Introduction

Nano-PCM with high heat storage capacity helps photovoltaic module to avoid the increase in temperature especially by fixing copper heat sinks at the rear surface of PV.

Saha et al. [13] presented experimental and numerical studies to investigate the effectiveness and performance of a TSU as a thermal management device for electronic components. For the configuration studied, the lowest operating temperatures are attained with about 8% volume fraction of TCE and with a larger number of fins. It is found that the duration of constancy of temperature is directly related to the amount of PCM, but the value of that constant temperature depends on the volume fraction of TCE. Saha and Dutta [14] studied numerically and experimentally thermal management of electronics using PCM-based heat sink subjected to cyclic heat load. A modified PCM-based heat sink was designed such that the thermal resistance of the heat flow path during the cooling period was significantly reduced and was comparable to that of heat flow path during the heating period. It was found that the performance of modified PCM-based heat sink was superior to that of the conventional one.

Many researchers introduced an experimental works to show the effect of operating temperature, PCMs type and addition of nanoparticles on the on PV system performance. Wei et al. [16] and Hasan et al. [6] showed the effect of highly hot operating temperature on the performance of PV cell. Chandel and Agarwal [5] reported that PCM technologies need to be optimized in terms of its material and the configurations used with the PV panels system. Al Siyabi et al. [2] investigated experimentally the effect of two different PCMs with different thickness and melting temperature for power ratings. Huang et al. [7,8,9,10,11] introduced a different experimental and numerical studies on the integration of a suitable PCM with a PV panel to mitigate the panel temperature rise. The studies verified the likelihood and dominance of the PV–PCM system. The results demonstrated that the temperature rising of the system was reduced by about 30 °C when compared with the datum of a single flat aluminum plate.

Kaviarasu and Prakash [12] demonstrated that despite the high latent heat storage of PCMs, their low thermal property calls for the incorporation of nanomaterials. The results disclosed that the high-surface-to-volume ratio of nanoparticles affected on the thermal properties of the base PCM. Sharma et al. [15] presented a combined cooling solution of a passive type for Building-Integrated Concentrated Photovoltaics (BICPV) by incorporating micro-fins, PCM and nanomaterial-enhanced PCM. The results displayed that there was a reduction in the average temperature at the center of the system of 10.7 °C when micro-fins with PCM was used and 12.5 °C when micro-fins with nanomaterial PCM was used. Al-Waeli et al. [3] experimentally investigated the effect of combined nano-PCM with heat sink configurations with applied heat fluxes on the photovoltaic rear surface temperature. The results displayed that the nano-PCM improved the electrical efficiency of the PV from 8.07 to 13.32%, compared with the conventional PV.

Abdelrahman et al. [1] investigated experimentally the use of PCM to augment the PV performance with fixing hollow copper cylindrical fins at the rear surface of Aluminum plate and submerged this system in tank of RT35HC. The results explored that the enhancement in temperature reduction reached 52.3% by adding the nanoparticles to RT35HC. Accordingly, hollow copper cylindrical fins, PCM and nano-PCM can be successfully used as a TCE to control the PV temperature and increase its efficiency.

Therefore, the present work introduces an experimental study for three different types of PCMs with different operating temperature (RT28HC, RT35HC and RT44HC). Moreover, the used PCMs are used individually pure or mixed with nanoparticles of Al2O3, to show their effects on front surface temperature behavior of PV panels. The effect of the following parameters; heat sink configuration, PCM type, PCM- with nanoparticles (Al2O3) at various volume fraction and heat flux; 820, 514 and 279 W/m2 that simulate average solar intensities for June to October, March to May and November to February, respectively, are studied in the present work.

Experimental setup and procedures

The test section presented in Fig. 1 was established and built up by Abdelrahman et al. [1] as a modeling system for PV panel. The test section is constructed from two aluminum surfaces, heating section, Nano-PCM tank and heat sinks. The two aluminum surfaces have dimensions 220 × 110 × 4 mm, those have three grooves to fix the thermocouples to record surfaces temperature. The nano-PCM tank is made from Perspex material and has 10-mm thickness, the depth of tank is 20 mm and its internal dimensions are 220 × 110 mm. Three heat sinks configurations are consisting of hollow cylindrical fins (11, 18 and 22) made from copper are soldered to a copper sheet which is fixed to the rear aluminum surface. The three configurations have a volume fractions (fins to the PCM container) of 2.85%, 4.67% and 5.7% for fins, 11, 18 and 22, respectively.

