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Performance of photovoltaic water pumping systems under the influence of panel cooling
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
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Performance of photovoltaic water pumping systems under the influence of panel cooling M.Mohanraj a,*, P.Chandramohan b, M.Sakthivel c and KamaruzzamanSopian d a
Department of Mechanical Engineering, Hindusthan College of Engineering and Technology, Coimbatore 641032, India Department of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore 641022, India c Department of Mechanical Engineering, K. L. Deemed to be University, Guntur 522502, India d Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia b
In this paper, the performance of a photovoltaic water pumping system was experimentally investigated under the influence of panel cooling using air and water as working fluids. The experimental observations have been made under the climatic conditions of Coimbatore city in India during the year 2017. The system performance was evaluated in four different cooling modes such as: (a) with air cooling over the top surface of the panel; (b) with air cooling over the bottom surface of the panel; (c) with water cooling over the top surface of the panel and (d) with water cooling over the bottom surface of the panel. The performances of a photovoltaic water pumping system working with four different panel cooling modes are compared with the system without panel cooling. The economical and environmental impacts have been assessed for a period of twenty years. The results showed that, the water cooling provided over the bottom surface of the panel has significant performance enhancement when compared to other cooling modes. The economic assessment results showed that, the photovoltaic water pumping systems using water cooling over the bottom surface of the panel has payback period of 7.3 years with 13.7% return on investment and 10.9% internal rate of return. The trial experiments confirmed that, it is possible to reduce the carbon-dioxide emissions by about 20.4 tons during the period of twenty years life when compared to the grid connected water pumping systems powered by coal based power plants. Introduction The fast depletion of conventional fossil energy sources and its critical impacts on the environment have created the research interest in identifying a sustainable energy option for water pumping systems. In India, the potential availability of solar energy provides a good solution to the energy related issues for water pumping applications [1]. Solar energy is integrated with water pumping systems either in the form of photovoltaic electric power obtained through photovoltaic panel to power the electrical motor of a pump or in the form of solar thermal energy harvesting
through solar thermal collectors to power the Rankine cycle. Out of these two options, the solar photovoltaic is an ideal option for remote water pumping applications due to its simplicity of installation with less maintenance [2]. Earlier reported reviews confirmed that, photovoltaic water pumping systems (PVWPSs) are having potential in the agriculture sector [3–7]. Approximately 58% of Indian geographical areas have good solar irradiation potential, which could fulfil the increasing power requirements, especially for agricultural water pumping [8]. The direct-coupled PVWPSs are commonly used for low head water pumping in agricultural applications due to its less maintenance when compared to the battery buffered PVWPS [9]. Moreover, it is observed
*Corresponding author. M., M. ([email protected]) 1755-0084/ã 2019 Published by Elsevier Ltd. https://doi.org/10.1016/j.ref.2019.10.006
31
ORIGINAL RESEARCH ARTICLE
Nomenclature
ORIGINAL RESEARCH ARTICLE
A A0 a0 C cp E EI egap g G h H I i k k0 m n N Ncs Nms P q Q Q0 R t T U V v x
Photovoltaic panel area (m2) Completion factor Constant Constant Specific heat (kJ/kgK) Electric output of the photovoltaic cell (W) Environmental impacts of water pumping (Tons of CO2) Material band gap Gravitational constant (9.81 N/s2) Solar irradiation (W/m2) Heat transfer coefficienct (W/m2K) Head (m) Current (A) Discount rate (%) Thermal conductivity (W/mK) Boltzmann constant (1.381 1023 J/K) Mass (kg) Number of months Number of years Number of cells connected in series Number of modules connected in series Pumping power (W) Charge of electron (assumed as 1.60217733 1019 C) Heat transfer (W) Pump discharge (m3/h) Resistance (V) Time (s) Temperature (K) Overall heat transfer coefficienct (W/m2K) Votlage (volts) Velocity (m/s) Thickness of the material (mm)
Greek symbols
a b d m s e t h rw
Absorbsivity Temperature coefficient Carbon-dioxide emission factor Temperature coefficient of short circuit current (A/ K) Stefan Boltzman constant 5.68 108 W/m2 K4 Emissivity of the surface Transmissivity through glass Efficiency (%) Density of water (kg/m3)
Subscripts
a c c-td c-g c, ref conv,g conv,td EVA
32
Ambient Cell Cell to tedlar Cell to glass Cell, reference Convective heat loss from glass surface Convective heat loss from tedlar surface Ethylene vinyl acetate
Renewable Energy Focus Volume 31, Number 00 December 2019
g i L, ref m mp, ref mp, ref o,c o,ref pv rad,g rad,td ref s sc td
Glass Inverter Light, reference Maximum Maximum power point, reference Maximum power point, reference Open circuit Open circuit at reference Photovoltaic Radiation heat loss from glass Radiation heat loss from tedlar Reference Series resistance Short circuit Tedlar
Abbreviations
AC CF DC EVA INR IRR NPV PBP PVWPSs ROI
Alternative current Cash flow Direct current Ethylene vinyl acetate Indian Rupees (1 US Doller = 72.00 INR) Internal rate of return Net present value Payback period Photovoltaic water pumping systems Return on Investment
that, ac motors are performing better when compared to the d.c motors and requires less maintenance [10]. Therefore, many research investigations have been focused on photovoltaic assisted a.c water pumping systems. The photovoltaic cells get heated and its performance was dropped during peak sunshine hours. However, the maximum panel power output will be expected during peak sunshine hours. Many research efforts have been made for improving the performance of photovoltaic panels using water and air as cooling medium [11]. In a related work, Abdolzadeh and Ameri [12] improved the performance of a PVWPS by spraying water over the top surface of the photovoltaic panels. It was reported that, the efficiency of the photovotlaic panels, pump subsystem and the total system were improved by 3.26%, 1.40% and 1.35%, respectively at 16 m operating head. In another work, Kordzadeh [13] investigated the performance of a PVWPS under the influence of panel cooling using film layer of water spray over the panel surface at Kerman city in Iran. It was reported that, the photovoltaic panel efficiency was improved by about 3.7% when compared to the photovoltaic panel without cooling, which improves the performance of the pump efficiency. Similarly, Habiballahi et al. [14] improved the photovoltaic electrical efficiency; pump efficiency and overall efficiency of a PVWPS by about 2%, 4%, and 1%, respectively under the influence of water spraying over the bottom surface of the panel. Gopal et al. [15] investigated the performance of a PVWPS under the influence of panel cooling using air as working fluid and reported with significant performance improvement when compared to the system without panel cooling. Many
Renewable Energy Focus Volume 31, Number 00 December 2019
Experiments The performance investigations have been made under the meteorological conditions of Coimbatore city (latitude of 10.98 N and longitude of 76.96 E) in India during the months of February 2017, March 2017, April 2017, June 2017 and September 2017.
Experimental setup The schematic diagram of a direct coupled PVWPS (using A.C. power input) experimental setup is shown in Figure 1. The PVWPS was installed in a sump with 500 l water storage capacity. The setup consists of a 380 W mono block centrifugal pump assisted by a variable frequency drive and four photovoltaic panels (with dimensions 1.6 m 1 m) of total area 6.4 m2 with a rated output power of 1100 W during peak sunshine durations. However, the output of the photovoltaic panels fluctuates between 400 W and 1000 W depending on the ambient conditions. The specifications of the centrifugal pump and photovoltaic panel are given in Table 1 and Table 2, respectively. The delivery pipe has a control valve for varying the delivery head. The schematic diagrams of panel cooling (using air and water) arrangements are illustrated in Figure 1(b–e). Air cooling arrangement provided over the top surface of the panel consists of 40 W centrifugal fan distributed
evenly through nozzle outlets. Similarly, the cooling arrangement provided over the bottom surface of the panel consists of an axial flow fan with rated input power 40 W and baffle arrangements to ensure better panel cooling. The photovoltaic panel with water cooling over the top surface of the panel was provided by tapping water from the pump discharge. The nozzle outlets were placed along the top surface of the panel to spill out the water and provide uniform cooling. The water flows over the top and bottom surfaces of the panel was controlled by a solenoid valve. The cooling arrangement at the bottom surface of the panel was provided with nozzle outlets located perpendicular to the bottom surface of the panel at a distance of 70 mm. The water ejected from the nozzles sprayed over the bottom surface of the panel and provides uniform cooling. The panel is placed at an inclination of 11 according to the latitude of Coimbatore [27].
Instrumentation Sixteen calibrated K-type thermocouples were fixed at different locations (as mentioned in Figure 1) over the top and bottom surfaces of the photovoltaic panel to measure the glass and tedlar temperatures. All the thermocouples were connected to a digital temperature indicator and also to the computer through a data logger. Based on the measured glass and tedlar temperatures, the cell temperature was theoretically predicted using mathematical equations. Ambient wind velocity flows over the photovoltaic panel surface was measured using a cup type anemometer. The availability of solar irradiation was measured using a pyranometer. The instantaneous current, voltage and power output of the panel were measured using ammeter, voltmeter and Wattmeter, respectively. The discharge of water pump was measured using a rotameter connected in the discharge line. Similarly, the water consumption for cooling of panel was measured separately using a separate rotameter. The power consumed by the pump and cooling fan was measured using separate Wattmeter. The suction and delivery pressures were measured using vacuum gauge and pressure gauge, respectively. The speed of the pump was measured using a digital tachometer. The detailed specifications of the measuring instruments are listed in Table 3.
Experimental procedure The experimental observations were made at every ten minutes interval during 9.00 am to 17.00 pm on clear sunny days with minimum fluctuations of solar irradiation. Before conducting experiments using photovoltaic panel, the centrifugal pump was tested using a variable frequency drive at different heads ranging from 5 m to 25 m with the frequency ranges between 25 and 50 Hz. Based on the experimental observations, the polynomial equations were developed for predicting the performance of a centrifugal pump at different power inputs. Initially, the experiments were carried in a PVWPS without the influence of panel cooling for a constant pumping head of 15 m. The performance parameters such as, power output of the photovoltaic panel, power consumption of the motor and discharge of the pump were experimentally measured at 10 min interval to study the transient behaviour of the system. But, the hourly performance variations were considered for comparison. After the reference test without panel cooling, the performance was measured using air as cooling medium over the top and bottom surface of the panel. The air velocity flowing 33
ORIGINAL RESEARCH ARTICLE
research investigations have been reported in open literature to cool the photovoltaic panels by active and passive heat sinks (using air and water as working fluids) to maintain the cell temperature in the range between 25 and 35 C [16–19]. The economical and environmental benifits of PVWPSs have been investigated by many researchers. The PVWPSs are economically viable for small scale water pumping applications in remote locations when compared to diesel powered water pumping systems [20,21]. It is also observed that, the PVWPSs have good energy performance in terms of productivity, reliability and cost effectiveness with considerable reduction in carbon-dioxide emissions during the period of 25-years lifespan when compared to the conventional grid connected water pumping systems [22]. It is possible to reduce the payback period of PVWPSs by optimizing the size of photovoltaic panels using maximum power point tracking algorithm [23]. The decrease in price of the photovoltaic panels and its accessories has improved the economical viability of PVWPSs when compared to grid connected and diesel powered water pumps [24,25]. Also, it is confirmed that, the PVWPSs are reliable and economical for both developed and developing countries [26]. The cited literature confirmed that, many research and development investigations have been reported on the performance improvements of a PVWPS. However, the performance comparison of a PVWPS under the influence of panel cooling using air and water over the top and bottom surfaces of the panel has not been reported in open literature. Hence, an attempt has been made in this research work to investigate the performance of a PVWPS under the influence of panel cooling in following four modes: (a) air cooling over the top surface of the panel; (b) air cooling over the bottom surface of the panel; (c) water cooling over the top surface of the panel and (e) water cooling over the bottom surface of the panel and are compared with the PVWPS without panel cooling. In addition, the economical and environmental feasibility of the PVWPS are evaluated for the period of twenty years.
ORIGINAL RESEARCH ARTICLE
ORIGINAL RESEARCH ARTICLE
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE FIGURE 1
Schematic diagrams of photovoltaic water pumping systems.
over the panel surfaces were maintained at 2.5 0.2 m/s [28]. Further, the performance of the system was evaluated using water cooling arrangement over the top and bottom surfaces of the panel. The velocity of water spilled over the panel surface was controlled using a solenoid control valve. The velocity of water spilled over the entire top and bottom surfaces were maintained at 1 0.2 m/s [28]. All the performance parameters were measured experimentally for the other four modes of operation. Experimental observations have been made for the period of one month under each mode to study 34
the nature of variations and also to eliminate the erroneous data. The experimental observations with similar ambient variations on 24th day of February 2017 (without panel cooling), 23rd day of March 2017 (with air cooling over the top surface of the panel), 21st day of April 2017 (with air cooling over the bottom surface of the panel), 23rd day of June 2017 (with water cooling over the top surface of the panel), 23rd day of September 2017 (with water cooling over the bottom surface of the panel) were considered for performance comparison.
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
TABLE 1
uncertainty in the independent variables. The relative errors in photovoltaic efficiency, pump efficiency and overall efficiency were calculated as 0.2%, 0.1% and 0.22%, respectively.
