Design & Sizing of Stand-alone Solar Power Systems A house Iraq

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1 Design & Sizing of Stand-alone Solar Power Systems A house Iraq Ali Najah Al-Shamani 1,2, Mohd Yusof Hj Othman 1, Sohif Mat 1, M.H. Ruslan 1, Azher M. Abed 1, K. Sopian 1. 1 Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, Bangi, Malaysia. 2 Al-Musaib Technical College, Al-Furat Al-Awsat Technical University, Babylon, Iraq. ali.alshamani@yahoo.com, myho@ukm.edu.my, drsohif@gmail.com, hafidz@ukm.my, azhermuhson@gmail.com, ksopian@yahoo.com Abstract: - Exploitation the solar energy to power electric appliances starts by converting the energy coming from the sun to electricity. Photovoltaic is the direct conversion of the solar energy into electricity. Photovoltaic systems can be used to exploit the solar energy in almost all kinds of applications. Exploiting of solar energy for domestic use is one avenue where the energy emitted from the sun is converted into electricity to power most if not all the appliances available at our homes and residences. In Iraq there are other reasons why the use of solar energy so necessary, firstly, appropriate climatic conditions, secondly, delayed electricity supply projects for remote areas. Building a photovoltaic system is the process of designing, selecting and calculating the ratings of the equipment s employed in the system. This process depends on a variety of factors such as geographical location, solar irradiation, and load requirements. In this paper, the author has been present the components required for the design of a stand-alone photovoltaic system that will power all electric appliances at a medium-energy-consumption residence in Hilla City. Key-Words: - Stand-alone, solar irradiance, days of autonomy, photovoltaic system, load profile, system sizing. 1. Introduction The sun provides the energy to sustain life in our solar system. In one hour, the earth receives enough energy from the sun to meet its energy needs for nearly a year [1]. Photovoltaic is the direct conversion of sunlight to electricity. It is an attractive alternative to conventional sources of electricity for many reasons: it is safe, silent, and non-polluting, renewable, highly modular in that their capacity can be increased incrementally to match with gradual load growth, and reliable with minimal failure rates and projected service lifetimes of 20 to 30 years [2, 3]. It requires no special training to operate; it contains no moving parts, it is extremely reliable and virtually maintenance free; and it can be installed almost anywhere. The intensity of the sunlight that reaches the earth varies with time of the day, season, location, and the weather conditions. The total energy on a daily or annual basis is called irradiation and indicates the strength of the sunshine. Irradiation is expressed in Wh.m- 2 per day or for instance kwh.m-2 per day. Different geographical regions experience different weather patterns, so the site where we live is a major factor that affects the photovoltaic system design from many sides; the orientation of the panels, finding the number of days of autonomy where the sun does not shine in the skies, and choosing the best tiltangle of the solar panels. Photovoltaic panels collect more energy if they are installed on a tracker that follows the movement of the sun; however, it is an expensive process. For this reason they usually have a fixed position with an angle called tilt angle β. This angle varies according to seasonal variations [4]. For instance, in summer, the solar panel must be more horizontal, while in winter, it is placed at a steeper angle. Many researchers presented procedure to design stand-alone photovoltaic systems [5-7]. The idea of this paper is to introduce the procedures employed in building and selecting the equipment s of a stand-alone photovoltaic system based on the Watt-Hour demand. As a case study, a residence in Hilla, Iraq with medium energy consumption is selected. ISBN:

