Yazarlar
- Ozden, Talat(16)
- Akinoglu, Bulent G.(15)
- Sezer, İsmet(11)
- Basoglu, Mustafa Engin(9)
- Özden, Talat(8)
- Akpinar, Adem(7)
- Terhan, Meryem(7)
- Başoğlu, Mustafa Engin(6)
- Cakmak, Recep(6)
- Erol, Ismail(6)
- Peker, Iskender(6)
- Turan, Rasit(6)
- Akpinar, A.(5)
- Ar, Ilker Murat(5)
- Kömürcü, Murat Ihsan(5)
- Sezer, Ismet(5)
- Altas, Ismail H.(4)
- Altuner, Elif Esra(4)
- Benli, Tolga(4)
- Bozbeyoglu, Pinar(4)
- Kaygusuz, K.(4)
- Tunç, Merve Tuğçe(4)
- Akyol, Mehmet(3)
- Altan, Aytaç(3)
- Barut, Abdulkadir(3)
- Bilgin, Atilla(3)
- Genc, Omer(3)
- Kankal, Murat(3)
- Kaygusuz, Abdullah(3)
- Kaygusuz, Kamil(3)
- Ozden, T.(3)
- Pilatin, Abdulmuttalip(3)
- Saribiyik, Oguz Yunus(3)
- Searcy, Cory(3)
- Timurkutluk, Bora(3)
- Toros, Serkan(3)
- Turan, İsmet(3)
- Yanarates, Cagfer(3)
- Yanarateş, Cağfer(3)
- Çakmak, Recep(3)
Yayınlar
- MakaleYalnız künye2019Theoretical investigation on combustion characteristics of ethanol-fueled dual-plug SI engine
Altın, İsmail; Bilgin, Atilla; Sezer, İsmet
In this study, effects of equivalence ratio, spark timing and spark plug number and locations on combustion characteristics were theoretically investigated using an ethanol-fueled dual-plug SI engine. Two-zone quasi-dimensional model was used throughout analyses. Three spark plug configurations (diagonally, centrally and side located), three equivalence ratios (0.8, 0.9, and 1.0), and three spark timings (−30, −25, and −20 CA @ BTDC) were considered to analyze variation of total burn duration, mass fraction burned, cylinder pressure, and temperatures (exhaust and maximum burned gas). Variation of mass fraction burned and cylinder pressure were also investigated at lean mixture ratio and 2800 rpm (MBT engine speed). Lastly, the effect of engine speed on total burn duration, maximum cylinder pressure and aforementioned temperatures were investigated in the range of 1000–6000 rpm. The findings show that dual-plug configuration yields approximate combustion characteristics by comparison with centrally located single plug configuration in ethanol-fueled SI engine.
- BildiriYalnız künye2019Module Level Global Maximum Power Point Tracking Strategy
Basoglu, Mustafa Engin
Partial shading of photovoltaic (PV) modules can occur at any time due to the obstacles such as chimney, tree, antenna, bird flock etc. Due to such obstacles, the entire surface of the PV module cannot receive an equal amount of irradiance; Therefore, PV modules cannot operate at its maximum power point (MPP). In this paper, an improved version of a 0.8VOC model based global maximum power point tracking (GMPPT) strategy has been proposed. Single ended primary inductance converter (SEPIC) is used as a power converter between PV module and load. Effectiveness of the proposed technique is presented by experimental studies with the comparison of a full scanning approach. Results of experimental studies show that proposed GMPPT strategy outperforms than full scanning based algorithm known.
- MakaleYalnız künye2019Performance evaluation of ejector with different secondary flow directions and geometric properties for solid oxide fuel cell applications
Genc, Omer; Timurkutluk, Bora; Toros, Serkan
The mixing chamber length, secondary flow tube inclination angle, diffuser length and diverging angle as well as the direction of secondary flow on the ejector performance are numerically studied. The numerical results of 2560 different design points including the all combinations of the selected parameters indicate that the selected ejector geometric parameters have a great impact on the ejector performance. Within the parameter ranges considered, the best performance based on steam to carbon ratio and the entrainment is obtained from the ejector having a mixing chamber length of 30 mm, secondary flow tube inclination angle of 45°, diffuser length of 90 mm and diffuser diverging angle of 5°, regardless of the secondary flow direction. On the other hand, the parallel flow ejector, where the anode exhaust line flow direction is designed to be parallel to the primary flow direction, is found to exhibit slightly higher steam to carbon ratio and entrainment ratio compared to those of the counter flow ejector. Furthermore, it is seen that the parallel flow ejector can offer wider ranges of the ejector geometric parameters considered for a high performance whereas relatively rigid geometric parameters need to be selected for designing a counter flow ejector.