Characteristics
Specifications
Type of motor
A.C induction motor (Specially designed for solar applications) 3 220–440 V (Low voltage motor), 2.5 A 25–60 Hz 0.5 HP/0.375 kW Centrifugal pump 25.4 mm 25 m/1.6 m3/h
Phase Voltage, current Frequency/speed Power Pump type Suction/delivery pipe size Maximum head/discharge
TABLE 2
Specifications of photovoltaic panel. Characteristics
Value
Voltage at Pmax Current at Pmax Open circuit voltage Voc Short circuit current Isc Temperature coefficient
35.04 V and 7.85 A 43.99 V 8.39 A
Cell type Cell size Area of the panel
Multi crystalline 156 mm 156 mm 6.4 m2
Modeling of photovoltaic water pumping systems The PVWPSs consists of photovoltaic panels, inverter, variable frequency drive, AC induction motor (specially designed for PVWPS applications) and a centrifugal pump. The efficiency variations of inverter and motor under the influence of ambient conditions were negligible. However, the efficiency variations of photovoltaic panels and the pump subsystem are more significant. Hence, the influence of ambient conditions on the performance of photovoltaic panel and water pump systems are investigated. The equations used for predicting the cell temperature, power output of the panel, photovoltaic efficiency, pump discharge, pump efficiency and overall efficiency of the system are described in this section.
Modeling of photovoltaic panels
0.41% oC
The sectional view of a photovoltaic laminate is depicted in Figure 2a. The photovoltaic laminate consists of a tempered glass, tedlar, ethyl vinyl acetate, photovoltaic cell and aluminium fram
Uncertainity analysis The uncertainties in experiments were estimated using following relation given by Holman [29]: " 2 2 2 #1=2 @R @R @R wr ¼ w1 þ w2 þ . . . . . . . . . þ wn ð1Þ @x1 @x2 @xn " dhpv ¼
dPpv Ppv
" dhPump ¼
2
dQ Q
#1=2 dG 2 þ G
2
2 dhOverall
dhpv ¼4 hpv
þ
dP P
!2 þ
ð1aÞ
2 #1=2 ð1bÞ
dhpump hpump
!2 31=2 5
ð1cÞ
Here, R is a given function, wr is the total uncertainty, X1, X2, . . . .. Xn is the independent variables, w1, w2 . . . wn is the
TABLE 3
Specifications and accuracy of measuring instruments. Instrumentation
Specification (Range)
Accuracy
Rotameter Temperature sensor
0–200 LPM K type thermocouples (0–200 C) Digital type Digital Class-A (0–1200 W/m2) 16 channel indicator (0–200 C) 0–3000 rpm
1 LPM 0.2 C
Wattmeter Energy meter Pyranometer Digital temperature indicator Tachometer
2 W 0.5% 5 W/m2 0.1 C resolution 5 RPM
FIGURE 2
Heat transfer in photovoltaic panel laminate. 35
ORIGINAL RESEARCH ARTICLE
Specifications of motor and pump.
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
ORIGINAL RESEARCH ARTICLE
for supporting the panel. The photovoltaic cell is placed at below the tempered glass surface, which is protected by two layers of ethyl vinyl acetate (on the top and bottom surfaces). The tedlar improves strength to the panel and also prevents the moisture entry into the cell enclosure under high humid climates. The heat infiltration through the glass surface and tedlar surface into the cell enclosure is due to conduction. The top and bottom surfaces of the panel have both convective and radiative resistance. The conductive, convective and radiative thermal resistance in photovoltiac panel is shown in Figure 2b. The thermal properties of the materials used in the panel are listed in Table 4.
Prediction of cell temperature
the reference temperature assumed as 298 K. The convective heat loss from the glass surface hc,g-a and tedlar surfaces hc,td-a are given by following equations: hc;ga ¼ 2:3 þ 3vg
ð7Þ
hc;tda ¼ 2:3 þ 3vtd
ð8Þ
Here, vg represents the ambient wind velocity flows over the glass (m/s) and vtedlar represents the ambient wind velocity flows over the tedlar. The radiative heat transfer between the glass and ambient conditions hr,g-a is given by: ! 4 T g þ 273 ðT a þ 273Þ4 hr;ga ¼ eg s ð9Þ Tg Ta
The energy balance of a photovoltaic cell based on first law of thermodynamics is given by: dT cell t g acell G ¼ E þ mcell cpcell þ U cellg ðT cell T g Þ dt þ U celltd ðT cell T td Þ þ hc;ga þ hr;ga þ hc;tda þ hr;tda ð2Þ
The radiative heat loss from glass and tedlar surfaces hr,td-a is given by following equation: ! ðT td þ 273Þ4 ðT a þ 273Þ4 hr;tda ¼ etd s ð10Þ T td T a
Here, t g – transmissivity of the glass, acell – absorption coefficient of the solar cell, G – solar irradiation (W/m2), E – energy output of the panel (W), mcell – mass of the cell material (kg), cpcell – specific heat of the cell material (kJ/kgK), Tcell – cell temperature ( C or K), Tg – temperature of the cell ( C or K). Ucell-td – heat transfer coefficient between cell and teldhar (W/m2K), Ucell-g is the overall heat transfer coefficient between the cell and the glass. The conductive heat transfer coefficients through the glass and EVA are given by:
T cell;i ¼
U cellg ¼ xg kg
1 EV þ xkEV
ð3Þ
The conductive heat transfer coefficient through the tedlar and EVA are given by: U celltd ¼ xEV kEV
1 þ xktdtd
ð4Þ
Here, k is the thermal conductivity and x is the thickness of the cell. The subscripts g, EV and TD represents the glass, ethyl vinyl acetate and tedlar, respectively. The energy generation by the photovoltaic cell (E) is given by following equation: E ¼ hcell t g acell G
ð5Þ
The cell efficiency (hcell) is given by: hcell ¼ href ð1 bðT cell T ref Þ
ð6Þ
Here, href is the reference efficiency assumed as 0.18, b is the temperature coefficient, Tcell is the cell temeprature ( C) and Tr is
TABLE 4
Thermal properties of panel materials. Properties
Thickness (mm) Thermal conductivity (W/m K) Specific heat (kJ/kg K) Density (kg/m3) Transmissivity (–) Absorbsivity (–) 36
Materials Glass
Cell
Tedlar
EVA
4 0.98 0.8 2482 0.95 0.05
0.5 148 0.7 2328 0.09 0.91
1 0.033 1.01 1720 0.95 0.05
0.5 0.23 3.135 1720 0.95 0.05
Here, hr is the radiative heat transfer coefficient (W/m2 K), e is the emissivity of the glass is assumed as 0.9, s is Stefan Boltzman constant is assumed as 5.68 108 W/m2 K4. Tcell is the cell temeprature (in K or C). The solution to the differential Eq. (2) is given by: C 1 eat þ T cell;i1 eat a
ð11Þ
Here, C and a0 are the constants. The cell temperature is predicted using measured glass and tedlar temperatures. The value of constants are given by following equations: t g ac G 1 href b href T ref þ U cellg T g C¼ mc cp c þ U celltd T td ð12Þ
a¼
U cg þ U ctd b hr t g ac G mc c p c
ð13Þ
The thermo-physical properties of tedlar are given by following equations: (i) Thickness of the tedlar (t): 1 mm. (ii) Thermal conductivity of the tedlar (ktd): 0.033 W/mK (iii) Specific heat of the tedlar (cp): 1.01 kJ/kgK (iv) Density of the tedlar: 1720 kg/m3 (v) Mass of the tedlar: 1.7 kg/m2. (vi) Absorbsivity of tedlar: 0.05 Similarly, the themo-physical properties of ethylene vinyle acetate are given by: (i) Thickness of the tedlar (t): 0.5 mm (ii) Thermal conductivity of the glass (kg) : 0.23 W/mK (iii) Specific heat of the glass: 3.135 kJ/kgK (iv) Density of the glass: 1720 kg/m3 (v) Mass of the solar cell: 1.7 kg/m2. (vi) Absorbsivity of glass: 0.05
Prediction of PV output current The net difference between the photocurrent (Iph) and the diode current (ID) is given by [30]: G U þ IRs 1 ð14Þ I L;ref þ mI;SC ðT c T c;ref Þ I O exp I¼ Gref AV t
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
g ¼ A N c;s N ms I O ¼ I o;ref
Tc T c;ref
ð15Þ
3
exp
qM g 0
0
k A
1 T c;ref
1 Tc
maximum short circuit current and maximum open circuit voltage [30]. FF ¼
V mIm V oc I sc
Here, Voc is the open circuit voltage (V), I sc is the short circuit current (A), Vm is the maximum open circuit voltage (V), I m is the maximum short circuit current (A).
Modeling of centrifugal pumps
ð16Þ
A simplified mathematical model for a centrifugal pump is given by following equation [31]: 0
I O;ref
V oc;ref ¼ I L;ref exp 0 a ref
PðQ Þ ¼ aQ ð17Þ
Here, Io,ref – Saturation current at the reference condition (A), egap – Band gap of the material (1.17 eV for Si materials), Ns – Number of cells in series of the photovoltaic module, q – Charge of electron (assumed as 1.60217733 1019 C), A – Quality factor related the photovoltaic module, Io – Reverse saturation current (A). The value of a0 ref is calculated using following relation [30]: a0ref ¼
2V mp;ref V oc;ref I sc;ref I mp;ref I sc;ref I mp;ref þ ln 1 I sc;ref
ð18Þ
Here, Vmp, ref – Maximum power point voltage at reference condition (V), Imp, ref – Maximum power point current at reference condition (A), Isc, ref – Short circuit current at the reference condition (A). The term a is the function of temperature. It is given by following equation [30]: T c þ 273 0 a0 ¼ a ref ð19Þ T c;ref þ 273 The series resistance (Rs) of a photovoltaic panel is calculated using following equation [30]: 0 I þ V oc;ref V mp;ref a ref ln 1 Imp;ref sc;ref ð20Þ Rs ¼ I mp;ref Here, t g – transmissivity of the glass, mcell – mass of the cell material (kg), cpcell – specific heat of the cell material (kJ/kgK), Tcell – cell temperature ( C or K), Tg – temperature of the cell ( C or K), Ucell-td – heat transfer coefficient between cell and teldhar (W/m2K), E – electric output of the photovoltaic cell (W).
Prediction of photovoltaic electrical efficiency The electrical conversion efficiency of the photovoltaic panel is given by following equation [30]: hPV ¼
Ppv Apv G
ð22Þ
ð21Þ
Here, Apv is the photovoltaic panel area in m2, G is the solar irradiation in W/m2, Ppv is the photovoltaic panel output in terms of W.
Prediction of fill factor Fill factor (FF) of a solar cell is the ratio between actual maximum photovoltaic output power of the solar cells to the product of
0
3
þ bQ
0
2
0
þ cQ þ d
ð23Þ
Here, P – electrical power consumed by the pump, a, b, c and d – principal parameters of a pump model. The instantaneous pump discharge was predicted using Newton Raphson method or Secant method. After i iterations, the equation for predicting the instantaneous pump discharge using Newton Raphson method is given by following equation [31]: Q
0
¼Q
i
0
i1
f ðQ 0
0
f ðQ
i1 Þ 0
ð24Þ
i1 Þ
The instantaneous pump discharge using Secant method is given by following relation: 0
Q
0
iþ1
¼Q
0
0
i
f ðQ i Þ
0
Q i Q i1 0 0 f ðQ i Þ f ðQ i1 Þ
ð25Þ
The photovoltaic panel and centrifugal pump are the two subsystems. The characteristics of the photovoltaic panel output and the pump output are given by P and Q0 , respectively for different pumping heads (H). Based on the experimental trials, the following equations have been established: 0
PðQ ; HÞ ¼ aðHÞQ
0
3
þ bðHÞQ
0
2
0
þ cðHÞQ þ dðHÞ
ð26Þ
Here, a (H), b(H), c(H) and d(H) depends on total pumping. It can be given by following equations [31]: aðHÞ ¼ a0 þ a1 H þ a2 H 2 þ a3 H 3
ð27Þ
bðHÞ ¼ b0 þ b1 H þ b2 H 2 þ b3 H 3
ð28Þ
cðHÞ ¼ c0 þ c1 H þ c2 H 2 þ c3 H 3
ð29Þ
dðHÞ ¼ d0 þ d1 H þ d2 H 2 þ d3 H 3
ð30Þ
Here, ai, bi, ci and di represents the parameters of the mdoel. It depends on the parameters of the mdoel and pumping subsystem, Q is the pump discharge in m3/h and H represents the pumping head in m. Further, the pump efficiency is given by following relation: hpump ¼
r 9:81 Q H Pmotor
ð31Þ
Here, r represents the density of water and hpump represents the pump efficiency.