2 CASE STUDY: A RESIDENCE IN HILLA, IRAQ The geographical location of the Hilla City, Babylon, Iraq at latitude and longitude makes it a relatively sun-rich region with an annual solar irradiance of about 2200 kwh.m -2. This implies that solar energy systems would be very efficient in this part of the world. Some areas in the Hilla City, Babylon are still beyond utility grid reach especially those along the east border line. 2. System Description 2.1. Components Solar PV system includes different components that should be selected according to your system type, site location and applications. A Balance-of- System that wired together to form the entire fully functional system capable of supplying electric power and these components are: 1- PV module: It is made from semiconductor and convert sunlight to electricity. The PV converts sunlight into DC electricity. The most common PV modules include single and polycrystalline silicon and amorphous silicon with other technologies entering the market. 2- Battery stores energy for supplying to electrical appliances when there is a demand. Battery bank, which is involved in the system to make the energy available at night or at days of autonomy (sometimes called no-sun-days or dark days), when the sun is not providing enough radiation. These batteries, usually lead-acid, are designed to gradually discharge and recharge 80% of their capacity hundreds of times. Automotive batteries are shallowcycle batteries and should not be used in PV systems because they are designed to discharge only about 20% of their capacity [8]. 3- Solar charge controller regulates the voltage and current coming from the PV panels going to battery and prevents battery overcharging and prolongs the battery life. 4- Inverter converts DC output of PV panels or wind turbine into a clean AC current for AC appliances or fed back into grid line. It is one of the solar energy system's main elements, as the solar panels generate dcvoltage. Inverters are different by the output wave format, output power and installation type. It is also called power conditioner because it changes the form of the electric power. The efficiency of all inverters reaches their nominal efficiency (around 90 percent) when the load demand is greater than about 50 percent of rated load [9]. 5- Load is electrical appliances that connected to solar PV system such as lights, radio, TV, computer, refrigerator, etc Configuration The photovoltaic systems are classified according to how the system components are connected to other power sources such as standalone (SA) and utility-interactive (UI) systems. In a stand-alone system depicted in Figure 1, the system is designed to operate independent of the electric utility grid, and is generally designed and sized to supply certain DC- and/or AC electrical loads. PV Array Charge Controller Battery (a) (b) DC Load Inverter AC Load Fig. 1: Stand-alone photovoltaic System (a) Block ISBN:

3 Diagram (b) Schematic Diagram 3. System sizing System sizing is the process of evaluating the adequate voltage and current ratings for each component of the photovoltaic system to meet the electric demand at the facility and at the same time calculating the total price of the entire system from the design phase to the fully functional system including, shipment, and labor Residence Device As a first step, the electrical devices available at the residence are itemized with their power ratings and time of operation during the day to obtain the average energy demand in Watt-hour per day as shown below in Table 1. The total average energy consumption is used to determine the equipment sizes and ratings starting with the solar array and ending with system wiring and cost estimate as explained below Sizing of the Solar Array Before sizing the array, the total daily energy in Watt-hours (E), the average sun hour per day Tmin, and the DC-voltage of the system (VDC) must be determined. Once these factors are made available we move to the sizing process. To avoid under sizing, losses must be considered by dividing the total power demand in Wh.day-1 by the product of efficiencies of all components in the system to get the required energy E r. To avoid under sizing we begin by dividing the total average energy demand per day by the efficiencies of the system components to obtain the daily energy requirement from the solar array: daily average energy consuption E r = product of component s efficiencies (1) E = η overall To obtain the peak power, the previous result is divided by the average sun hours per day for the geographical location T min. daily energy requirement P p = minimum peak sun hours per day = E (2) r T min The total current needed can be calculated by dividing the peak power by the DC- voltage of the system. PPPPPPPP pppppppppp II DDDD = SSSSSSSSSSSS DDDD VVVVVVVVVVVVVV = PP pp (3) VV DDDD Modules must be connected in series and parallel according to the need to meet the desired voltage and current in accordance with: Table 1: Residence Devices and Daily Energy Consumption Individual Load Qty. V Amps Watts AC * Use h/d * Use d/w 7 days W.h AC Ceiling Fan Coffee Maker Iron Computer& Accessories Light, 4 Comp. 4* Radio Refrigerator Television Washing Machine AC Total Connected Watts: 2555 AC Average Daily Load: Total Average Energy Consumption approximated to 5700 ISBN:

