Journal of Cleaner Production 324 (2021) 129223 Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro Efficient heat batteries for performance boosting in solar thermal cooking module S.M Santhi Rekha a, 1, Vaithinathan Karthikeyan b, 1, Le Thi Thu Thuy c, Quach An Binh d, Kuaanan Techato e, f, Venkatramanan Kannan g, Vellaisamy A.L Roy h, Sukruedee Sukchai a, **, Karthikeyan Velmurugan a, * a School of Renewable Energy and Smart Grid Technology (SGtech), Naresuan University, Phitsanulok, 65000, Thailand Department of Materials Science & Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong Institute of Research and Applied Technological Science, Dong Nai Technology University, Dong Nai, 76000, Viet Nam d Department of Academic Affairs and Testing, Dong Nai Technology University, Dong Nai, Viet Nam e Faculty of Environmental Management, Prince of Songkla University, Hat Yai, 90112, Thailand f Environmental Assessment and Technology for Hazardous Waste Management Research Center, Faculty of Environmental Management, Prince of Songkla University, Hat Yai, 90112, Thailand g Department of Physics, SCSVMV Deemed University, Kanchipuram, 631561, India h James Watt School of Engineering, University of Glasgow, Glasgow, G12 8QQ, United Kingdom b c A R T I C L E I N F O A B S T R A C T Handling editor: Mingzhou Jin Heat batteries show outstanding charging and discharging thermal energy capability with the latent heat of fusion (Hm) for solar thermal application In this work, novel magnesium nitrate hexahydrate (MNH) based heat batteries are fabricated and tested for 1000 sequential thermal cycles The MNH heat batteries demonstrate a high level of operational stability with the least corrosive rate Real-time performance of the heat batteries was studied by incorporating them in the parabolic solar thermal cooking module The developed MNH heat batteries based solar cooking module illustrates excellent heat retention capacity over h after the sunshine Temperature profiles under no load and full load conditions reveal the moderation and enhancement in the solar thermal cooking module’s operational efficiencies The solar cooking module’s efficiency with the heat batteries reaches a maximum of 22.8% and 42.5%, under no load and full load conditions, respectively Real-time cooking ca pacity with different edible materials under both outdoor and indoor environments proves the effective per formance Further, it is estimated that MNH heat batteries can be in full performance for a minimum of years with maintenance-free and emission-free operations Keywords: Salt hydrate Thermal cycling Corrosion rate Heat battery Solar cooking Introduction With increasing global energy demand, conventional fossil fuel sources induce global warming by releasing toxic greenhouse gases into the atmosphere (Sharif et al., 2021) In this aspect, sustainable and renewable energy sources for day-to-day activities can benefit both environmentally and economically (Barba et al., 2019; Zayed et al., 2021) As reported, the process of heating alone consumes about 35% of the global electricity generated, whereas the total efficiency of any fossil fuel-based power plant is limited to a maximum of 25% (Ravi Kumar et al., 2021; Zhou et al., 2020) These factors lead us in search of the surplus source of energy for heating and cooling applications, wide spread solar insolation in the atmosphere stands as the only potential source of renewable energy (Liu et al., 2020; Ma et al., 2019) Solar insolation in the atmosphere can be harvested into heat or electrical power by solar conversion technologies As most daily processes require a medium temperature of around 150 ◦ C, solar thermal energy conver sion can fulfil industrial and household applications (Cardenas et al., 2017; Huang et al., 2019) Solar thermal cooking stands as a powerful application that avoids atmospheric pollution through biomass and * Corresponding author ** Corresponding author E-mail addresses: sukruedeen@nu.ac.th (S Sukchai), karthi230407@gmail.com (K Velmurugan) Authors contributed equally https://doi.org/10.1016/j.jclepro.2021.129223 Received April 2021; Received in revised form 16 September 2021; Accepted 30 September 2021 Available online October 2021 0959-6526/© 2021 Elsevier Ltd All rights reserved S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 12th week However, aluminum CR increased to 15 mg/cm2-yr Overall, stainless steel (SS) shows a lower CR for SP21E than copper (Cu) and other materials (Ferrer et al., 2015) Supportively, P Moreno et al study also reveals that SS has low CR for MgSO4.7H2O, Zn(NO3)2.4H2O, Na2S2O3.5H2O and K3PO4.7H2O over 12 weeks immersion of PCMs (Moreno et al., 2014) Salt molecules are initiating the corrosion process with some specific metals and it is necessary to find the suitable metal for the selected inorganic PCM to avoid the corrosion and leakage issue (Calabrese et al., 2019; Dindi et al., 2020; Jaya Krishna and Shinde, 2017) The final step is utilizing the selected PCM for solar thermal cooking application directly as salt hydrate does not require any thermal additives like organic PCMs Several types of solar cooking techniques exist, among which parabolic dish type solar cooking unit gains atten tion for community cooking As a parabolic dish type cooker is not attached to the cooking unit like a box type, favors handling the cooking container at peak sunshine hours also by non-focusing the container ´lez-Avil´es et al., 2018; whereas it is difficult for box type cooking (Gonza Lecuona et al., 2013) Moreover, once the cooking items are filled in a cooking pot and placed inside the box, it is difficult to open and stir the cooking item which makes parabolic dish type cooker is technical feasible for community cooking (Ahmed et al., 2020; Onokwai et al., 2019; Senthil, 2021) Other than easy handling, parabolic cooker can track the sun in both single axis and double axis to enhance the thermal efficiency and cooking speed (Al-Soud et al., 2010; Devan et al., 2020) The above literature study and Table reveals that selecting salt hy drates can simplify the thermal conduction resistance during char ging/discharging period with the advantage of being non-flammable ˙ and low cost Initially few salt hydrates were examined for sequential thermal cycling due to its resistance in supercooling effect and phase separation In this aspect, our study focuses on the use of novel MNH heat batteries for construction of the cooking module Here we have investigated in detail the properties of MNH heat battery’s performance ˙ addi for over 1000 continuous heating and cooling thermal cycles In tion, corrosion study is performed to prioritize the lifetime for solar cooking module without damage or performance degradation We perform the real-time testing for the solar cooking module under load and no-load conditions to emphasis on the advantages of MNH heat batteries We report over 50% increase in the parabolic solar cooking modules performance with the incorporation of heat battery design in the system natural gas combustion (Mawire et al., 2020; Singh, 2021) (Hosseinza deh et al., 2021) On the other hand, the solar cooking method maintains the nutrients level in the cooking, especially as compared to the con ventional cooking method, following that taste and aroma are also maintained at a high degree level (Saxena et al., 2018) Various tech nologies in solar thermal energy harvesting for cooking applications have been developed in recent years, like parabolic concentrator mod ule, box-type module, pressurized steam generator module and others (Naveen et al., 2020; Palanikumar et al., 2019; Vengadesan and Senthil, 2021) However, solar insolation uncertainty around the day reminds the importance of using a buffered heat storage system for uninterrupted ˙ the recent decades, phase change materials based cooking service In heat batteries are widely examined for solar cooking module owing to the high latent heat of fusion with stable charging and discharging temperature, unlike sensible heat materials (Coccia et al., 2020; Omara et al., 2020; Saxena et al., 2011) Initially, selecting PCM types is the key parameter in thermal application, depending upon the use temperature For medium tem perature applications, PCMs like paraffin wax, fatty acids and salt hy drates are widely used (Omara et al., 2020) Though paraffin waxes suffer the limitation in operating temperature, fatty acids are limited to their low thermal conductivity (KPCM) compared to salt hydrates (Kar thikeyan et al., 2020) Secondly, selecting PCM charging or melting temperature is the necessary task for any thermal application as PCM’s operation is truly relying on its Tm (Velmurugan et al., 2021) Several reports prove that salt hydrates based PCMs are widely examined for medium temperature application owing to higher KPCM and non-flammable (N Kumar et al., 2019; Yang et al., 2020) Some works on salt hydrates like calcium chloride hexahydrate were studied for over 1000 heating and cooling thermal cycles to examine the thermal sta bility of the PCM for longer period operation, where at every 100th thermal cycle, PCMs samples were examined for digital scanning calo rimeter (DSC) analysis to find the stability of the PCM Tm and Hm Minor variation in Tm and Hm is noted for the 10th and 100th thermal cycles; after the 200th cycle, variation becomes negligible in finding PCM sta bility Calcium chloride hexahydrate shows stable endothermic and exothermic peaks at the 1000th thermal cycle, which means this PCM is highly recommended for storing thermal energy (Tyagi and Buddhi, 2008) El-Sebaii et al examined magnesium chloride hexahydrate for solar cooking purposes by accelerating continuous 1000 heating and cooling cycles Noticeable variation in PCM Tm and Hm was observed over 1000 thermal cycle though it is negotiable in terms of thermal stability and the supercooling effect occurred up to 300 thermal cycles within a range of ◦ C–3.2 ◦ C, beyond 500th thermal cycle supercooling becomes zero which concludes magnesium chloride hexahydrate is the best material for thermal energy storage (El-Sebaii et al., 2011) How ever, salt hydrate has an unstable property such as super cooling and phase separation after several hundreds of thermal cycling, which means some parts of the PCMs will remain solid or liquid (Peng et al., 2019; Tan et al., 2020) Purohit and Sistla reported incongruence in several inor ganic PCMs melting and solidification process for Na2S2O3.5H2O, Al2(SO4)3.8H2O, Na2SO4.10H2O, Na2HPO4.12H2O, and Na2HPO4.7H2O (Purohit & Sistla) Evidently, Shukla et al.’s study reveals that sodium hydroxide and Disodium tetra borate performed the 1st thermal cycle and for the 2nd thermal cycling, it does not melt even at high temper ature Following that, ferric nitrate shows insignificant performance in cooling cycling, after providing sufficient time, also failed to become solid and barium hydroxide failed to melt at 1st cycle (Shukla et al., 2008) To avoid the failure in storing thermal energy, it is mandatory to examine the stability of novel salt hydrates by accelerating continuous heating and cooling cycles (Khan et al., 2016; Schmit et al., 2020) Thirdly, salt hydrates show high corrosive with metal over a longer period of storage in metal tank (El-Sebaii et al., 2009; Salgado et al., 2020; Vasu et al., 2017) SP21E inorganic salt shows 7–8 mg/cm2-yr of corrosion rate (CR) for aluminium (Al) and carbon (C) over the first week; gradually, carbon CR decreased to less than mg/cm2-yr over Material and methods Thailand lies above the equatorial line with adequate sunshine of 300 days minimum in a year Considering this abundant solar potential in Thailand, the solar cooking method is widely encouraged to reduce fossil fuel consumption On the other hand, solar cooking should be efficient, maintenance-free and low-budget system As mentioned earlier, several types of solar cooking modules exist in the commercial market Most of them are high cost, fragile, and not convenient for offsunshine hour cooking due to a lack of thermal energy storage facility This study purposes a parabolic concentrator solar cooking module with a hassle-free cooking process as the cooking primarily relies on boiling type At the same time, a large area of collector can harvest the heat energy and concentrate it into a smaller receiver/cooking pot without wasting the heat energy In this study, a standard design of parabolic solar concentrator with a radius of 0.75 m and a depth of 0.27 m are used From this structural design, the focal length of 0.52 m was calculated using the formula: f = D2 /16h, where D and h are the diameter and depth, respectively For efficient focusing of the solar irradiance, a high-quality solar reflection mirror is attached along the surface area of the parabolic concentrator A parabolic solar concentrator with a focal length of 0.52 m is used in this study with a cooking power of 125 W In this aspect, to develop an efficient and sustainable cooking system for the remote community, we Location Experimental tool Cooker type Heat storage Methodology Outcomes Saxena et al (Saxena et al., 2020) India Real-time outdoor cooking Solar box type Paraffin wax Carbon powder, mixed with paraffin wax and paraffin wax, are used as three different thermal energy storage materials filled in copper tubes and placed in the bottom of the box type cooker for higher heat retention Coccia et al (Coccia et al., 2018) Italy Real-time outdoor cooking Solar box type This study selected a higher melting temperature PCM (145.14 ◦ C) for faster cooking after sunshine hours Saxena et al (Saxena, 2013) India Real-time outdoor cooking Solar box type Ternary mixture of nitrate and nitrate salts Stearic acid Saxena and Karakilcik (Saxena and Karakilcik, 2017) Saxena and Agarval (Saxena and Agarwal, 2018) India Real-time outdoor cooking Solar box type Sand: Carbon (4:6) The natural and readily available materials like sand and carbon are used as thermal energy storage material in a ratio of 4:6 are examined as heat batteries for box type cooker India Real-time outdoor condition Solar box type Small hollow copper balls A duct-like solar air heater is introduced to enhance the convection heat mode with the help of DC fans and a 200 W halogen lamp placed inside the duct to improve the heat convection Khallaf et al (Khallaf et al., 2020) Egypt Numerical simulation and real time outdoor condition Quonset solar cooker NA Light weight and dome type transparent solar cooker is designed to achieve higher heat absorption Cocking layer is separated into two for increasing the operational performance of the system Kanyowa et al (Kanyowa et al., 2021) India Real-time outdoor condition Scheffler dish type solar cooker NA Scheffler dish type solar cooker is examined to find the losses that occur during the operation as the system which is installed in 2001 at Om Shanti Retreat Center, Haryana, India Every day 6000 meals are cooked in a day with a maximum of 200 days per year Keith et al (Keith et al., 2019) Australia Real time outdoor condition Parabolic dish type solar cooker Stearic acid Incorporation of stearic acid in the cooking pot enables to maintain the stable temperature in the active layer, whereas the cooking can be done under the regulated temperature The amount of PCM filled in the cooking pot is less, favouring the cooked food item hot for later serving purposes Senthil (Senthil, 2021) India Real time outdoor condition Parabolic dish type solar cooker Paraffin wax Internal thermal heat distributions transfer the heat from the receiving focal point to PCM and the active cooking layer It is noted that paraffin wax-associated box-type solar cooker yields better performance under real-time conditions Comparatively, pure carbon powder and paraffin wax attained lower efficiency than paraffin wax-carbon composite Effective time responses are studied for developing a novel thermal energy storage system for box type cooking of rice, egg and mutton takes 71, 98 and 121 for complete cooking, respectively It is noted that solar salt maintains the cooking chamber temperature between 170 ◦ C and 130 ◦ C, which is 107.98% higher than the conventional solar cooker Maximum stagnation temperature in the cooking layer reached 145 ◦ C Stearic acid as heat battery retained the heat inside the cooking layer temperature about 64 ◦ C, which can be utilized to cook rice, boiling milk, beans, fishes and other low cooking temperature items during the off-sunshine hours During the peak sunshine hour, cooking layer temperature reached the maximum of 136 ◦ C A sand: carbon as heat battery achieved a cooking power and thermal efficiency of 44.81% and is 37.1%, respectively A duct-type solar air heat channel fastens the cooking process as compared to the conventional box type cooker Copper hollow balls are placed over the absorber plate to increase the heat transfer from the absorber plate to the cooking pot as copper thermal conductivity is high Higher cooking efficiency achieved for sliced potatoes, rice and egg as compared to pulses and boneless mutton Overall thermal efficiency is attained maximum of 45.11% and cooking power is 60.20 W The novel Quonset solar cooker design reduces the radiation heat loss and infrared loss during the sunshine hours Separation of two cooking compartments increases the incident energy on the absorber plate as it is partitioned by a reflecting mirror, which acts as an additional source to the solar cooker Glycerol is used as cooking fluid to increase the efficiency from to 92% whereas the water lies around 6–35% Due to the age of the system, several losses occur in the system during cooking process This system performed almost every sunshine hour to cook the meal of 6000 per day It was noted that thermal efficiency of the system claimed to be 70–80% and overall efficiency of up to 25% Real-time cooking study reveals that average cooking time for rice is 71 which is lower than barely and lentil dishes with an average cooking time of 92 and 95 min, respectively It is recommended that the developed parabolic dish type solar cooker payback period is less than 52 weeks for the four membered families To reach the water temperature at 90 ◦ C, with and without PCM takes 120 and 90 min, respectively PCM associated cooking pot takes more time to heat the water though it performs stable operation and heat retention for off sunshine cooking purposes Two different configurations of the box-type solar cooker were developed and examined with stearic acid as heat battery for off sunshine cooking purpose (continued on next page) Journal of Cleaner Production 324 (2021) 129223 Author S.M.S Rekha et al Table Recent literature study of heat batteries associated solar cooker Table Experimental instrument range Range Hotplate Sensitive balance (METTLER TOLEDO) Graphtec datalogger K-type thermocouple Pyranometer Fluke TiX560 0–500 ◦ C 0–310 g 20 channel, − 100 ◦ C–1370 ◦ C − 200 ◦ C–1260 ◦ C 0–4000 W/m2 90 Hz, − 20 ◦ C–1200 ◦ C Result and discussion Parabolic dish type solar cooker Magnesium Nitrate is a naturally occurring inorganic compound with utmost attraction towards water molecules, forming a stable Magnesium Nitrate hexahydrate (MNH) MNH has a monoclinic crystal structure in the space group of P21/c with water molecules attached to the Mg ions, as illustrated in Fig (a) MNH naturally possesses the property to store thermal energy through phase transformation in the material and release the stored energy in latent heat and sensible heat This property makes MNH a low-cost, reliable, and earth-abundant Phase Change Material (PCM) in the salt hydrate group Fig shows the in-depth analysis of the change in material properties at the interval of 200 cycles up to 1000 thermal cycles One thermal cycle consists of a material solid-liquid melting phase and a liquid to solidification phase This thermal cycle study explains the material’s stability over an oper ational lifetime, corrosive nature, and dissociation chemistry, which are mandatory before employing the material for real-time applications An excellent Phase Change Material stands without any change in latent heat, weight loss and melting time over 1000 thermal cycles (A Sharma and Shukla, 2015; R K Sharma et al., 2016) Generally, the thermal dissociation in metal salt hydrate based PCM involves the release of weakly bonded water molecules followed by nitrogen, carbon as CO2 and NO2 based on their chemical composition In the case of MNH, the pristine material exhibits phase transformation at around 90 ◦ C as observed from the DSC curve plot in Fig (c), the dissociation starts to Real time outdoor condition Thailand Present study Instrument have fabricated a well-investigated MNH heat batteries-based solar cooking module for uninterrupted thermal energy supply during the day and night Selected novel MNH as heat battery was used for studying the variation in Tmelt and Hm under repetitive thermal cycles Thermal cy cles were conducted using hot plates and k-type thermocouples for over 1000 cycles For every 200 cycles, the weight change, Hm, melting temperature were recorded Corresponding studies for analyzing the chemical bonding dissociation was performed using PerkinElmer FT-IR spectrometer The UV–Vis absorbance spectrum used to observe water molecules’ dissociation was performed using PerkinElmer UV–Vis spectrometer Differential Scanning Calorimetry was performed using Mettler Toledo DSC1 for every 200th thermal cycle Corrosion analysis was performed by calculating the surface roughness profile analyzed from Olympus BH2 optical microscopy images Performance of MNH based solar cooking module experimented at School of Renewable En ergy and Smart Grid Technology (SGtech) in Naresuan University, Thailand Step 1: MNH filled in all 28 PCM tubes (heat battery), heat transfer fluid is filled next to the PCM layer and the active layer is empty (without load) and step 2: MNH filled in all 28 PCM tubes, heat transfer fluid is filled next to the PCM layer and active layer is filled with water (with load) K-type thermocouples are used to measure the system’s temperatures, thermocouples in PCM tubes with equal intervals of PCM tubes, one thermocouple inside the heat transfer fluid layer, cooking layer and focal receiver point of the bottom (cooking pot) All temperatures are recorded in min’ intervals using Graphtec Datalogger and solar radiation is collected from PV research unit, School of Renewable Energy and Smart Grid Technology (SGtech) in Naresuan University Table shows the instruments operating range used in this study MNH Stearic acid filled in a rectangular container with a maximum capacity of 75% in each container kW pump is used to circulate the heat transfer fluid between the collector to receiver and receiver to cooking oven using different mass flow rate Parabolic concentrator with a diameter of 1.495 m and depth of 0.268 m is used in this study with a focal length of 0.52 and cooking power of 125 W This parabolic dish type solar cooker found to be interesting in cooking for small community To ensure the lifetime and mechanical breakage from the natural or artificial harm, solar reflecting glasses are made into the dimension of 2.5 sq.cm Compared to the conventional system, the use of MNH as heat batteries for solar cooking supports efficient functioning with over 1000 thermal cycles The main novelty of this study is that MNH is DSC examines thermal stability, and other form of material analyzing tools and later examined for solar cooking purpose under Thailand climatic condition India Sasi Kumar and Pandian (S Kumar and Pandian, 2019) Real time outdoor condition parabolic trough collector Stearic acid Overall average efficiency for energy and exergy are 22% and 2.6%, respectively At peak sunshine, when the rim angle is 82◦ heat gain of the receiver is 2095 W and storage tank capacity is 13 kW Waste engine oil as fluid performs better than water which is times higher The system’s mechanical stability is noted throughout the study, and zero solar reflecting mirror breakage is noted MNH as green batteries for storing the heat energy gained higher response in stabilizing the temperature inside the cooking layer Based on the corrosion test conducted against aluminum and stainless steel, a high corrosion rate was noticed for aluminum, leading to the use of stainless steel in MNH-assisted solar cooker fabrication In both no load and full load condition, MNH associated solar receiver performs better and higher efficiencies are extracted In real time cooking condition, 200 g of bean takes not more than 10 min, egg boils in 10 min, rice takes 20 and some vegetable takes 35 at maximum Keeping a cooking pot in insulation holds the temperature inside the cooking layer till the next day’s sunshine with a reasonable decline in temperature drop over the time Further, it is recommended that this system is suitable for medium community scale, low cost, no training is required to operate the system, easy separation of parabolic dish and receiver part makes maintenance-free system Methodology Cooker type Experimental tool Location Author Table (continued ) Journal of Cleaner Production 324 (2021) 129223 Heat storage Outcomes S.M.S Rekha et al S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Fig (a) Crystal structure and bonding representation of the Mg(NO3)2.6H2O Thermal cycle dependent changes in the Phase Change Materials properties up to 1000 cycles (b) UV–Visible absorbance spectrum (c) DSC curves showing the melting point of the material (d) XRD pattern of the material explaining the disso ciations (e) FT-IR spectrum showing the bonding transformations (f) Mass of the material (g) Time taken for melting and solidification of the material appear after the 600th cycle where the Magnesium nitrate hexahydrate starts to lose the water molecules slowly forming magnesium nitrate monohydrate structure then after the 800th thermal cycle they start to form the Magnesium oxide phase as they release NO2 gases from Mg (NO3)2 composition This thermally induced chemical dissociation is evidently observed from the XRD pattern recorded at each thermal cycle stage Fourier Transform Infrared spectroscopy reveals this mechanism with the disappearance of peaks around 800 cm− 1, 1300 cm− and 1700 cm− 1, which corresponds to the hydrogen and nitrogen bonding in water molecules and Mg(NO3)2 structure Differential Scanning Calorimetry analysis reveals the linearly decreasing melting temperature of the PCM from around 90 ◦ C–80 ◦ C The melting temperature broadens clearly, signifying the change in the chemical composition of the material induced by thermal stress The change in the melting temperature directly affects the material’s thermal energy storage capacity, which means the reduction in heat capacity and the inability to steady release of heat when the PCM discharges However, the chemical stability of MNH up to 800th thermal cycle proves its efficiency as a low-cost S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 high-performance PCM in the salt hydrates group Fig (f) and (g) show the material mass loss over the thermal cycle as it loses the water molecules and hardens to form MgO crystals Another advantage over MNH use is the slower and stable temperature heat discharging prop erty, as seen in Fig (g), demonstrating slower solidification over the melting time Additionally, the UV–Vis absorbance spectra support our claim for the stable and slower chemical dissociation in MNH over the long 1000 thermal cycles The absorbance increases with the increase in the number of thermal cycles because the pristine MNH are transparent to visible light with more water molecules They start to lose the water molecules the capacity to absorb light for the wide bandgap MgO crys tals Thus, the detailed material property analysis proves that the MNH are highly efficient over 800 operating cycles which is more than years of time, making the system economically beneficial Low and medium temperature phase change materials are mostly paraffin waxes and metallic salt hydrates in high thermal conductive aluminum or stainless-steel enclosures Hence their nature to withstand the entire system lifetime inside the container without corroding or damaging is mandatory (Ferrer et al., 2015; Vasu et al., 2017) We performed the corrosion study for the MNH using the stainless-steel container, in which for every 200 thermal cycles the stainless-steel container was imaged using optical