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Engineering Science and Technology, an International Journal 18 (2015) 475e484

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Tracing of shading effect on underachieving SPV cell of an SPV gridusing wireless sensor network

Vivek Kaundal a, Amit Kumar Mondal a, *, Paawan Sharma a, Kamal Bansal b

a Dept. of Electronics Instrumentation and Control, University of Petroleum and Energy Studies, Dehradun, Indiab Dept. of Electrical, Power & Energy, University of Petroleum and Energy Studies, Dehradun, India

a r t i c l e i n f o

Article history:Received 5 January 2015Received in revised form24 February 2015Accepted 17 March 2015Available online 27 April 2015

Keywords:Shading effectWireless sensor networkZigBeeSolar photovoltaicAVR microcontrollerDust effect

* Corresponding author.E-mail addresses: vkaundal@ddn.upes.ac.in (V. Kau

com (A.K. Mondal), paawan.sharma.in@ieee.org (P.upes.ac.in (K. Bansal).

Peer review under responsibility of Karabuk Univ

http://dx.doi.org/10.1016/j.jestch.2015.03.0082215-0986/© 2015 Karabuk University. Production anlicenses/by-nc-nd/4.0/).

a b s t r a c t

The environmental and economic merits of converting solar energy into electricity via photovoltaiccells have led to its enormous growth in this sector. Besides material and design parameters, there aremany other factors which locally affect Photovoltaic cell like partial shading, humidity, dust, birddroppings, air velocity etc. However, the effect due to a single solar photo voltaic cell being connectedto a serial or parallel network (to form a grid) has never been deliberated extensively. In this paper asystem design that will detect the underperforming panel in the entire grid is proposed and validated.All the Photo voltaic panels in a grid are connected with current sensors, which are connected tomicrocontrollers and these microcontrollers are locally connected with the wireless sensor network.With the help of wireless sensor network, grid monitoring for individual panel has been achieved forthe first time with proposed system. The grid and control room is also connected wirelessly whichenables the engineer monitoring the grid to meticulously locate the individual solar photovoltaic cellwhich is underachieving and solve the issue pertaining the same. The proposed system design hasbeen validated with the help of data obtained with Centre for Wind Energy Technology (CWET), Govt.of India.”.© 2015 Karabuk University. Production and hosting by Elsevier B.V. This is an open access article under

the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Rapid fossil fuel consumption and the green house effect haveprompted the world to devote considerable resources for theresearch and development [29] [40]; of Solar Photo Voltaic (SPV)generation systems as solar energy is free, inconsumable andclean source of energy. The Solar energy received by the Earth is15000 times more than the World's commercial energy con-sumption [18]. Developing countries like India is getting 5000trillion kWh per year energy incident over its land area, with mostparts of the country receiving 4e7 kWh per m2 per day [32]. Inmost part of India, clear sunny day is experienced for 250e300days a year [33] and the annual radiation varies with1600e2200 kWh/m2 [33].

ndal), akmondal1603@gmail.Sharma), kamalbansal@ddn.

ersity.

d hosting by Elsevier B.V. This is a

For remote electrical power supply, stand-alone photovoltaicsystems are developed [7,9]. Evolution of SPV array is leading to thedesign and installation of large sized PV plants. The structure of theSPV plant is governed by suitable parallel and series connections ofthe SPV cells [10,17], in this way it forms a grid connected photo-voltaic systems [24].

The panel monitoring and control is the most important part ofsuch systems. Lot of research is going on improving the efficiency ofSPV's and large amount of money is invested by various govern-ments to achieve so [39].

For any SPV, output characteristic depends on the environmentalconditions. The output power is function of the temperature and theirradiance values of the sitewhere panel is placed. This power variesas a result of any temperature and/or shining variations. However,performance analysis of this scheme in real conditions is generally adifficult task because several factors like ground clearance of SPVpanels, soil (sandy, dusty, metallic rich etc.) condition of the sur-rounding area/soil particle size etc. are acting on it.

If any of the panel in the grid is not working then the entiregrid's performance gets degraded and it is very difficult to locate

n open access article under the CC BY-NC-ND license (http://creativecommons.org/

Table 1Summary of selected reported dust effects on solar photovoltaic (SPV) device performances for the period of 1942 to the present.

Reference Location Type of solar device Period of study Key findings Comments and conditions

Hottel and Woertz [20] Boston, MA, USA Solarethermal collectors 3 months Maximum degradation during the test periodwas 4.7%

A correction factor of 0.99 (for a4500 tilt angle)

Dietz [11] NY, USA Glass samples 3 months At tilt angles between 000 and 5000 , the reductionin solar radiation due to dirt was 5%

Sayigh [43] Saudi Arabia Solar collectors 25 days Heat-collection reduction of 30% after 3 dayswithout wiping

Anagnostou andForrestieri [6]

Cleveland, OH, USA PV modules 1 year - Degradation is site dependent.- Washing doesnot eliminate all degradation.- Permanent lossin maximum power reaches a steady value afterseveral hundred days

Local condition is mostdamaging

Murphy andForman [35];Forman [15]

Lexington, MA, USA PV module (glass) 18 months Measurement of soil accumulation and modelCleaning using gloss meter

Nimmo, Saed [36] Saudi Arabia Solar collectors& PVmodules (glass)

6 months 26% and 40% reduction of efficiency from solarcollector and PV panels, respectively

Dry conditions

Wakim [47] Kuwait PV modules (glass) 6 days 17% reduction in efficiency of moduleEl-Shobokshy et al. [13];Zakzouk [49]

Saudi Arabia CPV 1 month Open-circuit voltage did not change, and short-circuit current and cell efficiency showed a largechange with dust deposition

Concentrating PV study; effecton dust accumulation on celltemperature investigated;Modeling of series resistanceeffects

Bajpai and Gupta [8] Nigeria Silicon solar cell 4 months Poor efficiency due to scattering of incomingradiation by dust particles

Ryan et al. [41] Oregon, USA Solar module array (glass) 6 years Unwashed solar cell array has degraded at a rateabout 1.4% per year

Fluctuations in degradation(rates) do exist and long-termtesting of degradation is needed

Said [42] Saudi Arabia Solar collectors& PVmodules (glass)

1 year 7% reduction per month for PV panels and 2.8%to 7% for solar collectors

Pande [37] India PV module (glass) 1 year Reduction in current value due to dust was upto 30%

Alamoud [4] Riyadh, Saudi Arabia PV module (glass) 1 year Efficiency decreased by 5.73%e19.8% dependingon the type of the module when exposed tooutside environment

Compared modulespecifications to manufacturer'sclaims (differences). Hot, aridconditions

Adanu [2] Ghana PV system (glass) 4 years Effect of dust particles in atmosphere generallyreduces the solar irradiance and the energyoutput from the PV array

Time of day data reported.Cleaning by wiping of modulesurface

Kattakayam et al. [25] India PV module (glass) Laboratory work The loss of power due to accumulation of dustand the increase in temperature of the panelcan be significant

Careful analysis of IVcharacteristic from operatingPV field. Provides informationon instrumentation formonitoring

Goossens,Van Kerschaever [16]

Israel PV modules (glass) Laboratory work Fine dust deposition on the cell has significanteffect on power output. Considered effects ofdue to air borne dust concentration and windvelocity. Reported losses in solar intensity oncells, open-circuit voltage, fill factor, short-circuit current and power as function ofaccumulation time. Power losses greater than95%

Reported IeV characteristics asa function of the dust density

Hassan et al. [3] Saudi Arabia PV modules (glass) 6 months 33.5% and 65.8% reductions in efficiency after 1month and 6 months.

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Kobayashi et al. [27] Tokyo, Japan PV module (glass) Laboratoryexperiments

Changing the aspect ratio of PV cell used for PVmodule results in degradation output of 80% orless with 3% of spot dirt on the module area.

Primarily ‘‘dirt spot’’ analysis;Some correspondence to theshape of the solar cell in themodule. Also, studied cellcircuit-configuration effects.

