Solar Energy 144 (2017) 321–334
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Experimental investigation of jet array nanofluids impingement in photovoltaic/thermal collector Husam Abdulrasool Hasan a,⇑, Kamaruzzaman Sopian a,⇑, Ahed Hameed Jaaz a, Ali Najah Al-Shamani a,b a b
Solar Energy Research Institute, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia Al-Musaib Technical College, Al-Furat Al-Awsat Technical University, 51009 Babylon, Iraq
a r t i c l e
i n f o
Article history: Received 3 September 2016 Received in revised form 5 December 2016 Accepted 15 January 2017 Available online 25 January 2017 Keywords: Photovoltaic thermal (PVT) collectors Nanofluid Electrical performance Thermal performance Jet impingement
a b s t r a c t The effect of nanoparticles (SiC, TiO2 and SiO2) with water as its base fluid on the electrical and thermal performance of a photovoltaic thermal (PVT) collector equipped with jet impingement have been investigated. A PVT collector was tested indoor at set levels of solar irradiances and mass flow rates. The system consists of four parallel tubes and 36 nozzles that directly injects the fluid to the back of the PVT collector. The electrical performance of the PVT collector was determined based on the mean temperature of the PVT absorber plate. The SiC/water nanofluid system reported the highest electrical and thermal efficiency. The electrical, thermal, and combined photovoltaic thermal efficiencies were 12.75%, 85%, and 97.75%, respectively, at a solar irradiance of 1000 W/m2 and flow rate of 0.167 kg/s and ambient temperature of about 30 °C. Moreover, the Pmax of PVT with SiC nanofluid increased by 62.5% compared to the conventional PV module. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction A photovoltaic thermal collector (PVT) converts solar irradiance into electricity and thermal energy, while a conventional photovoltaic solar cell converts photons emitted by the sun into electricity. The PVT absorber plate convert the heat from the PV cells into thermal energy. The generation of electricity and heat by the PVT make the collector more efficient than the solar thermal collectors or conventional PV. Many experimental and numerical studies aspire to improve the electrical and thermal efficiency of the PVT (Tyagi et al., 2012; Ji et al., 2007; Shan et al., 2014; Ziapour et al., 2014). Working fluids are used to cool the PV solar cells, examples being water, air, and nanofluids (Daghigh et al., 2011; Chen et al., 2014; Xu and Kleinstreuer, 2014; Abu-Bakara et al., 2014; Sardarabadi et al., 2014). Despite the fact that PVT design is crucial towards its performance, studies on it remains scarce in literature. Ibrahim et al. (2011) indicated that the thermal efficiency of a sheet-and-tube collector is 2% lower than that of other collectors (such as free flow, channel, and dual-absorbers). Cerón et al. (2015) numerically analyzed the effect of liquid on the performance of tube-on-sheet flat-plate solar collectors, while Zhang et al. (2014) investigated the electrical and thermal performance of a novel design of solar photovoltaic/loop with a heat-pipe ⇑ Corresponding authors. E-mail addresses:
[email protected] (H.A. Hasan), ksopian@ukm. edu.my (K. Sopian). http://dx.doi.org/10.1016/j.solener.2017.01.036 0038-092X/Ó 2017 Elsevier Ltd. All rights reserved.
collector. They reported that the thermal and electrical efficiency system are 9.12% and 58%, respectively, while the overall exegetic efficiency of the system was 14.92%. Using nanofluids as a working fluid significantly improved the overall performance of photovoltaic/thermal without the need to alter the structural design (Xu and Kleinstreuer, 2014). Literature reported many works involving heat transfer using nanofluids as working fluids due to the nanoparticles’ higher conductive heat transfer coefficient (Khanafer and Vafai, 2011), its transient local heat transfers and Brownian motion, and surface electrical charges (Koo and Kleinstreuter, 2005; Michaelides and Feng, 1994; Lee et al., 2006; Wu et al., 2009). The use of different types of nanofluids in solar collector systems for different applications were reviewed in Nagarajan et al. (2014). Suganthi et al. (2014) experimentally analyzed the effect of the ZnO/ethylene-glycol/water and ZnO/ ethylene-glycol nanofluids as a working fluid for enhancing heat transfer. The results showed that the heat transfer coefficients increased with increasing thermal conductivity of the nanofluids. Bhattarai et al. (2012) experimentally and theoretically investigated the transient process of a PVT collector equipped with a sheet-and-tube water based system, while He et al. (2014) investigated the performance of a PVT system in a thermo-electric heating and cooling unit. They reported that the electrical and thermal efficiencies of the PVT system were 16.7% and 23.5%, respectively. Dehra (2009) studied a 2D thermal model for a PV unit to calculate the temperature distribution of a solar wall and
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Nomenclature Ac b Cp H F0 FR GT hfi k _ m N Qu I t UL Ut v
a
h
area of PVT collector (m2) width of PVT collector (m) specific heat (J/kg °C) nozzle-PV spacings (m) the efficiency factor of PVT collector the heat removal of efficiency factor overall solar radiation (W/m2) the heat transfer coefficient (W/m2 °C) the thermal conductivity (W/m °C) mass flow rate of jet water (kg/S) total number of glasses effective useful heat gain (W) solar irradiance (W/m2) temperature (°C) effective overall heat transfer coefficients (W/m2 °C) top losses coefficient (W/m2 °C) wind speed (m/S) effective absorptance collector tilt angle
the ventilation for ducts used in a photovoltaic hybrid system by increasing the solar irradiation from 200 to 700 W/m2. Xu and Kleinstreuer (2014) analyzed the performance of photovoltaic thermal co-generation system using a 2D model coupling thermal analysis and CFD simulations. Nanofluids was used for both the heating and cooling systems. The results showed that the efficiency increased to 70% for systems using nanofluids as its working fluids. Researchers are currently focusing on heat transfer enhancement using nanofluids. Limited thermophysical properties and the poor thermal conductivity of conventional fluids (pure water, ethylene-glycols) led the research community in a search for alternatives that could enhance heat transfer. Several researches reported that using nanofluids effectively improved thermal conductivity, and consequently, heat transfer performance. Nanofluids is regarded as a viable heat transfer fluid due to its better stability and an anomalous increase in thermal conductivity even at small volume fraction of suspended nanoparticles. Despite thermal conductivity being directly related to heat transfer capabilities of fluids, viscosity governs the ease of flow, pressure drop, and consequently pumping power during transport. The advantages of using nanofluids include (i) higher thermal conductivities compared to that predicted by currently available macroscopic models, (ii) excellent stability, and (iii) negligible penalty in pumping power due to pressure drop and pipe wall abrasion. Preparing nanofluids is an important step towards using nanoparticles to improve the thermal conductivity of conventional heat transfer fluids. Researchers have experimented with different types of nanoparticles, such as metallic particles (Cu, Al, Fe, Au, and Ag), non-metallic particles (Al2O3, CuO, Fe3O4, TiO2, and SiC), and carbon nanotubes. The thermal conductivity of nanofluids varies with size, shape, and the material of the nanoparticles dispersed in the base fluids. For example, nanofluids containing metallic nanoparticles were found to have a higher thermal conductivity compared to nanofluids containing non-metallic (oxide) nanoparticles. The particle size is inversely correlated with the thermal conductivities of nanofluids. Furthermore, nanofluids containing spherical nanoparticles exhibit a smaller increase in thermal conductivity compared ro nanofluids containing cylindrical (nano-rod or tube) nanoparticles. Barrau et al. (2014) experimentally analyzed the effect of hybrid jet impingement/micro channel cooling device on the performance of densely packed concentrated photovoltaic (CPV) receivers. Jet impingement/micro channel cooling was used in
e s g
effective emittance effective transmittance efficiency
Subscripts a ambient abs effective absorber thickness c solar cell g glass i inlet of fluid j jet water o outlet of fluid p plate of absorber pm mean plate of absorber PV photovoltaic solar cell PVT photovoltaic thermal r reference value w wind
order to keep the photovoltaic cells within their nominal operating temperature range. The experimental results showed that the thermal resistance coefficient and temperature uniformity provided by the cooling device met the requirements for the CPV receivers. Barrau et al. (2010) experimentally tested a new hybrid cooling scheme for high heat flux management and power devices. The benefits of micro-channel and jet impingement cooling technologies were analyzed in the context of improving the temperature uniformity of the cooled object. The experimental results showed a global decrease of the temperature of the heat sink in the direction of the fluid flow. Barrau et al. (2012) analyzed the performance of a new hybrid jet impingement/micro-channel cooling scheme for densely packed PV cells at high concentrations. The hybrid cooling scheme offers a minimum thermal resistance coefficient of 2.18 105 K m2/W, with a pressure drop being lower in the micro-channel devices. The results showed that the net PV output of PV receiver was higher when cooled by the hybrid design compared to when cooled by the micro-channels. Rosell et al. (2011) numerically investigated a new hybrid jet impingement/microchannel cooling scheme for utilization in a high heat-flux thermal management of electronic and power devices. The device was developed to improve the uniformity of the temperature of the cooled object. The results showed that pressure loss increased faster than the average heat exchange coefficient alongside the Reynolds number, while the average heat transfer coefficient and pressure loss increase alongside the dimensionless density of the channels. Royne and Dey (2007) experimentally analyzed the effect of a cooling device based on jet impingement for cooling densely packed photovoltaic cells at high concentrations. The device consists of an array of jets where the cooling fluid is drained around the sides normal to the surface. The results showed that the inherently non-uniform heat transfer distribution of jet arrays has little effect on the expected electrical performance of the PV array. This work investigates the effects of jet impingement using different types of nanofluids (nanoparticles), namely SiO2, TiO2, and SiC, with water as the base fluid, on the electrical, thermal, and combined PVT efficiencies. The PVT collector with an array of jet impingement was indoor tested under a solar simulator. The PVT collector was exposed to solar irradiance levels of 500–1000 W/m2 and water mass flow rates of 0.05–0.17 kg/s. All of the nanoparticles were dispersed in pure water at a 1 wt.% concentration.