Fig. 1
figure 1

A schematic drawing for test section [1]

Full size image

Three types of PCMs “RT28HC, RT35HC and RT44HC” are used in the present study. These PCMs are used individually pure or mixed with Al2O3 nanoparticles. Table 1 represents the properties of the used PCMs. The nano-PCMs in the current study are prepared by mixing the Al2O3 nanoparticles of concentrations from 0.11 to 0.77% by volume, with 0.11% six equal increments, with melted PCM by using ultrasonic vibrator for three hours. The applied voltage to the heating section is regulated by a voltage regulator to simulate the different applied heat fluxes of 279, 514 and 820 W/m2 in the simulated system.

Table 1 Thermophysical properties of RT28HC, RT35HC, RT44HC ([4], Rubitherm data sheet)
Full size table

Figure 2 shows the three staggered configurations configuration of heat sinks at the rear aluminum surface after putting a conductive material to overcome the thermal contact resistance. Each heat sink is constructed of hollow cylindrical copper fins with 20-mm height, 8-mm inner diameter and 2-mm thickness. These fins are soldered to a thin copper plate of 1-mm thickness. The details of heat sinks are presented in Table 2. There are other parameters studied with the three configurations; heat fluxes, pure PCMs and nano-PCMs.

Fig. 2
figure 2

Fins heat sinks configurations

Full size image
Table 2 Details of the heat sink configurations
Full size table

As introduced before by Abdelrahman et al. [1], six thermcouples of k-type are distributed on both upper and lower aluminum plates, three on each side, to measure the front and rear surface temperatures. Also, as presented in Fig. 3, three thermocouples are located inside the PCM container with heat sink which repeated vertically in three levels.

Fig. 3
figure 3

Thermocouples positions inside PCM tank with heat sink fins

Full size image

Figure 4 shows three dimension of fins configurations and there staggered distributions.

Fig. 4
figure 4

Three-dimensional of fins soldiered to aluminum plate

Full size image

Results and discussion

The experimental setup has been validated with [8] as introduced before by Abdelrahman et al. [1] and a worthy agreement with the former study shows the assurance in the experimental test rig and the measuring techniques. Furthermore, Abdelrahman et al. [1] results revealed that the FST increases as the heat flux increases, and a higher temperature of 74.5 °C was obtained at the highest heat flux of 820 W/m2 after 75 min. In the current study, several parameters such as heat flux, PCM type, copper fins configuration and nanoparticles concentrations mixed with PCMs are experimentally investigated. The results of the above-mentioned parameters are presented below to show their effect on the front surface temperature.

Effect of fins configurations

Figure 5 represents the effect of PCM type on FST at T∞ = 21 °C at three heat fluxes of 279, 514 and 820 W/m2. The figure shows that the temperature increases till reaches the maximum during the charging then it decreases again during the discharging. The same trend is observed for all studied heat fluxes.

Fig. 5
figure 5

Front surface temperature variation with time without PCM at T∞ = 21 ± 1 °C

Full size image

Figure 6 shows the variation of front surface temperature with time for exploring the effect of using the three different PCMs and heat sink configurations at different heat flux values and comparing with free surface. It is noted that using heat sinks with PCMs offer advantage for overcoming the drawback of lower PCM thermal conductivity. The figure demonstrates that there are reductions in front surface temperature for all heat sink configurations with three PCM types. The results show that configuration 3 achieves lower front surface temperature due to having larger numbers of fins when compared with other heat sink configurations. Also, the highest reduction in free surface temperature is obtained for configuration 3 using RT44HC when compared with the base plate at heat flux 820 W/m2 as a result of its high heat storage capacity.

Fig. 6
figure 6

Effect of configurations on the FST with different PCM a Configuration 1 b Configuration 2 c Configuration 3

Full size image

Effect of PCM type

Figure 7 represents the effect of PCM type on FST for the three heat sinks at T∞ = 21 °C. It reveals that for a fixed heat flux and configuration, the PCM-type influences the FST. The whole enhancements from the three types of pure PCMs compared to the free surface are represented in Table 3. The results show that RT44HC has the highest enhancement of about 51% compared to the free surface at heat flux 820 W/m2 with configuration 3. This high enhancement is assigned to the combined effect of configuration and pure PCM (RT44HC) which has high heat storage capacity and combination of latent and sensible heat.

Fig. 7
figure 7

Effect of PCM type with heat sink configuration 3 on the peak FST at different heat fluxes

Full size image
Table 3 Enhancement percentages of FST compared to the free surface at different heat sink configurations, pure PCM types and heat fluxes
Full size table

Figure 8 represents the whole enhancement percentage for heat sink configuration 3 with the three types of PCMs compared to the free surface without PCM. The results show that RT44HC has the highest enhancement compared to the other two PCMs at all heat fluxes. Generally, the achieved enhancement is due to the combined effect of finned surface configuration and PCM. Also, the high heat storage capacity and latent and sensible heat combination of RT44HC lead it to have the best performance compared to the other two PCMs.

Fig. 8
figure 8

Enhancement percentages of FST compared to the free surface at different PCM types and heat fluxes = 820 W/m2

Full size image

Effect of mixture (PCM-Nanoparticles)

Figure 9 represents the effect of mixing AL2O3 nanoparticles with the three used types of PCMs for the heat sink configuration 3. The effect of PCM type mixed with Al2O3 nanoparticles at three different volume fractions of 0.22%, 0.44% and 0.77% for configuration no. 3 and heat flux of 820 W/m2. It demonstrates that adding AL2O3 to PCM enhances the FST when compared to the free surface or heat sink configuration with pure PCM. Also, it shows that as the volume concentration of Al2O3 nanoparticles increases, it leads to decrease in the temperature of frontal surface. So that, the results indicate that the addition of Al2O3 to the PCMs enhance the FST when compared to the free surface or heat sink configuration with pure PCM.

Fig. 9
figure 9

Effect of PCM-nanoparticles mixture on FST at T∞ = 21 °C

Full size image

Moreover, the figure demonstrates that for the smallest nanoparticle’s concentration through the tested range, 0.11% by volume, there is nearly no effect when compared with the using of pure PCM for all studied PCMs. For configuration 3 and Al2O3 nanoparticles concentration of 0.77% at heat flux of 820 W/m2 are 52.3% and 54.2%, respectively.

Furthermore, the results recorded a highest reduction of 12.5% and 57.7% compared to PCM (RT44HC) only, in the FST at heat flux of 820 W/m2 when using configuration 3 only and with 0.77% nanoparticles concentration, respectively.

Figure 10 shows the enhancement percentage in peak FST compared to the free surface for different pure PCMs and PCM-Al2O3 mixtures with concentration of 0.11% to 0.77% with all tested heat fluxes. The figure demonstrates that the high enhancement percentages in peak FST are obtained for the three used types of PCMs and they increased slightly with adding Al2O3 to the PCMs. Furthermore, it is noted that the enhancement percentages increase with all nanoparticle’s concentration, except for the smallest nanoparticle’s concentration of 0.11%, that shows no effect for all studied PCMs when compared with corresponding pure PCM.

Fig. 10
figure 10

Enhancement percentage in peak FST of pure PCMs and PCM-nanoparticle mixtures with heat sink configurations (at T∞ = 21 °C) a q = 820 W/m2, b q = 514 W/m2, c q = 279 W/m2

Full size image

The results recorded the highest enhancement in the peak FST of 57% at heat flux of 820 W/m2 and Al2O3 nanoparticles concentration of 0.77% for configuration 3 and RT44HC compared to the free surface. While the pure RT44HC with configuration 3 achieves enhancement in the peak FST of 51.7% when compared to the free surface at the same heat flux.

On the other hand, Fig. 11 shows the enhancement percentage in peak FST for different PCM-Al2O3 mixtures with concentration of 0.11% to 0.77% and heat sink configurations at all heat fluxes and compared to the corresponding pure PCM. It is noted that the enhancement percentages increase with an increase in nanoparticle’s concentration, except for the smallest nanoparticle’s concentration of 0.11%, that shows no effect for all studied PCMs when compared with corresponding pure PCM. The figure demonstrates that the highest enhancement in the peak FST of 11.1% at heat flux of 820 W/m2 and Al2O3 nanoparticles concentration of 0.77% with configuration 3 and RT44HC-Al2O3 mixtures when compared with the corresponding pure RT44HC.

Fig. 11
figure 11

Enhancement percentage in peak FST of PCM-nanoparticle mixtures with heat sink configurations (at T∞ = 21 °C) a q = 820 W/m2, b q = 514 W/m2, c q = 279 W/m2

Full size image

Conclusions

The present work introduces a study on passive thermal control of photovoltaic cells and comparing different types of PCMs (RT35HC, RT28HC and RT44HC) at different heat fluxes around the year of 820, 514 and 279 W/m2 to predict and compare the thermal performance of aluminum-heated plate simulating PV solar cell. Experiments are conducted, and the results are obtained for the different mixing types of PCMs with AL2O3 nanoparticles at different volume fraction in range of 0.11% to 0.77%, to reach to steady state. The foremost conclusions of the present experimental work are:

  • Using PCM reduces the surface temperature of the PV system, and consequently leads to enhancing its performance.

  • The results indicate that the enhancement is increased gradually as volume fraction of AL2O3 nanoparticles increased in the used Nano-PCMs through the tested range of 0.11% to 0.77%.

  • The highest reductions in the FST are 52.3%, 54.2% and 57.7% which occurred with configuration 3, heat flux of 820 W/m2 and AL2O3 nanoparticles concentration of 0.77% for PCMs types RT35HC, RT28HC, and RT44HC, respectively.

  • Using nanoparticles with PCM reduce the FST of the simulated PV cells which means that the life time of photovoltaic cell will be increased.