Vanadyum Redoks Akışkan Akü Enerji Depolama Sistemli Bir Rüzgar Tarlası İçin Enerji Üretim Ve Depolama Analizi

Abstract

Rüzgar hızındaki anlık, kısa ve uzun periyotlu değişimler, rüzgar enerji sistemlerinin güç ve gerilim çıktılarında önemli dalgalanmalara sebep olur. Bu dalgalanmalar, yerel şebeke ile uyumlu gerilim ve frekansta güç kalitesinin, enerji planlanmasında arz - talep güç dengesinin ve güç akış kontrolünün sağlanması bakımından zorluklar yaratır. Dengeleme ve Uzlaştırma Yönetmeliği'ne göre, rüzgar enerjisine dayalı üretim tesisleri gün öncesinde saatlik üretim tahmini yapmak ve dengesizliğe düşmemek üzere tahminlerinde isabetli olmak durumundadırlar. Rüzgar enerji santrallerinde elektrik üretimi, konvansiyonel santral üretimleri gibi programlanabilen bir yapıya sahip olmadığından, bu üreticilerin gün öncesi üretim tahminlerinde sıkça dengesizliğe düşülmektedir. Eksik ya da fazla tahminlerin yol açtığı dengesizlik, üreticiye ek maliyet getirebilmektedir. Güç üretim sistemlerinde rüzgar enerjisi kullanımının, sistem ve piyasa işletiminde verimlilik ve güvenilirlik üzerinde yarattığı bu sorunların çözümüne ihtiyaç vardır. Enerji depolama sistemleri rüzgar enerji santralleriyle birlikte kullanıldığında şebekeye sürekli, sabit ve kararlı güç üretimi sağlanacak ve rüzgardan elde edilen elektrik enerjisinin talep enerjiden yüksek olduğu dönemlerde fazla enerji depolanarak, talep gücün arttığı dönemlerde kullanılabilecektir. Piyasa koşullarında maliyetlerin uygun olması durumunda, yüksek kapasiteli bölgesel depolama sistemlerinin kullanımının piyasa işletimine önemli katkı yapabileceği düşünülmektedir. Elektrik enerjisi, kullanılacağı uygulamaya (güç veya enerji uygulamaları) bağlı olarak elektriksel, kimyasal, mekanik ve ısıl yollarla depolanabilmektedir. Bu çalışmada, rüzgar enerji santrallerinde üretilen elektrik enerjisinin depolanmasında; büyük miktarda enerjiyi uzun süre depolayabilmeleri, kendiliğinden deşarj sürelerinin uzun olması ve ihtiyaca hızlı yanıt verebilme özelliklerinden dolayı, kimyasal yolla enerji depolama yöntemlerinden biri olan vanadyum redoks akışkan aküler (VRB) ele alınmıştır. Bu tez çalışmasında, tasarlanan bir rüzgar tarlasının vanadyum redoks akışkan akü enerji depolama sistemleriyle desteklenmesi durumu için enerji analizleri yapılmıştır. Bu analizler için seçilen bir bölgede yapılan ölçümlerden edinilen iki yıllık rüzgar verisi ve bölgenin topografik haritası, bir rüzgar atlası analiz ve uygulama programı olan WAsP®'ta işlenerek farklı rüzgar çiftliği konfigürasyonları denenmiş ve en yüksek enerji üretim tahmini sonucunu veren konfigürasyon, VRB enerji depolama sistemi uygulamasında kullanılmak üzere seçilmiştir. Enerji analizi için tasarlanan rüzgar tarlasında, biri 1,8 MW diğeri 3 MW olmak üzere iki adet türbin kullanılmıştır. Her iki model türbinin rüzgar tarlasında birer ve ikişer adet kullanılmasıyla ve iki türbinin birlikte kullanılmasıyla oluşturulan VRB enerji depolamalı ve enerji depolamasız, jeneratörlü ve jeneratörsüz, şebekeden bağımsız sistemler için enerji üretim - depolama hesapları ve analizleri yapılmıştır. Bu analizler için 14 farklı sistem oluşturulmuş ve Matlab® ortamında yazılan programlarla elde edilen analiz sonuçları karşılaştırılmıştır. Analiz sonuçları, VRB'lerin rüzgar enerji sistemlerinde enerji depolama sistemi olarak kullanılmasının, düşük çevrim verimleri nedeniyle henüz uygulanabilir olmadığını göstermiştir. Çevrim verimlerinin artması ve/veya akü maliyetlerinin piyasa koşullarında tercih edilecek şekilde düşmesi durumunda VRB'ler, sağladıkları avantajlar sayesinde şebekeden bağımsız rüzgar sistemleri için uygulanabilir duruma gelecek ve yaygınlaşacaktır.