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2. Experimental setup The photovoltaic/thermal collector was tested with different nanofluids in a jet array impingement at the lab of Solar Energy Research Institute (SERI) in the National University of Malaysia (UKM). A solar simulator (also artificial sun) was used to provide illumination that represents sunlight, whose purpose is to provide a controllable and changeable solar irradiance in an indoor test facility under laboratory conditions to test the solar cells. The artificial solar simulator at the laboratory was made from 45 of halogen tungsten lamps (Brillanta), with each lamp having an output power of 500 W. The lamps were arranged in 8 columns, as per Fig. 3. The solar irradiance is controlled using a regulator. In this work, the solar irradiance was set to 500–1000 W/m2. The construction of the photovoltaic thermal collector is displayed in Fig. 1(a) and (b). The PV module in this work was constructed from 36 pieces of thin wafers of polycrystalline silicon, measuring 156 mm by 156 mm, and is 200 lm thick, as shown in Fig. 1. Table 1 shows the electrical characteristics of the polycrystalline silicon photovoltaic module. Jet impingement will be directly applied to the back of the PV module for cooling, as per Fig. 2. A total of 36 nozzles were used to jet the nanofluids and water for this purpose. The coolant fluids (nanofluids) used in the experiments are pure water, Silicon Carbide/water, Titanium Dioxide/water, and Silicon Dioxide/water. All of the nanoparticles were dispersed in water at a 1 wt.% concentration using a
Table 1 Typical electrical characteristic of polycrystalline silicon photovoltaic module. Electrical performance under STC
Value
Unit
Maximum power (Pmax) Current at Pmax (Imp) Voltage at Pmax (Vmp) Short-circuit current (Isc) Open-circuit voltage (Voc) Dimensions Glass thickness Cell number
110 6.4 17.2 6.9 21.7 1490 675 4 36
W A V A V mm mm pcs
high-speed stirrer, and an ultrasonic vibrator was used for 2 h continuously to stabilize the resulting mixtures. 2.1. Experimental procedures The experimental setup and complete measuring system for the PVT collector are shown in Figs. 3 and 4, respectively. The experimental testing was conducted under steady-state conditions to evaluate the performance of the PVT system. The PVT equipped with the jet impingement system was exposed to solar irradiances of 500, 600, 700, 800, 900 and 1000 W/m2. The effect of different nanofluids (SiC, TiO2, and SiO2) at 1 wt.% concentration on electrical and thermal efficiencies were investigated. The influence of water mass flow rates of 0.050, 0.067, 0.083, 0.010, 0.117, 0.133, 0.150, and 0.167 kg/s were duly tested. A total of 18 thermocouples were uniformly fixed to the back of the PV module to determine the mean PV temperature, while other thermocouples were fixed to the top of the PV modules, water tank, at the base of the PVT collector, and the inlet and the outlet of the tubes to measure the resulting temperatures. A data-acquisition system made up of 32 channels was connected to a computer so that the data can be recorded from the PVT collector and stored every minute. These data can be used to calculate the electrical and thermal efficiencies of the PVT collector that changes with the water mass flow rates and solar irradiance levels vis-à-vis the different types of nanofluids. A water pump was used to activate the jet water to cool the PV module. The hot water collected in the thermal collector, connected to the heat exchanger and storage tank forms a close-loop system that is shown in Fig. 4.
