Koray Ulgen

Experimental and theoretical investigation of effects of wall’s thermophysical properties on time lag and decrement factor

Energy saving policies are necessary to control energy consumption, use energy efficiently and effectively, and reassess available production and consumption systems. In this context, the objectives of this study are to investigate the thermal behaviours of opaque wall materials under solar energy change, and the interaction between thermophysical characteristics of opaque wall materials and solar energy falling onto exterior surface of the wall affects interior environment. Parameters of characteristics used in wall formation, their positions, wall thermal behaviours, and “time lag” and “decrement factor” having effect on the changes of conditions of interior space were investigated experimentally for different wall formations. The experimental findings were compared with the results of equations derived by using an analytic methodology.

Optimum tilt angle for solar collectors

A solar collector is required to absorb solar radiation and transfer the absorbed energy into a heat transfer fluid with a minimum of heat loss. In assessing the performance of a collector, it is therefore important not only to determine its ability to absorb solar radiation but also to characterize its heat losses. The ability of a collector to absorb solar radiation is largely determined by its optical and geometric properties. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation in tilt angle affects the amount of solar radiation reaching the collector surface. In this study, a mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. It is found that the optimum tilt angle changes between 0° (June) and 61° (December) throughout the year. In winter (December, January, and February) the tilt should be 55.7°, in spring (March, April, and May) 18.3°, in summer (June, July, and August) 4.3°, and in autumn (September, October, and November) 43°. The yearly average of this value was found to be 30.3° and this would be the optimum fixed tilt throughout the year.

Estimation of Wind Power Potential Using Weibull Distribution

The main objective of the present study is to estimate wind power potential using the two Weibull parameters of the wind speed distribution function, the shape parameter k (dimensionless) and the scale parameter c (m/s). In this regard, a methodology that uses three various techniques (maximum likelihood, least squares, and method of moments) for estimating the Weibull parameters was given first. The methodology was then applied to a region in Turkey. Finally, the parameter techniques were compared to Monte-Carlo simulation in different sample sizes, and the best parameter estimation techniques belonging to the sample sizes were also determined.

Solar Radiation Models. Part 2: Comparison and Developing New Models

Solar engineers, architects, agriculturists, and hydrologists in many applications of solar energy require a reasonably accurate knowledge about the availability of solar resources at any place. For this purpose, in the past, several empirical models have been developed in order to estimate the solar radiation around the world. The main objective of the present study is twofold, namely: (1) to compare some existing models used for estimating the monthly average daily global solar radiation on a horizontal surface (H) for Turkeys big cities such as Istanbul, Ankara and Izmir, which cover approximately 30% of the population of Turkey, and (2) to develop some empirical models for these cities. Experimental data for Izmir were measured in the Solar-Meteorological Station of the Solar Energy Institute at Ege University. The present models were then compared with the 25 models, of which 12 were given in Part 1 of this study (defined as national models), while the remainder (called international models), presented here, and used for calculating H. The main percentage error (MPE), the root mean square error (RMSE), the main bias error (MBE) and the t-statistic (t-stat) methods were used for evaluating the performance of the models studied. It may be concluded that the present models predict the values of H for the three big cities better than other available models.

Optimization of a Wind/PV Hybrid Power Generation System

This study investigates the wind and solar electricity generation availability at the Solar Energy Institute of Ege University, Izmir, Turkey. The main purpose of this study is to design an appropriate wind-PV hybrid system to cover the electricity consumption of the Institute. In order to do this, monthly average solar irradiation and wind speed data are used, which were measured, consisting of hourly records over an eight-year period from 1995–2002. Simple models were developed to determine wind, solar, and hybrid power resources per unit area. Correlations between the solar and wind power data were carried out on an hourly, daily, and monthly basis. It is shown that the hybrid system can be applied for the efficient and economic utilization of these resources.

Prediction of solar radiation parameters through clearness index for Izmir, Turkey

The need for meteorological parameters is essential in the design and study of solar energy conservation devices. Other uses of such information include agricultural studies, meteorological forecasting, environment, and energy conversion. In this study, the ratio of monthly average hourly diffuse radiation to monthly average hourly global radiation (I d /I) was correlated with the monthly average hourly clearness index (k T ) in the form of the polynomial relationships for the city of Izmir in the western part of Turkey. Experimental data were measured in the Solar-Meteorological Station of Solar Energy Institute in Ege University over a 5 year period from 1994 to 1998. The values of the monthly average-daily hours of bright sunshine (S) varied between 3.54 and 12.28. The values of the monthly average-daily clearness index (K T ) ranged from 0.41 to 0.66, averaged for the same period. The frequency distribution of the clearness index was also given. It can be concluded that the present models estimate the values of I d for Izmir, and possibly elsewhere with similar climatic conditions, reasonably well if the values of I are known or can be predicted.

Solar Radiation Models. Part 1: A Review

Solar energy occupies one of the most important places among the various possible alternative energy sources. In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. In other words, a reasonably accurate knowledge of the availability of the solar resource at any place is required by solar engineers, architects, agriculturists, and hydrologists in many applications of solar energy such as solar furnaces, concentrating collectors, and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of the present study is to review solar radiation models available in the literature for both Turkey in general and some of the provinces. In this regard, a total of 41 models developed between 1983–2002 was given. Of this, 15 models were for the whole of Turkey, while the remainder were for some of Turkeys provinces such as Antalya, Elazig, Gebze, Istanbul, Izmir, Konya and Trabzon. It may be concluded that the models investigated predict the solar radiation reasonably well for the projections.

A Study on Evaluating the Power Generation of Solar-Wind Hybrid Systems in Izmir, Turkey

Turkey is abundant in terms of renewable energy resources. Residential and industrial utilization of solar energy started in the 1980s, while the first Build-Operate-Transfer (BOT) windmill park, located at Alacati, Izmir, was commissioned in 1998. Additionally, power generation through solar-wind hybrid systems has recently appeared on the Turkish market. This study investigates the wind and solar thermal power availability in Izmir, located in the western part of Turkey. Simple models were developed to determine wind, solar, and hybrid power resources per unit area. Experimental data, consisting of hourly records over a 5 yr period, 1995–1999, were measured in the Solar/Wind Meteorological Station of the Solar Energy Institute at Ege University. Correlations between solar and wind power data were carried out on an hourly, a daily, and a monthly basis. It can be concluded that possible applications of hybrid systems could be considered for the efficient utilization of these resources.

Comparison of the diffuse fraction of daily and monthly global radiation for Izmir, Turkey

In this study, empirical correlations were developed to establish a relationship between the daily diffuse fraction (Kd) and the daily clearness index (KT) for the city of Izmir in Turkey. Hourly global and diffuse radiation measurements on a horizontal surface were performed in the Solar-Meteorological Station of the Solar Energy Institute in Ege University over a 5 year period from 1994 to 1998. The present models were then compared to the 16 models available in the literature in terms of the widely used statistical indicators, namely, correlation coefficient (R2), main percentage error (MPE), main bias error (MBE), root main square error (RMSE), and the t-statistic (t-stat) combining the last 2 errors. It may be concluded that the present models predict the values of Kd as a function of KT for Izmir better than other available models, while all the models tested appear to be location-independent models for diffuse radiation predictions, at least for Izmir.

Solar Energy Applications in Turkey

Solar energy technologies offer a clean, renewable and domestic energy source, and are essential components of a sustainable energy future. Turkey lays in a sunny belt between 36° and 42° N latitudes and is geographically well situated with respect to solar energy potential. The objective of the present study is to investigate many aspects of solar energy applications in Turkey, giving the brief historical development and Turkeys solar energy potential and consumption. The following applications were taken into consideration: solar water heating, steam generation, solar cooker, solar drying, solar houses, and photovoltaics (PVs). In the early 1960s, solar energy was realized as an alternative energy in Turkey, while in the mid-1970s, solar thermal utilization technologies began gaining the 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. Among all the above solar thermal utilization methods, the solar water heating has been, and will still have, the greatest emphasis in Turkey, reaching a total annual production capacity of 1,000,000 m2. Recently, the number of the PV installations has significantly increased and Turkeys total PV installed capacity is expected to be 3 MWp in 2010.