Effect of Wind Speed and Temperature on Efficiency of PV Module

Abstract

In this research, effect of ambient temperature and wind speed on the performance and efficiency of PV module has been investigated. Results of performance ratio, efficiency, energy generation and capacity factor are compared. Satellite and measured data of irradiance, wind speed and ambient temperature are evaluated for five year from 2014 to 2018 for the city of Hyderabad. While analysis is performed for Cadmium Telluride material of PV module after selecting suitable manufacturers for the power ratings of 425W, 440W, 210W, 215W and 435W. For these power ratings, two manufacturers of solar PV modules are selected i.e. First Solar (series 6) and Reel Solar. Results achieved after analysis reflected that when effect of ambient temperature was considered without applying the effect of wind, module temperature was found to be greater in value in comparison with the case when effect of wind speed was also applied simultaneously. Similarly, when effect of wind was applied performance factors for PV module like efficiency, capacity factor, performance ratio and energy generation were higher. Measured data was collected as reference and satellite data was compared with it and errors for different parameters was calculated.

1 Introduction

Conventional energy generation methods are affecting our environment directly. In recent years, due to enormously increased consumption of fossil fuels, environmental parameters like air quality, water, landscape, climatic conditions, wildlife, etc. are effected badly. Overall energy consumption of the world is increasing day by day while fossil fuels are going to deplete in coming decades. Therefore, world is shifting to renewable energy resources as they are sustainable and offer solution to environmental problems. Solar energy from the sun falling to the surface of the earth annually is 10,1000 times greater than annual energy needs of the world. Solar energy has proved to be an extremely environmental friendly energy source as it doesn’t affect the sustainability of human activities [1]. Recently, India has made significant development in field of renewable energy and policies are in consideration to enhance solar energy potential to an enormous amount of 175 GW in 2022 [2]. In last decade, in the field of renewable energy an annually growth rate of approximately 22 percent has been observed in India. In the year of 2013-2014 India produced approximately 53.22 billion units from renewable resources and 3.35 billion units from solar energy [3].

Pakistan being a developing country has approximately 67 % of energy mix based on conventional fossil fuels. Geographical location of Pakistan makes it an ideal place for solar energy production units. Total estimated potential for solar energy is approximately 2,900,000 MW. But need of the hour is to formulate an effective energy policy with coherent strategic model for implementation [4]. In May, 2012, the very first solar power plant in the history of country with two units of 178 kW each of was inaugurated in Islamabad. A photovoltaic solar power station of capacity 1000 MW is also installed at Quaid-e-Azam Solar Park. While many solar stations are under installation in different provinces of the country [5].

PV modules are basically photovoltaic cells which produce electricity when solar radiations fall on the surface of module panels. Performance of a PV module is dependent on ambient temperature, module temperature, wind speed, wind direction, humidity, incident light and direction of irradiation [6]. In this research, effect of ambient temperature and wind speed on the performance and efficiency of PV module has been investigated. Results of performance ratio, efficiency, energy generation and capacity factor are compared. Satellite and measured data of irradiance, wind speed and ambient temperature are evaluated for five year from 2014 to 2018 for the city of Hyderabad. While analysis is performed for Cadmium Telluride material of PV module for the power ratings of 425W, 440W, 210W, 215W and 435W.

2 Literature Review

2.1 Effect of Ambient Temperature on PV Module

PV module performance is directly dependent on the ambient temperature at a geographical location. When ambient temperature increases, radiations falling on the PV module also increase which leads to greater electron flow and at same time PV module temperature also increases. As greater excitation energy is available at increased ambient temperature, a greater current is generated [7]. However, with the increase in current with increased ambient temperature, potential barrier across the material of semiconductor starts decreasing and ultimately voltage across PV module also reduces. As power for a PV module is function of voltage and current. So, with reduction in voltage, power also decreases according to the relation as follows:

𝑃_𝑀 = V × I× EF

Where, EF is the fill factor and is dependent on material type. EF explains the capacity of a material to absorb radiations and whether the material will be choked at greater radiations or not. While, V and I are representing voltage and current respectively [8]. Furthermore, value of fill factor also decreases with the increase in ambient temperature as at exposure to greater radiations from the sun, material can be chocked. Thus, two factors are decreasing in the above equation with the increase in the ambient temperature so power for PV module will decrease ultimately [9]. Efficiency for the PV module is given as:

Where, I_sc is short circuit current, V_ocis open circuit voltage, EF is fill factor and P_opt is optical power [10]. As power of PV module decreases with increase in ambient temperature, its performance ratio, efficiency, capacity factor and energy generation decreases. Value of power of PV module with the increase in ambient temperature is dependent on material type of the PV module. Power drop parameter is denoted by β and its value is usually given by the module’s manufacturer [11].

2.2 Effect of Wind Speed on PV Module

Working of the PV module is not affected directly with the wind speed. Wind have cooling effect on the PV module structure and affects performance ratio, efficiency, capacity factor and energy generation [12]. Flow of wind on the surface of PV module, results in the heat transfer between PV module and air through process of convection. Heat transfer by the process of convection is dependent on convection coefficient, h. Convection coefficient is further dependent on fluid velocity [13]. Heat transfer by convection is given as:

𝑄𝑐 = A × h × ∆𝑇

ℎ = 3.830 × 𝐿−0.5 × 𝑉0.5

So, as fluid or wind speed increases, convection rate also increases and ultimately more heat transfer occurs resulting in the decrease of PV module temperature [14]. With decrease in the PV module temperature, performance ratio, efficiency, capacity factor and energy generation increase. Thus, PV module performance improves with the increase in wind velocity. But this relation is valid until a certain value of wind velocity i.e. approximately 15 m/s because above this value turbulent flow increases in the wind and convection effect is not smooth. Recently, many researches are under study to decrease the PV module temperature by adding heat exchanger to the module so that greater heat transfer can be achieved to improve the performance of PV module. Wind also plays an important role in the evaporative cooling of PV module. An experimental study to improve the PV module performance by evaporative cooling to reduce the PV module temperature was conducted in which a coating of synthetic clay was applied at backside of PV module. Heat transfer rate is given as:

Where, h is coefficient for convective heat transfer, p is fin parameter and k is thermal conductivity. It was observed with the increase in wind speed, rate of evaporative cooling increases and ultimately PV module performance improves [15].

2.3 Performance Parameters for PV Modules

Parameters to evaluate the performance of a PV systems are performance ratio, actual efficiency and capacity factor. Performance ratio deals with the ratio of final yield to reference yield of the PV systems. Mathematically,

Where, Rp is performance ratio, Yf is final yield and Yr is the reference yield of the PV system. It is dependent on PV module losses which cause its actual efficiency to deviate from the manufacturer’s efficiency. It can be determined from the ratio of power generated at actual efficiency to power generated at the efficiency of the module or it can also be computed from the ratio of actual efficiency to module efficiency. Moreover, PV module losses are dependent on wind speed, ambient temperature and irradiance. It is independent of power or efficiency of PV module. Thus, performance ratio under similar conditions for different modules made of similar material can be same [16].

Actual efficiency of a PV module is amount of energy actually generated as compared to the amount of energy might have generated w.r.t to standard irradiance falling on the module. Amount of energy generated by PV module is dependent on module temperature, irradiance falling on the module and manufacturer’s efficiency. The general efficiency of a PV module is represented as the ratio of output energy of the system to the input energy from sun. Analytically,

Efficiency provided by manufacturer is different for different type of PV module materials. Module temperature and irradiance for a PV module at a specific location is not in our control, but selection of suitable material can be done. Actual efficiency calculation for a PV module is not defined by a single accurate model rather different models are applicable for specific materials and for specific locations [17].

Capacity factor for a specific PV module deals with the energy actually generated for a provided time period to the amount of maximum energy that the PV module can produce in the same time period [18]. Capacitor factor is dependent on a number of factors for a PV module like module temperature, irradiance, wind speed, incident light and period of time for electricity generation [19].

3 Methodology

3.1 Selection of the manufacturer

We were required first to select five manufacturers of PV modules for provided power ratings and then to select best one after making comparison of performance and efficiency of PV modules of five manufacturers.

3.1.1 Justification of selection

Given material under study for PV module is Cadmium Telluride which has very few number of manufacturers as it an advanced material. For the given power ratings of 425W, 440W and 210W, no single manufacturer was found producing PV modules of all power ratings of 425W, 440W and 210W. We found some manufacturers which were producing PV modules of two given power ratings but manufacturer’s data was not available like module efficiency and incomplete data sheet and this information is very criterial for efficiency and performance analysis. So we have selected two manufacturers of solar PV modules i.e. First Solar and Reel Solar.

Module efficiency, panel area, power rating, temperature coefficient and NOCT temperature for PV modules of Reel Solar and First Solar is presented below;

Table 1: Data for PV modules of Reel Solar [20]

Manufacturer: Reel Solar
*Power rating*	*Module efficiency*	*β /degree*	TNOCT
210W	13.60 %	-0.280	45 degree
215W	14.0 %	-0.280	45 degree

Table 2: Data for PV modules of First Solar (Series 6) [21]

Manufacturer: First Solar (series 6)
*Power rating*	*Module efficiency*	*β /degree*	TNOCT
425W	17.20 %	-0.320	45 degree
435W	17.60 %	-0.320	45 degree
440W	17.80 %	-0.320	45 degree

3.2 Mathematical modelling

To evaluation different parameters of performance ratio, actual efficiency, energy generation, module temperature and capacity factor mathematically modelling is very important. Firstly, we will develop a mathematical model of the module temperature for without and with applying effect of wind speed on module to make a comparison. Thus, module temperature without wind effect is calculated by using following model:

Where, T_M, T_a, NOCT and GHI are module temperature, ambient temperature, normal operating cell temperature and irradiance on the module panel on a specific day respectively. Now to evaluate the wind effect of PV module, consider the following equation:

