you cannot generally take the sun in the perpendicular direction in a year. For this purpose, systems that follow the sun have been developed such as single-axis and double-axis trackers. These systems are always follow the sun with electro-mechanic parts and the solar radiation is absorbed optimally. They offer effiency improvements ranging from 10 to 30%, but when considered in terms of initial installation costs, this extends the time of return and due to this fact, the investors are not preferred these systems. In this study, the optimal tilt angles for different climate zones of Turkey are determined. The analyzes were carried out with data from 43 stations which were taken TARBIL (Agricultural Monitoring and Information System) project. In the first section, the current status of conventional energy sources and the rate of penetration of renewable energy sources into the energy system over the years have been examined. In addition, the hypothesis and aim of this study is introduced and the literature review is summarized. In the second section, some basic concepts such as direct radiation, reflected radiation, diffusive radiation are explained. Then, the model used in this study with the basic concepts on solar radiation calculations on inclined surfaces is determined. Later in the third section, a climate map for different climatic zones of Turkey are colored. This map is based on a study made for Turkey's climatic zones. There are seven climatic and geographical zones in Turkey, however these climatic zones are different from the Turkey's geographical zones. For instance, the climate in the coastal regions of the Black Sea and the Mediterranean and in the inner parts of these regions vary with the effect of the mountains. After determining the climate zones, the selection of TARBİL measuring stations was determined by certain criteria and 43 stations were selected for this study. Monthly average daily solar radiation values of all stations are given in the graphs. In the fourth section, solar radiation calculations on the inclined surfaces which are described in the second section are made and then, according to these results with the 1⁰ intervals between 0-90⁰, optimal tilt angles were investigated with different scenarios such as monthly, seasonally, semi-yearly and yearly. These processes have been applied for all climate zones and also for Turkey. According to obtained results, for 'A' climate zone which represents the northern Marmara, certain deviations were determined in optimal tilt angles in autumn and winter seasons. This situation caused from the cloudiness of the region. For 'B' climate zone which stands for the Aegean, southern Marmara and western Mediterranean, cloudiness rate in the whole year is less and for that reason, there is a general agreement between results. For 'C' climate zone that represents the coastal of Black Sea, cloudiness rate is very high compared to other regions and also this zone has the lowest solar radiation capacity in Turkey. The optimal tilt angles for this zone has distinct deviations in autumn and winter. The 'D' climate zone which is the biggest climate zone of Turkey cover the whole Central Anatolia, inner parts of Black Sea and Mediterranean Regions has a good solar potential. There is also good correlation between the results. The 'E' climate zone is the smallest region and covers the north part of Eastern Anatolia Region. This region has also good potential however in autumn and winter, there are some deviations in the optimal tilt angles due to the cloudy days. The 'F' and 'G' regions which include respectively Southeastern Anatolia and the coastals of Mediterranean are the highest solar radiation capacity in Turkey. Especially, the 'F' climate zone has a high clearness index. As a general, all of the investigated climate zones has some correlations in terms of monthly, seasonally, semi-yearly and yearly optimal tilt angles. This situation can be understood easily when a general assessment made for Turkey. When the different scenarios are compared with each other, it is determined that, the monthly tilt angle adjusting has %5 more solar radiation than the yearly fixed tilt angle. On the other hand, other two scenarios which are seasonally and semi-yearly have %4 and %3.5 more solar radiation per square meter. Besides, four different regression equations such as linear, second, third and fourth order polynomial are derived for all climate zones. These equations are depend on solar declination and at any day of the year, they give the optimal tilt angle value. All of regression models are statistically tested with Mean Bias Error (MBE), Mean Absolute Error (MAE), normalize MBE, normalize MAE, Root Mean Square Error (RMSE) and R2 test. In error test results, are given in Appendix C. In the last section, the general procedure of this study was summarized and the results obtained in fourth section were discussed. According to these results, monthly optimal tilt angles for Turkey are {58,51,37,21,6,0,2,15,32,46,58,60} between January and December. Seasonally analized optimal tilt angles are {55,20,5,43} for winter, spring, summer and autumn. Semi-yearly optimized tilt angles are 49 and 12 for winter-autumn and summer-spring months respectively. Finally, the yearly fixed angle for Turkey is determined as 27⁰. ±1⁰ or ±2⁰ deviations on the optimal tilt angles do not change the solar radiation on inclined surface distinctly. Therefore, these values can be used for solar applications.