International Conference on Emerging Trends in Electrical, Electronics and Sustainable Energy Systems (ICETEESES–16)
Importance of Phase Change Material (PCM) in Solar Thermal Applications: A Review V.K. Dwivedi1, Prabhakar Tiwari2 and Sumit Tiwari3 Abstract—Present study is an attempt to study of different heat storage methods and their application for sustainable development. Solar energy is a prime source of energy which is responsible for other renewable sources directly or indirectly. The major drawback of solar energy is its availability in day time only. Thermal storage devices can overcome this drawback as they can store the energy in day time that can be utilized in off sunshine hours. In the present study classification of thermal storage methods has been done. Further different application of phase change material (PCM) has been discussed. Study shows that PCM can be successfully integrated nearly with all the solar thermal devices. This study will also help to understand to store maximum thermal energy that reduce the requirement of conventional fuels like coal, oil etc. Further, it will help in reducing greenhouse gasses and climatic changes.1 Keywords: Cell Efficiency, Phase Change Material, Photovoltaics, Solar Water Heater
I.
INTRODUCTION
Energy is the fourth most important element for human after air, water and food [1]. In other words it can be considered as backbone of human activities. Energy plays vital role in economic development of any country. Historically, wood and coal were used as primary energy source. As the population growth and 20th century industrial revolution occurred, global energy demand also increased. It is being world-wide accepted that for balanced sustainable development currently used conventional energy means i.e. fossil and nuclear fuel have to be replaced by renewable energy sources. Sustainable development means that energy demand is met without any environmental impact. Renewable energy includes solar, tidal, wind, hydropower and biogas which have potential to encounter world-wide energy demand in a sustainable manner. Among all renewable energy methods, solar energy has lot of capabilities. The major drawback with solar energy is its availability in day time only. Thus, some energy storage is required to run solar 1Professor
and Head, ME Dept. Galgotias College of Engg. & Tech., Gr. Noida, UP., India 2Professor and Head, EE Dept. Galgotias College of Engg. & Tech., Gr. Noida, UP., India 3Centre for Energy Study, Indian Institute of Technology Delhi New Delhi, India E-mail:
[email protected],
[email protected],
[email protected]
operated devices during night time. Phase change material (PCM) is also known as latent heat storage material which has good ability to store and release high amount of heat for a required temperature range. [1,2]. II. THERMAL ENERGY STORAGE METHODS Thermal energy storage (TES) method can be divided into three categories: • Sensible heat storage; • Latent heat storage; • Thermochemical storage. A. Sensible Heat Storage Sensible heat storage is a heating of a material in which amount of heat stored depends on specific heat, amount of material and temperature difference between initial and final condition. Amount of heat can be calculated by [3] Tf o
Q=
∫ mc dT = mc p
p
(T fo − T fi )
(1)
Tf i
TABLE 1: SELECTED LIST FOR SOLID AND LIQUID MATERIALS USED FOR SENSIBLE HEAT STORAGE [4] Medium Rock Brick Concrete
Fluid Type solid solid solid
water Caloriea HT43 Engine oil Ethanol Organic Propanol Organic Butanol Organic Isobutanol Organic Isopentanol Organic Octane Organic
liquid oil oil liquid liquid liquid liquid liquid liquid
Temperature Density Range (0C) (kg/m3) 20 2560 20 1600 20 19002300 0-100 1000 12-260 887 160 888 Upto 78 790 Upto 97 800 Upto 118 809 Upto 100 808 Upto 148 831 Upto 126 704
Specific Heat (J/kg K) 879 840 880 4190 2200 1880 2400 2500 2400 3000 2200 2400
B. Latent Heat Storage Latent heat storage (LHS) depends on phase change of material. In this method heating of material occurs until its phase changes. A lot of energy is absorbed inside the material due to phase change and it is known as the latent heat of vaporization or fusion. When temperature of phase change material increases, first its heat stored in its initial phase (solid) is released. After certain temperature, phase 978-1-5090-2118-5/16/$31.00 ©2016 IEEE
Importance of Phase Change Material (PCM) in Solar Thermal Applications: A Review 43
change occurs and transformation of solid into liquid takes place. Until all the solid material is converted into liquid state, temperature will be constant. In this transformation large amount of energy is absorbed in the material. After complete transformation again temperature of liquid material increases and energy is stored in sensible way. Amount of stored energy can be calculated as [3],
Q=
Tf
Tm
∫ mc dT + mL + ∫ mc dT p
Ti
p
(2)
Tm
Q = m[c p (Ti − Tm ) + L + mc p (Tm − T f )]
(3)
C. Thermochemical Storage Thermochemical storage depends on the concept of reversible endothermic chemical reactions. Chemical heat is the energy which is required to dissociate structures in a chemical compound and further energy will be recovered when a synthesis reaction takes place [5]. Among all above thermal storage methods, latent heat storage method is best for solar thermal devices. In present paper phase change material is a prime concern.
