Hybrid Micro-Power Energy Station; Design and Optimization by Using HOMER Modeling Software Iyad. M. Muslih 1, Yehya Abdellatif 2 1 Department of Mechanical and Industrial Engineering, Applied Science University, Amman, Jordan 2 Department of Electrical and Computer Engineering, Applied Science University, Amman, Jordan. Abstract - Hybrid Optimization Model for Electric Renewables (HOMER) software was utilized to find the optimum design of a hybrid micro-power energy station by minimizing the cost of energy based on different capacity shortage percentages. A full investigation of site conditions and restrictions was done to optimize the design and implementation of a hybrid power station. In addition, this paper took into consideration the economic impact and design tradeoffs in order to optimize the cost and performance of the energy system. Many combinations of conventional and renewable energy resources were considered for this hybrid energy station. From the analysis of the HOMER model results, the optimum hybrid power station was suggested, based on the current fuel price, wind speed, and solar conditions. The optimization function objective is to minimize the Net Price Cost (NPC) and the Cost of Energy (COE) with zero percentage of capacity shortage. Keywords: Renewable Energy, Optimization, Cost of Energy, Hybrid Station, HOMER. 1 Introduction The significant increase in demand for energy by several emerging nations has driven the global energy consumption to unprecedented levels. As a result, the cost of energy has reached new levels and is expected to continue to rise. The ramifications of this large increase in energy cost, will pose serious challenges to the economies of most developing nations. In addition, harmful emissions from fossil fuel are causing serious environmental and health problems, and are believed to be the main culprit behind the global warming phenomenon. [1] For economical and environmental reasons and to reduce dependency on imported energy, many countries need to invest in alternative and renewable energy. It is possible to combine traditional technology with renewable energy technologies in order to minimize fossil fuel energy production cost by effective utilization of renewable energy resources for energy production. The U.S. National Renewable Energy Laboratory (NREL) developed a micro-power Hybrid Optimization Model for Electric Renewables (HOMER) to assist engineers in finding the best design of a micro-power system among various power generation systems across a wide range of applications [2] [3]. A micro-power system is a system that generates electricity and/or heat to serve a primary load. By using HOMER, it is much easier to design a system that is capable of matching the energy availability from different technologies (such as wind, solar, and diesel generators) with the local load profile. [4][5] Several studies have been done demonstrating the ability to design hybrid configurations of renewable energy systems in order to maximize the performance while minimizing the cost. These studies stopped short of the complete analysis of all aspects of the hybrid power components by not addressing the optimization and implementation of the system. This paper will address all possible combinations of PV solar energy, wind energy, and diesel power generators that can satisfy the load demand. All variables with full detailed specifications were considered for all available energy resources in the selected location for the hybrid station. [6-11] 2 Methodology Hybrid Optimization Model for Electric Renewables (HOMER) software is utilized to find the optimum sizing of the Hybrid station by minimizing the cost of the hybrid power system with a specific load demand based on different capacity shortage percentages. This research will consider two aspects of the design process; the simulation and optimization aspects. In the simulation process, every possible power system will be simulated for each hour of the day to determine the technical feasibility for each combination of micro-power systems. This simulation process is performed on the basis of a life cycle cost which includes the total cost of installing and operating the system
over the project s lifespan. In the optimization process, the model simulates the various configurations of the simulation process and suggests the single most technically feasible configuration at the lowest life cycle cost, where the minimization of the objective function is formulated based on different technical and economical constraints of the local area.[2] 3 Study Area and Load Profile The study area in this research is a village, Kamsha, which is located in Jordan. The village power needs is presently supplied through the national electricity grid. The location of the suggested hybrid micro-power station is located at (32' 07" N and 35' 54" E) and the elevation of the site is 2951 ft above sea level [12]. The location is shown in Figure 1. Figure 2. Daily and seasonal electrical load profiles. 4 The Proposed Micro-Power System The schematic diagram of the proposed micro-power system in this study is shown in Figure 3. Figure 3. Diesel, Wind and Solar Hybrid Configuration Figure 1. The suggested location of the hybrid micro-power station The AC load is a combination of electricity loads mainly used for domestic lighting and powering TV and radio sets, refrigeration units and electrical motors used for water pumping for domestic use. The AC load profile considered for a block of homes in the village has a scaled annual load average of 35 kwh/d with a 4.5 KW peak load and a load factor of 0.321. The daily load profile is given in Figure 2 with a maximum load of 12 KW for the hours between 17 and 22 of the day. The daily load is duplicated for all days of the year with a random variability from day to day as 15%. The load profile for the year is shown in Figure 2. This study considers three different types of power supply technologies based upon the availability of local resources in the area: a solar PV unit, two small size wind power generation units, a diesel power generation unit. The system includes a set of storage batteries, a converter and other hardware parts necessary of the hybrid system. 4.1 Diesel Unit Given the fact that the energy available from wind turbines and solar PVs is highly intermittent and occurs mostly at certain times of the day; the diesel power generator was used as a primary power generation option, to increase the reliability of the hybrid supply station. An AC diesel power generation unit of a size of 8 KW is considered. The capital cost of the unit is 6500 dollars and the operation and maintenance (O&M) is 0.2 dollars/h. The
lifetime is 15000 in operating hours. The replacement cost of the diesel unit is 5500 dollars. The price of fuel at the time of study is taken as 0.8/L in US dollars with no limit on diesel consumption per year. The fuel properties of the diesel power generator were set as: a lower heating value of 43.2 MJ/kg, a density of 820kg/m 3, a carbon content of 88% and sulfur content of 0.33%. The efficiency curve of the unit is shown in Figure 4. [2][13] Figure 5. Daily radiation and clearness index of the location. 4.3 Wind Unit The wind data collected for the suggested location and the wind scaled speed with monthly averages for the year are given in Figure 6. [2][14][15][17] Figure 4. The efficiency curve of the diesel power generator. 4.2 PV Solar Unit The daily radiation and clearness index for the selected location of the hybrid power station is shown in Figure 5. [2][14][15] The PV modules used in the proposed system are assumed to have a capital cost of 3,400 dollars/kw without considering other auxiliary components of system. The modules life time is estimated by the manufacturer to be 25 years with an O&M of 100 dollars/year. A horizontal axis monthly adjustment is considered to increase the effectiveness of PV unit. [16] Figure 6. Wind speed with monthly averages for the year. For the wind power generation, two units of small size wind turbine are considered, 3 KW and 10 KW. For the 3 KW unit, the capital cost is 11000 dollars with a life time of 15 A B Figure 7. The power curve for: (a) 3 KW wind turbine, (b) 10 KW wind turbine.
years, a hub height of 20 m, and a replacement cost of 7000 dollars. The O&M is taken as 300 dollars /year. The power curve of this 3 KW unit is shown in Figure 7-a. For the 10 KW unit, the capital cost is 27000 dollars with a life time of 15 years, a hub height is 20 m, and a replacement cost of 23000 dollars. The O&M is taken as 350 dollars /year. The power curve of this 10 KW unit is shown in Figure 7-b. [18-19] 4.4 Storage Battery Bank The battery type used in the proposed system is Surrette 6CS25P from the manufacture Rolls/Surrette. The Nominal voltage is 6 V and Nominal capacity of 1,156 Ah (6.94 KWh). The minimum state of charge is 40% and maximum charge rate is 1 A/Ah with a maximum charge current of 41 A. The lifetime throughput is 9,645 KWh. The cost of one battery is taken as 1200 dollars and a life time of 4 years with a replacement price of 1100 dollars and the O&M cost is 50 dollars/year. The relation between the battery capacity in Ah and the discharge current in A is given in Figure 8-a. The relation between the cycles of failure and the depth of discharge is given in Figure 8-b.[2][20] The capacity of the rectifier relative to inverter is 100% with an efficiency of 85%.[2] 5 Results and Analysis All possible hybrid configurations were used as input values for HOMER in order to find the optimum configuration based on the available resources. The model has the capability to calculate the net present cost (NPC) and the cost of energy (COE) from the installation and operation of different power generation technologies over the given life cycle of the project which is considered as 25 years. For each possible case of energy type combinations, the total net present cost (NPC), the system capacity mix, and the energy mix are analyzed. It should be noted that the total NPC is HOMER s main economic output on which different system types are ranked. (a) (b) Figure 8. (a) The relation between the battery capacity and the discharge current. (b) The relation between the cycles of failure and the depth of discharge. 4.5 Converter A converter is required for the system in which DC components serve an AC load or vice-versa. The size of the used converter is taken as 10 KW with a capital cost 12500 dollars and the O&M coast is 100 dollars/year. The converter efficiency is 90% with a lifetime of 20 years and the converter can operate simultaneously with an AC generator. Considering a wind speed of 4 m/s and a fuel price of 0.8 dollars/l, the optimum hybrid system based on the NPC and COE is given in Table 1. The system is made of an 8 KW of PV, an 8 KW diesel power generator, 12 batteries and a 4 KW converter. The capital cost of the system is 63,100 dollars and the operating cost is 3484 dollars. The total NPC is 105601 dollars and the COE is 0.678 dollars/kwh which is less than the national grid tariff for Jordan which is 1.59 dollars/kwh.[21]
Table 1. All possible hybrid power configurations considering a wind speed of 4 m/s and a fuel price of 0.8 dollars/l. And by considering a wind speed of 5 m/s and a fuel price of 0.8 dollars/l, the optimum hybrid system based on the NPC and COE is given in Table 2. The system is made of a 6 KW of PV, a 3 KW wind turbine, an 8 KW diesel power generator, 8 batteries and a 4 KW converter. The capital cost of the system is 62,500 dollars and the operating cost is 3322 dollars. The total NPC is 103148 dollars and the COE is 0.662 dollars/kwh which is lower than the previous case. Taking both the wind speed and diesel price as the two major variables in the system; the optimal configuration of the hybrid station can be suggested as shown in figure 9-a, 9-b, 9-c. with 0% capacity shortage, 5% capacity shortage, 10% capacity shortage, respectively. The shortage percentage is shown on the gird of each figure Table 2. All possible hybrid power configurations considering a wind speed of 5 m/s and a fuel price of 0.8 dollars/l. (a)
(b). (c) Figure 9. Optimal configuration of the hybrid station with; (a) 0% capacity shortage, (b) 5% capacity shortage, (c) 10% capacity shortage, respectively. 6 Conclusions Based on the results and analysis of the HOMER model, the optimum hybrid power station based on the current fuel price, the average wind speed, and the local site conditions is made of; a 6 KW of PV power generation unit, a 3 KW wind turbine unit, an 8 KW diesel power generator, 8 Surrette 6CS25P batteries and a 4 KW converter and a 4 KW rectifier. The capital cost of the system is 62,500 dollars and the operating cost is 3322 dollars. The total NPC is 103148 dollars and the COE is 0.662 dollars/kwh with zero percentage capacity shortage which less than the current national gird price.