37
ORIGINAL RESEARCH ARTICLE
Here, G – Global solar radiation falls on the surface (W/m2), Gref– Reference global solar radiation falls on the surface at 1000 W/m2, Tc, ref– Reference solar cell temperature (assumed as 298 K), Tc, – Cell temperature (assumed as 298 K), IL, ref – Light current at reference condition, mi,sc – Temperature coefficient of short circuit current (A/ C), Rs – Series resistance, IL, ref – reference light current taken from manufacturer data sheet. The constant g is given by:
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ORIGINAL RESEARCH ARTICLE
Prediction of overall efficiency of the system
Environmental impact assessments
The overall cascading efficiency of PVWPS is given by following equation:
The environmental impact assessment of a PVWPS is assessed in terms of carbon dioxide emissions during its entire life time by comparing with grid connected and diesel powered water pumping systems. The environmental impact was assessed for the period of twenty years.
hoverall ¼ hPV hi hm hP hf an
ð32Þ
ORIGINAL RESEARCH ARTICLE
Here, hoverall, hPV, hi, hm, hP, hfan represents the overall efficiency, photovoltaic efficiency, inverter efficiency, motor efficiency, pump efficiency and fan efficiency, respectively. The efficiency of motor and inverter are not influenced by ambient parameters (such as, solar irradiation, ambient temperature and the wind velocity). Here, the efficiency of the inverter and motor are assumed with constant value of 0.90 and 0.95, respectively based on experimental trials. The efficiency of a cooling fan used for cooling of photovoltaic panels is assumed as 0.95.
Economical assessments The cost involved in installing a PVWPS includes the cost of major components such as photovoltaic panels, inverters, motor-pump assembly and pipes. The PVWPSs do not require running costs during its life time. In contrast, the grid connected and diesel powered water pumping systems require high running costs. The economical feasibility of the PVWPSs was assessed in terms of pay back period (PBP), return on investment (ROI) and internal rate of return (IRR) with following assumptions: (a) Life of the system: 20 years (b) Working hours: 8 h per day for 365 days in a year (c) Pumping head: 15 m (d) Discharge: 10,000 l per day (e) Electricity cost: INR 8/kWh. (f) Initial cost of the motor-pump subsystem: INR 12,000 (g) Cost of photovoltaic panels: INR 44,000 (h) Cost of inverter: INR 22,000 (i) Replacement of pumps once in ten years. (j) Replacement cost of the pump after 10 years: INR 10,000 (k) Air cooling accessories over the top surface of the panel: INR 7000 (l) Air cooling accessories over the bottom surface of the panel: INR 7000 (m) Water cooling accessories over the top surface of the panel: INR 12,000 (n) Water cooling accessories over the bottom surface of the panel: INR 12,000 (o) Annual maintenance cost INR 1000, (p) Discount rate: 0.04–0.32 The payback period (PBP), return on investment (ROI) and net present value (NPV) of a PVWPS are given by following equations: PBP ¼
Investment Savings
ð33Þ
ROI ¼
Savings 100 Investment
ð34Þ
NPV ¼
CF ðI þ iÞn
The functional unit description is the main factor of environmental impact assessment of water pumps, which needs to be identified and quantified. The functional unit is a measure of the function to be studied and it provides a reference to which the inputs and outputs can be related. It needs two systems for comparison. In this work, the environmental impacts of the PVWPS are compared with conventional grid connected and diesel powered water pumping systems.
System boundaries The system boundaries define the processes considered for evaluating the environmental impacts of the water pump. The environmental impacts caused during production, transportation and disposal stages were ignored in this work due to lack of data. The environmental impacts of the PVWPS are evaluated only for the usage phase for comparison. Based on the trial experiments in diesel captive power generation plants, it is observed that, the diesel power generators consuming 0.35 to 0.4 l of diesel per kWh of electricity. The carbon-dioxide emissions per litre of diesel are estimated to be about 2.6 kg. [32]. The carbon-dioxide emissions produced during power generation is estimated as 1.04 kg per kWh. The coal based power plants will emit 0.90 kg of carbondioxide per kWh of electricity [33]. The carbon-dioxide emissions of water pumping systems are quantified by following relation: EI CO2 ¼ d Epump n N
ð36Þ
Here, EI is the environmental impact due to carbon-dioxide emissions in tons, d is the carbon-dioxide emission factor, Epump is the energy savings (in kW.h), n is the no of days in a year and N is the number of years.
Results and discussion The experimental results observed in a PVWPS under the influence panel cooling (using air and water) over the top and bottom surfaces of the panel were investigated. The performance of a PVWPS was evaluated based on the experimental observations. The experimental observations and energy performance of PVWPSs under the influence of panel cooling are discussed in this section.
Ambient variations
ð35Þ
The discount rate at which the net present value is zero is called internal rate of return (IRR). Here, the CF represents the cash flow and i represents the interest rate and n represents the number of year.
38
Functional unit
The performance of photovoltaic panels are influenced by solar irradiation, ambient temperature, wind velocity, ambient relative humidity and dust accumulated over the top surface of the panel [34]. However, the influence of dust and relative humidity has not influencing the instantaneous performance. Hence, the influence of dust accumulation and relative humidity were ignored in this work. The variations of solar irradiation, ambient temperature and ambient wind velocity were observed during
Renewable Energy Focus Volume 31, Number 00 December 2019
Similarly, the ambient temperature variations observed during experimentation with five modes of operation are shown in Figure 3b. The ambient temperature has influenced the convective cooling over the top surface of the panel. During experimentation, the ambient temperatures were varied between 28 C to about 38 C with an average ambient temperature of about 32 C. High ambient temperature has affecting the photovoltaic power output, which will reduce the pumping efficiency. During experimental observations with five different modes of operation, the maximum differences in ambient temperatures were observed within 2 C. The ambient wind velocity variations during experimentation with five different modes are depicted in Figure 3c. The ambient wind velocity was varied between 1.1 m/s and 4 m/s with an average value of 2.5 m/s. The variations of ambient wind velocity have influencing the cell temperature due to the direct cooling of glass surface. Hence, the influence of ambient wind velocity is quantified in terms of cell temperature variations.
Validation of mathematical models The results obtained using mathematical model was validated experimental results. The comparison between the experimentally observed and analytically predicted overall efficiency of the system during the sunny day on 24.02.2017 (without panel cooling) is shown in Figure 4. The overall efficiency of the system depends on efficiency of the photovoltaic panel subsystem, inverter subsystem, electrical motor subsystem and pump subsystem. The system overall efficiency was varied between 1.2% and 1.9%. The predicted overall efficiency of the system was found to be closer to the experimental values with 0.1% deviations.
Performance comparison The performances of a PVWPS under the influence of panel cooling using air and water over the top and bottom surfaces of the panel are described in this section.
Photovoltaic panel cell temperature
FIGURE 3
Variation of ambient conditions during experimental observations.
Generally, the cell temperature was maintained at 25 1 C to achieve maximum power output. However, maintaining 25 C is not possible during peak sunshine hours, which affects the photovoltaic output. The variations of cell temperature with panel cooling (using air and water as cooling medium) and without panel cooling are compared in Figure 5a. It is observed that, the cell temperature was varied from about 31 C to about 62 C with an average temperature of about 47 C in the case of panel without cooling. The air cooling over the bottom surface of the panel has reduced the temperature variations in the range between 30 C and 43 C with an average temperature of about 36 C. The water cooling of panel over the bottom surface has reduced the cell temperature variations in the range between 30.6 C and 37.8 C with an average temperature of about 32 C. It is observed that, cooling arrangement provided over the bottom surface of the panel has significant reduction in cell temperature when compared to the cooling arrangement provided over the top surface. Furthermore, it is confirmed that, water provides effective cooling of panels when compared to air due to its high specific heat and higher heat transfer coefficient when compared to air as cooling medium [35]. 39
ORIGINAL RESEARCH ARTICLE
experimentation of a PVWPS in five different modes are described in this sub-section. The solar irradiations observed during experimentation with a PVWPS in five modes of operation are illustrated in Figure 3a. It is observed that, the fluctuations in solar irradiation were found to be within 50 W/m2. The solar irradiation was varied from about 100 W/m2 to the maximum value of about 950 W/m2 with an average solar irradiation of about 550 W/m2. As expected, the solar irradiation gets increased during morning hours and reached maximum solar irradiation of about 950 W/m2 during 13.30 h and gets reduced in the afternoon hours. During experimentation, the length of sunshine was observed as 11 h per day. But, the potential sunshine availability (above 200 W/m2) for water pumping applications is around 8–9 h per day. Moreover, it is observed that, Coimbatore has enough annual solar irradiation potential to support a PVWPS.
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FIGURE 4
Comparison between experimental and theoretical prediction of overall efficiency.
Photovoltaic panel power output The power output of photovoltaic panels under the influence of cooling is depicted in Figure 5b. As expected, the photovoltaic power output was increased with increase in solar irradiation. During peak sunshine hours, the panels get heated under the influence of solar irradiation and drop its electrical conversion efficiency. The panels need to be cooled and maintain its temperature in the range between 25 C and 35 C to achieve maximum conversion efficiency. In this research work, air and water were used as a cooling medium to reduce the panel surface temperature. The photovoltaic power output (without panel cooling) was varied between 145 W and 610 W with energy output of 3.1 kW h per day. Similarly, the photovoltaic power output in the case of air cooling over the top surface the panel was varied between 170 W and 630 W with output of 3.4 kW h per day. The photovoltaic power output in the case of panel air cooling over the bottom surface of the panel has power output in the range between 175 W and 635 W with output of 3.6 kW h per day. The panel output was observed in the range from 185 W to 650 W in the case of water cooling over the top surface of the panel with output of 3.9 kW h per day. A significant improvement in photovoltaic power output was observed in the range from 200 W to 680 W by providing water cooling over the bottom surface of the panel with output of 4.2 kW h per day. The results confirmed that, the performance of a PVWPS was significantly improved using water cooling over the bottom surface of the panel, which is similar to the earlier research investigations [14,18].
Photovoltaic panel efficiency The variations of photovoltaic panel efficiency during experimentation in five different modes are compared in Figure 5c. The photovoltaic efficiency was influenced by solar irradiation, ambient temperature and ambient wind velocity. It is observed that, the panel efficiency without panel cooling was varied between 10% and 11.4%. The panel efficiency was improved in the range between 10.6% and 12% and in the range between 11.3% and 12.4% under the influence panel cooling using air and water over the bottom surface of the panel, respectively. The photovoltaic efficiency gets reduced during the peak sunshine hours due to the effect of heating. The results confirmed that, the water cooling arrangement provided at the bottom surface was observed to be more effective when compared to air cooling due to its higher heat tranfer coefficient. 40
FIGURE 5
Performance of photovoltiac panels.
The panel efficiency results observed in this work are similar to the earlier work reported by Habiballahi et al. [14].
Performance of a pump The performance of a motor-pump subsystem was tested in a laboratory and its performance characteristics are illustrated in Figure 6a. The pump head decreases from 25 m to 6 m with increase in pump discharge from 0.2 m3/h to 1.6 m3/h, respectively. In addition, the variation of hydraulic efficiency at fixed pumping head of 15 m is shown. It is observed that, the maximum pump hydraulic efficiency of about 40% was observed with the pump discharge of 1 m3/h.
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compared to the system without the influence of panel cooling. The water cooling over the bottom surface of the panel has enhanced the pump discharge to about 0.19 m3/h compared to the air cooling on bottom surface of the panel. The results confirmed that, pump discharge was significantly improved by maintaining the cell temperature in the range between 25 and 35 C. The results confirmed that, the pump discharge was improved by providing water cooling over the bottom surface of the panel. The pump efficiency variations under the influence of panel cooling at constant pumping head of 15 m are illustrated in Figure 6c. It is observed that, the pump efficiency was varied from 10% and 22% in the case of PVWPS without panel cooling. An increase in pump speed was observed under the influence of panel cooling. The pump efficiency was improved in the range from 10.6%–23.8% and in the range from 11.3%–25.6% for the case of PVWPS using air cooling provided over the top and bottom surfaces, respectively. Similarly, the pump efficiency was improved in the range from 11.7%–26.18% and in range from 11.8%–29.7% in the case of PVWPS using water cooling provided over the top and bottom surfaces, respectively. About 7.7% improved pump efficiency was observed during the peak sunshine hours when compared to the system without panel cooling due to the increased photovoltaic power output from the photovoltaic panels under the influence of panel cooling over the bottom surface of the panel. In a similar work, the pump efficiency under the influence of panel cooling over the bottom surface of the panel was improved by 4% [14].
Performance of an overall system The overall efficiency of a PVWPS is depicted in Figure 7. It is observed that, the overall efficiency of a PVWPS (without panel cooling) was varied between 0.9% and 1.79%. The overall efficiency of the system was varied between 1.0% and 2.1% and in the range between 1.0 and 2.3% in the case of air cooling over the top surface the panel and in the case of air cooling over the bottom surface of the panel, respectively. Similarly, the overall efficiency was varied in the range from 1.1%–2.42% and from 1.2% to 2.84% in the case of water cooling over the top and bottom surfaces of the panel, respectively. It is observed that, panel cooling over the bottom surface of the panel using water has achieved the maximum overall efficiency of about 2.84%. The overall efficiency FIGURE 6
Performance of a water pump sub system.
The variations of pump discharge under the influence of panel cooling at constant pumping head of 15 m are compared in Figure 6b. The pump discharge fluctuates according to the availability of solar irradiation. The pump discharge is directly proportional its speed. The air cooling arrangement provided over the top and bottom surface of the panel has enhanced the pump discharge to about 1.32 m3/h and 1.41 m3/h, respectively, which is found to be about 0.32 m3/h and 0.41 m3/h higher when compared to the PVWPS without cooling. Similarly, the water cooling provided over the top and bottom surface of the panel has enhanced the pump discharge to about 1.48 m3/h and 1.60 m3/h, respectively, which is found to be about 0.48 m3/h and 0.60 m3/h higher when
FIGURE 7
Variation of overall efficiency of a PVWPS against time. 41
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TABLE 5
Performance of a PVWPS during peak sunshine hours (solar irradiation above 850 W/m2). Cooling mode
Photovoltaic panel
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Without cooling Air cooling over the top surface the panel Air cooling over the bottom surface of the panel Water cooling over the top surface the panel Water cooling over the bottom surface of the panel
Pump
Overall system
Power output (W)
Efficiency (%)
Discharge (m3/h)
Efficiency (%)
Efficiency (%)
610 625 635 650 680
10.4 10.9 11.1 11.4 11.8
0.97 1.35 1.45 1.48 1.60
22.0 23.8 25.6 26.2 29.7
1.79 2.10 2.30 2.42 2.84
improvement observed in this work was found to be slightly higher than earlier work reported by Habiballahi et al. [14]. The summary of performance results observed in a PVWPS during peak sunshine hours (above 850 W/m2) are consolidated in Table 5. It is observed that, the water cooling provided over the bottom surface of the panel was observed to be more effective when compared to other modes of panel cooling. Moreover, the performance comparisons with earlier research investigations are compared in Table 6. It is noticed that, the performance of pump subsystem has 7.7% improved hydraulic efficiency with 1.01% improved overall efficiency when compared to the efficiency of the system without panel cooling. A significant improvement in pump hydraulic efficiency with minor improvement in overall efficiency were observed when compared to the earlier research reported by Habiballahi et al. [14]. Thin film photovoltaic cells have retained its performance even at high temperatures. Hence, further research is essential to explore the possibility of using thin film photovoltaic panels to over the drawbacks with exiting mono crystalline and multi crystalline photovoltaic cells. Such research investigations are in progress at author’s research laboratory.
the cell temperature in the range between 25 C and 35 C to achieve maximum performance. The influence of photovoltaic panel cooling has significantly improved the photovoltaic efficiency, pump efficiency and overall efficiency of the total system. Moreover, it is confirmed that, water cooling over the bottom surface is more effective when compared to the other cooling modes.
Influence of pumping head The influence of pumping head at constant solar irradiation and cell temperature (600 W/m2 and 35 C) is depicted in Figure 8b. It is observed that, the pump efficiency and overall efficiency of the system are significantly influenced by pumping head [36]. An increase in pumping head has decreased the pump efficiency and overall system efficiency. The pump efficiency was dropped from about 32% to about 18% with increase in head from 5 m to 25 m. Similarly, the overall efficiency of the pumping system was
Parameteric analysis The performance of a PVWPS is influenced by solar irradiation, ambient temperature, ambient wind velocity and head [20]. The influence of solar irradiation, ambient temperature and wind velocity are quantified in terms of photovoltaic cell temperature. The influences of photovoltaic cell temperature and head on the performance of PVWPS are predicted theoretically.
Influence of cell temperature The influence of cell temperature on the performance of a PVWPS is illustrated in Figure 8a. It is observed that, an increase in cell temperature from 30 C to 62 C has dropped the photovoltaic electrical efficiency from 12.6% to 9%, pump efficiency from 24% to 16% and overall efficiency from 2.4% to 0.9% due to reduction in photovoltaic power output. Hence, it is essential to maintain TABLE 6
Performance comparison with other reported investigations.
Cooling medium Cooling surface Photovoltaic efficiency Pump efficiency Overall efficiency
42
Present work
Habiballahi et al. [14]
Water Bottom of the panel 1.3% 7.7% 1.01%
Water Bottom of the panel 2% 4% 1%
FIGURE 8
Performance of photovoltaic water pumping system under the influence of cell temperature and head.
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Economical analysis of PVWPS with different modes of panel cooling. Cooling modes
Payback period (years)
Return on investment (%)
Internal rate of return (%)
Without panel cooling Air cooling above the panel Air cooling below the panel Water cooling above the panel Water cooling below the panel
8.6 8.5
11.6 11.7
8.2 8.5
8.1
12.3
9.3
7.9
12.7
9.8
7.3
13.7
10.9
dropped from about 1.9% to 0.9% due to increase in pumping head from 5 m to 25 m.
Economic analysis The investment on PVWPS (without panel cooling) for the period of twenty years (8 h of pump operation per day) for pumping 10,000 l of water has a payback of 8.6 years. The PVWPS using air cooled panels over the top and bottom surfaces of the panel has a payback of 8.5 and 8.1 years, respectively. Similarly, the payback for water cooled panels over the top and bottom surfaces has 7.9 and 7.3 years, respectively. The payback, return on investment and internal rate of return of PVWPS using different cooling modes are given in Table 7. The net present value of the investment was estimated for the period of twenty years for a discount rate from 4% to 34% are plotted in Figure 9. It is observed that, the internal rate of return for the PVWPS using panel cooling over the bottom surface is about 10.95%. The economical analysis confirmed that, the PVWPS with effective panel cooling is an economically feasible option for water pumping applications in remote locations facing shortage of electricity. The influence of panel cooling using water over the bottom surface has reduced the payback period by about 1.3 years when compared to the panel without cooling.
cooling medium was assessed for the period of twenty years life. The electricity consumption for pumping 10,000 l of water per day for the head of 15 m was considered for comparison. The duration of pump operation is 8 h per day. The environmental impacts caused during manufacturing and disposal stages were ignored in this work due to lack data. The electricity consumption of 380 W centrifugal pump for pumping water for 8 h duration is about 3.1 kW h per day. The power generated by photovoltaic panels has fulfilled the requirements for water pumping system and also for running the panel cooling accessories. The annual electricity consumption of a pump is estimated to be about 1131 kW h. The emissions for generating 1131 kW h of electricity using coal based power plants and diesel power generators have been estimated to be about 1018 kg of CO2 and for diesel 1176 kg of CO2, respectively. It is observed that, PVWPSs could reduce 20.36 and 23.52 tons of CO2 emissions during its life cycle period of twenty years when compared to the grid connected and diesel powered water pumping systems, respectively. The PVWPS has significant reduction in carbon-dioxide emission when compared to conventional grid connected and diesel powered water pumping systems [37].
Conclusion The experimental results concluded that, the cooling of panel using water over the bottom surface has reduced the cell temperature in the range between 25 and 38 C. The cooling of panel using water over its bottom surface has improved the photovoltaic efficiency, pump efficiency and total efficiency by about 1.4%, 7.7% and 1.01%, respectively during peak sunshine hours when compared to the PVWPS without cooling. The economic analysis showed that, the PVWPS has 7.3 years payback period with 13.7% return on investment and 10.9% internal rate of return. The economical analysis confirmed that, the investment in PVWPS with panel cooling over the bottom surface is economically feasible. It is possible to reduce 20.4 and 16.1 tons of CO2 emissions during the period of twenty years when compared to the grid connected and diesel powered water pumping systems, respectively.
Environmental impact assessments The environmental impact of a PVWPS under the influence of panel cooling over the bottom surface of the panel using water as
Conflict of interest There is no conflict of interest in this research submission.
Acknowledgement Authors would like to thank Flow Tech Power, Coimbatore-India for providing the facility to carry out this project. References
FIGURE 9
Net present value of the investment after twenty years at different discount rates.
[1] C. Gopal, M. Mohanraj, P. Chandramohan, P. Chandrasekar, Renew. Sustain. Energy Rev. 25 (2013) 351–370. [2] R. Rawat, S.C. Kaushik, R. Lamba, Renew. Sustain. Energy Rev. 57 (2016) 1506–1519. [3] S.S. Chandel, M.N. Naik, R. Chandel, Renew. Sustain. Energy Rev. 76 (2015) 163–175. [4] V.C. Sontake, V.R. Kalamkar, Renew. Sustain. Energy Rev. 59 (2016) 1038–1067. [5] D.H. Muhsen, T. Khatib, F. Nagi, Renew. Sustain. Energy Rev. 68 (2017) 70–86. [6] G. Li, M.Y. Jin, M.W. Akram, X. Chen, Renew. Sustain. Energy Rev. 79 (2017) 440–458. [7] M. Aliyu, G. Hassana, S.A. Saida, M.U. Siddiquic, A.T. Alawamid, I.M. Elamin, Renew. Sustain. Energy Rev. 87 (2018) 61–76. [8] T.V. Ramachandra, R. Jain, G. Krishnadas, Renew. Sustain. Energy Rev. 15 (2011) 3178–3386. [9] A. Mokeddem, A. Midoun, D. Kadri, S. Hiadsi, I.A. Raja, Energy Convers. Manage. 52 (2011) 3089–3095.
43
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TABLE 7
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[10] [11] [12] [13] [14] [15]
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[16] [17] [18] [19] [20] [21] [22] [23] [24]
44
M. Moechtar, M. Juwono, E. Kantosa, Energy Convers. Manage. 31 (1991) 521–527. H.G. Teo, P.S. Lee, M.N.A. Hawlader, Appl. Energy 90 (2012) 309–315. M. Abdolzadeh, M. Ameri, Renew. Energy 34 (2009) 91–96. A. Kordzadeh, Renew. Energy 35 (2010) 1098–1102. M. Habiballahi, M. Ameri, S.H. Mansour, J. Sol. Energy Eng. 137 (2015) 1–8. C. Gopal, M. Mohanraj, P. Chandramohan, M. Sakthivel, S. Bhero, Therm. Sci.: Sci. J. 21 (2017) 399–410. A. Fudholi, K. Sopian, M.H. Yazdi, M.H. Ruslan, A.H. Ibrahim, A. Kazem, Energy Convers. Manage. 78 (2014) 641–651. H.M.S. Bahaidarah, A.A.B. Baloch, P. Gandhidasan, Renew. Sustain. Energy Rev. 57 (2016) 1520–1544. S. Nietic, D. Coko, A. Yadav, F. Grubiic-Cabo, Energy Convers. Manage. 108 (2016) 287–296. J. Siecker, K. Kusakana, B.P. Numbi, Renew. Sustain. Energy Rev. 79 (2017) 192–203. I. Odeh, Y.G. Yohanis, B. Norton, Sol. Energy 80 (2016) 51–64. L. Qoaider, D. Steinbrecht, Appl. Energy 87 (2010) 427–435. K. Meah, S. Ula, S. Barrett, Renew. Sustain. Energy Rev. 12 (2008) 1162–1175. T.P. Correˆa, S.I. Seleme, S.R. Silva, Renew. Energy 41 (2012) 220–226. P.E. Campana, H. Li, J. Zhang, R. Zhang, J. Liu, J. Yan, Energy Convers. Manage. 95 (2015) 32–41.
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[25] P.E. Campana, H. Li, J. Yan, A. Olsson, Int. J. Green Energy 13 (2016) 831–839. [26] I. Yahyaoui, A. Atieh, A. Sena, T. Fernando, Sol. Energy 144 (2017) 376–391. [27] E.D. Mehleri, P.L. Zervas, H. Sarimveis, J.A. Palyvos, N.C. Markatos, Renew. Energy 35 (2010) 2468–2475. [28] N. Arcuri, F. Reda, M. De Simone, Sol. Energy 105 (2014) 147–156. [29] J.P. Holman, Experimental Methods for Engineers, Tata Mc Graw Hill Publishers, New Delhi, 2007. [30] R.A. Chenni, M. Makhlouf, T. Kerbache, A. Bouzid, Energy 32 (2007) 1724–1730. [31] A. Hamidat, B. Benyoucef, Energy Policy 37 (2009) 1489–1501. [32] J.L. Silveira, J.A. Carvalho, I.A.C. Villela, Renew. Sustain. Energy Rev. 11 (2007) 524–535. [33] M.G. Rasul, S. Moazzem, M.M.K. Khan, Energy 64 (2014) 330–341. [34] S. Mekhilef, R. Saidur, M. Kamalisarvestani, Renew. Sustain. Energy Rev. 16 (2012) 2920–2925. [35] F. Spertino, A.D. Angola, D. Enescu, P.D. Leo, G.V. Fracastoro, R. Zaffina, Sol. Energy 133 (2016) 119–140. [36] M. Benghanem, K.O. Daffallah, S.N. Alamri, A.A. Joraid, Energy Convers. Manage. 77 (2014) 334–339. [37] P. Purohit, A. Michaelowa, Renew. Sustain. Energy Rev. 12 (2008) 181–199.
