International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 2013Design of a Solar Charge Controller for a 100 WP solar PV SystemIshtiak Ahmed Karim 1, Abid Azad Siam 2, Navid Ahmed Mamun 3, Irin Parveen 4, SwaramitaSaha Sharmi 51,2,3,4,5Department of Electrical and Electronic EngineeringAhsanullah University of Science and TechnologyDhaka, BangladeshAbstractIJERTThis paper presents a low cost Solar Charge ntroller to control and coordinate the functionsproperly. Details of design for the construction of SCCusing crystal oscillator, ceramic resistors, LightEmitting Diodes (LED) and MOSFET are presented.The source code for the ATmega8 microcontroller iswritten in Arduino IDE to obtain accurate and efficientautomatic control action. Accordingly, battery can bedisconnected from solar cell when overcharging andreconnected while discharging. The loads can bedisconnected according to the over current and underflow current limit for both battery and PV. Theproposed charge controller is equipped with LEDs todisplay the battery charging /discharging status, chargelevel and short circuit condition via microcontroller.The construction and operation of our proposed smartsolar charge controller indicates that it is cost effectiveand functions properly.voltage regulator. It regulates the voltage and currentthat is coming from the solar panels and going to thebattery. Most of the batteries are fully charged at 14 to14.5 volts. On the other hand, battery's life timedrastically reduces due to the discharge over the levelof 70%-80%; at this discharge level the battery voltagenormally goes down to 11.5 volts. Each battery has acertain limit of capacity. Battery lifetime reducesdrastically due to overcharging and deep discharging.As battery is a very expensive component of a SolarHome System, it is necessary to protect the batteriesfrom being over charged or deeply discharged. In thiscase charge controller plays a vital role to protect thebattery [1].A series charge controller disables further currentflow into batteries when they are full. A shunt chargecontroller diverts excess electricity to an auxiliary or"shunt" load, such as an electric water heater, whenbatteries are full.Charge controllers stop charging a battery whenthey exceed a set high voltage level, and re-enablecharging when battery voltage drops back below thatlevel. Pulse width modulation (PWM) and maximumpower point tracker (MPPT) technologies are moreelectronically sophisticated [2].KeyWords: SCC, Arduino IDE, SHS,microcontroller, crystal oscillator, LED, MOSFET.1. IntroductionOne of the best ways to get power to remote, offgrid locations, whether in developed or developingcountries is through Solar Home System (SHS). Thesystem consists of Solar PV, battery, and a solar chargecontroller. In most cases consumers consume solarenergy at evening hours. So, solar energy is stored intobatteries. A solar charge controller is similar to theIJERTV2IS110639www.ijert.orgFigure 1. SHS with series controller3989

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 2013Figure 2. SHS with shunt controllerBattery condition and corresponding state of chargethat we gathered from reading of formerly usedbatteries for solar system is used to measure the PWMstates. The following chart represents a clear idea aboutbattery condition that are generally used includingcharging and discharging both:Table 1. Solar Charge Controller status set points12 V Battery100%67%34%1%IJERTState of charge 131211 102. Theoretical BackgroundFigure 3. Charge controller and battery wiringThere are various brands manufacturing solarcharge controller in the foreign markets which areIJERTV2IS110639developed according to the requirements of SHS.These SCC are very costly for under-developedcountries like Bangladesh, especially at the rural areas.Solar Panel and battery are expensive as well. So, it isdifficult for the consumers in rural areas to afford theadditional costs for the expensive SCC in their solarenergy system.To make the SCCs available to the rural consumerswithin the affordable cost, a sophisticated solar chargecontroller has been developed. This SCC is very simplein construction and cost effective. The operationprocess is also very simple, easy to maintain and aboveall user friendly. The proposed SCC consists of avoltage regulator, a microcontroller, a crystaloscillator, three MOSFET and LEDs. According to thevoltage level at battery terminal, which is set by themicrocontroller, it controls the charging of battery fromsolar panel and hence improves the operational life of abattery. It also prevents the battery from completedischarging by disconnecting the load from the batterywhen the voltage level reaches to a critical value set bythe microcontroller. It is our purpose to propose a costeffective SCC that improves the existing solar chargescontroller devices and the battery life of the solarsystem. This SCC can fulfil nearly all requirementswhich are needed for proper operation and protectionof SHS.This section covers the details regarding theimportance of Battery is SHS. A battery is one or moreelectro-chemical cells that convert stored chemicalenergy into electrical energy. Since the inventionbatteries they have become a common power sourcefor many household and industrial applications. Thereare two types of batteries: primary batteries (disposablebatteries), and secondary batteries (rechargeablebatteries), among them secondary batteries are moreefficient and popular for its multipurpose uses. For thecharging and discharging facilities the secondarybatteries are exceedingly used for the solar panel powersystem. Despite having a very low energy-to-weightratio and a low energy-to-volume ratio, their ability tosupply high surge currents means that the cellsmaintain a relatively large power-to-weight ratio.These features, along with their low cost, make themideal for using in SHS.Because of the chemical reactions within the cells,the capacity of a battery depends on the dischargeconditions such as the magnitude of the current, theallowable terminal voltage of the battery, temperaturewww.ijert.org3990

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 2013chemistry, does not suffer from memory effect to quitethis extent. When a battery reaches the end of itslifetime, it will not suddenly lose all of its capacity;rather, its capacity will gradually decrease. Lead-acidbatteries should never be discharged to below 20% oftheir full capacity, because internal resistance willcause heat and damage when they are recharged.Battery life can be extended by storing charge of thebatteries, as in controlling the cover charge of batterieswhich slows the chemical reactions in the battery. Suchstorage can extend the life of these types of batteries byabout 5%. To reach their maximum voltage, batteriesmust be stopped to store of charge. As a result, due tothese drawbacks and lifespan improvement process ofthese types of batteries like lead-acid batteries if weuse SCC properly then lifespan of batteries can beextended.Basically here battery charging rate is kept normal,neither fast nor slow. The discharge limit will not gounder the 50%. The microcontroller can senseaccording the program that when it is needed to chargeand when at nearly full charged it is needed to cut offfrom the Solar Panel. For further operation thisproposed SCC can control the movement of the loadaccording the charge and discharge of the battery.IJERTand other factors [3]. The available capacity of abattery depends upon the rate at which it is discharged.If a battery is discharged at a relatively high rate, theavailable capacity will be lower than expected. Thespeed of recharging for lead-acid batteries may beincreased by manipulation [4]. The battery capacitythat battery manufacturers print on a battery is usuallythe product of 20 hours multiplied by the maximumconstant current that a new battery can supply for 20hours at 68 F (20 C ), down to a predeterminedterminal voltage per cell i.e. a battery rated at 100Ahwill deliver 5A over a 20 hour period at roomtemperature. However if it is instead discharged at50A, it will have a lower apparent capacity [5].For low values of current drawn from batteryinternal self-discharge must be included. In practicalbatteries, internal energy losses, and limited rate ofdiffusion of ions through the electrolyte, cause theefficiency of a battery to vary at different dischargerates. When discharging at low rate, the battery’senergy is delivered more efficiently than at higherdischarge rates [6], but if the rate is too low, it willself-discharge during the long time of operation, againlowering its efficiency. Rechargeable batteries selfdischarge more rapidly than disposable alkalinebatteries, especially LEAD-based batteries; a freshlycharged PbSO4 loses 10% of its charge in the first 24hours, and thereafter discharges at a rate of about10% amonth [7]. Although rechargeable batteries have theirenergy content restored by charging, somedeterioration occurs on each charge/discharge cycle.Lead-acid batteries tend to be rated cycles before theirinternal resistance permanently increases beyondusable values. Day by day this resistance increases sothe rated cycle rate also decreases and by that thelifespan decreases. Normally a fast charge, rather thana slow overnight charge, will shorten battery lifespan.However, if the overnight charger is not “smart” andcannot detect when the battery is fully charged, thenovercharging is likely, which also damages the battery[8].Degradation usually occurs because electrolytemigrates away from the electrodes or because activematerial falls off the electrodes. Lead-acid batteriessuffer the drawback that they should be fullydischarged before recharge. Without full discharge,crystals may build up on the electrodes, thusdecreasing the active surface area and increasinginternal resistance. This decreases battery capacity andcauses the “memory effect”. These electrode crystalscan also penetrate the electrolyte separator, therebycausing shorts. Lead-acid although similar inIJERTV2IS1106393. System Structure3.1 Controlling UnitFigure 4 shows the flowchart of Charge ControllerLogic Circuit Program. All the status of solar andbattery are observed by the microcontroller by thefollowing algorithm. The whole decision is taken bythe microcontroller alone. It follows the program whichis burned into it. This program is written on the basis oftheoretical concept to increase the battery efficiency.The main theme of whole process and controllingcan be summarized as follows:i. If battery voltage is less than 5.5V, controllerdetermines it a short circuit condition and load isdisconnected immediately.ii. If battery voltage is less than 10V, controller turnson the battery charging and load is disconnectedfrom battery (for 12V load).iii. If battery voltage is greater than 15V, controllerturns off the battery charging.iv. If battery voltage is greater than and equal 12V,load can be connected with battery normally (for12V load).www.ijert.org3991

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 2013iii.iv.Charging unitControl lyUnitMOSFETswitchingSolarPanelBatteryLoadFigure 5. Functional block diagram of a SCC(i) Power supply unit (PSU)IJERTA PSU consists of some necessary equipment suchas diodes, ceramic resistors, inductive coil, capacitorsand voltage regulator. In this circuit, in Figure 5, weused Solar Panel as an input. From Solar Panel, poweris delivered to battery via two Diodes. These twoDiodes do not allow the flow of charge from battery tothe solar panel reversely at night due to the potentialdifference among battery and Solar Panel. This outputfrom the two Diodes is connected to a filter circuitwhich consists of a bank of capacitors and inductor.The output is fed to the voltage regulator. For our SCCcircuit we needed fixed 5V supply, which is generatedfrom voltage regulator. After the voltage regulatorthere are some optional filters units which may be usedto prevent farther noise. This pure signal (5V) is sent tothe ATMega8 microcontroller.(ii) Load distribution unitFigure 4. Flowchart of Charge Controller LogicCircuit Program3.2 Functional Blocks of Our SCCFigure 5 shows the whole process that can bedescribed by using four functional blocks. In this wayit is easier to understand the individual operation ofstep by step process of the whole system. The SCC isdivided into four major blocks:i.Power supply unitii.Load distribution unitIJERTV2IS110639In a SHS all ( )ve ends of loads are connected withthe ( )ve end of battery. Then the (-)ve switching isestablished by using MOSFETs. The positive end ofbattery is directly connected with the positive end ofload. To control the load switching we have usedmicrocontroller and MOSFET. The microcontrollerchecks the overall status of the system. If therequirement is fulfilled then microcontroller sends thesignal to the MOSFETs. Thus they establish thenegative switching (to reduce heat in the circuit) withthe load. So the circuit is closed and load is connectedwith the battery.www.ijert.org3992

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 2013is then lit to make a acknowledge signal. The overallbattery charge is also observed with a set of LEDs(iii) Charging unitHere the charging is controlled by themicrocontroller and switching by the MOSFET. Herealso the (-)ve switching concept is used. The ( )ve endof Solar Panel is connected to the ( )ve end of batteryvia two blocking Diodes. The whole voltage status ofboth the Solar Panel and the battery go tomicrocontroller analogue inputs to compare with thelogic that is set inside the microcontroller. If the entirerequirement is fulfilled then microcontroller sends aswitching signal to the MOSFET. After that, the circuitis closed and power flows from the Solar Panel to thebattery. Otherwise the microcontroller does not sendany signal to the MOSFET. As a result the circuitremains open leading to no power flow from the SolarPanel to the battery. In this way battery is charged.(iv) Control unitAccording to the flow chart a program is written inArduino IDE and loaded to the microcontroller. Here,the microcontroller initially gets the solar panel andbattery voltage through its two analogue-pins anddigitizes it. If the battery voltage is less than the setvalue, it sends pulse to the MOSFET to charge thebattery disconnecting the load. If the battery voltage isgreater than the High Voltage Disconnect set point thenit sends another pulse to the MOSFET to stop chargingthe battery and connecting to the load. The actual SCCis illustrated in Figure 6. Figure 7 illustrates a buckconverter module that sets its duty cycle automaticallyto maintain a steady 14V power supply to the SCC.Figure 8 shows the actual wave shape during charging.IJERTIn this part the status of solar and battery is sent tothe microcontroller to compare with the logic which isprogrammed from the first in microcontroller. Thecrystal oscillator is used to generate stream pulse tomicrocontroller. The purified 5V signal comes fromvoltage regulator to microcontroller through filter. Thedecisions which are required according the logic ofmicrocontroller are sent to LEDs for observing thewhole status of the SCC. As we have described theoperation of solar charge controller partly, so wholeoperation is combination of those four functionalblocks, total work is done at a time.When input connector gets input from solar powersupply, it generates the operating voltage for thecircuit, as well as to store the charge in battery. Thisoperating voltage operates the microcontroller andLEDs after regulating this voltage using voltageregulator.Microcontroller takes decision when battery isbecome over charged. This decision is given bymicrocontroller to MOSFET whether it has to open ornot. If stored charge is available in the battery for thepermitted loads according the power of battery, thewhole setup is ready to operate and makes a smoothoperation.Microcontroller also performs the protectionoperation in this SCC. If there is any short circuitcondition in the SCC or in the system it automaticallydetects the fault and interrupts all the power flow bothfrom the Solar Panel to the Battery and from thebattery to the load preventing further damage. A LED4. Hardware ImplementationIJERTV2IS110639Figure 6. Actual hardware of the SCC for a 100WPSHSwww.ijert.orgFigure 7. Buck converter Module for SCC3993

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 2 Issue 11, November - 20135. ConclusionCost effective solar charge controller has beendesigned and implemented using Atmel ATMega8microcontroller to have efficient system and muchlonger battery lifetime. From the overall analysispresented, it can be concluded that our proposed SCCcan be commercially used to optimize the energy crisisin the rural areas.6. ReferencesFigure 8. Charging wave shape5. Result and AnalysisIJERTThe project has been tested according its operationalpurposes. Maximum power rating of the experimentedsolar charge controller is 100W according batterycapacities, so the system has been tested by both two15W DC light and 20W DC fan, which is operatedsuccessfully.For load distribution unit positive switching methodwas used. But this method was found to produce moreheat. As a result, we adopted negative switchingmethod which produced less heat than before. All( )ve ends are connected with each other but the (-)veends are controlled by switching using MOSFETs.For charging unit the instruction of the batterymanufacturer has been strictly followed. The upper andlower limits are carefully set so that the battery is notdamaged.For control unit, there were some distortions ofsignal when it was observed into the oscilloscope. Weused two times of rated LC filter circuit to reduce thenoise and send the pure signal to microcontroller for itsproper operation. A crystal oscillator is used to ensurea stream of clock pulse to the microcontroller.Our SCC had to go through plenty of test runs andShort Circuit Tolerance tests before the optimumperformance was achieved. The project completedsuccessfully with all the features of operations of thesolar charge control system as desired.An over charge alarm can be added farther toprotect batteries from over charging. A data loggermodule can also be added to the system. The systemcan be farther upgraded to MPPT to increase the SCCefficiency. Besides, while using in the commercialschemes the device needs to be modified and corrected.If all these modifications can be added for the furtherbetterment a perfect and proper solar power system canbe manufactured.[1] Mohammad Shariful Islam, Low Cost Solar ChargeController (Lambert Academic Publishing, 2012)[2] Everett M. Barber and Joseph R. Provey, Convert YourHome to Solar Energy (Taunton Press, 2010)[3] Thomas P J Crompton, Battery Reference Book(Newnes, 2000)[4] Christian Glaize, Sylvie Genies, Lead-NickelElectrochemical Batteries (John Wiley & Sons, 2012)[5] Isidor Buchmann. Batteries in a Portable World (BatteryUniversity, 2011.[6] Dr. Shahidul Islam Khan, Solar Home System, inCharge Controller (Bangladesh, 2013)[7] Isidor Buchmann. Batteries in a Portable World (BatteryUniversity, 2011).[8] R. M. Dell, David Anthony James Rand, UnderstandingBatteries (Royal Society of Chemistry, 2001)IJERTV2IS110639www.ijert.org3994

system consists of Solar PV, battery, and a solar charge controller. In most cases consumers consume solar energy at evening hours. So, solar energy is stored into batteries. A solar charge controller is similar to the voltage regulator. It regulates the voltage and current that is coming from the solar panels and going to the battery.