The optimization of the design and implementation of hybrid renewable energy systems is dependent on the geographic location and not just on the available renewable energy resources. A location is selected in Jordan where the government suggested the area to be one of few promising locations for renewable energy systems with a well developed infrastructure to facilitate the implementation, operation and management of the optimal hybrid power station. It should be noted that, although the application and implementation of renewable energy systems for domestic or commercial application are primarily dependent on the availability of the renewable resources on the specific site of concern, there are number of economic considerations and design tradeoffs to be taken into consideration in order to optimize cost and performance. 7 References [1] Salah abdallah, et al. "National grid, Diesel and Photovoltaic Power Generation Systems in Jordan: An Engineering and Economical Evaluation " Energy Sources Part B: Economics, Planning & Policy, Oct2010, Vol. 5 Issue 4, p370-383, 14p. [2] National Renewable Energy Laboratory, HOMER Getting Started Guide Version 2.68, NREL, 2010. [3] Iqbal MT, A feasibility study of a zero energy home in Newfoundland, Renewable Energy, 29 (2) 277289, 2004 [4] Designing High Reliability Power Systems for PEMEX Using HOMER, Arturo Romero Paredes Rubio, World Renewable Energy Congress VIII, Denver, Colorado, 2004. [5] Georgilakis PS, State-of-the-art of decision support systems for the choice of renewable energy sources for energy supply in isolated regions, International Journal of Distributed Energy Resources, 2 (2) 129-150, December 2005 [6] Shaahid SM, El-Amin I, Rehman S, Al-Shehri A, Bakashwain J, Ahmad F, Potential of autonomous/offgrid hybrid wind-diesel power system for electrification of a remote settlement in Saudi Arabia, Wind Engineering, 28 (5) 621-628, 2004. [7] Iqbal MT, Pre-feasibility study of a wind-diesel system for St. Brendan s, Newfoundland, Wind Engineering, 27 (1) 3951, 2003 [8] Rehman S et al, Feasibility study of hybrid retrofits to an isolated off-grid diesel power plant, Renewable & Sustainable Energy Reviews, 11 (2007) 635-653 [9] Juhari Ab. Razak, Kamaruzzaman Sopian & Yusoff Ali, Optimization of Renewable Energy Hybrid System by Minimizing Excess Capacity. International Journal of Energy, Issue 3, Vol. 1, 2007, pp. 77 81 [10] Kamel, S. & Dahl, C.,The Economics of Hybrid Power Systems for Sustainable Desert Agriculture in Egypt, Energy, Vol. 30, 2005, pp 1271 1281. [11] Ashok, S. Optimised Model for Community Based Hybrid Energy System. Renewable Energy, Vol. 32, No. 7, 2007, pp. 1155 1164. [12] Google Earth. 1600 Amphitheatre Parkway, Mountain View, CA 94043, United States. http://www.google.com/earth/index.html as of 25-2-2011 [13] http://www.hondapowerequipment.com/gen.htm as of 25-2-2011 [14] The Hashimite Kingdom of Jordan, Meteorological Department, Climate Division, Jordan Climatic Data, 2007. [15] Surface Meteorology and Solar Energy; A renewable energy resource web site Rel.6.0.http://eosweb.larc.nasa.gov/cgibin/sse/sse.cgi?+s01#s01T as of 25-2-2011 [16] The Potential of Solar Energy Application in Jordan. 1983. Assessment and Analysis of Available Energy Resources, Royal Scientific Society, Vol.3, Amman- Jordan. [17] Habali, S.A.; Hamdan, M.A.S.; Jubran, B.A. and Zaid, Adnan.I.O. 1987. Wind Speed and Wind Energy Potential of Jordan, Solar Energy 38(1): 59-70. [18] http://www.gepower.com/prod_serv/products/wind_turbi nes/en/index.htm [19] http://www.mpshq.com/products/wind_turbines/index.ht ml as of 25-2-2011 [20] http://www.surrette.com/content/specifications-renewable as of 25-2-2011 [21] Jordan National electrical Company. http://www.nepco.com.jo/english_etariff.html