Financial Payback Analysis of Small Wind Turbines for a Smart Home Application in Istanbul/Turkey

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1 Financial Payback Analysis of Small Wind Turbines for a Smart Home Application in Istanbul/Turkey Enes Ugur*, Onur Elma, Ugur Savas Selamogullari, Mugdesem Tanrioven, Mehmet Uzunoglu Department of Electrical Engineering, Yildiz Technical University, Istanbul, Turkey, {enesugur,onurelma, selam, tanriov, Abstract Small-scale wind turbines are promising renewable energy devices driven by the aim of carbon savings at energy generation. However the use of small-scale wind turbines in residential areas is still very narrow because of low wind speeds, high turbulence intensity, and the perception of the potential for a high aerodynamic noise produced by wind turbines. Furthermore, their high costs make it essential to assess the turbines carefully before deciding to purchase so that the optimum performance and costs can be obtained. In this study, power curves of best-selling small scale wind turbines in Turkey are compared using experimentally collected one year wind data for the use in a smart home environment at Davutpasa Campus, Istanbul. The total annual energy production of the wind turbines and financial payback periods are calculated. With the results of performed analysis, it is possible to define the most profitable small wind turbine to be used in related applications in Istanbul and in areas where wind speed is similar. Keywords- small wind turbine; smart home; financial payback; annual energy yield; wind speed. I. INTRODUCTION Increasing energy demand, together with concerns about climate change, energy dependency and increasing energy prices have significantly expanded the role of renewable energy sources over the last years [1, 2]. Nevertheless, making the power generation greener is not enough to solve all problems. Because of the growing electricity demand, current electric power systems are loaded much more than normal and faced with more frequent failures. These factors push the power system to be more efficient and the consumption to be smarter that will help to reduce instant demand. Smart home solutions are indispensable for the matter of smarter consumption, because residential energy consumption represents an important part of the total electricity demand [3]. Another innovative solution for more efficient power systems is distributed generation close to demand side. With distributed generation (also called as micro generation), energy for individual building or collection of buildings can be produced at the demand side using mostly renewable energy sources [4]. Distributed generation is regarded as an essential technology for energy production to partially compensate customer demand. It has advantages of electricity generation at the point of use, reduction of CO2 emissions in the surrounding area, and low-cost installation since it is mounted on the building. Additionally, distributed generation can reduce consumers electricity costs as well as decreasing energy usage through behavior change [6]. Renewable energy sources together with smart home concept provide a huge potential to utilize this technologies in the urban areas. Therefore, a renewable energy supplied smart home has been built at Yildiz Technical University with a $0.5 million budgeted project. The smart home is equipped with solar panels, small wind turbine and power conditioning systems and it can operate both in grid-parallel mode and in stand-alone mode. A battery bank is used to store excess renewable energy and there is also a charger for electrical vehicles. It is possible to monitor electrical demand and generation data and to manage energy storage and demand response. A small scale wind turbine has been used at the project in combination with photovoltaic panels as wind and solar power are highly complementary renewable sources which provide a huge potential to utilize this non-polluting energy technologies in the urban area [4, 5]. In this manuscript, financial payback analyses of small scale wind turbines are carried out to evaluate commercially available turbines in Turkey before selection of the wind turbine for the smart home project. Current situation of wind turbines in urban areas is evaluated and discussed by the approach of financial payback duration of small wind turbines in such areas. The paper is organized as follows: Section II presents current discussions about urban wind and small scale wind turbines. Data measurements, performance analysis approach are given in Section 3. Energy yield and financial payback of each wind turbine are calculated and results are given in Section IV. Finally, the study is concluded with relevant discussions. II. SMALL SCALE WIND TURBINES Small wind turbines are classified regarding to the swept areas (< 25 m 2 ) and generally used for autonomous off-grid applications. This brings the advantage of providing free energy source for the urban residents as well as being independent from energy providers [7, 8]. The biggest potential for off-grid systems lies in the developing countries where there are many houses far from grid and the grid connection will be very expensive. Other potential applications are on agricultural farms, sailing boats and telecommunication towers [9]. Whilst turbines can mount on buildings, they can also be pole-mounted turbines well positioned to be exposed to the prevailing wind direction. In the last decade, there has been

