DESIGN AND IMPLEMENTATION OF A SOLAR ...

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

DESIGN AND IMPLEMENTATION OF A SOLAR CHARGE CONTROLLER WITH VARIABLE OUTPUT. Osaretin C.A.1 and Edeko F.O.2 1,2,

Department of Electrical/Electronic Engineering,

Faculty of Engineering, University of Benin, Benin City. Nigeria. [email protected] , [email protected] ABSTRACT The aim of this project is to design and construct a solar charge controller, using mostly discrete components. The charge controller varies its output to a step of 12V; for a battery of 200Ah rating. The design consists of four stages which include current booster, battery level indicator, battery charge controller and power supply unit. The designed system is very functional, durable, economical, and realisable using locally sourced and affordable components. This work is a prototype of a commercial solar charge controller with protection systems that will prevent damages to the battery associated with unregulated charging and discharging mechanisms. Keywords: indicator, protection, discrete.

booster,

controller,

1.0INTRODUCTION Photovoltaic solar systems can be divided into two basic categories – grid connected and offgrid (also called stand alone or isolated) solar systems. The grid connected systems feed the electricity produced by solar panels to the grid using an inverter. When the electricity is needed during night or periods with little sunlight, the energy is taken back from the grid. In isolated systems, the excess electricity is usually stored in batteries during the day and batteries are used to power the appliances in times when photovoltaic panels do not produce enough energy. Solar regulators (also known as charge controllers) play an important role in isolated solar systems [Korenčiak et al, 2011]. Their goal is to ensure the batteries are working optimally, mainly to prevent overcharging (by disconnecting solar panels, when batteries are full) and to prevent too deep discharge (by disconnecting the load when necessary) [Cook,1998]. Battery lifetime reduces

drastically due to overcharging and deep discharging. Battery is a very expensive component of a Solar Home System; hence it is necessary to protect batteries from being over charged or deeply discharged. In this regard, a charge controller plays a vital role to protect the battery [Ashiquzzaman et al, 2011]. One of the best ways to get power to remote, off-grid locations in Nigeria, is through Solar Home System (SHS). The system consists of photovoltaic panel, battery, and a solar charge controller. Solar energy is stored into batteries. A solar charge controller regulates the voltage and current that is coming from the solar panels and going to the battery [Neha, 2013]. The charge controller is a switching device that controls the charging and discharging of the battery. This will protect the batteries from damage and hence prolong the lifespan of the battery [Kondracki et al, 2014].

Figure 1: Block Diagram of a typical non-grid tied Photovoltaic (PV) System. Photovoltaic System consists of a PV / Solar Panel (module), charge controller, batteries and power inverter. The PV / Solar Panel (module) or array converts the sunlight energy into DC electrical energy. The charge controller conditions the DC electrical voltage and current 40

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produced by the PV / Solar Panel (Module) or array to charge a battery. The battery stores the DC electrical energy so that it can be used when there is no solar energy available (night time, cloudy days etc.). DC loads can be powered directly from the PV / Solar Panel (Module) / Battery. The inverter converts the DC power produced by the PV / Solar Panel (Module) / stored in the battery into AC power to enable powering of AC loads. [Samlex, 2014] 2.0 SOLAR CHARGE CONTROLLER A charge controller or alternatively a charge regulator is basically a voltage and/or current regulator, to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels and going to the battery. Most “12 volt” panels produce about 16 to 20 volts, so if there is no regulation, the batteries will be damaged from overcharging [James and Dunlop, 2012]. The obvious question then comes up – “why aren’t panels just made to put out 12 volts?” The reason is that if you do that, the panels will provide power only when cool, under perfect conditions and full sun. This is not something you can count on in most places. The panels need to provide some extra voltage so that when the sunlight is low in the sky, or you have heavy haze, cloud cover, or high temperatures, you still get some output from the panel, so the panel has to put out at least 12.7 volts under worst case conditions. The primary function of a charge controller is to maintain the battery at highest possible state of charge. The charge controller protects the battery from overcharge and disconnects the load to prevent deep discharge. Ideally, charge controller directly controls the state of the battery. The controller checks the state of charge on the battery between pulses and adjusts itself each time. This technique allows the current to be effectively “tapered” and the result is equivalent to “constant voltage” charging [Samlex, 2014]. Without the charge control, the current from the PV module will flow into a battery proportional to the irradiance, whether the battery needs to be charging or not. If the battery is fully charged, unregulated charging will cause the battery voltage to reach

exceedingly high levels, causing severe gassing, electrolyte loss, internal heating and accelerated grid corrosion. Therefore, charge controller maintains the health and extends the lifetime of the battery. 2.1 Types of Solar Charge Controllers The two types of charge controllers most commonly used in today’s solar power systems are pulse width modulation (PWM) and maximum power point tracking (MPPT). Both adjust charging rates depending on the battery’s maximum capacity as well as monitor the battery temperature to prevent overheating [Noor and Ayuni, 2009]. 2.1.1 Pulse Width Modulation (PWM) Charge Controller Pulse width modulation (PWM) charge controller is the most effective means to achieve constant voltage battery charging by adjusting the duty ratio of the switches (MOSFET). In PWM charge controller, the current from the solar panel tapers according to the battery’s condition and recharging needs. When a battery voltage reaches the regulation set point, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery; yet charging continues to return the maximum amount of energy to the battery in the shortest time. The voltage of the array will be pulled down to near that of the battery. PWM system has the following advantages:     

Higher charging efficiency Longer battery life Reduced battery over heating Minimizes stress on the battery Ability to de-sulfate a battery

A PWM controller is not a DC to DC transformer. The PWM controller is a switch which connects the solar panel to the battery. When the switch is closed, the panel and the battery will be at nearly the same voltage. Assuming a discharged battery, the initial charge voltage will be around 13V, and assuming a voltage loss of 0.5V over the cabling plus controller, the panel will be at =13.5V. The voltage will slowly increase with increasing 41

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

state of charge of the battery. When absorption voltage is reached, the PWM controller will start to disconnect and reconnect the panel to prevent overcharge (hence the name; pulse width modulated charge controller) [Vitronenergy, 2014]. 2.1.2 Maximum Power Point Tracking (MPPT) Charge Controller Nowadays, the most advanced solar charge controller available is the Maximum Power Point Tracking (MPPT). It is more sophisticated and more expensive. It has several advantages over the PWM charge controller. It is 30 to 40% more efficient at low temperature. The MPPT is based around a synchronous buck converter circuit. It steps the higher solar panel voltage down to the charging voltage of the battery. It will adjust its input voltage to harvest the maximum power from the solar panel and then transform this power to supply the varying voltage requirement of the battery plus load. It is generally accepted that MPPT will outperform PWM in a cold temperature climate, while both controllers will show approximately the same performance in a subtropical to tropical climate. The MPPT charge controller is a DC to DC transformer that can transform power from a higher voltage to power at a lower voltage [vitronenergy, 2014]. The amount of power does not change, therefore, if the output voltage is lower than the input voltage, the output current will be higher than the input current, so that the product P=VI remains constant. Hence, in order to get the maximum out of a solar panel, a charge controller should be able to choose the optimum current-voltage point on the currentvoltage curve: the Maximum Power Point. An MPPT does exactly that. The input voltage of a PWM controller is, in principle, equal to the voltage of the battery connected to its output. The solar panel, therefore, is not used at its Maximum Power Point, in most cases. 2.2 Comparison Between MPPT and PWM Charge Controller If maximizing charging capacity is the only factor considered when specifying a charge controller, everyone would use a MPPT controller, but two technologies are different, each with its own advantages. The decision

depends on site conditions, system components, size of array, load and cost of a particular solar panel system. They are compared as follows.  Temperature conditions An MPPT controller is better suited for colder conditions. The MPPT controller is able to capture the excess module voltage to charge the batteries. It produces up to 20-25% more charging than a PWM controller. The PWM type is unable to capture excess voltage because the pulse width modulation technology charges at the same voltage as the battery. But when solar panels are deployed in warm or hot climates, there is no excess voltage to be transferred making the MPPT unnecessary and negating its advantage over a PWM.  Array Voltages PV array and battery voltages should match for PWM but PV array voltage can be higher than battery voltage for MPPT.  Battery Voltage PWM operates at battery voltage, so it performs well in warm temperature and when battery is almost full while MPPT operates above the battery voltage, so it can provide “boost” in cold temperatures and when the battery is low.  System Size PWM is typically recommended for use in smaller systems where MPPT benefits are minimal, while MPPT is recommended for a 150W-200W or higher sized systems to take advantage of its benefits.  Cost MPPT controllers are typically more expensive than PWM controllers but are more efficient under certain condition, so they can produce more power with the same number of solar modules than a PWM control. 2.3 Charge Cycle of a Charge Controller Most quality charge controller units have what is known as a 3-stage charge cycle as follows: i. Bulk: In this stage, the battery will accept all the current provided by the solar array. The value of this current will be equal to the Short Circuit Current Isc of the solar array [Samlex, 2014]. During the bulk 42

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

phase of the charge cycle, the voltage gradually rises to the bulk level (usually 14.4 to 14.6volts) while the batteries draw maximum current. When bulk voltage level is reached, the absorption stage begins. ii. Absorption: During this phase, the voltage is held constant (maintained at bulk voltage level) for a specified time (usually an hour) while the current gradually tapers off as the batteries charge up. This is to avoid over-heating and over-gassing the battery. The current will taper off to safe levels as the battery becomes more fully charged. [Samlex,2014] iii. Float: When a battery becomes fully charged, dropping down to the float stage will provide a very low rate of maintenance charging while reducing the heating and gassing of a fully charged battery. When the battery is fully recharged, there can be no more chemical reactions and all the charging current is turned into heat and gassing. The purpose of float is to protect the battery from long-term overcharge [Samlex, 2014]. After the absorption time phase, the voltage is lowered to float level. This is typically (usually 13.4 to 13.7volts) for a 12V battery and the batteries draw a small maintenance current until the next cycle.

2.4 Charge Controller Designs There are two basic methods for controlling or regulating the charging of a battery; they are shunt and series regulation [Ishtiak et al, 2013]. While both of these methods are effectively used, each method may incorporate a number of variations that alter their basic performance and applicability. When the MOSFET switch is connected in series with the PV Array and the battery, the Controller is called Series Type. When it is connected in parallel across the PV Array / the Battery, it is called Shunt Type. In Series Type, the MOSFET Switch is kept open when the battery is fully charged. The PV Array stops supplying current during this period. In the Shunt Type, when the battery is fully charged, the MOSFET switch is kept closed to shunt (divert) the full short circuit current of the PV Array away from the battery. [Samlex, 2014] 2.4.1 Series Controller Design A series charge controller disables further current flow into batteries when they are full.

The relationship between the current and the voltage during the 3-phases of the charge cycle is shown in Figure 2.

Figure 3: Solar Home System with a series charge controller [Ishtiak et al, 2013] This type of controller in Figure. 3 works in series with the array and the battery [Marufa, 2012]. There are several variations to the series type controller, all of which use some type of control or regulation element in series. Relay or solid-state switch either opens the circuit between the array and the battery to discontinuing charging, or limits the current in a series-linear manner to hold the voltage of the battery at a high value. Figure 2: A graph showing the relationship between the current and voltage during the 3 phases of the charge cycle. [Sunpower, 2013] 43

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

2.4.2 Shunt Controller Design A shunt charge controller diverts excess electricity to an auxiliary or "shunt" load, such as an electric water heater, when batteries are full.

Figure 4: Solar Home System with a shunt charge controller [Ishtiak et al, 2013] The shunt controller regulates the charging of a battery from the PV array internal to the charge controller. All shunt controllers must have a blocking diode in series between the battery and the shunt element to prevent the battery from short-circuiting when the array is regulating [Marufa, 2012]. The regulation element in shunt controllers is typically a power transistor or MOSFET, depending on the specific design. Advantages of Series Type of Charge Controller A series Type of Charge Controller has the following advantages over a Shunt Type i. Lesser switching noise: during charging. ii. Less susceptible to high voltage transient disturbances. iii. The voltage applied across the Series MOSFET switch is lesser and so experiences lesser stress and is, therefore, more reliable. iv. A Shunt Type requires a schottky diode in series with the battery to prevent short circuiting of the battery during the time the MOSFET switch shunts the PV Array. In a Series Type, this schottky diode is not required and hence lower voltage drop, less heating and consequent lower losses. Reverse leakage through the schottky is also eliminated. [Samlex, 2014]

actual state of charge of the battery, charge current, discharge current, type and age of the battery). For a normal full loaded battery with no charging or discharging current, the battery voltage is about 12.4volts to 12.7volts. When charging current is flowing, the voltage jumps to a higher level e.g. 13.7V (depending on the current), and when loads are switched on, the voltage drops down to a lower level e.g. 12volts or 11.8volts (also depending on the current). 2.6 Deep Discharge Protection When a battery is deeply discharged, the reaction in the battery occurs close to the grids and weakens the bond between the active materials and the grids. When we deep discharge a battery repeatedly, loss of capacity and lifespan eventually occurs. To protect the battery form deep discharge, most charge controllers include an optional feature to disconnect the system loads once the battery reaches a low voltage or low state of charge condition. If the voltage of the system falls below 11.5volts for a minimum period of 20sec, then the charge controller will be switched off for a minimum 30 seconds. The delay of 30 seconds is integrated to protect the system against a swinging situation [Marufa, 2012]. 2.7 Component Selection for Controller Design In light of the foregoing appraisal of design styles, the following components will form an integral part of the design and hence, their importance and working principles are discussed. A list of necessary components required to carry out the design on this project are as follows (i)

Diodes

These are simply blocking diodes which ensure that the current flows only one way, so that the battery doesn’t discharge when the output from the solar panel is low.

2.5 Overcharge Protection

(ii)

In a 12V battery system, the voltage varies between 10.5 to 14.4volts, (depending on the

This part of the circuit ensures that once the charging cut off voltage is reached by the 44

Zener Diodes

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

battery, the charging stops. The zener diode is rated at 6.8V as breakdown voltage. (iii) MOSFET The metal-oxide-semiconductor field effect transistor is used for amplification or switching electronic signals. It ensures cut off of the load in low battery or overload conditions. (iv) Transistor It is used to bypass the solar energy to a dummy load while the battery gets fully charged. Once the battery is fully charged, it draws all the current thus protecting the battery. (v) Indicators Indicators are provided by a green LED for fully charged battery, while a set of red LEDs are used to indicate under charged, overcharged and deep discharge conditions. Voltage Regulators (vi) LM317 It is a 3-terminal adjustable voltage regulator which can supply an output voltage adjustable from 1.2V to 37V. It can supply more than 1.5A of load current to a load. We can modify the voltage by changing the value of the resistor connected to a pin of the voltage regulator. These resistors determine the voltage that the voltage regulator adjusts to and outputs. (vii) LM7812 It is a fixed linear voltage regulator integrated circuit. It is commonly used in electronic circuits requiring a regulated power supply due to their ease of use and low cost. They produce a voltage that is positive relative to a common ground. This IC has three terminals. Other components used to realize these circuits are op-amp, filter capacitor and relay.

3.0 DESIGN OF SOLAR CHARGE CONTROLLER Based on the block diagram of Figure. 5, the design is as follows:

Figure 5: The block diagram of a solar controller. 3.1 Current Booster The current booster allows the maximum value of current from the solar panel to flow through to battery. The main component of the current booster is the LM317, transistor and blocking diodes.

Figure 6: The current booster The LM317 keeps the voltage constant and can handle a maximum of 1A; so if the panel produces a current of less than 1A, the transistor does not conduct and the current flows through the LM317 to charge the battery. If current is above 1A, the transistor conducts because there is a voltage drop across that is large enough to be the base voltage of the transistor to be turned on. To ensure that the transistor does not conduct when the current is still less than or equal to 1amp, we calculate the value of .

45

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The drop should be less than 0.7V for the transistor not to conduct so; hence

that it is fully charged and it needs to stop charging and it is cut off with the help of the charge controller circuit. The diode near is reversed biased and doesn’t conduct.

V=I

From the voltage divider rule; to get equation (3)

(1)

V=0.7V; I=1A, the value of

is 0.7Ω

At above 1amps, the voltage drops exceeds 0.7V and the transistor conducts and the excess current flows through to the battery via the pass transistor. To get the resistor value divider rule; (

(

=

, we use voltage

)

=12V=voltage from the battery

Assuming =10V (reference voltage) i.e. at 12V, the inverting terminal should be 10V

) (

=1.25V (LM317 rating), required) = 14.2V, Assume =2288Ω (as a practical value) Diode

,

and

(which is =220Ω ∴

are blocking diodes.

Let

)

=10kΩ, hence

=2kΩ

The values of and using equation (4)

The diodes used here should be able to withstand a fault current of more than 10A. The diode 6A1D is used in this circuit with forward current =15A and peak inverse voltage PIV=100V.

( and

can also be calculated

) are current limiting resistors

3.2 Battery Level Indicator This circuit monitors the level of charge of the battery. The circuit diagram is shown in Figureure 7;

Where = = =

=12v, =500Ω

=2v,

=20mA,

3.3 Battery Charge Controller The circuit diagram as shown in Figure.8

Figure7: Battery level indicator The circuit used an Op amp, LM358 as comparator. If the voltage that appears across the inverting terminal is higher than the reference voltage, the output of the comparator is low, which will be forward biased with the diode close to , making it come on, indicating

Figure 8: Battery charge controller The circuit makes use of a comparator IC (LM358) and a relay with a contact of 30A. 46

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When the IC is positively saturated, it means the battery needs to charge; the transistor conducts, collector current flows, the relay is energized and the contact closes, current then flows to the battery to charge it. When negatively transistor doesn’t energized and the seizes to flow to charge.

saturated (when full), the conduct, the relay is decontact opens and current the battery and it doesn’t

The transistor used is BC547 and to ensure that it operates at cut off or saturation, we make:

3.4 POWER SUPPLY UNIT This circuit acts as a stable power supply to the battery level indicator. The reason why this circuit is embedded in the charge controller is because it curtails unstable power output through the use of a fixed voltage regulator (7812) that gives a constant (fixed) regulated output voltage of 12V; the reference voltage for all comparator circuits which the voltage of the battery is compared with. The circuit diagram is shown in Figureure 9.

as a

is an optional filter capacitor ( ); it is present in the circuit, incase there is an AC signal. The fixed voltage regulator is a DC device and won’t regulate, if there is an AC signal.The fixed voltage regulator (7812) has a regulated output voltage of 12V

=Impedance of coil relay (A value of 400Ω was used for )

is a current limiting resistor connected in series with an LED (power indicator) that indicates that the circuit is on.

=Base resistance of the transistor (

)

practical value).

The diode used is 6A1D. It is a free-wheeling diode. It removes residual current generated by the inductor as it creates a free wheel till the current dampens out. The practical value of

=12V,

used is 1kΩ

Figure 9: Power supply unit

47

=2V,

(10mA-20mA)

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3.5 Mode of Operation: The complete circuit diagram of the charge controller is shown in Figure 10.

Figure10 : Complete circuit diagram of a solar charge controller

The solar charge controller circuit is made up of four stages, namely; the current booster, the power supply unit, the battery level indicator and the battery charge controller. The current booster ensures that maximum current is gotten from the output of the solar panel through the use of a pass transistor (MJ2955); this current goes through to charge the battery, a variable voltage regulator (LM317) sets a constant output voltage of 14.2V to charge the battery and blocking diodes that ensure that current flows in the required direction.

The battery level indicator monitors the charge of the battery through the use of a comparator which compares a reference voltage, to the voltage of the battery and indicates through LEDs if the battery is fully charged or undercharged. The power supply unit supplies a constant output voltage of 12V to the comparator circuits in the design to ensure that unstable power output is avoided and this is used as the reference voltage which is compared to the battery’s voltage. The battery charge controller cuts off the battery from charging when fully charged through the use of a comparator IC and a relay. When the battery is not full, the IC is positively saturated, the transistor conducts, the relay is energized 48

JOURNAL OF ELECTRICAL AND ELECTRONIC ENGINEERING VOL 12, NO 2, ISSN 1118 – 5058 NOVEMBER 2015

and the contact closes ensuring that the current flows through to charge the battery. When the battery is charged full, the IC is negatively saturated, the transistor doesn’t conduct, the relay is de-energized and the contact opens and current seizes to flow to the battery. 4.0 CONSTRUCTION PROCEDURE The circuit is first designed and simulated using Proteus software after which the system was constructed and enclosed in a 15cm by 25cm plastic container. 5.0 TESTING/RESULTS The functionality of the charge controller depends on the fixed voltage output of 14.2V from the current booster block of the solar charge controller; hence the test data includes reading from a 200Ah, 12V battery charged for approximately 12hrs under varying weather conditions. i. Initial battery voltage level was 9.83V. ii. Battery voltage level after first 6hrs under exposure of panel to intense sunlight was 11.3V. iii. Battery voltage level after approximately 12hrs under exposure of panel to reduced sunlight intensity was 12.2V. 6.0 OBSERVATIONS/RESULT ANALYSIS i. After proper connection of the solar panel and battery leads to their respective terminals on the solar charge controller, the power and undercharging LEDs turn ON to indicate battery charging. ii. After 12 hours and 20 minutes of charge, the optimum charge LED turns ON indicating full charge and undercharge LED turns OFF indicating that no more current is getting to the battery. Generally the circuit performed satisfactorily.

worked satisfactorily and can be used in a solar home system to solve problems of power supply in Nigeria. REFERENCES [1] Korenčiak P., Fiedler P. “Charge Controller For Solar Panel Based Charging of Lead Acid Batteries, Faculty of Electrical Engineering and Communication, Department Of Control and Instrumentation, 2011, Brno University Of Technology pg 11.

[2] Cook G. F. “Solar Charge Controller for Medium Power Applications” February / March 1998, pg 42. [3] Ashiquzzaman M. , Afroze N., Hossain J. M. , Zobayer U., and Hossain M.M. “Cost Effective Solar Charge Controller Using Microcontroller” Canadian Journal on Electrical and Electronics Engineering Vol. 2, No.12, Dec. 2011. Pg 2. [4] Ishtiak A. K., Abid A. S., Navid A. M. , Irin P. S. Saha S. “Design of A Solar Charge Controller for a 100WP Solar PV System” International Journal of Engineering Research & Technology (IJERT) Vol. 2 Issue 11, November – 2013, pg 1.

[5] Everett M. and Provey J. R. “Convert Your Home to Solar Energy”, (Taunton Press, 2010), pg 15-27. [6] Kondracki, Ryan; Collins, Courtney; Habbab, Khalid “Solar Powered Charging Station”, University of Bridgeport, Bridgpeort, CT, USA. ASEE 2014 Zone I Conference, April 3-5,2014, pg 3.

7.0 CONCLUSION

[7] “Basics on Mppt Charge Controller”, n.d., instructables, instructable article, viewed June 19th, 2015,m.instructables.com/id/AROUNDSOLAR-CHARGE-CONTROLLER-Version30/steps2/Basic-on-MPPT-charge-controller/ accessed 14/07/2015.

This work has produced a low cost, reliable and functional solar charge controller, using locally sourced and available components. The product

[8] James P., Dunlop P. E. “Batteries and Charge Controller In Stand-Alone Photovoltaic Systems Fundamentals And Applications”. 49

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Florida Solar Energy Centre, University of Central Florida, 1997. Pg 24, 28, 29, 42. [9] Kuale M. “Basic Electrical Circuit And Electronic Components Testing” A., published by Multi-International services, Benin city, Nigeria,2000. Pg 12-15. [10] Marufa F “Designing Smart Charge Controller for the Solar Battery Charging Station”., 2012, BAAC University, Dhaka, Bangladesh. Pg 34-47. [11] Mohammed S. I. “Low Cost Solar Charge Controller”, Lambert Academic publishing. 2012, pg 10-15. [12] Nelson J “Physics of Solar Cells – A Text For Undergraduates”. Physics of Solar Cells- A Text for Undergraduates, Imperial College Press, November 11, 2013.Pg 10-25 [13] Neha K “Project Report on Solar Charger Circuit Using IC LM317”, Indian Institute of science, Bangalore. 2013, Pg 4-7. [14] Noor J. & Ayuni B. M. “Photovoltaic Charge Controller, Universiti Malaysia, Pahang, Malaysia. 2009”, Pg 4,5. [15] www.victronenergy.com article “Which Solar Charge Controller: PWM or MPPT?” Vitron Energy B. V. 2014, accessed 7/06/2015. [16]www.solar-electric.com/solar-chargecontroller-basicshtml accessed 21/10/2015. Solarelectric.com article, viewed June, 2015. [17] “Charge Controllers”, 2013, Sunpower article,www.freepower.com/chargecontrollers.p hp, accessed 16/09/2015. [18] Samlexsolar “30amp Solar Charge Controller” SCC-30AB, Owner's Manual, 2014. Pg 29-33.

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