Electrical Efficiency Investigation on Photovoltaic Thermal Collector with Two Different Coolants

Abstract

The design and development of a photovoltaic thermal (PVT) collector were developed in this study, and electrical and electrical thermal efficiency were assessed. To improve system performance, two types of coolants were employed, liquid and liquid-based MnO nanofluid. Flow rates ranging from 1 to 4 liters per minute (LPM) for the interval of 1.0 LPM were employed, together with a 0.1% concentration of manganese oxide (MnO) nanofluid. Various parametric investigations, including electrical power generation, glazing surface temperature, electrical efficiency, and electrical thermal efficiency, were carried out on testing days, which were clear and sunny. Outdoor studies for the aforementioned nanofluids and liquids were carried out at volume flow rates ranging from 1 to 4 LPM, which can be compared for reference to a freestanding PV system. The research of two efficiency levels, electrical and electrical thermal, revealed that MnO water nanofluid provides better photovoltaic energy conversion than water nanofluid and stand-alone PV systems. In this study, three different domains were examined: stand-alone PV, liquid-based PVT collector, and liquid-based MnO nanofluids. The stand-alone PV system achieved a lower performance, the liquid-based MnO performed better, and the liquid-based PVT achieved an intermediate level.

1. Introduction

Global accords aimed at reducing greenhouse gas (GHG) emissions have been widely praised in recent years by governments worldwide [1,2,3]. This issue is gaining traction, especially in oil-rich Middle Eastern nations such as Saudi Arabia, the United Arab Emirates, and Iran, which have put considerable expenditure into developing their solar energy potential. They suggest enhancing the use of various renewable energy resources such as solar, wind, bioenergy, and others [4,5], and among these, solar energy is popular. It has the advantage of being free of charge, feasible, durable, has a low maintenance cost, is environmentally sound, and has diverse applications. Nonetheless, it has its drawbacks. For example, increasing the temperature of the solar panel by 10 °C produces a 0.5% decrease in electrical efficiency for silicon cells, and cooling the solar panel may be required for improved efficiency.

Air or water may be used as a cooling liquid to cool the solar panel temperature [6,7,8,9,10,11]. The performance of the solar panel may be improved in two ways. First, solar panel cooling is a medium for waste heat storage. As a traditional cooling method, air and water usually cool the solar panel. Nevertheless, it has its virtues and merits. Because of the above, many researchers are using nanomaterials as a superior cooling fluid to boost thermal and electrical performance. Consequently, general performance can be improved, and successful studies worldwide have been conducted.

Choi and Estman [12] introduced nanofluids as a cooler in PVT systems, sparking interest due to their better thermos-physical characteristics compared to standard fluids. Nanofluids are solid–liquid synthesized, consisting of nanoparticles with diameters typically ranging from 1–100 nm drifting in water [13]. Many tests have shown that water nanofluids have a considerably higher heat transfer coefficient than basic fluids [14,15,16]. However, the heat transfer enrichment when utilizing nanofluids in photovoltaic thermal collectors has a few weaknesses, namely, a pressure drop of the system [17], a restricted period of stability, and the cost of nanoparticles being higher.

Sardarabadi et al. [18] experimented with using water as a base for SiO₂ nanofluid, at various concentrations, in PVT systems. They concluded that total performance was attained at 3.6% for 1 wt% and 7.9% for 3 wt%, which were compared with PVT water only. Ghadiri et al. [19] used an indoor PVT system to analyze water and ferrofluid with various compositions. Compared to a hybrid system, the overall efficiency was 45%. Sardarabadi et al. [20] presented three kinds of nanoparticles (MnO, TiO₂, ZnO) with deionized water with a concentration of 0.2 wt%.

Al-shamani et al. [21] researched various nanofluids, experimenting with various flow rates. The results show that SiC attained the highest electrical performance, about 13.52%, and also reached the greatest overall efficiency of 78.24%. Soltani et al. [22] conducted an investigational study in a hybrid system using water nanofluid, determining that total enactment and power generation were enriched by 3.13% and 52.4%, respectively. The authors also revealed that utilizing the SiO₂ enhanced total performance and power generation, at rates of 3.29% and 43.36%, correspondingly. Al-Waeli et al. [23] presented the influence of Silicon chloride/water nanofluid on the hybrid system, which was enhanced to 23.9% and 99.23% in terms of electrical and heat power efficiency, respectively. They also found a superior overall performance of about 88.9% compared with the PV system.

Mohammad Sardarabadi et al. [18] investigated the silica nanofluid and its efficiency in PVT systems, which showed an improvement in overall efficiency and exergy of about 7.9% and 24.3%, respectively. Ag/water nanofluid was processed via an electrical wire explosion for long-term stability [24,25]. Srimanickam et al. [26] investigated the energy and exergy efficiency of various air channel configurations with two types of air mass flow rates. The results showed that electrical, thermal, and exergy efficiency were obtained at 13.9%, 25.9%, and 49.4%, respectively. Srimanickam et al. [27] experimented with five types of mild steel air channels with two kinds of mass flow rates. The results showed that electrical and thermal efficiencies were attained at 14.27% and 20.81%, respectively.

Solar cells typically operate at 60–80% electrical efficiency in field conditions, equating to 9.5–10.5%, which may increase by 10–30% if chilled [28]. Ibrahim et al. [29] tested the PVT collector, including the installed spiral flow absorber, for heat transfer activities. The experiment results revealed that both photovoltaic and thermal systems were more effective. When the amount of solar radiation was 1321 W/m², the total and electrical efficiency of PVT were 65 and 12%, correspondingly. Alzaabi et al. [30] conducted an experimental study to demonstrate how photovoltaic modules enhanced electricity efficiency through efficiently utilizing PVT water cooling. This system was designed to monitor thermal and electrical efficiency in the environment of a Middle Eastern country.

A polycrystalline photovoltaic module was linked to a heat collector in the hybrid system. Additionally, the test included chilled and passively cooled PV module performance. The experiment’s findings revealed an increase in efficiency of 15% and 20% in electric and thermal outputs, respectively, and 60% and 70% in total and exclusive of cooling operations. Hussain et al. [31] built an experimental PVT system of honeycomb construction. The study used a coherent system comprising solar heat and photovoltaic modules. System efficiency was boosted by putting heat exchangers alongside the solar unit and using air as a receiver. Electrical and thermal efficiencies were 37.0% and 9.0%, respectively, including and excluding the honeycomb.

Wang et al. [32] created and tested a sophisticated dual PVT system based on air. The experiment results show that the efficiency of oscillatory absorbers increased to 15.0%, compared to the moderate efficiency of heat-collecting at 43.8%. These results were obtained at an ambient temperature and irradiance of roughly 70 degrees Celsius and 582 watts per square meter, with an electrical efficiency of 6% and thermal efficiency of 36.2%. Buonomano et al. [33] investigated the electrical efficiency of PVT and conventional solar modules using an economic comparison. Four unglazed flat-structure PVT systems for polycrystalline silicone were created as part of the system. PV has a 17.9% electrical efficiency and a 26.0% overall efficiency (11.6% electrical and 14.4% thermal efficiency).

The electrical and thermal efficiencies of PVT were 26.0% and 13.0%, respectively. Sahin et al. [34] used energy and exergy calculations to investigate the thermodynamic parameters of a solar panel. They observed that energy efficiency varied from 7% to 11%, and exergy ranged from 2% to 8%. Gaur et al. [35] investigated a mathematical model for electrical and thermal assessments of a liquid-based photovoltaic heating system with and without phase transition material.

In this study, the electrical energy and electrical thermal energy were carried out in the liquid and liquid-based MnO nanofluids at a flow rate of 1–4 LPM. The novelty of this investigation is using a liquid-based MnO nanofluid as a coolant. This type of nanofluid has been shown to have superior thermal properties compared to traditional coolants, including higher thermal conductivity and improved heat transfer. Using more effective coolants in PVT systems potentially increases energy production and cost savings. The concentration of liquid-based MnO used in this study was 0.1%, which enhances performance better than a liquid-based PVT system. The following parametric studies also handled electrical power generation, glazing surface temperature, electrical efficiency, and electrical thermal efficiency. These studies correlate highly with previous literature studies.

2. Experimental Details

2.1. Study Area

The results come from tests conducted at Avadi, near Chennai (the capital of Tamil Nadu, Southern India). The study site is coordinated at 13.0827° N, 80.2707° E. Under Köppen’s Climate Classification, Chennai has a tropical wet–dry summer and dry climatic conditions. The city is on the thermal equator and on the coast, which keeps seasonal temperatures from significantly varying. With an average relative humidity of 69%, the average environmental temperature varies from 24.8 °C to 33.1 °C, and average sunshine hours are 7.8.

2.2. PVT System Description

The proposed methodology was fabricated to analyze the efficiency of nano-PCM and nanofluid PVT systems, which were compared to liquid PVT systems and stand-alone PV modules simultaneously. Further, water as a coolant at variable flow rates was conducted into the PVT system, and nano-PCM and nanofluid with different concentrations and flow rates were carried out via the photovoltaic thermal collector. The final system is a self-contained PV module that operates normally. Figure 1 depicts a photograph of the experimental procedure. Figure 2 depicts a schematic depiction of the experimental setup.

To build a photovoltaic thermal collector, a multi-silicon glass panel of 1640 mm × 992 mm × 35 mm was acquired. Due to the insulation effect of the platform, a 0.4 mm copper sheet was employed on the rear of the solar panel for heat absorption. Furthermore, the copper tube is utilized as a heat absorber from the rear side of the solar panel with magnitudes of 1.0 cm external and 0.8 cm internal diameters. The performance of the solar panel at the typical test settings is shown in

Table 1. Performance of solar panels at the standard test conditions.

Parameter	Value
Pmax	260 W
Amps in Pmax	8.42 A
Volts in Pmax	30.9 V
Current in Maximum Load	8.89 A
Voltage in Maximum Load	37.7 V
Weight	18.2 Kg

. The photovoltaic thermal system was mounted at an angle of 13° to the South hemisphere. Readings were taken at 15-minute intervals every day between 8 a.m. and 5 p.m. for all weather conditions and output powers. Figure 3 shows a copper tube coupled with a solar panel.

To increase heat transmission and reduce material costs, nanofluid as a coolant used in the PVT system was constructed. The selection of competent drivers with reasonable costs that may be sold together is, therefore, an essential consideration. The system may be separated into three parts: the collector, the system supporter, and the stand-alone system. The water pump specifications are shown in

Table 2. Details of Water Pump.

Parameter	Value
Brand	Lakshmi
Model	SP 50
Phase	1
Hp	0.25
Wattage	185

.

3. Nanofluid Preparation and Characterization

Throughout the studies, manganese chloride (MnCl2), glycine, ammonia, distilled water, polyethylene glycol (PEG-400), and distilled water were used. All the compounds used in the investigation were analytical-grade reagents and were not further purified. The amount of 0.5 M of manganese chloride solution was added to 50 mL of purified water and agitated for 30 min. The amount of 0.3 M of glycine was added to 50 mL of distilled water and stirred for 30 min, and finally, the two were mixed together. To this solution, NAOH was continuously added to get a PH of 10, turning the solution a brownish color. The residual solution was evaporated overnight at 80 °C in a hot air oven. Finally, the mixture was kept in a muffle furnace for 3 h at 750 °C. Manganese oxide powder is now ready. The preparation of nanoparticles and nanofluid in the laboratory is revealed in Figure 4. An SEM image of the MnO nanoparticle is shown in Figure 5.

4. Analytical Methodology

Electrical Performance

The electrical efficiency of a PV module can be defined as the ratio of the actual electrical output of the PV module to the rate of solar energy incidence on the module. It is mathematically expressed as [36,37].

The electrical power output of the device is given by:

$${\eta }_{el}=\frac{V_{mp}{I}_{mp}}{\dot{S}}=\frac{{\dot{E}}_{el}}{\dot{S}}$$

(1)

The electrical efficiency of the device is defined as the ratio of the electrical power output to the total power input:

$${\eta }_{el}=\frac{{\dot{E}}_{el}}{\dot{S}}$$

$${\dot{E}}_{el} = V_{mp} I_{mp}$$

(2)

$$\dot{S}=G{N}_s{N}_m{A}_{mod}$$

(3)

This Equation (2) can be used to evaluate the electrical efficiency of a solar module, taking into account factors such as the number of cells in series and parallel, the module area, and the incident solar irradiance.

$$A_{mod}=L_1{L}_2$$

(4)

The equation provided relates the module area (A_mod) of a rectangular solar panel to its length (L₁) and width (L₂).

We convert conventional electrical efficiency to the thermal efficiency equivalent of electrical efficiency using the following equation:

$${\eta }_{el thermal} = \frac{{\eta }_{electrical}}{C_f}$$

(5)

where C_f is the conversion factor of the thermal power plant, and its value may be taken as 0.36 for countries such as India.

5. Results & Discussions

This experimental investigation used water and water-based MnO Nanofluid at four different flow rates of 1–4 LPM. Measurements were taken every 30 s between 8:00 and 17:00 on an average experimental day. The temperature of the gradient panels grew throughout the day as sun irradiation increased, according to the findings.

5.1. Weather Data Analysis

The weather information comprises the ambient temperature, wind speed, and solar radiation averages on the experimental days. This research was carried out during June and July 2021. Various meteorological data for the test days are displayed in

Table 3. Various meteorological data of the test day.

Flow Rate [Litres per Minute]	Solar Radiation [W/m2]	Wind Speed [m/s]	Ambient Temperature [°C]
1.0–4.0 LPM	538.98–1017.27	1.2–5.8	26.84–33.66

.

The average meteorological data of an experimental day is depicted in Figure 6, where solar radiation, wind speed, and ambient temperature appear as a canopy structure. This gives real-world data from a specific location where the system’s projected performance, based on solar radiation, wind speed, and ambient temperature, may be determined. The diurnal average incoming solar radiation dispersion for the experiment period creates a megaphone shape, with the largest value at noon being 1017.07 W/m² and the smallest value being 538.98 W/m² at 8 a.m., according to this graph. The average daily air temperature climbs from 26.84 °C at 8:00 a.m. to 33.66 °C at noon, and decreases to 28.23 °C at 5:00 p.m.

5.2. Investigation of Liquid as a Coolant in a Photovoltaic Thermal Collector

Each coolant has advantages and disadvantages. Liquid was used as a coolant in this study because of its heat-carrying capacity and natural availability. Water was explored as a coolant in a photovoltaic thermal collector in terms of energy collected, the difference in the input and output temperature of the channel and fluid flow rate, fluid heat capacities, solar irradiance, and panel area.

Figure 7 displays the variations in electrical power obtained, with time for all tested liquid flow rates ranging from 1 to 4 LPM. Equation (2) is used to calculate electrical power for all four flow rates in conjunction with a stand-alone PV system. Electrical power increased up to 12 p.m., when it began to fall due to increasing solar intensity. Because a stand-alone PV system does not have a cooling facility, a large glazing surface was acquired on the testing days. This single PV system generated less electricity than the other cooling systems. The life period of the stand-alone PV system was shorter when compared to alternative cooling PVT systems. Furthermore, this image resembles a mushroom form, symbolizing how morning progressively increases till midday and then decreases until dusk. In general, as the flow rate grew, so did the electrical output of the PV panels. The following diagrammatic depiction shows the maximum electrical power generations as 188 W, 197 W, 203 W, 208 W, and 215 W at flow rates ranging from 1 to 4 LPM.

Figure 8 displays the trends in the glazing surface obtained over time for all tested flow rates of 1–4 LPM of liquid. The surface temperature of solar panels or glazing was monitored using thermocouples, which displayed the temperature in a data logger. When sunlight strikes the solar panel, the temperature of the glazing surface rises, which is communicated to the solar panel’s rear side, known as the Tedlar side. The temperature on the Tedlar side was also monitored using thermocouples attached to a data recorder. Conduction heat transmission occurs on the glazing surface, while convective heat transfer occurs on the Tedlar surface. Because the Tedlar surface is closed, the Tedlar temperature was always greater than the glazing temperature. Furthermore, hotter ambient air travels through the Tedlar side, contributing to a rise in Tedlar temperature. However, the glazing surface is exposed to the environment and is in touch with wind, contributing to the drop in its surface temperature. For the four flow rates of 1–4 LPM with a freestanding PV system, the highest glazing surface temperatures were 69.2 °C, 68.5 °C, 67.8 °C, 67.1 °C, and 66.4 °C.

Figure 9 demonstrates the time-dependent trends in electrical efficiency for all examined liquid flow rates ranging from 1 to 4 LPM. The electrical efficiency of the photovoltaic thermal system was evaluated using Equations (1), (3), and (4). During the electrical energy analysis, characteristics, such as maximum power point voltage, maximum power point current, solar radiation, and solar panel area, were evaluated for all designs. There was a rise in glazing surface temperature and lower electrical efficiency from 9 h to 12 h, then vice versa till 16 h. It was discovered that when the glazing surface temperature was at its highest, electrical efficiency was at its lowest between 11:00 a.m. and 1:00 p.m. Electrical efficiency, like electrical power, improved as the coolant flow rate increased. The use of nanofluid resulted in an improvement in the electrical efficiency of the PV system. The maximum electrical efficiency reached in this research investigation was 12%, close to what Waeli et al. accomplished with similar types of power [38,39,40], and used liquid as a coolant to reach maximum electrical efficiencies of 10.3%, 10.8%, 11.2%, 11.6%, and 12.1 %.

Figure 10 demonstrates the time-dependent trends in electrical thermal efficiency for all tested flow rates of 1–4 LPM of liquid. Equation (5) calculates the electrical efficiency of the photovoltaic thermal system. In India, the conversion factor of the thermal power plant (0.36) was established, and electrical efficiency converts into electrical thermal efficiency via this factor. Electrical thermal efficiency has evolved as a result. From dawn to midday and into the evening, both electrical efficiency and electrical thermal efficiency followed similar trajectories. The greatest achievable efficiencies are 28.7%, 30.1%, 31.2%, 32.1%, and 33.4%.

5.3. Investigation of Liquid-Based MnO as a Coolant in Photovoltaic Thermal Collector

Despite having a larger heat-carrying capacity, water has its own challenges, such as leaks, weak showing, and other connected issues. In this experimental study, water-based MnO nanofluid outperformed all other fluids in all categories. An efficiency analysis was performed utilizing MnO nanofluid as the working fluid to increase the performance of the solar thermal collector. The liquid photovoltaic thermal collector was used as a reference to confirm the efficiency enhancement of the photovoltaic thermal collector employing MnO nanofluid as the working fluid. The cooling nanofluids in PVT systems are determined by certain parameters, such as the fluid’s viscosity, density, and thermal conductivity, which are greater in nanofluids than in the base fluid [41,42].

Figure 11 depicts the time-dependent fluctuations in electrical power achieved for all investigated liquid-based MnO nanofluid flow rates ranging from 1 to 4 LPM. As previously stated, Equation (2) may be used with a stand-alone PV system to create electrical power for all four flow rates. The generation of electrical power demonstrates the lifetime of the PV or PVT system as well as the application elements of the concerned system. The average electrical power production at flow rates ranging from 1 to 4 LPM was 152.3 W, 164.5 W, 169.1 W, 175.1 W, and 182.8 W. At flow rates ranging from 1 to 4 LPM, the greatest electrical power produced was 188 W, 203 W, 209 W, 216 W, and 226 W.

The trends in the glazing surface obtained over time for all investigated flow rates of 1–4 LPM of liquid-based MnO nanofluid are shown in Figure 12. Every 1 °C increase in temperature over the recommended operating temperature on the PV panel surface results in a 0.5%drop in efficiency. Overheating solar cells generates thermal stress, reducing the lifespan of PV cells [7,8,9]. The average glazing surface or solar panel temperatures were 57.1 °C, 55.4 °C, 54.2 °C, 53.1 °C, and 52.5 °C for flow rates ranging from 1 to 4 LPM. The greatest glazing surface temperatures for the four flow rates of 1–4 LPM with a freestanding PV system were 69.2 °C, 67.1 °C, 65.7 °C, 64.4 °C, and 63.7 °C.

The graph in Figure 13 depicts the trends in electrical efficiency obtained over time for all investigated flow rates of 1–4 LPM of liquid-based MnO nanofluid. The MnO nanofluid module attained the highest electrical efficiency because the surface temperature of the PVT system was lower than that of a solo PV module. The use of MnO nanofluids improved electrical efficiency as well, improving electrical efficiency at a flow rate of 4 LPM, greater than other flow rates and a stand-alone PV system. Because MnO nanoparticles have better thermal conductivity than water, they may remove more heat from a system in less time. The average glazing surface or solar panel temperatures were 9.2%, 11.1%, 11.5%, 11.9%, and 12.6% for flow rates ranging from 1 to 4 LPM. The greatest glazing surface temperatures were 10.3%, 12.4%, 12.9%, 13.4%, and 14.2% for the four flow rates of 1–4 LPM with a freestanding PV system.

The trends in electrical efficiency achieved over time for all investigated flow rates of 1–4 LPM of liquid-based MnO nanofluid are shown in Figure 14. Electrical efficiency and electrical thermal efficiency factors were directly reliant on one another. The average electrical thermal efficiencies were 25.4%, 30.5%, 31.8%, 33.1%, and 35.1% for flow rates ranging from 1 to 4 LPM. The greatest electrical thermal efficiencies for the four flow rates of 1–4 LPM with a freestanding PV system were 28.7%, 34.4%, 35.8%, 37.3%, and 39.6%.

6. Conclusions

The goal of this research was to study the performance of a recently designed photovoltaic thermal collector. Four different flow rates of liquid and liquid-based MnO nanofluids were measured and compared to a stand-alone PV system. The following is a summary of the research findings:

• Electrical efficiency was achieved in a spectrum of 8.2% to 12.1% for liquid-type PVT systems, and 9.4% to 14.2% for liquid-based MnO nanofluid PVT systems;
• Electrical thermal efficiency was achieved in a range of 22.9% to 33.3% for liquid-type PVT systems, while electrical thermal efficiency was achieved at a limit of 26.1% to 39.6% for liquid-based MnO nanofluid PVT systems.