Stand-alone Photovoltaic System for a Cabin in Marsa-allam 1,2 Hammad Abo-Zied Mohammed 1 Electrical Engineering Department, Assiut University, Assiut, Egypt 2 On leave to Al Jouf University, Al Jouf, Skaka, Saudi Arabia Abstract- This paper presents the complete design of a stand-alone Photovoltaic (PV) system to supply electric power for a cabin in Marsa-allam city, Egypt according to its energy requirements. Typical energy consumption daily profiles for the two seasons (Autumn and summer) are assumed when the cabin is most used. This system can be installed on the roof and the south side of the cabin. Homer software is used as the sizing and optimization tool to determine the size and specifications of photovoltaic system components, system cost and estimation of corresponding produced electrical power. The results ow that the sizing of PV stand-alone system depends on the load data, the solar resource data and the investment cost of system components. This system provides electricity to the cabins in Marsa-allam. It is found that, the system is very economical. Also, this system has the advantage of maintaining a clean environment. Simulation results and analyses are presented to validate the proposed system configuration. Keywords: Photovoltaic, standalone system, Maximum Power point tracking, Boost Converter. I. INTRODUCTION Conventional methods of generating electricity can produce pollutants such as carbon dioxide, the main gas responsible for global warming. The only resource needed to power a solar cell is sunlight; through the photovoltaic effect the energy contained in the sun light can be converted directly to electrical energy. Photovoltaic systems represent a silent, safe, not pollutant and renewable source of electrical energy [1]. The central component of any photovoltaic power system is the solar cell. It is the transducer that directly converts the sun's radiant energy into electricity. The technology for using solar cells to produce usable electrical energy is known and proven. Since its initiation in 1975, the U.S. Department of Energy (DOE) National Photovoltaic program has sponsored the design and implementation of nearly 40 system applications classed as "stand-alone" systems with less than 15 kw peak in power rating. The purpose of this paper is to enable a system design engineer to perform the preliminary system engineering of the stand-alone Photovoltaic Power System (PVPS). This preliminary system engineering includes the determination of overall system cost-effectiveness, the initial sizing of arrays and battery systems, and the considerations which must be specifically addressed in the subsequent detailed engineering stage of the project. As a stand-alone electrical system, the PVPS will be a self-sufficient system which includes an array field, power conditioning and control; battery storage, instrumentation and converter. While the intent of this paper is for low-power applications, serving loads up to 15 kw in size, the theory and sizing methods are not dependent upon the generating capacity of the system or the peak demand of the loads, but only on the desired reliability criteria chosen. This paper provides a design of stand-alone PV system for a cabin in Marsa-allam City including suggested load profiles, sizing of a PV system for supplying the electrical load of the cabin using Hybrid Optimization Model for Electric Renewable (Homer) software. Homer contains a number of energy component models and evaluates suitable technology options based on cost and availability of resource. Analysis with Homer requires information on economic constraints and control methods. It also requires input on component types, their numbers, costs, efficiency, lifetime, etc. Sensitivity analysis could be done with variables having a range of values instead of a specific number. This allows one to aertain the effects of change in a certain parameter on the overall system [2]. II. PV SYSTEM SIZING Sizing of stand-alone PV system starts by data collection of the available solar energy radiation of the selected location and estimating the energy consumption of the cabin. To get optimum design of PV system, it is important to collect meteorological data (solar radiation and temperature) for the site under consideration (the Marsa-allam). Table I ows the monthly average values of global solar radiation over Marsa-Alam [3]. It is clear from the table that solar energy incident on the region is very high especially during summer months, when the 47
cabin is most used, with average daily radiation during June 8.01 KWh/m 2 /day. Table I - The monthly average values of daily global solar radiation (Kwh/m 2 /day) in Marsa-Alam Month Daily Radiation in Kwh/m 2 /day January 3.8 February 4.65 March 5.8 April 6.9 May 7.6 June 8.2 July 8 August 7.6 September 6.7 October 5.1 November 3.95 December 3.1 have the energy consumption (6.120 KWh /day). The typical daily load profile during the two seasons is own in Fig. (1). Load type Table III The daily load energy consumption No. Of Units Rated Power (W) Hours Used/ day Summer KWh/day Autumn KWh/day Lights 4 15 12 720 720 Refrigerator 1 200 24 4800 4800 Television 1 100 2 200 200 Microwave 1 200 1 200 200 Kettle 1 200 1 200 200 Total KWh/day 0216 0216 The electrical loads of cabin consist of four lamps, refrigerator, television, microwave, and kettle. The preferred method for determining PV system loads is a bottom-up approach in which every daily load is anticipated and summed to yield an average daily total. For PV systems designed to power simple loads, such as electric light or other appliance, this method is easy. Simply look at the nameplate power rating on the appliance to calculate its power consumption in watt. The total load demand of the cabin is about 760 W as own in table II. However, these loads do not work all at one time on the contrary, working for a ort time. Table II Typical electrical appliances in a cabin Appliance Watts Lights, 4 Fluoreents 4x15 Refrigerator 200 Television 100 Microwave 200 Kettle 200 Total Load 760 Finally all the different loads in the building need to be estimated on a typical day and sum them. Table III provides the calculations of the power and energy of the cabin. The daily load profiles were determined by calculating the power demand (Kwh/day) for all load types in the Cabin during the two seasons (Autumn and Summer). The estimated daily energy consumption is given in Table III. It is own that, autumn and summer 48 Fig. 1 Daily load profile during the Summer and Autumn The sizing procedure is as follow [4]: 1- PV Array sizing For a PV system powering loads that will be used every day, the size of the array is determined by the daily energy requirement divided by the sun-hours per day. For systems designed for non-continuous use (such as hools, governmental offices, etc.), multiply the result by the days per week the loads will be active divided by the total number of days in the week. Also, the PV array out power can be determined by equation (1) [5,6]. (1) Where: P pv : PV array output power E : The average daily load energy consumption KWh/day Ps : the peak solar power intensity ɳ BS : the efficiency of the system balance Ra : the average solar radiation (KWh/m 2 /day) K : Loss factor The value of the loss factor (K) depends on the circuit losses, module temperature losses, and dust. The value of the system balance efficiency depends on the inverter losses and wiring losses.
