Yazarlar
- Kankal, Murat(17)
- Şan, Murat(17)
- Akinoglu, Bulent G.(14)
- Ozden, Talat(14)
- Nacar, Sinan(10)
- Barut, Abdulkadir(9)
- Akpinar, Adem(6)
- Akyol, Mehmet(6)
- Akçay, Fatma(6)
- Cakir, Mehmet Ali(6)
- Pilatin, Abdulmuttalip(6)
- Sezer, İsmet(6)
- Terhan, Meryem(6)
- Özden, Talat(6)
- Işık, Fatih(5)
- Kömürcü, Murat Ihsan(5)
- Pala, Fahrettin(5)
- Turan, Rasit(5)
- Akyol, Hikmet(4)
- Artan, Seyfettin(4)
- Hayaloğlu, Pınar(4)
- Peker, Iskender(4)
- Sezer, Ismet(4)
- Özbek, Adem(4)
- Adali, Zafer(3)
- Akpinar, A.(3)
- Akpinar, Muhammet Vefa(3)
- Altuner, Elif Esra(3)
- Ayaydın, Hasan(3)
- Başoğlu, Mustafa Engin(3)
- Bilgic, Abdulbaki(3)
- Bozbeyoglu, Pinar(3)
- Coruh, Emine(3)
- Eraslan, Selim(3)
- Erol, Ismail(3)
- Kaygusuz, Abdullah(3)
- Kaygusuz, Kamil(3)
- Mete, Emrullah(3)
- Nizetic, S(3)
- Okkan, Umut(3)
Yayınlar
- BildiriYalnız künye2018Seasonal Variation of the Monthly Efficiencies of Thin Film PV Modules
Özden, Talat; Turan, Raşit; Akmoǧlu, Bülent Gültekin; Zaz, Y.; Essaaidi, M.
Outdoor testing of solar photovoltaic (PV) modules must be carried out at different climates as PV power plants nowadays are installed and continues to be installed in many countries. Present study is outdoor testing results and analyses of 5 thin film modules in Ankara, Turkey. The analyses are carried out using monthly efficiencies of the modules that are derived using the energy yield and input. The average efficiencies of the CIS, CIGS and μc-Si/a-Si thin film modules are. We present the monthly and average efficiencies and discuss their variations with the parameter: input, ambient temperature and relative humidity. We also carried out seasonal analyses using Pearson's correlation coefficient and find out that the efficiencies are differently dependent on the above mentioned parameters. This arose a new open question on differentiation of the strength of the effect of each parameter on the monthly efficiencies.
- BildiriAçık Erişim2018Determining photovoltaic module performance and comparisons
Karaveli, Abdullah Bugrahan; Ozden, Talat; Akinoglu, Bulent G.
Knowing electricity production potential of a photovoltaic (PV) system prior to installation is very beneficial for the investor to see the feasibility of the investment. There are three procedures that can be followed to calculate the potential electricity production of any system under different conditions. These are installation of sample systems and gathering data over time, the use of some databases/software programs to reach the performances and developing new model/methodology to make these estimations. It is obvious that installation of PV systems everywhere is neither technically nor economically conceivable. On the other hand, global software programs may not reflect local conditions to calculations. Consequently, there is a need to develop methodology that is able to derive location specific equations and coefficients and make accurate estimations. Its accuracy can be controlled by validating the results for some locations with the measured values from already installed PV power plants (PV PP). So, in this study we initially develop a methodology to calculate efficiency and electricity production performance of some modules for Ankara and compare the results with the measured values owing to the system installed on the roof of the Middle East Technical University Solar Energy Research Center (METU GUNAM) in Ankara/Turkey. The methodology initially calculates solar irradiation falling on the modules that is the input. Then the performance of the module is calculated by using developed methodology. There are also some online software programs to calculate the performances, such as EU PVGIS and PV WATTS. We analyzed and used these software programs and compare their results with the results of newly developed methodology. As proven through mean-bias error (MBE), root-mean-square error (RMSE) and mean absolute error (MAE) statistical comparison methods, the methodology of this study has given the most accurate results.
- BildiriAçık Erişim2018Impacts of a photovoltaic power plant for possible heat island effect
Demirezen, Emre; Ozden, Talat; Akinoglu, Bulent G.
Today, solar energy conversion technologies take a significant place within the efforts of obtaining renewable and sustainable energy around the world, and show a rapid progress. One of the most common technologies is photovoltaic power plants (PVPP) which are built using PV modules that provide electricity directly from sunlight. These plants are qualified as one of the pioneering applications among clean energy production methods. However, as the modules cover large areas and as they are produced by mostly dark-colored solar cells, an environmental debate has already been opened via some recent studies in the literature: Do they alter the solar reflectivity (albedo) of the region's surface where they are installed, and in turn affect the typical microclimate characteristics of that region such as the local air temperatures, humidity, pressure and wind speed? Considering also the additional heat that the modules radiate while producing electricity, the main probable result should be expected as Heat Island Effect (HIE). HIE has been particularly discussed for about last 10 years. Basically, this effect defines the day-night and inter-seasonal variations of local temperatures due to artificial changes on the natural land surface. Accordingly, when an urbanized area is compared with the neighboring rural areas, the difference is specifically named as Urban Heat Island (UHI) effect. In the present work, we are conducting a field research with in-situ measurements taken by the two weather monitoring stations inside and outside a PVPP in the district Tavsanli (Kutahya, Turkey). We also provide the meteorological data of Tavsanli station from Turkish State Meteorological Service (TSMS), which is the nearest weather monitoring station to the PVPP under inspection. These stations have been collecting the data of air temperature, relative humidity, average wind speed and atmospheric pressure every 10 minutes since October 2017. We used two statistical methods to compare and interpret the first 8-month data of all the three stations. We considered the statistical significance tests for both the first 8 months as a whole and dividing it into two 4 months before and after the PVPP becomes operational. We found that the measurements of the three stations differ significantly for most of the weather parameters. We also carried out pairwise tests and showed that each pair has significant differences for most parameters.
- BildiriAçık Erişim2017Effect of Ambient Conditions on Monthly Performances of Three Different PV Arrays
Özden, Talat; Akinoglu, Bulent G.; Turan, Rasit; Martinez, V; Gonzalez, J
Solar PV cells may be mainly divided into two parts as crystalline and thin film. Mono-crystalline silicon (e.g. Mono-Si) and microcrystalline based amorphous silicon and other thin films (e.g. gc-Si/a-Si and CdTe thin films) are widely used PV cells in the arrays. The outdoor performances of these systems depend on some climatic parameters and conditions, and it is important to understand how the monthly efficiencies vary with these parameters. In the present study, the data obtained from three grid connected PV arrays of Mono Si, a-Si/p.c-Si and CdTe thin film that were operated for 41 months in Ankara-Turkey is analyzed. The results showed that Mono-Si an-ay performance depends on the 5 parameters of outdoor climatic conditions while a-Si/gc-Si and CdTe thin film arrays performances arc not significantly affected by the variation of the climatic parameters. The possible reasons are discussed in details.
- BildiriYalnız künye2017Artificial intelligent models for thermodynamic properties of R152a and R134a refrigerants in automobile air conditioning systems
Kalkisim, Ahmet Tahir; Bilen, Kadir; Hasiloglu, Abdussamet; Sobh, T.; Elleithy, K.
With the increase in environmental awareness, the quest for alternative refrigerants for automobile air conditioning systemsis a necessity for the protection of the ozone layer and the prevention of global warming. Therefore, it is important that the refrigerant to be used as an alternative must be at least thermodynamically sufficient and within specified environmental limits. In this study, R152a refrigerant which is an alternative gas for R134a that's use in automobile air conditioning systems will be removed within a certain schedule has been examined thermodynamically. Artificial intelligent model was generated and compared by using data obtained from the examination. Through this model, system was tested with untrained data. The generated model has been very close to test data and successful in high precision.