- MakaleYalnız künye2018CO2 emisyonu- enerji tüketimi ve ekonomik büyüme arasındaki nedensellik ilişkisi: G7 ülkeleri üzerine ekonometrik bir analiz
Polat, Melike Atay; Özkök, Canan Sancar
Günümüzde çevre kirliliğinin artan boyutlara ulaşması ve küresel ısınmanın olumsuz etkilerinin hafifletilmesi yönündeki çabalar CO2 salınımına neden olan enerji kaynaklarının kullanımı sorununu gündeme getirmiştir. Ekonomik büyüme ve daha ileriki bir aşama olan ekonomik kalkınma enerji kaynaklarının kullanımını hızlandırır. Bu süreç enerji rezervlerinin tükenmesi yanında CO2 emisyonu düzeyinde de artışa neden olur. Bu nedenle de CO2 emisyonunun azalması, enerji tasarrufu sağlanması ve ekonomik performansın ayarlanması açısından bu üç değişkenin optimal düzeyinin birlikte formüle edilmesi gerektirmektedir. Bu çalışmada, G7 ülkelerinde CO2 emisyonu, enerji tüketimi ve ekonomik büyüme arasında ilişki olup olmadığını araştırılmıştır. Bu amaçla, G7 ülkelerinin 1980-2011 dönemi verileri kullanılarak panel birim kök, panel eş bütünleşme ve panel nedensellik testleri kullanılmıştır. Birim kök testi sonuçlarına göre düzeyde durağan olmayan değişkenler uzun dönemde eş bütünleşiktir. Çalışmanın panel nedensellik testi sonuçları, G7 ülkelerinde CO2 emisyonu ile GSYH ve enerji tüketimi ile GSYH arasında çift yönlü nedensellik ilişkisi olduğunu göstermiştir. Bu çalışmanın sonuçları politika yapıcılar için G7 ülkelerinde enerji verimliliğindeki artışın teknolojik açıdan önceliklendirilmesini ve çevre dostu politikalarda ortak hareket planları uygulamalarını öncelikli kılmaktadır.
- Derleme MakaleAçık Erişim2018Nano materyal içerikli katkıların yakıt özelliklerine ve motor performansına etkileri
Sezer, İsmet
Bu çalışma; dizel, biyodizel, su içeren emülsiyon yakıtları ve çeşitli yakıt karışımları gibi dizel motor yakıtlarında nano materyal içerikli katkıların kullanılmasının motor performansı ve emisyonlara etkileri üzerine yapılmış çeşitli çalışmaların sonuçlarından derlenmiştir. Dizel motorlarda zararlı egzoz emisyonlarını azaltması için üç farklı teknik uygulanmaktadır. Zararlı emisyonları azaltmak için uygulanan tekniklerden ilki motor tasarımda ve yakıt püskürtme sisteminde değişiklikler yapılarak yanmanın iyileştirilmesidir. Ancak bu pahalı ve zaman alıcı bir süreçtir. İkinci teknik katalitik konvertör ve partikül filtresi gibi çeşitli egzoz gazı azaltıcı sistemler kullanmaktır. Ancak, bu sistemler dizel motorun performansını olumsuz yönde etkiler. Dizel motorlarda, emisyonları azaltmak ve aynı zamanda dizel motorun performansını artırmak için kullanılan üçüncü teknik ise çeşitli yakıt katkılarının kullanılmasıdır. Dizel motorlardan yayılan en önemli kirleticiler azot oksit (NOx) ve partikül madde (PMis) emisyonlarıdır. Uygulamada, NOx ve PM emisyonlarını birlikte azaltmak oldukça zordur. Emisyonları azaltmanın ve motor performansını artırmanın en iyi yolunun nano materyal içerikli katkıların ve suyla emülsiyonlaştırılmış yakıtların kullanımı olduğu birçok araştırmacı tarafından bildirilmektedir. Bu derlemede çeşitli dizel motor yakıtlarında farklı nano materyal içerikli katkıların kullanımının yakıt özellikleri ve motor performansına etkileri incelenmiştir.
- MakaleAçık Erişim2018Güneş Enerji Santralleri İçin Uygunluk Haritasının Elde Edilmesi: Bir Uygulama
Eroğlu, Hasan
Günümüzde güneş enerjisi, hayatımızın en önemli ve kaçınılmaz bir parçası haline gelen yenilenebilirenerji kaynaklarından (YEK) biridir. Her geçen gün dünya üzerindeki güneş enerji santrali (GES) sayısı katlanarakartmaktadır. Uygulama sayısı artan bu santrallerin çevresel, ekonomik ve sosyal açıdan en uygun yer tayinlerininyapılması oldukça büyük önem arz etmektedir. Bazı durumlarda santral kurulum yerini etkileyen bir önemli kriterinbile göz ardı edilmesi oldukça büyük zararlara neden olabilmektedir.Bu çalışmanın amacı, literatürdeki çalışmalarda eksikliği tespit edilen ve GES kurulumunu etkileyen kriterlerinönerilmesi, GES kurulumunu etkileyen tüm kriterlerin birbirlerine göre önem derecelendirme değerlerininbulunması ve kriterlere ait örnek bir çalışma alanında coğrafi veriler yardımıyla GES için uygunluk haritasının eldeedilmesidir. Kriterlerin ağırlık değerlerinin bulunmasında Bulanık Analitik Hiyerarşi Yöntemi (FAHP), verilerinişlenmesinde de coğrafi bilgi sistemleri kullanılmıştır. Bu amaçla 14 ana kriter ve bu kriterlere ait 70 alt kriterkonuyla ilgili uzman görüşleri, anketler ve literatürdeki çalışmalardan yararlanılarak belirlenmiştir. Çalışmanınsonunda, çalışma alanında GES’ler için en uygun, uygun ve izin verilmeyen yerlerin gösterildiği uygunluk haritasıelde edilmiştir. Bu çalışma, GES’lerin yer tespitinde daha doğru, çevresel, ekonomik ve sosyal GES santralikurulumunu netice veren geniş yelpazedeki kriterlerle araştırmacılara faydalı olacaktır.
- MakaleAçık Erişim2018Nano materyal içerikli katkıların yakıt özelliklerine ve egzoz emisyonlarına etkileri
Sezer, İsmet
Bu çalışma; dizel, biyodizel, su veya alkol içeren emülsiyon yakıtları ve çeşitli yakıt karışımları gibidizel motor yakıtlarında nano materyal içerikli katkıların kullanılmasının yakıt özellikleri, motorperformansı ve egzoz emisyonlarına etkileri üzerine yapılmış çalışmaların sonuçlarından derlenmiştir.Dizel motorlar iyi performans ve güvenilirlik karakteristiklerine sahip olmasına rağmen dizelmotorlardan yayılan egzoz gazları içinde yarı yanmış veya yanmamış hidrokarbonlar, karbondioksit,karbonmonoksit, partikül madde (is) ve azot oksitler gibi zararlı emisyonlar bulunur. Dizel motorlardazararlı egzoz emisyonlarının azaltılması için üç farklı teknik uygulanmaktadır. Zaralı emisyonlarıazaltmak için uygulanan tekniklerden ilki motor tasarımda ve yakıt püskürtme sisteminde değişiklikleryapılarak yanmanın iyileştirilmesidir. Ancak bu pahalı ve zaman alıcı bir süreçtir. Emisyonları azaltmakiçin uygulanan ikinci teknik katalitik konvertör ve partikül filtresi gibi çeşitli egzoz gazı cihazlarınınkullanılmasıdır. Ancak, bu cihazlar dizel motorların performansını olumsuz yönde etkilemektedir. Dizelmotorlarda, emisyonları azaltmak ve aynı zamanda motorun performansını artırmak için kullanılanüçüncü teknik ise çeşitli yakıt katkılarının kullanılmasıdır. Dizel motorlardan yayılan en önemlikirleticiler azot oksitler (NOx) ve partikül madde (PMis) emisyonlarıdır. Uygulamada, NOx ve PMemisyonlarını birlikte azaltmak oldukça zordur. Emisyonları azaltırken motor performansını artırmanınen iyi yolunun nano materyal içerikli katkıların ve su veya alkol ile emülsiyonlaştırılmış yakıtlarınkullanımı olduğu birçok araştırmacı tarafından bildirilmektedir. Bu derleme çalışmasında çeşitli dizelmotor yakıtlarında farklı nano materyal içerikli katkıların kullanımının yakıt özelliklerine ve egzozemisyonlarına etkileri literatüre dayalı olarak incelenmiştir. Bu şekilde, nano metaryal içerikli katkılarınetkilerinin bir arada değerlendirilmesi amaçlanmıştır.
