Published on International Journal of Engineering & Industry
Publication Date: September, 2019
Wai Phyo Aung, Theingi Linn & Ni Ni Htay Lwin
Prof. and HOD, Electronic Engineering Department, TU (Loikaw)
Assistant Lecturer, Electronic Engineering Department, TU (Loikaw)
Loikaw, Kayah State, Myanmar
Journal Full Text PDF: Design Calculation of a Solar Power System For PTP Microwave Link Subscriber.
The solar power system which outputed 220 Vac is to be designed to support the point to point microwave link project which provide the internet access for rural area using ePMP Force 180 5GHz subscriber module. The power consumption is considered for the purpose of subscriber at the receiving site of microwave link. The study or system consideration of PV solar panel, Battery, Inverterand also solar charge controller are carried out in this project as a portion of Research for Microwave Link internet access.The design calculation of a solar power system for 10W of Antenna and 40 W of Laptop are sucessfully done in this research paper. Our research is very useful for rural area or dissister situation.
Keywords: Solar Power System, Internet Access, Microwave Link, Inverter, Solar Charge Controller.
1. INTRODUCTION TO OFF-GRID SOLAR POWER SYSTEM
One might encounter such solar system when there is no grid in such a rural area or even when the utility power pricing is quite high. Here, the solar panels become the utility company and generate the needed energy by one’s home or any energy dependent system. There may be no option other than to go with an off-grid solar system. Off-grid systems require more care and maintenance but can give a strong sense of independence, so one is no longer being subjected to the risk of a loss of power from the utility grid. Off-grid solar systems where the solar energy is generated and consumed in the same place meaning it does not interact with the main grid at all. Picture 1. shows a simple schematic for the off-grid solar PV system. (N.H.A. Dulaimi, 2017)
Picture 1. Off-Grid Solar Power System(N.H.A. Dulaimi, 2017)
1.1 Components of Off-grid PV System
The system can be seperated into PV array, Battery Bank, Charge Controller, Inverter and Load.
A solar PV Array is comprised of PV modules, which are fixed accumulations of PV Cells. A PV array is the entire electric power creating unit. It comprises of any number of PV modules. The most crucial segment of any solar PV system is the PV module, which are made out of various interconnected solar cells. Solar PV modules are associated together into strings to meet different vitality needs, as appeared in Picture 2. The solar system is associated with an inverter that changes over the Direct Current (DC) created by the sun powered PV cluster into Alternating Current (AC) perfect with the power provided from the lattice. Air conditioning yield from the inverter is associated with the home’s electrical board or utility meter, contingent upon the design. (N.H.A. Dulaimi, 2017)
Picture 2. Solar Cell, Solar Module, Solar Panel and Solar Array(N.H.A. Dulaimi, 2017)
DC to AC Inverter is an exceptional kind of power inverter that transforms direct current (DC) into alternating current (AC) and sustains it into an existing electric grid in grid-connected solar PV systems and to the AC electric appliances in the case of an off-grid solar PV system. It Changes the DC output yield of the solar PV panels or into an AC current for AC-functioning electric appliances.
A charge controller decides how much current ought to be injected into the batteries for its most ideal electric performance. As it decides the efficiency of the whole solar PV system, it affects the operating life of the batteries and it is considered to be a vital segment in the solar PV system. There are several types of charge controllers being manufactured but the most two common types are the PWM (Pulse with Modulation) and MPPT (Maximum Power Point Tracker) simultaneously. These two kinds are commonly used in nowadays solar PV systems. Both adjust charging rates depending on the battery’s charge level to allow charging closer to the battery’s maximum capacity as well as monitor battery temperature to prevent overheating which is preferable in order to sustain the battery bank life span.
Battery Bank stores electric energy for providing to electrical devices when there is a need. There might be periods when there is no daylight. Night times, evenings and shady days are cases of such circumstances outside our ability to control. Keeping in mind the end goal to give power amid these periods, abundance vitality, within the day, is put away energy in these battery banks and is utilized to power loads at whatever point required. Normally a battery bank consists of number of batteries which are wired in series or parallel according to needed battery bank by the solar PV system.
Load means is the electrical appliances that connected to the solar PV system such as lights, TV, PC’s, etc. It could be AC or DC appliances. (N.H.A. Dulaimi, 2017)
2. REVIEW ON PHOTOVOLTAIC SOLAR ENERGY
Nowadays a great variety of different PV installations is available on the market including on- and off-grid systems with or without battery as a storage system; hybrid systems as combination of a PV system and another energy source (e.g. wind and hydro power) are progressively getting more attention (Picture 3).
Picture 3. Types of SPV System configurations
As can be seen from Table 1, each photovoltaic technology has its own benefits and intolerances to certain issues. Therefore, it is rather difficult to single out only one tech-nology as the most optimal option for any PV installation by comparing potential efficien-cies and prices. For example, despite its low efficiency, thin-film solar cell might be a feasible option if there is no space issue. The choice of suitable PV technology should be based on the site conditions and all possible issue the site might be exposed to.
Table 1. Strengths and Shortcomings of Different Photovoltaic Technologies(A. Makarova, 2017)
2.1 Solar Geometry
Even though the key parameters of solar geometry are included in a simulation model, it is critical to understand how the position of the sun might affect the performance of a PV system. The position of the sun is defined mainly by the angles illustrated in Picture 4.
Picture 4. Relative position of the Sun to a point on the surface(A. Makarova, 2017)
Solar azimuth angle, αs, is the angle between the position of the sun and the south (north-south axis).Solar elevation angle or the altitude of the sun, γs, is the angle between the horizon and the center of the disk of the sun. The altitude might be expressed through declination angle and the local altitude as following:
γs = 90 degree – declination angle +latitude, Equation (1)
where declination angle stands for the angle between the sun and the equator.
Depending on the day of the year, the value of declination angle varies within [-23.45, 23.45].
Solar zenith angle is the angle between the sun and the vertical, the zenith. Zenith angle also depends on the declination angle and the latitude.Position of the sun and rotation of the Earth define solar local time that is conventionally used in PV applications. Local solar time differs from the Coordinated Universal Time (UTC) by +/- 45 min depending on the day of the year, longitude and whether the day-light-saving shift is applied.The depth or the distance travelled by the sun beam through the atmosphere is also defined by the position of the sun. The depth in that case affects the amount of radiation to be scattered, absorbed and reflected in the atmosphere. The effective atmospheric depth gets affected by the angle between the sun beams and the ground.
2.2 PWM Solar Charge Controller
A PWM Solar Charge Controllers holds the voltage more constant. If it has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a “finish” or “trickle” charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress.The block diagram of a PWM Solar Charge Controller is shown in picture 5.
Picture 5. Block Diagram of a PWM Solar Charge Controller (A. Makarova, 2017)
The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery. The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not.
3. SYSTEM CONSIDERATION AND DESIGN CALCULATION
The point to point microwave link is designed to provide internet access for rural area using ePMP Force 180 5GHz subscriber module. The two sites are 1.45 km away from each other. GPS is used to determine the latitude and longitude of two sites location. Google Earth Pro software is used to check for line-of-sight in choosing potential terminal site locations. In this system, system consideration, design and analysis of line-of-sight microwave link and hardware implementations are to be carried out. In the analysis, path profile, Fresnel zone, link budget and other parameters are implemented using the link planner software. Our research portion to design and construct a suitable solar power system is to be considered at the receiving site which represent maximum load of 10W + 40 W Power consumption. The overall system is shown in picture 6 and the subscriber site with laptop as a load is our research portion.
Picture 6. The overall block diagram of a point to point microwave link
3.1 Design and Calculation of Solar Power System for Receiving side
For the receiving side of our project, we assigned computer laptop is to be used and therefore, we need to enlarge battery and inverter power consumption. We got the specifications that Receiving Antenna( ePMP Force 180) will consume 10 W for maximum and Laptop is normally 40 W. Consideration processes are all the same to transmission side but the data are changed.
Picture 7. Connection Diagram of Receiver Side
3.1.1. Determine Power Consumption Demands
The first step in designing a solar PV system is to find out the total power and energy consumption of all loads that need to be supplied by the solar PV system as follows:
To calculate total Watt-hours per day for each appliance used, add the Watt-hours needed for all appliances together to get the total Watt-hours per day which must be delivered to the appliances.
Total appliance use =(10Wx1hour)+(40Wx1hour)
To calculate total Watt-hours per day needed from the PV modules, multiply the total appliances Watt-hours per day times 1.3 (the energy lost in the system) to get the total Watt-hours per day which must be provided by the panels.
Total PV panels energy needed = 50 x 1.3
= 65 Wh/ day
3.1.2. Size the PV modules
Different size of PV modules will produce different amount of power. To find out the sizing of PV module, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the PV module and climate of site location. We have to consider panel generation factor which is different in each site location. For Thailand, the panel generation factor is 3.43. To determine the sizing of PV modules, calculate as follows:
Total Wp of PV panels capacity needed = 65/3.43 = 18.95Wp
To calculate the total Watt-peak rating needed for PV modules, divide the total Watt-hours per day needed from the PV modules by 3.43 to get the total Watt-peak rating needed for the PV panels needed to operate the appliances.
To calculate the number of PV panels for the system, divide the answer obtained by the rated output Watt-peak of the PV modules available
to you. Increase any fractional part of result to the next highest full number and that will be the number of PV modules required.
3.1.3. Inverter sizing
An inverter is used in the system where AC power output is needed. The input rating of the inverter should never be lower than the total watt of appliances. The inverter must have the same nominal voltage as your battery.
For stand-alone systems, the inverter must be large enough to handle the total amount of Watts you will be using at one time. The inverter size should be 25-30% bigger than total Watts of appliances. In case of appliance type is motor or compressor then inverter size should be minimum 3 times the capacity of those appliances and must be added to the inverter capacity to handle surge current during starting.
Total Watt of all appliances = 10+40 = 50 W
For safety, the inverter should be considered 25-30% bigger size.
The inverter size should be about 65 W or greater.
3.1.4. Battery sizing
The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is specifically designed for to be discharged to low energy level and rapid recharged or cycle charged and discharged day after day for years. The battery should be large enough to store sufficient energy to operate the appliances at night and cloudy days. To find out the size of battery, calculate as follows:
Total appliances use = (10 W x 1 hour) + (40 W x 1 hour)
Nominal battery voltage = 12 V
Days of autonomy = 1 days
Battery capacity(Ah) = (Total Watt-hours per dayused by appliances)/((0.85×0.6×12) x Days of autonomy)
= ([(10Wx1 hour)+(40Wx1 hour)])/(0.85×0.6×12 x 1)
= 8.169 Ah
3.1.5. Solar Charge Controller Sizing
The solar charge controller is typically rated against Amperage and Voltage capacities. Select the solar charge controller to match the voltage of PV array and batteries and then identify which type of solar charge controller is right for your application. Make sure that solar charge controller has enough capacity to handle the current from PV array.
For the series charge controller type, the sizing of controller depends on the total PV input current which is delivered to the controller and also depends on PV panel configuration (series or parallel configuration).
According to normal practice, the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array, and multiply it by 1.3;
Solar charge controller rating = Total short circuit current of PV array x 1.3.
One 10 Watt Cambium emp force 180 used 1 hours per day.
One 40 Watt Laptop used for 1 hours per day.
The system will be powered by 12 Vdc, 50 Wp PV module.
PV module specifications : Pm=10Wp
Vm = 17.8Vdc
Im = 0.57 A
Voc = 22.0 V
Isc = 0.6 A
Solar charge controller rating = (4 strings x 0.6 A) x 1.3 = 3.12 A
So, the solar charge controller should be rated 4 A at 12 V or greater.
4. TEST AND RESULTS
The Testing results are shown in Picture 8 to Picture 10 and the conclusion of receving site power system is mentioned in Table 2.
Picture 7. Flowchart of Implementing Solar Power System Design
Picture 9. (a) Two PV are in Series (b) Testing the Power System
Picture 10. Testing with PTP microwave Link subscriber
Table 2. The Design Specification of the proposed system
5. DISCUSSION AND CONCLUSION
For the main research or application of point to point microwave link, Microwave Engineering antenna and necessary parameters were deeply analyzed and determined based on the principal theories and principles about microwave propagation. Many formulas from microwave communication system principles are used to obtain all the significant parameters to be considered for the design. The design of the solar PV system for the point to point microwave link was conducted through a multi-staged criterion in order to best optimize the selection of the ratings of the main components needed by the solar PV System.The results showed promise for solar PV system. The location where the PV panel is installed in has the best solar suitability from solar designing point of view; it should be strongly considered for solar PV system as this technology becomes more affordable relative to fossil fuels.
The first author of this paper serve as a advisor of annual departmental research: Design and Implementaion of a Point to Point Microwave link with Its Solar Power System. This research paper carried out the essential power supply system and as a partially research paper, the author express only for the site of receving load condition. The full design of a Solar Power System for 70 Ah, 1000 W application was successfully done.
The authors would like to express their thanks to all the members of Board of Study of TU (Loikaw) to give permission of their Departmental Research, “ Design and Implementation of Point-to-Point Microwave Link with Its Solar Power System”, which make to carried out this research paper. Daw Nyo Nyo Khaing, Professional Engineer of Electronic Engineer is also acknowledgable for her kind consults of the main departmental reseach and specially to Design off-grid Solar Power Systems at both transmission and receiving site of PTP microwave link.