- BildiriYalnız künye2017A day ahead hourly solar radiation forecasting by artificial neural networks: A case study for Trabzon province; [Yapay Sinir Aǧlari ile Gün Öncesi Saatlik Güneş Radyasyonu Tahmini: Trabzon İli Örneǧi]
Çevik, Sibel; Çakmak, Recep; Altaş, Ismail Hakki
The integration of renewable energy sources to the electrical grid leads to some issues in the grid because of intermittent and variable characteristics of renewable energy sources such as wind and solar. It has been predicted that the solar based electricity production will has highest annual increase rate among the other renewable sources. Due to the intermittent and volatile nature of the solar energy in an electricity grid where photovoltaic systems are intensive, load planning is essential. Therefore, day ahead solar radiation forecasting will contribute to the load planning studies. Artificial neural networks are one of the methods that are applied frequently and successfully in forecasting studies. In this study, a cause effect based artificial neural network (ANN) has been designed and performed for day ahead hourly solar radiation forecasting in Trabzon province. A similar day selection algorithm has been utilized to get more accurate forecasting by the ANN. The designed ANN has been trained and tested in MATLAB simulation environment without using ready codes of MATLAB ANN toolbox. The obtained results reveal that the designed ANN forecasts the solar radiation with acceptable error for a place such as Trabzon which has rainy and cloudy weather conditions.
- Kitap BölümüYalnız künye2017Green development: Case of Turkey, Norway, and China
Doğru, Bülent; Beken, Hikmet Gülçin
The focus of this chapter is to assess green or sustainable development concept because of its increased importance throughout the world. Droughts, environmental degradation, air pollution, greenhouse gas emissions are important problems that the humankind have been facing since the Industrial Revolution. Renewable energy sources can be used to overcome these problems. The general tendency of modern-day societies is to transform traditional production techniques and development models to new renewable energy sources and also move towards to sustainable development path. Therefore, this study tries to explain current status of Norway, China and Turkey in terms of their renewable energy sources and policy implementations.
- MakaleAçık Erişim2017Long term outdoor performances of three different on-grid PV arrays in central Anatolia – An extended analysis
Ozden, Talat; Akinoglu, Bulent G.; Turan, Rasit
Long term outdoor testing of the PV systems at different climatic conditions or different systems under the same ambient conditions are extremely important in producing policies for the transition to renewables. The present research is the testing of three different PV systems under the same climatic conditions of central Anatolia, after four years of operation. The systems consist of a mono-Si, an a-Si thin film and a CdTe thin film arrays. Different calculation procedures of the input solar irradiation on tilted surface are used for comparison. Performances together with degradation rates are computed using different procedures and also using the measured solar data of 20 km away from the installed systems. The accuracy is verified using 4 months of simultaneous measurements. The results showed that the aforementioned different input calculation procedures of the performances are important and determinant. The 44-months-average efficiencies of these three systems are calculated to be 11.86%, 6.40% and 5.30%, respectively. The degradation rates of these systems are obtained as 0.40%, 1.88% and 10.60%, respectively. Although the degradation rates that are calculated for the first two systems are quite similar to those appeared in the literature, CdTe system is considerably higher than those given in the literature.
- MakaleYalnız künye2016Therotical investigation of the effects of diesel fuel, biodiesel fuel and their blends on internal combsution engines
Sezer, Ismet
In this study; the effects of diesel fuel, the soybean oil methyl ester (SOME) biodiesel fuel and their blends at various percentages on the spray and combustion characteristics and engine performance and exhaust emissions of diesel engines investigated as theoretically. For this purpose, a model has been built for a direct injection diesel engine in a commercial vehicle by the Diesel-RK software program that can be used liberally on the net. The obtained values for diesel (D) and biodiesel (BD) fuels and D-BD fuel blends via the constructed model were compared. The results of the study show that BD fuel generally provides a close brake thermal efficiency values to diesel fuel. Additionally, BD fuel causes decrements in engine power and particulate matter (PM-soot) emission and increments in specific fuel consumption and nitric oxides (NOx) emission. On the other hand, D-BD fuel blends at various blend ratios have usually given the spray, combustion, performance, and emission values between those of diesel and biodiesel fuels.
- BildiriAçık Erişim2016The comparison of performance by using alternative refrigerant R152a in automobile climate system with different artificial neural network models
Kalkisim, A.T.; Hasiloglu, A.S.; Bilen, K.; Durak, R.; Tuzemen, S.
Due to the refrigerant gas R134a which is used in automobile air conditioning systems and has greater global warming impact will be phased out gradually, an alternative gas is being desired to be used without much change on existing air conditioning systems. It is aimed to obtain the easier solution for intermediate values on the performance by creating a Neural Network Model in case of using a fluid (R152a) in automobile air conditioning systems that has the thermodynamic properties close to each other and near-zero global warming impact. In this instance, a network structure giving the most accurate result has been established by identifying which model provides the best education with which network structure and makes the most accurate predictions in the light of the data obtained after five different ANN models was trained with three different network structures. During training of Artificial Neural Network, Quick Propagation, Quasi-Newton, Levenberg-Marquardt and Conjugate Gradient Descent Batch Back Propagation methodsincluding five inputs and one output were trained with various network structures. Over 1500 iterations have been evaluated and the most appropriate model was identified by determining minimum error rates. The accuracy of the determined ANN model was revealed by comparing with estimates made by the Multi-Regression method.
- Kitap BölümüYalnız künye2016Green development: Case of Turkey, Norway, and China
Doğru, Bülent; Beken, Hikmet Gülçin
The focus of this chapter is to assess green or sustainable development concept because of its increased importance throughout the world. Droughts, environmental degradation, air pollution, greenhouse gas emissions are important problems that the humankind have been facing since the Industrial Revolution. Renewable energy sources can be used to overcome these problems. The general tendency of modern-day societies is to transform traditional production techniques and development models to new renewable energy sources and also move towards to sustainable development path. Therefore, this study tries to explain current status of Norway, China and Turkey in terms of their renewable energy sources and policy implementations.
- MakaleYalnız künye2016Effect of seasonal changes on the combustion characteristics of impregnated cedar (Cedrus libani A. Rich.) wood
Fidan, M. Said; Yaşar, Ş. Şadiye; Yaşar, Mehmet; Atar, Musa; Alkan, Elif
Wood is an irreplaceable material used as decorative and structural element both indoors and outdoors. When used as a structural material, wood has several superior characteristics in comparison to other structural constituents, although it is adversely affected by fires as well as biotic pests and abiotic effects. In this study, cedar (Cedrus libani A. Rich.) wood samples were impregnated using either Tanalith-E or Wolmanit-CB as detailed in ASTM-D 1413-76 and surface-treated using water-based or synthetic varnish. The impregnated and varnished samples were left outdoors with the aim of investigating the effect of seasonal changes. The samples were later subjected to combustion analysis as detailed in the combustion test standard ASTM-E 160-50. The results of the study indicated that the weight loss was lower during winter (87.82%), for samples that were impregnated using Wolmanit-CB (88.90%) and those that were treated with synthetic varnish (88.45%). On the other hand the O2 and CO2 contents were determined to be the highest in fall during combustion without flame (18.16% and 17.96%, respectively); the CO content was the highest during combustion without flame for the winter samples (28,907 ppm) and the NO content was the highest during combustion without flame for the spring samples (76.15 ppm). In conclusion, the winter samples that were impregnated using Wolmanit-CB and treated with synthetic varnish were determined to be safer to employ in areas with high fire risk.
- MakaleAçık Erişim2015Outdoor efficiency analyses and comparison of on-grid CdTe and μc-Si/a-Si thin-film PV systems for three years in Ankara - Turkey
Ozden, Talat; Yardim, Ugur; Akinoglu, Bulent G.; Turan, Rasit; Turan, R; Gunes, M; Sariciftci, NS; Varlikli, C
The present paper is mainly a comparison of the performances of two PV systems under outdoor conditions in Ankara. The systems are grid connected and consist of two PV arrays. The types of these PV arrays are CdTe thin film and amorphous silicon/micro-crystalline-based (μc-Si/a-Si) arrays. They are operated for 3 years; 2012-2014. Yearly averages of monthly efficiencies of these two systems working under the same ambient conditions are 6.88%, 6.65%, 6.80% and 6.64%, 5.86%, 5.25% for μc-Si/a-Si and CdTe, respectively. Using these values, simple calculation results for the degradation rates per year are about 0.39%/year and 6.98%/year, respectively for these two types of systems.
- MakaleYalnız künye2015Organic maturity and hydrocarbon potential of liassic coals from the eastern Pontides, NE Turkey
Eker, C.S.; Sipahi, F.; Akpnar, I.
Organic matter content, type of organic material, and thermal maturity of Lias-aged coals of the Gumushane and Bayburt areas were investigated. The total organic carbon contents of coals in the Gumushane area range from 0.39-35.46 wt%, and in the Bayburt area range from 0.02-50.64 wt%. The Gumushane (except Güvercinlik field) and Bayburt areas coals have low hydrogen index values. The coal samples contain a mixture of Type II and Type III kerogens. Based on average Tmax values Liassic coals in the Gumushane and Bayburt (except Cerci field) areas are mature, and potential yields are low.
- MakaleYalnız künye2014Exergetic analysis of using the gaseous fuels in spark ignition engines
Sezer, Ismet; Bilgin, Atilla
This paper aims to investigate the use of alternative gaseous fuels in spark ignition engines via an exergy analysis. A quasi-dimensional two-zone thermodynamic cycle model is used for this purpose. The intake and exhaust processes are computed by a simple approximation method, and the processes (that is, compression, combustion, and expansion) are simulated in detail. The turbulent flame propagation process is used for the combustion simulation. The second law of thermodynamics is applied to the cycle model to perform the exergy analysis. The exergy transfers associated with heat, work, and exhaust; the irreversibilities, thermomechanical exergy, fuel chemical exergy, and total exergy have been computed in the exergy analysis. A distribution of the fuel exergy, the energy-based (the first law) efficiency, and the exergetic (the second law) efficiency were also calculated during the exergy analysis. Thus, the effects of using natural gas and liquefied petroleum gas on the exergetic terms and the efficiencies are investigated. The results of the study show that investigated alternative gaseous fuels have affected the variations in the exergy transfers, irreversibilities, and efficiencies. The gaseous fuels are suitable from the exergy point of view because of the lessened exergy destruction rate, but they suffer from the engine performance reduction.
- MakaleAçık Erişim2014Estimating aboveground biomass using landsat TM imagery: A case study of Anatolian Crimean pine forests in Turkey
Günlü, A.; Ercanli, İ.; Başkent, E.Z.; Çakır, G.
Forests play an important role in carbon circulation, and the productivity of forest ecosystems can be evaluated by evaluating its biomass. Evaluation of biomass aids the determination and understanding of changes in forest ecosystems. Because of the limitations of ground measurements of biomass, in recent times, satellite images have been broadly applied to estimate aboveground biomass (AGB). The objective of this study is to examine the relationships between AGB and individual band reflectance values and ten Vegetation Indices (VIs) obtained from a Landsat TM satellite image for a Anatolian pine forests in northwestern Turkey. Multiple regression analysis is utilized to predict the AGB. The AGB model using TM 1 and TM 2 had an adjusted R2of 0.465. Another AGB model using Enhanced Vegetation Index (EVI) and Normalized Difference 57 (ND57) had an adjusted R2 of 0.606. Our results reveal that VIs present better estimation of AGB in Anatolian pine forests as compared to individual band reflectance values.
- MakaleYalnız künye2014The performance of alternative refrigerant gas R152a as Mobile air conditioning refrigerant
Bilen, Kadir; Kalkisim, Ahmet T.; Solmus, Ismail; Yong, J.Y.; Liew, P.Y.; Klemes, J.J.; Varbanov, P.S.
In this study, the possible alternative replacement of R134a with R152 in the air conditioning (AC) system of an automobile has been investigated theoretically. The properties of the R152a is presented and compared with three different refrigerants (R134a, R22 and R12). At a constant condenser temperature, the effect of evaporator temperature (Te=-20 °C - 0 °C) and compressor speed (n = 600 - 2,000 rpm) on the cooling load, the condenser heat load, compressor work, the mass flow rate of refrigerant and performance coefficient of the AC system have been examined with the help of a commercial computer program for refrigerants investigated. It was found that R152a and R134a do not lead to any significant difference on the performance of the refrigeration system. This result shows that with small modifications on the AC systems of current automobiles commonly using R134a, R-152a can be used as an alternative refrigerant since their compression ratios are almost the same.
- MakaleYalnız künye2013Evaluation of wind energy potentiality at coastal locations along the north eastern coasts of Turkey
Akpinar, Adem
This study aims to determine and evaluate wind energy potentiality along coastal locations at the North Eastern of Turkey. For this purpose, the present study has statistically analysed wind power potentials and wind characteristics from six meteorological stations (Sinop, Samsun, Ordu, Giresun, Trabzon, and Hopa) along the North Eastern (NE) geo-political coastal region of Turkey using the hourly or 3-hourly wind speed data measured at 10 m height during 9 years. The diurnal, monthly, and seasonal mean wind speed and wind power density at all the stations are assessed to have remarkable variations. The annual and seasonal frequency distributions and dominant wind directions of the all locations are determined. It is observed that the monthly mean wind speed in this region ranges from 1.53 m/s to 4.06 m/s. The maximum annual mean wind power density was found to be 59.96 W/m2 at Sinop while the maximum annual mean wind energy density was obtained to be 525.25 kWh/m2/year at the same station. It is further shown that Sinop, Hopa, and Trabzon have the higher wind power potential than other locations and their potential are close to each other.
- MakaleYalnız künye2013Effects of charge properties on exergy balance in spark ignition engines
Sezer, Ismet; Bilgin, Atilla
This study investigates the effects of the air-fuel mixture (charge) properties on the exergy balance in spark ignition engines. A thermodynamic cycle model including compression, combustion and expansion processes is used. The principles of the second law are applied to the cycle model to perform an exergy analysis. Variation of the exergetic variables during the investigated portion of the cycle are examined as a function of the charge properties, i.e., fuel-air equivalence ratio, residual gas fraction and initial charge temperature. The results show that increasing fuel-air equivalence ratio causes an increase in irreversibilities and also exergy losses with heat transfer and exhaust gases, but enriching the air-fuel mixture beyond the stoichiometric ratio makes no significant contribution to the exergy transfer with work transfer. A slightly lean mixture also gives the best first and second law efficiencies. It is observed that there is a linear relation between the residual gas fraction and the exergetic variables. An increase in the residual gas fraction decreases the irreversibilities and exergy losses aside from the exergy transfer with work transfer. However, increasing the residual gas fraction positively affects the first and second law efficiencies because of the diluting of the charge. Increase of initial charge temperature creates a reduction in the irreversibilities and the exergy losses and, it also results in a lower exergy output by work transfer. Further, increase of initial charge temperature negatively influences the first and second law efficiencies.
- MakaleYalnız künye2013Assessment of wave energy resource of the Black Sea based on 15-year numerical hindcast data
Akpinar, Adem; Kömürcü, Murat I.hsan
In this study, the existence and variability of wave energy resource potential of the Black Sea based on 15-year hindcast data is described in detail. The hindcasts of wave parameters were carried out by using the third generation wave prediction model (Simulated WAves Nearshore - SWAN), which is one of the most popular numerical wave models and has been widely used for estimating ocean waves. The model was forced with the ECMWF ERA Interim wind fields and applied with a spatial resolution of about 0.0167°. ×. 0.0167° and a model time step of 6. h to resolve efficiently offshore and nearshore wave conditions. The results were presented in the form of charts of the spatial distribution of significant wave height and wave power, on a monthly, seasonal and annual basis. Annual energy was calculated in the study region with the hindcast data set covering 15. years (1995-2009). The areas with the highest wave energy resource were determined and the south west coasts of the Black Sea are suggested as the best site for the installation of a wave farm. It was determined the western parts of the Black Sea (especially the south-west) are exposed to energetic waves more than the eastern parts.