- MakaleYalnız künye2018Hybrid global maximum power point tracking approach for photovoltaic power optimisers
Basoglu, Mustafa Engin; Çakir, Bekir
A new hybrid global maximum power point (MPP) tracking (MPPT) method is introduced in this study by using an improved 0.8 VOC model-based algorithm containing a smart power scanning procedure which is based on the sign of a change of photovoltaic (PV) module power. By courtesy of this procedure, the global MPP is determined effectively and within a small scanning time interval. The effectiveness of the proposed global MPPT algorithm has been validated by experimental studies. One of the buck-boost converter types, a single-ended primary inductance converter was implemented in this context. Experimental results show that tracking efficiency in the proposed algorithm is very satisfactory since blind scanning is prevented. Furthermore, it is presented in the experimental results that tracking efficiency is bigger in the proposed shading detection approach by up to 11.29% than the other technique which monitors voltage and current variations. In addition, there are no high software and hardware burdens which make this MPPT algorithm applicable especially in the smart alternating current module, module-integrated converters, PV power optimisers, and module level distributed MPPT applications.
- DüzeltmeYalnız künye2018Retraction notice to “Regional sustainable water and energy development projects: A case of Southeastern Anatolia Project (GAP) in Turkey” (Renew Sustain Energy Rev (2011) (16/2) (1146–1156)(S136403211100551X)(10.1016/j.rser.2011.11.015))
Akpinar, A.; Kaygusuz, K.
This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. The authors have plagiarized part of a paper that had already appeared in Renewable Energy, Volume 39 (2012), Pages 17–23, DOI: 10.1016/j.renene.2011.08.006. Although the authors were contacted for a reaction, we were unsuccessful in obtaining a response. One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.
- BildiriAçık Erişim2018Thermal modeling and verification of pv module temperature and energy yield using outdoor measurements for Ankara, Turkey
Tuncel, Bilge; Akinoglu, Bulent G.; Ozden, Talat; Balog, Robert S.
Ankara is in the Central Anatolia region of Turkey where the climate is dry-continental with an annual solar insolation of around 1750 kWh/m 2 . In the transition to renewable energy, detailed analyses are required to ensure effective and economic utilization of the available solar resource. An essential part of these analyses is to calculate expected energy yield. For photovoltaic (PV) systems, this includes the effect of temperature on the PV efficiency, which determines the power yield of the PV modules. In this study, a first-principles thermal modeling approach is improved by adding the speed and direction of wind across the PV module into a forced convection term as well as including the temperature dependency of the module conversion efficiency. The analytical model is based on the principle of conservation of energy and uses meteorological data that are readily available from most state meteorological services. The mathematical analysis is suitable to predict the performance of a proposed PV installation without the time and expense of installing and monitoring a pilot system. The mathematical model is compared against measured data from the METU-GUNAM Outdoor Test Facility in Ankara to validate the methodology. Preliminary analyses showed that the model performs well especially during sunrise and sunsets shoulders of the diurnal cycle with a deviation of only a few W/m 2 for the electrical power yield and about 2°C for the module temperature. However, these deviations could become as large as 12 W/m 2 and 8°C at solar noon which suggests that the model still requires further improvement. In general, this error was found to be less that obtained by using basic explicit correlation methods and offers the advantage that it can be used for other geographical environments for which insolation and meteorological data is available without needing to construct a test-site.
- BildiriAçık Erişim2018Performance and degradation analyses of two different pv modules in central anatolia
Ozden, Talat; Akinoglu, Bulent G.; Kurtz, Sarah
Ankara (latitude: around 40°N) is in Central Anatolia and the climate is dry continental. Due to the rapid transition to renewable energy policies of Turkey it is now a must to complete truthful feasibility analyses for solar power systems countrywide. Long term performance and degradation analyses have been carried out by the authors for three different arrays and many research results appearing in the literature are summarized. Present research analyzes the outdoor testing results of two PV modules monthly data. One of the modules has multi crystalline silicon (Poly-Si) cells and the other is thin film silicon (amorphous Si / microcrystalline Si tandem structure - a-Si/μc-Si) cells. The results showed that in five years the average yearly efficiency decreases from 14% to 11% for Poly-Si (14.72% is the nameplate Standard Test Condition (STC) efficiency) and from 8% to 6% for thin film modules (9.15% is STC efficiency). Our calculations are based on measured solar global-horizontal irradiance from which we calculated plane-of-array irradiation using an anisotropic sky model. We present the details of these analyses and degradation rates for the two types of modules to be used in long term feasibility analyses.
- BildiriAçık Erişim2018Daily and monthly module temperature variation for 9 different modules
Özden, Talat; Tolgay, Doga; Akinoglu, Bulent G.
One of the main parameter affecting the efficiency of PV modules is the module temperature. In this respect, outdoor testing of modules is very important to determine the temperature dependent performances and degradation rates. In this work, we analyzed the module temperatures of 9 different modules tested in the outdoor testing facility of METU-GUNAM, Ankara (latitude ∼40°N, in Central Anatolia and the climate is dry continental). The tested module types are two CIS (identical), one μc-Si/a-Si, one Poly-Si, three Mono-Si (two identical), one HIT and one bifacial. The module temperatures can reach up to 76°C while the ambient is around 39 °C during summer days. Monthly average module temperatures can reach up to 33.7°C (CIS) while the monthly average ambient is at 26.0°C and drops down to 1 °C while average ambient temperature is about the same as average module temperature. The results showed that the monthly averages of module temperatures differences are maximum during summer (∼3.5°C) and minimum during winter (1.1°C). It is interesting that the two CIS modules have the highest monthly average module temperature and although they are supposed to be identical their temperatures differ significantly. Bifacial and HIT module temperatures are lower than the Mono-Si modules. One of the two identical Mono-Si modules was not cleaned and its module temperature is always lower than the one that was cleaned periodically, as expected. In this work, we also present the results and discussions on the spatial variations of measured module temperatures of PV panels.
- BildiriYalnız künye2018Optimal scheduling of time shiftable loads in a task scheduling based demand response program by symbiotic organisms search algorithm
Cakmak, R.; Altas, I.H.
Demand side management is one of the key issues in smart electrical grid studies. Power demand of consumers can be managed via demand response(DR) programs. Task scheduling (TS) based demand response is one of the DR schemes. Objective of the TS approach is to schedule activation time of the appropriate time-shiftable loads to reduce power consumption in peak-demand hours. Heuristic optimization methods can be used to provide this objective. Symbiotic Organisms Search (SOS) and Cuckoo Search (CS) algorithms are two of the most recent heuristic methods. In this paper, scheduling of the time-shiftable home appliances executed by SOS and CS algorithms. Time-shiftable home appliances of the consumers and run time tolerances of them aggregated by mini public survey to achieve results which close to reality. Obtained results are indicated the superiority of the SOS algorithm and demonstrated the positive effects of the demand side management on the electrical grid.
- BildiriYalnız künye2018On the Yearly Performance of a Bifacial PV Module in Central Anatolia - Turkey
Özden, Talat; Turan, Raşit; Aklnoǧlu, Bülent Gültekin; Zaz, Y.; Essaaidi, M.