Elminir et al. [14] Helwan, Cairo, Egypt PV cells and glass 7 months Decreases in PV output of about 17.4%/month Provides information as afunction of tilt angle. Includes achemical analysis of the dust.

Kimber et al. [26] California andSouth-western USA

PV system (grid-connected) 1 year ‘‘Soiling’’ study for utility-connected PV system.Efficiency and energy losses (typical 0.2% perday without rainfall)

Restorative nature of rainfallwell documented. Variouslocations provided in theseportions of USA.

Ibrahim [21] Laboratory Tests andKuwait

Solar cells (large-area10 cm*6 cm)

10 days Current losses of greater than 13% and voltagelosses of greater 0.86% (5%e15% loss in peakpower)

Also studied shadowing of cells

Sulaiman et al. [45] Malaysia PV modules Laboratoryexperiment

18% or reduction in peak power whendepositing dust on PV module. 6% powerreduction difference between mud and talcumdeposition

Zorrilla-Casanovaet al. [50]

Spain PV module (glass) 1 year In dry seasons, energy losses exceed 20% over 3-month periods. Annual average losses in PVoutput were 4.4% (with natural cleaning byrain). Proposed regular, periodic cleaningscheduled for modules

Provided simple model,simulated with ray-tracingmethods to explain thebehavior of dust-induced losesin solar PV modules. Looked atboth fixed and tracking systemsof PV panels; Evaluated time-of-day losses.

Pavan et al. [31] Italy PV system (1 MW) Investigated two 1-MW PV systems; Soil typeand washing technique control the losses. 6.9%loss with sandy soil and 1.1% with morecompact soil

All measurement under STC.Regression model used(superior to performance rationwhich is influenced by seasonalvariations in temperature andplant availability)

Jiang et al. [22] China PV module (glass) Dust deposition layer 0e22 g/cm 2 , PVefficiency decreased by 26% (linearrelationship). No difference between cell types

Note that modulesencapsulated with epoxy(organic) degrade more.

Mohamed andHasan [34]

Libya PV Modules Outdoor Testing PV modules exposed for a period from Februarythrough May in Sahara environment. Reportedsignificant though gradual reduction in power.Cleaning procedures.

Object of study is to evaluatethe cleaning needed to keep thePV output at a sufficient level.Weekly washing (water) keptpower loses in the 2%e5% range

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Fig. 1. Variation of Voc and Isc with irradiance level [19].

Fig. 2. Variation of irradiance level with relative humidity [19].

Fig. 3. On-Site Controller Schematic- Transmitter Side.

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that one panel which is actually affected. The solution to thisproblem could be a technology known for some years now namedwireless sensor network.We canmonitor and control the panel andincrease its efficiency accordingly. The most important factor thathinders the Panel efficiency is the shading effect [17]. Partialshading is one of the main causes that reduce the energy yield ofthe SPV array.

In this paper we are reporting a real time solution for moni-toring the temperature, humidity, voltage and current of SPV andits surrounding. The diagnostic featurewithin the SPV arrangement(Parallel or Series) to find which SPV is affected due to partialshading and lowering the overall output performance of the system[12]. The proposed system is low cost and the data is acquired usingmicrocontrollers. Data transmission is done wirelessly to themaster station for further analysis and interpretation.

1.1. Shading effect

Today, commercially available Si SPV panels have their cellsconnected in series. In order to avoid reverse voltage due toshadowing or other abnormalities, bypass diodes are connected inparallel with each set of 18 cells [5], which forms the sub modules[38]. Furthermore, a SPV module comprises of number of submodules in series [28], and higher output voltage is obtained byconnecting several modules in series of a SPV array. For higherpower, these SPV arrays are connected in parallel. The partialshading of a photovoltaic array reduces its output power capabilityand has been shown experimentally by Cheng-D Sera et al. [48].They connected two photovoltaic modules in series and in parallelunder different illumination conditions. The illumination was uni-form throughout the surface area of the panels. They presented theimpact of shading on I-V and P-C curves of a SPV cell and explainedthe reduction in output power due to the partial shading effect.

2. Related work

2.1. Effect of dust on SPV cell performance

Dust deposition is a function of various environmental andweather conditions [44]. Dust settlement mainly relies on manyfactors like chemical properties, size, weight, shape, site specificfactors, tilt angle, surface finish, humidity, wind speed etc. [23,30].As the wind speed increases, dust deposition will also increases.Dust deposition is also relative to the panel clearance from theground [16].

Throughout the period of solar research, studies have shownreduced performance of SPV under dust accumulation and relatedenvironmental factors. Based on the time dependent degradation, acorrection factor or a guideline for cleaning frequency has beendeveloped. Dust accumulation also occurs at varying rates indifferent parts of the world. Various types of research has beendone to prove the dust accumulation effect and is been listed inTable 1.

2.2. Effect of humidity on SPV cell performance

The effect of humidity can be seen in two aspects: first is theeffect of water vapour on the irradiance level of sunlight and secondis the humidity ingression on the SPV cell enclosure.When light rayhits a water droplets, it gets refracted, reflected or diffractedresulting in the reduction of reception level of the direct compo-nent of solar radiation. Humidity alters the irradiance level in a nonlinear manner causing variations in Voc and Isc, resulting in the dropof efficiency [19]. The effect of humidity on irradiance and irradi-ance on voltage and current are shown in Figs. 1 and 2.

When SPV cells are exposed for longer time to humid condi-tions, due to the high content of water vapour in the air it causesencapsulant delamination [46].

3. Proposed system for increasing efficiency.

The shading on panels is very important factor that will reducethe efficiency of SPV panels. If one panel undergoes failure theentire grid gets affected. Shading can be because of dust particles,humidity effect, temperature variation, buildings, trees etc. In this

Fig. 4. Control Room Schematic- Receiver Side.

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section we will elaborate the block diagram of the structure, circuitand prototype model that was made for the 100 kWh SPV panelsinstalled in the University of Petroleum & Energy Studies at theDehradun- India Campus. Figs. 3 and 4 are the block diagram of themodel for the proposed data acquisition system from a remoteisolated site to the control room. The SPV system constitutes of aphotovoltaic generator in combination with series and parallelconnected SPV modules.

Fig. 5. Circuit design o

The measured parameters (e.g. temperature, humidity, current)are acquired on-site (transmitter side) and then wirelessly passedon the control room (receiver side).

3.1. Sensor interface and circuit description (schematics of nodes)

The prototype circuit is controlled by an AVR Series micro-controller. In the transmitter side, analog sensors like current,temperature and humidity are connected with PORT A (ADCConversion Port) of AVR microcontroller as shown in Fig. 5. Datacollected from the above sensors are processed and transmittedwirelessly via ZigBee transceiver (IEEE 802.15.4) which is con-nected to Rx and Tx pins (USART PORT) of AVR Series microcon-troller. In the receiver side values of current, temperature andhumidity sensor will be received via ZigBee transceiver moduleshown in Fig. 6.

The current sensor resolution is 10mV/�C, whereas the ADC porthas a VCC of 5 V with a resolution of 1024 levels. This comes around0.0403 V/level (0.05 V/level approximately). Hence, the ADC valuehas to be divided by 2 to give correct value. The data is receivedserially at the transceiver (master node) end. The threshold valuebelow which an SPV panel is considered faulty is decided by aconsiderable comparative drop in the successive current readings.The prototype designed and installed set up is shown in Fig. 7. Inthe prototype model we have used Atmega 16 microcontroller butthe algorithm used can be implemented in any microcontroller andprocessor.

f transmitter side.

Fig. 6. Circuit design of receiver side.

Fig. 7. Circuit design of receiver side.

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The reading with multi meter and microcontroller are slightlydifferent showing an error with current sensor because of itsfluctuating value. The value will be considerable. In the algorithmsyntax is used to stop the fluctuation. Another option is to integrateceramic capacitors with current sensor to stop the fluctuations.Fig. 8 shows the shading effect on the PV panels. The sendingcommands/values and receiving commands/values of sensors aredisplayed in the liquid crystal display.

4. Algorithm for node designing in wireless sensor network.

The above proposed system is designed using an algorithmwritten in AVR6 software. The firmware is then burned into themicrocontroller using a cross compiler. In this section, the algo-rithm that was written for the solar panel grid is explainedmethodically Fig. 9.

Algorithm for Slave nodes installed with panel Fig. 10

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Algorithm for Master node installed in control Room

5. Results & discussions

The proposed system has been designed and evaluatedwith gridlog of the in house (University of Petroleum and Energy Studies)100 kWh SPV panels. In this paper we have shown the datameasured on three different panels from the same grid for 2 days.From Table 2 and Figs. 11e13. The fashion of trend (from graph)verifies that the data is valid; also the minor offset which is comingis due to the connection/wiring losses. From Table 2 and Fig. 11 it's

been clear that during August 1st, 2014 from 1328 h to 1630 h andbeyond there is a sharp decline in current value of solar panel 2 andits battery current due to shading and solar panel 1and 3 are givingexpected outputs. Same scenario is seen on August 2nd, 2014during 1315 h due to shading only. The effect can also be seen inFig. 2 of Battery current plot. The overall effect has been shown inFig. 3, fromwhere it can be verified that due to decline in the solarampere rating there has been a decrease in battery ampere ratingalso. The readings obtained from the individual panels and

Fig. 9. Flowchart for Algorithm and WSN network working.

Fig. 8. Shading on SPV Array.

Fig. 10. Flowchart for Algorithm and WSN network working for a single node.

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transmitted wireless to control room. By creating the proposednetwork, individual panel monitoring is done and we can rectifythe problem in the particular panel from the entire grid. The pro-posed systems is verified against the available Centre for Windenergy Technology (CWET) (2014) [1] online data, and also UPES isone of the nodal centre for CWET.

Owing to large size of the current grids, it is very difficult tomonitor the individual panels. The proposed system will help inefficiently identifying the underperforming panels in a grid. Using awireless sensor network in the proposed system comes with

inherent advantages of reduced cost and less noise interference incomparison to a wired network. The propose system has beendesigned and installed in prototype model with 100 kWh of paneland data is recorded for thirty eight days. In this paper thirty eightdays of data is mentioned and graphs have been plotted accord-ingly. The total time taken for complete processing for a batch ofdata sets is less than 10 ms approximately. IVOLT1 is the voltage ofsolar panels, IAMP1 is the current value of solar panel, BVOLTS isthe battery voltage, BAMPS is the battery current and SAMP is thesolar AMP. Shading effect comes in the solar panel when theampere rating (SAMPS) of solar is less than 20 A. These values willbe coming wirelessly from the slave nodes to the master node.

Fig. 11. Analysis of Solar Ampere versus time.

Fig. 12. Analysis of Battery Ampere versus time.

Table 2Analyzed two day data.

S.No. Time Date Solar PanelAmps-1

Solar PanelAmps-2

Solar PanelAmps-3

BatteryAmpere-1

BatteryAmpere-2

BatteryAmpere-3

Temperature ofbattery-1

Temperature ofbattery-2

Temperature ofbattery-3

1 7:15 1-8-14 5.6 5 5.0 �6 �6 �6 32.5 32.5 32.52 10:05 1-8-14 28.9 26 27 62 61 61 31 32 313 13:28 1-8-14 15.4 5.0 15.4 59 �6 58 32 32 324 16:30 1-8-14 11.2 6 11.2 �130 �5 �130 32 33 325 19:00 1-8-14 31 29 30 28 26 26 31 33 336 7:00 2-8-14 5.1 5 6 �4 �5 �4 31 33 327 10:00 2-8-14 54 51 56 76 75 75 32 33 328 13:15 2-8-14 122 120 6 53 55 �4 34 34 329 16:22 2-8-14 65 63 61 24 22 21 33 33 3310 19:05 2-8-14 17 18 16 42 43 44 32 33 33

Fig. 13. Conclusive data analysis of Solar ampere versus Battery ampere w.r.t time.

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