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Performance of photovoltaic water pumping systems under the influence of panel cooling M.Mohanraj a,*, P.Chandramohan b, M.Sakthivel c and KamaruzzamanSopian d a
Department of Mechanical Engineering, Hindusthan College of Engineering and Technology, Coimbatore 641032, India Department of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore 641022, India c Department of Mechanical Engineering, K. L. Deemed to be University, Guntur 522502, India d Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia b
In this paper, the performance of a photovoltaic water pumping system was experimentally investigated under the influence of panel cooling using air and water as working fluids. The experimental observations have been made under the climatic conditions of Coimbatore city in India during the year 2017. The system performance was evaluated in four different cooling modes such as: (a) with air cooling over the top surface of the panel; (b) with air cooling over the bottom surface of the panel; (c) with water cooling over the top surface of the panel and (d) with water cooling over the bottom surface of the panel. The performances of a photovoltaic water pumping system working with four different panel cooling modes are compared with the system without panel cooling. The economical and environmental impacts have been assessed for a period of twenty years. The results showed that, the water cooling provided over the bottom surface of the panel has significant performance enhancement when compared to other cooling modes. The economic assessment results showed that, the photovoltaic water pumping systems using water cooling over the bottom surface of the panel has payback period of 7.3 years with 13.7% return on investment and 10.9% internal rate of return. The trial experiments confirmed that, it is possible to reduce the carbon-dioxide emissions by about 20.4 tons during the period of twenty years life when compared to the grid connected water pumping systems powered by coal based power plants. Introduction The fast depletion of conventional fossil energy sources and its critical impacts on the environment have created the research interest in identifying a sustainable energy option for water pumping systems. In India, the potential availability of solar energy provides a good solution to the energy related issues for water pumping applications [1]. Solar energy is integrated with water pumping systems either in the form of photovoltaic electric power obtained through photovoltaic panel to power the electrical motor of a pump or in the form of solar thermal energy harvesting
through solar thermal collectors to power the Rankine cycle. Out of these two options, the solar photovoltaic is an ideal option for remote water pumping applications due to its simplicity of installation with less maintenance [2]. Earlier reported reviews confirmed that, photovoltaic water pumping systems (PVWPSs) are having potential in the agriculture sector [3–7]. Approximately 58% of Indian geographical areas have good solar irradiation potential, which could fulfil the increasing power requirements, especially for agricultural water pumping [8]. The direct-coupled PVWPSs are commonly used for low head water pumping in agricultural applications due to its less maintenance when compared to the battery buffered PVWPS [9]. Moreover, it is observed
*Corresponding author. M., M. ([email protected]) 1755-0084/ã 2019 Published by Elsevier Ltd. https://doi.org/10.1016/j.ref.2019.10.006
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Nomenclature
ORIGINAL RESEARCH ARTICLE
A A0 a0 C cp E EI egap g G h H I i k k0 m n N Ncs Nms P q Q Q0 R t T U V v x
Photovoltaic panel area (m2) Completion factor Constant Constant Specific heat (kJ/kgK) Electric output of the photovoltaic cell (W) Environmental impacts of water pumping (Tons of CO2) Material band gap Gravitational constant (9.81 N/s2) Solar irradiation (W/m2) Heat transfer coefficienct (W/m2K) Head (m) Current (A) Discount rate (%) Thermal conductivity (W/mK) Boltzmann constant (1.381 1023 J/K) Mass (kg) Number of months Number of years Number of cells connected in series Number of modules connected in series Pumping power (W) Charge of electron (assumed as 1.60217733 1019 C) Heat transfer (W) Pump discharge (m3/h) Resistance (V) Time (s) Temperature (K) Overall heat transfer coefficienct (W/m2K) Votlage (volts) Velocity (m/s) Thickness of the material (mm)
Greek symbols
a b d m s e t h rw
Absorbsivity Temperature coefficient Carbon-dioxide emission factor Temperature coefficient of short circuit current (A/ K) Stefan Boltzman constant 5.68 108 W/m2 K4 Emissivity of the surface Transmissivity through glass Efficiency (%) Density of water (kg/m3)
Subscripts
a c c-td c-g c, ref conv,g conv,td EVA
32
Ambient Cell Cell to tedlar Cell to glass Cell, reference Convective heat loss from glass surface Convective heat loss from tedlar surface Ethylene vinyl acetate
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g i L, ref m mp, ref mp, ref o,c o,ref pv rad,g rad,td ref s sc td
Glass Inverter Light, reference Maximum Maximum power point, reference Maximum power point, reference Open circuit Open circuit at reference Photovoltaic Radiation heat loss from glass Radiation heat loss from tedlar Reference Series resistance Short circuit Tedlar
Abbreviations
AC CF DC EVA INR IRR NPV PBP PVWPSs ROI
Alternative current Cash flow Direct current Ethylene vinyl acetate Indian Rupees (1 US Doller = 72.00 INR) Internal rate of return Net present value Payback period Photovoltaic water pumping systems Return on Investment
that, ac motors are performing better when compared to the d.c motors and requires less maintenance [10]. Therefore, many research investigations have been focused on photovoltaic assisted a.c water pumping systems. The photovoltaic cells get heated and its performance was dropped during peak sunshine hours. However, the maximum panel power output will be expected during peak sunshine hours. Many research efforts have been made for improving the performance of photovoltaic panels using water and air as cooling medium [11]. In a related work, Abdolzadeh and Ameri [12] improved the performance of a PVWPS by spraying water over the top surface of the photovoltaic panels. It was reported that, the efficiency of the photovotlaic panels, pump subsystem and the total system were improved by 3.26%, 1.40% and 1.35%, respectively at 16 m operating head. In another work, Kordzadeh [13] investigated the performance of a PVWPS under the influence of panel cooling using film layer of water spray over the panel surface at Kerman city in Iran. It was reported that, the photovoltaic panel efficiency was improved by about 3.7% when compared to the photovoltaic panel without cooling, which improves the performance of the pump efficiency. Similarly, Habiballahi et al. [14] improved the photovoltaic electrical efficiency; pump efficiency and overall efficiency of a PVWPS by about 2%, 4%, and 1%, respectively under the influence of water spraying over the bottom surface of the panel. Gopal et al. [15] investigated the performance of a PVWPS under the influence of panel cooling using air as working fluid and reported with significant performance improvement when compared to the system without panel cooling. Many
Renewable Energy Focus Volume 31, Number 00 December 2019
Experiments The performance investigations have been made under the meteorological conditions of Coimbatore city (latitude of 10.98 N and longitude of 76.96 E) in India during the months of February 2017, March 2017, April 2017, June 2017 and September 2017.
Experimental setup The schematic diagram of a direct coupled PVWPS (using A.C. power input) experimental setup is shown in Figure 1. The PVWPS was installed in a sump with 500 l water storage capacity. The setup consists of a 380 W mono block centrifugal pump assisted by a variable frequency drive and four photovoltaic panels (with dimensions 1.6 m 1 m) of total area 6.4 m2 with a rated output power of 1100 W during peak sunshine durations. However, the output of the photovoltaic panels fluctuates between 400 W and 1000 W depending on the ambient conditions. The specifications of the centrifugal pump and photovoltaic panel are given in Table 1 and Table 2, respectively. The delivery pipe has a control valve for varying the delivery head. The schematic diagrams of panel cooling (using air and water) arrangements are illustrated in Figure 1(b–e). Air cooling arrangement provided over the top surface of the panel consists of 40 W centrifugal fan distributed
evenly through nozzle outlets. Similarly, the cooling arrangement provided over the bottom surface of the panel consists of an axial flow fan with rated input power 40 W and baffle arrangements to ensure better panel cooling. The photovoltaic panel with water cooling over the top surface of the panel was provided by tapping water from the pump discharge. The nozzle outlets were placed along the top surface of the panel to spill out the water and provide uniform cooling. The water flows over the top and bottom surfaces of the panel was controlled by a solenoid valve. The cooling arrangement at the bottom surface of the panel was provided with nozzle outlets located perpendicular to the bottom surface of the panel at a distance of 70 mm. The water ejected from the nozzles sprayed over the bottom surface of the panel and provides uniform cooling. The panel is placed at an inclination of 11 according to the latitude of Coimbatore [27].
Instrumentation Sixteen calibrated K-type thermocouples were fixed at different locations (as mentioned in Figure 1) over the top and bottom surfaces of the photovoltaic panel to measure the glass and tedlar temperatures. All the thermocouples were connected to a digital temperature indicator and also to the computer through a data logger. Based on the measured glass and tedlar temperatures, the cell temperature was theoretically predicted using mathematical equations. Ambient wind velocity flows over the photovoltaic panel surface was measured using a cup type anemometer. The availability of solar irradiation was measured using a pyranometer. The instantaneous current, voltage and power output of the panel were measured using ammeter, voltmeter and Wattmeter, respectively. The discharge of water pump was measured using a rotameter connected in the discharge line. Similarly, the water consumption for cooling of panel was measured separately using a separate rotameter. The power consumed by the pump and cooling fan was measured using separate Wattmeter. The suction and delivery pressures were measured using vacuum gauge and pressure gauge, respectively. The speed of the pump was measured using a digital tachometer. The detailed specifications of the measuring instruments are listed in Table 3.
Experimental procedure The experimental observations were made at every ten minutes interval during 9.00 am to 17.00 pm on clear sunny days with minimum fluctuations of solar irradiation. Before conducting experiments using photovoltaic panel, the centrifugal pump was tested using a variable frequency drive at different heads ranging from 5 m to 25 m with the frequency ranges between 25 and 50 Hz. Based on the experimental observations, the polynomial equations were developed for predicting the performance of a centrifugal pump at different power inputs. Initially, the experiments were carried in a PVWPS without the influence of panel cooling for a constant pumping head of 15 m. The performance parameters such as, power output of the photovoltaic panel, power consumption of the motor and discharge of the pump were experimentally measured at 10 min interval to study the transient behaviour of the system. But, the hourly performance variations were considered for comparison. After the reference test without panel cooling, the performance was measured using air as cooling medium over the top and bottom surface of the panel. The air velocity flowing 33
ORIGINAL RESEARCH ARTICLE
research investigations have been reported in open literature to cool the photovoltaic panels by active and passive heat sinks (using air and water as working fluids) to maintain the cell temperature in the range between 25 and 35 C [16–19]. The economical and environmental benifits of PVWPSs have been investigated by many researchers. The PVWPSs are economically viable for small scale water pumping applications in remote locations when compared to diesel powered water pumping systems [20,21]. It is also observed that, the PVWPSs have good energy performance in terms of productivity, reliability and cost effectiveness with considerable reduction in carbon-dioxide emissions during the period of 25-years lifespan when compared to the conventional grid connected water pumping systems [22]. It is possible to reduce the payback period of PVWPSs by optimizing the size of photovoltaic panels using maximum power point tracking algorithm [23]. The decrease in price of the photovoltaic panels and its accessories has improved the economical viability of PVWPSs when compared to grid connected and diesel powered water pumps [24,25]. Also, it is confirmed that, the PVWPSs are reliable and economical for both developed and developing countries [26]. The cited literature confirmed that, many research and development investigations have been reported on the performance improvements of a PVWPS. However, the performance comparison of a PVWPS under the influence of panel cooling using air and water over the top and bottom surfaces of the panel has not been reported in open literature. Hence, an attempt has been made in this research work to investigate the performance of a PVWPS under the influence of panel cooling in following four modes: (a) air cooling over the top surface of the panel; (b) air cooling over the bottom surface of the panel; (c) water cooling over the top surface of the panel and (e) water cooling over the bottom surface of the panel and are compared with the PVWPS without panel cooling. In addition, the economical and environmental feasibility of the PVWPS are evaluated for the period of twenty years.
ORIGINAL RESEARCH ARTICLE
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Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE FIGURE 1
Schematic diagrams of photovoltaic water pumping systems.
over the panel surfaces were maintained at 2.5 0.2 m/s [28]. Further, the performance of the system was evaluated using water cooling arrangement over the top and bottom surfaces of the panel. The velocity of water spilled over the panel surface was controlled using a solenoid control valve. The velocity of water spilled over the entire top and bottom surfaces were maintained at 1 0.2 m/s [28]. All the performance parameters were measured experimentally for the other four modes of operation. Experimental observations have been made for the period of one month under each mode to study 34
the nature of variations and also to eliminate the erroneous data. The experimental observations with similar ambient variations on 24th day of February 2017 (without panel cooling), 23rd day of March 2017 (with air cooling over the top surface of the panel), 21st day of April 2017 (with air cooling over the bottom surface of the panel), 23rd day of June 2017 (with water cooling over the top surface of the panel), 23rd day of September 2017 (with water cooling over the bottom surface of the panel) were considered for performance comparison.
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ORIGINAL RESEARCH ARTICLE
TABLE 1
uncertainty in the independent variables. The relative errors in photovoltaic efficiency, pump efficiency and overall efficiency were calculated as 0.2%, 0.1% and 0.22%, respectively.
