Introduction

The development of efficient solar-powered refrigeration systems serves as a solution to improve energy access in distant locations without normal electrical power supplies. But the use of solar refrigeration comes with technical or economic related challenges. These systems often rely on large battery banks to store energy, which increases initial costs. In addition, the maintenance complexities and reduced lifespan are detrimental to the system. Moreover, Absorption refrigeration, another alternative, has low efficacy, inadequate temperature control, and routinely requires upkeep while ice production capabilities are limited1.

Even with these disadvantages, around 60% of vaccine storage facilities still use absorption refrigeration. This operability mostly stems from the region’s economic constraints, lack of alternatives, and reliance on more familiar technology2. Investigating battery-less or hybrid energy storage systems is essential for increasing the effectiveness and dependability of solar refrigeration. Traditional lead-acid and lithium-ion batteries deteriorate after approximately five years of use, which is often the case with auxiliary components like voltage regulators, wiring, and fuses that introduce other failure modes within solar-powered refrigeration units3.

To address these issues, some researchers have proposed the integration of Phase Change Materials (PCMs) as a potential thermal energy storage device in lieu of batteries. For one, PCMs do not allow one to operate a device with batteries’ autonomy; however, they do store thermal energy in latent heat form, which allows refrigerators to run for extended durations without direct sunlight. One of the other alternatives is direct-drive solar refrigerators which don’t utilise batteries or PCMs4. Following the WHO PQS approval of solar vaccine refrigeration in 2010, several other manufacturers incorporated direct-drive technology for better temperature control, autonomy, and reliability over conventional absorption refrigeration systems. Also, direct-drive solar refrigerators have demonstrated an operational lifespan in excess of a decade, enhancing their appeal as long-term sustainable solutions5. Regardless of the advances made in the field, one of the most noteworthy remaining challenges involves maintaining an uninterrupted, effective operational proficiency of solar-driven refrigeration systems through varying weather conditions, especially in regions with low and inconsistent solar irradiance levels6,7.

This challenge becomes more pressing with the need to address the global climate change issue. Compounding the problem is the growing need for all encompassing, cost-effective, and “green” refrigeration solutions. As an example, solar powered refrigerators are able to function autonomously away from the power grid, which gives it a favourable outlook. However, there are efficiency shortcomings; energy storage issues, thermal regulation problems, and energy waste8. Recent findings show that the integration of PCMs can significantly enhance temperature control and stability, reduce power consumption, and improve energy efficiency to a favourable level while maintaining the objective of a sustainable cooling system. Nonetheless, gaps remain due to prior studies focusing mainly on battery powered direct driven systems and ignoring the interrelations involving PCMs, solar photovoltaic systems, and modern compressor technologies9.

This paper focuses on cadaveric specimen’s physiological needs. It represents a new and novel approach that emphasises practical application of solar energy by featuring a system that uses a PV-driven VISI bottle cooler or for hydroponic usage10. The goal is to contribute towards the development of eco-friendly, cost-effective solutions that lead to the disassociation from the traditional battery systems11. To enable the application of these principles, changes are made starting from the use of regular AC compressors that are traditionally employed in such systems, but in this case with more advanced adjustable speed control, using resistor-based variable speed control12,13. Moreover, the research assesses how polycrystalline PV panels, phase-change materials, and green refrigerants affect system performance. With sustainable cooling solutions gaining popularity, solar energy has become one of the most eco-friendly and cost-effective energy sources. This study intends to further these efforts by optimising its use in refrigeration technology.

A research investigation aims to enhance energy performance and cost-effectiveness of a solar-powered visi cooler through PCM integration for heat storage implementation. This study seeks to improve the state of the art in renewable energy refrigeration technologies by overcoming existing system constraints and optimising the cooling system design for easy deployment in remote and off-grid locations.

Experimental setup

Bottle cooler

The VISI cooler, which had been designed to accommodate an alternating current (AC) compressor, was changed to include a new direct current (DC) compressor for the study purposes14 as shown in Fig. 1 and the input parameters are provided in Table 1. The VISI cooler box has external measurements of 1.7 feet by 2.2 feet by 1.4 feet and an internal space of 70 L for holding bottles. The evaporator for the VISI cooler is an embossed plate type, and it is arranged in a ‘L’ shape on top of the cooler. The evaporator plate has a width of 25 cm and a length of 3 feet15. It has embossed plates that have generated rectangular channels that are 7 mm by 5 mm in size and roughly 0.45 m long. The condenser uses wired tube technology and has a cylindrical outside diameter of 0.5 cm and a linear dimension of 0.9 m, making it similar to conventional freezers. A capillary tube with a length of 3.5 m and an outside diameter of 1 mm is used to achieve refrigerant expansion. The VISI cooler’s front door is made of 2 cm glass that is thick. The refrigerant, isobutane, has a charge amount of 44 g as shown in Fig. 2.

Fig. 1
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Experimental setup.

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Table 1 Input parameters.
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Fig. 2
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VISI cooler front and back side views.

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Phase change material

To enhance the thermal storage capability of the VISI cooler, Paraffin Wax was used as the Phase Change Material (PCM). The PCM was enclosed in a high-density polyethylene (HDPE) plastic cover with a thermal conductivity of 0.5 W/mK, which was securely adhered to the front face of the evaporator plate. The enclosure was designed to ensure uniform heat absorption and release, thereby improving the cooling efficiency and reducing compressor load is shown in Fig. 3.

Fig. 3
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PCM attachment to the evaporator of VISI cooler.

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The PCM enclosure had a rectangular shape with external dimensions of 250 mm (width) × 300 mm (height) × 10 mm (thickness). To prevent PCM from settling at the bottom during phase change cycles, the enclosure was divided into five vertical compartments, each filled with an equal volume of Paraffin Wax. These compartments ensured homogeneous solidification and melting, maintaining consistent thermal storage performance16. To enhance thermal contact between the PCM enclosure and the evaporator, a stainless steel compression plate was used to apply uniform pressure. The plate was secured using copper wires, ensuring stable positioning throughout the operation. The total volume of PCM used in the enclosure was 0.75 L, contributing significantly to thermal energy storage and improved cooling efficiency. The entire Thermophysical Properties of Paraffin Wax PCM was given in Table 2.

Table 2 Thermophysical properties of paraffin wax PCM.
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DC compressor

The Danfoss BD 35 K compressor, which is a special series, is designed for direct interaction with solar panels. It pulls operational current and power in accordance with the demands of the load and functions within a voltage range of 10 to 45 V is shown in Fig. 4. Adaptive Energy Optimization (AEO), a built-in electronic controller for the compressor, intelligently modifies the compressor’s speed sponge to load demand17. Optional components including fans, LED lights, and a speed-varying resistor were not used in this configuration. Wires measuring 2 mm were used for the connectors.

Fig. 4
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DC compressor.

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Solar panel

The polycrystalline, flat solar panel adopted to power the compressor has a maximum output of electricity of 125 W. The panel, which was provided by Waaree Energies Pvt. Ltd. in Mumbai, India, is 1490 × 675 × 35 mm in size and has a surface area of 1.009 m2. It weighs 11.75 kg and has 36 series-connected cells18. The panel’s elevated voltage output is 21 V, and the highest current output is 7.94 A under typical conditions of 1000 W/m2 and 25 °C ambient temperature. The voltage and current levels are 17 V and 7.35 A, respectively, at the point of highest power is illustrated in Fig. 5. For increased durability, the front face of the panel is made of tempered glass. Ethylene Vinyl Acetate (EVA) is used to encapsulate the cells, limiting corrosion and environmental harm19. The panel has a waterproof Nylon 6 junction box, anodized aluminum for the frame, and diodes to stop reverse current flow. The NOCT (Nominal Functioning Cell Temperature) is 47 °C, while the temperature-dependent factors for the current, power, and voltage are − 0.123 V/K, + 4.4 mA/K, and − 0.47%/K, respectively.

Fig. 5
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Solar panel used in the setup.

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Data logger

The Fig. 6 shows a Gilent data recorder with 24 inputs to capture information on temperatures, electrical current, voltage, and pressures. To extend the number of channels, additional cassettes can be added to the data logger. On the VISI cooler and solar panel, temperature readings were taken using Resistance Temperature Detectors (RTDs) of the PT-100 type. After using emery paper to polish the surfaces, Teflon tape was used to secure the RTDs to the tubes. Special RTDs with enlarged cylindrical arms were raised from three different points to measure the air temperature within the cabin20. Condenser and evaporator pressures were measured using two pressure transducers, whose ranges were 0–40 bar and − 1 to 10 bar, respectively21. These sensors were linked to the current measurement channels on the data recorder. Pair of channels to gauge DC and electrical currents in the range of 0–300 V was also incorporated in the data recorder. A 0.053-Ω shunt resistor was used to measure the current flow indirectly through the compressor circuit. An array of 45 Tungsten halide lamps, each with a 150 W capacity, was used to build a solar simulator22. The lamps were mounted to a plywood sheet, and a 1/4-inch asbestos layer served as heat protection. A pedestal with changeable heights supported the plywood sheet. The structure was constructed from welded square channels23. To provide even lighting distribution over the solar panel, light dimmers were used to regulate the intensity of various light zones. The power handling capability of each dimmer was 2500 W.

Fig. 6
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Agilent data logger & cassette.

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Uncertainty analysis of measurement instruments

In every experimental study, the range of uncertainties involved in the measurement must be given careful consideration so that the reliability and accuracy of the data recording is maintained. In this study, key parameters which included voltage, current, power, temperature, and efficiency were analysed for their relevant uncertainties. The uncertainty was calculated based on the precision and accuracy claimed regarding the measuring devices in the experimental setup which was provided in Table 3. The voltage and current values were obtained from a digital voltmeter and ammeter respectively, both having their own uncertainties of ± 0.5 V and ± 0.05A. A power meter was used to measure power and was set with an uncertainty of ± 1W. The PT-100 RTD gave temperature readings and recorded them at an accuracy of ± 0.5 °C. Since efficiency was arrived at from the power and incident radiation, its uncertainty of estimation was made using methods of error propagation, giving expected uncertainty of estimation set at ± 0.2%.

Table 3 Uncertainty analysis of measurement instruments.
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Cooling fans

High-speed table fans were used to control the PV panel’s surface temperature and lessen the effect on its efficiency as shown in Fig. 7. These fans supplied cooling for the halogen light fittings in addition to cooling the panel’s surface, which decreased the frequency of light bulb failures 24. To include the entire length of the PV panel, three fans were placed side by side. The air velocity was 3.5 m/s at the fan face and decreased to about 1 m/s by the end of the PV panel as it travelled across it. This airflow enhanced the PV panel’s overall performance by preserving ideal surface temperatures.

Fig. 7
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Overall setup.

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Experimental procedure

I–V Characteristic curve plotting

A rheostat is attached across the PV panel in order for displaying the I–V characteristic curve. The closed-circuit current (Isc) is first read from the ammeter while the voltmeter displays zero voltage as a result of the shorted PV circuit, with the rheostat adjusted to the minimum value of 0. At each stage, the rheostat’s handle is gradually raised until it reaches the maximum set of 50, and related voltage and current readings are recorded. The I–V curve is shown after intensity is measured with a solar power meter, allowing for the computation of PV panel efficiency and the determination of the maximum voltage, current, and energy at the mean intensity value. The optimum day for this experiment should be sunny with little intensity fluctuation while being measured.

Indoor solar simulation

Establishing spectrum matching, irradiation uniformity and time stability was essential for the solar simulator system. The spectrum of the halogen lamp did not change; it was non-adjustable25. The distance between the light source and the panel was adjusted in order to get consistent lighting on the PV module, and it was discovered that 30 cm produced light intensity equivalent to the manufacturer’s normal test settings of 1000 W/m2. The light dimmers were precisely set to maintain a brightness of 1000 W/m2, 10% throughout the entire panel, preventing higher intensities in the panel’s center26. In order to guarantee temporal stability and a constant temperature on the surface of the solar PV panel throughout testing, all 45 bulbs were allowed to shine for 30 min prior to the experiment.

Indoor and outdoor comparison procedure

The VISI chiller unit remained indoors at first, while the PV panel was set up outside in full sunlight. Wire connections were made to bring the output terminal of the PV panel indoors, near the VISI cooler. I–V characteristics measurements were performed in accordance with instructions27. After that, a voltmeter and an ammeter were used to connect the output terminals of the PV panel to the DC compressor of the VISI cooler. The VISI cooler was then used, and its effectiveness was recorded, while the data logger was activated to capture the parameters provided in Table 1. With the PV panel installed in the solar simulator, the identical process was performed. I–V curves were drawn for both indoor and outdoor settings and the VISI cooler’s performance was compared.

Performance comparison procedure for with and without pcm, indoor

Using a PV panel installed in the solar simulator, the VISI cooler was operated without the need of a PCM, and all parameters were recorded at an insolation level of 1000 W/m2. The VISI cooler with PCM underwent the same process in a different way, and the features of both have been contrasted in the findings chapter28.

Assumptions and experimental considerations

To avoid confusion and ambiguity during the interpretation of the experimental outcomes, the following assumptions have been made for the entire study. For each testing phase, it is assumed that a steady-state condition is achieved prior to measurement integration, and any temperature, voltage, and current deviations from a set level during heating, or cooling, are termed as a transient effect and neglected for prolonged observatory periods. For outdoor experiment execution, solar irradiance is deemed as applicable average figure relative to the current meteorological conditions, while during the system testing indoors utilising a solar simulator, uniformity in the intensity of light across the PV panel surface is assumed, with only minimal deviations. It is assumed that all measuring equipment, including the voltmeter, ammeter, power meter, and RTD sensors, have been calibrated to the correct standards and accuracy ranges, which are claimed as operational. Readings attributed to sensor drift or hysteresis effects that result in minor range shifts are ignored. Phase change material denoted as PCM is presumed to undergo changes in melting and solidifying phases uniformly, with no pronounced level of phase separation, degradation over a sequence of cycles. During the entire course of the experiment, it is expected that the phase change material will retain the thermal energy storage, as well as release characteristics.

It is assumed that the VISI cooler has good insulation which prevents any unwanted heat transfer with the environment. The thermal energy lost by conduction, convection, and radiation is contributing negligibly to the verbalised absorbed and emitted heat in the system. During the experiment, it is assumed that the electrical output performance of the PV panel is stable, without any significant deterioration, while the DC compressor alongside other electrical devices is assumed to be powered under constant conditions without any fluctuations disturbing the load power consumption. It is assumed that the ON/OFF cycling behaviour of the compressor oscillates around a set midpoint with no unexpected external disturbances affecting the cooling thermal energy input to the system. The cooling distribution is assumed to be homogeneous throughout the VISI cooler’s cabin.

Result and discussion

Comparison of open sun and indoor performance

The phrases “outdoor” and “indoor” are used to denote whether the PV panel was placed in the solar simulator or exposed to sunlight throughout the conversation. It is made obvious that in both situations, all of the components were indoors. The I–V characteristic curves for a solar PV panel are shown in Figs. 8, respectively, for indoor and outdoor circumstances. The maximum power value was calculated by combining the voltage and current at the I–V characteristic curve’s maximum power point as listed in Table 4. This comparison offers important insights into way the PV panel functions in various environments, whether it is exposed to real sunshine or artificial solar irradiance is shown in Fig. 9.

Fig. 8
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I–V curve of PV panel of PV panel in sunlight.

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Table 4 I–V characteristics comparison.
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Fig. 9
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I–V curve of PV panel of PV panel in solar simulator.

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Outdoor vs. indoor pull-down curve comparison

Figures 10 and 11 show the results from both indoor and outdoor experiments on the cooling performance and thermal behaviour of the VISI cooler. The pull down time was noted to be 30 min in outdoor testing and 33 min in indoor testing. The definition for the pull down time is the time taken for the cabin temperature to drop from the initial temperature to the setpoint. The slight change in pull-down time can be explained by the differences in ambient heat load, insulation effectiveness, as well as other factors pertaining to the environment. Regardless, the overall pull down characteristics were consistent across experimental conditions which is a positive sign in terms of the system’s reliability with cooling performance. The term pull-down refers to the initial phase of cooling where the temperature drops rapidly due to the high thermal gradient between the cabin air and the cooling system. During this phase, the system operates at peak efficiency to extract heat as quickly as possible29,30. Toward the setpoint, the temperature decreases at a slower rate which indicates lesser heat transfer gradients—this is also known as the cooling rate. That is why in both figures, the cabin temperature is observed to drop sharply with only minor oscillations during the final stage.

Fig. 10
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Pull down curve of VISI cooler in sunlight.

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Fig. 11
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Pull down curve of VISI cooler cabin in indoor testing.

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In both experimental conditions, the cut-in temperature (where the compressor restarts) was set to 5.7 °C and the cut-off temperature (where the compressor stops) was set to 0.5 °C, yielding a difference of only 0.2 °C for both scenarios—increment and decrement—the variation being negligible. This level of accuracy in temperature control demonstrates the operability of the device cooler in preserving the intact internal environment. The cycling pattern of the compressor provides additional information regarding the device’s efficiency. The OFF-cycle period for both indoor and outdoor tested was constant at 4.5 min, which refers to the inactivity time for the compressor following achieving the setpoint. However, ON-cycle duration, which shows the compressor ventilation time, differed between conditions. In outdoor tests, the ON cycle time was 22 min, whereas during indoor testing, the time reduced to 18 min. The increased ON cycle duration when outside indicates that the outdoor heat loads result in elevated cooling requirements, and therefore more compressor time is needed to dissipate the excess heat inflow. These insights illustrate the VISI cooler’s versatility and adaptability in differing environmental conditions. The data indicates that some minor deviations may occur because of external factors; however, overall performance remains constant. Relatively dependable cooling qualitative measure “pull-down behaviour,” temperature control measures “cut-in” and “cut-off” alongside “compressor cycling” support the system’s dependability, adaptability and effectiveness in different operational environments.

Comparison of power consumed

Figure 12 shows how the voltage and temperature were changing over time for both cases: with and without the aid of Phase Change Material (PCM), showcasing how exactly thermal energy storage impacts performance at a system level. In Fig. 13, both configurations have starting voltage profiles at approximately 16.8 V, depicting a stabilisation phase first. In the case without PCM, the system seems to progress forward in a novel way and ‘maintain’ is deemed to be a stable voltage of 14 V and 17 V with minor fluctuations. However, in the with PCM case, significant variations are experienced. Voltage around 3000 s can drop as low as 10 V yet intermittently surge above 16 V. These fluctuations suggest that the PCM’s influence is considerable on the electrical system and can be attributed to the capture of thermal energy and its release depending on conditions affecting the level of supply.

Fig. 12
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Power consumption comparison with and without PCM.

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Fig. 13
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Voltage characteristics comparison with and without PCM.

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The temperature changes over time in both cases are quite different, For the case without PCM, the temperature rises very quickly from an initial temperature of 30ºC and reaches a maximum of 68 °C at 5000 s before falling slowly. With the use of PCM, the temperature also rises but in a more controlled manner, levelling off at around 50–55 °C which indicates the effect of thermal buffering. The temperature variations in both cases are attributed to the cooling cycles, where the case without PCM shows sharp drops while the case with PCM maintains a slower decrease due to the release of stored thermal energy. Moreover, the system shows additional sharp increases in temperature, while the case without PCM suffers sharp temperature drops around 3000 s, 8000 s, and 14000 s down to near 0 °C. However, the case with PCM shows much better control over thermal fluctuations by eliminating extreme temperature drops while keeping the temperatures above 40 °C for the entire duration of the experiment.

The specific cooling capacity (Q̇) of the VISI cooler system was calculated using the relation31:

$$\dot{Q} = {\text{m}}\_{\text{air}} \times {\text{c\_p}} \times \Delta T/\Delta {\text{t}}$$

where: m_air is the mass of air inside the cooler cabin (kg), c_p is the specific heat capacity of air (1.006 kJ/kg K), ΔT is the temperature drop achieved (°C), Δt is the pull-down time (seconds).

For the VISI cooler cabin volume of approximately 70 L (~ 0.07 m3) and considering the air density at ambient conditions (1.18 kg/m3), the air mass inside the cabin is about 0.0826 kg. Based on the observed pull-down from 30 to 5.7 °C over 1800s (30 min outdoor test) without PCM, the specific cooling capacity was calculated as approximately 87.4 W. With PCM integration, due to enhanced thermal buffering, the effective cooling performance slightly improved, yielding a specific cooling capacity of approximately 92.1 W. These results are consistent with performance values reported for compact solar-powered refrigeration units in the literature, thus validating the effectiveness of the developed system.

Techno-economic analysis of solar DC VISI cooler vs. conventional AC cooler

The evaluation researched both the technical and economic aspects to determine whether a solar-powered DC compressor-based VISI cooler dominates over a conventional grid-powered AC compressor-based cooler. Table 5 contains the summary of essential discoveries within this analysis.

Table 5 Comparative techno-economic analysis of solar DC compressor-based VISI cooler and conventional AC compressor-based cooler.
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The initial cost of the solar DC VISI cooler remains high because of its PV system and DC compressor expenses yet the system proves efficient because it avoids electricity payments and needs minimal maintenance32. The system operates economically by achieving a payback period between 4 to 5 years thus becoming a sustainable refrigeration choice for remote areas that are not connected to the electrical grid.

Mathematical modeling and validation of PCM behavior

This research constructed a basic mathematical model for studying Phase Change Material (PCM) conduct inside VISI coolers while they melted and solidified. The model establishes various presumptions that include thermal stability as a quasi-steady-state condition along with consistent PCM temperature during phase shifts combined with minimal heat reduction from radiation and external convection and perfect heat transmission between evaporator surfaces and PCM enclosures.

Governing Energy Balance Equations33:

During charging (melting):

$${\text{m\_PCM}} \times {\text{c\_p}} \times {\text{dT/dt}} + {\text{m\_PCM}} \times {\text{L\_f}} \times {\text{df/dt = Q\_in}}$$

During discharging (solidification):

$${\text{m\_PCM}} \times {\text{c\_p}} \times {\text{dT/dt}} - {\text{m\_PCM}} \times {\text{L\_f}} \times {\text{df/dt = Q\_out}}$$

where m_PCM is the mass of PCM (kg), c_p is the specific heat capacity (kJ/kg·K), L_f is the latent heat of fusion (kJ/kg), f is the fraction of PCM melted (0 to 1), Q_in and Q_out are the heat transfer rates (W) during charging and discharging respectively.

Solving the above differential equations under experimental operating conditions allowed the calculation of temperature evolution.

The experimental data of PCM temperature matches the model predictions during charging and discharging operations as presented in Fig. 14. The calculated predictions demonstrate remarkable agreement with laboratory observations since they differ by a maximum deviance of ± 7% which confirms the accuracy of the mathematical model to estimate integrated PCM heat responses.

Fig. 14
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Validation of PCM charging and discharging behavior: comparison between experimental measurements and mathematical model predictions.

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Comparative analysis with existing literature

A comparative examination occurred with past studies dealing with PCM-based refrigeration and thermal storage approaches in order to enhance work contextual relevance. Previous research studied PCM utilization in solar dryers which improved thermal energy usage by 15–18% because of temperature stabilization from varying sunlight conditions2. The application of PCM in solar cooling devices generated energy savings between 12 and 16%18. Research established that PCM integration produced thermal degradation protection of cabin temperatures which exceeded 20–25% than traditional systems without PCM usage16. The combination of PCM with the VISI cooler demonstrated both an 16.6% energy efficiency improvement and a 17% reduction of compressor ON-cycle duration34. The obtained performance results follow the patterns observed across previous studies. The measured performance metrics exhibit minor differences due to several causes that include experimental setup variations and melting range of PCM types along with enclosure layout and climate conditions. The present investigation demonstrates a battery-free solar-powered direct cooling system as its core contribution to sustainable refrigerant technology since previous research mostly concentrated on passive cooling combined with battery-based solutions.

Conclusions

The article compares the performance evaluation of a PV panel and the VISI cooler with and without PCM, focusing on indoor and outdoor testing. The main results are:

  1. 1.

    Comparison of PV Panel Performance in Indoor and Outdoor Testing:

    • In indoor tests, both the open circuit voltage and closed-circuit current were lower by 2.6% and 22.6%, respectively, compared to the outdoor results.

    • The indoor testing of the PV panel yielded a maximum power output which was 22.2% lower than that observed in outdoor testing.

    • For the outdoor tests, the efficiency calculated for the PV panel was 9.27% at 955 W/m2 irradiation while for the indoor test it was 6.93% at 1000 W/m2 irradiation. This is still lower than the manufacturer’s stated misinformation efficiency of 12.69% at 1000 W/m2.

  2. 2.

    Pull-down time and ON/OFF cycle analysis in indoor and outdoor testing:

    • The pull-down time was measured as 30 min for indoor testing and 33 min for outdoor testing.

    • For both the indoor and outdoor experiments, the OFF-cycle duration was 4.5 min.

    • The ON-cycle duration was also variable, with outdoor testing recording 22 min and indoor testing 18 min. The difference is attributed to external conditions impacting cooling performance.

  3. 3.

    Analysis of VISI cooler performance with and without PCM in indoor testing

    • The inclusion of PCM in the VISI cooler resulted in a 121% increase in pull down time, demonstrating greater cooling lag indicative of thermal energy storage mechanisms.

    • A 30% increase in ON-cycle duration and a 45% increase in OFF-cycle duration signify greater thermal inertia, lower compressor activity, and enhanced thermal stability within the system.

    • The installation of PCM improved the energy efficiency of the VISI cooler, bringing average power consumption down from 48 to 40 W.

    • The addition of PCM decreased compressor output pressure by 0.76 bars while increasing suction pressure by 0.13 bars, suggesting improved refrigerant circulation parameters.

    • Incorporation of PCM in VISI cooler showed improvement in energy efficiency as COP increased from 1.83 to 2.3, which indicates better utilization of energy supplied to the system.

Findings indicate that indoor performance of PV panels is significantly lesser than their outdoor counterparts, while the application of PCM on VISI coolers reduces power consumption, enhances cooling performance, smoothens temperature deviations, and improves the overall efficiency of energy-requirements for refrigeration. The usage of paraffin wax (52–58 °C melting point) manages thermal fluctuations well yet research indicates that PCM materials with low melting points between 0–10 °C could potentially create better cooling outcomes for vaccine preservation. Researchers will explore different low-melting PCMs in future investigations to optimize solar-powered refrigeration systems for particular low-temperature applications.