microscope and scanning electron microscope as shown in Fig The captured surface images reveal the impact of MNH etching throughout thermal cycles The optical micro scope images captured analyzed the ImageJ software to extract the surface profile and calculate the roughness parameter Ra The surface plot clearly demonstrates the increase in the container surface’s roughness profile over the thermal cycles as the value of Ra varies be tween 80 and 220 with an average value of 120 The analysis shows that no obvious intensified corrosion behaviors are observed between particular cycles For the thermal cycles after 600, the roughness varies widely as the MNH becomes more concentrated oxide Since magnesium nitrate monohydrate formation, the corrosion nature seems to increase as the MgO concentration increases In the case of 800th and 1000th thermal cycles the surfaces are observed to be etched deeply, signifying a larger roughness profile The SEM image shows the in-depth investi gation on the etching profile of MNH, which starts after the 600th cycle Moreover, no aggressive corrosion behaviour was observed at charging cycle, the heat storage capacity of the PCM is not affected by the corrosion in the container surface Supporting the material property shown in Fig 1, the corrosion studies also reveal that the MNH performs as a good PCM with least corrosive nature for a maximum of up to 800 thermal cycles, which benefits any system economically (Ferrer et al., 2015) From the above-detailed analysis of the phase change stability and operational lifetime, we implement the real-time demonstration of the MNH-PCM based parabolic solar concentrator cooking module We intend to enhance the well-established solar cooking module’s efficiency with incorporating MNH-PCM for stable heat flow around the focal point, thereby providing an effective low-loss cooking process Heat Transfer Networks explains the direction of the heat flow and the po tential resistance involved in it Here we investigate the difference and the advantage of using MNH-PCMs in the solar concentrator cooking module Fig (a) shows the heat transfer mechanism involved in the parabolic concentrator cooker design with and without MNH-PCM incorporation In this system, cooking process involves three modes of heat transfer path: (1) aperture focal at direct cooking pot; (2) aperture focal at heat transfer fluid layer and (3) aperture focal at PCM tubes Heat transfer mode mechanism involves direct transfer of heat energy from the solar energy concentration aperture region at the receiver’s focal point to the active layer by conduction Depending on the type, heat energy inside the active layer is transferred via conduction or convection to the load In heat transfer mode 2, an intermediate buffer layer is added, which holds a heat conduction fluid that moderates the heat flow between the solar energy concentrator and the active layer The heat transfer layer directs the heat flow to the active layer from the focal point via conduction and convection, enabling a stable tempera ture supply to the load via the active layer without any heat loss In heat transfer mode 3, we involve the function of MNH-PCM and the heat transfer fluid layers between the incident solar concentrator focal aperture and the active layer for enhancing the efficiency of the para bolic solar energy concentrated cooking module Here the PCM stored in the stainless-steel tube receives the thermal energy from the concen trator and stores it in specific heat capacity through phase change, transfers the surplus uniformly to the heat transfer fluid The heat transfer fluid spreads the thermal energy uniformly along the surface of the active layer, thereby increasing the system’s efficiency both under load and without load conditions It should be noted that during realtime performance, the active layer will receive thermal energy from the above mentioned three modes of heat flow mechanisms The active layer of the module transfers thermal energy directly to the load, which is the cooking materials Further, the parabolic solar concentrator-based cooking module with the design as mentioned in Fig is performed The increase in the module’s efficiency with the use of MNH-PCM (heat battery) is studied through the temperature profile analysis under a good solar isolation day under no load and full load conditions, as shown in Fig Here the full load conditions are performed with the active layer (i.e., cooking area) fully filled with water and for no-load condition the active layer was left empty MNH-PCM are filled in the PCM tubes as shown in Fig (b) and (c), heat transfer fluid is filled and perfectly sealed to prevent leaks We understand that for the intermediate temperature (120–240 ◦ C) solar cooking module, the use of water as load test fluid will not help in determining the total system performance Hence the use of test load fluid with higher boiling point must be used to determine the system performance as mentioned by Sagade et al.(A A Sagade et al., 2018) However, our system operating temperature is demonstrated to a maximum of 120 ◦ C only And in order to demonstrate the real-time cooking capability of our system, we have used water as load test fluid and cooking medium in our experiment Under no load condition for the recorded solar irradiance of the day, the active layer temperature (TCOOK) rises to a maximum of 77 ◦ C at the peak sunshine hours Whereas the parabolic solar concentrator focal receiver point (TFOCAL) reaches to a maximum of 84 ◦ C which helps in charging the MNH heat battery by changing to liquid phase and from there the thermal energy (TPCM) released by the heat batteries are almost steady throughout the day as observed in Fig (d) On the contrary, it is observed that the temperature of heat transfer fluid shoots to 85 ◦ C, equivalent to the TFOCAL The reason behind this massive temperature difference is that the MNH has high energy density of 121.10 J/g and the low specific heat capacity of air in the active layer, this factor along with the continuous heating source from solar concentrator increases the heat transfer fluid temperature (TFLUID) significantly As the active layer is encapsulated to prevent heat loss it attains vacuum as there is no load, more TFOCAL in creates higher TCOOK, which is transferred to the heat transfer fluid as the active layer is in a vacuum and it starts to increase the TFLUID abruptly On the other hand, the active layer receives the heat through many scenarios, as shown in Fig (a) If the heat is transferred by single channel which is through PCM, heat transfer fluid and active layer, there will be a minor initiation in creating a vacuum under no load test condition But the active layer receives a minor amount of heat directly from the parabolic dish how ever, this is under control when the active layer is filled with cooking item and it never over-shoot the temperature Unfortunately, leaving the active layer empty with a closed environment behaves opposite to the full load condition Generally, no load test is performed to find the operational mechanism and consistency of the developed system, this study reveals that active layer must be filled with cooking stuff unless the vacuum inside the active layer could increase the heat transfer fluid temperature as well as PCM temperature which could degrade the thermophysical property of both materials Unlike, vacuum inside the active layer could harm the total system and those who are operating the S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Fig Corrosion analysis of MNH in Stainless steel container under different thermal cycles using the representation of Optical Microscope images (column 1), Roughness plot Ra (column 2), Scanning electron microscopy images (column 3) S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Fig (a) Represents the Heat Transfer Network model in the system (b) and (c) shows the cooking container, the PCM container tubes (d) solar concentrator dish construction model from the parabolic concentrator Necessity of MNH heat batteries in this study is clearly noticed in Fig (h), MNH assisted solar cooker effi ciency reached a maximum of 24% and without MNH heat batteries is 8.3% only This no-load study proves that the parabolic solar concentrator-based cooking module without MNH heat batteries fails to utilize the entire received thermal energy with no stabilization in ther mal receiver temperature, which lowers the system’s efficiency Under full load condition, water is filled in the thermal receiver’s active layer, resulting in huge thermal variation observed under direct sun exposure as shown in Fig (e) As the full load testing was also system A decrease in solar irradiance directly diminishes the TFOCAL though TCOOK temperature is maintained stably with the steady supply from the MNH heat batteries As mentioned earlier, total 28 MNH heat batteries are attached to the thermal receiver module for uninterrupted thermal supply to the active layer and load material Fig (f) demonstrates the uniform temperature profile of MNH heat batteries at different places proves the MNH attached thermal receiver’s effectiveness There is no major fluctuation in PCM tubes until 14:00 which means the receiver’s focal point is high and entire cooking pot receives the stable heat source S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Fig (a)MNH-PCM based Parabolic Solar concentrator cooking system (b) and (c) Infrared images of parabolic solar concentrator and thermal energy receiver at focal point Solar irradiance dependent temperature profile of different solar cooking module layers (d) without load and (e) with load (f) and (g) demonstrate the uniform temperature profile in the PCM storage containers under no load and load, respectively (h) and (i) demonstrates the efficiency of the system under no load and load conditions, respectively S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 performed in a day filled with good solar irradiance, the results show a maximum TFOCAL of up to 120 ◦ C The heat batteries are charged from the TFOCAL, which reaches a peak temperature of 107 ◦ C and TFLUID showing 102 ◦ C with the active layer temperature reaching 100 ◦ C as the load keeps drawing the heat constantly The heat batteries provide constant heat energy for the cooking module even as the solar irradiance starts to fall at the end of the day Fig (g) demonstrates a uniform temperature profile for the heat batteries over the day The use of heat batteries in the solar cooking module hugely benefits by regulating the temperature supply to the active and load layers, thereby protecting the cooking materials Under any abnormal fluctuations in the solar irradiance, the heat batteries help moderate the active layer temperature to maintain the system’s efficiency constant and be suitable for the cooking condi tions throughout the day The efficiency of the parabolic solar cooking module associated with MNH heat battery is the ratio of thermal energy in the cooking receiver pot (Qoutput) (including the thermal energy presents in the PCM (QPCM), heat transfer fluid (QFLUID) and cooking layer (QCOOK)) to the incident energy of parabolic dish/cooking pot (Qinput) as expressed in Eq (1) ηwith MNH = Qoutput QPCM + QFLUID + QCOOK ( ) = Qinput I ηo Ap + Ac Δt = mL + mcp− FLUID ΔTFLUID+ mcp− COOK ΔTCOOK ( ) I ηo Ap + Ac Δt (1) For parabolic solar cooking module without the MNH heat battery, the efficiency is calculated using Eq (2) where the cooking or receiving part of the parabolic dish is operated with only heat transfer fluid layer and cooking layer, in this concept, the system encounters sudden ther mal fluctuations with respect to solar radiation: ηwithout MNH = Qoutput mcp− = Qinput FLUID ΔTFLUID + mcp− COOK ΔTCOOK ( ) I ηo Ap + AC Δt (2) Fig (i) demonstrates about 50% rise in the cooking system effi ciency with load compared to no load condition The investigation shows that the use of MNH heat batteries significantly helps to grow the system efficiency during the day irrespective of the solar irradiance fluctuations The operational performance of MNH heat batteries and heat Fig Infrared thermal images of the parabolic solar concentrator and thermal receiver under real-time operating conditions 10 S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Fig (a) Full day profile of solar irradiance and PCM temperature and (b) Heat retention capacity of the system after off-sunshine hours between (17:30 to 22:00 h) Table Time taken for cooking different food materials Application Mode of cooking Cooking materials Cooking batch in a day Quantity (g) Cooking time (min) Boiling Outdoor Outdoor Outdoor Outdoor Outdoor Indoor Indoor Outdoor Outdoor Outdoor Green bean Green bean Green bean Green bean Red bean Red bean Red bean Chicken Rice Yellow bean Yellow bean porridge Potato Sweet potato Egg Pasta Egg Egg Vegetables Vegetables 200 200 200 200 200 200 200 250 250 200 15 10 10 10 20 15 30 10 20 10 200 10 250 250 220 35 15 30 4 pieces 250 piece piece 200 200 15 15 20 15 35 60 Boiling Outdoor Boiling Frying Indoor Outdoor Outdoor Outdoor Indoor Outdoor Outdoor Outdoor Outdoor Fig (a) Heat retention of MNH Heat batteries with respect to Solar irradi ance (b) Real-time performance of the MNH heat batteries based Solar parabolic cooking module with different cooking ingredients the direction as shown in Fig (i) and Fig (j) Table demonstrates the time take for cooking different food materials both during the sun shine and after sunshine hours To observe the thermal response of the developed heat-battery-based solar cooking module, we measured the temperature profile of an entire day between 7:00 a.m to 10:00 p.m., demonstrating the heat retention property of the developed MNH-assisted solar cooker at a fluctuating solar irradiation profile as shown in Fig Heat retention time in solar cooking system plays the important role in determining the system performance and capacity during fluctuations in solar irradiance (A A Sagade et al., 2019) To overcome this disadvantage of fluctuating solar irradiance during the day and to enlarge the heat retention time, in our system we have incorporated the use of MNH heat batteries The per formance of these heat batteries in improving the system efficiencies during off sunshine hours are widely discussed and depicted experi mentally in Fig 6(a) and (b) Table and Fig shows the different cooking materials of both outdoor and indoor operating condition under a larger heat retention time Table shows the average time taken to cook Green bean and mung split bean in outdoor conditions is 3500 s For Red bean and Mung split bean the average time taken to cook indoor conditions is 7000 s and 7500 s respectively transfer fluid associated with the thermal receiver part of the cooking module are studied using the thermal imaging infrared profile as shown in Fig During early sunshine hours, side view of the thermal receiver temperature around its focal point is maintained at 69.2 ◦ C and the heat battery temperature at 47.3 ◦ C At top view, active layer temperature shows about 52 ◦ C at center point and the area around heat transfer fluid reached to 59.4 ◦ C During peak sunshine, focal point temperature corresponds a maximum of 115.7 ◦ C, which is lower than the early sunshine hour profile for the heat batteries are still in charging mode During the sunshine, the receiver’s bottom and top view temperature is 98.5 ◦ C and 72.1 ◦ C, respectively Fig (h) shows the importance of MNH heat batteries for the concentrated solar cooking module, during off sunshine parabolic reflector temperature is 38 ◦ C and heat batteries temperature is 59.5 ◦ C Without MNH, the thermal receiver temperature would be lesser than reflector temperature, lowering the system’s thermal efficiency The parabolic concentrator cooking module’s main benefit is the convenience of using it during off-sunshine hours (Ebers viller and Jetter, 2020; Zamani et al., 2015) In the present study, the thermal receiver is designed in a way to remove from the stand and cook indoors with the help of MNH heat batteries It is necessary to keep in action to insulate the thermal receiver as MNH dissipates heat in both 3.1 Cooking pot heat loss Cooking pot or receiver is a cylindrical shaped container that expe riences mainly three mode of heat transfer loss during the charging period firstly lateral surface wall of the cooking pot losses some of the 11 S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 heat energy by radiation and convection to the sky and surroundings due to sky and wind speed (QSL) Secondly, top surface of the cooking pot losses thermal energy to the sky and surroundings, however, top surface is combined with surface of PCM, heat transfer fluid and cooking/active layer which dissipates freely to the surrounding (QTL) The final mode of heat loss is through the bottom surface of the cooking pot, which is a similar mode of heat loss compared to top surface heat loss (QBL) Based on the heat loss analysis the total thermal loss in the system is tabulated in Table Lateral surface wall of the cooking pot loss, measurement devices are calibrated, and the possible error percentage are listed in Table 3.3 Safety issues MNH is non-toxic material, and it is well sealed in the PCM tubes where the leakage is zero to cooking item or other layers; moreover, heat transfer fluid layer presents in between PCM tubes and cooking layer However, during cooking it is necessary to wear gloves to resist the heat from the cooking pot and must step aside the focal point of the receiver to avoid the heat shock from the parabolic dish Overall, developed parabolic dish type solar cooker is safety for cooking purposes in both outdoor and indoor cooking and must handle with little care compared to conventional electric or LPG cooking In this system, cooking pot is not attached to the parabolic dish, which eases cleaning the cooking layer after cooking If necessary, parabolic dish focal point can be moved from the cooking pot for cleaning purposes Secondly, this system re quires less maintenance as it is free from electrical device, if the system is accidently damaged it requires maintenance Refilling the PCM and heat transfer fluid will be done by anyone without looking for a tech nical expert Overall, this system is suitable for any grade of citizens in the country to operate and maintenance purposes however care must be taken during the operation or refilling the MNH and heat transfer fluid (3) QSL = USL ASL (TPCMtube − Tair ) where, 1 ΔXPCMtube = + USL hCSL + hRSL KPCMtube hCSL = 5.7 + (3.8 ×wind) and hRSL = (TPCMtube + TSky )2 Top surface of the cooking pot loss, ( ) QTL = UTL Ttop − Tair εPCMtube σ(TPCMtube + TSky ) (4) where, 1 ΔXcookingpot = + UTL hCTL + hRTL Kcookingpot Conclusion hCTL = [2.8 + (3 × wind)] × ATL This study demonstrates the heat batteries assisted solar parabolic [ ( )( )2 ] [ ( )( )2 ] hRTL = εPCMtube σ APCMTL TPCMtube + TSky TPCMtube + TSky + εFLUIDcover σ AFLUIDTL TFLUIDcover + TSky TFLUIDcover + TSky [ ( )( )2 ] + εcookinglayercover σ AcookinglayerTL Tcookinglayercover + TSky Tcookinglayercover + TSky Bottom surface of the cooking pot loss, cooking module for uninterrupted operation during the sunshine and off-sunshine hours Initially, we demonstrated the importance of selecting efficient heat battery materials for medium temperature latent heat storage with a detailed analysis of their thermal cycle performance and corrosion nature The material property analysis proves the positive response of the material on both environmental and economic aspects by demonstrating excellent heat retention properties over 1000 thermal cycles Further, the heat transfer network analysis helps design the solar cooking module to avoid a complicated heat flow path between the MNH heat batteries and active cooking layer We demonstrate the thermal infrared analysis to observe the internal temperature variations (5) QBL = UBL (Tbottom − Tair ) where, 1 ΔXcookingpot = + UBL hCBL + hRBL Kcookingpot hCBL = [2.8 + (3 × wind)] × ABL ] [ ] [ hRBL = εPCMtube σAPCMtubeBL (TPCMtube + Tair )(TPCMtube + Tair )2 + εFLUIDcover σAPCMtubeBL (TFLUIDcover + Tair )(TFLUIDcover + Tair )2 [ ] ( )( )2 + εcookinglayerover σAPCMtubeBL Tcookinglayerover + Tair Tcookinglayerover + Tair Overall heat loss co-efficient is the summation of U1 = USL + UTL + occurring around the heat batteries under real-time conditions It is well established that the heat batteries deliver a steady heat transfer of a minimum of 80 ◦ C for h even after the intense sunshine hours, making the system more efficient later From this design and analysis, the experimental heat retention time of the solar cooking system extends over 300 after sunshine hours Overall thermal energy flow in the system is regulated through the buffer heat battery layer, which shoots the system efficiency over 45% compared with the conventional UBL Total loss in the developed MNH assisted solar cooker is calculated by summing Eq (3), Eq (4) and Eq (5), QLoss = QSL + QTL + QBL 3.2 Uncertainty analysis In order to make sure the accuracy of the experimentation results, the equipment involved in preparing the PCM preparation and thermal 12 S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 Table Time taken for each cooking materials in different days Food material Mode of Cooking Day/batch Time Sec Green bean Outdoor Outdoor Outdoor ˙ Indoor ˙ Indoor ˙ Indoor 1/1 1/2 1/3 1/4 1/5 1/6 2/1 2/2 2/3 2/4 2/5 2/6 4500 3000 3000 4500 6000 10500 3000 3000 4500 4500 7500 10500 Red bean Outdoor Outdoor Outdoor ˙ Indoor ˙ Indoor ˙ Indoor Mung split bean Mung split bean Table Solar cooker heat gain and heat loss co-efficient Parameter QPot (kJ) QPCM (kJ) QFLUID (kJ) QCOOK (kJ) QGain (kJ) QSL (kJ) QTL (kJ) QBL (kJ) QLoss (kJ) QTotal (kJ) Range 220 433 84 392 1128 119 15.5 15.4 149.9 1278 Acknowledgement Table Instrument used in the experiment and its error factor Instrument Parameter Error Hotplate Sensitive balance (METTLER TOLEDO) Graphtec datalogger PCM melting PCM weighing ± 1.20% ± 0.001% ± 0.05% K-type thermocouple Pyranometer Fluke TiX560 Temperature recording (TAIR, TCOOK, TFLUID, TPCM, TFOCAL) Temperature measurement (TAIR, TCOOK, TFLUID, TPCM, TFOCAL) Solar radiation Temperature recording (TAIR, TCOOK, TFLUID, TPCM, TFOCAL) The authors would like to thank the School of Renewable Energy and Smart Grid Technology, Naresuan University for providing generous funds and lab facilities to complete the research Appendix A Supplementary data Supplementary data to this article can be found online at https://doi org/10.1016/j.jclepro.2021.129223 ± 0.30% ± 0.25% ± 0.4% Nomenclature Area of solar cooker side Surface ASL APCMTL Area of PCM tube top surface Area of solar cooker top surface ATL AFLUIDTL Area of fluid layer top surface AcookinglayerTL Area of cooking layer top surface ABL Area of solar cooker bottom surface APCMBL Area of PCM tube bottom surface AFLUIDBL Area of fluid layer bottom surface AcookinglayerBL Area of cooking layer bottom surface Ap Aperture area Ac Collector area Cp-FLUID Specific heat capacity of the heat transfer fluid Cp-COOK Specific heat capacity of cooking material hCTL Convection heat transfer co-efficient of solar cooking pot top surface Radiation heat transfer co-efficient of solar cooking pot top hRTL surface hCBL Convection heat transfer co-efficient of solar cooking pot bottom surface hRBL Radiation heat transfer co-efficient of solar cooking pot bottom surface Convection heat transfer co-efficient of solar cooking pot side hCSL surface hRSL Radiation heat transfer co-efficient of solar cooking pot side surface I Solar irradiation KPCMtube Thermal conductivity of PCM tube L Latent heat of fusion M Mass QSL Solar cooker side surface heat loss method The maximum efficiency is 30% during sunshine hours and 45% during off sunshine hours We have demonstrated the real-time practical cooking of food items without any interruption from the solar irradiance fluctuations Thus, examined MNH associated solar cooker study will reference future works on storing solar thermal energy in day-to-day applications CRediT authorship contribution statement S.M Santhi Rekha: Experimentation, data collection Vaithina than Karthikeyan: Conceptualization, Methodology, Writing – original draft Le Thi Thu Thuy: Visualization, Investigation Quach An Binh: Visualization, Investigation Kuaanan Techato: Writing – review & editing Venkatramanan Kannan: Resources, Validation, Supervision Vellaisamy A.L Roy: Writing – review & editing Sukruedee Sukchai: Resources, Validation, Supervision Karthikeyan Velmurugan: Re sources, Validation, Supervision Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper 13 S.M.S Rekha et al Journal of Cleaner Production 324 (2021) 129223 QTL QBL QPot QPCM QFluid QCOOK QGain QLoss QTotal Qoutput Qinput RAP-R Solar cooker top surface heat loss Solar cooker bottom surface heat loss Thermal energy in cooking/active layer Thermal energy in PCM Thermal energy in heat transfer fluid Thermal energy of the cooking material Thermal energy gain Thermal energy loss Total thermal energy Thermal energy of the cooking pot Incident solar radiation and input parameters of the cooker Resistance in transferring the heat energy from aperture to cooking pot RCPB-R Resistance in receiving/absorbing the heat energy by cooking pot RCPB-C Resistance in transferring the heat energy from bottom cooking pot to inner cooking layer by conduction RCPI-C + RCPI-CONV Resistance in transferring the heat energy from inner cooking layer to cooking item by conduction and convection RHTFO1-R Resistance in receiving/absorbing the heat energy by heat transfer fluid layer RHTFO1-C Resistance in transferring the heat energy from heat transfer fluid outside layer to inside layer by conduction RHTFI1-C + RHTFI1-CONV Resistance in transferring the heat energy from heat transfer fluid inside layer to the palm oil by conduction and convection RHTFI2-C Resistance in transferring the heat energy from heat transfer fluid inside layer to outside layer by conduction RHTFO2/CPI-C + RHTFO2/CPI-CONV Resistance in transferring the heat energy from heat transfer fluid outside layer or cooking pot inside layer to cooking item by conduction and convection RPCMtubeO1-R Resistance in receiving/absorbing the heat energy by PCM tube RPCMtubeO1-C Resistance in transferring the heat energy from PCM tube outside layer to inside layer by conduction RPCM-C + RPCM-CONV Resistance in transferring the heat energy from PCM tube inside layer to the PCM by conduction and convection RPCMtubeI2 – PCMtubeO2/HTFI1 Resistance in transferring the heat energy from PCM tube inside layer to outside layer or heat transfer fluid inside layer by conduction RHTF-C + RHTF-CONV Resistance in transferring the heat energy from PCM tube outside layer or heat transfer fluid inside layer to the palm oil by conduction and convection RHTFI2/HTFO2/CPI Resistance in transferring the heat energy from heat transfer fluid layer to outside layer or cooking pot inside layer by conduction RCPI-C + RCPI-CONV Resistance in transferring the heat energy from heat transfer fluid outside layer or cooking pot inside layer to cooking item by conduction and convection TPCMtube Temperature of PCM tube Temperature of sky TSky Tair Air/ambient temperature TFLUIDcover Temperature of fluid top surface Tcookinglayercover Temperature of cooking layer top cover Temperature of solar cooker bottom Tbottom USL Solar cooking pot side surface heat transfer loss Solar cooking pot top surface heat transfer loss UTL UBL Solar cooking pot bottom surface heat transfer loss Wind Wind speed εPCMtube PCM tube emissivity ΔXPCMtube Thickness of PCM tube ΔXcookingpot Thickness of cooking/active 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evaluation of a solar cooker with low cost heat storage material Int J Sustain Green Energy 6, 57–63 15 ... + εcookinglayercover σ AcookinglayerTL Tcookinglayercover + TSky Tcookinglayercover + TSky Bottom surface of the cooking pot loss, cooking module for uninterrupted operation during the sunshine... QGain QLoss QTotal Qoutput Qinput RAP-R Solar cooker top surface heat loss Solar cooker bottom surface heat loss Thermal energy in cooking/ active layer Thermal energy in PCM Thermal energy in heat. .. construction of the cooking module Here we have investigated in detail the properties of MNH heat battery’s performance ˙ addi for over 1000 continuous heating and cooling thermal cycles In tion, corrosion