Introduction

The global energy demand, environmental challenges, and resource sustainability have raised several issues with substitute energy sources based on non-fossil fuels with clean and suitable renewable energy sources [1, 2]. As known, the vast majority of global energy is supplied by exhaustible and polluting sources of energy in the form of fossil fuels i.e., petroleum, coal, and natural gas. Where it contributes 80% to the current world energy supply [3, 4]. As a result of the above-mentioned problems, researchers have been trying over the last several decades to explore the possible alternative power sources from renewable energy resources. Furthermore, a decade ago humans expected that a sustainable power source could achieve the prerequisite of energy. Solar, wind, biomass, and hydro are the sources of sustainable energy in a natural form [5,6,7]. Solar energy in the form of a solar photovoltaic system (SPV) could provide an alternative favorable and environmentally friendly to substitute conventional fuel for power generation.

Egypt has high sun-oriented insolation as a perfect condition for generating electrical energy from sunlight. The Egyptian government has grown its own sun-oriented-based electricity generation by presenting particular approaches and subsidizing for expanding the energy capacity generation from solar [8].

As known, the photovoltaic cell directly converts solar energy (sunlight) into electrical energy [9]. Despite the huge benefits of using a solar photovoltaic system, the main drawback of it is limited efficiency, which ranges between 12 and 20% [10]. Solar irradiance, wind, temperature, and dust accumulated are the main parameters, which influence the generation of the output energy of the SPV system. The main factor in degrading the generation of SPV modules is dust accumulation on the top surface of the module which causes huge energy losses during long-term utilization. So, the subject of SPV system performance degradation due to dust deposition has become a major concern [11, 12]. The negative impact on the covering glass of solar cells decreases the spectral transmittance, reduces SPV power generation efficiency, and decreases lifespan [11]. Dust accumulation effect on the SPV performance exposed to outdoor conditions at various sites was widely experimented [13]. Egypt like all countries in tropical regions of the Middle East and Saharan Africa is particularly vulnerable to the accumulation of dust on the surface of photovoltaic systems [8].

In grid-connected solar installations, SPV modules are connected in series, forming strings that are then connected in parallel. In this scenario, a fault in a single cell in an SPV module affects all the modules electrically connected to it. In this context, techniques related to the operation and maintenance of SPV modules acquired greater attention [14,15,16]. Overall energy efficiency and thermal efficiency can be increased by using an optimization process [15]. Several factors are behind the degradation and reduce the performance of SPV modules such as high temperature, solar radiation, wind speed, as well as dust ……etc. [17, 18]. The accumulated dust in SPV modules is one of the parameters that influence energy conversion, and it can be significant in many regions [19]. Dust accumulated density, compositions of dust and dust particle size have a negative impact on the SPV performance exposed to outdoor conditions [20]. The short circuit current is significantly reduced at higher dust density under weather conditions also, the found that after 5 months of exposure, the power loss of the SPV module is 12.7% [21]. The reduction in output power of SPV by 12.47% and in efficiency by 11.86%, in the Jordanian southern province of Al Karak has been reported [18]. They explained that the reduction in power and efficiency was caused by decreasing the short circuit current of the SPV module under dust conditions. In addition, the dust particles disperse the sun rays falling on the SPV module surface, causing a reduction in power output. Styszko et al. [19] studied the effect of dust deposition on the PV front cover glass during the non-heating season in Kraków. The results showed that the dust particles reduce and scatter the intensity of the total radiation incident on the SPV modules, which leads to a decrease in the conversion efficiency. This means that the dust accumulated on the SPV module blocks solar radiation to enter directly into the solar cell, which leads to the loss in the output power of the SPV modules.

As reported, several studies have been done on the effect of dust on the output power and the efficiency of the SPV modules [8, 17, 22,23,24]. Also, most of the reported studies have been conducted in the laboratory, whereas only a few were conducted outdoor. However, the effect of different accumulated dust densities on the performance of the SPV still needs more attention. The aim of this work is to investigate the dust effect on the performance of the SPV modules under Cairo, Egypt weather conditions. The electrical parameters measured are (I–V) and Pmax as well as the panel front and back side temperature and irradiation. The measurements were investigated and evaluated on cloudless days outdoor. This could make the study more representative of the environment surrounding the solar panels compared to conducting experiments in the laboratory. In addition, the study was conducted with the help of Infrared Thermography (IRT). This could also, help in the accurate detection of the working temperature of the SPV modules and detecting the hot spot location of the SPV panel. Also, a deep investigation by integration of IRT and temperature sensor for accurate detection of the SPV front and back side temperature, as well as the interaction between front and back side temperature of SPV modules.

Materials and methods

Study region

Egypt is characterized by a desert climate. The climate is mostly dry and hot. Cairo, which is the capital of Egypt, is located at 30.04167° latitude North and 31.23528° longitude West. The solar radiation of Cairo is 4.7 kWh/m2/day, and the average annual ambient temperature is 22.1 ℃. The average annual humidity is 55% and the annual wind speed is 4.02 m/s.

Materials

The performance of five modules exposed to outdoor conditions in Cairo, Egypt (30.04167° N, 31.23528° E), were studied. The details of outdoor conditions during the experiments are shown in Supporting Information Fig. S1. The modules were faced towards the south and tilted at Cairo latitude of 30°. The specifications of the tested solar SPV modules are listed in Table 1.

Table 1 The used SPV system specifications
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The backside temperature of the five modules was measured using five K-type thermocouples attached to each back surface of the module and connected to the Arduino board type of Mega 2560 Rev3. The Arduino board was connected to a Raspberry Pi board (4 B-8GB) that saves all recorded temperatures and easily processed data after that as shown in Supporting Information Fig. S2. The thermocouple generates a small voltage proportional to the temperature difference between their two ends. The Arduino Mega 2560 Rev3 board run a program to instruct the Arduino to read the data by analog to digital converter (ADCs) to measure the voltage and convert it to temperature values then send it to the laptop.

The frontside temperature of the five modules was detected using an IR camera. Supporting Information Fig. S3 shows a schematic diagram (a) and a complete setup of the experiments (b). As shown in Fig. S3, different devices were used to detect and measure different parameters with the experiments. The specifications of the used measuring device are listed in Table 2.

Table 2 Technical specifications of the measuring devices
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Accumulated dust materials used in this study were collected from the same location as the experiments. The components of dust were analyzed using an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin Elmer, Avio 200, USA); EC was tested using Thermo Fisher Scientic (XL 600, Japan) as listed in Table 3.

Table 3 Accumulated dust compositions
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A Carl-Zeiss Merlin II eld emission scanning electron microscope was used to characterize the surface morphology of the dust sample as shown in Supporting Information Fig. S4.

Test procedure

To make sure of the impact of the dust materials, glass panel 1 m2 was installed at the same location of the experiments with the same latitude angle of the PV module. The weight of the glass plate was measured when it is clean and after accumulating dust on it daily for two consecutive months from 17 May to 17 July 2022. These months are the dustiest days in Egypt [25]. Four different dust densities of 6, 12, 18, and 24 g/m2 were used compared to the clean SPV module (control). The dust densities were selected based on the maximum dust density during the dustiest days in Egypt Supporting Information Fig. S5.

The sunlight intensity, DC current, DC voltage, ambient temperature, relative humidity, backside, and front side temperature of the five modules were measured every hour for 8 h daily from 9 AM to 4 PM.

The power (P) and efficiency (η) can be calculated using the following equation [26]:

$$P_{\max } = I_{\max } V_{\max } ,$$
(1)

where \(I_{\max }\) is the maximum current in amperes (A); \(V_{\max }\) is the maximum voltage in (V).

The efficiency of the solar module is determined as stated in equation [27]:

$$\eta = \frac{{P_{\max } }}{E \times A}.$$
(2)

where \(P_{\max }\) is the maximum power output (W); E is the available global irradiance (W/m2); A is the surface space of the solar PV module (m2).

The loss of conversion efficiency with dust accumulation \(\eta_{{{\text{loss}}}}\) can be calculated using the following equation [28]:

$$\eta_{{{\text{loss}}}} \left( \% \right) = \left( {1 - \frac{{PV_{d} }}{{PV_{nd} }}} \right) \times 100,$$
(3)

where \(PV_{d}\) is the maximum power output of the photovoltaic panel with dust accumulation (W) and \(PV_{nd}\) is the maximum power output of a clean panel (W).

Measuring errors and uncertainty

The uncertainty analysis for measurements and calculations was done using the accuracy values from the calibration and the provided specification for different devices shown earlier in Table 2 as follows [29]:

$$e_{r} = \left[ {\left( {\frac{\partial R}{{\partial V_{1} }}e_{1} } \right)^{2} + \left( {\frac{\partial R}{{\partial V_{2} }}e_{2} } \right)^{2} + \cdots + \left( {\frac{\partial R}{{\partial V_{n} }}e_{n} } \right)^{2} } \right]^{0.5} .$$
(4)

The calculated uncertainty was found to be \(\pm 0.512\%\) which is accepted in low-risk applications.

Results and discussions

Since the key objective of this study was to investigate the effect of different dust densities accumulated on the performance of the SPV modules, the panels working temperature, maximum power, and efficiency of the SPV modules were recorded and measured at cloudless days in the outdoor condition. This made the study more representative of the environment surrounding the solar panels compared to conducting experiments in the laboratory.

Front and backside temperature of SPV modules

A deep investigation of dust influence on the working temperature for the SPV modules has been conducted where not previously been studied. For accurate detection of solar panels temperature, the frontside temperature of the solar panels was measured by an IRT camera as mentioned in "Study region". While the back temperature of the panels was detected as average values of five temperature sensors fixed on the rear surface of solar panels as explained in "Study region". This action was used because the reflection of the temperature for the solar panels' chassis with thermography makes image processing difficult.

Figure 1 shows the relation between hourly frontside (line) and backside (column) temperatures of solar SPV modules under different dust densities as compared with the clean module during the daytime. As can be seen from Figs. 1, 2, and Supporting Information Fig. S6 for the frontside and backside temperatures of the SPV modules, the working temperatures of SPV modules were found to be increased markedly with the daytime from 9 am to a peak at 11–12 noon then decreased. This is normal because the maximum solar radiation occurrence at 11–12 noon, as reported in Supporting Information Fig. S1, caused more generation of radiation which led to increasing the temperature of the SPV modules [30].

Fig. 1
figure 1

Effect of dust accumulation on frontside (line) and backside (column) temperatures of solar photovoltaic modules

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Fig. 2
figure 2

Thermal images of solar photovoltaic modules under different dust densities over daytime

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For the frontside, the temperature of the clean SPV module was higher than the dusty modules under different dust-accumulated densities. This may be because the dust accumulated on the SPV modules caused reflection of the solar radiation leading to a lowering of the frontside temperature of dusty modules compared with clean SPV modules [31]. It is noteworthy that, the dust with the accumulated density of 6 g/m2 has no remarkable effect on the frontside temperature of the SPV module as compared to the clean module. However, when the dust accumulated density on the SPV modules was increased from 6 to 24 g/m2 the frontside temperature decreased significantly. This may be because of the large amount of dust accumulated on the SPV modules (Fig. 2) and Supporting Information Fig. S6.

More specifically, the frontside temperature of the SPV modules was found to be ranged from 42 to 58 ℃, 37 to 55 ℃, 36 to 53 ℃, and 36 to 50 ℃ for clean and dusty modules with a density of 6 g/m2, 12 g/m, 18 g/m2, and 24 g/m2, respectively, during daytime. These results can also be reflected in Fig. 2 and Supporting Information Fig. S6 of the IRT for the SPV modules under different conditions. As can be seen from Figs. 2 and S6 the surface temperature of the SPV module under dust conditions tended to be lower as compared with the clean SPV module during the daytime.

As a result of the effect of dust accumulated on the frontside temperature of the SPV module, we can conclude that when the dust accumulated by high density on the SPV modules its frontside temperature decreased remarkably due to the highest reflection of the solar radiation by high accumulated of the dust.

On the other hand, the situation was in the opposite trend, as seen in Fig. 1, for the backside temperature of SPV modules. Where the dust accumulated on the SPV modules led to an increasing in the backside temperature of the SPV modules under different dust densities as compared with the clean SPV module. This phenomenon may be because the accumulated dust causes trapping and concentration of the heat inside the SPV modules. This results in the reflection of the heat on the backside of the SPV modules making them higher temperature than the clean SPV module [32].

As evident, from Fig. 1, when the dust density that accumulated on the SPV modules increased from 6 to 24 g/m2 the backside temperature of the SPV modules significantly increased. More specifically, the backside temperature of the SPV modules was found to be higher by 2–6%, 4–10%, 5–11%, and 5–13% when the accumulated dust densities were 6, 12, 18, and 24 g/m2 respectively as compared with clean SPV module. This could also explain the hot spot that occurred on the backside of SPV modules under higher accumulated dust densities i.e., 18 and 24 g/m2. Furthermore, the highest accumulated dust density (24 g/m2) caused a remarkable effect in increasing the backside temperature of the SPV modules up to 67 ℃ at 12 O'clock noon compared with 57 ℃ for the clean module at the same time. The results, from Fig. 1, concluded that the dust accumulated caused more warming of the backside modules.

It is noteworthy from Fig. 1, that the backside temperature was found to be higher than the frontside temperature of the SPV modules during the daytime under different accumulated dust conditions. The results, also, indicated that the difference between front and back side temperatures of the SPV modules were highest under 12, 18, and 24 g/m2 of dust densities compared with 6 g/m2 and clean SPV modules. This may be because of more trapping of the heat due to the high-density dust accumulated on the SPV modules. Whereas the difference between backside and frontside temperatures of the SPV modules were found to be in the range of 1–4 ℃, 2–7 ℃, 4–11 ℃, 7–17 ℃, and 7–20 ℃ for clean, 6 g/m2, 12 g/m2, 18 g/m2, and 24 g/m2 respectively.

Current–voltage curves of SPV modules

Figure 3 describes the hourly current–voltage characteristics for dusty and clean SPV modules under different conditions. Figure 3 reveals a lot of information for better understanding and analyzing the degradation that occurs in current–voltage characteristics of SPV modules under dusty and clean conditions.

Fig. 3
figure 3

Effect of dust accumulation on current (line) and voltage (column) of solar photovoltaic modules

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As can be seen from Fig. 3, the output currents of the SPV modules were found to be increased markedly with the daytime from 9 am to peak at 11–12 noon then decreased sharply with the time up to a minimum at 4 pm. This is normal because the maximum solar radiation occurrence at 11–12 noon, as reported in Supporting Information Fig. S1, caused more generation of radiation which led to increasing the output current of the SPV modules [15]. On the other hand, the voltage of the SPV modules was found to be high at 9 am with the range of 32.3–32.6 V then decreased to 31.5–31.9 V at 11–12 noon in addition to being approximately constant until 4 pm. This phenomenon maybe because, under high solar radiation, the temperature of the modules was high (Fig. 1) leading to a decrease in the voltage of the SPV modules [13].

By comparing the curves in Fig. 3, a remarkable reduction in the current with a slight reduction in voltage for the dusty modules as compared with the clean module was noticed, which clearly shows the effect of dust deposition on the SPV modules' surfaces. This maybe also due to the dust accumulated on the SPV modules led to increase in their backside temperatures (Fig. 1), resulting in reducing the output current of the dusty modules compared with clean module [20, 33]. The results indicated, also, that the dust accumulated on the SPV modules led to a decrease in the solar irradiation received resulting in the degradation of their output currents as compared with clean SPV module. This means, the dust leads to a decrease in the transmittance of solar cell glazing and causes a significant degradation of the solar conversion efficiency of SPV modules [34]. Thus, the dust accumulation on the SPV module blocks the solar radiation to enter directly into the solar cell [17]. It is noteworthy that when the dust density accumulated was 6 g/m2, 12 g/m2, 18 g/m2, and 24 g/m2 the output currents of the SPV modules were found to be lower by 7–10%, 15–18%, 22–34%, and 30–45% as compared with clean SPV module. While the voltage of the SPV modules was found to be lower by 0.1–1.2% when the dust was accumulated on the SPV modules as compared with the clean SPV module.

Output power and efficiency of SPV modules

Figure 4 describes the output power from dusty and clean SPV modules under different conditions during the daytime. As can be seen from Fig. 4, the output power of the SPV modules was increased with the daytime from 9 am to peak at 11–12 noon then decreased sharply with the time up to a minimum at 4 pm. This is normal because the utmost solar radiation received on the SPV modules at 11–12 noon caused more current generation as seen in Fig. 3 [35]. It is clearly seen that, from Fig. 4, the value of the initial output power at 9 am are 239, 208, 197, 184, and 163 Watt for clean and dusty SPV modules under different dust densities of 6 g/m2, 12 g/m2, 18 g/m2, and 24 g/m2 respectively. The corresponding values were found to be 272, 245, 230, 211, and 190 watts, respectively, at 11–12 noon in addition to 61, 57, 50, 40, and 33, respectively, at 4 pm.

Fig. 4
figure 4

Effect of dust accumulation on the output power of solar photovoltaic modules, output power: columns and percentage of reduction as compared with clean module: lines)

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Furthermore, the dust accumulated on the SPV modules has a remarkable effect on the reduction of the modules power as compared to clean module. The output power of the dusty SPV modules were found to be lower by 6–12%, 12–18%, 21–34%, and 30–45% as compared with clean SPV module when the dust densities were 6 g/m2, 12 g/m2, 18 g/m2, and 24 g/m2, respectively. These results agree with Zeshan et al. [36] who found that the average output power was reduced up to 22% for June, 16% for July, and 18% for August due to the accumulation of dust on the surface of the polycrystalline PV modules, exposed to the outdoor operating conditions in Pakistan.

The reduction in the output power of the dusty SPV modules maybe because of the higher temperature of the dusty SPV modules due to accumulated dust resulting in reduction in the modules current which finally reduced the output power of the dusty modules compared with clean module [10, 37]. Comparing the output power curves in Fig. 4, it is clearly seen that, the sharp reduction in the output power occurred when the dust densities were high i.e., 18 g/m2 and 24 g/m2 at 4 pm. This is possibly attributed to two negative factors i.e., dust accumulated and reduction in solar radiation at sunset. This has a considerable effect in hampering the SPV modules to absorb solar radiation [18, 38, 39].

Furthermore, Fig. 5 represents the effect of dust accumulated on the output efficiency of the SPV module. As can be seen from Fig. 5a, the hourly efficiency of the dusty SPV modules was found to be lower than the efficiency of the clean SPV module. This may be because the dust accumulated with high density reduced the output power from the SPV modules compared with the clean SPV module (Fig. 4) resulting in higher efficiency generation in the case of clean module than dusty modules. It is noteworthy that, the highest accumulated dust density has a remarkable effect in reducing the SPV module efficiency up to a minimum i.e., 10% (Fig. 5b). Whilst the average efficiency of the clean SPV module was found to be 16% (Fig. 5b). Further, the dust accumulated by the densities of 6 g/m2, 12 g/m2, 15 g/m2, and 24 g/m2 reduced the output efficiency of the SPV modules by 13%, 19%, 25%, and 38% respectively as compared with the clean SPV module. These results agree with Karmouch et al. [40] who found that the deposition and accumulation of dust significantly reduced the efficiency of solar cells by reducing the transmission of sunlight. They found approximately a 10.49% reduction in efficiency after 16 weeks. They also recommended using a self-cleaning system product, especially in dusty areas with low rainfall to prevent dust accumulation and to improve the energy performance modules.

Fig. 5
figure 5

Effect of dust accumulation on efficiency of solar photovoltaic modules: a hourly efficiency and b average efficiency

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Conclusion

The current study aims to investigate the effect of dust accumulation on the performance of the SPV modules. When the dust accumulated by high density on the SPV modules its frontside temperature decreased remarkably due to the highest reflection of the solar radiation. As well as the dust accumulated on the SPV modules caused more warming of the backside modules. A decrease in output current and voltage of dusty SPV modules compared to clean SPV module. These results are explained as the solar radiation is blocked to enter directly into the solar cell by dust accumulating on the top surface of the SPV module which acts as a barrier against the sunlight resulting in a decrease in its power generation and efficiency. In addition, the power output and efficiency of the dusty SPV modules decreased by 6–45% and 13–38%, respectively, compared to the clean module. The future work of this study is to design a new system for cooling and cleaning the PV modules using artificial intelligence after the thermal images of PV modules processing to determine the accurate time for cooling and cleaning operations.