Characteristics
Specifications
Type of motor
A.C induction motor (Specially designed for solar applications) 3 220–440 V (Low voltage motor), 2.5 A 25–60 Hz 0.5 HP/0.375 kW Centrifugal pump 25.4 mm 25 m/1.6 m3/h
Phase Voltage, current Frequency/speed Power Pump type Suction/delivery pipe size Maximum head/discharge
TABLE 2
Specifications of photovoltaic panel. Characteristics
Value
Voltage at Pmax Current at Pmax Open circuit voltage Voc Short circuit current Isc Temperature coefficient
35.04 V and 7.85 A 43.99 V 8.39 A
Cell type Cell size Area of the panel
Multi crystalline 156 mm 156 mm 6.4 m2
Modeling of photovoltaic water pumping systems The PVWPSs consists of photovoltaic panels, inverter, variable frequency drive, AC induction motor (specially designed for PVWPS applications) and a centrifugal pump. The efficiency variations of inverter and motor under the influence of ambient conditions were negligible. However, the efficiency variations of photovoltaic panels and the pump subsystem are more significant. Hence, the influence of ambient conditions on the performance of photovoltaic panel and water pump systems are investigated. The equations used for predicting the cell temperature, power output of the panel, photovoltaic efficiency, pump discharge, pump efficiency and overall efficiency of the system are described in this section.
Modeling of photovoltaic panels
0.41% oC
The sectional view of a photovoltaic laminate is depicted in Figure 2a. The photovoltaic laminate consists of a tempered glass, tedlar, ethyl vinyl acetate, photovoltaic cell and aluminium fram
Uncertainity analysis The uncertainties in experiments were estimated using following relation given by Holman [29]: " 2 2 2 #1=2 @R @R @R wr ¼ w1 þ w2 þ . . . . . . . . . þ wn ð1Þ @x1 @x2 @xn " dhpv ¼
dPpv Ppv
" dhPump ¼
2
dQ Q
#1=2 dG 2 þ G
2
2 dhOverall
dhpv ¼4 hpv
þ
dP P
!2 þ
ð1aÞ
2 #1=2 ð1bÞ
dhpump hpump
!2 31=2 5
ð1cÞ
Here, R is a given function, wr is the total uncertainty, X1, X2, . . . .. Xn is the independent variables, w1, w2 . . . wn is the
TABLE 3
Specifications and accuracy of measuring instruments. Instrumentation
Specification (Range)
Accuracy
Rotameter Temperature sensor
0–200 LPM K type thermocouples (0–200 C) Digital type Digital Class-A (0–1200 W/m2) 16 channel indicator (0–200 C) 0–3000 rpm
1 LPM 0.2 C
Wattmeter Energy meter Pyranometer Digital temperature indicator Tachometer
2 W 0.5% 5 W/m2 0.1 C resolution 5 RPM
FIGURE 2
Heat transfer in photovoltaic panel laminate. 35
ORIGINAL RESEARCH ARTICLE
Specifications of motor and pump.
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ORIGINAL RESEARCH ARTICLE
for supporting the panel. The photovoltaic cell is placed at below the tempered glass surface, which is protected by two layers of ethyl vinyl acetate (on the top and bottom surfaces). The tedlar improves strength to the panel and also prevents the moisture entry into the cell enclosure under high humid climates. The heat infiltration through the glass surface and tedlar surface into the cell enclosure is due to conduction. The top and bottom surfaces of the panel have both convective and radiative resistance. The conductive, convective and radiative thermal resistance in photovoltiac panel is shown in Figure 2b. The thermal properties of the materials used in the panel are listed in Table 4.
Prediction of cell temperature
the reference temperature assumed as 298 K. The convective heat loss from the glass surface hc,g-a and tedlar surfaces hc,td-a are given by following equations: hc;ga ¼ 2:3 þ 3vg
ð7Þ
hc;tda ¼ 2:3 þ 3vtd
ð8Þ
Here, vg represents the ambient wind velocity flows over the glass (m/s) and vtedlar represents the ambient wind velocity flows over the tedlar. The radiative heat transfer between the glass and ambient conditions hr,g-a is given by: ! 4 T g þ 273 ðT a þ 273Þ4 hr;ga ¼ eg s ð9Þ Tg Ta
The energy balance of a photovoltaic cell based on first law of thermodynamics is given by: dT cell t g acell G ¼ E þ mcell cpcell þ U cellg ðT cell T g Þ dt þ U celltd ðT cell T td Þ þ hc;ga þ hr;ga þ hc;tda þ hr;tda ð2Þ
The radiative heat loss from glass and tedlar surfaces hr,td-a is given by following equation: ! ðT td þ 273Þ4 ðT a þ 273Þ4 hr;tda ¼ etd s ð10Þ T td T a
Here, t g – transmissivity of the glass, acell – absorption coefficient of the solar cell, G – solar irradiation (W/m2), E – energy output of the panel (W), mcell – mass of the cell material (kg), cpcell – specific heat of the cell material (kJ/kgK), Tcell – cell temperature ( C or K), Tg – temperature of the cell ( C or K). Ucell-td – heat transfer coefficient between cell and teldhar (W/m2K), Ucell-g is the overall heat transfer coefficient between the cell and the glass. The conductive heat transfer coefficients through the glass and EVA are given by:
T cell;i ¼
U cellg ¼ xg kg
1 EV þ xkEV
ð3Þ
The conductive heat transfer coefficient through the tedlar and EVA are given by: U celltd ¼ xEV kEV
1 þ xktdtd
ð4Þ
Here, k is the thermal conductivity and x is the thickness of the cell. The subscripts g, EV and TD represents the glass, ethyl vinyl acetate and tedlar, respectively. The energy generation by the photovoltaic cell (E) is given by following equation: E ¼ hcell t g acell G
ð5Þ
The cell efficiency (hcell) is given by: hcell ¼ href ð1 bðT cell T ref Þ
ð6Þ
Here, href is the reference efficiency assumed as 0.18, b is the temperature coefficient, Tcell is the cell temeprature ( C) and Tr is
TABLE 4
Thermal properties of panel materials. Properties
Thickness (mm) Thermal conductivity (W/m K) Specific heat (kJ/kg K) Density (kg/m3) Transmissivity (–) Absorbsivity (–) 36
Materials Glass
Cell
Tedlar
EVA
4 0.98 0.8 2482 0.95 0.05
0.5 148 0.7 2328 0.09 0.91
1 0.033 1.01 1720 0.95 0.05
0.5 0.23 3.135 1720 0.95 0.05
Here, hr is the radiative heat transfer coefficient (W/m2 K), e is the emissivity of the glass is assumed as 0.9, s is Stefan Boltzman constant is assumed as 5.68 108 W/m2 K4. Tcell is the cell temeprature (in K or C). The solution to the differential Eq. (2) is given by: C 1 eat þ T cell;i1 eat a
ð11Þ
Here, C and a0 are the constants. The cell temperature is predicted using measured glass and tedlar temperatures. The value of constants are given by following equations: t g ac G 1 href b href T ref þ U cellg T g C¼ mc cp c þ U celltd T td ð12Þ
a¼
U cg þ U ctd b hr t g ac G mc c p c
ð13Þ
The thermo-physical properties of tedlar are given by following equations: (i) Thickness of the tedlar (t): 1 mm. (ii) Thermal conductivity of the tedlar (ktd): 0.033 W/mK (iii) Specific heat of the tedlar (cp): 1.01 kJ/kgK (iv) Density of the tedlar: 1720 kg/m3 (v) Mass of the tedlar: 1.7 kg/m2. (vi) Absorbsivity of tedlar: 0.05 Similarly, the themo-physical properties of ethylene vinyle acetate are given by: (i) Thickness of the tedlar (t): 0.5 mm (ii) Thermal conductivity of the glass (kg) : 0.23 W/mK (iii) Specific heat of the glass: 3.135 kJ/kgK (iv) Density of the glass: 1720 kg/m3 (v) Mass of the solar cell: 1.7 kg/m2. (vi) Absorbsivity of glass: 0.05
Prediction of PV output current The net difference between the photocurrent (Iph) and the diode current (ID) is given by [30]: G U þ IRs 1 ð14Þ I L;ref þ mI;SC ðT c T c;ref Þ I O exp I¼ Gref AV t
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ORIGINAL RESEARCH ARTICLE
g ¼ A N c;s N ms I O ¼ I o;ref
Tc T c;ref
ð15Þ
3
exp
qM g 0
0
k A
1 T c;ref
1 Tc
maximum short circuit current and maximum open circuit voltage [30]. FF ¼
V mIm V oc I sc
Here, Voc is the open circuit voltage (V), I sc is the short circuit current (A), Vm is the maximum open circuit voltage (V), I m is the maximum short circuit current (A).
Modeling of centrifugal pumps
ð16Þ
A simplified mathematical model for a centrifugal pump is given by following equation [31]: 0
I O;ref
V oc;ref ¼ I L;ref exp 0 a ref
PðQ Þ ¼ aQ ð17Þ
Here, Io,ref – Saturation current at the reference condition (A), egap – Band gap of the material (1.17 eV for Si materials), Ns – Number of cells in series of the photovoltaic module, q – Charge of electron (assumed as 1.60217733 1019 C), A – Quality factor related the photovoltaic module, Io – Reverse saturation current (A). The value of a0 ref is calculated using following relation [30]: a0ref ¼
2V mp;ref V oc;ref I sc;ref I mp;ref I sc;ref I mp;ref þ ln 1 I sc;ref
ð18Þ
Here, Vmp, ref – Maximum power point voltage at reference condition (V), Imp, ref – Maximum power point current at reference condition (A), Isc, ref – Short circuit current at the reference condition (A). The term a is the function of temperature. It is given by following equation [30]: T c þ 273 0 a0 ¼ a ref ð19Þ T c;ref þ 273 The series resistance (Rs) of a photovoltaic panel is calculated using following equation [30]: 0 I þ V oc;ref V mp;ref a ref ln 1 Imp;ref sc;ref ð20Þ Rs ¼ I mp;ref Here, t g – transmissivity of the glass, mcell – mass of the cell material (kg), cpcell – specific heat of the cell material (kJ/kgK), Tcell – cell temperature ( C or K), Tg – temperature of the cell ( C or K), Ucell-td – heat transfer coefficient between cell and teldhar (W/m2K), E – electric output of the photovoltaic cell (W).
Prediction of photovoltaic electrical efficiency The electrical conversion efficiency of the photovoltaic panel is given by following equation [30]: hPV ¼
Ppv Apv G
ð22Þ
ð21Þ
Here, Apv is the photovoltaic panel area in m2, G is the solar irradiation in W/m2, Ppv is the photovoltaic panel output in terms of W.
Prediction of fill factor Fill factor (FF) of a solar cell is the ratio between actual maximum photovoltaic output power of the solar cells to the product of
0
3
þ bQ
0
2
0
þ cQ þ d
ð23Þ
Here, P – electrical power consumed by the pump, a, b, c and d – principal parameters of a pump model. The instantaneous pump discharge was predicted using Newton Raphson method or Secant method. After i iterations, the equation for predicting the instantaneous pump discharge using Newton Raphson method is given by following equation [31]: Q
0
¼Q
i
0
i1
f ðQ 0
0
f ðQ
i1 Þ 0
ð24Þ
i1 Þ
The instantaneous pump discharge using Secant method is given by following relation: 0
Q
0
iþ1
¼Q
0
0
i
f ðQ i Þ
0
Q i Q i1 0 0 f ðQ i Þ f ðQ i1 Þ
ð25Þ
The photovoltaic panel and centrifugal pump are the two subsystems. The characteristics of the photovoltaic panel output and the pump output are given by P and Q0 , respectively for different pumping heads (H). Based on the experimental trials, the following equations have been established: 0
PðQ ; HÞ ¼ aðHÞQ
0
3
þ bðHÞQ
0
2
0
þ cðHÞQ þ dðHÞ
ð26Þ
Here, a (H), b(H), c(H) and d(H) depends on total pumping. It can be given by following equations [31]: aðHÞ ¼ a0 þ a1 H þ a2 H 2 þ a3 H 3
ð27Þ
bðHÞ ¼ b0 þ b1 H þ b2 H 2 þ b3 H 3
ð28Þ
cðHÞ ¼ c0 þ c1 H þ c2 H 2 þ c3 H 3
ð29Þ
dðHÞ ¼ d0 þ d1 H þ d2 H 2 þ d3 H 3
ð30Þ
Here, ai, bi, ci and di represents the parameters of the mdoel. It depends on the parameters of the mdoel and pumping subsystem, Q is the pump discharge in m3/h and H represents the pumping head in m. Further, the pump efficiency is given by following relation: hpump ¼
r 9:81 Q H Pmotor
ð31Þ
Here, r represents the density of water and hpump represents the pump efficiency.
37
ORIGINAL RESEARCH ARTICLE
Here, G – Global solar radiation falls on the surface (W/m2), Gref– Reference global solar radiation falls on the surface at 1000 W/m2, Tc, ref– Reference solar cell temperature (assumed as 298 K), Tc, – Cell temperature (assumed as 298 K), IL, ref – Light current at reference condition, mi,sc – Temperature coefficient of short circuit current (A/ C), Rs – Series resistance, IL, ref – reference light current taken from manufacturer data sheet. The constant g is given by:
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
Prediction of overall efficiency of the system
Environmental impact assessments
The overall cascading efficiency of PVWPS is given by following equation:
The environmental impact assessment of a PVWPS is assessed in terms of carbon dioxide emissions during its entire life time by comparing with grid connected and diesel powered water pumping systems. The environmental impact was assessed for the period of twenty years.
hoverall ¼ hPV hi hm hP hf an
ð32Þ
ORIGINAL RESEARCH ARTICLE
Here, hoverall, hPV, hi, hm, hP, hfan represents the overall efficiency, photovoltaic efficiency, inverter efficiency, motor efficiency, pump efficiency and fan efficiency, respectively. The efficiency of motor and inverter are not influenced by ambient parameters (such as, solar irradiation, ambient temperature and the wind velocity). Here, the efficiency of the inverter and motor are assumed with constant value of 0.90 and 0.95, respectively based on experimental trials. The efficiency of a cooling fan used for cooling of photovoltaic panels is assumed as 0.95.
Economical assessments The cost involved in installing a PVWPS includes the cost of major components such as photovoltaic panels, inverters, motor-pump assembly and pipes. The PVWPSs do not require running costs during its life time. In contrast, the grid connected and diesel powered water pumping systems require high running costs. The economical feasibility of the PVWPSs was assessed in terms of pay back period (PBP), return on investment (ROI) and internal rate of return (IRR) with following assumptions: (a) Life of the system: 20 years (b) Working hours: 8 h per day for 365 days in a year (c) Pumping head: 15 m (d) Discharge: 10,000 l per day (e) Electricity cost: INR 8/kWh. (f) Initial cost of the motor-pump subsystem: INR 12,000 (g) Cost of photovoltaic panels: INR 44,000 (h) Cost of inverter: INR 22,000 (i) Replacement of pumps once in ten years. (j) Replacement cost of the pump after 10 years: INR 10,000 (k) Air cooling accessories over the top surface of the panel: INR 7000 (l) Air cooling accessories over the bottom surface of the panel: INR 7000 (m) Water cooling accessories over the top surface of the panel: INR 12,000 (n) Water cooling accessories over the bottom surface of the panel: INR 12,000 (o) Annual maintenance cost INR 1000, (p) Discount rate: 0.04–0.32 The payback period (PBP), return on investment (ROI) and net present value (NPV) of a PVWPS are given by following equations: PBP ¼
Investment Savings
ð33Þ
ROI ¼
Savings 100 Investment
ð34Þ
NPV ¼
CF ðI þ iÞn
The functional unit description is the main factor of environmental impact assessment of water pumps, which needs to be identified and quantified. The functional unit is a measure of the function to be studied and it provides a reference to which the inputs and outputs can be related. It needs two systems for comparison. In this work, the environmental impacts of the PVWPS are compared with conventional grid connected and diesel powered water pumping systems.
System boundaries The system boundaries define the processes considered for evaluating the environmental impacts of the water pump. The environmental impacts caused during production, transportation and disposal stages were ignored in this work due to lack of data. The environmental impacts of the PVWPS are evaluated only for the usage phase for comparison. Based on the trial experiments in diesel captive power generation plants, it is observed that, the diesel power generators consuming 0.35 to 0.4 l of diesel per kWh of electricity. The carbon-dioxide emissions per litre of diesel are estimated to be about 2.6 kg. [32]. The carbon-dioxide emissions produced during power generation is estimated as 1.04 kg per kWh. The coal based power plants will emit 0.90 kg of carbondioxide per kWh of electricity [33]. The carbon-dioxide emissions of water pumping systems are quantified by following relation: EI CO2 ¼ d Epump n N
ð36Þ
Here, EI is the environmental impact due to carbon-dioxide emissions in tons, d is the carbon-dioxide emission factor, Epump is the energy savings (in kW.h), n is the no of days in a year and N is the number of years.
Results and discussion The experimental results observed in a PVWPS under the influence panel cooling (using air and water) over the top and bottom surfaces of the panel were investigated. The performance of a PVWPS was evaluated based on the experimental observations. The experimental observations and energy performance of PVWPSs under the influence of panel cooling are discussed in this section.
Ambient variations
ð35Þ
The discount rate at which the net present value is zero is called internal rate of return (IRR). Here, the CF represents the cash flow and i represents the interest rate and n represents the number of year.
38
Functional unit
The performance of photovoltaic panels are influenced by solar irradiation, ambient temperature, wind velocity, ambient relative humidity and dust accumulated over the top surface of the panel [34]. However, the influence of dust and relative humidity has not influencing the instantaneous performance. Hence, the influence of dust accumulation and relative humidity were ignored in this work. The variations of solar irradiation, ambient temperature and ambient wind velocity were observed during
Renewable Energy Focus Volume 31, Number 00 December 2019
Similarly, the ambient temperature variations observed during experimentation with five modes of operation are shown in Figure 3b. The ambient temperature has influenced the convective cooling over the top surface of the panel. During experimentation, the ambient temperatures were varied between 28 C to about 38 C with an average ambient temperature of about 32 C. High ambient temperature has affecting the photovoltaic power output, which will reduce the pumping efficiency. During experimental observations with five different modes of operation, the maximum differences in ambient temperatures were observed within 2 C. The ambient wind velocity variations during experimentation with five different modes are depicted in Figure 3c. The ambient wind velocity was varied between 1.1 m/s and 4 m/s with an average value of 2.5 m/s. The variations of ambient wind velocity have influencing the cell temperature due to the direct cooling of glass surface. Hence, the influence of ambient wind velocity is quantified in terms of cell temperature variations.
Validation of mathematical models The results obtained using mathematical model was validated experimental results. The comparison between the experimentally observed and analytically predicted overall efficiency of the system during the sunny day on 24.02.2017 (without panel cooling) is shown in Figure 4. The overall efficiency of the system depends on efficiency of the photovoltaic panel subsystem, inverter subsystem, electrical motor subsystem and pump subsystem. The system overall efficiency was varied between 1.2% and 1.9%. The predicted overall efficiency of the system was found to be closer to the experimental values with 0.1% deviations.
Performance comparison The performances of a PVWPS under the influence of panel cooling using air and water over the top and bottom surfaces of the panel are described in this section.
Photovoltaic panel cell temperature
FIGURE 3
Variation of ambient conditions during experimental observations.
Generally, the cell temperature was maintained at 25 1 C to achieve maximum power output. However, maintaining 25 C is not possible during peak sunshine hours, which affects the photovoltaic output. The variations of cell temperature with panel cooling (using air and water as cooling medium) and without panel cooling are compared in Figure 5a. It is observed that, the cell temperature was varied from about 31 C to about 62 C with an average temperature of about 47 C in the case of panel without cooling. The air cooling over the bottom surface of the panel has reduced the temperature variations in the range between 30 C and 43 C with an average temperature of about 36 C. The water cooling of panel over the bottom surface has reduced the cell temperature variations in the range between 30.6 C and 37.8 C with an average temperature of about 32 C. It is observed that, cooling arrangement provided over the bottom surface of the panel has significant reduction in cell temperature when compared to the cooling arrangement provided over the top surface. Furthermore, it is confirmed that, water provides effective cooling of panels when compared to air due to its high specific heat and higher heat transfer coefficient when compared to air as cooling medium [35]. 39
ORIGINAL RESEARCH ARTICLE
experimentation of a PVWPS in five different modes are described in this sub-section. The solar irradiations observed during experimentation with a PVWPS in five modes of operation are illustrated in Figure 3a. It is observed that, the fluctuations in solar irradiation were found to be within 50 W/m2. The solar irradiation was varied from about 100 W/m2 to the maximum value of about 950 W/m2 with an average solar irradiation of about 550 W/m2. As expected, the solar irradiation gets increased during morning hours and reached maximum solar irradiation of about 950 W/m2 during 13.30 h and gets reduced in the afternoon hours. During experimentation, the length of sunshine was observed as 11 h per day. But, the potential sunshine availability (above 200 W/m2) for water pumping applications is around 8–9 h per day. Moreover, it is observed that, Coimbatore has enough annual solar irradiation potential to support a PVWPS.
ORIGINAL RESEARCH ARTICLE
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FIGURE 4
Comparison between experimental and theoretical prediction of overall efficiency.
Photovoltaic panel power output The power output of photovoltaic panels under the influence of cooling is depicted in Figure 5b. As expected, the photovoltaic power output was increased with increase in solar irradiation. During peak sunshine hours, the panels get heated under the influence of solar irradiation and drop its electrical conversion efficiency. The panels need to be cooled and maintain its temperature in the range between 25 C and 35 C to achieve maximum conversion efficiency. In this research work, air and water were used as a cooling medium to reduce the panel surface temperature. The photovoltaic power output (without panel cooling) was varied between 145 W and 610 W with energy output of 3.1 kW h per day. Similarly, the photovoltaic power output in the case of air cooling over the top surface the panel was varied between 170 W and 630 W with output of 3.4 kW h per day. The photovoltaic power output in the case of panel air cooling over the bottom surface of the panel has power output in the range between 175 W and 635 W with output of 3.6 kW h per day. The panel output was observed in the range from 185 W to 650 W in the case of water cooling over the top surface of the panel with output of 3.9 kW h per day. A significant improvement in photovoltaic power output was observed in the range from 200 W to 680 W by providing water cooling over the bottom surface of the panel with output of 4.2 kW h per day. The results confirmed that, the performance of a PVWPS was significantly improved using water cooling over the bottom surface of the panel, which is similar to the earlier research investigations [14,18].
Photovoltaic panel efficiency The variations of photovoltaic panel efficiency during experimentation in five different modes are compared in Figure 5c. The photovoltaic efficiency was influenced by solar irradiation, ambient temperature and ambient wind velocity. It is observed that, the panel efficiency without panel cooling was varied between 10% and 11.4%. The panel efficiency was improved in the range between 10.6% and 12% and in the range between 11.3% and 12.4% under the influence panel cooling using air and water over the bottom surface of the panel, respectively. The photovoltaic efficiency gets reduced during the peak sunshine hours due to the effect of heating. The results confirmed that, the water cooling arrangement provided at the bottom surface was observed to be more effective when compared to air cooling due to its higher heat tranfer coefficient. 40
FIGURE 5
Performance of photovoltiac panels.
The panel efficiency results observed in this work are similar to the earlier work reported by Habiballahi et al. [14].
Performance of a pump The performance of a motor-pump subsystem was tested in a laboratory and its performance characteristics are illustrated in Figure 6a. The pump head decreases from 25 m to 6 m with increase in pump discharge from 0.2 m3/h to 1.6 m3/h, respectively. In addition, the variation of hydraulic efficiency at fixed pumping head of 15 m is shown. It is observed that, the maximum pump hydraulic efficiency of about 40% was observed with the pump discharge of 1 m3/h.
Renewable Energy Focus Volume 31, Number 00 December 2019
compared to the system without the influence of panel cooling. The water cooling over the bottom surface of the panel has enhanced the pump discharge to about 0.19 m3/h compared to the air cooling on bottom surface of the panel. The results confirmed that, pump discharge was significantly improved by maintaining the cell temperature in the range between 25 and 35 C. The results confirmed that, the pump discharge was improved by providing water cooling over the bottom surface of the panel. The pump efficiency variations under the influence of panel cooling at constant pumping head of 15 m are illustrated in Figure 6c. It is observed that, the pump efficiency was varied from 10% and 22% in the case of PVWPS without panel cooling. An increase in pump speed was observed under the influence of panel cooling. The pump efficiency was improved in the range from 10.6%–23.8% and in the range from 11.3%–25.6% for the case of PVWPS using air cooling provided over the top and bottom surfaces, respectively. Similarly, the pump efficiency was improved in the range from 11.7%–26.18% and in range from 11.8%–29.7% in the case of PVWPS using water cooling provided over the top and bottom surfaces, respectively. About 7.7% improved pump efficiency was observed during the peak sunshine hours when compared to the system without panel cooling due to the increased photovoltaic power output from the photovoltaic panels under the influence of panel cooling over the bottom surface of the panel. In a similar work, the pump efficiency under the influence of panel cooling over the bottom surface of the panel was improved by 4% [14].
Performance of an overall system The overall efficiency of a PVWPS is depicted in Figure 7. It is observed that, the overall efficiency of a PVWPS (without panel cooling) was varied between 0.9% and 1.79%. The overall efficiency of the system was varied between 1.0% and 2.1% and in the range between 1.0 and 2.3% in the case of air cooling over the top surface the panel and in the case of air cooling over the bottom surface of the panel, respectively. Similarly, the overall efficiency was varied in the range from 1.1%–2.42% and from 1.2% to 2.84% in the case of water cooling over the top and bottom surfaces of the panel, respectively. It is observed that, panel cooling over the bottom surface of the panel using water has achieved the maximum overall efficiency of about 2.84%. The overall efficiency FIGURE 6
Performance of a water pump sub system.
The variations of pump discharge under the influence of panel cooling at constant pumping head of 15 m are compared in Figure 6b. The pump discharge fluctuates according to the availability of solar irradiation. The pump discharge is directly proportional its speed. The air cooling arrangement provided over the top and bottom surface of the panel has enhanced the pump discharge to about 1.32 m3/h and 1.41 m3/h, respectively, which is found to be about 0.32 m3/h and 0.41 m3/h higher when compared to the PVWPS without cooling. Similarly, the water cooling provided over the top and bottom surface of the panel has enhanced the pump discharge to about 1.48 m3/h and 1.60 m3/h, respectively, which is found to be about 0.48 m3/h and 0.60 m3/h higher when
FIGURE 7
Variation of overall efficiency of a PVWPS against time. 41
ORIGINAL RESEARCH ARTICLE
ORIGINAL RESEARCH ARTICLE
Renewable Energy Focus Volume 31, Number 00 December 2019
ORIGINAL RESEARCH ARTICLE
TABLE 5
Performance of a PVWPS during peak sunshine hours (solar irradiation above 850 W/m2). Cooling mode
Photovoltaic panel
ORIGINAL RESEARCH ARTICLE
Without cooling Air cooling over the top surface the panel Air cooling over the bottom surface of the panel Water cooling over the top surface the panel Water cooling over the bottom surface of the panel
Pump
Overall system
Power output (W)
Efficiency (%)
Discharge (m3/h)
Efficiency (%)
Efficiency (%)
610 625 635 650 680
10.4 10.9 11.1 11.4 11.8
0.97 1.35 1.45 1.48 1.60
22.0 23.8 25.6 26.2 29.7
1.79 2.10 2.30 2.42 2.84
improvement observed in this work was found to be slightly higher than earlier work reported by Habiballahi et al. [14]. The summary of performance results observed in a PVWPS during peak sunshine hours (above 850 W/m2) are consolidated in Table 5. It is observed that, the water cooling provided over the bottom surface of the panel was observed to be more effective when compared to other modes of panel cooling. Moreover, the performance comparisons with earlier research investigations are compared in Table 6. It is noticed that, the performance of pump subsystem has 7.7% improved hydraulic efficiency with 1.01% improved overall efficiency when compared to the efficiency of the system without panel cooling. A significant improvement in pump hydraulic efficiency with minor improvement in overall efficiency were observed when compared to the earlier research reported by Habiballahi et al. [14]. Thin film photovoltaic cells have retained its performance even at high temperatures. Hence, further research is essential to explore the possibility of using thin film photovoltaic panels to over the drawbacks with exiting mono crystalline and multi crystalline photovoltaic cells. Such research investigations are in progress at author’s research laboratory.
the cell temperature in the range between 25 C and 35 C to achieve maximum performance. The influence of photovoltaic panel cooling has significantly improved the photovoltaic efficiency, pump efficiency and overall efficiency of the total system. Moreover, it is confirmed that, water cooling over the bottom surface is more effective when compared to the other cooling modes.
Influence of pumping head The influence of pumping head at constant solar irradiation and cell temperature (600 W/m2 and 35 C) is depicted in Figure 8b. It is observed that, the pump efficiency and overall efficiency of the system are significantly influenced by pumping head [36]. An increase in pumping head has decreased the pump efficiency and overall system efficiency. The pump efficiency was dropped from about 32% to about 18% with increase in head from 5 m to 25 m. Similarly, the overall efficiency of the pumping system was
Parameteric analysis The performance of a PVWPS is influenced by solar irradiation, ambient temperature, ambient wind velocity and head [20]. The influence of solar irradiation, ambient temperature and wind velocity are quantified in terms of photovoltaic cell temperature. The influences of photovoltaic cell temperature and head on the performance of PVWPS are predicted theoretically.
Influence of cell temperature The influence of cell temperature on the performance of a PVWPS is illustrated in Figure 8a. It is observed that, an increase in cell temperature from 30 C to 62 C has dropped the photovoltaic electrical efficiency from 12.6% to 9%, pump efficiency from 24% to 16% and overall efficiency from 2.4% to 0.9% due to reduction in photovoltaic power output. Hence, it is essential to maintain TABLE 6
Performance comparison with other reported investigations.
Cooling medium Cooling surface Photovoltaic efficiency Pump efficiency Overall efficiency
42
Present work
Habiballahi et al. [14]
Water Bottom of the panel 1.3% 7.7% 1.01%
Water Bottom of the panel 2% 4% 1%
FIGURE 8
Performance of photovoltaic water pumping system under the influence of cell temperature and head.
Renewable Energy Focus Volume 31, Number 00 December 2019
Economical analysis of PVWPS with different modes of panel cooling. Cooling modes
Payback period (years)
Return on investment (%)
Internal rate of return (%)
Without panel cooling Air cooling above the panel Air cooling below the panel Water cooling above the panel Water cooling below the panel
8.6 8.5
11.6 11.7
8.2 8.5
8.1
12.3
9.3
7.9
12.7
9.8
7.3
13.7
10.9
dropped from about 1.9% to 0.9% due to increase in pumping head from 5 m to 25 m.
Economic analysis The investment on PVWPS (without panel cooling) for the period of twenty years (8 h of pump operation per day) for pumping 10,000 l of water has a payback of 8.6 years. The PVWPS using air cooled panels over the top and bottom surfaces of the panel has a payback of 8.5 and 8.1 years, respectively. Similarly, the payback for water cooled panels over the top and bottom surfaces has 7.9 and 7.3 years, respectively. The payback, return on investment and internal rate of return of PVWPS using different cooling modes are given in Table 7. The net present value of the investment was estimated for the period of twenty years for a discount rate from 4% to 34% are plotted in Figure 9. It is observed that, the internal rate of return for the PVWPS using panel cooling over the bottom surface is about 10.95%. The economical analysis confirmed that, the PVWPS with effective panel cooling is an economically feasible option for water pumping applications in remote locations facing shortage of electricity. The influence of panel cooling using water over the bottom surface has reduced the payback period by about 1.3 years when compared to the panel without cooling.
cooling medium was assessed for the period of twenty years life. The electricity consumption for pumping 10,000 l of water per day for the head of 15 m was considered for comparison. The duration of pump operation is 8 h per day. The environmental impacts caused during manufacturing and disposal stages were ignored in this work due to lack data. The electricity consumption of 380 W centrifugal pump for pumping water for 8 h duration is about 3.1 kW h per day. The power generated by photovoltaic panels has fulfilled the requirements for water pumping system and also for running the panel cooling accessories. The annual electricity consumption of a pump is estimated to be about 1131 kW h. The emissions for generating 1131 kW h of electricity using coal based power plants and diesel power generators have been estimated to be about 1018 kg of CO2 and for diesel 1176 kg of CO2, respectively. It is observed that, PVWPSs could reduce 20.36 and 23.52 tons of CO2 emissions during its life cycle period of twenty years when compared to the grid connected and diesel powered water pumping systems, respectively. The PVWPS has significant reduction in carbon-dioxide emission when compared to conventional grid connected and diesel powered water pumping systems [37].
Conclusion The experimental results concluded that, the cooling of panel using water over the bottom surface has reduced the cell temperature in the range between 25 and 38 C. The cooling of panel using water over its bottom surface has improved the photovoltaic efficiency, pump efficiency and total efficiency by about 1.4%, 7.7% and 1.01%, respectively during peak sunshine hours when compared to the PVWPS without cooling. The economic analysis showed that, the PVWPS has 7.3 years payback period with 13.7% return on investment and 10.9% internal rate of return. The economical analysis confirmed that, the investment in PVWPS with panel cooling over the bottom surface is economically feasible. It is possible to reduce 20.4 and 16.1 tons of CO2 emissions during the period of twenty years when compared to the grid connected and diesel powered water pumping systems, respectively.
Environmental impact assessments The environmental impact of a PVWPS under the influence of panel cooling over the bottom surface of the panel using water as
Conflict of interest There is no conflict of interest in this research submission.
Acknowledgement Authors would like to thank Flow Tech Power, Coimbatore-India for providing the facility to carry out this project. References
FIGURE 9
Net present value of the investment after twenty years at different discount rates.
[1] C. Gopal, M. Mohanraj, P. Chandramohan, P. Chandrasekar, Renew. Sustain. Energy Rev. 25 (2013) 351–370. [2] R. Rawat, S.C. Kaushik, R. Lamba, Renew. Sustain. Energy Rev. 57 (2016) 1506–1519. [3] S.S. Chandel, M.N. Naik, R. Chandel, Renew. Sustain. Energy Rev. 76 (2015) 163–175. [4] V.C. Sontake, V.R. Kalamkar, Renew. Sustain. Energy Rev. 59 (2016) 1038–1067. [5] D.H. Muhsen, T. Khatib, F. Nagi, Renew. Sustain. Energy Rev. 68 (2017) 70–86. [6] G. Li, M.Y. Jin, M.W. Akram, X. Chen, Renew. Sustain. Energy Rev. 79 (2017) 440–458. [7] M. Aliyu, G. Hassana, S.A. Saida, M.U. Siddiquic, A.T. Alawamid, I.M. Elamin, Renew. Sustain. Energy Rev. 87 (2018) 61–76. [8] T.V. Ramachandra, R. Jain, G. Krishnadas, Renew. Sustain. Energy Rev. 15 (2011) 3178–3386. [9] A. Mokeddem, A. Midoun, D. Kadri, S. Hiadsi, I.A. Raja, Energy Convers. Manage. 52 (2011) 3089–3095.
43
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TABLE 7
ORIGINAL RESEARCH ARTICLE
ORIGINAL RESEARCH ARTICLE
[10] [11] [12] [13] [14] [15]
ORIGINAL RESEARCH ARTICLE
[16] [17] [18] [19] [20] [21] [22] [23] [24]
44
M. Moechtar, M. Juwono, E. Kantosa, Energy Convers. Manage. 31 (1991) 521–527. H.G. Teo, P.S. Lee, M.N.A. Hawlader, Appl. Energy 90 (2012) 309–315. M. Abdolzadeh, M. Ameri, Renew. Energy 34 (2009) 91–96. A. Kordzadeh, Renew. Energy 35 (2010) 1098–1102. M. Habiballahi, M. Ameri, S.H. Mansour, J. Sol. Energy Eng. 137 (2015) 1–8. C. Gopal, M. Mohanraj, P. Chandramohan, M. Sakthivel, S. Bhero, Therm. Sci.: Sci. J. 21 (2017) 399–410. A. Fudholi, K. Sopian, M.H. Yazdi, M.H. Ruslan, A.H. Ibrahim, A. Kazem, Energy Convers. Manage. 78 (2014) 641–651. H.M.S. Bahaidarah, A.A.B. Baloch, P. Gandhidasan, Renew. Sustain. Energy Rev. 57 (2016) 1520–1544. S. Nietic, D. Coko, A. Yadav, F. Grubiic-Cabo, Energy Convers. Manage. 108 (2016) 287–296. J. Siecker, K. Kusakana, B.P. Numbi, Renew. Sustain. Energy Rev. 79 (2017) 192–203. I. Odeh, Y.G. Yohanis, B. Norton, Sol. Energy 80 (2016) 51–64. L. Qoaider, D. Steinbrecht, Appl. Energy 87 (2010) 427–435. K. Meah, S. Ula, S. Barrett, Renew. Sustain. Energy Rev. 12 (2008) 1162–1175. T.P. Correˆa, S.I. Seleme, S.R. Silva, Renew. Energy 41 (2012) 220–226. P.E. Campana, H. Li, J. Zhang, R. Zhang, J. Liu, J. Yan, Energy Convers. Manage. 95 (2015) 32–41.
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[25] P.E. Campana, H. Li, J. Yan, A. Olsson, Int. J. Green Energy 13 (2016) 831–839. [26] I. Yahyaoui, A. Atieh, A. Sena, T. Fernando, Sol. Energy 144 (2017) 376–391. [27] E.D. Mehleri, P.L. Zervas, H. Sarimveis, J.A. Palyvos, N.C. Markatos, Renew. Energy 35 (2010) 2468–2475. [28] N. Arcuri, F. Reda, M. De Simone, Sol. Energy 105 (2014) 147–156. [29] J.P. Holman, Experimental Methods for Engineers, Tata Mc Graw Hill Publishers, New Delhi, 2007. [30] R.A. Chenni, M. Makhlouf, T. Kerbache, A. Bouzid, Energy 32 (2007) 1724–1730. [31] A. Hamidat, B. Benyoucef, Energy Policy 37 (2009) 1489–1501. [32] J.L. Silveira, J.A. Carvalho, I.A.C. Villela, Renew. Sustain. Energy Rev. 11 (2007) 524–535. [33] M.G. Rasul, S. Moazzem, M.M.K. Khan, Energy 64 (2014) 330–341. [34] S. Mekhilef, R. Saidur, M. Kamalisarvestani, Renew. Sustain. Energy Rev. 16 (2012) 2920–2925. [35] F. Spertino, A.D. Angola, D. Enescu, P.D. Leo, G.V. Fracastoro, R. Zaffina, Sol. Energy 133 (2016) 119–140. [36] M. Benghanem, K.O. Daffallah, S.N. Alamri, A.A. Joraid, Energy Convers. Manage. 77 (2014) 334–339. [37] P. Purohit, A. Michaelowa, Renew. Sustain. Energy Rev. 12 (2008) 181–199.