**4.3. Flowrate**

Gangadevi et al. [35] experimentally examined that the electrical, thermal and overall efficiency

efficiency of PV/T system. As per the results, electrical and thermal efficiency of this system is linearly proportional to mass flowrate. Best results are obtained at low concentration of nanofluid. Electrical, thermal and overall efficiencies of the various PV/T systems working with different

Efficiency enhancement of PVT systems being cooled by the nanofluids is due to the enhanced thermal conductivity of the nanofluids. Increase in thermal conductivity is dependent on con-

Various factors such as the concentration of nanofluid, flowrate of nanofluid, size of the nanoparticle, geometry of microchannel, type of base fluid and irradiance influence the efficiency of nanofluid-based PV/T system. Effects of these factors are discussed in the subsequent sections.

Increase in irradiance cause the module temperature to escalate as more heat reaches the surface. Khanjari et al. [2] investigated environmental parameters that affect the efficiency of a

tion increased from 200 W/m<sup>2</sup> *k* to 800 W/m<sup>2</sup> *k* the electrical efficiency of system decreased from 11.41% to 10.12% for pure water and 11.4% to 10.23% for alumina nanofluid whereas, thermal efficiency increased from 65–79% for pure water and 76–91% for alumina nanofluid. As the absorber plate temperature increased from 291 K to 324 K the electrical efficiency decreased from 11.1% to 9.4% for water and 11.2% to 9.5% for alumina nanofluid whereas, the thermal efficiency did not change with increasing inlet temperature of fluid after reaching a primary value. Similarly, the system efficiency was found to escalate with decreasing irradiation i.e. the maximum overall efficiency of the system was found to increase from 78.60% to 80.58% and 73.58% to 75.93% for 1 wt% and 3 wt% respectively, when the irradiation value decreased from 1100 *<sup>W</sup>*⁄*m*<sup>2</sup> to 600 *<sup>W</sup>*⁄*m*<sup>2</sup> [37]. Effect of irradiance found by Al-Waeli et al. [38] has been presented in

Researchers have found contradictory results when it comes to concentration enhancement of nanofluids. Manikandan and Rajan [39] harnessed sand for the cooling of PV/T system in order to enhance the efficiency. They tested 0.5, 1 and 2 vol% concentration and the collection efficiency ratio for these concentrations was found to be 3.6%, 11.2% and 26.9% whereas the solar collection efficiency increased by 9% and 16.5% for 0.5% and 2% respectively. Sardarabadi and Fard [40] also examined that increasing the mass fraction of nanoparticles from 0.05 to 10 wt%, the thermal performance of the system increased by four times. Wei An. [24] examined the

O3

/water nanofluid got increased by 13%, 45% and 58% respec-

/*water*) via CFD simulation. As the absorbed solar radia-

nanofluid based cooling. Mustafa et al. [36]

/water) on the

O3

numerically tested the effect of mass flowrate and concentration of nanofluid (TiO2

**4. Factors affecting efficiency of nanofluid-based PV/T systems**

<sup>2</sup> *O*<sup>3</sup>

of PV module being cooled by Al2

48 Microfluidics and Nanofluidics

nanofluids is expressed in the **Table 1**.

PV/T system cooled by nanofluids (*A l*

**4.1. Irradiance**

**Table 2**.

**4.2. Concentration**

tively as compared to water based and 1 wt% Al2

centration, size and type of the nanoparticle [4].

Sathieshkumar et al. [46] concluded that both electrical and thermal efficiency of the PV/T system increases with increasing flow rate but after a certain flowrate magnitude the efficiencies of the system start to decline. Overall energy efficiency is found to be higher in turbulent regime whereas overall exergy efficiency is higher in laminar regime [47]. Mustafa et al. [36] numerically tested the effect of mass flowrate and concentration of nanofluid (TiO2 /water) on the efficiency of PV/T system. As per the results, the electrical and thermal efficiency of this system was found to be linearly proportional to mass flowrate.

Hasan et al. [48] observed that increasing the mass flowrate increased the cell efficiency linearly. As the mass flowrate increased from 0 to 1.666 kg/s the electrical efficiency of the cell increased from 8% to 16.5% at 500 W/m<sup>2</sup> solar irradiance in case of SiC-water nanofluid. Mean photovoltaic temperature decreased from 87° *C* to 41° *C* as the mass flowrate changed from 0 to 1.666 kg/s at 1000 W/m<sup>2</sup> solar irradiance in case of SiC. Karami and Rahimi. [34] observed that temperature of the module decreased from 62° *C* to 32.5° *C* when the flow rate increased from zero to 300 ml/min. Khanjari et al. [41] observed that increase in inlet fluid velocity (from 0.05 m/s to 0.23 m/s) increase the first law (energy) efficiency but decreases the second law (exergy) efficiency (from 15.40% to 12.50% for silver). Lelea et al. [14] observed lower maximum module temperature for nanofluid based cooling as compared to water cooling at lower Re number. Whereas, at higher Re (Re > 1000) the maximum module temperature overlaps for nanofluid based cooling and water-based cooling of PV module.

PV/T system in laminar regime outperforms turbulent regime. More PV efficiency can be achieved in turbulent regime but it requires higher pumping power thus making the overall system efficiency lesser [15]. Although heat transfer in case of higher Reynolds numbers is seemed to increase because of greater Brownian motion of particles but too high a Reynolds number requires higher pumping power which eventually reduces the overall performance of the microchannels containing nanofluids [49]. Xu and Kleinstreur [50] concluded that increased concentration elevates the system efficiency when cooled by Al2 O3 /water nanofluid. Higher inlet Reynolds number yields higher cell efficiency but too high a Reynolds number is not favorable. Low inlet temperature of nanofluid is capable to produce pronounced cooling effect. Height of channel containing nanofluid is also of much consideration, slight variation in channel height varies the required pumping power and significant change in entropy generation rate.

found that a PV system being cooled by water only, performed better than the systems cooled by either ethylene glycol only and water-ethylene glycol (50% water and 50% ethylene glycol).

Maadi et al. [54] stated that for metalloids the viscosity of the nanofluids gets increased and the specific heat capacity is decreased, which is not favorable. This is because, at a given mass fraction the volume of the metalloid nanofluids is increased due to high density. Hasan et al.

improved the maximum power output by 62.5%, 57%, 55% and 50% as compared to the con-

cooling purpose to analyze the efficiency betterment. Following the experimental results, SiC/

mass flowrate, SiC/water nanofluid based PV/T system showed 13.529% electrical efficiency

10.302% electrical efficiency respectively. PV/T system utilizing water solely for cooling,

Kolahan et al. [56] examined the entropy generation in PV/T system due to the addition of

least thermal and total entropy generation. Thermal entropy generation was found to be maximum at inlet, turning points and outlet, due to high temperature differences. For metallic nanofluids, increase of mass fraction caused density and viscosity elevation. Increased mass fraction reduced the velocity which in turns reduced the frictional entropy generation. For metalloid nanofluids, reverse is the case. For ZnO the frictional entropy was decreased by 10.87%

pure water. Addition of nanoparticles causes more prominent reduction in thermal entropy generation compared to the frictional entropy generation. Considering the entropy generation

Extensive experimentation has been conducted to examine the effect of magnetic on the performance of nanofluids [66–70]. If the Ferro-nanoparticle is used in the system, employing alternating magnetic field around the channels can improve the efficiency of the system. Experimental results also depicted that the alternating magnetic field improved the system performance whereas, the constant field did not produce significant efficiency enhancement when compared with the no field condition. The system efficiency was found to be 71.91% when there was no field applied, whereas, the efficiency went up to 73.58% in the presence of alternating magnetic field (50 Hz) in case of 1 wt% and 1100 *<sup>W</sup>*⁄*m*<sup>2</sup> [37]. Shape of nanoparticle and type of magnetic field can influence the performance of nanofluid. Sheikholeslami et al. [66,

flowing in a porous cavity. Following the results, platelet shape of nanoparticles depicted

view point, metallic nanofluids produce better results than the metalloid nanofluids.

67] numerically analyzed the effect of non-uniform magnetic field on Fe<sup>3</sup>

as a surfactant). Following the results, ZnO/water produced least frictional entropy, *SiO*<sup>2</sup>

produced maximum pressure drop and frictional entropy generation and *Al*<sup>2</sup> *<sup>O</sup>*<sup>3</sup>

, SiO2

/water nanofluid based PV/T systems depicted 10.978% and

/water by 1 wt% and 3 wt% nanofluids (along with acetic acid

/*water* the frictional entropy was increased by 0.94% compared to

, TiO2

Application of Nanofluids for Thermal Management of Photovoltaic Modules: A Review

nanofluids and pure water

irradiance and 0.170 kg/s

/*water* and ZnO/

/*water* produced

/*water*

51

and SiC based nanofluid for the

http://dx.doi.org/10.5772/intechopen.74967

/*water*, *TiO*<sup>2</sup>

O4 -H<sup>2</sup>

O nanofluid

[48] observed that cooling the PVT by impinging SiC, TiO2

water nanofluid outperformed rest of the nanofluids. At 1000 W/m2

nanoparticles both numerically and experimentally. They used *Al*<sup>2</sup> *<sup>O</sup>*<sup>3</sup>

ventional PV module. Al-Shamani et al. [55] tested SiO2

/water and SiO2

approached 9.608% electrical efficiency.

water by 0.2 wt% and SiO2

at 10 wt%, whereas, for *SiO*<sup>2</sup>

**4.6. Nanoparticle type**

whereas, TiO2
