Solar Panel System for Eco Shelter in Refugee Camps

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Eco shelter Power

Contents

Aim:

Literature Review:

Type of solar system:

PV or Photovoltaic  Direct:

Batteries

Charge controller

Design charge controller

Hardware

Design Hardware:

microcontroller

Design software

Inverter:

Size the inverter:

conclusion:

References

Abstract

This report aimed to improve the life in refugee camps, by designing and building a solar panel system. In the designing stage: report research and discussed the available option in term of the choosing solar panel. Then discussed the types of batteries suitable for this project. In the implementation stage,  types of charge controller were discussed in deep details. In the final stage the hardware and software of the charge controller was illustrated with related comments.

Aim:

The big picture of project design and build solar panel system of Eco-shelter. Which is integrated with necessary appliances and keeping it with a possible minimal power consumption and send all the system information such as show life battery and efficiency of the solar panel to the main office that will be mentor all the shelters and evaluate the system if it needs to upgrade or not? This tent will allow for a beneficiary to cook, charge their phone and have LED lighting depending only on the solar energy. The system generally will be built using solar panels, batteries to conserve the power and use it at night, and converter to power most appliances that need AC and DC to work. Then coding a total monitor system which will be consisting of a monitor controller which will be monitoring the power interning charge controller, the batteries state, and the power consumers through AC inverter. Then send all the information that will be collected at the main office

War, hunger, and corruption led the refugee crisis. People are facing a long journey to find asylum with minimal stuff that only to keep them alive. According to the red cross, more than half of the world’s refugees which is about 60 percent come only from five countries. A scary percentage of missing children which can lead this crisis to create other serious problems such as human trafficking. Besides that, This creates a growing economic problem for any government received huge numbers of refugees or even for any third world government that its citizens suffer from poverty with no electricity and infrastructures. For these reasons the shelter help to reduce death rate because of hunger by offers, the basics need to live decent live such as oven and light. The security system could save women and Childs from getting abused or kidnapping. To raise awareness society about this problem and show them they are real web build to give a public a general view of the camp. The whole project builds and design to be environmentally friendly with the minimal cost possible based solar panel and batteries reading.

Objective :

  • Economical system
  • Apply basic appliance
  • Read solar voltage
  • Read battery voltage
  • Measure temperature

Literature Review:

Renewable energy one of debatable abundant resource that earth has.  Solar generated electricity by using technology field test and improved upon since 19th century when contest notice that there is specific material able to produce electric current. To have this effect, two layers of some conductors joined.one of them carry some electrons when the sunlight hit the layer absorb the photons. This process effect electron leads it moving from layer to other and that what produces an electrical charge. On another word,  When the sun hit the modules on solar photovoltaic installation, the module converts the solar energy into electricity that can be used. Where the electricity is being drawn from PV installation home power performance will stay the same.

Type of solar system:

PV or Photovoltaic  Direct:

It considers the simplest type of the. The PV-direct system can make it of as few as two components, solar panel, and the device powered, such as pump or fan connecting directly to each other. Often there is a controller or linear current booster between the tow and some fuse no more than that. It is very basic; power produced when the sun shines then PV generates electricity, and as much as the sun is bright the panel produced more power which leads to increase the performance of the appliances. However, the device stops when the sun not available. The key of this system is a straightforward where the solar makes the power and device consume what it can have when the sun is bright, and the panel is making more power which leads the performance of the device will be great than when it is overcast, early morning or late afternoon. The key is to use the power when it has it and not need it when the sun is not available. As an example pump, it will be plumbing to a tank or cistern during the day, allowing to use the water all day and night without having to utilize batteries it is easy to store water or power (“Introduction to Solar Electric Systems – calendar,” 2017)

Aladdin Solar, 2017)

Advantages:

  • DC device {Pump or Fan}
  • Run when sun shining
  • Grid-tied  :
  • The most residential system these days are grid-tied.  The electricity has to be available to a utility company. This system required only solar, GTI Grid tie inverter and meter as in the figure.  It simply generates the power from the solar panel during the day then convert it to AC then use directly from home. If it generates extra power, it will save it back to grid as credit so when it has no enough power or there is no sun, could use this credit to buy power.  The meter is optional, to track electrical consumption.

Advantages:

  • No need batteries
  • Able to save more money with meter

(Grid-tied system, n.d.)

  • Off grid

It good options who want to use electricity at the time it required. Off grid system is content battery bank to, charge controller and inverter if there AC devices. Unlike Grid tie no need utility grid, so it does not have electric bills. When the sun generates the power, it charges the batteries which allow using electricity when at night or when no sun and because of that this project build based on off grid system. (“Off Grid Solar Systems Shop Solar,” n.d.)

(“Off Grid Solar Systems Shop Solar,” n.d.)

Type of solar panel

There are three basic type’s

Type Characteristic

(type of solar panel, 2017)

  • Made by polycrystalline
  • It called multi-crystal
  • Less expensive
  • Less efficient around 16%
  • Good performance at high temperature
  • Performance drop when sunlight is low
  • Need small area to give power

(type of solar panel, 2017)

  • Made by monocrystalline
  • Great efficient around 15% -20%
  • Quite expensive
  • Good performance at normal temperature
  • Performance drop when sunlight is low
  • need a small area to give power

(type of solar panel, 2017)

  • Not crystal it made from thin layer of silicon
  • Cheapest
  • Lowest efficiency around 12%
  • Good performance at high temperature
  •  Need large area to give power
  • Performance slightly effected in low sunlight

(Lombaedi, 2012)

Batteries

To save the energy from the solar panel batteries are used. It stores it to use it later when there is no energy in solar panels. One of the keys to this project it allows users to have appliances when there is no sun. There was a variety of options when it related to batteries it comes different size with different price depends on what the system requires.  It usually comes as 6 or 12 volts but still there other value of voltage. If it uses more than one, it could be connected in series to raise the voltage or parallel to increase the capacity without change voltage. To find the capacity it measured in amp per hour. This measurement to find how many times the battery needs to be empty. Since it is solar system deep-cycle which is different from care batteries. Even though it works if used car batteries but it the batteries will die quickly. There are four basic type of batteries which could use in solar system

  • Marine or Golf chart: it is one of the deep cycle types. It used on boats and a good option for low cost in the small system. Possibly could last around seven years
  • Flooded type: it type of lead acid that need to add water. There are many manufacturers made this particular type such as Trojan. It has a reasonable price since it last long time. Not recommended to use it indoor through charging because it produces gas which could lead to an explosion.
  • Gel:   it sealed type, and it does not produce hydrogen gas. Lastly, It improves it in lifespan and become much batter so that it could compare it with AGM., also, the price reduction.
  • AGM: it higher quality type of sealed types.  As Gel it not makes gas when it is charging and has good performance. Also, it has a long life, slow self-discharge but it more expensive.

(Lombaedi, 2012) (O’Connor, 2016)

Although lead acid most commonly in the off-grid system but the difference between lithium-ion battery make it a debatable options. It seems lithium ion excelled in many points despite it has been standard for extended time. From disparity between lead acid and lithium:

  • Size and Wight:


(O’Connor, 2016)

Lithium is much lighter from most of the type of batteries.  From the figure above it  approve lithium-ion about half the volume and third of the Wight


  • Superior Resilience:

In general, most of battery’s get an effect from over discharge and high temperature.  Lead acid one

(O’Connor, 2016)

Of this type where cannot handle this efficacy and could badly damage if there dramatic drop. From the figure above it is clear that lithium -ion able to discharge much more than lead acid with without causing any damage. On the other hand, when lead acid is discharged below 50%, It going to misplace potential cycles. From the table below it shows brief difference between them. One of the target goal it to keep project economical as result lead acid was select Despite the advantages of lithium ion batteries. (O’Connor, 2016) (Blooomfied & Robert, 2016)

Lithium-ion Batteries Lead Acid Batteries
  • Expansive
  • Light
  • Efficient
  • Longer life time
  • Fast recharge
  • Cheaper
  • Heavy and large
  • Less Efficient
  • Short life time when it compares it with lithium.

(Boxwell, 2013) (Lombaedi, 2012) (O’Connor, 2016)

Calculation size panels and the batteries. These calculation based on two company Alte and specialist on renewable energy selling product related to renewable energy. They  Allow buyer check the size of the system to know what exactly looking for and how it is going cost. The battery used in this system is 12V.

  • First list the appliances that need to use then to find

total = Quantity × Power used × Hours used in day

Appliances/ Loads Quantity Power used Hours used in day Total
Bulb 2 3 3 18
phone charger 1 5 1 5
Microwave 1 600 0.5 300
Total power pear hour Wh 323
  • Second, to find the size the battery by taking total power per hour needs to. Watt hours that need daily = 323 Wh
  • Days without the sun or that expect to be cloudy because in these days panel cannot produce power, so batteries need to enough power to feed the loads. More day select the batteries will be expensive.
  • Assuming it is three days
  • The depth of the discharge %. As much discharge before recharging the batteries dead faster. If the depth around 20% it will stay longer, but it is going to need great battery size it only uses less than quarter. As a result, 50% is best commune percentage sizing guide.
  • Temperature multiplier, cooling weather have bad on the capacity of batteries bank. It is better to keep it indoors especially in winter as an option. Refugees that target on Europe may face problem to installing the system what is about batteries position. From the figure equivalent value that the temperature expected. As result of high percentage of refugees that target Europe, the temperature will be around -1.1 °C.

(Rimstar.org, 2017)

From that information, battery bank could be found by

=

Avr daily Watt × Days without sun× Temperature multiplier Depth of discharge

=

323t × 3× 1.4 0.5  = 2713.2 WH

  • System voltage if the system 12V

The capacity what need in the battery  =

Battery bank  battry  volrage  =

2713.2 WH  12V  = 266 AHr as minimum.

a a   To reach this value and there is no exactly 266 Ahr  it going to need four batteries 6V 150AH Connect  two of them in series to have double voltage  and  other two in parallel to reach 300AH since it double the capacity as in figure


(Noonan, 2004)

Since the battery bank capacity is known the size, the solar panel can be calculated  in two-way first by:

First method:

  • Daily watt hour= 323

  • Worst case peak sun: it differs percentage of brightness or full sunshine of the sun each continent.  It counts on how it is near from the equator which affects the amount of energy in the solar panel. From the map in the figure. If Europe is the targeting worst case peak will around 1.9 h

(map of the amount of solar energy in her, n.d.)

  • Indeed to add around 71% factored as approximate the inefficiencies in solar panel system. It shows what it needs for the power system to have enough electricity to counterbalance in annual consumption.  (Kinnea, 2016)

Size solar panel it needs =  daily watt-hour  ÷ worst case peak sun  ÷ efficiency =

=   323wh ÷ 1.9h ÷ 0.7 = 243 W at least  it need

Second method:

It relates to the specific size of the solar panel. If it wants 80 w from the data sheet of solar panel

Description

80W-12V poly 840×670×35mm

Net weight Electrical data under STC
Nominal

Power

Max-power

Voltage

Max power

Current

Open circuit

Voltage

Short circuit

Current

Pump Vmpp Imp Voc Isc
KG W V A V A
6.8 80 18 4.44 21.6 5

Daily watt hour = 323

Solar array voltage = 12V, the cost of the wires depends on the thickness of the wires which could be effected from the current from the solar array. It is cheap as much as it thin.

Daily  =

daily watt houer solar array voltage

=

323Wh 12V= 26.9 amp h/day

Approximation number of hours that the sun will be full shining =2h/ day

I in worst case sunshine =

26.9 amp h/day2h  = 13.5 amp

Parallel strings that may need:

=

IIsc=

13.5 amp5  amp= 3 parallel string

Series l strings that may need:

=

Volt of solar array Solar Panel Maximum power voltage=

12 18=  0.6 which mean no series string.

So it needs three panels connect it in parallel with the same wattage. The Three are going to be connected in parallel as in figure positive terminals together and negative together while in series each different sign together. In parallel the total voltage not change while the power reaches what is a need to handle appliances usage which is around 240 Wat least so with value 3× 80w = 240 w. while in series it is going to add to together then to get high voltage. It is a good option if need to the high input voltage.

(solar panel connection, 2017)

Solar Panel Maximum power current = 5 amp

Solar Panel Maximum power voltage  = 18 V

Charge controller

The main purpose of using charge controller I control the battery and make sure it is on healthy because of overcharge and discharge quick damage the battery. As result of this process, it allows the battery live longer. On other word charge controller, able to control the battery charging in the same time control charge drop in the load. The way charge control work is it monitors the battery if it has enough charge or kept charge from solar.  Where the battery reaches to full to stop the process, it cut charging from solar power when there is no power from solar. It runs the load. There is two different type of charge controller MPPT and PWM. Both of them commonly used on off grid system and have excellent efficiency. (Boxwell, 2013)

MPPT: from the curve, it shows the relation between voltage and current that generates from the panel. The best possible current rate to voltage to produce maximum power point. In this stage, it will change depended condition.

  • Pross:
  1. High efficiency special in cool weather
  2. Aloe to oversize array
  • Cons :
  1. Double size PWM
  2. Short lifespan with many electronic devices

(MPPT carve, n.d.)

PWM: it allows current flow from the panel to the battery until it reaches max voltage for charge stage after that the charge controller will turn off quickly between the panel and battery.

  • Pros :
  1. Around half the price of MPPT
  2. Long lifespan because of less thermal stress
  3. Small size
  • Cons :
  1. Sensitive when it related to size panels and battery bank
  2. Can not use it with 60 cell panel

Design charge controller

Hardware

The basic PWM Circuit is two switches one for the battery and the other for the load.  There are many several types of transistors, and each type has their characteristics based on that it has advantages and disadvantages depends on for what using it.

Certain kinds of transistors are used mainly for switching some application. Other transistors utilized as switching and amplification. Also, there are other transistors have a special characteristic such as phototransistor which depends on light to produce current. It looks like a bipolar transistor. It has only two terminals as result of remove base and replaces it with the light sensitive area, so it off when the surface covered or kept dark arising from no current flow from collector to emitter.

  • Type of Transistors

The main two types of the transistor are Bipolar junction ( BJT) transistors and Field effect (FET) transistors. Transistor FET has two type JEFT and MOSFET As shown in the figure.

The Field Effect transistor (FET)

Metal Oxide Semiconductor

(MOSFET)

Junction FET (JFET)

Depletion Mode

Enhancement mode

Depletion mode

N-Channel

P-Channel

P-Channel

N-Channel

P-Channel

N-Channel

-JFET

Junction field effect transistor is the first type of field effect transistor which developed before MOSFET usually used as voltage control resistance. It has two type P-type (hole), and N-type (electrons) channel and both operate in the same way but the difference on the direction of current flow and polarity of bias. The construction of JEFT small piece of Silicon dioxide which is the gate, in the end, is Source, and the other end is Drain. Beneath the gate depletion layer which creates a channel.

(JEFT, 2017)

From the figure, it is shown that is there is a direct connection between drain and source. Depletion layer controlled the amount of current that flows in a channel by raise or decrease the thickness of the layer.

When Gate- source voltage VGS = 0

Voltage drain-source VDS  controlled the amount of current flow from source to drain. From figure VDS=0.6V it observed depletion layer thin and normally by increasing value of VDS can result in increased value of current. JEFT act as a voltage-controlled resistor when the value of VDS below then pinched-off Vp and called Ohmic region. However, when VDS equal or greater than Vp which is saturation or active region JEFT become a good conductor. By raising the number of VDS   could cause increase thickness of depletion layer without stop current flow.

(JEFT Mode, n.d.)

When Gate- source voltage VGS = maximum

Drain current getting decrease as result of increasing VGS as a consequence of the depletion layer thickness completely blocks conduction channel causing no current flow through the channel. This result called to cut off region and JEFT act like an open circuit. The p channel JFET characteristic is the same except by raising positive voltage Gate-Source, the drain current decreases.

MOSFET:

Metal Oxide Semiconductor or IGFET contraction distinct from JEFT. Both type enhancement and depletion the gate has insulator very thin layer Metal Oxide which is electrically insulated P or N channel from the figure. However, it could easily be damaged as result of a build up a significant amount of static charge caused by of high input resistance. It acts like voltage controller resistor as JFET when current flow from drain to source through the channel.

(MOSFET, n.d.)

Depletion-mode and Enhancement-mode:

Unlike Enhancement modeless commonly used. When VGS = 0V make it normally closed as in JEFT is still allow to current flow see figure, so it requires to voltage to turn it off, therefore, to avoid that Enhancement Mode improved. In Enhancement, the transistor is OFF when there is no voltage Gate-Source and require VGS to turn it ON which is equivalent to Normally Open switch.


:

(Dpleation and Enhancment Mode, 2017)

From the table, it can be summarise switching of MOSFET and JFET. As result of construction depletion mode MOSFET like JEFT, the switches work in same way.

Type VGS= +V VGS  = 0 V VGS=  -V

MOSFET

N-Channel     Depletion Mode ON ON OFF
P-Channel OFF ON ON
N-Channel Enhancement Mode ON OFF OFF
P-Channel OFF OFF ON

JFET

N-Channel Depletion Mode ON ON OFF
P-Channel OFF ON ON

MOSFET vs. JFET

Though both transistors MOSFET and JFET essentially not the same composition, they both are under field effect transistor and reach almost same function. Both of them act as a voltage controlled transistor. Also, they have a small gain, in contrast, bipolar junction transistor, which is preferred when it related to amplifier application because it could give rise to the reduced value of gain. For this reason, in the simple amplifier circuit, neither MOSFET nor JFET  is often used. When it comes to the input impedance JEFT is less than MOSFET. On the other hand input impedance on the MOSFET, about 100,000 times more resistive compares it with JFET which around 1014 Ω

Comparison

                                                    JFET-MOSFET
Operation Voltage controlled
Gain Low gain
Input impedance Only Depletion type. Less input compare it with MOSFET usually around 109 Ω Depletion type or Enhancement type. More than JFET about   1014 Ω
Price Cheap because it is less complicated manufacturing expensive comparing with the JFET
Gate formed As diode As capacitor
Vulnerability to damage Since it has great input capacitance, vulnerability to damage from electrostatic discharge (EDS) less than MOSFET Capacitance is lower as result of metal oxide that caused to isolate gate from drain-source. This lead to high voltage which able to break through and vulnerability to damage is significant
Common used Less popularity  Widely used today

BJT:

The Bipolar Junction transistor is made up of two PN junction creating three terminals which are base, collector, and the emitter. This type of transistors differ from FET transistors which are current regulation devices, and it is the only kind which could turn it on be current input owing to lowest input resistance that BJTs have compared to other transistors. However, it has the greatest amplification as result of the low resistance. It controls the current moving into base (b)  region effect amount of electrons attracted from the emitter, so small changes in Ib current could create significant changes in current flow between emitter, collector region. From the figure, when voltage Vbe reaches 0.7 V the depletion layer of base-emitter reduce, and as result of high voltage Vce wich close to the base, current flow across common- base depletion layer. It has two types NPN and PNP work working the same but the only difference polarity of each type and in their biasing. As in FET BJT has three terminal active devices. By application of small signal voltage, it able to either insulation or conduction. It has two fundamental functions for digital electronics as a switch or analog electronics as an amplifier.  (Lazaridis, & Upton, 2016)  Like FET it able to operate in three regions:

BJT Operation

  • Active region:

Transistor act as amplifier

  • Saturation region:

Transistor act as switch, and it is fully ON

  • Cut-off:

Transistor act as switch, and it is fully ON

.

(“Bipolar Transistor Animation”, 2017)

When it related to the power transistors, electronic design engineers prefer power MOSFTs over power BJT because of the advantages of power MOSFETs. It is easier to provide constant voltage than a steady current since MOSFET is voltage controlled device gate drive circuit less complex than BJTs base drive. Another good point in MOSFETs that parallel operation is easier than BJTs because it has positive temperature coefficient for resistance while negative temperature and during parallel operation current sharing resistor is required. Lastly, MOSFETs can switch much faster than BJTs

From the table, can summarize the difference between BJTs and MOSFTs:

BJT MOSFET
Type Minority carrier device Majority carrier device
Controlling  By Base By Gate
Controlling device  Current Voltage
Temperature coefficient Negative Positive
Paralleling  Difficult Simple
Losses  Low High
Drive circuit Complex Simple
Frequency of switching  Low High

Design Hardware:

There is a variety of MOSFET type depends on the project required. Since the MOSFET that used in this project controlled by Arduino and the output of the Arduino 5V, most have gate threshold voltage VGS(the) range to 5V.  For example IRF530 and IRF9540N:

From data sheet

IRF530

Static Test condition MIN Type Max Unit
Gate source gate threshold voltage VDS  = VGS  , ID  = 250µA 2.0 _ 4.0 V

IRF9540N

Static Test condition MIN Type Max Unit
Gate source gate threshold voltage VDS  = VGS  , ID  = – 250µA -2.0 _ -4.0 V

Two switches require one to manage power flow from the solar panel and the second to control power drop into the battery then to the load. NPN BJT general purpose used as a driver the purpose of using MOSFET driver is the ability to allow low input power that comes from the controller and makes it to high current drive input. To protect the circuit from reverse current and polarity power that may happen when panel = 0V while full battery charge,  power diode used because of ability to hold the large value of current. Over voltage happened for many reasons and one of them lighting which could very bad over voltage. It anticipates on PV system as result connection cables, so TVS diode used to protect from lighting.  Since 80w solar panel have short circuit current = 5 amp by multiply 125% To select right value of fuse = 5 ×1.25 = 6 amp as minimum. As recommendation adds around 10 amp in case, need to upgrade the system.

How is work:

From the schematic the power flow from the panel terminal to TVS and power diode it will control over voltage. Then voltage divider one will measure voltage come from panels the output connect to Arduino Analog pin 0. Despite that, the power flow will not be able to flow through battery until switch one ON. BJT transistor 1 is a driver for most one whit R3 which connect to Digital    Arduino pin three while R4 to push up for the gate. If the switch one ON battery will start to charge. Next second voltage divider to measure Battery voltage and connect to Arduino Analog pin 1. After that switch 2 to drive the load and BJT 2 as BJT 1  is the driver to the MOSFET-Only in night loads automatically ON while switch 2 ON which mean battery fully charge or healthy and load turn off automatically if the battery run out depends on the specific value of the software.  The first step first switch build the by using oscilloscope  and two power supply used one as 12V second 5V as microcontroller

it is on when 5V on it turn it off when 5V = 0V since it successfully work next step build the same switch and connect When it both of them ON  load ON  when one of them OFF load OFF.



Then build it on another breadboard because of this type of breadboard can not handle high current. The new board can handle around 3 amp, so the 2.5 amp fuses use as a testing stage.


Heatsink:

Thermal resistance is equal difference temperature between two point divide power dissipation across the device

Thermal resistance state is resistance for heat to be transferred through medium it could quantify that regarding the difference between temperatures in two pins divided by the power dissipated the amount of the power generating that heat measured in degree C per watt

ϴ =

T1-T2 PD= °C / W


In the way that can model this regarding the resistances for heat transfer is we can model this in three resistors in series. Their resistance from junction to case, from case to sink and from sink to ambient as in figure

(electronics believed, 2017)

ϴJC

ϴSA

ϴCS

T junction

T Heatsink

T Ambient

TCase  

So from the figure the total thermal resistance

ϴJA =  ϴJC + ϴCS + ϴSA 

From the equation

ϴJA =

TJ- TA PD

So there two definitions of ϴJA resistance one beside on definition of thermal resistance and other beside on fact that can model the system as series of thermal resistances

From the data sheet of IRF9540N

Absolute maximum ratings:

Parameter Max. Units
TJ Operating Junction 175 °C

Thermal performance:

Parameter Type Max. Units
ϴJC Junction to case 1.1 °C / W
ϴCS Case to sink
ϴJA Junction to Ambient 62

Without heat sink:

When it is testing the maximum current could drive 2.5 amp because the bread board cant handles more than that. If  it assumes in worst case that current = 2.5amp  power drive equal

PD = I2 D × RDS 

=2. 52× 0.117 = 0.7 w

And maximum power dissipation of the mosfet  with out heat sink:

PD=

TJ- TA ϴJA

TA In worst case = 30 °C

=

175 °C-30 °C62   = 2.3 W

So it saves to test it without heat sink

If assume it is using solar panel 80 W maximum options with current I= 5 A from the datasheet.

So Power dissipated In the MOSFET is:

PD = I2 D × RDS

= 52A × 0.117Ω  = 4.4 W

ϴJA = ϴJC + ϴCS + ϴSA 

TJ-TA = ( ϴJC + ϴCS + ϴSA  ) x PD 

TJ=  ϴJA × PD + TA

=  62 °C/w  × 4.4W + 30°C =302.8

°C   Too hot could damage transistor

So need a heatsink to cool the Mosfet. To fine

ϴJA = ϴJC + ϴCS + ϴSA 

TJ-TA = ( ϴJC CS + ϴSA  ) x PD 

ϴSA =

TJ-TA PD  − ϴJC + ϴCS

           =

175°C-30°C4.4W– 1.1

°C+ 0.5

°C= 32.32

°C/W

From this result show that the maximum thermal resistance of heat sink with junction temperature = 175°C and need heatsink below the result. The specification heatsink that used in this project according to the data sheet

  • For use with          TO-220
  • Length                                50.8mm
  • Width                                  42mm
  • Hight                                  25mm
  • Thermal Resistance         14 °C /W
  • Mounting                          clip

To be more sure about selection of this heat sink by finding junction temperature after using heatsink by  thermal resistance of heat sink :

TJ−TA = ( ϴJC CS + ϴSA  ) x PD 

TJ = ( ϴJC CS + ϴSA  ) x PD  + TA

= (1.1 °C /W +0.5 °C /W +14 °C /W) x 4.4 W + 30°C = 98.6 °C

So the heatsink  will reduce the  junction temperature when compare it without heatsink.

(“sizing a heat sin for heavy load”, 2012) (Edmunds, n.d.)

microcontroller:

A microcontroller is a potent tool because of the ability to engineers to create special purpose design. Also, it is flexible due to the capability make designs partially software and other hardware. Currently; the world almost depends on microcontrollers. It is a small computer in signal integrated circuit, often used in automatically to controlled devices and products for example in power tool, engine control system and medical devices. There are multiple types of microcontrollers, and each of them has different features and price. Despite that, most of them could give the same result. There is three type which is most commonly used to control PWM, Microchip PIC, Arduino, and Raspberry PI. Pic it more excellent and power usually use for the educational purpose it expensive compares it with other   Arduino is open source which most commonly used, it is development platform with it is own and free to download (IDE) integrated development environment. It makes it for hopes, and it is easy to reach sources and no need to take study. On the other hand, Raspberry PI general purpose computer and slightly complex application but when it needs sensor Arduino or Pic performance better.

Arduino  Raspberry PI
Price  Around £36  Around £ 46
Size 7.6 x 1.9 x6.4 cm 8.6 cm x 5.4cm x 1.7cm
Memory 0.002M 512MB
Clock speed 16MHz 700 MHz
Multitasking No  Yes
Operation system Noun Linux distribution
IDE Arduino IDLE, anything with Linux support

            Design software

Sensores are going to read data from the analogue pin on Arduino board. Which meant going to limit the input voltage between 0-5 V into an intgare value between 0 to 1023. It takes around 0.0001s to read that input.

Voltage sensors by using voltage divider

  • 5V= ADC count 1024
  • 1 ADC count = (

    4.841024) = 4.726m

  • R1  =100KΩ,    R2 = 20K Ω
  • Vout   = VIn 

    R2      R1+ R2

  • VIN   = Vout ×

    R1+ R2 R2

  • VIN   = Vout ×

    R1+ R2 R2

  • VIN   = ADC count 0.004726×

    100K+20K20K    what analogue pin going to read

Current sensor ACS712

Sensitivity 100mV = 0.1V/A from the data sheet

Current Rating ACS712ELC-05A ACS712ELC-20A ACS712ELC-30A
Scale Factor 185 mV per Amp 100 mV per Amp 66 mV per Amp
  • Vsensor_base=Vcc2=4.842=2.42

Assuming that IC is getting Vcc exactly equal to 4.84. A slight change of Vcc will have huge impact on the calculations

  • Vsensor_out=Vcc2+ sensitivity*I=4.842+ 0.1I=2.42+(sensitivity*I)- Base value at 0Amps
  •  controller input

VIN=ADCcount 0.004726

  • Controller input should be equal to sensor output:

VADC= Vsensorout

I

DCcount* 0.004726= 2.42+sensitivity*I

  I =

(ADCcount* 0.004726)-2.42sensitivity

I =

(ADCcount* 0.004726)0.1- 24.2=

ADCcount* 0.04726- 24.2

Temperature:

From the data sheet of LM35

Sensitivity = 10 mV/°C

Temp in C  =

4.81024× ADC count  × 100   analog pin going to read

Battery charge stages:

Each different type of batters have different charge stage, the figure below is for the lead iced battery since project test it on it. The bright of the sunlight could damage the batteries when it produces voltage bigger than batteries. In general lead acid charge range from simple to complex but it has three main stages of charging

(charging stage, n.d.)

