International Journal of Electrical and Computer Engineering (IJECE) Vol.
No.
February 2019, pp.
ISSN: 2088-8708.
DOI: 10.
11591/ijece.
Review of water-nanofluid based photovoltaic/thermal (PV/T) systems Nur Farhana Mohd Razali.
Ahmad Fudholi.
Mohd Hafidz Ruslan.
Kamaruzzaman Sopian Solar Energy Research Institute.
Universiti Kebangsaan Malaysia.
Malaysia
Article Info
ABSTRACT
Article history:
Solar energy is secure, clean, and available on earth throughout the year.
The PV/T system is a device designed to receive solar energy and convert it into electric/thermal energy.
Nanofluid is a new generation of heat transfer fluid with promising higher thermal conductivity and improve heat transfer rate compared with conventional fluids.
In this review, the recent studies of PV/T using nanofluid is discussed regarding basic concept and theory PV/T, thermal conductivity of nanofluid and experimentally and theoretically study the perfromance of PV/T using nanofluid.
A review of the literature shows that many studies have evaluated the potential of nanofluid as heat transfer fluid and optical filter in the PV/T system.
The preparations of nanofluid play an essential key for high stability and homogenous nanofluid for a long The thermal conductivity of nanofluid is depending on the size of nanoparticles, concentration and preparation of nanofluids.
Received Jan 28, 2018 Revised May 31, 2018 Accepted Jun 14, 2018 Keywords:
Electrical Energy analysis Exergy analysis Solar energy Copyright A 2019 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Ahmad Fudholi.
Solar Energy Research Institute.
Universiti Kebangsaan Malaysia, 43600 Bangi Selangor.
Malaysia.
Email: a.
fudholi@gmail.
INTRODUCTION
The inclining population and increasing energy demand lead to decreasing current energy sources.
Problems arising in environmental pollution and climate change contributed from burning fossil fuels, encourage the researchers to conduct studies in renewable energy.
Malaysia is located at the equatorial, possess average hot climate throughout the year .
AC-33AC), the monthly solar radiation received approximately around 400-600 MJ/m2.
These potential factors will make this country as one of the developing country in harnessing solar energy.
Solar energy has greater benefits than conventional energy due to clean energy sources, no release of pollutant, high reliability, estimated life span 20-30 years and low maintenance.
Malaysia continued to emphasis in development of renewable technology majorly in solar energy through education, research and policies.
Solar energy converts to electric energy using photovoltaic The cons of this pv cell are declining in efficiency conversion when temperature raised and only responsive to a portion of the solar spectrum.
The solar cell conversion efficiency is in the range 6-18%, which is a value measured at the Nominal Operating Temperature (NOCT) and the rest of solar radiation received are reflected and absorbed as heat energy.
The low efficiency and high cost of PV cell brings the idea of hybrid PV/T.
The hybrid PV/T is the integration of solar thermal collector and PV module.
The advantage of PV/T enhances the electrical energy produce, removes waste heat from PV module and minimized the usable space.
Moreover, solar energy will convert to thermal energy as stored in air or water.
PV/T collector can be classified into three categories.
water PV/T collector, air PV/T collector and the combination of water/air PV/T collector.
PV/T builds up from glass cover, solar cell, encapsulated materials and collector attached at the back.
In terms of physical structure applied, the module could be Journal homepage: http://iaescore.
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ISSN: 2088-8708
classified as flat plate, concentrated and building integrated types.
The absorber functions to asorb heat and simultaneously cool down the PV module.
The collected heat will be in the form of air or water .
Nanofluid is produced by dispersing nanoparticle into basefluid with a typical size of less than 100 nm in a liquid.
Nanofluids have been proposed as a replacement for conventional cooling fluid regards to their greatly enhanced thermal properties.
Zeinali et al.
investigated the convective heat transfer of nanofluids in laminar flow through a channel with a square-cross section resulted in increasing heat transfer when the size of nanoparticle is smaller and volume fraction is increased.
Work have been largely carried out on nanofluid for the past decades.
Experiments showed a significant increase for thermal conductivity by dispersion of less than 1% volume fraction of nanofluids.
The ideal thermal properties of nanofluid with higher thermal conductivity and heat transfer, smaller and compact design of PV/T will become possible without lessening the desired output.
Faizal et al.
calculated efficiency, size reduction, cost and embodied energy saving solar collector thermal using various metal oxide nanofluids.
CuO2.
SiO2.
TiO2, and Al2.
The short payback period, less CO2 emissions and size reduction can be achieved compared to a conventional solar collector.
However the stability of nanofluid and the aggregation of nanoparticles after a certain period hindered the maximum potential of nanofluids.
The physical and chemical treatment must be conducted during preparation of the Stability of nanofluids has a good correlation with enhancement of thermal conductivity, where the better the dispersion, the higher thermal conductivity.
Exergy analysis has become an essential tool in the system design, analysis, and optimization of thermal systems .
Recently, energy and exergy analysis for nanofluid based PVT systems were Lari and Sahin .
reported that PV energy efficiency was 13.
2% for PVT nanofluid system.
Khanjari et al.
reported that PV, thermal and PV/T energy efficiencies was 10-13.
7%, 55% and 90% respectively, and PV/T exergy efficiency was 15%.
However, in this review we focused on nanofluid-based PV/T system.
WATER BASED PVT SYSTEM
The first reported study on a flat plate PV/T was presented by Wolf in 1976.
Studies focusing on PV/T collector has been carried out by other researchers since then.
The result achieved by Bargene and Lovik .
simulation showed that overall efficiency of the PV/T system could reach 60-80%.
Charalambus et al.
identified some parameters to effect PV/T perfromance such as mass flow rate, inlet temperature working fluid, number of covers, absorber to fluid thermal conductance, absorber plate and design of PV/T collector itself.
A water or nanofluid based PV/T systems as shown in Figure 1, has similar structure as the conventional flat plate solar collectors.
The absorber consist of tube is attached to the PV panel in order to use for heating purposes.
The water based PV/T system could achieve the enhance cooling effectiveness compared to the air based system due to the high thermal mass of the of water over the air.
Zondag et al.
evaluated seven different designs of PV/T water collector.
The designs are categorised to sheet and tube, channel, free flow and two absorber.
Although the sheet and tube design is indicated 2% less in efficiency than the channel design, it is the easiest design for manufacturing process.
Thus, this design is the most promising compared to other designs Figure 1.
Flat plate water-nanofluid based PVT systems Chow et al.
developed a single glazed flat plate water heating PV/T collector and discovered overall efficiency of PV/T depends on fin efficiency and the bonding collector between the collector and the sheet underneath the module.
The testing of of a PV/T solar boiler with a water storage tank conducted by Zondag et al.
found that the covered sheet and tube system was the most promising PV/T concept for tap water heating.
This PV/T system could achieve annual average solar efficiency of about 61.
The comparison of technical characteristics of water and air based PV/T system indicated in Table 1.
There are Review of water-nanofluid based photovoltaic/thermal (PV/T) systems (Nur Farhana Mohd Razal.
A ISSN: 2088-8708 numerous method have been discussed in order to enhance performance of the PV/T such as suspending a thin aluminum sheet, use of fins attached to the PV rear surface and using CPC to increase the radiation falling on array of solar cells.
However, the study of nanofluid as a coolant in PV/T system is a new and emphasis study must be conducted as expected interesting outcome in enhancement of PV/T overall Table 1.
The Characteristics Comparison of Air and Water Based PV/T PV/T models Air based PV/T Average efficiency (%) Advantages Low cost Simple structure Water based PV/T Low cost High thermal mass Low flow volume Disadvantages Low thermal mass Large air volume High heat loss Poor thermal removal effectiveness Still high PV temperature Complex structure THERMAL CONDUCTIVITY OF NANOFLUIDS Thermal conductivity of solids and metals are higher than liquids.
One of the technique proposed to increase the efficiency of thermal conductivity heat transfer fluid is a suspension of particles in fluids.
Researchers conducted many experiments and theoretical studies in suspension of micro sized of particles in fluid since the published of Maxwell theoretical work.
However, this method failed to be commercialized for its erosion and additional flow resistance.
Choi .
termed nanofluid, fluid suspended with nanoparticle, from his research in Agonne National Laboratory.
USA.
Nanofluids foreseen to be a next generation heat transfer fluids for its new exciting properties compare to pure liquids.
Thermal conductivity is the most preferable parameter to be evaluated by researchers and many experimental works recorded the result of this parameter obeservation.
Thermal conductivity measured by three methods.
transient hot wire, the steady state parallel plate technique and temperautre oscillation Since thermal conductivity is the most important parameter responsible for enhanced heat transfer many experimental work being reported on this aspect.
Alumina and copper oxide are the most common nanoparticle used by many researchers in their experimental investigations.
The investigation of silica is limited compared to other nanoparticles.
Temperature, particle size, dispersion and stability play an important role in determining thermal conductivity of nanofluids .
Das et al.
examined the effect of temperature on the thermal conductivity for nanofluids containing Al2O3 and CuO .
They observed that a 2 to 4 fold increase in thermal conductivity over the temperature range of 21 AC to 52 AC.
Their results suggest that nanofluids is suitable for device with high energy density and work at a temperature higher than the room temperature.
The remarks of enhancement in smaller nanofluids of thermal conductivity are explained by stochastic motion.
Hwang et al.
compared the thermal conductivity among four nanofluid (MWCNT/water.
CuO/water.
SiO2/water, and CuO/EG) and found the highest thermal conductivity is achieved by MWCNT up to 11.
3 % at 1 vol% .
PREPARATION OF NANOFLUIDS
Nanofluids are produced by suspending nanometer scale solid particle into the base fluid such as water, oil and ethylene glycol.
The major problem in producing nanofluid is an aggregation and inhomogeneous of colloidal suspension.
The techniques for producing nanofluid are the single step and two step method.
The single step early proposed by Akoh et al.
, called as VEROS (Vacuum evaporation onto Running Oil Substrat.
The pro and cons of this technique is the agglomeration of the nanoparticle is minimized while on the other hand, only low vapour pressure fluids are adequate with this process.
This method is highly cost and lacking in producing nanofluid in large scale.
The two step method is more popular in nanofluid synthesis nowadays considering nanoparticles are able to purchase from companies.
Nanoparticles are being produced as a powder and then mixed with base fluid.
Ultrasonication is used to disperse nanoparticles in base fluid and reduced the agglomeration.
Adding of surfactant or dispersant to nanofluid is used to attain the stability of suspension, such in experiments conducted by Murshed et al .
and Hwang et al.
Other mothed such as a pH value variation of nanofluid or surface active agent will change surface properties of nanoparticles except for utasonication.
This is the most economic method to be practiced in industry.
Int J Elec & Comp Eng.
Vol.
No.
February 2019 : 134 - 140
Int J Elec & Comp Eng
ISSN: 2088-8708
NANOFLUIDS BASED PVT SYSTEMS
The use of nanofluid as heat transfer fluid in the PV/T system proved to result in better performance.
Sardarabadi et al.
investigated experimentally the effects of silica/water nanofluids on thermal and electrical efficiency of PV/T.
The different concentration of nanofluid indicated that overal energy efficiency and total exergy increase with higher concentration of nanofluids.
The efficiency PV/T equipped with a collector compared with no collector show significantly higher perfomance.
Ferrofluid has unique characteristics of the rheological and thermo physical properties under an external magnetic field.
Ghadiri et .
evaluated the effect of ferrofluid as coolant on the overall efficiency of PV/T.
The results found that 50% increase in overall efficiency when ferrofluid was placed under alternating magnetic field with 50 Hz Nanofluid is applied as volumetric solar absorbers and flowing heat transfer medium in following Study of PV/T systems with MgO nanofluids applied to the top of silicon PV panel by Yun and Zhu .
evaluated the transmittance of MgOAewater nanofluids when concentration is at 0.
02 %wt, 0.
06 %wt 1 %wt respectively.
The inferred result is regular transmittance decrease with increase mass fraction.
The electrical output of solar cells increases with lower concenctrations of nanofluid and thinner layers of nanofluid at the top of PV cells.
Using one step method.
Jing et al.
prepare of highly dispersed SiO2/H2O with various particle sizes.
They circulate the nanofluid both above the PV panel to filter IR part of the incident light and below the PV cell to remove the heat generated in the photoeletric conversion process.
This design is helpful in reduce the operation temperature of PV cell and expected to improve PV/T efficiency.
Advantage of liquid filter is that they can be controlled dynamically by pumps, magnetic/electric field and temperature changes.
Table 2 summarized the discussion above.
Table 2.
Summary of Performance of Nanofluids Based PV/T Systems Author Type of Nanofluids Particle size, nm Sardarabadi et SiO2/water Mass %wt 1, 3 Ghadiri et al.
Fe3O4/water 1, 3 Yun CHUI and Qunzhi ZHU .
MgO/water 02, 0.
Jing et al.
SiO2/water 5, 10, 25, 2 v% for Taylor et al.
Au.
SiO2.
Al, 01 %v Results For 1 %wt and 3 %wt energy efficiency increase up to 3.
6% and Total exergy increased by adding nanofluid For 3 %wt, the overall efficiency impoved by 45% When alternating magnetic field .
is applied, overall efficiency increase up to 50% Transmittance of nanofluids decreases when mass fraction and film thickness increase.
The overall efficiency of the PV/T system with a 2mm thick liquid layer is beyond 60% Transmittance of of nanofluid with particle size of 5 nm and 2 v% ca be as high as 97% very cose to pure water.
Thermal conductivity of nanofluid with smaller nanoparticles is higher than larger nanoparticles.
Volume fraction of 0.
0011% is required to achieve optimum filters.
CONCLUSION
From this review it can be concluded that Nanofluid aims to replace the existing fluid due to the limitations of previous fluid in terms of thermal conductivity, heat transfer coefficient and scattering stability involving micrometer-sized particles.
Effective heat transfer can increase the efficiency of PV/T system operation and power generation.
Performance of PV/T based nanofluids will increase in terms of overall efficiency compared to conventional fluid, thus smaller and compacted PV/T system using nanofluid can be Hence it will reduce the weight, energy and cost of manufacturing.
The thermal conductivity of nanofluid enhanced with smaller particle size of nanoparticles, higher volume fraction and stable The preparation of nanofluid is an important parameter to optimize use of superior thermal properties for practical application.
ACKNOWLEDGEMENTS
The authors would like to thank the UKM for funding (GP-K020.
and (GGP-2017-.
REFERENCES