• Energy Research

Optimal torque (OT) control is a widely used method for maximum power point tracking (MPPT) due to its simplicity. In order to overcome the adverse impacts of turbulent wind speed variations on MPPT, in several methods, modification factors have been proposed to dynamically modify the ideal power curve for OT control. However, this paper finds that the update cycles used in existing methods to adjust power curve modification factors are very long and hence these factors are difficult to be updated in a timely manner along with the wind speed variations. This thereby may deteriorate the effectiveness of wind energy extraction. Therefore, an optimal decreased torque gain (DTG) control method is proposed in this paper. Based on the persistence method, an offline mapping from the wind speed and rotor speed to optimal modification factors is established via optimal control theory. The power curve can be periodically modified online through the mapping relationship. In this method, the update cycles for these power curve modification factors are shortened from tens of minutes to seconds. The simulations and experiments show that the proposed method is more efficient than others in terms of energy extraction under varying wind speeds, especially for turbulent wind cases.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009 ; Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2009 ; Bu çalışmada, binalarda soğutma enerjisini azaltmak için alınabilecek önlemlerden biri olan bina cephesinde güneş kontrolü konusu ele alınmış ve günümüzde geniş bir çeşitliliğe sahip olan gölgeleme araç türleri incelenmiştir. Bunun yanısıra güneş kontrol elemanı seçim kriterleri ele alınmış, bu gereçlerin avantajları ve dezavantajları ortaya konulmuştur. Çalışmanın uygulama kısmında ise, bir örnek çalışma binası ele alınmıştır. Binanın bir cephesinde gölgeleme araçlarının enerji performans değerlendirmesi için bilgisayar tabanlı enerji simulasyon programlarından biri olan Energy Plus tabanlı, ‘DesignBuilder’ programı kullanılmıştır. Bina önce gölgeleme olmaksızın sonra mevcut haliyle simule edilmiş, ardından cephede değişik gölgeleme alternatifleri incelenmiştir. Bunun için farklı gereç türleri ve fiziksel özellikleri, konumlarının yanısıra kontrol tipleri gibi parametreler değiştirilerek her durumda sağlanabilecek maksimum enerji tasarrufu potansiyeli irdelenmiştir. Bulunan sonuçlar binanın gölgeleme olmaksızın haliyle ve birbirleriyle karşılaştırılmıştır. Aynı bina, mevcut gölgeleme araçlarının yararlılık oranını iki farklı iklimde karşılaştırabilmek için Türkiye’nin Antalya şehri koşullarında da incelenmiş ve bulunan sonuçlar birbiriyle kıyaslanmıştır. Çalışmada bu bina için en iyi olacak çözüme ulaşmaya çalışılırken aynı zamanda belli koşullara göre gölgeleme araçlarının tasarım kriterleri de analiz edilmeye çalışılmıştır. ; In this work, subject of solar control in building facades is dealed as one of the techniques for reducing cooling energy demand in buildings and shading device types are examined which have a wide range at present time. Shading device selection criteria are analysed and advantages and disadvantages of shading device types are indicated. In the application part of this work, a case study building is examined. For ...

The aspect of dust accumulation on the surface of photovoltaic (PV) modules should be thoroughly understood in order to minimize possible obstacles affecting energy generation. Several elements affect the amount of pollutant gathered on the surface of a solar device, mainly its localization, which is irreversibly linked to factors such as annual rainfall, occasional snow coverage, or, in a dry climate, increased blow of dust during sandstorms and higher concentration of soil particles in desert areas. Other than weather conditions in the region, PV installation type also plays an important role as a more horizontal position is favorable for the accumulation of soil. The research carried out and presented in this paper was done for dust accumulated naturally on PV modules kept in outdoor conditions and dust artificially sieved onto the front glass cover of modules. The experiment performed by the authors, including artificially deposited dust, defined the linear relationship between surface dust density of different types of contaminants and efficiency decline up to 10% for two different PV modules. The additional field study carried out in external conditions for a coastal region in Northern Poland concluded that, after one year, exposition photovoltaic conversion efficiency can be over 10% lower, with a slight performance improvement for the autumn season characterized by heavy rainfall.

Single-crystal Ni-rich layered oxide materials LiNi1−x−yCoxMnyO2 (NCM, 1 – x − y ≥ 0.6) are emerging as promising cathode materials that do not show intergranular cracks as a result of the lack of grain boundaries and anisotropy of the bulk structure, enabling extended cyclability in lithium-ion batteries (LIBs) operating at high voltage. However, SC-NCM materials still suffer from capacity fading upon extended cycling. This degradation of capacity can be attributed to a reconstruction of the surface. A phase transformation from layered structures to disordered spinel/rock-salt structures was found to be responsible for impedance growth and capacity loss. Film-forming additives are a straightforward approach for the mitigation of surface reconstruction via the formation of a robust protection layer at the cathode’s surface. In this work, we investigate various additives on the electrochemical performance of single-crystal LiNi0.83Co0.11Mn0.06O2 (SC-NCM83). The results demonstrate that the use of 1% lithium difluoroxalate borate (LiDFOB) and 1% lithium difluorophosphate (LiPO2F2) additives substantially enhanced the cycling performance (with a capacity retention of 93.6% after 150 cycles) and rate capability in comparison to the baseline electrolyte (72.7%) as well as electrolytes using 1% LiDFOB (90.5%) or 1% LiPO2F2 (88.3%) individually. The superior cycling stability of the cell using the combination of both additives was attributed to the formation of a conformal cathode/electrolyte interface (CEI) layer, resulting in a stabilized bulk structure and decreased impedance upon long-term cycling, as evidenced via a combination of state-of-the-art analytical techniques.

To reduce the condensation pressure of the refrigerant in the summer, refrigeration system has been developed, in which, during periods of high air temperature, the heat of condensation is removed to the coolant, which was pre-cooled at night due to radiative cooling. A methodology has been developed for determining the main characteristics of the elements of the proposed system and calculating its daily energy consumption. The calculation shows that the proposed system with a nominal refrigerating capacity of 10 kW, using the R404a refrigerant, allows in the climate of the city of Shymkent to reduce the condensation temperature to +32.9°C, and daily energy consumption by 6.5% compared to an ordinary vapor compression refrigeration machine.

In this thesis the galactic cosmic ray spectrum during Forbush decreases was studied by using daily cosmic ray data of the neutron monitor stations obtained from the High resolution neutron monitor database (NMDB). Following the method of the coupling coefficients as considered by Wawrzynczak and Alania (2010), the cosmic ray intensity in the heliosphere and the spectral index were calculated for different Forbush decreases. Also the solar, interplanetary and geomagnetic activity which associated by the selected episode of Forbush decreases were studied analytically. In this work according to Wawrzynczak and Alania (2010) the daily galactic cosmic ray intensity in the heliosphere during the Forbush decreases was calculated for various values of spectral index (γ) in a particular range (0.5-2 with step 0.01) by using the program of Matlab. Αn acceptable γ has to be corresponded to the values of the cosmic ray intensity in the heliosphere that are almost the same for all neutron monitors due to the fact that they are independent of topical characteristics. For the calculations of spectral index three different coupling functions were applied in order to find out the most appropriate coupling function for the calculation of the cosmic ray spectrum. Firstly the total function of Clem and Dorman (2000), secondly the function of Belov and Struminsky (1997) including a separate term E^3.17 extending the first for low kinetic energies to the neutron monitors with rigidity between 1GV < Rc< 2.78 GV, were found to be suitable for the study of Forbush decreases. Finally, the recently established yield function of Mishev et al. (2013) was applied first time for Forbush decreases. The results and the calculations of this thesis for the cosmic ray energy spectrum are very important for Space Weather applications. ; Στην παρούσα διατριβή μελετήθηκε το ενεργειακό φάσμα της γαλαξιακής κοσμικής ακτινοβολίας κατά την διάρκεια μειώσεων Forbush χρησιμοποιώντας δεδομένα από την Υψηλής Ανάλυσης Βάση Μετρητών Νετρονίων (NMDB). ...

Abstract District heating systems are widely used to supply heat to different groups of heat consumers. The district heating system offers great opportunities for combined heat and power production. In this paper decreasing district heating supply temperature is analysed in the context of combined heat and power plant operation. A mathematical model of a CHP plant is developed using both empirical and theoretical equations. The model is used for analysis of modified CHP plant operation modes with reduced district heating supply temperature. Conclusions on the benefits of new operation modes are introduced.

AbstractAccording to the industry ecology theory, in the simulating flowing way between substance and energy in the nature ecology, to design the industrial production systems can use less resource reasonably and reduce emissions. As the most important large iron & steel enterprise in Inner Mongolia, applying the theory of industrial ecology, the Baogang Group gains great achievement in energy saving and emission reduction in recent years. Based on the industrial ecology theory, this paper mainly analyzes the practice of energy-saving and ejection-decreasing of the BaoGang Group.