Cabeza et al. [17] categorized PCM into three groups: • Cooling applications upto 21 0C, • 22–28 0C for comfort in building applications, • 29–60 0C for hot water applications • High temperature applications requiring PCM of between 60 and 120 0C. IV. APPLICATIONS OF PCM IN SOLAR SYSTEMS A. Solar Water Heating Systems Kumar [18] designed a latent heat storage setup. Further, development and evaluation of the performance have been done by using a box type solar collector for the hot water requirements during evening and morning. System was consisting of three finned heat exchangers as shown in Fig. 2. In the system (Fig. 2) paraffin wax having melting temperature of 54 0C was used as a heat storage material. The performance of paraffin wax for desirable temperature range of hot water (15 l and 20 l) found to be very good.
III. PHASE CHANGE MATERIAL PCM can be classified as shown in Fig. 1. PCM can be broadly classified into four types namely solid–solid, solid–liquid, solid–gas and liquid–gas types [6]. Among all PCM solid–solid type are fairly good to use because of its small volume change property, no gas or liquid formation, negligible sub-cooling, non-toxicity, corrosion resistance, high thermal efficiency and fair service life. It also has some drawbacks like its high cost and poor thermal conductivity [1, 7-8]. Solid–solid type PCM can be divided into cross-linked high density polyethylene, layered calcium titanium and polyatomic alcohol [1]. Solid–liquid [4, 10-16] can be divided into three subcategories namely inorganic, organic and composite. Further on the basis of chemical and thermal properties inorganic and organic PCM can be divided into hydrous salt, metal paraffin, fatty acid respectively.
Fig. 2: Water Heating System by Kumar [18]
Fig. 3: Water Heating System by Kumar [19]
Fig. 1: Classification of Phase Chance Material (PCM)
978-1-5090-2118-5/16/$31.00 ©2016 IEEE
Paraffin based two water heating system have been designed by Shukla [19]. Among two systems one had tank in tank type storage as shown in Fig. 3 and the second
44 International Conference on Emerging Trends in Electrical, Electronics and Sustainable Energy Systems (ICETEESES–16)
had a reflector with integrated type storage. Experiment has been done with two systems on the basis of 24h cycle and systems are found to be 45% and 60% efficient respectively. Canbazoglu et al. [20] were developed water heating system with and without (conventional) PCM as shown in Fig. 4. Further both systems compared with each other and found that outlet temperature of the heat storage tank with the PCM was greater, by 6 0C, than the system without a PCM. The total mass of PCM filled in three rows of polyethylene bottles used in the heat storage tank was approximately 180 kg.
Fig. 4: Cross-Section of Storage Unit with PCM and Collectors [20]
B. Building Heating is required for buildings situated in cold climatic zone. Numerical study has been done with inorganic phase material (NH4Al (SO4)2.12H2O) [21]. It was found that heat absorption and storage in PCM is more effective when temperature of heat source is 26.5 0C which is larger than the phase transition temperature.
Temperature dependent cell efficiency can be written as [24]
ηc = ηo (1 − βo (Tc − To ))
(5) From eq. (4) and (5) cell efficiency can be calculated ηc
⎡ α τ β ⎧ ⎫⎤ η re f ⎢1 − β r e f ⎨ ( T a − T re f ) + c g I ( t ) ⎬ ⎥ U Lm ⎩ ⎭⎦ ⎣ = η re f β re f τ g β ⎡ ⎤ I (t ) ⎥ ⎢1 − U Lm ⎣ ⎦
(6) It is clear from the above equations that as the temperature of PV increases its efficiency decreases. To reduce the temperature of PV module PCM can be placed behind the PV and further absorbed heat can be utilize by some means. Yin et al. [25] have developed a photovoltaic thermal system with combination of heat storage (water) using PCM as shown in Fig. 5. In figure it is clear that water is heated by heat energy coming from the PV. Water circulation occurs due to thermo siphon through the PCM. This heat can be utilized for later applications.
Fig. 5: PV Module with Water Heating System [25]
Optimum thickness of PCM has been found about 0.03m with 6.5% increase in PV efficiency. Figure 6 [26] shows trombe wall integrated with PV and PCM (BiPVT system with PCM). Thermal modeling has been done and found that cavity temperature decreases up to 7 0C during cooling phase. Due to temperature decrement in system its electrical efficiency is found to be increased by 10%.
C. Heat Management in Photovoltaics PV is one of the means which makes the thermal systems self-sustainable. PV can be integrated with buildings, water heating systems, greenhouse and drying systems etc. When sunlight incidents on the PV module, it’s not only converted into electricity but also into thermal energy [22, 23]. Total energy received by module= Thermal energy lost from top surface of the PV module+ Thermal energy lost from bottom surface of the PV module+ Electrical energy. α cτ g β c It Am = U tca (Tc − Ta ) Am + U bcr (Tc − Tr ) Am + τ g β cη c I t Am
(4)
Fig. 6: BIPVT System with PCM Wallboard [26]
978-1-5090-2118-5/16/$31.00 ©2016 IEEE
Importance of Phase Change Material (PCM) in Solar Thermal Applications: A Review 45
V. CONCLUSION
[9]
From the present study following conclusion can be made: • As the cell temperature increases corresponding efficiency decreses. • PCM is one of the way by means of which the solar thermal devices can give better output. • In the case of building heating applications it was found that for optimum result the temperature of heat source is 26.5 0C higher than the transition temperature of PCM. Thermal energy for a clear day found to be 2.2 kWh, 0.723 and 4.1 kWh respectively. • In the case of PV module cooling, PCM showed very good results. It’s application not only increases electrical efficiency but also give opportunity for utilization of thermal energy. In future studies it is required to enhance the properties of PCM like it’s conductivity for better results. Presently the cost of PCM is also high so, the new materials with different combinations may be analysed to reduce the cost.
[10] [11]
[12] [13] [14] [15] [16]
[17] [18]
REFERENCES [1]
[2] [3] [4] [5] [6] [7] [8]
Xi P, Duan Y,Fei P, Xia L, Liu R,Cheng B. Synthesis and thermal energy storage properties of the poly urethane solid–solid phase change materials with a novel tetra hydroxyl compound. Eur Polym J 2012; 48: 1295–303. Oro E, Graciade A, CastellA, FaridMM, CabezaLF. Review on phase change materials (PCMs) for cold thermal energy storage applications. Appl Energy 2012; 99:513–33. Lane GA. Solar heat storage: latent heat material, vol. I: background and scientific principles. Florida: CRC Press; 1983. Sharma A, Tyagi VV, Chen CR, Buddhi D. Review on thermal energy storage with phase change materials and applications. Renew Sustain Energy Rev 2009; 13:318–45. Khartchenko NV. Advanced energy systems. Berlin: Institute of Energy Engineering & Technology University; 1997. Regin AF, Solanki SC, Saini JS. Heat transfer characteristics of thermal energy storage system using PCM capsules: a review. Renew Sustain Energy Rev 2008; 12: 2438–58. Lane GA. Low temperature heat storage with phase change materials. Int J Ambient Energy 1980; 1: 155–68. Liu M, Saman W, Bruno F. Review on storage material sand thermal performance enhancement techniques for high temperature phase change thermal storage systems. Renew Sustain Energy Rev 2012;16: 2118–32.
978-1-5090-2118-5/16/$31.00 ©2016 IEEE
[19]
[20]
[21]
[22] [23]
[24] [25]
Abhat A. Low temperature latent thermal energy storage system: heat storage materials. Sol Energy1983; 30:313–32. Zuca S, Pavel PM, Constantinescu M. Study of one dimensional solidification with free convection in an infinite plate geometry. Energy Convers Manag 1999; 40:261–71. Lee T, Chiu YH, LeeY, Lee HL. Thermal properties and structural characterisations of new types of phase change material: an hydrous and hydrated palmitic acid/camphene solid dispersions. Thermo chim Acta 2014; 575:81–9. Shukla A, Buddhi D, Sawhney RL. Thermal cycling test of few selected inorganic and organic phase change materials. Renew Energy 2008; 33:2606–14. Feldman D, Shapiro MM. Fatty acids and their mixtures as phasechange materials for thermal energy storage. Sol Energy Mater Sol C 1989;18:201–16. Hasan A. Phase change material energy storage system employing palmitic acid. Sol Energy 1994; 52:143–54. Dimaano MNR, Escoto AD. Preliminary assessment of a mixture of capric and lauric acids for low-temperature thermal energy storage. Energy1998; 23:421–7. Sari A, Karaipekli A. Preparation, thermal properties and thermal reliability of palmitic acid/expanded graphite composite as formstable PCM for thermal energy storage. Sol Energy Mater Sol C 2009; 93:571–6. Cabeza LF, Castell A, Barreneche C, deGracia A, Fernández AI. Materials used as PCM in thermal energy storage in buildings: a review. Renew Sustain Energy Rev 2011;15:1675–95. Kumar B. Design, development and performance evaluation of a latent heat storage unit for evening and morning hot water using a box type solar collector. Project Report, M. Tech. (Energy Management), Indore, India: School of Energy and Environmental Studies, Devi Ahilya University; 2001. Shukla A., “Heat transfer studies on phase change materials and their utilization in solar water heaters. Thesis Report, Ph.D. Energy & Environment, Indore, India: School of Energy and Environmental Studies, Devi Ahilya University; 2006. Canbazoglu S, Sahinaslan A, Ekmekyapar A, Aksoy YG, Akarsu F. Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar waterheating system. Energy Buildings 2005; 37(3):235–42. Zhihua Zhou, Zhiming Zhang, Jian Zuo, Ke Huang, Liying Zhang. Phase change materials for solar thermal energy storage in residential buildings in cold climate. Renewable and Sustainable Energy Reviews 2015; 48 :692–703 Ingersoll JG. Simplified calculation of solar cell temperatures in terrestrial photovoltaic arrays. J Sol Energy Eng 1986; 108:95–101. Tiwari GN, Tiwari S, Dwivedi V.K., Sharma S, Tiwari V. Effect of water flow on PV module: A case study. International IEEE Conference Energy Economics and Environment (ICEEE) 2015; 1 7, DOI: 10.1109/EnergyEconomics.2015.7235080. Evans D. L., “Simplified method for predicting PV array output,” Sol. Energy 1981; 27: 555–560. Yin HM, Yang DJ, Kelly G, Garant J. Design and performance of a novel building integrated PV/thermal system for energy efficiency of buildings. Sol Energy 2013; 87:184–95.
