Design & implementation of a photo-voltaic high intensity discharge

(HID) street lighting system Definition:

At first glance on the title ofthe research paper it is quite clear that we want todesign and control the out-door (streets, roads etc)lighting system. In which main source of energy will besolar and lamps in the system will be “high intensitydischarge”.

So, first of all we should aware to the basicterminologies used in the title of the research paper.

1. Photo-voltaic:

It means conversion of lightinto electricity. Now in this project we will usephotovoltaic panel (solar panel) for the conversion ofsun energy into electricity. PV panel is a series-parallel array of thousands of photo-voltaic cells.A device which converts light energy into electricalenergy is called photovoltaic cell. It is basically ap-n junction device in which the potential barrierbetween the p and n regions is used to drive a currentthrough external circuit when light is incident on thejunction. The current is directly proportional to theintensity of light.

Principle of operation of PV cell: The photoelectric effect is the basic physical processby which a PV cell converts sunlight into electricity.When light shines on a PV cell, it may be reflected,absorbed, or pass right through. But only the absorbedlight generates electricity.

The energy of the absorbed light is transferred toelectrons in the atoms of the PV cell. With theirnewfound energy, these electrons escape from theirnormal positions in the atoms of the semiconductor PVmaterial and become part of the electrical flow, orcurrent, in an electrical circuit. A special electricalproperty of the PV cell—what we call a “built-inelectric field”—provides the force, or voltage, neededto drive the current through an external “load,” suchas a light bulb.

2. High intensity discharge light: High-intensity discharge lamps are a type of arc lampor electric gas discharge lamps which produces light bymeans of an electric arc between tungsten electrodes.This tube is filled with both gas and metal salts. Thegas facilitates the arc's initial strike. Once the arcis started, it heats and evaporates the metal saltsforming plasma, which greatly increases the intensityof light produced by the arc and reduces its powerconsumption.

It has following advantages over incandescent orfluorescent lamp:

a.High efficacy (lumens per watt)b.Long life timec.Long distance lightd.Initial investment vs Annual saving

Design & Implementation: The PV street lighting system is shown in the figures below:

Figure 1

Figure 2

Charge controller:

It is also knownas charge regulator. In the PV lighting system it isused to charge the Lead-acid battery. It also regulatesthe power from the solar panel primarily to preventovercharging the battery. Overcharging batteries reducebattery life and may damage the battery.

The operation of many charge controllers is based onthe principle of pulse-width modulation. Also, some

controllers include a charging method that maximizescharging, called maximum power point tracking.

The PWM controller produces a series of pulses tocharge the batteries instead of a constant charge. Thebattery voltage is constantly monitored to determinehow to adjust the frequency of the pulses and the pulsewidths. When the batteries are fully charged and thereis no load to drain them, the controller produces veryshort pulses at a low rate or no pulses at all. Whenthe batteries are discharged, long pulses at a highrate are sent or the controller may go into a constantcharging mode. The output voltage of a panel varieswith the amount of sunlight and with the airtemperature. For this reason, solar panel with voltageratings higher than the battery voltage must be used inorder to provide sufficient charging voltage to thebattery under less than optimum conditions.

A 12 V panel may produce 20 V under optimum conditionsbut can produce only a certain amount of current. Forexample, if a panel can produce 8A at 20 V it is ratedat 160 W. Batteries like to be charged at a voltage alittle higher than their rated voltage. If a 12 Vbattery is being charged at 14 V, and it is drawing themaximum 8 A from the solar panel, the power deliveredto the battery is 112W instead of the 160 W produced bythe solar panel at 20 V.The battery only store 70% ofthe available energy because the 12 V battery cannotoperate at 20 V.

MPPT charge controller eliminate much of the energyloss found in the other types of controllers andproduce much higher efficiencies. The MPPT is basicallya DC-to-DC converter. In which output can be adjustedfor maximum power.

For example, if a 160 W solar panel produces 20 V at 8A, it needs to be reduced to approximately 13.6 V tocharge a 12 V battery. A normal charger will not beable to provide more than 8 A at 13.6 V ( or 109 W),which means the panel is not being used efficiently andonly 76% of the available power from the solar panel isused. An MPPT charge controller can supply about 11 Aat 13.6 V (150 W), thus decreasing the charging timeand producing a better match between the panel and thebattery. In this case, the panel is being used moreefficiently because it is able to deliver about 94 % ofthe available power to the battery.

Its circuit diagram is shown below:

Inverter:

It converts dc voltage into ac. Itscircuit diagram is shown on next page:

The circuit mainly consists of two stages viz: theinverter, and the automatic relay changeover.During day time for so long the sun light remainsreasonably strong, the panel voltage is used forcharging the battery and also for powering the invertervia the relay changeover contacts. The automaticchangeover circuit preset is set such that theassociated relay trips OFF when the panel voltage fallsbelow 13 volts.The above action disconnects the solar panel from theinverter and connects the charged battery with theinverter so that the output loads continue to run usingthe battery power.

Circuit Description: Resistors R1, R2, R3,R4 along with T1, T2 and the transformer form theinverter section. 12 volts applied across the centertap and the ground starts the inverter immediately,however here we do not connect the battery directly atthese points, rather through a relay changeover stage.

The transistor T3 with the associated components andthe relay forms the relay change over stage. The LDR iskept outside the house or at a position where it cansense the day light.

 The P1 preset is adjusted such that T3 just stopsconducting and cuts off the relay in case the ambientlight falls below a certain level, or simply when thevoltage goes below 13 volts. Thisobviously happens when the sun light becomes too weakand is no longer able to sustain the specified voltagelevels. However as long as sun light remains bright,the relay stays triggered, connecting the solarpanel voltage directly to the inverter (transformercenter tap) via the N/O contacts. Thus the inverterbecomes usable through the solar panel during day time.

The solar panel is also simultaneously used forcharging the battery via D2 during day time so that itcharges up fully by the time it gets dusk.

The solar panel is selected such that it nevergenerates more than 15 volts even at peak sun lightlevels.

The maximum power from this inverter will not be morethan 60 watts.

Parts List for the proposed solar inverter with chargercircuit intended for science projects.

R1, R2 = 100 OHMS, 5 WATTS

R3, R4 = 15 OHMS, 5 WATTS

T1, T2 = 2N3055, MOUNTED ON SUITABLE HEATSINK

TRANSFORMER = 9-0-9V, 3 TO 10 AMPS

R5 = 10K

R6 = 0.1 OHMS 1 WATT

P1 = 100K PRESET LINEAR

D1, D2 = 6A4

D3 = 1N4148

T3 = BC547

C1 = 100uF/25V

RELAY = 9V, SPDT

Intelligent Street Lighting Using a ZigBee Network of Devices and Sensors: The use of a remote-control systembased on intelligent lamp posts that send informationto a central control system, thus simplifyingmanagement and maintenance issues. Researchers havedeveloped a street lamp system using the general-packetradio service (GPRS), power-line carrier, or GlobalSystems for Mobile Communications (GSM) transmissions.The control is implemented through a network of sensors

to collect the relevant information related to themanagement and maintenance of the system, transferringthe information via wireless using the ZigBee protocol.

DEVICES AND METHODS: Fig. 3shows the conceptual scheme of the proposed system. Itconsists of a group of observation stations on thestreet (one station for each lamp post) and a basestation typically placed in a building located nearby.It is a modular system, easily extendable.The measuring stations monitor the street conditionsand the intensity of sunlight and, based on them, theydecide to turn the lamps on or off. The conditionsdepend on the pattern of the street where the lightsare located and on the solar irradiation at a givenpoint of the street, with frequent changes, dependingon weather conditions, season, geographical location,and many other factors. For these reasons, we decidedto make each lamp completely independent in themanagement of its own lighting. The on-street stationalso checks if the lamp is properly working and sendsthe information through the wireless network to thebase station for processing data. If any malfunction isdetected, the service engineer is informed through agraphical interface and can perform corrective actions.

Figure. 3

A. Monitoring Stations: Themonitoring station located in each lamp post consistsof several modules: the presence sensor, the lightsensor, the failure sensor, and an emergency switch.These devices work together and transfer all of theinformation to a microcontroller which processes thedata and automatically sets the appropriate course ofaction. A priority in the transmission of informationis assigned to each sensor, for example, the emergencyswitch takes precedence over any other device.1) Presence Sensor:

The task of thepresence sensor is to identify the passage of a vehicleor pedestrian, giving an input to turn on a lamp or agroup of lamps. This function depends on the pattern of

the street; in case of a street without crossroads, asingle sensor is sufficient (or one at each end in caseof a two-way street), while for a street requiring moreprecise control, a solution with multiple presencedetectors is necessary. This feature enables switchingon the lamps only when necessary, avoiding a waste ofenergy. The main challenge with such a sensor is itscorrect placement. The sensor should be placed at anoptimal height, not too low (i.e., to avoid anyerroneous detection of small animals) nor too high (forexample, to avoid failure to detect children). A studyof the sensor placement enables deciding the optimalheight according to the user needs and considering thespecific environment in which the system will work. Wediscovered that in field tests, the SE-10 PIR motionsensor offers good performance and is quiteaffordable.2) Light Sensor: A light sensor canmeasure the brightness of the sunlight and providesinformation. The purpose of this measurement is toensure a minimum level of illumination of the street,as required by regulations .The sensor must have highsensitivity in the visible spectrum providing aphotocurrent high enough for low light luminancelevels. For this reason, the phototransistor TEPT5700(By Vishay Semiconductors) has been selected. Based onthe measured luminance, the microcontroller drives thelamp in order to maintain a constant level ofillumination. This action is obviously not requiredduring daylight time, but it is desirable in the earlymorning and at dusk, when it is not necessary tooperate the lamp at full power but simply as a

“support” to the sunlight. This mode enables savingelectric power supplied to the lamp because the lamp isregulated by the combined action of the sensor and themicrocontroller to ensure the minimum illuminationrequired.3) Operating Control: This sensor isuseful to improve fault management and systemmaintenance. Thanks to this sensor (in this case, aHall sensor), it is possible to recognize when the lampis switched on. The system is able to recognize falsepositives, because identified parameters are comparedwith the stored data (e.g., lamps are switched offduring daylight and the sensor incorrectly detects afault, but the microcontroller does not report themalfunction because of additional logic functions).Theinformation is reported through the ZigBee network tothe station control unit, where the operator isinformed about the location of the broken-down lamp andcan send a technician to replace it. The system currentis 1.5 A, so a sensor suited to detect this current isnecessary. An appropriate threshold value to detect theoperation of the lamp has been set between 1 and 1.5 A.The chosen sensor is the ACS756 [20] of the AllegroMicrosystems, an economical and precise solution for acor dc currentsensing, particularly suitable for communicationsystems. Thanks to this sensor, it is possible to storein the microcontroller’s memory the current value whichflows in the LED lamp in normal operating conditions,enabling the online power consumption measurement.4) Emergency Device:

The systemhas an emergency button, which can be useful in case ofan emergency. This device excludes the entire sensorsystem with the objective to immediately turn on thelamp. The light will remain on for a preset time. Afterthat, the button must be pressed again. This preventsthe system from being accidentally active even when thenecessity ends. Obviously, this device does not workduring the day, when there is no need for artificiallight.5) Control Unit: The sensors transfer thecollected information to a controller which runs thesoftware to analyze the system. Figure shows thecontrol software flowchart. After the initial setting,the system is controlled by the light sensor whichactivates the microcontroller only if the sunlightillumination is lower than a fixed threshold. In thiscase, the system reads the state of the emergencybutton, and switches on the lamp if this is activated.The same happens in case of a vehicle or a pedestrian.Once the lamp has been switched on, the operatingsensor starts the monitoring and, in case of faultdetection, an alarm is sent to the control center. Ifno fault is detected, the microcontroller measures thecurrent flux by the Hall sensor memorizing the currentvalues. The entire operation is regulated by a timerwhich enables the system to work for the predeterminedtime. At the stop input, the lamp is turned off and thecycle restarted. The algorithm has been written in PicBasic and runs on the microcontroller.

Control software flowchart

Schematic image of an on-street station

B. Base Control Station: Thebase control station is the hub of the system since it allows thevisualization of the entire lighting system. The transmissionsystem consists of a ZigBee device that receives information onthe state of the lamps and sends it to a terminal. The processingunit consists of a terminal with a serial Universal AsynchronousReceiver-Transmitter (UART) interface which receives informationabout the state of the lamps provided by a ZigBee device. Theterminal is required for a graphical display of the results.Moreover, data on lamps’ operation are associated with the lampaddress; consequently, all faults are easily identified. Thegraphical interface enables monitoring the state of the system(upper section of Fig. 4) with the state of the lights and thepower consumption of each lamp (lower section of Fig. 4).Theoperator will have a graphical representation of the lamplocation within the area where the system is installed. Pressingthe button “Power Consumption Data,” a second window appearswhere power consumption and working time of any lamp are given.

Fig. 4. Lamp control system GUI and measurement of powerconsumption

C. ZigBee Network: ZigBee is awireless communication technology based on theIEEE802.15.4 standard for communication among multipledevices in a wireless personal-area network (WPAN).ZigBee is designed to be more affordable than otherWPANs (such as, for example, Bluetooth) in terms ofcosts and, above all, energy consumption. A ZigBeepersonal-area network (ZBPAN) consists of at least onecoordinator, one (or more) end device(s) and, if

required, one (or more) router(s). The network iscreated when a coordinator selects a channel and startsthe communication, henceforth, a router or an enddevice can join the network. The typical distance of aZigBee transmission range, depending on the environmentconditions and the transmission power, shifts from tensto hundreds of meters, and the transmission power isdeliberately kept as low as possible (in the order of afew mill watts) to maintain the lowest energyconsumption.In the proposed system, the network is built totransfer information from the lamp posts to the basestation control. Information is transferred point bypoint, from one lamppost to another where each lamppost has a unique address in the system. Each lamp postcan only send the information to the nearest one, untilthe information reaches the base station. Thus,transmission power is limited to the required low valueand the signals sent by the lampposts do not interferewith each other. In case of failure of one lamp, thechosen transmission distance between the lamppostsensures that the signal can reach the next operationallamp post without breaking the chain. The ZigBeewireless communication network has been implementedwith the use of Digi-MaxStream radio-frequencymodules called XBee modules, which are available inStandard and Pro versions (pin-to-pin compatible). TheStandard Xbee modules have an operation range of tensof meters indoors and hundreds of meters outdoors,while the XBee Pro modules have a wider spread range inthe order of hundreds of meters indoors and of about1.5 km outdoors, because the Pro modules have highertransmission power, but imply higher consumption (aboutthree times the consumption of the Standard version).

The receiver has very high sensitivity and a lowprobability of receiving corrupted packets (less than1%). The modules should be supplied by 3 V from a dcsource; the current consumption is in the order of 50mA (for XBee) and 150–200 mA (for XBee PRO) in uplinkand in the order of 50 mA in downlink (identical forboth versions); moreover, they support a sleep modewhere consumption is less than 10 A. The XBee modulesare distributed in three versions of antennas: with anon-chip antenna, a wire antenna, and with an integratedconnector for an external antenna.Conclusion: In this project all thetechnologies used are modern which is cost effective interm of long span time, reliable and more beneficiaryas compared to old techniques except LID lamp. In thisarea, light-emitting diode (LED) technology is the bestsolution because it offers many benefits.

Low power consumption Long lumen constancy Long and predictable lifetime Quick turn on/off and dimming No need of rectifier

References http://energy.gov/eere/energybasics/articles/high-

intensity-discharge-lighting-basics http://www.solarconnexion.com/how-solar-works/ http://whatis.techtarget.com/definition/electric-arc http://science.howstuffworks.com/electric-arc-info.htm

https://www.americanlightingassoc.com/Lighting-Fundamentals/Light-Sources-Light-Bulbs.aspx

http://www.warehouse-lighting.com/articles/post/2012/09/24/HID-vs-Fluorescent-High-Bays.aspx

http://www.msue.msu.edu/objects/content_revision/download.cfm/revision_id.510908/workspace_id.-4/lighting.html/

http://homemadecircuitsandschematics.blogspot.in/2012/11/solar-invertercharger-circuit-for.html

“Electronic devices conventional current version “ninthedition by Floyd.

“Remote-Control System of High Efficiency and Intelligent Street Lighting Using a ZigBee Network ofDevices and Sensors” by Fabio Leccese.