Bulk, Absorption, and Float. In bulk, the stage is around 80% of the recharge during this stage charger keep current constant in contrast voltage that gets increased. Where ever current is applied at this stage it should not use the battery over around 125 degrees Fahrenheit if it flooded battery or 100 degrees Fahrenheit if it AGM battery. Second stage absorption as can seen from the graph where it holds voltage but the current decrease in this stage reaming 20% of the charge. Last stage float, it is not charging the battery as it maintains it.  Charge voltage reduces around 13V to 13.8V. And only about 1% of the current it used. (Bell, 2014)

How is work:

First of all, Arduino going to measure solar panel voltage then check it with battery voltage.

If the value of solar panel great than a battery, it will keep sending width pule modulation to switch 1 to keep charge battery to charge the battery until it becomes greater than solar panel value then it will not send any signals. If the battery voltage becomes around 14.3V, it means it in bulk stage and fully charges. Also, create a function to protect the circuit when the battery reaches low stage it going disconnect the load.

Inverter:

The primary role of power inverters in PV system is to convert the DC { direct current ) power from the batteries bank or another source of energy usually 12V into 120V AC  at 60 Hz also known as a DC-AC inverter. It is available in many different selections, price and efficiency depend on the purpose.

Oscillator circuit used by series of steps to reach inversion. The way inverter work that DC circuit flow with an electromagnet to the end of the circuit. Then, current hit the magnet caused activation to the magnet. As result of that current direction would change to the opposit side cutting power. Input values for DC-AC could be 12V, 24V, 48V, 110V, 125V, and 250V. From the figure, there is three major output generated forms of AC square wave, modified sine wave, and pure sine wave. The square wave is the very standard type and used to run simple appliances. However, it is seldom used because the limiting of equipment that fit and the noise it causes. (“DC-AC Inverters Information | Engineering360”, n.d.)

(theory circuit, n.d.)

Modified sine wave or sometimes called Quasi-sine waveforms nearly like a square wave, but it has stepping forms. It is most popular and economical when compare it with pure sine wave, it works good with most equipment, even though the efficiency could decrease with some equipment like pumps or refrigerator motor as a consequence it needs more power from inverter due to that decrease. The brightness of florescent lights will be slightly less more than supposed to be and may cause a buzz or annoying noise. Also, any device with an electronic timer will not work accurately. Some items will not work at all such as light dimmers. In general, this type of inverter would only recommend for a small system. (“Inverter Basics and Selecting the Right Model,” n.d.)

On the other hand, Pure sine waveforms output exactly that same to the power coming out from the electrical socket.  In contrast modified sine wave that may damage most sensitive device such as digital clock and laptop computer, it able to run all appliances on the market because it designed for a sine wave. Beside that it reduces humming noise in some devices and because of low harmonic distortion performance of some device like motor will be faster and quieter. However, it is very expensive pure sine wave is more appropriate in this system since microwave is one of the appliances and will only produce full output in this inverter. (Doucet, Eggleston & Shaw, 2007)  (“DC-AC Inverters Information | Engineering360”, n.d.)

Pros

Cons

 Modified sine wave Pure sine wave
  • Not expensive
  • Good for simple system
  • Recommended for off grid system
  • Work with most devices
  • More efficiency
  • Not good with digital clocks
  • Less efficiency
  • high THD
  • Very expensive

Size the inverter:

After calculation loads which use daily then found battery capacity and from that size of the solar panel are find. At almost done to complete the design of solar panel system. To calculate size, the inverter has to add all AC watts sine the only microwave is AC watt which equals 600W. For that, the inverter can handle at least 600W with the consideration that price. From Amazon

conclusion:

Echo shelter builds based on grade system since it allows to use appliances at night and that exactly what project target. To give refugees life with basic daily need. To make this shelter economical Polycrystalline panel select because it it has good price compare it with monocrystalline. With same reason with lead acid. To control swatches, PWM has performance. To improve the project is replace voltage regulator with buck converter for more efficiency. Replace the LCD with TFT LCD so it can display colorful image. Also, add a light sensor on LCD, so it will turn off when it does not use it to save more power. For better power generate from panels add a solar tracker. Create three LED for solar, battery and loads, so when the solar connect it will turn green and when it off turn red. Battery LED will turn green if the battery charge healthy if it fully charges it turns to blue and when discharge it turns to red. Lastly, if the load is connect led will turn green if it red it is mean no connect. These led will help the users to easy figure out the problem it there is any.

References

Reference:

(Esquenazi, & R. Barron, 2015)

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