3. Mathematical model of the PVT solar collectors with jet impingement The performance of the PVT collectors equipped with jet impingement was analyzed to calculate the electrical (gele) and thermal efficiencies (gth). This include the electrical gain and ratio of the useful thermal gain of the PVT system at multiple solar irradiance. Table 2 shows the different parameters of the photovoltaic thermal collector. The overall photovoltaic efficiency and thermal efficiency, or combined efficiency (gPVT) determines the combined performance of the photovoltaic thermal collector PVT system (Zondag et al., 2003; He et al., 2011; Zhang et al., 2012; Radziemska, 2009):
gPVT ¼ gTH þ gele
Fig. 1. The photovoltaic thermal (PVT) system (a) PVT jet impingement solar collector, (b) photograph of PVT solar collector.
ð1Þ
The determination of the thermal performance of the PVT system was based on multiple parameters. In this work, the thermal performance of the PVT system was determined using different values of the water mass flow rates and solar irradiances. The design of the PVT collector was similar to the single sheet glazing flat/plate solar collector. The electrical and thermal performance of the PVT system was calculated using the Hottel–Whillier equations (Hottel and Whillier, 1958). The actual rate of the useful heat
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Fig. 2. PV/Thermal collector with jet Nanofluids impingement.
PV/T
Heat exchanger
Water tank Water pump Fig. 3. Experimental setup.
energy (Qu) and the solar radiation (G) were used to determine the thermal efficiency of a conventional flat/plate solar collector (Al-Shamani et al., 2016), and is expressed as:
The heat removal efficiency factor (FR) can be calculated using the formula reported in Zhang et al. (2012), which is:
gth ¼ Q u =G
FR ¼
ð2Þ
The effective collected useful heat gain from the flat-plate solar collector can be calculated simultaneously, and expressed as:
_ Cp ðTo Ti Þ Qu ¼ m
ð3Þ
where Cp is Specific Heat (J/kg °C), To is outlet temperature (°C), and Tj is the jet temperature. The Hottel–Whillier equation (Hottel and Whillier, 1958) was used to calculated the heat gain:
Q u ¼ Ac F R ½GT ðsaÞPV U L ðT i T a Þ
ð4Þ 2
where Ac is area of the PVT Collector (m ), GT is overall Solar Radiation (W/m2), UL is effective overall Heat Transfer Coefficients (W/m2 °C), s is the effective transmittance, a is effective absorbance, and Ta is the ambient temperature.
_ p mC AC U L F 0 1 exp _ p mC AC U L
ð5Þ
where the collector efficiency factor is F 0 . The overall loss coefficient (UL) of the solar collectors can be calculated by the sum of the edge (Ue) and top (Ut) loss coefficients, and expressed (Hottel and Whillier, 1958) as: UL ¼ Ue þ Ut
ð6Þ
ke pl ð7Þ Ue ¼ Lc Ac 91 3 28 > > < rðT pm þ T a ÞðT 2pm þ T 2a Þ N 1= 7 6 Ut ¼ 4 þ h ie 5 1 eP > > ðe þ 0:00591Nhw Þ þ 2Nþf 1þ0:133 N : c T pm T a hw ; eg T pm
ðNþf Þ
ð8Þ
where
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Fig. 4. Schematic diagram of PVT jet impingement solar collector.
Table 2 PVT solar collector characteristics. Description
Symbol
Value
Unit
Ambient temperature Collector area Number of glass cover Emittance of glass Emittance of plate Fluid thermal conductivity Specific heat of working fluid Back insulation conductivity Back insulation thickness Insulation conductivity Edge insulation thickness Absorber conductivity Absorber thickness Transmittance Absorptance Number of nozzles Diameter of nozzle
Ta Ac N eg ep kf Cp kb lb ke lb kabs labs
20 1 1 0.88 0.95 0.613 4180 0.045 0.05 0.045 0.025 51 0.002 0.88 0.95 36 0.001
°C m2 – – – W/m °C J/kg °C W/m °C m W/m °C m W/m °C m – – – m
s a – d
2
C ¼ 520ð1 0:000051b Þ
f ¼ ð1 þ 0:089hw 0:1166hw ep Þð1 þ 0:07866NÞ 100 e ¼ 0:43 1 T pm T pm ¼ T i þ
Q Ac
ð1 F R Þ F R UL Tup þ Tbm Tpm ¼ 2
ð9Þ ð10Þ ð11Þ ð12Þ ð13Þ
where Tpm is the mean temperature of the PV module, and Tup is the up-plate temperature.
Tbm
ðT1 þ T1 þ T3 þ T4 þ T5 þ T6 þ T7 þ . . . þ T18 Þ ¼ 18
ð14Þ
where Tbm is the mean temperature of the back PV module, as shown in Fig. 7. Eq. (20) Hottel and Whillier, 1958 was used to calculate the forced convection heat transfer coefficient (hw), while Eq. (21) Royne and Dey, 2007 was used to determine the natural heat transfer coefficient (hnat):
hw ¼ 2:8 þ 3:0v hnat ¼ 1:78ðT pm T a Þ
ð15Þ ð16Þ
The overall convection heat transfer (hc) Hottel and Whillier, 1958 can be determined using the following formula:
hc ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 3 3 hw þ hnat
ð17Þ
The overall thermal efficiency of the PVT system can be calculated using the following formula:
gth ¼ F R ðsaÞ F R U L
Ti Ta GT
ð18Þ
The electrical efficiency of the PV module (Hottel and Whillier, 1958; Watmuff et al., 1977; Vokas et al., 2006; Tiwari and Sodha, 2006; Al-Shamani et al., 2016) can be determined using the following equation:
gele ¼ gr ð1 cðT c T r ÞÞ
ð19Þ
where Tr is the reference temperature, (gr = 0.12) is the PV solar cell reference efficiency, and c is a temperature coefficient (c = 0.0045 °C). 4. Results and discussions The performances of the PVT collector equipped with jet impingement and different types of nanofluids were investigated
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is shown in Fig. 5, as I-V and P-V plots for the PV module at multiple levels of solar irradiance. The results showed that the Isc increase from 2 A to 5.56 A when the solar irradiance increase from 500 to 1000 W/m2. Meanwhile, the Voc indicate increases from 16.43 V to 18.44 V for similar conditions. The influence of using jet impingement of water and nanofluids as coolant fluids in the PVT system on the electrical characteristics is shown in I-V, P-V plots. Figs. 5–9 shows the I-V and P-V plots for the PVT collector with and without nanofluids (SiO2, TiO2, and SiC) at 1 wt.% concentration under different levels of solar irradiance at a flow rate of 0.166 kg/s. From the results, it can be clearly seen that the Isc of
at multiple solar irradiance levels. The values Voc and Isc were then recorded. The temperatures (PVT collector (front and back), ambient, inlet and outlet) were also recorded and measured to determine electrical and thermal efficiencies and power for the PVT collector. 4.1. The effect of using water and nanofluids I-V and P-V curves for PVT collector The effect of different solar irradiance (500, 600,700,800,900 and 1000 W/m2) on the electrical characteristic of the PV module
8
80
I-V curve,I=1000W/m2 I-V curve,I=900W/m2 I-V curve,I=800W/m2 I-V curve,I=700W/m2 I-V curve,I=600W/m2 I-V curve,I=500W/m2 2 P-V curve,I=1000W/m P-V curve,I=900W/m2 P-V curve,I=800W/m2 P-V curve,I=700W/m2 P-V curve,I=600W/m2 P-V curve,I=500W/m2
7.5 7 6.5 6
70
60
5.5 50
4
40
3.5 3
Power (W)
Current (A)
5 4.5
30
2.5 2
20
1.5 10
1 0.5 0
0
2
4
6
8
10
12
14
16
18
0 22
20
Voltage (V)
13 12.5 12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
120
I-V curve, I=1000 W/m2 I-V curve, I=900 W/m2 I-V curve, I=800 W/m 2 I-V curve, I=700 W/m2 I-V curve, I=600 W/m2 I-V curve, I=500 W/m 2 P-V curve, I=1000 W/m2 P-V curve, I=900 W/m2 P-V curve, I=800 W/m2 P-V curve, I=700 W/m2 P-V curve, I=600 W/m2 P-V curve, I=500 W/m2
110 100 90 80 70 60 50 40 30 20 10
0
2
4
6
8
10
12
14
16
18
Voltage (V) _ = 0.167 kg/s. Fig. 6. I-V and power curves of PVT-SiC nanofluid, m
20
0
Power (W)
Current (A)
Fig. 5. I-V and P-V curves of PV module.
327
12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
I-V curve, I=1000 W/m2 I-V curve, I=900 W/m 2 I-V curve, I=600 W/m 2 I-V curve, I=700 W/m2 I-V curve, I=500 W/m2 I-V curve, I=800 W/m 2 P-V curve, I=1000 W/m2 P-V curve, I=900 W/m 2 P-V curve, I=600 W/m 2 P-V curve, I=500 W/m 2 P-V curve, I=700 W/m 2 P-V curve, I=800 W/m 2
100 90 80 70 60 50
Power (W)
Current (A)
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40 30 20 10
0
2
4
6
8
10
12
14
16
18
20
0
Voltage (V)
10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
100
I-V curve, I=1000 W/m2 I-V curve, I=900 W/m2 I-V curve, I=800 W/m2 I-V curve, I=700 W/m2 I-V curve, I=600 W/m2 I-V curve, I=500 W/m 2 P-V curve, I=1000 W/m2 P-V curve, I=900 W/m2 P-V curve, I=800 W/m2 P-V curve, I=700 W/m2 P-V curve, I=600 W/m2 P-V curve, I=500 W/m2
90 80 70 60 50 40
Power (W)
Current (A)
_ = 0.167 kg/s. Fig. 7. I-V and power curves of PVT-TiO2 nanofluid, m
30 20 10
0
2
4
6
8
10
12
14
16
18
20
0
Voltage (V) _ = 0.167 kg/s. Fig. 8. I-V and power curves of PVT-SiO2 nanofluid, m
PVT with SiC nanofluid increased from 5.7 A to 9 A when the solar irradiance increased from 500 to 1000 W/m2. The Voc indicated an increase from 19 V to 20 V under similar conditions. The Isc of PVT with jet impingement of TiO2 nanofluid increased from 5.5 A to 8.25 A when the solar irradiance increased from 500 to 1000 W/m2. The Voc indicate an increase from 19 V to 19.2 V under similar conditions. The Isc of PVT with jet impingement of SiO2 nanofluid increased from 5.5 A to 6.75 A when the solar irradiance increased from 500 to 1000 W/m2. The Voc indicated an increase from 18.2 V to 19 V under similar conditions. The Isc of PVT with jet impingement of pure water increased from 4.6 A to 8.4 A when the solar irradiance increased from 500 to 1000 W/m2. The Voc indicated an increase from 18.3 V to 19.8 V under similar conditions.
4.2. Pmax for PVT collector with different solar irradiance The maximum power of the investigated PVT system is shown in Fig. 10. It can be clearly seen from the results that the power of the PVT collector is directly proportional to solar irradiance. The PVT using SiC nanofluid has the highest Pmax at a mass flow rate of 0.1666 kg/s, followed by TiO2 nanofluid, SiO2 nanofluid, and pure water. The improvement of heat transfer coefficient when using nanofluids as a coolant fluid decreased the mean temperature of the PV module, which also increased the maximum power of the PVT. The usage of SiC nanofluid, TiO2 nanofluid, SiO2 nanofluid, and pure water as coolant fluids in the PVT collector, improved the Pmax of the PVT collector to 62.5%, 57%, 55%, and 50%, respectively.
H.A. Hasan et al. / Solar Energy 144 (2017) 321–334
12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
100
2 I-V curve,I=1000 W/m 2 I-V curve,I=900 W/m I-V curve,I=800 W/m2 I-V curve,I=700 W/m22 I-V curve,I=600 W/m I-V curve,I=500 W/m2 P-V curve,I=1000 W/m2 P-V curve,I=900 W/m2 P-V curve,I=800 W/m2 P-V curve,I=700 W/m22 P-V curve,I=600 W/m P-V curve,I=500 W/m2
90 80 70 60 50 40
Power (W)
Current (A)
328
30 20 10
0
2
4
6
8
10
12
14
16
18
20
0 22
Voltage (V) _ = 0.167 kg/s. Fig. 9. Current (I) and power (P) over voltage (V) of PVT-water, m
130 120 110
PVT-SiC nanofluid PVT-TiO2nanofluid PVT-SiO2nanofluid PVT-water PV module
100
Power(W)
90 80 70 60 50 40 30 20 500
600
700
800
2
Solar Irradiance (W/m )
900
1000
Fig. 10. The maximum power of PVT system with nanofluids and pure water at mass flow rate of 0.1666 kg/s under different solar irradiance.
4.3. The effect of mass flow rate on electrical efficiency of PVT and the mean PVT temperature The effect of different mass flow rates of jet impingement using nanofluids and water on the electrical efficiency of the PVT collector and the mean PV temperature are shown in Figs. 11–19. The test was conducted using the PVT collector equipped with jet impingement of different types of nanofluids (SiO2, TiO2, and SiC) at 1 wt.% concentration under different levels of solar irradiances and mass flow rates of 0–0.166 kg/s. The results indicated that the mean temperature of the PVT is inversely proportional to the mass flow rates at all levels of solar irradiance, while the
mean temperature of the PVT is directly proportional to the levels of solar irradiance. The experimental results of using jet impingement of SiC nanofluid in the PVT system are shown in Fig. 11, and it can be seen that the electrical efficiency of the PVT collector increases from 8% to 16.5% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. Meanwhile, the electrical efficiency for PVT system increased from 8% to 12.8% when the mass flow rate changes from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The experimental results of using jet impingement of TiO2 nanofluid in the PVT system is shown in Fig. 12. The electrical efficiency for the PVT collector indicated an increase from 8% to 15.5% when the mass flow rate changed from
329
electrical efficiency (%)
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17 16.5 16 15.5 15 14.5 14 13.5 13 12.5 12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7
I=500 W/m 2 I=600 W/m2 I=700 W/m 2 I=800 W/m 2 I=900 W/m2 I=1000 W/m2
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
Mass flow rate (kg/s) Fig. 11. Calculated electrical efficiency for PVT-SiC nanofluid with different mass flow rates under different solar irradiance.
16 15.5 15 14.5
electrical efficiency (%)
14 13.5 13 12.5 12 11.5 11 10.5 10
I=500 W/m2 I=600 W/m2 I=700 W/m2 I=800 W/m2 I=900 W/m2 I=1000W/m2
9.5 9 8.5 8 7.5 7
0
0.02
0.04
0.06
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0.1
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0.16
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Mass flow rate (kg/s) Fig. 12. Calculated electrical efficiency for PVT-TiO2 nanofluid with different mass flow rates under different solar irradiance.
0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. Meanwhile, the electrical efficiency of the PVT system increased from 8% to 12.3% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The experimental results of using the jet impingement of SiO2 nanofluid in the PVT system is shown in Fig. 13. It can be clearly seen that the electrical efficiency for PVT collector increased from 8% to 14.4% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. Meanwhile, the electrical efficiency for PVT system increases from 8% to 11.8% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The experimental results of using jet impingement of water in the PVT system are shown in
Fig. 14. It can be seen from the results that the electrical efficiency for the PVT collector increased from 8% to 13.5% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. Meanwhile, the electrical efficiency for PVT system increased from 8% to 11.4% when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The mean PVT plate temperature of using jet impingement of the SiC nanofluid in PVT system are shown in Fig. 15. It can be seen from the results that the mean PVT plate temperature decreased from 87 °C to 41 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The mean PVT plate temperature decreased from 65 °C to 30 °C when the mass flow rate changed
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15 14.5 14 13.5
electrical efficiency (%)
13 12.5 12 11.5 11 10.5 10 9.5
I=500W/m2 I=600 W/m2 I=700 W/m2 I=800 W/m2 I=900 W/m2 I=1000 W/m2
9 8.5 8 7.5 7
0
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Mass flow rate (kg/s) Fig. 13. Calculated electrical efficiency for PVT-SiO2 nanofluid with different mass flow rates under different solar irradiance.
14 13.5 13
electrical efficiency (%)
12.5 12 11.5 11 10.5 10 9.5 I=500 W/m2 I=600 W/m2 I=700 W/m2 I=800 W/m2 I=900 W/m2 I=1000 W/m2
9 8.5 8 7.5 7
0
0.02
0.04
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0.08
0.1
0.12
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Mass flow rate (kg/s) Fig. 14. Calculated electrical efficiency for PVT-water with different mass flow rates under different solar irradiance.
from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. The mean PVT plate temperature of using jet impingement of TiO2 nanofluid in PVT system are shown in Fig. 16. It can be seen from the results that the mean PVT plate temperature decreased from 87 °C to 45 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The mean PVT plate temperature decreased from 65 °C to 35 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. The mean PVT plate temperature of using jet impingement of SiO2 nanofluid in the PVT system are shown in Fig. 17. It can be seen from the results that the mean PVT plate temperature decreased from
87 °C to 50 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. Meanwhile, the mean PVT plate temperature decreased from 65 °C to 40 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 500 W/m2. The mean PVT plate temperature of using jet impingement of pure water in the PVT system is shown in Fig. 18. It can be seen from the results that the mean PVT plate temperature decreased from 87 °C to 57 °C when the mass flow rate changed from 0 to 0.1666 kg/s at a solar irradiance of 1000 W/m2. The mean PVT plate temperature decreased from 65 °C to 45 °C when the mass flow rate changed from 0 to
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100 I=1000 W/m2 I=900 W/m2 I=800 W/m2 I=700 W/m2 I=600 W/m2 I=500 W/m2
mean PVT plate temperature (oc)
90
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50
40
30 0
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Mass flow rate (kg/s) Fig. 15. Measured mean plate temperature for PVT-SiC with different mass flow rates under different solar irradiance.
100 I=1000 W/m2 I=900 W/m2 I=800 W/m2 I=700 W/m2 I=600 W/m2 I=500 W/m2
mean PVT plate temperature (oc)
90
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30 0
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Mass flow rate (kg/s) Fig. 16. Measured mean plate temperature for PVT-TiO2 with different mass flow rates under different solar irradiance.
0.1666 kg/s at a solar irradiance of 500 W/m2. The results of electrical efficiency for PVT and PV module with different types of nanofluids and pure water with changing mass flow rates are shown in Fig. 19, and it can be seen that the electrical efficiency for PVT is directly proportional to the mass flow rates from 0 to 0.1666. It can also be seen that the highest electrical efficiency was shown by the PVT-SiC nanofluids, followed by the PVT-TiO2
nanofluids, PVT-SiO2 nanofluids, and PVT Water. The PV module without cooling has lowest electrical efficiency. The results of thermal efficiency for PVT with different types of nanofluids and pure water with changing mass flow rate are shown in Fig. 20. It can be seen that the thermal efficiency for the PVT increases with the changing mass flow rate from 0 to 0.1666. It was also confirmed that the highest thermal efficiency was shown by the PVT-SiC
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100 2
I=1000 W/m 2 I=900 W/m I=800 W/m2 I=700 W/m2 I=600 W/m2 I=500 W/m2
mean PVT plate temperature (oc)
90
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50
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30 0
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Mass flow rate (kg/s) Fig. 17. Measured mean plate temperature for PVT-SiO2 with different mass flow rates under different solar irradiance.
100 I=1000 W/m2 I=900 W/m2 I=800 W/m2 I=700 W/m2 I=600 W/m2 I=500 W/m2
mean PVT plate temperature (oc)
90
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40
30 0
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Mass flow rate (kg/s) Fig. 18. Measured mean plate temperature for PVT-water with different mass flow rates under different solar irradiance.
nanofluids, followed by the PVT-TiO2 nanofluids, PVT-SiO2 nanofluids, and PVT Water. Thus, it can be clearly seen that the thermophysical properties of the nanofluids significantly improved the thermal and electrical efficiencies of the PVT. The heat transfer coefficients increased when nanofluids are used as a coolant fluid in the PVT collector, due to the fact that the nanoparticles are of higher thermal conductivity compared to pure water. 5. Conclusions The influence of jet impingement with different types of nanofluids on the thermal efficiency, electrical efficiency, and the
output of the PVT collector have been investigated. The results using PVT with different nanofluids and a conventional PV module were compared. The thermal efficiency of the PVT increased at mass flow rates of 0–0.1666 kg/s. It was also confirmed that the highest thermal efficiency was shown by the PVT-SiC nanofluid, followed by PVT-TiO2 nanofluid, PVT-SiO2 nanofluid, and PVT Water. The PVT-SiC nanofluid reported the highest electrical efficiency, followed by PVT-TiO2 nanofluid, PVT-SiO2 nanofluid, and PVT Water. The PV module without cooling reported the lowest electrical efficiency. Furthermore, the enhanced thermo-physical properties of nanofluids significantly improved the PVT’s thermal and electrical efficiencies. The heat transfer coefficient increased
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13.5 PVT-SiC nanofluid PVT-TiO2 nanofluid PVT-SiO2 nanofluid PVT-water PV
13 12.5
electrical efficiency (%)
12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7
0
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Mass flow rate (kg/s) Fig. 19. The variation of electrical efficiency with different mass flow rates for the PVT collector water and nanofluids at solar irradiance of 1000 W/m2.
100 90
Thermal efficiency (%)
80 70 60 50 40 30
PVT-SiC nanofluid PVT-TiO 2 nanofluid PVT-SiO2 nanofluid PVT-water
20 10 0
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Mass flow rate (kg/s) Fig. 20. The variation of thermal efficiency with different mass flow rates for the PVT collector water and nanofluids at solar irradiance of 1000 W/m2.
when the nanofluids are used as a coolant fluid in the PVT collector, due to the fact that the nanoparticles has a higher thermal conductivity compared to pure water. The PVT using SiC nanofluid reported the highest Pmax at a mass flow rate of 0.1666 kg/s, followed by TiO2 nanofluid, SiO2 nanofluid, and pure water. The usage of SiC nanofluid, TiO2 nanofluid, SiO2 nanofluid, and pure water as coolant fluids in the PVT collector improved the Pmax of the PVT by 62.5%, 57%, 55%, and 50%, respectively. It has been shown that the SiC/water nanofluid performed better electrically and thermally compared to other working fluids.
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