Solar Power System Design for a Transmitter of Point to Point Microwave Link

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Published on International Journal of Engineering & Industry
Publication Date: September, 2019

San San Thwe, Theingi Linn & Wai Phyo Aung
Lecturer,M.E(EC), Electronic Engineering Department, TU(Loikaw)
Assistant Lecturer, Electronic Engineering Department, TU(Loikaw)
Prof. and HOD, Electronic Engineering Department, TU(Loikaw)
Loikaw, Kayah State, Myanmar

Journal Full Text PDF: Solar Power System Design for a Transmitter of Point to Point Microwave Link.

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 9 W of TP Link Router 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.

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)

Table 1. Strengths and Shortcomings of Different Photovoltaic Technologies(A. Makarova, 2017)

2.1. PWM Solar Charge Controller
A PWM solar charge controller stands for “Pulse Width Modulation”. These operate by making a connection directly from the solar array to the battery bank. During bulk charging, when there is a continuous connection from the array to the battery bank, the array output voltage is ‘pulled down’ to the battery voltage. As the battery charges, the voltage of the battery rises, so the voltage output of the solar panel rises as well, using more of the solar power as it charges. As a result, you need to make sure you match the nominal voltage of the solar array with the voltage of the battery bank. *Note that when we refer to a 12V solar panel, that means a panel that is designed to work with a 12V battery. The actual voltage of a 12V solar panel, when connected to a load, is close to 17.8 Vmp (Volts at maximum power). This is because a higher voltage source is required to charge a battery. If the battery and solar panel both started at the same voltage, the battery would not charge.
A 12V solar panel can charge a 12V battery. A 24V solar panel or solar array (two 12V panels wired in series) is needed for a 24V battery bank, and 48V array is needed for 48V bank. If you try to charge a 12V battery with a 24V solar panel, you will be throwing over half of the panel’s power away. If you try to charge a 24V battery bank with a 12V solar panel, you will be throwing away 100% of the panel’s potential, and may actually drain the battery as well.

Picture 3. 12V Solar Panel with PWM Charge Controller charging a low 12V battery

2.2 MPPT Solar Charge Controller
An MPPT solar charge controller stands for “Maximum Power Point Tracking”. It will measure the Vmp voltage of the panel, and down-converts the PV voltage to the battery voltage. Because power into the charge controller equals power out of the charge controller, when the voltage is dropped to match the battery bank, the current is raised, so you are using more of the available power from the panel. You can use a higher voltage solar array than battery, like the 60 cell nominal 20V grid-tie solar panels that are more readily available. With a 20V solar panel, we can charge a 12V battery bank, or two in series can charge up to a 24V battery bank, and three in series can charge up to a 48V battery bank. This opens up a whole wide range of solar panels that now can be used for your off-grid solar system.

Picture 4.12V Solar Panel with MPPT Charge Controller charging a low 12Vbattery
2.3 The Key Features of a Solar Charge Controller
• Multistage charging of battery bank – changes the amount of power set to the batteries based on its charge level, for healthier batteries.
• Reverse current protection – stops the solar panels from draining the batteries at night when there is no power coming from the solar panels.
• Low voltage disconnect – turns off attached load when battery is low and turns it back on when the battery is charged back up.
• Lighting control – turns attached light on and off based on dusk and dawn. Many controllers are configurable, allowing settings for a few hours or all night, or somewhere in between.
• Display- may show voltage of battery bank, state of charge, amps coming in from solar panel.

2.4. 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.

Picture 5.Block diagram of photovoltaic System

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 transmission site which represent maximum load of 10W + 9 W Power consumption. The overall system is shown in picture 6 and the Access Point site with TP link router 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 Transmitter Site
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 TP link router is normally 9 W. Consideration processes are all the same to transmission side but the data are changed.

Picture 7. Connection Diagram of Transmission Site Solar Power System

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)+(9Wx1hour)
= 19Wh/day
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 = 19 x 1.3
= 24.7 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:

3.1.3 Total Wp of PV panel capacity needed = 19 / 3.43
= 7.2 Wp

3.1.4 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.

3.1.5 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.

3.1.6. 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.
For grid tie systems or grid connected systems, the input rating of the inverter should be same as PV array rating to allow for safe and efficient operation.
Total Watt of all appliances = 10+9 = 19 W
For safety, the inverter should be considered 25-30% bigger size.
The inverter size should be about 24.7 W or greater

3.1.7. 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) + (9 W x 1 hour)
Nominal battery voltage = 12 V
Days of autonomy = 1 days
Battery Capacity (Ah) = (Total Watt-hours per day used by appliances x Days of autonomy)/
(0.85 x 0.6 x nominal battery voltage)
Battery capacity = ([(10 W x 1 hour) + (9 W x 1 hour)] x 1)/(0.85 x 0.6 x 12)= 3.1 Ah

3.2 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 9 Watt TP Link Router used for 1 hours per day.
The system will be powered by 12 Vdc, 19 Wp PV module.
PV module specifications :
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.

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 8. (a) Two PV are in Series (b) Earthing

Picture 9. Flowchart of Implementing Solar Power System Design

Picture 10. Testing with Transmitter of PTP microwave Link

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 20 Ah, 300 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.