2 growing interest in building-mounted micro wind turbines. The wind turbines also differ in design as vertical axis and horizontal axis wind turbines. The horizontal-axis wind turbines must be oriented in the direction of prevailing wind and they can't work effectively when the wind direction changes too fast. The horizontal axis turbines also have two types as: downwind designs and upwind designs that passively turn using a tail fin. A carefully designed and well-integrated wind turbine according to the surrounding environment can produce significant amount of energy, regardless of turbine's scale. On the other hand, small wind turbines market has a trend to change continuously towards to the larger network-connected systems. Despite their potential, small-scale wind turbines are not yet widely accepted in urban areas for reasons such as, low wind speed, high-level turbulence and high aerodynamic noise produced by turbines. There are several studies in literature showing that most of small scale wind turbines did not meet the performance stated by the manufacturers [8-13]. First of all, it is important to understand the limitations and constraints of urban wind. Small wind turbines in urban areas are generally located in places where the produced energy is more important than the best location for wind usage in the region. Therefore, these turbines are forced to work in low and medium wind speed areas. Moreover, they are generally designed to work nominal at high wind speeds and have bad start at low wind speeds which affects their energy yield. analysis of each turbine. Additionally, under the assumption of their having similar reliability, they will have proportional repair costs to their prices, so ranking of turbines financial paybacks would be the same. B. Wind Speed Measurements The energy yield of a wind turbine is dependent on the wind speed and wind distribution of the site. For measurements, hourly meteorological data is collected to enable the calculation of the energy yield of wind turbines from power curves. Davis VantagePro2 weather station is used to measure and store wind speed data for 12 month long period (01/01/12 31/12/12) at Yildiz Technical University (YTU) Davutpasa Campus in Istanbul, Turkey (Figure 1.a). It can be also seen on Fig. 1.b, a small part of the wind speed data measurements. This particular site has a low average wind speed of 3.5m/s. Each turbine is assumed as working on same height tower for evaluating each turbine at equal elevations. C. Financial Payback Analysis In this study, 10 most popular small-scale wind turbines in Turkey market are compared. Important technical specifications of these turbines are summarized in Table I. The given cost of each turbine systems is taken as a quotation from manufacturer s representatives or dealers in Turkey. One of turbines has been chosen as 10 kw Bergey Excel to provide a wide scale comparison from 0.4 kw to 10 kw. III. WIND TURBINE ANALYSIS A. Methodology of Analysis This section provides a method to evaluate the suitability and economic feasibility of small-scale wind turbine applications in urban areas. Wind turbines can be compared according to parameters such as rated power, annual energy yield or cost. However, it is required to determine a single parameter to evaluate all the turbines under equal conditions since they have different rotor diameters and costs. The annual energy yield per swept area and cost per generated electricity is two of suggested parameters for comparison in the literature [6]. In this study, financial payback period is used as comparison parameter, which is obtained by dividing the total system cost by the price of the annual energy yield calculated using current energy rates in Turkey. For end users, total system cost of a wind turbine is more important than the energy yield per swept area. Customers also care about if the turbine is sufficient to meet their power demands or not as well as when they can get good return on their investments. The selected parameter, financial payback period, is not only provides idea about feasibility analysis of installing wind turbines but also gives indirect impression about the amount of released emissions for manufacturing and installing wind turbines since there is relation between the amount of material used and the price of the device. For calculations, it is assumed that turbines have an unlimited life time and they will work at same efficiency as given in their power curve throughout their life-time. Although repair and maintenance costs may be significant costs in reality, they have been also neglected in this study because it needs detailed reliability and robustness Figure 1 a) Davis VantagePro2 Weather Station b) A part of the wind speed data

3 Turbines Primus Air 30 TABLE I IMPORTANT SPECIFICATIONS OF CONSIDERED WIND TURBINES Zephyr Airdolphin Passaat Skystream 3.7 Turby 500 Montana Bergey Excel Turbine Type HAWT HAWT HAWT HAWT HAWT HAWT VAWT HAWT HAWT HAWT Number of blades Rotor diameter Swept area [m2] Rated power [kw] Rated wind speed [m/s] Cut-in wind speed [m/s] Cut-out wind speed[m/s] n/a n/a n/a Cost (Euro) Cost per power[ /kw] The cost per nominal power is also given in Table I as foreknowledge before the analysis. Although all companies give the nominal power at different wind speeds, cost per nominal power gives an idea about possible system costs. Fig. 2 shows the manufacturer s published power curves for a wind speed range between 0 25 m/s. IV. RESULTS AND DISCUSSION Details of the calculations will be given in this section step by step together with the discussion on obtained results. The financial payback periods of the selected small scale wind turbines will be calculated using the following approach. First, the manufacturer s power curve will be used to determine the energy yield for a given site. The wind speed data taken from measurements will be used to determine the energy production of each hour using manufacturer s power curve. Then, annual energy yield for each turbine will be obtained by integrating the energy yield over the year. Financial payback period will be found by dividing the total system cost by the price of the annual energy yield with current Euro-cent energy rates in Turkey. A. Annual Energy Yields Instantaneous power outputs of each wind turbine for the wind speed data taken from measurements is calculated with models designed at Matlab-Simulink environment. These models are based on the manufacturer s power curves which shows predicted instantaneous power output as a function of wind speed (Fig. 2). For calculations, hourly collected meteorological wind speed data for 12 month long period is used. It should be again noted that the measurement site has a low average wind speed of 3.5m/s. Calculated annual energy yield of each turbine is given in Table 2. The results also depicted in Fig. 3 for comparison. As it s expected annual energy yield of turbines is increasing with their nominal power output. Only two exceptions to these results are 200 and Turby which showed over performance and lower performance respectively than expected. This performance differences is mainly based on the variance of rated wind speed values at which the rated powers are given. The rated power of 200 is defined at 11.6 m/s wind speed while Turby s rated power is given at 14 m/s. Another reason for Turby s low performance can be explained with its power curve at Fig. 1. Turby has the second narrowest working wind speed interval between all turbines and its output is sharply decreasing after 14 m/s. B. Financial Payback Periods Calculated annual energy yield of each turbine then multiplied with current Euro-cent energy rates in Turkey to calculate annual profit obtained by producing free energy from wind turbines. The results are given in Table 2. Financial payback period is calculated from the price of the annual energy yield by dividing the total system cost by annual profit. The results are given in Table 2 and also represented in Fig. 3 for comparison. The financial payback periods presented in Table II shows that most of the turbines wasn t able to make a financial payback lower than 25 years while the maximum life time of Figure 2 The manufacturer s published power curves Figure 3 Calculated Annual Energy of Considered Wind Turbines

4 Turbines Primus Air 30 TABLE II PERFORMANCE ANALYSIS OF CONSIDERED WIND TURBINES Zephyr Airdolphin Passaat Skystream 3.7 Turby 500 Montana Bergey Excel Cost (Euro) Calculated Ann. Energy[kWh/year] Annual Profit[ /yr] Financial Payback Period [year] wind turbines is given around 20 years. Although small scale wind turbines need some improvements at their technology, wind turbines are not the main problem at high financial payback periods; it is the wind itself. The measurement area has low wind speed values so this is extensively affecting the results. From this result, the main consideration is wind speed values while taking a decision of building a green looking small wind turbine at urban areas. Between compared wind turbines 500 gives the best performance with 20 years of financial payback period. 200, Bergey Excel, Montana and Skystream 3.7 are other challenging alternatives. Turby shows the most deficient performance. Together with reasons explained for its low annual energy yield, Turby s high cost is making the financial payback period much more badly. Zephyr Airdolphin is another product which suffer from its high price. Primus Air 30 can only produce 200 Wh per day, which makes its payback period higher even it is the cheapest product. Figure 4 Financial Payback Periods of Considered Wind Turbines V. CONCLUSION In this study, a comparison of 10 most popular small-scale wind turbines in Turkey market is presented. Financial payback period is used as comparison parameter, which is obtained by dividing the total system cost by the price of the annual energy yield calculated using experimentally collected one year wind data. With the results of performed analysis, it is possible to define the most profitable small wind turbine to be used in related applications in Istanbul and in areas where wind speed is similar. It s calculated that the annual energy yield of the products is changing from 76.2 kwh to kwh. Using current energy rates in Turkey the turbines has financial payback period changing from 20 to 112 years. While 500 showed the best performance with 20 years, Turby had the worst with 112 years. The main problem is proposed as low wind speeds. Only low wind speed disadvantage of using wind turbines in urban areas has been studied within scope of this study. High-level turbulence and high aerodynamic noise problems should also be studied to evaluate using of small scale wind turbines in urban areas better. ACKNOWLEDGMENT This study is supported by Istanbul Development Agency Fund under Grant KCE-27. REFERENCES [1] European Commission Climate Action, The EU climate and energy package, March [2] C.O.P. Marpaung, A.Soebagio and R.M. Shrestha, The Role of Carbon Capture and Storage and Renewable Energy for CO2 Mitigation in the Indonesian Power Sector, in Proc. The 8th International Power Engineering Conference (IPEC 2007), 3-6 December, 2007, pp [3] M. Pipattanasomporn, M. Kuzlu, S. Rahman, "An Algorithm for Intelligent Home Energy Management and Demand Response Analysis," IEEE Transactions on Smart Grid, vol.3, no.4, pp , Dec [4] [A.S. Bahaj, L. Myers and P.A.B. James, "Urban energy generation: Influence of micro-wind turbine output on electricity consumption in buildings, " Energy and Buildings, vol. 39, no. 2, pp , Feb [5] P.A.B. James et al., "Implications of the UK field trial of building mounted horizontal axis micro-wind turbines," Energy Policy, vol. 38, no. 10, pp , Oct [6] S.O. Ani, H. Polinder and J.A.Ferreira, "Energy yield of small wind turbines in low wind speed areas," in Proc. 3rd IEEE International Conference Adaptive Science and Technology (ICAST), Nov. 2011, pp [7] B. Holdsworth, "Options for micro-wind generation," Renewable Energy Focus, vol. 10, no. 2, pp , March April [8] M.F. Sissons et al., "Pole-mounted horizontal axis micro-wind turbines: UK field trial findings and market size assessment," Energy Policy, vol. 39, no. 6, pp , June [9] L. Ledo, P.B. Kosasih, P. Cooper, "Roof mounting site analysis for micro-wind turbines," Renewable Energy, vol. 36, no. 5, pp , May [10] S. L. Walker, "Building mounted wind turbines and their suitability for the urban scale-a review of methods of estimating urban wind resource," Energy and Buildings, vol. 43, no. 8, pp , August [11] B. Holdsworth, "Options for micro-wind generation: part two," Renewable Energy Focus, vol. 10, no. 3, pp , May June [12] B. Holdsworth, "Options for micro-wind generation: part 3," Renewable Energy Focus, vol. 10, no. 5, pp , Sep. Oct [13] [K. De Decker. (2008, Sep. 02). Urban windmills harm the environment [Online]. Available:

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