The number of series modules is determined by dividing the designed system voltage and the module voltage. The number of string in parallel is calculated by dividing the design array output power by the selected module output power and the number of the series module [6, 7]. 2- Inverter The function of an inverter is to convert the DC voltage to AC voltage at desired magnitude and frequency. For stand-alone systems the inverter ould be sized to provide 125% of the maximum loads you wi to run simultaneously at any one moment. III. SYSTEM ANALYSIS The PV system is analysis by using HOMER program. A stand-alone PV system consists of a primary renewable energy source (solar energy), batteries for energy storage and power inverter to maintain the flow of energy between the AC and DC sides. Figure (2) ows the proposed heme as implemented in the Homer simulation tool. Monthly average data of global solar radiation in the Marsa-allam are used as the solar energy resource. This is own in Fig. (3). Fig. 3 Monthly average data of global solar radiation in the Marsa-allam 1- Economic and constraints The installation, replacement and maintenance cost of all components of PV system are own in table IV. Table IV Cost of different components of PV system Initial cost PV 4500 Converter 800 Battery 100 h Cost Replacement 3500 750 100 Maintenance 0 40 $/year 5 $/year Fig. 2 HOMER implementation of the stand alone PV system From HOMER program, the net present cost consists of the installation, replacement and maintenance cost of the all components of the PV system. The net present cost is own in Fig. 4. The live time of PV arrays is 20 years. The value of the interest rate is 10 %. The battery Surrette battery Engineering SuretteTM 6CS25P models (6V, 1156Ah, 6.94KWh) are considered in the model. 49
Fig.6 Monthly average electric production Fig. 4 the net present cost The optimizing result of HOMER simulates for the given solar radiation, load data, economics and constraints is own in Fig. 5. This configuration is a stand-alone PV system that supplies the electrical energy to the load with the lowest net present cost. Fig. 5 The optimization result of HOMER IV. SOLAR ARRAY CHARACTERISTICS Solar cells are devices that convert photon into electrical potential in a PN junction, of which equivalent circuit is own in Fig. 7. Due to the complex physical phenomena inside the solar cell, manufacturers usually present a family of operating curves (V-I) as own in Fig. 8. These characteristics are obtained by measuring the array volt-ampere for a different illumination values. From these characteristics, the optimum voltage or current, corresponding to the maximum power point, can be determined. It is clearly seen in Fig. 8 that the current increases as the irradiance levels increase. The maximum power point increases with a steep positive slope proportional to the illumination. The design data of a battery is: The battery Surrette battery Engineering 6CS25P models (6V, 1156Ah, 6.94KWh) The number of batteries is one SuretteTM R s I The design data of a solar cell is: The rating is 1 KW 2- Electrical Energy production The monthly average electric production is own in Fig. 6. The annual output energy production of PV array is 1661 KWh/year. The annual electrical load consumption is 1162 KWh/year. The excess electricity is 267 KWh/year about 16 % of the total PV energy production. I D R Fig.7 Equivalent circuit of PV array. V 50
PV power in Watt Pv voltage in Volt INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.2 NO.3 October 2013 25 20 15 10 5 G=0.2 G=0.4 G=0.6 G=0.8 G=1 Where the coefficient K 1, K 2 and m are defined as: K 1 0.01175, K K /( ) 2 4 V oc m, K4 ln(( K1 1)/ K1), K ln[( I(1 K1) Impp)/ K1I m ln( K / K 3 4)/ln( V mpp / V oc) 3 ], 0 0 1 2 3 4 5 6 PV current in Amp 90 80 70 60 50 40 30 20 10 G=0.2 G=0.4 G=0.6 G=0.8 0 0 1 2 3 4 5 6 PV current in Amp Fig. 8 V-I and P-I characteristics at constant temperature. G=1 I mpp is the current at maximum output power, V mpp is the voltage at maximum power, I is the ort circuit current and Voc is the open circuit voltage of the array. Equation (3) is only applicable at one particular operating condition of illumination G and cell temperature T c.the parameter variations can be calculated by measuring the variation of the ort-circuit current and the open-circuit voltage in these conditions using the parameters at the normal illumination and cell temperature. Equation (3) is used for the I-V and P-V characteristics for various illumination and fixed temperature ( 25[ o C] ) in Fig. 8. The main parameters which influence the illumination levels on a surface at a fixed tilt on earth are the daily and seasonal solar path, the presence of clouds, mist, smog and dust between the surface and the sunlight, and the ade of the object positioned such that the illumination level is reduced, etc. The equation of the PV output current I is expressed as a function of the array voltagev I I q( V IRs ) KTk I o e -1}- ( V IRs )/ - R Where V and I represent the PV output voltage and current, respectively; R and R are the series and s (2) unt resistance of the cell (in Fig. 7); q is the electronic charge; I is the light-generated current; Io is the reverse Saturation current; K is the Boltzman constant, and T is the temperature in K. Equation (2) can be k written in another form as [7, 8, 9] 1 [ e K V m 1]}- ( V IRs )/ 2 I I { 1 K R (3) V. CONCLUSIONS This paper is focused on the modeling, design, and simulation of a stand-alone PV system for supplying the electrical load for a cabin in Marsa-Allam city. The paper suggested load profiles, sizing of a PV system for supplying the electrical load of the cabin using Hybrid Optimization Model for Electric Renewable (Homer) software. The required data for Hybrid optimization model are daily load profile, and The monthly average values of daily global solar radiation (Kwh/m 2 /day) in Marsa-Alam. Also, the type and the cost of the system elements like as PV, batteries, and the converter. Then by using the Homer software, the complete design will be completed. The system design means that the rating and the number of the PV unit will be calculated, and the rating, type of batteries will be determined. Also the rating of the converter will be determined. This includes sizing, simulation and economic estimation of the system. The results ow that stand-alone PV system sizing depends on load data, solar radiation, and investment cost of the system components. The results ow that (design data) a 1 KW PV array capacity and 1 (6V, 1156 Ah, 6.94 KWh) batteries are needed to supply 51
the electrical load of the cabin. PV systems are renewable and environmental friendly power sources. For further work which can be done in the same area, using small solar energy in villages as units of energy and used in operating units of agricultural mechanization. References [1] D. Cruz Martins, R. Demonti and R. Ruther, "Analysis of utility interactive photovoltaic generation system using a single power static inverter", Photovoltaic Specialists Conference. Conference Record of the Twenty-Eighth IEEE, Page(s):1719 1722, 2000. [2] Soeren B. Kjaer, John K. Pedersen and Frede Blaabjerg, A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules, IEEE Transactions on Industry Applications, Vol. 41, No. 5, Sep. 2005. [3] Egyptian solar radiation atlas, Cairo, Egypt, 1998. [4] A. A. Hassan1, A. A. Nafeh1, F. H. Fahmy, Mohamed A. El-Sayed, "Stand-Alone Photovoltaic System for an Emergency Health Clinic," Proc. International Conference on Renewable Energies and Power Quality (ICREPQ 10), March 2010. [5] G.E. Ahmad, "Photovoltaic-powered rural zone family house in Egypt", Renewable Energy, volume 26, page(s): 379 390, 2002. [6] Friedrich Sick and Thomas Erge, "Photovoltaics in Buildings- A Design Handbook for Architects and Engineers", Freiburg, Germany, 1996. [7] B. G. YU, A. G. Abo-Khalil, M. Matsui, G. J Yu, Sensorless Fuzzy Logic Controller for Maximum Power point Tracking of Grid, IEEE proc. of International Conference on Electrical Machines and Systems, vol. 1, Dec. 2009. [8] F. Shu-Min and Z. Xieng-Peng, A Novel Maximum-Power-Point Tracking Control Method for Photovoltaic Grid-Connected System, IEEE Electrical and Control Engineering Conference (ICECE), June 2010, pp. 4920 4921. [9] M. A. Elgendy, B. Zahawi and D. J. Atkinson, Assessment of P&O MPPT Algorithm Implementation Techniques for PV Pumping Applications, IEEE Transactions on Sustainable Energy, Vol. 3, No. 1, Jan. 2012, pp. 21-33. Authors Profiles Hammad abu-zied was born in Assiut, Egypt, in 1969. He received the B.S. and M.S. degrees in Electrical Engineering from Assiut University in 1993 and 1998 respectively. The Ph.D. degree in Electrical engineering from Assiut University, and Darmstadt university, Germany, in 2004 (Cotutelle). Since 2004, he has been a staff member at the department of electrical engineering, Faculty of Engineering, Assiut university. His main fields of interest are Electric motors drives, power electronics applications, and renewable energy systems. He was lecturer in Omar El-Moktar university, Lybya from 2005 to 2010. Since September 2013, he is assistance professor in faculty of engineering, Al-Goof university, Saudi Arabia He is the author of one book, and more than 40 articles. Assiut university, Electrical Engineering Department, faculty of Engineering, Assiut, Egypt. 52