Where, T_M, T_a, NOCT, GHI, GHINOCT, τ, α, βSTC and hw,NOCT are module temperature, ambient temperature, normal operating cell temperature and irradiance on the module panel on a specific day, irradiance for normal operating conditions, transmissivity, absorptivity, power temperature coefficient and convection coefficient respectively [12]. Performance can be regarded as the ratio of actual efficiency to the module efficiency for a PV module system. Mathematically,

Annual energy generation by PV module of a specific power rating is denoted by AEG and mathematically it can be stated as:

Energy generation calculated annually from the above equation is in the units of W/m². Now, capacity factor for a specific PV module deals with the energy actually generated for a provided time period to the amount of maximum energy that the PV module can produce in the same time period. Mathematically formula of capacity factor for annual basis is as,

Where, A is representing the PV module area while P is module’s maximum power [22].

4 Results for satellite data

Relationship between different performance factors for a PV module are presented below in the form of graphs.

4.1 Without applying the effect of wind speed

Figure 1: Relationship between module efficiency and temperature without applying wind effect

Graph shows that as daily routine temperature varies, module temperature also varies with it and ultimately module efficiency which a function of module temperature also varies. It increases initially and after a certain value of module temperature, it decreases.

Figure 2: Relationship between module efficiency and irradiance without applying wind effect

Graph shows that as value of daily routine irradiance varies, daily module efficiency also varies. Efficiency increases initially then after a certain value of irradiance it decreases.

Figure 3:Relationship between performance ratio and module temperature without applying wind effect

Graph shows that as value of daily module temperature varies, module’s performance ratio also varies. Performance ratio increases initially then after a certain value of daily module temperature, it decreases because after this value efficiency of module decreases.

Figure 4: Relationship between PR values and years without applying wind effect

Graph shows that values of performance ratio for a PV module fluctuate in a year as with the variation of different seasons ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency.

Figure 5: Relationship between efficiency and years without applying wind effect

Graph shows that values of efficiency for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency.

Figure 6: Relationship between energy generation and years without applying wind effect

Graph shows that values of power generation for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency. As efficiency varies, energy generation is affected directly.

Figure 7: Relationship between module temperature and years without applying wind effect

Graph shows that module’s temperature for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature increases, module’s temperature also increases and vice versa.

5 Quality Data Check

The value of UCL is 320 and the value of LCL is 120. The mean value is 196.06.

Table 3: Quality data check values below LCL

Date	GHI Values below LCL
12-01-16	110.59
29-01-16	113.81
19-02-16	95.79
11-03-16	56.39

Table 4: Quality data check Values above UCL

Date/Time	Global Horizontal Irradiance (W/m2)
23-04-16	338.71
25-04-16	322.55
29-04-16	321.07
14-05-16	320.17
26-05-16	320.74
27-05-16	322.47
02-06-16	330.83
03-06-16	329.31
04-06-16	344.08
05-06-16	333.84
06-06-16	324.17
07-06-16	321.85

5.1 Graph of Quality data check

Figure 29: Data quality check applied on measure data

6 Discussion

Graph between module efficiency and temperature shows that as daily routine temperature varies, module temperature also varies with it and ultimately module efficiency which a function of module temperature also varies. It increases initially and after a certain value of module temperature, it decreases.

Graph between module efficiency and irradiance shows that as value of daily routine irradiance varies, daily module efficiency also varies. Efficiency increases initially then after a certain value of irradiance it decreases.

Graph between performance ratio and module temperature shows that as value of daily module temperature varies, module’s performance ratio also varies. Performance ratio increases initially then after a certain value of daily module temperature, it decreases because after this value efficiency of module decreases.

Graph between PR values and years shows that values of performance ratio for a PV module fluctuate in a year as with the variation of different seasons ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency.

Graph between efficiency and years shows that values of efficiency for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency. When effect of wind is applied, fluctuation is reduced.

Graph between years and EG shows that values of power generation for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature varies, module temperature varies which affects module’s efficiency. As efficiency varies, energy generation is affected directly.

Graph between module temperature and years shows that module’s temperature for a PV module fluctuate in a year as with the variation of different seasons, ambient temperature varies. As ambient temperature increases, module’s temperature also increases and vice versa. As effect of wind is applied, due to cooling effect of wind by convection, module’s temperature is little lower as compared to without application of wind affect.

7 Environmental & economic benefits and sustainability

Technologies of power production related solar energies produce no harmful emissions that can affect the sustainability of the environment. In recent years, due to enormously increased consumption of fossil fuels, environmental parameters like air quality, water, landscape, climatic conditions, wildlife, etc. are effected badly. Overall energy consumption of the world is increasing day by day while fossil fuels are going to deplete in coming decades. Therefore, world is shifting to renewable energy resources as they are sustainable and offer solution to environmental problems. Solar energy from the sun falling to the surface of the earth annually is 10,1000 times greater than annual energy needs of the world. Solar energy has proved to be an extremely environmental friendly energy source as it doesn’t affect the sustainability of human activities [1].