ENHANCEMENT OF PVT EFFICIENCY, THERMAL ENERGY STORAGE WITH EFFECTIVE PCM SELECTION AND COOLING TECHN

International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN (P): 2249–6890; ISSN (E): 2249–8001 Vol. 11, Issue 2, Apr 2021, 237-250 © TJPRC Pvt. Ltd.

ENHANCEMENT OF PVT EFFICIENCY, THERMAL ENERGY STORAGE WITH EFFECTIVE PCM SELECTION AND COOLING TECHNIQUES D. KAMESWARA RAO1*, K. SUDHAKAR REDDY2 & V. V. SUBBA RAO3 1,2

Department of Mechanical. Engineering, Mahatma Gandhi Institute of Technology, Hyderabad, India 3

University College of Engineering, JNT University, Kakinada, A.P, India

ABSTRACT The electrical efficiency of Photovoltaic(PV) panel decreases with increment of solar panel temperature. The Photo voltaic panel electrical efficiency depends on operating PV panel temperature, its material and its climatic conditions. Hybrid Photo Voltaic panel is the best method to obtain better efficiency with proper panel cooling. In PVT system the solar panel heat was removed with the help of cooling medium behind the solar panel. Thermal control of the PVT hybrid system maintained in a better way by passive cooling method with Phase change material. PCM major draw backs are high nucleation rate, large undercooling low thermal conductivity, and low PCM life cycle. We can enhance the PVT efficiency with proper address of PCM draw backs. PVT-PCM modules proposed for better enhancement in thermal storage potential 35 to 44% than the conservative water PVT system, with prolonged thermal storage accessibility and accelerated output

elevated electrical efficiency in PVT-PCM hybrid system. This research paper presents the research gap to find optimum process in cooling methods for PV panel with optimized hybrid model design with better selection of Phase change material, Fin design to increase the best PV panel efficiency by decreasing the temperature of the PV panel at all conditions.

KEYWORDS: PVT-PCM, Conductivity, Thermal storage & Nucleation Rate

Received: Jan 29 2021; Accepted: Feb 19, 2021; Published: Mar 10, 2021; Paper Id.: IJMPERDAPR202118

1. INTRODUCTION Photovoltaic technologies guarantee the security and diversity of the energy supply without any negative environmental impact in production of electricity. Photovoltaic cells that convert incident solar radiation of concentrated and spotted into direct current (DC) with 7 to 30% restoration efficiency depending on the material of the photovoltaic type and its material. Photo voltaic thermal or hybrid system is combination of solar collector and photovoltaic module to form a single system for generation of electricity and low heat for smaller applications. Sun solar radiation nearly 80 to 90% was absorbed and reflected as thermal energy. Due to this solar panel temperature increases results the reduced electrical conversion output and also decrease in solar cell life. PV panel temperature increment produces thermal vibrations resulting in mobility of charge carrier. This results the effectiveness of solar panel. The incident solar radiation on collector partially converted into electrical energy also thermal energy due to contact of absorber plate behind the panel. The objective of PVT/Hybrid system is to increase the electrical and thermal output to a considerable range. Properly modeled hybrid model can absorb thermal energy would utilized for low temperature applications there by cools PV panel results the higher conversion rate of electrical output.

Researchers stated that owing to several reasons like conductivity, heat capacity, density water systems works more effectively than PVT air modules. But water systems need more modifications to get leak-proof designed module. www.tjprc.org

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from 7.50 to 14.0 %.The selection criterion of PCM was very significant for enhancement of panel cooling to get the

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Besides the water, air cooling methods passive method with Phase change material was best solution to cool solar panel.