4 First, the number of parallel modules which equals the whole modules current divided by the rated current of one module Ir. whole module current NN pp = rated current of one module = II DDDD (5) II rr Second, the number of series modules which equals the DC voltage of the system divided by the rated voltage of each module V r. ssssssssssss DDDD vvvvvvvvvvvvvv NN ss = mmmmmmmmmmmm rrrrrreeee vvvvvvvvvvvvvv = VV DDDD (6) VV rr Finally, the total number of modules Nm equals the series modules multiplied by the parallel ones: NN mm = NN ss NN pp (7) 3.3. Sizing of the Battery Bank The amount of rough energy storage required is equal to the multiplication of the total power demand and the number of autonomy days E rough =E D. For safety, the result obtained is divided by the maximum allowable level of discharge (MDOD): energy storage required EE ssssssss = maximum depth of discharge = EE rrrrrrrr h (8) MMMMMMMM At this moment, we need to make a decision regarding the rated voltage of each battery V b to be used in the battery bank. The capacity of the battery bank needed in ampere-hours can be evaluated by dividing the safe energy storage required by the DC voltage of one of the batteries selected: CC = EE ssssssss VV bb (9) According to the number obtained for the capacity of the battery bank, another decision has to be made regarding the capacity C b of each of the batteries of that bank. The battery bank is composed of batteries The total number of batteries is obtained by dividing the capacity C of the battery bank in ampere-hours by the capacity of one of the battery C b selected in ampere-hours: NN bbbbbbbbbbbbbbbb = CC CC bb (10) The connection of the battery bank can be then easily figured out. The number of batteries in series equals the DC voltage of the system divided by the voltage rating of one of the batteries selected: NN ss = VV DDDD (11) VV bb Then number of parallel paths N p is obtained by dividing the total number of batteries by the number of batteries connected in series: NN pp = NN bbbbbbbbbbbbbbbb (12) NN ss Once the sizing of the battery bank is made available, we proceed to the next system component Sizing of the Voltage Controller According to its function it controls the flow of current. A good voltage regulator must be able to withstand the maximum current produced by the array as well as the maximum load current. Sizing of the voltage regulator can be obtained by multiplying the short circuit current of the modules connected in parallel by a safety factor F safe. The result gives the rated current of the voltage regulator I: II = II SSSS NN pp FF ssssssss (13) The factor of safety is employed to make sure that the regulator handles maximum current produced by the array that could exceed the tabulated value. And to handle a load current more than that planned due to addition of equipment, for instance. In other words, this safety factor allows the system to expand slightly. The number of controller equals the Array short current Amps divided by the Amps for each controller: II NN cccccccccccccccccccc = (14) AAAAAAss eeeeeeh cccccccccccccccccccc 3.5. Sizing of the Inverter When sizing the inverter, the actual power drawn from the appliances that will run at the same time must be determined as a first step Sizing of the System Wiring Selecting the correct size and type of wire will enhance the performance and reliability of a photovoltaic system. The National Electrical Code is NEC. 4. Result 4.1. Sizing of the Solar Array The select panel is (Mitsubishi - MF180UD4, 180- W, 24-V, 7.45-A). The Specification of PV panel Manufacturer: MITSUBISHI ELECTRIC. Model name: PV-MF180UD4. Cell type: Poly-crystalline Silicon. Number of cells: 50 cells. Maximum power rating STC (Pmax): 180 watts. Open circuit voltage (Voc): 30.4V. Short circuit current (Isc): 8.03A. ISBN:

5 Maximum power voltage (Vmp): 24.2V. Maximum power current (Imp): 7.45A. The daily energy requirement from the solar array can be determined as following: EE EE rr = = 5700 ηη oooooooooooooo 0.8 WWh KKKKh = 7125 = DDDDDD dddddd To obtain the peak power of the PV: PP pp = = kkkkkk EE rr TT mmmmmm = The total current needed can be calculated by: II DDDD = PP pp = = AAAAAAAA VV DDDD 24 Modules must be connected in series and parallel according to the need to meet the desired voltage and current in accordance with: First, the number of parallel modules: NN pp = II DDDD = PPPPPPPPPP = 11 PPPPPPPPPP II rr = Second, the number of series modules which equals to: NN ss = VV DDDD = 24 = 1 VV rr 24 Finally, the total number of modules NN mm = 11 1 = 11 PPPPPPPPPP The PV array of the system consists of 11 panels in parallel Sizing of the Battery Bank: Total Average Energy Use = 5700 W.h. Days of autonomy or the no-sun days = 3 days. According to the selected battery (UB-8D AGM AH, 12V-DC). The amount of energy storage required is, E rough = = 17.1 kwh, For Energy safety, EE ssssssss = EE rrrrrrrr h MMMMMMMM = = kkkkh The capacity of the battery bank needed can be evaluated: CC = EE ssssssss = = 1900 AAAAAAAA h VV bb 12 The total number of batteries is obtained by: NN bbbbbbbbbbbbbbbb = CC CC bb = = 7.6 BBBBBBBBBBBBBBBBBB = 8 BBBBBBBBBBBBBBBBBB The number of batteries in series equals to: NN ss = = 2 Then number of parallel paths N p is obtained by: NN pp = 8 2 = 4 The number of batteries needed is, N batteries =8 batteries. Four parallel branches and 2 series batteries Sizing of the Voltage Controller: According to selected controller (Xantrex C-60, 24- V, 60-A), the rated current of the voltage Controller I: I = I SC N p F safe = = Amps The number of controller equals to, N controller = I Amps each controller = 1.84 We need two regulators connected in parallel. = Sizing of the Inverter: The power of devices that may run at the same time is: P Total= 2555 Watt. The inverter needed must be able to handle about 2555-W at 220-Vac. Latronics inverter, LS- 3024, 3000-W, 24-Vdc, 220-Vac. 5. Conclusion The geographical location of Hilla, Babylon - Iraq makes it a relatively sun-rich region with an annual solar irradiance of more than 2200 kwh.m-2. There is a great tendency for the use of stand-alone photovoltaic stations distributed in remote areas due to the known benefits of this source of energy. This subject needs to be defined for people living in these areas. In this paper, the author introduces the procedures employed in building and selecting the equipment s of a stand-alone photovoltaic system based on the Watt-Hour demand. As a case study, a residence in Hilla, Iraq with medium energy consumption is selected. The factors that affect the design and sizing of every piece of equipment used in the system have also been presented. Over- and under-sizing have also been avoided to ensure adequate, reliable, and economical system design. The same procedures could be employed and adapted to applications with larger energy consumptions and could also be employed for other geographical locations, however, the appropriate design parameters of these locations should be employed. References: [1] R. A. Messenger and J. Ventre, Photovoltaic systems engineering: CRC press, [2] R. W. Ritchie, Using Sunlight for Your Own Solar Electricity: Build Your Own System, Become Independent of the Grid, Domestic Photo Voltaics: Ritchie Unlimited Publications, [3] D. G. F. Sonnenenergie, Planning and installing photovoltaic systems: a guide for installers, architects and engineers: Earthscan, ISBN:

6 [4] G. M. Masters, Renewable and efficient electric power systems: John Wiley & Sons, [5] S. I. Sulaiman, T. K. A. Rahman, I. Musirin, S. Shaari, and K. Sopian, An intelligent method for sizing optimization in gridconnected photovoltaic system, Solar energy, Vol. 86, No.7, 2012, pp [6] S. Weixiang, Design of standalone photovoltaic system at minimum cost in Malaysia, in Industrial Electronics and Applications, ICIEA rd IEEE Conference on, 2008, pp [7] R. Posadillo and R. López Luque, Approaches for developing a sizing method for stand-alone PV systems with variable demand, Renewable Energy, Vol. 33, No.5, 2008, pp ISBN: