**4.6. Nanoparticle type**

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

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

Due to the smaller size, nanoparticles have large surface area which is attributed to higher heat transfer rates. Nanoparticles have high thermal conductivity, but heat capacity is low. Nanoparticles are stable in the base fluid at high temperatures and they do not agglomerate in the water as well [51]. Energy and exergy efficiency of the system can be increased by increasing the size of the nanoparticle in the turbulent regime but in laminar regime the case is opposite. Yazdanifard et al. [15] interestingly found no effect of particle size on the efficiency. They used Titanium dioxide nanofluid and Aluminum oxide nanofluid for the cooling purpose but no significant efficiency alteration was observed. Whereas, Al-Shamani et al. [4] observed that heat transfer of the nanofluid decreased with a decrease in size of the nanoparticle. Therefore, there is still a need for further experimentation to conclusively narrate the effects of nanopar-

Not only the type of nanoparticle affects the performance of the PV/T system but the type of base fluid is also of same significance while predicting the performance of the system. Using base fluids such as ethylene-glycol, polyethylene glycol, cetyltrimethylammonium bromide water mixtures instead of water can considerably elevate the cell efficiency [15]. Addition of surfactant and selection of suitable pH of nanofluid can display pronounced effects [44]. Rajeb et al. [52] examined both numerically and experimentally the effect of variation in concentra-

ethylene glycol) on the efficiency of PV/T system being cooled by nanofluid. They observed that increasing the concentration of nanofluid increased the efficiency of the system. The system best performed when water was used as base fluid as compared to ethylene glycol base fluid. According to the drawn results, maximum electrical and thermal efficiency was found to be 13.55% and 77% respectively for Cu/water nanofluid based PV/T system, at 0.4 wt%. Whereas, they found 13.54% electrical and 60% thermal efficiency for Cu/ethylene glycol based PV/T system, at 0.4 wt%. Conclusively, Cu/water nanofluid based system outperformed

O3

/water based system in terms of electrical and thermal efficiency. Hosseinzadeh et al. [53]

and Cu) and type of base fluid (water and

varies the required pumping power and significant change in entropy generation rate.

O3

/water nanofluid. Higher inlet

concentration elevates the system efficiency when cooled by Al2

ticle size on the efficiency of the solar systems.

tion (0.1, 0.2 and 0.4 wt%), type of nanoparticle (Al2

**4.4. Nanoparticle size**

50 Microfluidics and Nanofluidics

**4.5. Base fluid**

Al2 O3 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. [48] observed that cooling the PVT by impinging SiC, TiO2 , SiO2 nanofluids and pure water improved the maximum power output by 62.5%, 57%, 55% and 50% as compared to the conventional PV module. Al-Shamani et al. [55] tested SiO2 , TiO2 and SiC based nanofluid for the cooling purpose to analyze the efficiency betterment. Following the experimental results, SiC/ water nanofluid outperformed rest of the nanofluids. At 1000 W/m2 irradiance and 0.170 kg/s mass flowrate, SiC/water nanofluid based PV/T system showed 13.529% electrical efficiency whereas, TiO2 /water and SiO2 /water nanofluid based PV/T systems depicted 10.978% and 10.302% electrical efficiency respectively. PV/T system utilizing water solely for cooling, approached 9.608% electrical efficiency.

Kolahan et al. [56] examined the entropy generation in PV/T system due to the addition of nanoparticles both numerically and experimentally. They used *Al*<sup>2</sup> *<sup>O</sup>*<sup>3</sup> /*water*, *TiO*<sup>2</sup> /*water* and ZnO/ water by 0.2 wt% and SiO2 /water by 1 wt% and 3 wt% nanofluids (along with acetic acid as a surfactant). Following the results, ZnO/water produced least frictional entropy, *SiO*<sup>2</sup> /*water* produced maximum pressure drop and frictional entropy generation and *Al*<sup>2</sup> *<sup>O</sup>*<sup>3</sup> /*water* produced 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% at 10 wt%, whereas, for *SiO*<sup>2</sup> /*water* the frictional entropy was increased by 0.94% compared to pure water. Addition of nanoparticles causes more prominent reduction in thermal entropy generation compared to the frictional entropy generation. Considering the entropy generation view point, metallic nanofluids produce better results than the metalloid nanofluids.

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, 67] numerically analyzed the effect of non-uniform magnetic field on Fe<sup>3</sup> O4 -H<sup>2</sup> O nanofluid flowing in a porous cavity. Following the results, platelet shape of nanoparticles depicted


**4.8. Circulation method**

**5.1. Environmental benefits**

**5.2. Economic benefits**

and PVT/Al2

**6. Conclusion**

O3

the efficiency compared to the passive cooling [38].

**5. Advantages of nanofluid-based cooling**

eliminate the emission of 16,974,57 tons of CO2

fluid based PV/T systems can omit the emission of 448 kg *CO*<sup>2</sup> *<sup>m</sup>*−2 *yr* −1

When cooling the PV module via nanofluid, the circulation method is also of much importance. If the circulation is done via passive method, the increasing intensity of light would cause a reduction in electrical efficiency and enhancement in thermal efficiency because natural convection is not that efficient. Thus, active convection cooling should be employed to obtain optimum results. Whereas, the elevation in thermal efficiency is due to the availability of enough time for the cooling fluid to exchange heat. However, the overall efficiency of the system gets increased if the cooling is employed. Pumping of nanofluid can further improve

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

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

53

Fossil fuel based power plants emit tons of noxious gases that detriment the environment. Since the solar power plants are emission free, production of electricity via this method can

PV/T system can provide an economical solution for industrial and domestic power demands. Studies indicate a significant reduction in energy consumption produced from conventional resources due to the use of such system [23, 59]. Taylor et al. [60] also narrated that a solar thermal based power plant of 100 MW capacity can save about \$3.5 million per annum if the nanofluid receiver is incorporated with it. Nanofluids need a smaller area for heat transfer thus making the PV system compact and reducing the costs [51]. The economic analysis depicted that the cost of energy produced by nanofluid based PV/T system is 82% less than the current prices in Saudi Arabia [33]. Nanofluid system is predicted to takes only 2 years for pay-back [26]. Sardarabadi et al. [61] evaluated that size reduction by 21, 32,33 and 34 from

Cooling of PV module by nanofluids significantly enhances electrical efficiency and thermal energy. Cooling causes the heat removal which in turns halts the development of thermal stresses, making the PV modules to last long and operate more efficiently. Employing nanofluids impedes entropy generation as well. Efficiency of this system escalates with increasing concentration of nanofluid up to a certain limit but as the concentration exceeds this optimum

respectively. By size reduction we mean the amount of material saved for the

energy viewpoint and 5,6,7 and 6 from exergy viewpoint for PVT/water, PVT/TiO2

same required energy and exergy outputs at the same conditions.

[58]. Hassani et al. [26] evaluated that nano-

, PVT/ZnO

.

**Table 2.** Effect of irradiance on efficiency [38].

highest Nusselt number (i.e. optimum heat transfer) under the influence of non-uniform magnetic field. In the presence of magnetic field, addition of nanoparticles can improve the heat transfer properties of nanofluids [68].

#### **4.7. Channel geometry**

Narrow channels offer higher enhancement in the heat transfer coefficient whereas the wide channels depict instabilities in lateral heat transfer. Roughness in the pipes also affects the magnitude of heat transfer. Pipes with greater roughness magnitude offer greater heat transfer due to the increased contact surface. In order to achieve higher performance, the temperature distribution inside the channel should be held uniform, the temperature should be kept low and the pressure drop should also be as minimum as possible [49]. Considering the **Table 3**, helical channel performs best because of greater surface contact of nanofluid with the rear surface of PV unit.


**Table 3.** Effect of channel geometry on efficiency.