The thermal efficiency of hybrid system was determined by equation ηthermal = m Cp(To – Ti) / (A.G) Where Cp” is specific heat[kj/kg/k], “m” is the flow rate [kg/s], “Ti”, “T0” are inlet, outlet temperature of fluid, A is area of collector surface [m2] and G represents received radiance collector plan [W/m2]. The PVT-system panel temperature can be maintained constantly with better cooling methods with smaller Photovoltaic cell surface and can be increased considerable panel life. Researchers confirmed efficiency of PVT cells decreases in range of 0.41 to 0.52% for each degree of increase in the temperature of the cells and also reduced panel life. The researchers performed experiments briefed about temperature 10° C increase will lead 5% reduction in PV panel efficiency. Researchers developed PVT model with active water cooling method on both sides of panel to reduce panel temperature to 24 to 26 0 c while comparing with conventional non cooling panel temperature 560 c. Phase change materials are using in thermal energy storage devices which it will release latent heat and sensible heat with greater energy management in devices. Thermal management of PVT panel with PCM was continuing study which was evident in number of research papers increase. This paper aim is to identify potential gap in this area, which can be investigated to enhance the PV technologies efficiency. Passive method of PCM cooling is more achievable cost-effectively compared to active (Forced air, water circulation) cooling methods which pump not necessary results no requirement of electricity. The temperature maintaining at low is always suggestible and economical rather than adopting a cooling system to increase small efficiency in system. In some cases PV cooling methods with high costs are acceptable in overall system design. Regulating temperature with PCM will gives better solution of storing thermal energy which will be used later for smaller heat applications. PCM heats sensibly with initial heating and when it reaches to maximum temperature PCM absorb latent heat. PCM continues after melting to het further as it melts. Thermal conductivity, elements of heat transfer and PCM volume influences the duration and temperature range of PCM. PCM after complete phase change material will start to heat again sensibly. In the design of PV / T hybrid systems, the key constraint was mass flow rate and convection heat transfer coefficient. The overall PVT efficiency can be improved with a high convection coefficient.

Figure 1: Panel Efficiency Depending on Temperature

This paper work aims to explore electrical, thermal performances with different modelled PVT modules underneath diversified ecological situations with PCM (Various types), without PCM, with different Geometrical shapes and one absorber plate with solar panel and other with pipes having different profile shape embedded behind the Photovoltaic panel.

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2. PVTCOLLECTOR TYPES AND PANEL COOLING

Figure 2. PV–Thermal Collector Classification

Pv-T Air and Water Collectors Air collectors are classified primarily on the basis of the pattern of air flow. These are rated with respect to the airflow on either side of the absorber, above the absorber plate, and below absorber with single and double pass absorber. The convective heat transfer for the front and back of the PVT panel can be calculated by natural and forced convection. The total heat of convection.

Qconv= Qn +Qf= (hfree +hforced).A.(Tpvt-Tamb) Where Qf and Qn are heat losses due to forced, natural convection and hfree and hforced forced and free convection coefficients, “A” is area of collector panel,Tpvt, Tamb are PV Panel temperature and Ambient air temperatures respectively.

Natural convection Heat transfer (Qn): According to Newton’s law of cooling Natural convection heat losses given by Qn= hfree. A.(Tpvt- Tamb).Forced convection Heat transfer (Qn): According to Newton’s law of cooling Forced convection heat losses given by Qf= hforced. A.(Tpvt- Tamb) Among air PV / T systems, Hegazy et al. [2] developed four basic modes, with air flowing above the absorber (model A) or below (model B) and in model C with a single passage on each side of the 'absorber or Model D with double passage as mentioned in Figure ure 3.0

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Figure 3: Photo Voltaic Air Collector Models

Figure 4: PVT Air Heater with Tedlar and without Tedlar with Glazed and un Glazed

A.Tiwari and M.S.Sodha et al [3] mentioned Hybrid PVT-AIR collector overall performance with different modulated con Figure urations with glazed, unglazed and with or without tedlar as shown in Figure no. 4. Efficiency betterment was observed in Hybrid PV-T system Model IV without tedler extracted heat was utilized for different applications like lighting, room heating and illumination.

PV-T water collectors are distinguished by water stream pattern, sheets and tubes, absorber types, and free flow channels. Water cooling of PVT panels can be divided into passive cooling and active cooling. Passive water-based cooling was effective, providing good thermal contact in PVT systems without the use of pumps and removing excess heat continuously. Active water-based cooling improves the performance of solar panels as the water flow increases. The advantage of active water cooling was greater heat transfer compared to natural and forced air convection and disadvantages of this system are huge investment in using the pump with high maintenance costs compared to natural and forced convection, and the short service life due to corrosion and leakage of fluid. Nizetic et al. [1] developed an experimental model on spray cooking technology for solar panels, with an added electrical efficiency of about 16.3% and drop in temperature about 25° C from 55° C for un cooled conventional panels.

In the work T.T Chow et developed the new PV-T water collector with the principle of thermo siphon to reduce the cost of pumping power. Figure ure 5a and 5b represents the cross section views of three adjacent water tubing in a sheet and tube PV-T collector and several integrated flat box absorber modules of PV-T collector respectively.

T.T Chow developed a new PV-T water collector model with the principle of thermal siphon to reduce the pump outlet cost. Figure ures 5a and 5b shows water pipes with three adjacent one after other seated and tube PV-T header and PVT collector module with integrated flat box absorber respectively.

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Figure 5.a) water Tubing in 3 adjacent in a Sheet and tube PVT Collector

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Figure 5.b) PV-T collector Module with Integrated flat-Box (From SCIJ)

2.1 PVT Panel Cooling with PCM PVT Solar Panel temperature was maintained constantly at a certain range with phase change material was inserted behind the panel it absorbs the heat and stores as heat energy. This latent heat of PCM is used to keep the Panel temperature at constant level for a long time. The absorbed/stored energy can be used for some other applications like space and water heating even though the initial investment was high. Stored thermal energy of PCM will increase the overall efficiency of PVT system without any utilization of electrical power.

Figure 6: Schematic Representation of PVT/PCM Module

3. THERMAL MANAGEMENT OF PVT SYSTEM WITH PCM PVT Hybrid systems thermal management can be effectively attained with passive mode and active mode of cooling.During passive mode of cooling phase change material did not use any mechanical and electrical power. A thermal storage system with PCM was popularized in past decades due to its availability potential and extended period of operation. During Active cooling uses liquid or air medium consumes power along with draw backs of leakage. In this transforming the heat of body as extended as there is no alteration in its existing phase by utilization of sensible energy. In this material transformation occurs, the PCM do not gain sensible heat, that is, the input of heat from an external source, but undergoes an endothermic process to absorb the surrounding heat. Melting period of PCM firms by thermal conductivity(k) and PCM Volume. The PCM uses latent heat energy, utilizes fractional heat energy the same as latent heat through a small change in temperature concerning a phase conversion. PCMS phase evolution temperatures fluctuate greatly with the material thermal properties, Chemical constitution.

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Figure 7: PCM Behavior with Increase in Temperature 3.1 PCM Classification Classification of Phase change material can be done in different methods that is based on its transition of phase, melting temperature of material, Low temperature (1600 C) PCM, medium temperature (1500 C-9000 C) PCM and high temperature(9000C) above and its matter combinations as mentioned in Figure ure 8a to 8d. Depending on their phase conversion mode, PCMs are gas to liquid, solid to solid, solid to liquid, and solid to gas. They are also divided according to their chemical uniqueness like eutectics organic and inorganic. PCM with solid to gas or liquid to gas phase conversion was partial in Thermal energy storage device, PVT-PCM systems due to the great amount of change linked with phase transformation.

Figure 8 a: Classification of Phase Change Material

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Figure 8 b. Based on Temperature Phase change Material Classification

Figure 8 c. PCM Classification used in Thermal Storage (From Scopus Journals)

Different PCM are available in market with different range of temperature and it is very difficult to find all good properties in one PCM to design the optimized PVT hybrid model. Paraffin wax is a organic PCM with high molecular weight solid with colorless with 3600 C range melting point and fusion heat around 210 - 230 kJ/kg. These PCMs are non acidic, easily recyclable with good latent heat with better nucleating property.

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Figure 8 d: Types of Phase change Material based on Phase Change

Organic materials obtainable in various temperature series with high fusion rate and nucleating property. The drawback beside this with organic PCMs are phase change transition with large volume, less thermal conductivity, flammability and low volumetric proportion in latent heat capacity storage. The inorganic PCM are obtainable with high fusion heat, thermal conductivity, non flammable and melting point. Inorganic PCM will suffer with super cooling, corrosiveness, and rapid phase separation and be short in thermal stability. PCM Eutectics will give better advantages than Organic and inorganic PCM with quick melting point and good volumetric thermal storage compactness.