With the tremendous increase in the photovoltaic (PV) power plants world-wide remarkable decreases in their installation prices per watt are attained mainly due to economic scale effect. This brings questioning to increase their energy yields by considering any possible way like fabricating bifacial solar modules. Present study is on the performance analysis of a bifacial PV module using one-year outdoor testing results in Ankara-Turkey. The module performed very well and reached a specific yield value of 1750 kWh/kWp. This value for Central Anatolia region is well above the values predicted (and suggested) by the local authorities. The efficiency and performance ratio variation with respect to ambient and module temperature are obtained. The calculated dependence of efficiency on the module temperature is found to be η=-0.073Tmod+18.05, and the maximum measured module temperature is about 70 °C. The results show that the bifacial modules have the potential to replace the mono facial modules that are now dominating the PV market.
- MakaleAçık Erişim2018Energy concept understanding of high school students: A cross-grade study
Takaoğlu, Zeynep Başkan
Energy is a difficult concept to be understood by students of all levels. Thus, the aim of the study is to determine how high school students at different levels perceive the energy and related concepts. In line with this purpose, 173 students in total of which 57 ones of the 9th grade, 94 ones of the 10th grade and 22 ones of the 11th grade participated in the study in which developmental research method of descriptive research design has been conducted. Four open-ended questions about energy and related concepts have been asked to the students in the study. As a result of the study, it is concluded that the students use energy instead of work, power, repulsion and pulling concepts and they consider energy as a feature specific to living creatures and moving situations. The potential and kinetic energy types are most expressed ones. The students frequently give examples from renewable and non-renewable energy types and they classify them accordingly. It is also concluded that they don’t have enough information about conservation of energy. It is thought that this misconception among the students emerges because energy and related concepts are taught them disconnected in different lessons of different disciplines and they do not understand preconceptions about energy and related notions. It is considered that the concept networks, concept maps, and conceptual change texts will help to relate energy concepts in students' minds.
- MakaleYalnız künye2018Geometric optimization of an ejector for a 4 kW SOFC system with anode off-gas recycle
Genc, Omer; Toros, Serkan; Timurkutluk, Bora
One of the important energy saving tools used in solid oxide fuel cell (SOFC) system is the anode off-gas recycling (AGR) via an ejector which allows the recirculation of the unused fuels in the anode exhaust gas including hot steam which is essential for the elimination of the carbon deposition and the initiation of the reactions in the reformer. In an ejector system developed for the SOFCs, the steam to carbon ratio (STCR) and entrainment ratio are the crucial parameters for the determination of the ejector performance. These parameters can be engineered by modifying the geometric dimensions and operation conditions. This study focuses on the determination of the maximum STCR value and entrainment ratio via numerical geometric analyses for a micro combined heat and power (μ-CHP) system based on 4 kW SOFC, utilizing methane. A detailed numerical procedure for designing an ejector is provided and the ejector performance is investigated for different critical dimensions (throat diameter, nozzle exit angle and nozzle position etc.). The results show that the nozzle position and the nozzle exit angle significantly affect STCR and the entrainment ratio. When the nozzle position increases and nozzle exit angle decreases, the entrainment ratio and STCR is found to increase. The entrainment ratio and STCR are determined as around 7.3 and 2.7, respectively for a specific design created in the study.
- 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.
- MakaleYalnız künye2018Constructal Placement of Discrete Heat Sources with Different Lengths in Vertical Ducts under Natural and Mixed Convection
Sarper, Bugra; Saglam, Mehmet; Aydin, Orhan
In this study, convective heat transfer in a discretely heated parallel-plate vertical channel which simulates an IC package is investigated experimentally and numerically. Both natural and mixed convection cases are considered. The primary focus of the study is on determining optimum relative lengths of the heat sources in order to reduce the hot spot temperature and to maximize heat transfer from the sources to air. Various values of the length ratio and the modified Grashof number (for the natural convection case)/the Richardson number (for the mixed convection case) are examined. Conductive and radiative heat transfer is included in the analysis while air is used as the working fluid. Surface temperatures of the heat sources and the channel walls are measured in the experimental study. The numerical studies are performed using a commercial CFD code, ANSYS FLUENT. The variations of surface temperature, hot spot temperature, Nusselt number, and global conductance of the system are obtained for varying values of the working parameters. From the experimental studies, it is showed that the use of identical heat sources reduces the overall cooling performance both in natural and mixed convection. However, relatively decreasing heat sources lengths provides better cooling performance.