Electrical power systems must provide consumer?s power demand securing grid frequency and grid voltage. However, since wind is an intermittent resource of power, short term and long term changes in the wind speed cause variations in the power and voltage outputs of wind energy conversion systems. These variations lead to difficulties in providing power quality that has consistent frequency and voltage with the local grid and providing power balance between demand and generation for energy planning. Imbalance between power demand and generation at a node in the system lead to changes in grid frequency that can affect the frequency at other points of the grid. Frequency control systems are needed to detect these changes and to bring grid frequency to its nominal value (50 Hz for Europe and Turkey). When grid frequency is below its nominal value, power generation must be increased and when it is above the nominal value, power generation must be limited. Also, variations in the power generated by wind energy conversion systems can cause reactive power generation creating phase difference between alternating current and voltage and accordingly power loss in the system. Power quality can decrease due to flicker (changes in the voltage amplitude) and harmonic (distortions in the sinusoidal structures of current and voltage) effects. Moreover, due to the liberalization of the electricity system, the market itself is responsible for matching supply and demand. The electricity supply has to be controlled to be very close to demand. According to the Balancing and Reconciliation Regulation of Turkey, wind producers have to predict their hourly energy productions for the next day and they must be accurate in their predictions to provide the balance. Since power generation in wind farms is not programmable as in conventional power plants, low or high predictions cause imbalance very often and the wind producers have to meet the imbalance costs. The use of wind power in electrical power systems reduces the efficiency and reliability of the system and market operations. Hence, these problems need to be solved. Energy storage is one of the technologies that can support wind energy integration. If energy storage systems are used together with the wind energy conversion systems, power can be provided steadily to the grid or to the load. Also, energy can be stored when the electrical energy, which is converted from the wind power, is higher than the energy demand and can be used when the energy demand increases. Likewise, it can be stored when electricity is cheaper and can be used when electricity is more expensive. In case the costs are acceptable in the market conditions, high capacity storage systems can contribute the market operation. Electrical energy can be stored using electrical, chemical, mechanical and thermal methods considering the application that the system will be used for. For power applications, technologies which can supply high power in a short time and for energy applications, technologies which can supply high amount of energy for hours or days of discharge period are used. To store electricity generated by wind energy conversion systems, technologies which are suitable for both applications are preferred. In this thesis, vanadium redox flow batteries (one of the chemical methods of energy storage) were discussed to store electrical energy produced by wind farms, because of their capacity to store high amounts of energy during long time periods, low self-discharge and fast response characteristics. In this thesis, a wind farm was designed using the Wind Atlas Analysis and Application Program (WAsP®) and energy analysis of this wind farm was achieved in case of the support with a vanadium redox flow battery energy storage system. For this analysis, wind speed and direction data collected from a measurement mast at a site and digitalized topographical map of the region were processed in WAsP® and three different wind farm configurations were tested using different wind turbine power curves. The wind farm configuration that gives the highest energy production estimation was chosen for the application of VRB energy storage system. For the analysis, 14 different systems were presented in 5 groups, energy production and storage calculations of these systems were done and graphed by written programs in Matlab® environment and results of the analyses were compared with each other. Systems in the first group (system 1-4) are standalone systems with VRB; systems in the second group (system 5-8) are standalone systems with VRB and generator; in the third group (system 9-10), there are standalone systems without VRB and generator; in the fourth group (system 11-12), there are standalone systems without VRB and with generator and in the last group (system 13-14), there are systems connected to the grid without VRB and generator. Systems in the same group differ from each other in terms of the capacities of the batteries and the energy consumptions. In the 4.8 MW wind farm that was designed for energy analysis, two wind turbines with 1.8 MW and 3 MW rated powers were used. Calculations for each system were done using both of the turbines ( for 4.8 MW wind farm), using only one model of the wind turbines (for 1.8 MW and 3MW wind farms) and two of each model of the turbines (for 3.6 MW and 6 MW wind farms). For standalone systems; net energies (difference between the amount of energy produced and the energy consumed), time periods where the net energy is not enough to meet the demand, where the battery is full and where the generator is working were calculated and compared to each other. Also, for the system connected to the grid, total energy taken from and given to the grid and total time periods where the energy was taken from and given to the grid were calculated for comparison with standalone systems. In these calculations, charge and discharge efficiencies were taken into consideration and the round-trip efficiency of the VRB system was taken as 72%. Results of the analyses can be summarized as the following: The most significant effects on the time periods where the battery is full and the energy produced cannot be stored any more are mostly caused from the installed capacity of the wind farm and the energy consumption. The influence of the battery capacity is less, but the ideal battery capacity must be determined considering the power generation and consumption when designing the system. Battery capacity more than needed will cause extra costs for the producer. Power can be supplied continuously using a generator in standalone systems with battery. However, the length of time where the battery is full will significantly increase and the need of fuel for the generator must be provided during the working hours of the generator in this situation. Adding extra capacity to the batteries does not have a significant effect on the time periods where the generator is working and where the battery is full. If the generator is needed in the system to meet power demand continuously, the cost of the generator and the fuel must be considered. Using battery in standalone systems did not lead to a significant decrease in the time period where the energy demand could not be provided, because low round-trip efficiencies of vanadium redox flow batteries cause an important amount of energy loss. If a proper generator is used instead of VRB in standalone systems, the length of time without energy will decrease or energy will be supplied continuously. The use of VRB in standalone systems has an important role on decreasing the length of time where there is energy loss due to production above demand or battery capacity. This effect is clearer in systems where the power demand and production is higher. The best solution to use the energy produced by autoproducers in wind energy systems having rated power below 500 kW in an optimum way is the integration of wind energy systems to the grid allowing two-way energy flow. Thus, the energy produced above demand will not be lost, demand will be provided without interruption and autoproducers will profit from the energy that is produced above the need. As the barriers on the optimization of grid integration and energy planning in the market are not overcome, the idea of using energy storage systems in wind farms and studies in this direction will continue. In conclusion, results of the analysis proved that the vanadium redox flow battery use in wind energy systems is not feasible yet due to their low round-trip efficiencies. In case of a proper increase in the round-trip efficiencies and/or decrease in the battery costs, VRBs can become very advantageous and feasible to store energy produced by wind farms.