Zekai Şen

Fuzzy algorithm for estimation of solar irradiation from sunshine duration

Solar irradiation and sunshine duration are intimately related phenomena and a model involving the relationship between them can best be derived by methods that explicitly take vagueness into account. In this paper, the theory of fuzzy sets, especially fuzzy modeling, is employed to represent solar irradiation and sunshine duration relations as a set of fuzzy rules. A fuzzy logic algorithm has been devised for estimating the solar irradiation from sunshine duration measurements. The main advantage of fuzzy models is their ability to describe the knowledge in a descriptive human-like manner in the form of simple rules using linguistic variables only. In this manner the classical Angstrom or any other type of regression equations can be replaced by a set of fuzzy rule bases. The fuzzy approach is applied for three sites with monthly averages of daily irradiances in the western part of Turkey.

On the regional wind energy potential of Turkey

Continuous uses of fossil fuels are bound to pollute the atmosphere and consequently unwanted greenhouse and climate change effects will come to dominate every part of the earth. It is, therefore, advised to exploit clean energy resources, and for many nations in the world to try to assess their environmentally friendly, clean energy resources such as wind energy. Hence, it is an urgent situation to determine the wind energy potential in every country. This paper gives the wind velocity, topography and wind energy variation maps obtained for Turkey with local and regional interpretations.

An application of the degree-hours method to estimate the residential heating energy requirement and fuel consumption in Istanbul

Cold season heating energy requirements in buildings can be estimated with the degree-hours method based on human comfort levels and available meteorological temperature records for a given area. Such estimations are especially significant for cities where fossil fuel consumption must be eliminated in favor of clean energy alternatives to reduce air pollution. This paper considers the city of Istanbul in Turkey and presents a detailed account for practical energy requirements and fuel consumption calculations.

Regional assessment of wind power in western Turkey by the cumulative semivariogram method

Regional patterns of wind energy potential along the western Aegean Sea coastal part of Turkey are evaluated by considering its regional variability through the use of cumulative semivariogram (CSV) models. This innovative technique provides clues about the regional variations along any direction. Since in the western Anatolian coast winds are predominantly northerly or east northerly or west northerly, the regional variability is investigated along the north-south direction. The CSV techniques yielded the radius of influence for wind velocity and Weibull distribution parameters. Dimensionless Standard Regional Dependence (SRD) functions are obtained from the sample CSV. These SRD functions help to make simple regional predictions for the wind energy or wind velocity distribution parameters. The methodology has been applied for predicting the wind velocity in Turkey along the Aegean sea coast. Similar predictions can be achieved for wind energy and Weibull distribution parameters.

Spatial interpolation and estimation of solar irradiation by cumulative semivariograms

The main purpose of this paper is to find a regional procedure for estimating the solar irradiation value of any point from sites where measurements of solar global irradiation already exist. The spatial weights are deduced through the regionalized variables theory and the cumulative semivariogram (CSV) approach. The CSV helps to find the change of spatial variability with distance from a set of given solar irradiation data. It is then employed in the estimation of solar irradiation value at any desired point through a weighted average procedure. The number of adjacent sites considered in this weighting scheme is based on the least squares technique which is applied spatially by incrementing nearest site numbers successively from one up to the total site number. The validity of the methodology is first checked with the cross validation technique prior to its application to sites with no solar irradiation records. Hence, after the cross-validation each site will have different number of nearest adjacent sites for spatial interpolation. The application is achieved for monthly solar irradiation records over Turkey by considering 29 measurements stations. It has been shown that the procedure presented in this paper is better than the classical techniques such as the inverse distance or inverse distance square approaches.

Wind power potential in Turkey and Akhisar case study

Wind energy potential in various parts of Turkey is becoming economical due to reductions in the wind turbine costs, and in fossil fuel atmospheric pollution. The global change program imposes restrictions for use of alternative renewable and environmentally friendly energy sources. Wind energy is among such energy potentials and its practical and economical use gain significance day by day. The first wind energy turbine site investigation and wind power application possibility have been presented for the Akhisar area within the eastern provinces of Turkey. Different wind turbine technologies are assessed according to the local wind speed variations. Locally and technologically suitable wind turbines are selected. Finally their locations are decided by expert views and field measurements with the usage of well known WASP software. It is calculated that a minimum of 31436 MWh/year wind can be generated in this site. In the calculations 10% error possibility is allowed.

Regional wind energy evaluation in some parts of Turkey

Abstract The main purpose of this paper is to propose a standard regional dependence function (SRDF) based on the concepts of semivariogram and especially cumulative semivariogram. In fact, SRDF is a function of regional dependence which decreases with distance. These functions present quantitatively the regional dependence of the wind phenomenon recorded at irregularly scattered sites over an area. The SRDF provides a unique opportunity for the establishment of a regional objective prediction method whereby the wind velocity and/or energy can be predicted by use of the weighted averages. The weightings are obtained through the SRDF provided that the distance between two sites is known. The implementation of the proposed methodology is presented for some wind velocity measurement stations in Turkey. For the application the experimental SRDF forms are first obtained from the available data and then these are employed directly in the regional estimation procedure. The reliability of the methodology is measured through the cross validation procedure and it is observed that the procedure is valid with less than 5% error. The same procedure can be used in any part of the world.

Variations and Trends in Turkish Seasonal Heating and Cooling Degree-Days

The potential effect of climate change on energy demand is important especially for the developing and non-oil-producing countries. Cooling and heating degree-day (CDD and HDD) concepts are among the most significant meteorological variables related to residential energy consumption. This paper presents the spatial and temporal characteristics of Turkish seasonal CDD and HDD in the context of climate change. CDD and HDD are defined objectively by truncation of the temperature series at any constant base temperature level. This leads to surpluses and deficits as deviations. The surpluses are instances for cooling and the deficits for heating. Depending on temperature fluctuations, the degree-day statistics at any location show local and seasonal variations. In this study, regional variations of seasonal HDD and CDD are mapped for Turkey and their relations to local topography and climatic features are examined with conclusive interpretations. The sequential version of Mann–Kendall rank statisticis applied to demonstrate any existence of possible non-linear trends in accumulated HDD and CDD over the seasons. Spatially coherent and statistically significant trends of HDD and CDD appear in some regions of Turkey. In general, the sign of the trends is inconsistent with General Circulation Models (GCM) predictions.

Angström equation parameter estimation by unrestricted method

Abstract Global solar irradiation is directly related to the sunshine duration record through a linear model which was first proposed by Angstrom in 1924. Generally, the parameter estimations of this model are achieved by using the regression technique based on the least squares method. This technique imposes procedural restrictions on the parameter estimations leading to under-estimations for clear sky condition and over-estimations in the case of overcast sky conditions. These restrictions include linearity, normality, means of conditional distribution, homoscedasticity, autocorrelation and lack of measurement error. In this paper, an alternative unrestricted method (UM) is proposed for preserving the means and variances of the global irradiation and the sunshine duration data. In the restrictive regression approach (Angstrom equation) the cross-correlation coefficient represents only linear relationships. By not considering this coefficient in the UM, some nonlinearities in the solar irradiation–sunshine duration relationship are taken into account. Especially when the scatter diagram of solar irradiation versus sunshine duration does not show any distinguishable pattern such as a straight line or a curve, then the use of UM is recommended for parameter estimations. The UM is contrasted with the Angstrom regression method for 27 solar irradiation stations in Turkey.

Rainfall distribution function for Libya and rainfall prediction

Monthly rainfall amounts are distributed according to different frequency distribution functions in different parts of the world. However, in extremely arid regions gamma probability distribution functions are most often found to fit the existing data well. Libyan monthly rainfall distributions are found to abide by gamma probability distribution function which is confirmed on the basis of chi-square tests. Almost all the rainfall sequences recorded for at least the last 20 years in Libya are investigated statistically and gamma distribution parameters are calculated at existing stations. The shape and scale parameters are then regionalized and hence it becomes possible to find the parameter values at any desired location within the study area and then to generate synthetic sequences according to the gamma distribution. Predictions of 10, 25, 50 and 100 mm rainfall amounts are achieved by this probability function.