Selection of Optimum Hybrid Stand Alone Systems

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1 Selection of Optimum Hybrid Stand Alone Systems Belgin Emre TÜRKAY Electrical Engineering Department, İstanbul Technical University, Ayazağa, Turkey itu.edu.tr Abstract-- A development area in Turkey was selected and the renewable energy potential on the area was analysed during the study; then the analyses of this potential, together with network, was made in terms of cost in meeting the demands of electricity on the region. The HOMER (NREL, US) program was used to simulate the system operation and calculate technical economic parameters for each configuration. The program requires input values such as technology options, component costs and reconciliation of resources, and arranges applicable combinations by net cost for different system configurations, using all these facts/information. As the pilot area, on which the energy to be obtained from renewable energy sources shall be utilised, Bursa in Turkey was preferred. traditional systems and to specify criteria and limits of its competitiveness. II. SYSTEM AND COMPONENTS Gözede Village existing in Kestel County of Bursa City was selected as the sample place in which modeling is installed and economical optimization is conducted. Figure 1 shows scheme of the energy system, which feeds the zone s load values. Keywords Renewable energy, Hybrid Sytem, Homer,Fuel Cell, Hydro plant, Hydrogen energy I. INTRODUCTION In the conducted study, optimum design for renewable energy system was determined for different situations according to capacity of resources (water, wind and sun), cost and load situations by using different input values to change certain boundary conditions. HOMER program determines whether renewable energy resources satisfy hourly electric demand or not. The program calculates energy balance for every 8760 hours in a year to simulate operation of the system. This optimization compares demand for electrical energy for each hour of the year with the energy supplied by the system for that hour and calculates the relevant energy flow for each component in the model. Basic principle is to minimize the cost while HOMER ensures control of the system. Cost of each controllable energy resource is expressed in two values, which are constant hourly cost and energy cost per kwh. These cost values are the costs required for power resources to generate energy at any time. HOMER program researches combination of resources by using these cost values to satisfy the load and finds the system, which can satisfy the load with the lowest cost, among the combinations, which can satisfy the demand [1]. The objective of the study is to analyze power generation by renewable energy resources as well as to compare such power generation with Figure 1: The system to be simulated In the system to be installed, excess power, which is produced by using solar panels (PV) and wind turbines (RT) in the system to be installed, is used in hydrogen production through electrolyzer (EL) and the obtained hydrogen is stored in tanks (HT). It has been planned to use the hydrogen in power generation through fuel cells (YP) in case of demand. Figures 2 and 3 show the system components characteristics in use. The wind turbine (Enercon 33) to be used in calculation with a rotor diameter of 33.4 m and tower height of 50 m was selected from the existing RT library of the HOMER program and the turbine, which has the most suitable power-energy characteristic for the wind speed under the analysis, was used. In calculations, RT s installation cost was assumed as 2000 $/kw. Replacement cost at the end of its lifecycle was assumed as 1500 $/kw. Also, annual operational and maintenance cost was assumed as 75 $/kw. ISSN: ISBN:

2 Power Resources Survey and Development Administration (Elektrik İşleri Etüt İdaresi) in II. REGIONAL LOAD AND ENERGY CHARACTERISTICS Figure 2: E33 Wind turbine s power characteristic PV panel cost was assumed as $8000 per kw and annual maintenance cost was assumed as $10 considering literature review and market researches. Figure 3 shows operational characteristic of the fuel cell, which was used in the system. In this study in which hybrid energy systems were used, data about daily load distribution for the region to which power is supplied account for the most important part in sizing the system in which simulation and optimization are made. In the study, Gözede Village, which is a hilly region, of Kestel County of Bursa City was selected. Obtaining meteorological data of the region in which the project is made and characteristics of components of the system to be used is very important in using wind turbine, solar panel, electrolyzer-hydrogen tank-fuel cell, inverter- converter and interconnection. Electrical load data of the region is as seen in Figure 4. Figure 3: Power and efficiency characteristics of the fuel cell Installation cost of the fuel cell was assumed as $3000/kW, replacement cost as $2500/kW and maintenance cost as $0.02/hour [14]. Installation cost of the electrolyzer was assumed as $2184/kW, replacement cost as $218.4/kW and maintenance cost as $43/year [14]. Cost of 3.2 kg hydrogen tank and storage was assumed as $2288, replacement cost as $195 and annual maintenance-repair cost as $9 [15]. Head is 145 meters in the plant in which small size river turbine was installed. Furthermore, nominal flow rate was assumed as 2500 L/s in design of the turbine by considering flow rate data of the river. Then, HOMER program calculated nominal power of the turbine as 2667 kw according to these data. The turbine will stop if flow rate is less than 25% of the nominal flow rate or equals to 110% of it. Turbine efficiency was assumed as 75%. The turbine generates alternative current (AC). Installation cost of the turbine was assumed as $1,100,000 by considering hydroelectric power plant projects of General Directorate of Electrical Figure 4: Load data of the region Solar characteristics and clearness index is given in Figure 5. Figure 5: Solar radiation data of the region Wind energy characteristic of the region versus months is as seen in Figure 6. Figure 6: Variation of wind speed during the year in the region ISSN: ISBN:

3 In this study, data from Gözede I hydroelectric power plant, which is installed on Deliçay Creek in Gözede Village of Kestel County of Bursa City and operated by TEMSA Power Generation LLC, were used as a small hydroelectric power plant. Figure 9: Monthly average energy generation in stand alone hybrid energy system Figure 7. Data on river s flow rate in the region Annual average flow rate is L/s. III.. STAND ALONE SYSTEM (SA) The quantity HOMER uses to represent the lifecycle cost of the system is the total system cost (SC). This single value includes all costs and revenues that occur within the project lifetime, with future cash flows discounted to the present. The SC includes the initial capital cost of the system components, the cost of any component replacements that occur within the project lifetime, the cost of maintenance and fuel, and the cost of purchasing power from the grid [2,3]. 32 units of E33 wind turbine, a water turbine with nominal power of 2667 kw, fuel cell at a power of 1500 kw and electrolyzer at a power of 2500 kw were used in the system selected by HOMER program as optimum according to the meteorological conditions of the region under study. Thus, investment cost is $33,610,000, annual operation and maintenance cost is $678,233 and total project cost is $42,280,088. Unit cost of electrical energy per kwh is $0,328 while the entire energy in use was satisfied by renewable energy resources. Energy supply satisfied 95% of the demand. Figure 10: Power generated by the wind turbine in stand alone hybrid energy system Figure 11: Power generated by the small river turbine in stand alone hybrid energy system Figure 12: Power generated by PV in the hybrid energy system Figure 8: Cost of stand alone hybrid energy system ISSN: ISBN:

4 Figure 13: Power generated by the fuel cell in the hybrid energy system IV. PRECISION ANALYSIS Meteorological conditions are very important in power generation with renewable energy resources. Variation in the factors like wind speed, solar radiation and river s flow rate changes quantity of the components to be used during optimization. To show effects of such variations, the cases that wind speed, solar radiation and river s flow rate increase by 25% were also simulated beside the existing meteorological conditions and optimum hybrid renewable energy systems were investigated. i) The case that wind speed increases by 25% In case that monthly average wind speeds increase by 25%, optimum, 26 units of E33 wind turbine, a water turbine with nominal power of 2667 kw, fuel cell at a power of 1000 kw, an electrolyzer at a power of 1500 kw and a 1000-kg hydrogen tank were used in the optimum energy system. Thus, installation cost is $25,251,000, annual operation and maintenance cost is $382,619 and total cost is $30,142,148. Unit cost of electrical energy per kwh is $0,233 while the entire energy in use was satisfied by renewable energy resources. Energy supply satisfied 95% of the demand. Figure 16. Power generated by the wind turbine in case that wind speed increases by 25% Figure 17. Power generated by small river water turbine in case that wind speed increases by 25% Figure 14. Cost chart in case that wind speed increases by 25% Figure 18. Hydrogen production in case that wind speed increases by 25% ii) In case that solar radiation increases by 25% Figure 15. Monthly power generation in case that wind speed increases by 25% In case that monthly average solar radiation increases by 25%, optimum, 26 units of E33 wind turbine, a water turbine with nominal power of 2667 kw, fuel cell at a power of 1000 kw, an electrolyzer at a power of 1500 kw and a 1000-kg hydrogen tank were used in the optimum energy system.thus, installation cost is $25,251,000, annual operation and maintenance cost is $382,619 and total cost is $30,142,148. Unit cost of electrical energy per kwh is $0,233 while the entire energy in ISSN: ISBN:

5 use was satisfied by renewable energy resources. Energy supply satisfied 95% of the demand. Figure 22: Hydrogen production in case that solar radiation increases by 25% iii) In case that flow rate increases by 25% Figure 19. Cost chart in case that solar radiation increases by 25% In case that monthly average flow rate increases by 25%, optimum, 24 units of E33 wind turbine, a water turbine with nominal power of 2667 kw, fuel cell at a power of 1000 kw, an electrolyzer at a power of 1500 kw and a 1000-kg hydrogen tank were used in the optimum energy system. Thus, installation cost is $24,288,500, annual operation and maintenance cost is $325,285 and total cost is $28,446,726. Unit cost of electrical energy per kwh is $0,220 while the entire energy in use was satisfied by renewable energy resources. Energy supply satisfied 95% of the demand. Figure 20. Monthly power generation in case that solar radiation increases by 25% Figure 23.Cost chart in case that solar radiation increases by 25% Figure 21. Power generated by small river water turbine in case that solar radiation increases by 25% Figure 24: Monthly power generation in case that flow rate increases by 25% Figure 22. Power generated by the fuel cell in case that solar radiation increases by 25% ISSN: ISBN:

6 Figure 25: Power generated by wind turbine in case that flow rate increases by 25% Figure 26: Power generated by small river turbine in case that flow rate increases by 25% Figure 27: Power generation by fuel cell in case that flow rate increases by 25% Figure 28: Hydrogen production in case that flow rate increases by 25% V. RESULTS Simulation and optimization studies were conducted for a hybrid energy system to be installed in Bursa City s Kestel County s Gözede Village under the existing and variable atmospheric conditions and the following results were obtained. If power is required to be generated with the help of renewable energy resources existing in the region, power amount to be generated by the small river power plant in winters and springs is important for the energy required by the load supplied by the system due to effect of precipitation falling and melting snow because the region is mountainous and gets high precipitation. Wind turbines to be installed may supply the required energy in the months in which precipitation is low. Solar radiation is low in the region according to solar radiation data. As a result the program did not deem the use of photovoltaic cell as appropriate. In the stand alone operation, it is aimed that the excess energy is converted into hydrogen with the help of electrolyzer and the hydrogen is stored in a hydrogen tank, when the generated power is higher than demanded power, to generate power by burning the hydrogen with the help of fuel cell when demand exceeds the power generation for preventing interruption in power supply. However, hydrogen production and storage is a developing and expensive technology; therefore, high costs occurred in 100% power supply. A unit power cost like 32.3 $cent/kwh cannot compete with today s unit power costs for now. In the stand alone operation, HOMER program did not deem the use of photovoltaic panel as appropriate due to high cost to be caused by photovoltaic panels because solar radiation is low in the region. Under operational conditions, 69% of the power was generated from wind turbines, 26% from small river power plant and 5% from the fuel cell. Power supply through the wind turbine and the fuel cell play very important roles in summers because flow rate decreases to almost nil. Optimization studies were conducted for stand alone and interconnected systems also in the precision analysis, in other words, in the analyses in which the existing meteorological conditions vary. HOMER program decreased number of wind turbines, which is 32 under the existing meteorological conditions, to 26 with an increase of 25% in wind speed under stand alone operational conditions and preferred a smaller-size fuel cell. This means that wind turbines in lower numbers may supply the demanded power and need for storage decreases. Considering the generated power, 74% of the generated power was generated by wind turbines, 23% by small river power plant and 3% by fuel cell. This shows that power generated by wind energy increased.the case in which solar radiation increases by 25% was simulated under stand alone operational conditions and it was seen that this increase had no effect on sizing the system. Solar radiation is so low that the use of photovoltaic panel causes higher costs even ISSN: ISBN:

7 an increase of 25% compared with the use of other components. The case in which flow rate increases by 25% was simulated under stand alone operational conditions and it was seen that this increase had no significant effect on the results in the existing meteorological conditions. 68% of the power was generated by wind turbines, 29% by small river power plant and 3% by the fuel cell. Under interconnected operational conditions, unit power costs per kwh decreased to nil when monthly wind speed increased by 25%. This means that cost of the generated power by the hybrid system decreased to almost nil at the end of its lifecycle. However, because 15 wind turbines were used, installation cost decreased and operational costs did not become expenditure anymore because power may be sold to the interconnected system or purchased from the interconnected system and they became a significant income. Meanwhile, 95% of the power was generated by renewable energy resources while power supply achieved 100%. VI. CONCLUSION As a result, unit power generation costs in hybrid systems installed in stand alone systems are higher compared with those occurred in interconnected hybrid energy systems. However, electrification costs for including the region in the interconnected system were ignored in our study. Therefore, because installation and operation of power lines also cause cost, the difference between stand alone and interconnected operational costs shall decrease. In deciding which system is selected, whether the cost for inclusion in the interconnected system and cost for the generated power will compensate each other or not in the course of years and which system will cause less cost should be considered. These are factors depending on distance to the closest power line, geographical conditions of the region and foreseeing possibility for development in the future. Also, the wind turbines, which were used in the project, have low power. Today, it is possible to use turbines with high nominal power. Because costs of high-power turbines are lower, unit cost for power generation will be lower. Stand alone systems will be able to compete with the interconnected systems in the future because of advances in technology, decreases in costs and developments in wind turbine, photovoltaic panel and hydrogen technology. [2]Beccali, M., Brunone, S., Cellura, M., Franzitta, V., Energy, economic and environmental analysis on RET-hydrogen systems in residential buildings, Renewable Energy vol 33, pp , March [3]Dalton, G.J., Lockington, D.A., Baldock, T.E., C ase study feasibility analysis of renewable energy supply options for small to medium-sized tourist accommodations, Renewable Energy 34 (2009) [4]Dalton, G.J., Lockington, D.A., Baldock, T.E., Feasibility analysis of stand-alone renewable energy supply options for a large hotel, Renewable Energy, vol 33, pp , July [5]Diaf, S., Diaf, D., Belhamel, M., Haddadi, M., Louche, A., A methodology for optimal sizing of autonomous hybrid PV/wind system, Energy Policiy vol.35, pp , [6]Elhadidy, M. A., Shaahid, S.M.,. Parametric study of hybrid (wind+solar+diesel) power generating systems, Renewable Energy, pp , October [7]Elkinton, M. R., McGowan, J. G., Manwell, J. F., Wind Power Systems for zero net energy housing in the United States,Renewable Energy,vol. 34, pp ,may Garde, R., Aguado, M., Ayerbe, E., Azcarate, [8]Khan MJ, Iqbal MT., Pre-feasibility study of stand-alone hybrid energy systems for applications innewfoundland, Renewable Energy, Vol.30,pp , [10]Lagorse, J., Paire, D., Miraoui, A., Sizing stand -alone street lighting system powered by a hybrid system using fuel cell, PV and battery, Renewable Energy 34,2009. [11] Leva, S., Zaninelli, D., Hybrid renewable energy-fuel cell system: Design and performance evaluation, Electric Power System Research, Vol. 79,pp , February [12]Painuly, J.P., Barriers to renewable energy penetration; a framework for analysis, Renewable Energy, Vol. 24,, pp.73-89,september [13]Turkay, B., Telli, A.Y., Economic Optimization of Stand Alone and Grid Connected Hybrid Energy Systems, ELECO International Conference, Turkey, Nov REFERENCES [1]Alphen, K., Sark, G.J.H., Hekkert, M., Renewable Energy Technologies in Maldivesdetermining the potential Rene&Sust E.Rev,vol.11,pp ,Oct ISSN: ISBN: