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

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Full length article

Tracing of shading effect on underachieving SPV cell of an SPV grid

using 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, India} b_{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 2015 Received in revised form 24 February 2015 Accepted 17 March 2015 Available online 27 April 2015 Keywords:

Shading effect Wireless sensor network ZigBee

Solar photovoltaic AVR microcontroller Dust effect

a b s t r a c t

The environmental and economic merits of converting solar energy into electricity via photovoltaic cells have led to its enormous growth in this sector. Besides material and design parameters, there are many other factors which locally affect Photovoltaic cell like partial shading, humidity, dust, bird droppings, air velocity etc. However, the effect due to a single solar photo voltaic cell being connected to a serial or parallel network (to form a grid) has never been deliberated extensively. In this paper a system 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 to microcontrollers 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 for theﬁrst time with proposed system. The grid and control room is also connected wirelessly which enables the engineer monitoring the grid to meticulously locate the individual solar photovoltaic cell which is underachieving and solve the issue pertaining the same. The proposed system design has been validated with the help of data obtained with Centre for Wind Energy Technology (CWET), Govt. of India.”.

1. Introduction

Rapid fossil fuel consumption and the green house effect have prompted the world to devote considerable resources for the research and development[29] [40]; of Solar Photo Voltaic (SPV) generation systems as solar energy is free, inconsumable and clean source of energy. The Solar energy received by the Earth is 15000 times more than the World's commercial energy con-sumption [18]. Developing countries like India is getting 5000 trillion kWh per year energy incident over its land area, with most parts of the country receiving 4e7 kWh per m2_{per day}_[32]_{. In}

most part of India, clear sunny day is experienced for 250e300 days a year [33] and the annual radiation varies with 1600e2200 kWh/m2_[33]_.

For remote electrical power supply, stand-alone photovoltaic systems are developed[7,9]. Evolution of SPV array is leading to the design and installation of large sized PV plants. The structure of the SPV plant is governed by suitable parallel and series connections of the 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 of such systems. Lot of research is going on improving the efﬁciency of SPV's and large amount of money is invested by various govern-ments to achieve so[39].

For any SPV, output characteristic depends on the environmental conditions. The output power is function of the temperature and the irradiance values of the site where panel is placed. This power varies as a result of any temperature and/or shining variations. However, performance analysis of this scheme in real conditions is generally a difﬁcult task because several factors like ground clearance of SPV panels, 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 entire grid's performance gets degraded and it is very difﬁcult to locate

* Corresponding author.

E-mail addresses:[email protected](V. Kaundal),akmondal1603@gmail. com (A.K. Mondal), [email protected](P. Sharma), kamalbansal@ddn. upes.ac.in(K. Bansal).

Peer review under responsibility of Karabuk University.

H O S T E D BY Contents lists available atScienceDirect

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Table 1

Summary 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 Keyﬁndings Comments and conditions

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

A correction factor of 0.99 (for a 4500_{tilt angle)}

Dietz[11] NY, USA Glass samples 3 months At tilt angles between 000_{and 50}00_{, the reduction}

in solar radiation due to dirt was 5%

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

without wiping Anagnostou and

Forrestieri[6]

Cleveland, OH, USA PV modules 1 year - Degradation is site dependent.- Washing does

not eliminate all degradation.- Permanent loss in maximum power reaches a steady value after several hundred days

Local condition is most damaging

Murphy and Forman[35]; Forman[15]

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

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

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

Dry conditions

Wakim[47] Kuwait PV modules (glass) 6 days 17% reduction in efﬁciency of module

El-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 large change with dust deposition

Concentrating PV study; effect on dust accumulation on cell temperature investigated; Modeling of series resistance effects

Bajpai and Gupta[8] Nigeria Silicon solar cell 4 months Poor efﬁciency due to scattering of incoming

radiation by dust particles

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

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

Said[42] Saudi Arabia Solar collectors& PV

modules (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 up

to 30%

Alamoud[4] Riyadh, Saudi Arabia PV module (glass) 1 year Efﬁciency decreased by 5.73%e19.8% depending

on the type of the module when exposed to outside environment

Compared module

speciﬁcations to manufacturer's claims (differences). Hot, arid conditions

Adanu[2] Ghana PV system (glass) 4 years Effect of dust particles in atmosphere generally

reduces the solar irradiance and the energy output from the PV array

Time of day data reported. Cleaning by wiping of module surface

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

Careful analysis of IV characteristic from operating PVﬁeld. Provides information on instrumentation for monitoring

Goossens,

Van Kerschaever[16]

Israel PV modules (glass) Laboratory work Fine dust deposition on the cell has signiﬁcant effect on power output. Considered effects of due to air borne dust concentration and wind velocity. Reported losses in solar intensity on cells, open-circuit voltage,ﬁll factor, short-circuit current and power as function of accumulation time. Power losses greater than 95%

Reported IeV characteristics as a 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 1

month and 6 months.

V . K aundal et al. / Engineering Science and Technology , a n International Journal 18 (20 15 ) 4 75 e 484 47 6

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

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

Primarily‘‘dirt spot’’ analysis; Some correspondence to the shape of the solar cell in the module. Also, studied cell circuit-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 a

function of tilt angle. Includes a chemical analysis of the dust. Kimber et al.[26] California and

South-western USA

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

Restorative nature of rainfall well documented. Various locations provided in these portions of USA.

Ibrahim[21] Laboratory Tests and

Kuwait

Solar cells (large-area 10 cm*6 cm)

10 days Current losses of greater than 13% and voltage losses of greater 0.86% (5%e15% loss in peak power)

Also studied shadowing of cells

Sulaiman et al.[45] Malaysia PV modules Laboratory

experiment

18% or reduction in peak power when depositing dust on PV module. 6% power reduction difference between mud and talcum deposition

Zorrilla-Casanova et al.[50]

Spain PV module (glass) 1 year In dry seasons, energy losses exceed 20% over

3-month periods. Annual average losses in PV output were 4.4% (with natural cleaning by rain). Proposed regular, periodic cleaning scheduled for modules

Provided simple model, simulated with ray-tracing methods to explain the behavior of dust-induced loses in solar PV modules. Looked at bothﬁxed and tracking systems of PV panels; Evaluated time-of-day losses.

Pavan et al.[31] Italy PV system (1 MW) Investigated two 1-MW PV systems; Soil type

and washing technique control the losses. 6.9% loss with sandy soil and 1.1% with more compact soil

All measurement under STC. Regression model used (superior to performance ration which is inﬂuenced by seasonal variations in temperature and plant availability)

Jiang et al.[22] China PV module (glass) Dust deposition layer 0e22 g/cm 2 , PV

efﬁciency decreased by 26% (linear

relationship). No difference between cell types

Note that modules encapsulated with epoxy (organic) degrade more. Mohamed and

Hasan[34]

Libya PV Modules Outdoor Testing PV modules exposed for a period from February

through May in Sahara environment. Reported signiﬁcant though gradual reduction in power. Cleaning procedures.

Object of study is to evaluate the cleaning needed to keep the PV output at a sufﬁcient level. Weekly washing (water) kept power loses in the 2%e5% range

V . K aundal et al. / Engineering Science and Technology , a n International Journal 18 (20 15 ) 4 75 e 484 47 7

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that one panel which is actually affected. The solution to this problem could be a technology known for some years now named wireless sensor network. We can monitor and control the panel and increase its efﬁciency accordingly. The most important factor that hinders the Panel efﬁciency is the shading effect [17]. Partial shading is one of the main causes that reduce the energy yield of the SPV array.

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

1.1. Shading effect

Today, commercially available Si SPV panels have their cells connected in series. In order to avoid reverse voltage due to shadowing or other abnormalities, bypass diodes are connected in parallel with each set of 18 cells[5], which forms the sub modules [38]. Furthermore, a SPV module comprises of number of sub modules in series[28], and higher output voltage is obtained by connecting several modules in series of a SPV array. For higher power, these SPV arrays are connected in parallel. The partial shading of a photovoltaic array reduces its output power capability and has been shown experimentally by Cheng-D Sera et al.[48]. They connected two photovoltaic modules in series and in parallel under different illumination conditions. The illumination was uni-form throughout the surface area of the panels. They presented the impact of shading on I-V and P-C curves of a SPV cell and explained the 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 and weather conditions [44]. Dust settlement mainly relies on many factors like chemical properties, size, weight, shape, site speciﬁc factors, tilt angle, surfaceﬁnish, 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 the ground[16].

Throughout the period of solar research, studies have shown reduced performance of SPV under dust accumulation and related environmental factors. Based on the time dependent degradation, a correction factor or a guideline for cleaning frequency has been developed. Dust accumulation also occurs at varying rates in different parts of the world. Various types of research has been done to prove the dust accumulation effect and is been listed in Table 1.

2.2. Effect of humidity on SPV cell performance

The effect of humidity can be seen in two aspects:ﬁrst is the effect of water vapour on the irradiance level of sunlight and second is the humidity ingression on the SPV cell enclosure. When light ray hits a water droplets, it gets refracted, reﬂected or diffracted resulting in the reduction of reception level of the direct compo-nent of solar radiation. Humidity alters the irradiance level in a non linear manner causing variations in Vocand Isc, resulting in the drop

of efﬁciency[19]. The effect of humidity on irradiance and irradi-ance on voltage and current are shown inFigs. 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 causes encapsulant delamination[46].

3. Proposed system for increasing efﬁciency.

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

Fig. 1. Variation of Vocand Iscwith irradiance level[19].

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

Fig. 3. On-Site Controller Schematic- Transmitter Side. V. Kaundal et al. / Engineering Science and Technology, an International Journal 18 (2015) 475e484

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section we will elaborate the block diagram of the structure, circuit and prototype model that was made for the 100 kWh SPV panels installed in the University of Petroleum& Energy Studies at the Dehradun- India Campus.Figs. 3 and 4are the block diagram of the model for the proposed data acquisition system from a remote isolated site to the control room. The SPV system constitutes of a photovoltaic generator in combination with series and parallel connected SPV modules.

The measured parameters (e.g. temperature, humidity, current) are acquired on-site (transmitter side) and then wirelessly passed on 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 (ADC Conversion Port) of AVR microcontroller as shown inFig. 5. Data collected from the above sensors are processed and transmitted wirelessly via ZigBee transceiver (IEEE 802.15.4) which is con-nected to Rxand Txpins (USART PORT) of AVR Series

microcon-troller. In the receiver side values of current, temperature and humidity sensor will be received via ZigBee transceiver module shown inFig. 6.

The current sensor resolution is 10 mV/C, whereas the ADC port has a VCCof 5 V with a resolution of 1024 levels. This comes around

0.0403 V/level (0.05 V/level approximately). Hence, the ADC value has to be divided by 2 to give correct value. The data is received serially at the transceiver (master node) end. The threshold value below which an SPV panel is considered faulty is decided by a considerable comparative drop in the successive current readings. The prototype designed and installed set up is shown inFig. 7. In the prototype model we have used Atmega 16 microcontroller but the algorithm used can be implemented in any microcontroller and processor.

Fig. 5. Circuit design of transmitter side. Fig. 4. Control Room Schematic- Receiver Side.

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The reading with multi meter and microcontroller are slightly different showing an error with current sensor because of its fluctuating value. The value will be considerable. In the algorithm syntax is used to stop thefluctuation. Another option is to integrate ceramic capacitors with current sensor to stop the fluctuations. Fig. 8 shows the shading effect on the PV panels. The sending commands/values and receiving commands/values of sensors are displayed in the liquid crystal display.

4. Algorithm for node designing in wireless sensor network. The above proposed system is designed using an algorithm written in AVR6 software. Theﬁrmware is then burned into the microcontroller using a cross compiler. In this section, the algo-rithm that was written for the solar panel grid is explained methodicallyFig. 9.

Algorithm for Slave nodes installed with panelFig. 10

Fig. 6. Circuit design of receiver side.

Fig. 7. Circuit design of receiver side.

V. Kaundal et al. / Engineering Science and Technology, an International Journal 18 (2015) 475e484 480

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Algorithm for Master node installed in control Room

5. Results& discussions

The proposed system has been designed and evaluated with grid log of the in house (University of Petroleum and Energy Studies) 100 kWh SPV panels. In this paper we have shown the data measured on three different panels from the same grid for 2 days. FromTable 2andFigs. 11e13. The fashion of trend (from graph) veriﬁes that the data is valid; also the minor offset which is coming is due to the connection/wiring losses. FromTable 2andFig. 11it's

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

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

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

inherent advantages of reduced cost and less noise interference in comparison to a wired network. The propose system has been designed and installed in prototype model with 100 kWh of panel and data is recorded for thirty eight days. In this paper thirty eight days of data is mentioned and graphs have been plotted accord-ingly. The total time taken for complete processing for a batch of data sets is less than 10

m

s approximately. IVOLT1 is the voltage of solar panels, IAMP1 is the current value of solar panel, BVOLTS is the battery voltage, BAMPS is the battery current and SAMP is the solar AMP. Shading effect comes in the solar panel when the ampere rating (SAMPS) of solar is less than 20 A. These values will be coming wirelessly from the slave nodes to the master node.

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. V. Kaundal et al. / Engineering Science and Technology, an International Journal 18 (2015) 475e484

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Fig. 11. Analysis of Solar Ampere versus time.

Fig. 12. Analysis of Battery Ampere versus time. Table 2

Analyzed two day data.

S.No. Time Date Solar Panel Amps-1 Solar Panel Amps-2 Solar Panel Amps-3 Battery Ampere-1 Battery Ampere-2 Battery Ampere-3 Temperature of battery-1 Temperature of battery-2 Temperature of battery-3 1 7:15 1-8-14 5.6 5 5.0 6 6 6 32.5 32.5 32.5 2 10:05 1-8-14 28.9 26 27 62 61 61 31 32 31 3 13:28 1-8-14 15.4 5.0 15.4 59 6 58 32 32 32 4 16:30 1-8-14 11.2 6 11.2 130 5 130 32 33 32 5 19:00 1-8-14 31 29 30 28 26 26 31 33 33 6 7:00 2-8-14 5.1 5 6 4 5 4 31 33 32 7 10:00 2-8-14 54 51 56 76 75 75 32 33 32 8 13:15 2-8-14 122 120 6 53 55 4 34 34 32 9 16:22 2-8-14 65 63 61 24 22 21 33 33 33 10 19:05 2-8-14 17 18 16 42 43 44 32 33 33

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