4. Selection of PCM for PV Thermal Systems The research was going with novel passive method of cooling using PCMs. The aim of the research work to obtain an improved PVT-PCM design by incorporation dissimilar PCMs in dissimilar ratios, different con Figure urations in geometrical fins and nonmaterial’s. Solar energy efficiency depends on thermal storage method efficiency owing to volatile and irregular incident solar power on PV panel. Phase change material stores better heat build-up per unit quantity through combining both sensible, latent heat capacity. The majority PCMs attract heat during the occurrence of phase change during a solid from to liquid phase cycle in day and release heat energy in the night time. This expertise improves solar thermal photovoltaic arrangement overall efficiency in terms of electrical and thermal energy. PCM selection mostly depends on Latent heat storage utilization in designing the PVT unit. PCM should have better desirable properties like physical, chemical stability, good thermal properties, economic viability and enhanced kinetic properties. It was very difficult to get better PCM with all properties in designing a PVT –PCM system. Researchers were facing a problem to select the better PCM and are mixing the PCM with composite materials to get the required properties for better efficiency enhancement. Hasan et al. [4] prepared the PCM required properties in following table 2.0 for better suitable PCM for PVT Hybrid system to increase the electrical efficiency.

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Table 2: Properties Required in PCM in PVT –PCM System S. No

Properties

1



Thermal

2



Physical

Required Properties  Desirable melting point for material consistency behavior.  Elevated latent fusion heat for every unit quantity to increase absorption heat rate.  Better thermal conductivity(k) of liquid and solid phases for better heat transfer rate and removal of heat  Superior thermal specific heat meant for added sensible thermal storage  PCM material should have reversibility nature with good response.  Wide variety of phase transition temperatures.  Better phase equilibrium to get good thermal heat storage capacity.  Better concentration for lesser container amount to ensure the low rate of suppression  Phase change transition with lesser volume to reduce the design size  Containment problem reduced with smaller vapour pressure  Better chemical stability and no degradation of material after a good number thermal cycles  Construction material life increased due to non-acidic property  No chemical breakdown  Better safety the material should have non-explosive, Non-poisonous, nonflammable and non-polluting.  No super cooling when it is freezing  better nucleation speed along with good crystal enlargement  Better rate of thermal transfer at all situations including isothermal conditions.

3



Chemical

4



Kinetic

5



Environmental

 

PCM material easy disposable, good recyclability and treatment.

Dwellng places should be comfortable with Odour free

6



Economic

  

Better price with good penetration in market Material easy availability and abundant.

Economic viability and effective cost

Figure 9: Stored Heat in PCM Versus Temperature

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Commercialization of PCM in market was limited due lack of thermo physical properties. The performance of PCM in thermal storage system was limited with high cost, non recyclability, variations in thermo physical properties with change in volume. The effect of the lower value of conductivity is reflected during the energy recovery or withdrawal with a significant temperature drop in the process. Therefore, phase change speed process (PCM melting / solidification) is not up to mark of expected level. In short, there may be enough power storage systems available, but the system cannot use at the required speed.

PCM was heated after using it is converted into liquid form, which may turn into leakage. PCM with composite materials with high density materials and by using porous material like wood or fiber may overcome the leakage problem.

PCM is finely circulated in polyethylene/ porous matrix, which controls flow of liquid PCM, and therefore can be cut indifferent shapes easily without any leakages. Ravindrakumar et al [5] explained in his studies about low conductivity PCM composites by mixing high conductivity graphite with required proportion.

4.1 PCM Thermal Stability While selecting the PCM the latent het of fusion and melting temperature will depends on number of thermal cycles, its usage to be evaluated before designing a thermal system. Thermal stability test will be conducted while selecting the PCM and data was not enough from earlier researches. To measure the fusion heat and PCM melting temperature Differential scanning calorimeter (DSC) was extensively using in laboratories. DSC test conducted with reference sample material and aluminum trioxide is best suggested material in DSC analysis.

4.1.1 Organic PCMs Organic PCM materials are stable and cover a broad variety of melting temperature between 00 c to 2000 C due their covalent bonds. Organic materials contain a smaller amount latent heat fusion / unit volume than the inorganic materials due to density difference between both the materials. Organic PCM are available in wide variety of temperature range with good thermal stability, high latent heat of fusion, considerable self nucleation with non corrosive nature. Organic PCM are divided into paraffin’s (mixture of pure alkenes) and non - paraffin’s (fatty acids, glycols etc.).

4.1.2 In-Organic PCMs These PCMs available with high latent heat fusion per unit volume with superior thermal conductivity. In-Organic PCM s is readily available with low cost and enhanced compatibility with conservative construction materials. Major draw backs of In-Organic PCMs are their super cooling, corrosiveness and less nucleation rate.

4.2 Eutectic PCMs A eutectic PCM is combination of two or more materials with similar compositions, which freeze and melts as single composite. This PCM can be made with compounds of organic, In Organic or mixing of both materials which it forms a crystal during crystallization. This Eutectic PCM advantage is melting and freezing done without any crystal separation in PCM compound. Eutectic PCM are more costly than the organic PCMs. The eutectic PCM can further classified as organic eutectic (Caprylic Acid, Capric Acid and Lauric Acid) and inorganic Eutectic.

4.3 Cooling Methods and PCM Review Summary This gives present and ongoing research work details to give better solution for PVT technology enhancement to discover

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research gap. Researchers were invented different cooling methods in their studies to cool PV panels with insertion of passive method PCM. This method found best alternative source to decrease panel heating and increase energy conversion along with panel life. PV panel cooling with passive and active methods have their own advantages and disadvantages. In this passive method does not maintain cell temperature at certain range. In active systems fluid circulation cost, its leakage and establish new device is a big difficulty.

In natural ventilation cooling method the attained cooling panel temperature was 44 to 760 C with zero maintenance, less initial cost, no requirement of electricity and longer panel life. The limitations in Natural ventilation PV cooling methods are more temperature variations in PV panel, less conductivity along with heat transfer rate. Natural ventilation method solar panel heat was not utilized, it also depends upon sp many influence factors like conduction and air wind direction. The draw backs in natural ventilation were overcome by forced ventilation with high rate of heat transfer with reduction in panel temperature. Forced ventilation method installation and initial cost was high and also it consumes more electrical power.PVT panel temperature was maintained efficiently with active water cooling method with panel temperate 26 to 280 c with high heat transfer rate with more system noisy and pumping power requirement. Thermo electric was new cooling method with compact size, less noisy and easy integration. PCM is the passive method of PV panel cooling method with better delay in panel temperature with long time maintenance without any noise and the removed heat used effectively to smaller applications. PCM disadvantages are material stability, life, flammability of material is an major issue along with disposal after cycle completion.

Smith et coll. [7] confirmed that the PVT-PCM are most favorable, under all climate variations between the two zones. He expressed that the start of energy is 6% environmental with a recovery period of 25 years.. Japs et coll. [8] stated that the better efficacy with the graphite mixing with PCM gives lesser payback period with high electrical efficiency.

Researchers were carried out an experimental and model analysis with the MAT lab software of the PV-PCM system with graphite was implanted with aluminum fins in PCM (paraffin wax) in four cases and obtained the maximum efficiency 12.79%. The PV-PCM microencapsulation simulation, MEPCM model was attached to the reverse side of the PVT panel and the photovoltaic panel floated on the surface of the water obtained step up in electrical efficiency about 2.0%.

Researchers optimized the PVT PCM system by developing a mathematical and numerical model for convection photovoltaic panels, water-based PVT systems and PVT-PCM based on the energy balance of different components (with different materials) in different flow conditions taking into account certain assumptions. into account. Research studies has shown that using PCM (passive heat exchange method) in PVT cooling has many advantages of high heat transfer rates, high heat storage capacity (due to latent heating ) as well as silent isothermal heat removal without noise and requirement of electrical energy. In addition to this, the disadvantages of PCM it is corrosive, toxic, flammable, and the high cost of PCM with disposal issues after completion of life cycles.

5. EXPERIMENTATION WITH PCM PV-PCM (Hybrid) system was fabricated which contains the PCM material and also incorporated fins arrangement to transfer the heat from solar panel to PCM as shown in Figure ure 10 to 13. Fins main function is to enhance the thermal conductivity for better heat transfer from solar panel to PCM. The Hybrid system was installed with eight thermo couples for temperature measurements at different locations of fins, PCM to get accurate data along with sensors to an arduino board which it converts the analog data to digital data and also to store the data. The selected Phase change material was placed into aluminum finned system and solar panel is attached to the finned PV-PCM hybrid system. The insertion of www.tjprc.org

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aluminum fins will decrease the PCM inverse result of crystalline separation. The selected PCM was assumed homogeneous and isotropic in solid and liquid state. Due to the system symmetry in vertical direction the side walls are thermally insulated, two dimensional and data from the sensors is collected with respect to time and simulated analysis.

Figure 10: Ansys Model with Fin System I

Figure 12 Aluminium Finned PVT Hybrid System I

Figure 14: Temperature in Finned system 1

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Figure 11: Ansys Model with Fin system II

Figure 13: Aluminium Finned PVT-PCM System II

Figure 15: Temperature in System 3 without fins

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Figure 16: PCM before placing in Hybrid System

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Figure 17: PCM after Panel Heating

During experimentation total surface area with Fin design I (Case I) was 195500 mm2 and temperature of solar panel 33.970 C. Total surface area with Fin design II (Case II) was 236240 mm2 and temperature of solar panel 32.980 C and in CASE III surface area in absence of fins was 93800 mm2 and solar panel temperature 35.9930 C. During analysis CASE – I the final temperature of thermal analysis was 29.09 0 c. For aluminum finned PV-PCM system 2 thermal analysis final temperature is 29.890 C for PCM II.

S. No 1 2

Table 4: Theoretical and Analytical Values Material Model Theoretical Value (Tt) Analytical Value (Ta) PCM I Model -A 33.97 0c 29.09 0c 0 PCM II Model -B 32.96 c 29.89 0c

The developed Hybrid system with better fin design (Geometry), PCM selection with higher thermal conductivity can be escalated the electrical efficiency to better value.

6. CONCLUSIONS In hybrid PVT technology, power competence has been the motivating force at the back of PCM research for the past decade. This article has reviewed an in-depth review of cooling techniques with PCM and non-PCM PVT systems with various fin and PCM materials used with conventional / modern cooling methods to find the improved conclusions of the research work. The development of PVT systems with various kind of PCM, their advantages and disadvantages with different control parameters were discussed. Research studies found that solar panel cooling done effectively with water and forced air methods and also stated natural ventilation cooling is most in efficient procedure. Improving PCM performance with nonmaterials has proven to be a better option to enhance the thermal properties of PCM material and increasing the performance of PVT system while cooling. The shape, size, and nano particles dispersed within the PCM must be taken into account in order to achieve better property improvements such as thermal conductivity and specific heat capacity. Researchers concluded with experimentation electrical efficiency 7.1 to 8.9% and thermal efficiencies 24 to 3.0 % respectively were elevated by insertion of PCM in new design system. Research technologies with PCM need to be optimized further with different fin materials to improve thermal conductivity, Fin shape and size, geometry of PVT system, PCM porous material, macro and microencapsulation of nanoparticles in PCM to improve rate of heat transfer from solar panel. Numerical research has been mentioned that thermal conductivity increment of 10% in PVT-PCM system increases the effectiveness of the hybrid system by 2.8 to 4.1 %. The selection of materials of photovoltaic cell and PCM play critical part in total effectiveness of system. PVT cooling techniques can be developed with new materials to meet

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global needs with good thermal conductivity to remove the heat from system. Phase change material thermal stability was required after repetitive number of cycle operations with better performance while using in PVT-Hybrid system. PCM was considered reliable and stable if thermal heat and PCM melting point were insignificant after repetitive thermal cycle operations. Micro encapsulation of PCM in PV Panel will give better cooling than other cooling methods in certain range of temperatures. Researchers have to develop PVT-PCM base models with suitable PCM of good thermal and mechanical properties to increase cooling performance and to enhance electrical efficiency.

Hybrid PVT model was developed and experimental analysis was conducted with PCM-Fins, PCM-without fins.

The experimental values were compared with theoretical and analytical values. We can reduce the solar panel temperature with better geometry of fin its size, PCM with suitable nano material encapsulation can be enhanced the electrical efficiency.

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Japs et al. Japs E, Peters S, Sonnenrein G, Krauter S. Energy-economic comparison of photovoltaic modules equipped with a layer of conventional and improved phase change material. In: Proceedings of the 40th IEEE Photovoltaic Specialist Conference (PVSC), Denver CO (USA) pp. 1348–52; 2014.

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