Integrated photovoltaic-thermal system utilizing front surface water cooling technique: An experimental performance response

Abstract

In the realm of photovoltaic-thermal (PVT) systems, optimizing operating temperatures for photovoltaic (PV) panels is a challenge. This study introduces a novel solution: a sprayed water PVT system that simultaneously harnesses energy and electricity. The aim is twofold: generate electricity through PV panels and produce hot water via a flat plate collector, using an innovative cooling mechanism. Water sprayed onto the PV panel's surface flows to a collector for storage. With varied flow rates, optimal panel efficiency occurs at a 45⁰ tilt angle, accompanied by lower collector outlet temperatures at higher flow rates. The collector achieves a peak thermal efficiency of 70.6 %, producing hot water at 84.6 °C. Notably, a significant PV panel efficiency enhancement, up to 16.78 %, especially at 1.56 L/min flow rate, is observed. The cooling technique consistently reduces panel temperatures from 45.08 °C to 34.12 °C. A self-cleaning spray mechanism improves efficiency by 2.53 %, resulting in an overall system efficiency of 83.3 %. This research offers an innovative approach to enhance energy generation and electricity in PVT systems, promising sustainable energy optimization.

Nomenclature

m

water mass flow rate (kg/s)

Cp

specific heat of fluid (joule/gram °C)

ΔT

temperature difference (⁰C)

Is

Solar radiation intensity (W/m²)

Ƞr

reference efficiency of panel

Β

temperature co-efficient (0045 °C)

Tsc

PV temperature (⁰C)

Tr

Reference temperature (⁰C)

EL

daily energy consumption

PSH

peak sun hours

Ƞs and Ƞiv

Efficiency of the system components

Sf

Safety factor represents the compensation of resistive losses and PV temperature losses

A_p

PV array area (m²)

GT

daily solar radiation (KWh/m²)

m

slope of saturation vapor pressure curve (paK-1)

Rn

Net irradiance (Wm-2)

Cp

Heat capacity of air (Jkg-1K-1)

ρa

air density (kgm-3)

ga

momentum surface aerodynamic conductance (KJ-1)

h

Convection heat transfer coefficient (W/m² K)

P_e

Electric power output from the PV panel (W)

σv

Latent heat of vaporization (Jkg −1)

T_{panel_front}

Front average panel temperature (°C)

Ƞmodule

efficiency of PV module

Ƞwire

efficiency of wire

CO

Convection number

ht

Heat transfer coefficient (W/m²k)

f

Friction factor

x

Quality

fr

Froude number

BO

Boiling number

CSP

Concentration solar power

ISSC

Integrated solar combined cycle

Nu

Nusselt number

K

conductivity of material

L

length of plate

RaL

Rayleigh number

γ

psychometric constant (paK-1)

V2

wind speed(m/s)

τ

transmission coefficient of glazing

α

absorption coefficient of plate

Tc

collector average temperature (^oC)

^U

Internal energy of PV panel (J)

V_w

Water spray flow (L/min)

Tp

Glass plate temperature (^oC)

T_{panel_back}

Backside panel temperature (°C)

1. Introduction

The energy sector performs a vital role in the prosperity and growth of a country. However, the whole world is largely dependent on fossil fuels [1]. As a result, large amounts of greenhouse gas are being emitted, which is unhealthy for the environment and future generations [2]. The global energy consumption trend projects that fossil fuels (oil, gas, coal) will contribute 60–78 % of the energy mix in 2040, although the renewable energy and nuclear energy trends are increasing faster [3,4]. Hence, using renewable energy sources for power generation instead of fossil fuel is a global challenge for providing a sustainable and secured power supply and keeping the environment pollution-free [5,6]. In this case, solar energy is one of the major pathways available in the world that has been harnessed for various applications since the long history of humanity [7]. Most solar irradiations absorbed through PV modules are converted into heat rather than into electrical power which is first major problem [2,8]. The second major problem with commercial PV technology is the cleaning problem, namely the impact on dust [9]. To avoid such performance, drop problems in PV modules, front surface water spray can be considered an emerging pathway in PV technology.

Furthermore, it is well known that when the PV panel's cell temperature increases, efficiency decreases, and almost 80–90 % of incident energy is wasted as a form of heat. This drawback can be recuperated by the integrated photovoltaic-thermal (PVT) system. Indeed, this issue is one of the major concerns for the researcher in recent years. To solve this difficulty, Niz etic et al. [10] has applied a water spray technique on the front surface. It helps to increase the electrical efficiency of the PV panel. In 2016, Niz etic et al. [8] has sprayed water on both sides of the PV panel and improved the performance of the second analysis from the first analysis and at the same time checked the feasibility. This author [9] also mentioned that water spray is a self-dust cleaning system that can boost PV panel performance. This phenomenon of water can be used to cool PV panel faster compare to other technique. So, it is clear that PV electrical efficiency can be improved by enhancing heat transfer. For instance, Khanjari et al. [11] and Verhelst et al. [12] have used nanofluid with water to enhance thermal efficiency. However, the used water spray and water with nanofluid is not further utilized. With this problem in mind, the author [13] has designed a new system, where water flows on the top surface of the PV panel, then passes through the collector and validates the PVT/W system. But in this system, the mass flow rate has been reduced for natural circulating water. In similar way, Sahay et al. [14] has flowed water to the top surface and passed it through the water collector. As a result, the performance of PVT/W system has improved significantly. Both Arman [13] and Sahay et al. [14] have placed the collector outside the PV panel, as solar radiation can occur directly on the collector.

Arman et al. [15] recently introduced an innovative technique involving forced water circulation to enhance Photovoltaic-Thermal (PVT) system efficiency. Their study demonstrates significant efficiency gains of 0.8–1 % across water flow rates of 2, 2.25, 2.75, and 3 L/min, surpassing other systems, concurrently boosting overall efficiency. However, unexplored dimensions include the impact of substituting water spray for flow within the PVT/W system and the performance implications of water flow rates below 2 L/min and beyond 3 L/min, alongside unexamined dust effects. In response, this study presents an integrated approach, situating the collector beside the PV panel, involving water spraying over the panel and circulating heated water through a collector using a piping network. This setup optimizes collector exposure to solar radiation, shaping a distinctive PVT system. Recent notable contributions to the PVT field are summarized in Table 1.

Table 1.

Summary of recent published study on PVT systems.

Ref.	Year	Ref. Technologies	Ref. Working environment	Ref. Findings	Aspect	Ref. Article	This Article
[16]	2018	Real time investigation of Photovoltaic thermos control with water	Performance of the PV panel was observed with and without water cooling in order to reduce the evaporative water losses. A laboratory based experimental set up is used for continuous and intermittent cooling.	It is observed that the continuous cooling system with a water pump of appropriate capacity improves the performance of PV panels while keeping the consumption of water to minimum. The difference in total energy produced between the two cases – continuous cooling and no cooling- amounts to almost 29.40 %.	Innovation and System	Focuses on the traditional water-cooling system	Introduces a novel sprayed water PVT system
					Approach Scale of Experiment	Based on a laboratory-scale setup	Represents an actual system's performance
					Scope of Study	Primarily explores the impact of water cooling	Integrates electricity, hot water, and cooling
					PV Panel Efficiency Improvement	Doesn't specify PV panel efficiency improvement	Reports a significant increase of up to 16.78 %
[17]	2021	Pulsed spray water cooling system for PV panel.	Two PV panel of which one of them having a spray cooling system, while the other one is not equipped with the cooling system in the direction of the south with angle of 30° with respect to the horizontal under the same conditions.	The electrical power output of the PV panel increases about 33.3 %, 27.7 %, and 25.9 % by using the steady-flow water spray cooling system, pulsed-spray cooling system with DC = 1, and 0.2 which reduced the cost of electricity about 46.5 % and 76.3 % respectively. The electrical efficiency decreases from 12.1 % to 11.5 % by the pulsed-spray cooling system instead of panel cooled down by the steady-flow cooling system.	Innovation and System	Focuses on traditional cooling techniques	Introduces a novel sprayed water PVT system
					Scope of Study	Concentrates on improving electrical efficiency and reducing water consumption	Simultaneously generates electricity and hot water with cooling
					Comprehensive Data	Lacks detailed data on system efficiency and temperature reduction	Provides data on system efficiency, temperature reduction, and more
[9]	2016	Simultaneously both side water spray cooling technique for PV panel.	A PV panel was equipped with a system of nozzles mounted at the front and rear sides to ensure proper water spray distribution on both sides at a specific angle of 17°	Experimental findings indicate that the suggested cooling strategy during peak solar irradiation can increase power output by 16.3 % (7.7 % effectively) and improve PV panel efficiency by 14.1 % (5.9 % effectively). Cooling both front and back panels lowers the temperature from 54 °C to 24 °C	Cooling Technique	Presents a water spray cooling technique	Introduces a sprayed water PVT system
					Energy Generation Approach	Focuses on enhancing electricity generation	Simultaneously generates electricity and hot water
					Detailed Efficiency Data	Offers data on increased electric power output and PV panel electrical efficiency, but less comprehensive data	Provides comprehensive data on system efficiency, temperature reduction, and self-cleaning mechanism
					Innovative Features	Focuses on boosting electricity	Includes an innovative cooling mechanism and peak thermal efficiency
					Water Flow Rates	Doesn't specify flow rates as a factor for efficiency	Mentions varied flow rates for optimal panel efficiency
[18]	2021	Conventional water-cooling using number of copper tubes.	A reference photovoltaic panel and a photovoltaic of poly crystalline silicon with water PV/T system employing a single copper absorber plate and absorber tube are the two types of photovoltaic systems that are developed.	According to the study, at a mass flow rate of 0.0166 kg/s, electrical efficiency increased by 6.08 % and temperature was reduced by 15.23 %. Open circuit voltage and short circuit current also increased by 3.45 % and 2.4 %, respectively.	Cooling Mechanism	Utilizes copper tubes and a single absorbing copper plate for cooling	Introduces a sprayed water PVT system and separate collector
					Performance Data	Offers limited data on open circuit voltage, short circuit current, temperature reduction, and electrical efficiency	Provides extensive data on system efficiency, temperature reduction, and self-cleaning mechanism
					Innovation and Advanced Features	Lacks mention of innovative features	Includes an innovative cooling mechanism with self-cleaning
[19]	2022	Water spray cooling for PV panel.	A three-dimensional computational model for water spray cooling of photovoltaic panels with self-cleaning effect.	For the optimum flow rate of 170 L/h, the electrical efficiency of the panel was 15.73 %, panel power output was 40.25 W and the pump power required was 0.77 W. A maximum power output of 39.48 W for the system was achieved at a flow rate of 170 L/h.	Nature of Study	Theoretical, focusing on computational modelling	Practical, based on experimentation and real-world data
					Scope of Implementation	Concentrates on the development of a computational model	Presents a full-scale implementation of a sprayed water PVT system
					Extent of Performance Data	Offers data on computational model validation and optimal flow rate	Provides extensive data on system efficiency, temperature reduction, and self-cleaning mechanism
					Focus on Heat Transfer Characteristics	Focuses primarily on the influence of water spray volume fraction on heat transfer	Explores a broader range of aspects, including hot water production and innovative PV panel cooling mechanisms
[20]	2022	Back surface cooling of PV panel.	The PV's back surface cooling; a cost-effective method for preheating the supply water for a reverse osmosis desalination system in addition to being easy and affordable is implemented.	The findings indicated that when the suggested cooling system is applied, the PV's power generation will increase by roughly 14.1 %. When the PV module with cooling system was tested, the electrical efficiency likewise achieved 19.8 %, compared to the 17.4 % attained without cooling.	Energy Generation Approach	Primarily aims to improve electrical power generation	Simultaneously generates electricity and produces hot water
					Scope of Cooling	Cooling is limited to the back surface of the PV module	Front side cooling and dust self-cleaning mechanism
					Comprehensive Data	Offers limited data on electrical power generation and efficiency	Provides extensive data on system efficiency, temperature reduction, dust effect and self-cleaning mechanism
					Hot Water Production	Does not mention hot water production as part of the cooling	Achieves hot water production as a part of the cooling system

In this study, the authors introduce a pioneering method involving water spraying on PV panels' front surface, with controlled water flow (2–3 L/min), meticulously assessing system performance, exergy and energy aspects, and the impact of dust. The study evaluates the feasibility of the proposed PVT/W system, featuring an inventive flat plate collector situated outside the PV panel, offering advancements over conventional setups. To address the water distribution, the study emphasizes Equal distance of mist nozzles, the integration of automatic pressure regulation for nozzles, adjustable nozzle settings, and periodic maintenance. These measures ensure a consistent and efficient distribution of water across the top surface of the solar panels, adding to the success of the proposed methodology. The experimental arrangement is positioned a top Rajshahi University of Engineering & Technology's Heat Engine lab.

The study introduces an innovative method involving controlled water spraying on the front surface of PV panels to improve system performance and assess exergy and energy efficiency, while also examining the impact of dust. Unlike traditional setups, this research explores a novel PVT/W system with a unique flat plate collector setup outside the PV panel. The study aims to design a solar water heating system with front surface water cooling, analyse its performance, examine dust effects, and generate electricity and hot water concurrently. Detailed analysis, spanning several months, enhances the reliability of findings, and the innovative front surface water spraying technique has the potential to significantly enhance the efficiency and feasibility of photovoltaic-thermal systems.

In summary, the novelty and motivations can be written as.

• 1.
  Innovative Water Spraying Technique

  • •
    Novelty: The introduction of a controlled water spraying method on the front surface of PV panels is a key innovation. This technique is distinct from traditional setups and aims to enhance system performance.
  • •
    Motivation: The motivation behind this innovation is to explore an unconventional approach that leverages water spraying for improving the efficiency of photovoltaic-thermal systems.
• 2.
  Separation of Collector Setup

  • •
    Novelty: The deliberate separation of the flat plate collector setup from the solar panel is a unique feature of this research. This departure from conventional integration provides more targeted water spraying.
  • •
    Motivation: The motivation is to optimize the water spraying technique by separating the collector setup, allowing for precise control and potentially improving overall system performance.
• 3.
  Active Repurposing of Sprayed Water:

  • •
    Novelty: The research actively repurposes the sprayed water, contrary to traditional practices where it is not further utilized. This novel aspect explores resource optimization in the proposed PVT/W system.
  • •
    Motivation: By repurposing sprayed water, the study aims to contribute to resource efficiency and sustainability, aligning with the broader goal of maximizing the utility of available resources.
• 4.
  Comprehensive Analysis over Months:

  • •
    Novelty: The study involves a detailed analysis spanning several months, adding depth and reliability to the findings. This comprehensive approach distinguishes it from shorter-term studies.
  • •
    Motivation: The motivation behind the extended analysis is to ensure the reliability of the research outcomes and provide a thorough understanding of the long-term implications and performance of the proposed PVT/W system.
• 5.
  Potential for Improved Efficiency and Feasibility:

  • •
    Novelty: The innovative front surface water spraying technique has the potential to significantly enhance the efficiency and feasibility of photovoltaic-thermal systems.
  • •
    Motivation: The primary motivation is to contribute to the advancement of solar energy technologies by introducing a method that has the potential to make photovoltaic-thermal systems more efficient and practical.

2. Setup configuration

An innovative method has been developed to enhance the efficiency of photovoltaic (PV) panels. This method includes applying a water spraying technique to the panels' top/front surface. Subsequently, the water collected is directed into an inlet, which leads to a collector. The ultimate aim is to obtain hot water from the outlet, suitable for various domestic applications. To achieve optimal results, the PV panel has been set at a carefully selected 45⁰ angle by Inclinometer, which has been identified as the most effective inclination for Rajshahi's specific conditions.

The experimental setup comprises several essential components. These include:

• (a)Photovoltaic (PV) panel: A single PV panel with a power output of 25 W.
• (b)Flat plate collector: A flat plate collector with an effective area of 14,936 cm². This collector is used to harness solar energy.
• (c)Water supply tank: A tank with a capacity of 1000 L. It provides the water required for the experiment.
• (d)Storage tank: An 80 L tank used for storing the water during the experiment.
• (e)Misting nozzles: These are specialized nozzles used to create a fine mist of water. They play a crucial role in the experiment.

To connect all these components, a piping network is utilized, ensuring smooth flow and interaction between each part of the setup.

For further details regarding the specifications of the PV panel and flat plate collector, please refer to Table 2 and Table 3, respectively.

Table 2.

Characteristics of solar PV panels.

Parameters	Dimensions
Solar panel	1 piece
Efficiency	18 % (approximately)
Rated output	25 W (Total)
Current at Max Power	1.10 amps
Open Circuit Voltage	22.40 V
Voltage at Max Power	18.20 V
No. of Cells	108
Dimensions	50 × 44 × 5 cm

Table 3.

Specification of flat plate collector.

Parameters	Dimensions	Units
Effective area	14,936	cm2
Length	180	cm
Width	86	cm
Inlet and outlet diameter	0.635	cm
Total area	16,000	cm2
Tube diameter	0.635	cm

2.1. Experimental setup

The sun's azimuth and solar altitude angles were determined for the specific geographical location of Rajshahi, Bangladesh, with coordinates at 24.3636°N, 88.6241°E [21]. The experimental setup has been illustrated in Fig. 1 (a) and Fig. 1 (b). In this configuration, water is intermittently sprayed through a PVC pipe. Each spraying session lasts for 2 min and occurs at 1-h intervals.

Fig. 1.

(a) System configuration layout, (b) Full experimental setup.

The water spraying is conducted to simulate the effects of solar irradiation on the efficiency of the PV (photovoltaic) panels. By subjecting the panels to intermittent water spraying, observation can be made regarding how the presence of water affects their performance under solar radiation. To achieve this, a flow control valve has been opened after each 1-h interval, allowing water to flow through the PVC pipe. The water flow occurs at specific mass flow rates, which have been tested at various levels. These include 0.56 L/min 1.56 L/min, 2.56 L/min, and 3.56 L/min.

Throughout the experiment, the flow rate is closely monitored using a flow meter sensor. This enables the accurate measurement and recording of the amount of water flowing through the system at any given time. Through the analysis of the data collected from the flow meter, insights can be gained into the relationship between water flow rate and the efficiency of the PV panels under simulated solar irradiation conditions.

Data Collection: During the water spraying process, a comprehensive set of sensors and instruments is utilized to collect valuable data. Thermistor sensors are specifically employed to measure temperature data from both the top and back surfaces of the PV (photovoltaic) panel, providing insights into the thermal behavior. Additionally, dedicated sensors (Figure A2 for Light Intensity Sensor, Figure A3 for Voltage-Current Sensor and specifications are shown in Table A3) are utilized to record the intensity and voltage-current data, enabling a detailed analysis of the electrical performance. To facilitate the data gathering process, an Arduino nano microcontroller is utilized (depicted in figure A1 and specification is given in Table A1) as the central hub. It acts as the interface between the sensors and the laptop, efficiently collecting and processing the data. The collected data is then conveniently displayed on a laptop screen using specially designed Arduino-based software, providing real-time access to the measurements. Relay Module (Figure A4 and specifications are shown in Table A4) is used also.

Calibration: Before embarking on the data collection process from the sensors, it is essential to undertake a meticulous manual calibration procedure. This calibration process plays a vital role in ensuring the accuracy and validity of the measurements obtained from the sensors.

A reliable baseline has been set for the sensor readings, ensuring precise and consistent measurements during the data collection process. Through pre-calibrating the sensors, potential errors, inaccuracies, or inconsistencies in the readings can be reduced or eliminated, resulting in more reliable and credible data.

Water Spraying: Three misting nozzles (Figure A9) are employed to delicately spray water onto the surface of the PV panel. The water is distributed at an average pressure of approximately 5.2 bar.

Water Flow and Circulation (Figure A10): Water sprayed onto the surface of the PV panel cascades down towards the bottom, where it is directed into an inlet connected to a collector. As it enters the inlet, the water's temperature is accurately measured using a thermistor sensor (Figure A5). Subsequently, the water is supplied to a flat plate collector, strategically positioned adjacent to the PV panel. To facilitate the circulation of water through the collector, a 12V DC pump is employed. The timing of the DC pump (Figure A11 and specifications are shown in Table A9) circuit (Figure A8) is carefully regulated to ensure optimal and effective water circulation within the system. DC adaptor ((Figure A7 and specifications are shown in Table A7) is used in this case. Water flow control valve (Figure A10 and specifications are shown in Table A8) is also used.

Water Outlet and Temperature Measurement: The water flowing out of the collector is carefully observed by water flow sensor (Figure A6 and specifications are shown in Table A6). and its temperature is accurately measured using a thermistor sensor (Figure A5 and specifications are shown in Table A5). Moreover, film thickness of water on the top surface of the PV panel is determined for different tested mass flow rates.

Data Collection Duration: In order to ensure precise measurements and account for performance fluctuations, data is collected consistently over multiple days, specifically during the time frame of 11 a.m. to 4 p.m.

3. Mathematical modelling

The mathematical formulations relevant to this experiment have been described and they are essential for the further works of this study.

3.1. PV panel heating rate aspect

The cooling frequency of a PV panel is determined by its heating rate. The heating rate of the PV module can be ascertained by calculating the module's temperature with respect to time. The module temperature can be determined using the following equation, referred to as equation (1) [22,23].

$$T_m=T_{amb}+\left(NOCT-25\right)\times \frac{E}{80}$$ (1)

Equation (2) indicates that the module temperature is influenced by solar irradiance, ambient temperature, and the normal operating cell temperature (NOCT). The NOCT, in turn, is determined by the ambient temperature during sunrise.

While the value of NOCT remains consistent, ambient temperature and solar radiance are subject to change [22,23].

$$\text{NOCT}={25}^{\mathrm{o}}\mathrm{C}+{\mathrm{T}}_{\text{rise}}$$ (2)

3.2. Cooling rate analysis

The cooling rate of PV modules significantly influences their performance. Consequently, specifying the cooling period of these modules involves assessing the cooling rate of the PV cells. The cooling rate can be calculated using the energy balance equation (3) [24]. The cooling time (t) is determined by equation (4) [24]below.

$$Q_{gainedbycoolingwater}=Q_{dissipatedfromthePVpanel}$$ (3)

$$m_w\times t\times C_w\times \Delta T_w=m_G\times C_g\times \Delta T_g$$ (4)

3.3. Analysis of water spray cooling on PV module surface

The objective of employing the applied water spray cooling technique was to enhance the extent of heat dissipation to the environment and achieve a reduction in the temperature of the panel [10,25]. The energy being supplied to the surface panel $A_p$, in terms of solar irradiation that is accessible to it, can be restated as follows [10,25]:

$${\dot{Q}}_{solar}=a\times G_s\times A_p$$ (5)

The formula provided below represents the heat loss from PV panels [25]:

$${\dot{Q}}_{loss}={\dot{Q}}_C+{\dot{Q}}_R+{\dot{Q}}_E$$ (6)

The calculation of total heat convection loss can be expressed in the following manner [10,25]:

$${\dot{Q}}_C={\dot{Q}}_{C,F}+{\dot{Q}}_{C,B}$$ (7)

The heat convection loss for the front surface of a PV panel can be quantified using the following equation [25]:

$${\dot{Q}}_{C,F}=h_{front}\times A_p\left(T_{panel\_front}-T_{air\_front}\right)$$ (8)

The complete heat loss due to radiation can be formulated in the following manner [25]:

$${\dot{Q}}_R={\dot{Q}}_{R,F}+{\dot{Q}}_{R,B}$$ (9)

So, the total heat loss from this system can be calculated by below mentioned equation [10],

$${\dot{Q}}_E={\dot{Q}}_{E,F}+{\dot{Q}}_{E,B}$$ (10)

3.4. Analysis of flat plate collector

When solar radiation reaches the opening of a flat plate collector, the collector receives the incident solar radiation [15].

$$Q_C=I\times A$$ (11)

Some of the radiation gets taken in by the glazing, some is sent back through reflection, and the remainder passes through the glazing as short-wave radiation, ultimately reaching the absorber plate. The conversion factor, which illustrates the proportion of solar rays that penetrate and the proportion that gets absorbed, is determined by multiplying the absorber's absorption rate with the cover's transmission rate (equation (12)) [26].

$$Q_C=I\times \left(\tau \alpha \right)\times A$$ (12)

A significant amount of heat is dissipated through convection and radiation. The magnitude of heat loss (Qo) is primarily influenced by the temperature of the collector and the overall heat transfer coefficient (U_L) [26].

$$Q_o=U_L\times A\left(T_c-T_a\right)$$ (13)

So, the useful energy extraction rate (Qu) [15] from the collector, achieved under steady-state conditions, is directly related to the absorbed useful energy rate by the collector, while accounting for the energy lost to the surroundings.

$$Q_U=Q_i\times Q_o=I\times \left(\tau \alpha \right)\times A-U_L\times A\left(T_c-T_a\right)$$ (14)

The measure of heat extraction from the collector is reflected by the quantity of heat that is conveyed by the fluid as it flows through it [15].

$$Q_U={m\times c}_p\times \left(T_o-T_i\right)$$ (15)

In certain scenarios, determining the average temperature of a collector can be quite challenging. This is why establishing a connection between the beneficial energy increase of a collector and the potential increase if the entire collector surface were at the temperature of the fluid inlet becomes essential. To address this, a novel concept is introduced, known as the “Collector Heat Removal Factor ($F_R$)” [27].

$$F_R=\frac{{m\times c}_p\times \left(T_o-T_i\right)}{I\times \left(\tau \alpha \right)\times A-U_L\times A\left(T_c-T_a\right)}$$ (16)

The “Hottel Whillier-Bliss equation” [28] is a widely employed approach for quantifying the useful energy gained by a collector, providing a means to determine collector energy gain.

$$Q_U=F_R\left[I\times \left(\tau \alpha \right)\times A-U_L\times A\left(T_c-T_a\right)\right]$$ (17)

The instantaneous thermal efficiency of a collector [15,27],

$${\eta }_{collector}=\frac{F_R\left[I\times \left(\tau \alpha \right)\times A-U_L\times A\left(T_c-T_a\right)\right]}{AI}$$ (18)

$${\eta }_{collector}=F_R\left(\tau \alpha \right)-F_R{U}_L\left[\frac{T_i-T_a}{I}\right]$$ (19)

3.5. Uncertainty analysis-

Thermal and electrical efficiency are the subject of an uncertainty analysis [15] to ensure the validity of the experiments. The definition of uncertainty for the function K is as follows: when K is dependent on ‘n' linear parameters that are independent from each other (denoted as s₁, s₂,. s_n), then K can be expressed as K K (s₁, s₂, . s_n):

$$\delta k=\sqrt{{\left(\frac{\partial k}{\partial s_1}\delta s_1\right)}^2+{\left(\frac{\partial k}{\partial s_2}\delta s_2\right)}^2+\dots \dots \dots \dots ..+{\left(\frac{\partial k}{\partial s_n}\delta s_n\right)}^2}$$ (20)

Where $\delta k$ the uncertainty of is function K and ${\delta V}_i$ is the uncertainty of $V_i$. Whereas, $\frac{\partial k}{\partial s_i}$ is the partial derivative of K with respect to $s_i$. The absolute uncertainties for all parameters are discovered to be $<$ 2.5 % on the basis of the uncertainty analysis.

3.6. Exergy analysis

The quasi-steady exergy equation for an experimental PVT system can be stated as [15,29],

$${\dot{\mathrm{\Sigma }Ex}}_{in}=\mathbf{\Sigma }{\dot{Ex}}_{out}+\mathbf{\Sigma }{\dot{Ex}}_{loss}$$ (21)

$${\dot{Ex}}_{sun}+{\dot{Ex}}_{mass,in}={\dot{Ex}}_{el}+{\dot{Ex}}_{mass,out}+{\dot{\mathrm{\Sigma }Ex}}_{dest}$$ (22)

$${\dot{\mathrm{\Sigma }Ex}}_{dest}=radiationloss\left({\dot{Ex}}_{dest,radiation}\right)+{Convectionalloss\dot{(Ex}}_{dest,convection})+{frictionalloss(\dot{Ex}}_{dest,friction})$$ (23)

Where,

$${\dot{Ex}}_{in}=inputenergyrate$$

$${\dot{Ex}}_{out}=Outputenergyrate$$

$${\dot{Ex}}_{dest}=destroyedenegyrate$$

The calculation of the input exergy harvested from the Sun can be expressed as follows [30],

$${\dot{Ex}}_{sun}=\dot{\dot{G}\left(1-\frac{T_{amb}}{T_{sun}}\right)}$$ (24)

Additionally, the mass flow rate of exergy is given by Ref. [15],

$${\dot{Ex}}_{mass,out}-{\dot{Ex}}_{mass,in}={\dot{m}}_f\left({\phi }_{out}-{\phi }_{in}\right)$$ (25)

Here,

$${\phi }_{out}=\left(h_{out}-h_{amb}\right)-T_{amb}\left(S_{out}-S_{amb}\right)$$ (26)

$${\phi }_{in}=\left(h_{in}-h_{amb}\right)-T_{amb}\left(S_{in}-S_{amb}\right)$$ (27)

The following equation shows the overall exergy of a PVT system [15],

$${\dot{Ex}}_{ov}={\dot{Ex}}_{el}+{\dot{Ex}}_{th}$$ (28)

Equation (28) can be used to determine the destroyed energy [15],

$${\dot{\mathrm{\Sigma }Ex}}_{dest}={\dot{Ex}}_{sun}-{\dot{Ex}}_{el}-{\dot{Ex}}_{th}$$ (29)

The following equations can be used to determine the electrical (${\epsilon }_{el}$), thermal (${\epsilon }_{th}$), and overall exergy (${\epsilon }_{ov}$) efficiencies of PVTs [15,20].

$${\epsilon }_{el}=\frac{{\dot{Ex}}_{el}}{{\dot{Ex}}_{sun}}=\frac{{\dot{Ex}}_{el}}{\dot{\dot{G}\left(1-\frac{T_{amb}}{T_{sun}}\right)}}=\frac{V_{oc}\times I_{sc}\times FF}{\dot{\dot{G}\left(1-\frac{T_{amb}}{T_{sun}}\right)}}$$ (30)

$${\epsilon }_{th}=\frac{{\dot{Ex}}_{th}}{{\dot{Ex}}_{sun}}=\frac{{\dot{m}}_f.C_{pf}\left[\left(T_{f,out}-T_{f,in}\right)-T_{amb}\mathit{ln}\left(\frac{T_{f,out}}{T_{f,in}}\right)\right]}{\dot{G}\left(1-\frac{T_{amb}}{T_{sun}}\right)}$$ (31)

$${\epsilon }_{ov}={\epsilon }_{el}+{\epsilon }_{th}$$ (32)

4. Experimental results and discussion

4.1. General circumstances

The suggested configuration was evaluated in a geographic region characterized by a standard alternation between wet and dry climatic conditions where temperature varying between 34 °C and 45.08 °C average. All the data were collected from 11 a.m. to 4 p.m. over a span of 8 days, as demonstrated in Fig. 2. This timeframe was selected due to its inclusion of the highest solar irradiation levels. While recording the series of measurements, solar intensity ranged from 128.8 W/m² to 746.2 W/m² (specific recorded average peak value was 663.42 W/m², as shown in Fig. 2).

Fig. 2.

Solar irradiance at the specific geographical location during the course of the experiment.

During the measurement series, the surrounding wind impact was negligible on the performance as the air velocities were under 2.19 m/s and the inlet water temperature was approximately constant at around 27 °C, which was the mean recorded temperature of the water entering the pipeline.

4.2. Cooling effect on electrical power

Fig. 3 shows the voltage and current of before cooling and after cooling condition. The panel has voltage capacity of 21 V and current capacity of 1.2 A. As the day time advances the voltage of the panel drops but the current of the panel increases. Highest obtained voltage is 20.43 V and lowest obtained voltage is 20.37 V. The highest current is found 1.098 A and the lowest is 0.89 A. The difference between highest voltage is 0.13 V, and the highest current difference for after cooling and before cooling is 0.21 A.

Fig. 3.

I–U characteristics curve for after cooling and before cooling condition.

Fig. 4 illustrates the relation between voltage and power output of the panel for before and after cooling condition under different solar radiation level. In average, 21.32 W is achieved as maximum electric power output from the panel at before cooling condition. After cooling the front surface of the panel, the maximum electric power output is 21.6 W in average. Also, the peak value of the electric power output is 22.2 W and 22.6 W at before and after cooling, respectively. Hudișteanu et al. [31] conducted research on the impact of cooling on the power output of photovoltaic panels, and the findings demonstrated a significant increase in energy production during the cooling period. So, it is clear that the power output is increased with increase in voltage which is caused by cooling effect.

Fig. 4.

Power output versus voltage for after and before cooling.

It would be better suggestion for further work to investigate the wind and humidity effect on panel performance in details for different mass flow rates. This implies that environmental factors beyond just cooling can influence the panel's efficiency. However, the impact of dust on the PV panel has been examined throughout the course of this experiment. It is worth mentioning that spray is a self-cleaning technique which removes the dust and helps to increase the panel performance. The self-cleaning technique mentioned (spray) is a method for removing dust from the panel's surface. This cleaning process contributes to the increased performance of the panel by keeping its surface clean and maintaining optimal light absorption [32].

4.3. Spraying effect on temperature

Fig. 5 (a), Fig. 5(b)–. 5 (c), and Fig. 5 (d) shows PV panel temperature before and after water spray cooling. Four figures contain the values of different day's readings from 11 a.m. to 4PM. When the water's mass flow rate is heightened, it leads to a decrease in the temperature of the panel. Increasing the mass flow rate enables the water to extract a greater amount of heat from the panel. Jasim et al. [33] explored the effects of spray angle and distance between the nozzle and PV panel, finding that reducing the spray angle to 20° increased the electrical efficiency to 18.763 % and decreased the average panel temperature. This phenomenon can be explained by the principles of heat transfer. When the water flow rate is increased, a greater volume of water is delivered to the PV panel's surface. As more water is supplied to the panel, it can extract a larger amount of heat from the PV panel. In 2020, Dieng et al. [34] developed a hybrid prototype featuring a heat exchanger that recovers solar energy as heat, thereby enhancing electrical output and generating hot water. These studies collectively showcase the potential of water extraction to improve PV panel efficiency and yield hot water. Water is known to have a high specific heat capacity, which means it can absorb a substantial amount of heat energy without experiencing a significant rise in temperature itself. This property makes water an effective medium for cooling purposes. As water flows over the surface of the PV panel, it absorbs heat from the panel, leading to a reduction in the panel's temperature. At a mass flow rate of 1.56 L/min, the panel temperature can be reduced by as much as 7.38 °C, resulting in a notable enhancement in the efficiency of the PV module. When the temperature of a PV panel is lower, it can convert more sunlight into electricity, as PV panel efficiency tends to decrease as temperature rises.

Fig. 5.

Panel temperature at mass flow rate (a) 0.56 L/min, (b) 1.56 L/min, (c) 2.56 L/min, and (d) 3.56 L/min.

Evidently, when the mass flow rate of the water stream rises, there is a noticeable decrease in the temperature of the panel. As the mass flow rate increases, a greater volume of water becomes capable of extracting more heat from the PV panel, resulting in temperature reduction. This phenomenon occurs because water possesses a high specific heat, enabling it to absorb heat as it moves across the panel's surface. Augmenting the water flow rate facilitates a higher quantity of water to absorb increased heat from the panel. From Fig. 5(a–d) it can be seen that at 1PM to 2 p.m. the temperature is highest and the reduction of temperature is lower as compare to the 11 a.m. to 12 p.m. and 3PM to 4 p.m.

4.4. Water spray flow variation influence

From Fig. 6 (a), it is observed that for constant mass flow rate the efficiency of the panel is increased by 1.07 % at 12 p.m. Also, the efficiency is reduced by increasing the time of day and after 2 p.m. the efficiency is increased again (mass flow rate 0.56 L/min). Similar case is happened in Fig. 6(b)–. 6 (c), and Fig. 6 (d) for mass flow of 1.56 L/min, 2.56 L/min, and 3.56 L/min, respectively. Because efficiency of the panel depends on radiation and temperature of the panel. Also, from above section 5.2, it is clear that the electrical voltage, current and power depends on panel temperature and solar radiation. Ramgolam et al. [35] arrived at a similar conclusion, emphasizing that water flow improves and stabilizes energy output efficiency. The efficiency of a PV panel is a complex interplay of several factors, including solar radiation, temperature, mass flow rate, and refractive index of any water layer present. The experiment's findings align with theoretical expectations, demonstrating that optimizing these variables can significantly impact the electrical efficiency of the panel. Additionally, the experiment highlights the importance of precise control of these variables to achieve the best performance from a solar panel system.

Fig. 6.

Panel efficiency (after and before cooling) at mass flow rate (a) 0.56 L/min, (b) 1.56 L/min, (c) 2.56 L/min, and (d) 3.56 L/min.

As a theoretical point of view, the efficiency will increase with increase in mass flow rate. For the reduction of 1 °C of panel temperature the efficiency of panel increases about 0.2 %–0.3 %. In this experiment, for the temperature reduction of 10.94 °C the top surface of PV panel electrical efficiency is obtained 16.53 % as shown in Fig. 7. But the highest electrical efficiency of PV panel is obtained 16.78 % at the reduction of temperature 7.38 °C for the mass flow rate 1.56 L/min (12 p.m.).

Fig. 7.

Variation panel electrical efficiency and temperature for different mass flow rates.

From Fig. 8, it is cleared that the efficiency is not increase with the increase of mass flow rate. The highest efficiency is obtained 16.78 % at mass flow 1.56 L/min. The effective increase of electrical efficiency is 4.19 %. Increasing mass flow rate of spraying water can absorb more heat from panel and help to increase efficiency. For mass flow of 2.56 L/min and 3.56 L/min the efficiency was decreased due to refractive index. The presence of a thin water layer on the panel, with a refractive index of 1.33, when situated between air and glass, minimizes the reflection of solar radiation, leading to increased solar penetration. Keeping the panel angle at 45⁰, it was not possible to control this refractive index of 1.33 after mass flow of 1.56 L/min. Increase refractive index from 1.33, resulting the efficiency drop as shown in Fig. 8.

Fig. 8.

Variation panel maximal electrical efficiency (after cooling) with different mass flow rates.

4.5. Dust effect on panel efficiency

Dust can reduce penetration of sun light. The build-up of dust on the solar panel cells obstructs them from receiving direct sunlight and creates a screening effect. Therefore, the performance of solar cell decreases until the cells cleaned manually or other ways. From this point of view, the efficiency is increased with removing dust. In this experiment the same result was examined. Fig. 9 illustrates the highest efficiency is found 14.6 % with at 12 p.m. with the presence of dust. After removing dust by spraying water from top surface of the PV panel, the efficiency was significantly increased by 2.53 %. The presence of dust on solar panels reduces their efficiency by obstructing direct sunlight and creating a screening effect. The efficiency can be restored and even improved by cleaning the panels to remove the dust, allowing them to function at their optimal performance levels. In 2017, Vekaria [36] suggested a cleaning system to mitigate power loss caused by dust build-up. Concurrently, in 2016, Zaihidee et al. [37] emphasized that a dust accumulation of 20 g/m2 could lead to a reduction in panel efficiency ranging from 15 % to 35 %.This experiment demonstrates the importance of regular maintenance and cleaning for solar panels to ensure they operate efficiently and generate maximum electrical output.

Fig. 9.

Effect on panel electrical efficiency for dust.

4.6. Flat plate collector performance

Fig. 10 illustrates the variation of collector water inlet and outlet temperature with different times of the day. The results show that the outlet water temperature increases significantly with the advance of the day time. But after 2 p.m. the curve goes to downward direction. The highest temperature was 84.6 °C at 1 p.m. The results also show that the highest temperature difference is 45.65 °C at 1 p.m. It is clear from Fig. 11 that increasing the mass flow rate of water, collector efficiency is increased for a certain time and then starts decreasing. This occurs because it takes a sufficient amount of time for the water to become hot. With an inlet mass flow rate of 1.56 L/min, the collector efficiency measures at 52.5 %. In the same flow rate the PV panel shows the highest efficiency. But, the highest thermal efficiency of collector was 70.6 % for the mass flow of 2.56 L/min due to highest solar irradiation. The behavior of the solar collector system based on the data presented. Solar collectors are complex systems that are influenced by various factors including solar irradiance, mass flow rate, and heat transfer processes, which can result in the observed trends in temperature and efficiency.

Fig. 10.

Inlet and outlet temperature of flat plate collector.

Fig. 11.

Variation collector thermal efficiency with different mass flow rates.

4.7. Exergy analysis

Fig. 12 illustrates the average exergetic efficiency of the PV panel, both prior to and following the implementation of cooling. The efficiency of water-cooling when applied through spraying is significantly greater compared to operating without the cooling system. The maximum exergetic efficiency (15.94 %) was achieved at a mass flow rate of 1.56 L/min. Interestingly, the loss of exergy decreases due to irreversibility with the minimization of entropy generation in the system [17]. The larger diameter and length of the collector usually generate less entropy; but in this system, as the diameters are fixed, there is no effect on the entropy. The mass flow of the water has caused a decrease in the system's entropy. It might be possible to decrease the entropy further by using nano fluids [19]. That will be an interesting area for future studies. As Arman et al. [21] mentioned, as the mass flow rate increases, so does the exegetic efficiency and reduces the thermal exergy of the panel. However, this experiment demonstrates that increasing the mass flow rate does not imply that the exegetic efficiency will increase indefinitely. Rather, mass flow continues to increase, while exergetic efficiency begins to decline after reaching a peak (Fig. 13(a–c)) and, this is the effect of operating parameters of PV panel, of which refractive index can be considered one of the reasons. This was one of the main objectives of the study.

Fig. 12.

Average electrical efficiency (exergetic) under before and after cooling condition.

Fig. 13.

Share of overall exergy and exergy loss (before cooling), (b) mass flow rate, 0.56 L/min and (c) mass flow rate 3.56 L/min.

4.8. Feasibility test and comparison from other techniques

In this proposed setup, water was extracted from a storage tank via a pipeline to generate a water spray at an average pressure of 5.2 bar. The flow rate of the water spray was measured using a flow meter. The losses in flow were noted, assuming that the mentioned pressure could be attained using a regular circulation pump operating at an average efficiency of 0.7. The flow loss data for different water flow rates were outlined in Table 4.

Table 4.

Flow loss in a relation to supplied water.

Water flow (delivery) (L/min)	Flow loss (L/min)
0.56	0.25
1.56	1.02
2.56	1.21
3.56	1.81

According to Table 4, the equivalent water flow loss ranged from 0.25 L/min to 1.81 L/min. From the proposed setup experiment, it was observed that maximum achieved power output was 22.6 W when applied water spray flow in order to cool the PV panel was 1.56 L/min. It was observed that before cooling the PV panel, the average maximum power output was 22.2 W with 1.63W of equivalent power loss.

Because of the effectiveness of the water spray technique as a self-cleaning mechanism for the PV panel, there was an enhancement in overall performance. While the increase in net power output wasn't substantial, the feasibility was successfully demonstrated.

As per Table 5, the impact of temperature errors is not deemed significant, given the assured measurement error of ±0.3 %. Similarly, the anticipated measurement error of ±3.0 % in the water flow sensor scenario does not exert a noteworthy influence relative to the administered water spray flow rate. This parallels the situation in solar irradiation measurement, where the confirmed measurement error stands at ±0.6 %. In the context of indirectly measured PV panel electric power output, the projected measurement error of approximately ±1.5 % also holds limited sway over the measured electric power output's magnitude. Nevertheless, it is advisable to account for these factors to attain more precise outcomes.

Table 5.

Inaccuracy in the measurements due to the utilized measuring equipment.

Sensor type	Error
Thermistor (temperature sensor)	±0.3 °C
Water flow	±3.0 %
Pyranometer	±0.6 %
Volt-Ampere meter	±1.5 %

The cooling technique discussed in this proposal shows clear promise in terms of its positive impact on the panel's performance. The obtained results are largely consistent with findings from other research studies, as indicated in Table 6.

Table 6.

Efficiency improvement with other reported research studies.

PVT system	Electrical Efficiency
PCM based PVT [22]	15.5 %
Air cooled PVT [23]	12.2 %
Water cooled PVT [24]	13.19 %
Natural flow of water [10]	12.2 %
Spray cooling (front surface) [25]	15.42 %
This study (spray cooling, front surface)	16.78 %

4.9. Discussion

The experimental results indicate that the proposed water spray cooling system has a positive impact on the performance of the photovoltaic-thermal (PVT) system. Here are the key findings:

• •Cooling Effect on Electrical Power: The application of water spray on the PV panel's front surface led to an increase in electrical power output. The maximum power output increased from 21.32 W before cooling to 21.6 W after cooling, with a peak value of 22.6 W. This aligns with previous research, highlighting the effectiveness of cooling in boosting energy production and implies that implementing such a cooling technique can significantly enhance energy generation in PVT systems, making them more efficient and productive.
• •Temperature Reduction: Increasing the mass flow rate of water spray led to a significant reduction in the panel's temperature. Lower panel temperatures improve efficiency, as PV panel performance tends to decrease as temperature rises. The study demonstrates that a mass flow rate of 1.56 L/min resulted in the most significant temperature reduction, by as much as 7.38 °C.
• •Collector Performance: The collector's efficiency increased with an increase in the water mass flow rate up to a certain point. Beyond that point, efficiency began to decline. This emphasizes the complex interplay of various factors, including solar irradiance and mass flow rate, on collector performance.
• •Exergy Analysis: Exergy analysis confirmed that water cooling significantly improved the exergetic efficiency of the PV panel, with the highest efficiency achieved at a mass flow rate of 1.56 L/min. This suggests the potential for optimizing variables to enhance panel performance.
• •Feasibility: The feasibility of the proposed system is supported by a modest increase in net power output. While the increase is not substantial, it demonstrates the practicality of the water spray technique as a self-cleaning mechanism for the PV panel.
• •Comparison to Other Studies: The study's results are in line with findings from other research, highlighting the potential of water spray cooling in improving panel performance. This technique can be a valuable addition to enhance photovoltaic-thermal systems.

In conclusion, the study underscores the positive impact of water spray cooling on the performance of photovoltaic-thermal systems, offering a cost-effective and practical method for improving electrical output and reducing temperature-related efficiency losses. The findings contribute to the body of knowledge on sustainable energy generation and emphasize the potential for further research and development in this area.

4.10. Implications

The experimental findings in this study have several important implications for the field of photovoltaic-thermal (PVT) systems and renewable energy research:

• •Improved Energy Generation: The application of water spray cooling on PV panels' front surfaces demonstrated a clear increase in electrical power output. This implies that implementing such a cooling technique can significantly enhance energy generation in PVT systems, making them more efficient and productive.
• •Temperature Control: The observed temperature reduction in the PV panels through water cooling emphasizes the importance of maintaining lower panel temperatures. This is crucial for maximizing PV panel efficiency, as elevated temperatures typically lead to reduced performance. Controlling temperature through cooling methods can mitigate this issue.
• •Collector Efficiency: The study's results highlight the complexity of collector efficiency, which is influenced by factors like solar irradiance and mass flow rate. Understanding these interactions is essential for optimizing collector performance in PVT systems.
• •Exergetic Efficiency: Exergy analysis revealed that water cooling substantially improved the exergetic efficiency of PV panels. This finding underscores the potential for enhancing the conversion of input energy into useable electrical energy. It also indicates the importance of controlling key variables in PVT systems to maximize efficiency.
• •Feasibility and Practicality: The modest increase in net power output after implementing water spray cooling demonstrates the feasibility and practicality of this technique. While the increase may not be dramatic, it suggests that the self-cleaning aspect of the method adds value to PVT systems, making them more sustainable.

5. Conclusions

In this study, a hybrid photovoltaic thermal water heating system, focusing on four different mass flow rates: 0.56 L/min, 1.56 L/min, 2.56 L/min, and 3.56 L/min. The results demonstrated the effectiveness of applying a water spray to the upper surface of the PV panel, leading to efficiency improvements ranging from 0.76 % to 4.19 %, depending on the water flow rate. This cooling method eliminated the need for additional heat transfer materials, enhancing the heat transfer between the PV panel and the collector. Key findings include an electrical panel efficiency of 16.8 %, with the highest efficiency of 16.78 % at 12 p.m. for a mass flow rate of 1.56 L/min, marking a significant 4.19 % increase. An exergy analysis revealed a maximum electrical exergy efficiency of 15.94 % at the same mass flow rate. The collector efficiency ranged from 43 % to 70.6 %, achieving a peak hot water temperature of 84.6 °C. Notably, under varying conditions, the panel's electrical efficiency was highest at 17.13 % (without dust) compared to 14.6 % (with dust), representing a substantial 2.53 % increase. Ultimately, the system's optimal overall energy efficiency reached 83.3 % at a mass flow rate of 2.56 L/min. These findings highlight the effectiveness of mentioned approach and its potential to enhance the efficiency and feasibility of solar energy systems.

6. Future recommendation

Future research should delve deeper into the impact of varying factors, including wind speed, humidity, and mass flow rates, on panel performance. This exploration can lead to more precise control strategies. Investigating advanced cooling techniques, such as nanofluids, and determining optimal mass flow rates for different conditions is essential to maximize energy production. Long-term performance assessments and maintenance protocols should be developed to ensure the durability and reliability of cooling systems in real-world applications. Additionally, cost-benefit analyses and advocacy for policy inclusion can promote the economic viability and widespread adoption of innovative cooling technologies in sustainable energy systems.

CRediT authorship contribution statement

Khodadad Mostakim: Writing – original draft, Supervision, Investigation, Conceptualization. Md Ridwanul Akbar: Validation, Methodology. Md Aminul Islam: Validation, Methodology. Md Kaviul Islam: Writing – review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A.

A1: Arduino Nano

Figure A1 shows the Arduino nano. It is used to produce a clock of precise frequency using constant voltage. There is one limitation using Arduino Nano i.e., it doesn't come with DC power jack, means it cannot supply external power source through a battery. Flash memory of Arduino Nano is 32 Kb. It has preinstalled bootloader on it, which takes a flash memory of 2 kb.

Fig. A1.

Arduino Nano.

Table A1.

Specification of Arduino nano

Parameters	Standard
Microcontroller	ATmega328
Architecture	AVR
Operating Voltage	5 V
Flash Memory	32 KB of which 2 KB used by bootloader
SRAM	2 KB
Clock Speed	16 MHz
Analog IN Pins	8
EEPROM	1 KB
DC Current per I/O Pins	40 mA (I/O Pins)
Input Voltage	7–12 V
Digital I/O Pins	22 (6 of which are PWM)
PWM Output	6
Power Consumption	19 mA
PCB Size	18 × 45 mm
Weight	7 g
Product Code	A000005

A2: Light Intensity Sensor

The BH1750 (Figure A2) is a digital ambient light sensor which uses I2C to communicate. Unlike using a photoresistor and having to convert the analog value, the BH1750 provides a digital value in lux (Lx) over a range of 1–65,535 lx. The module includes an on-board 3.3V regulator which makes the module compatible with 5V devices such as an Arduino. With this module there do not need to worry about adding pull-up resistors on the I2C lines since they already have on-board pull-up resistors connected to the 3.3V output of the on-board voltage regulator. The module's ADDR pin allows to configure the device for one of two available I2C addresses. The default address is 0 × 23, but pulling the ADDR pin high will change the device's address to 0 × 5C. The ADDR pin's maximum voltage is 3.6V.

Fig. A2.

Light intensity sensor.

Table A2.

Specification of light intensity sensor

Parameters	Standard
Supply Voltage	3.3–6 V
Supply Current	up to 190 μA
I2C Address:
Default	0 × 23
ADDR Pin High	0 × 5C
Resolution:
High Resolution Mode	1 lx
Low Resolution Mode	4 lx
Board Dimensions:
Length	18.6 mm (0.732″)
Width	14.5 mm (0.571″)
Weight (Including Pins)	1.1g (0.039oz)

A3: Voltage-Current Sensor

The INA219 is a current measuring chip which can also measure voltage - actually it can only measure voltage, but cheats by measuring voltage across a known resistance. The really useful feature of this chip is that it can measure current and voltage in an external system independently from the 5∼3V0 that the chip uses. It can be connected directly the measurement inputs with voltage sources from 0 to 26V and it does not matter which one powers up first. It also does not matter which way round the current measuring inputs are connected as they are protected to ±26V. Since it can measure current and voltage it can report the power used. It is an I2C device using an external shunt sense resistor which is attached to the high side voltage. The negative analogue input is used to measure the load voltage and hence, with the current measurement, the power dissipated in the load. The voltage current measuring sensor is mentioned below Figure A3.

Fig. A3.

Voltage-Current Sensor.

Table A3.

Specification of Voltage-Current Sensor

Parameters	Standard
Voltage Supply (Vs)	3V0 ∼ 5V5
Analogue inputs (Common mode range)	−0.3–26V
Resolution (ADC)	12 bits (15 bit)
Quiescent current (max)	0.7 mA, 1 mA
Power down mode current (max)	6, 15uA
Current error % A (max) B (max)	(±0.2, ±0.5) (±0.2, ±0.3)
Voltage error % A (max) B (max)	(±0.2, ±0.5) (±0.2, ±0.5)
Voltage error over full temperature (A, B)	1 %,1 %
Conversion time (9 bit res. ∼12 bit res.)	84∼532 μs
Operating temperature	−40 °C–125 °C

A4: Relay Module

2-Channel 5V Relay Module is a relay interface board (Figure A4), it can be controlled directly by a wide range of microcontrollers such as Arduino, AVR, PIC, ARM and so on. It uses a low-level triggered control signal (3.3-5VDC) to control the relay. Triggering the relay operates the normally open or normally closed contacts. It is frequently used in an automatic control circuit. To put it simply, it is an automatic switch to control a high-current circuit with a low-current signal.5V relay signal input voltage range, 0–5V. VCC power to the system. JD-VCC relay in the power supply. JD-VCC and VCC can be a shorted.

Fig. A4.

Relay module.

Table A4.

Specification of Relay module

Parameters	Standard
Supply voltage	3.75V–6V
Trigger current	5 mA
Current when relay is active	∼70 mA (single), ∼140 mA (both)
Relay maximum contact voltage	250VAC, 30VDC
Relay maximum current	10A

A5: Thermistor (temperature measuring sensor)

As illustrated in Figure A5, Thermistors change resistance with temperature changes. They are temperature-dependent resistors. They are perfectly suited to scenarios where one specific temperature needs to be maintained. They are sensitive to small changes in temperature.

Fig. A5.

Thermistor Sensor.

Table A5.

Specification of thermistor Sensor

Parameters	Standard
Resistance at 25°	C: 10K + - 1 %
B-value (material constant)	3950+- 1 %
Dissipation factor (loss-rate of energy of a mode of oscillation)	Approximately 7.5 mW/K (in air)
Thermal cooling time constant	≤ (in air) 20 s
Thermistor temperature range	−55 °C–125 °C

A6: Water Flow Sensor

Water flow sensor consists of a plastic valve body, a water rotor, and a hall-effect sensor as shown in Figure A6. When water flows through the rotor, rotor rolls. Its speed changes with different rate of flow. The hall-effect sensor outputs the corresponding pulse Signal.

Fig. A6.

Water Flow Sensor.

Table A6.

Specification water flow Sensor

Parameters	Standard
Working voltage	5V–24V
Maximum current	15 mA (DC 5V)
Weight	43 g
External diameters	20 mm
Flow rate range	1～30 L/min

A7: DC Adapter

Figure A7 represents an AC Adaptor that converts the electric currents received by the electrical output into a typically lower alternating current that an electronic device can use. The first of the windings receives the 120-V alternating current delivered to the electrical output, and creates an electric field in the iron core.

Fig. A7.

DC Adapter.

Table A7.

Specification of DC Adapter

Parameters	Standard
Model	AD9045
Input voltage	100–240V
Input current	1.2A
Frequency	50/600 Hz
Output	12V, 5A

A8: Vero Board

Veroboard is a printed circuit board that is designed with rows of copper tracks with holes drilled in then for electronic components to be soldered to construct electronic circuits as represented in Figure A8.

Fig. A8.

Vero board.

A9: Misting Nozzle

As shown in Figure A9, small orifice misting nozzles (plastic material, weight 32g) operate by forcing fluid through a very small orifice. The sheering forces break the fluid into fine droplets. Impingement misting nozzles operate impacting the fluid on pin just underneath the exit orifice. This breaks the liquid into very fine droplets.

Fig. A9.

Misting nozzle.

A10: Water Flow Control Valve

Water flow control valves are control units, when electrically energized or de-energized, either shut off or allow fluid flow (Figure A10). The actuator takes the form of an electromagnet. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring.

Fig. A10.

Water flow control valve.

Table A8.

Specification of water flow control valve

Parameters	Standard
Valve Type	2 Way, Normally Closed (NC)
Action	Direct Acting
Orifice	5.0 mm
Operating Pressure	Vacuum to 50PSI
Port Size (Tube OD)	Options: 3/8″ OD Tube 3/8″ Push-In Fitting 3/8″ Female NPT
Coil Duty	H Class, IP65, 100 % ED Continuous Duty
Voltage	Options: 12, 24 VDC; 24, 110/120 (50/60Hz), 220/240 VAC (50/60Hz)
Voltage Tolerance	±10 % of Specified Voltage
Coil Power	20W
Electrical Connections	DIN43650A, Option: Molded Cable, ATEX Explosion Proof
Installation	No Orientation (Optimum Position: Flow Horizontal & Solenoid Vertical)
Filter	Build in (one side)
Service	Air, Water, Liquid

A11: DC Water Pump

DC powered pumps use direct current from motor, battery, or solar power to move fluid in a variety of ways as illustrated in Figure A11. Motorized pumps typically operate on 6, 12, 24, or 32 V of DC power. Solar-powered DC pumps use photovoltaic (PV) panels with solar cells that produce direct current when exposed to sunlight.

Fig. A11.

DC water pump.

Table A9.

Specification of DC water pump

Parameters	Standard
Brand Name	Singflo
Model Number	FLO-2202
AMPS	2 A
Voltage	12 V
Flow	2–4.3 L/min
Max. pressure	70 PSI (4.8 bar)

Appendix B. Supplementary data

The following is the Supplementary data to this article: