Modeling of Monocrystalline PV Cell Considering Ambient Conditions in Baghdad City

The environmental conditions are important factors, because they affect both the efficiency of a photovoltaic module and the energy load. This research was carried out experimentally and modeling was done in MATLAB –Simulink by monitoring the variation in power output of the system with environmental conditions such as solar radiation, ambient temperature, wind speed, and humidity of Baghdad city. From the results, the ambient temperatures are inversely proportional to humidity and the output power performance of the system, while the wind speed is directly proportional with the output power performance of the system.


Introduction
Solar energy has the greatest potential of all the sources of renewable energy.If only a small amount of this form of energy could be used, it will be one of the most important supplies of energy specially when other sources in the country have depleted energy comes to the earth from the sun.The use of solar energy for electrical power generation dates back to space age when solar photo voltaic cells were used to power satellites orbiting around the earth.With passing time it was realized that solar photo voltaic can be used as a power source not just for satellites but as also the cleanest and greenest power source on earth.Solar Energy thus started being used not just for conventional purposes such as heating but also power generation [1].
Modern PV cells are capable of converting up to 15% of the sun's energy into DC electric power.Sunlight provides roughly 100 Watts per square foot to the earth's surface, so on a clear day a 1square foot PV panel can produce about 15 watts.Monocrystalline cell is also named single-crystal silicon cells and are the most common in the PV industry [1].
Single-crystal silicon has a uniform molecular structure compared to non-crystalline materials, its high uniformity results in higher energy conversion efficiency, more electricity is generated for a given area of exposure to the sunlight.The conversion efficiency for singlesilicon commercial modules ranges between 20-30%.Certainly, the performance of these cells depends on ambient parameters including: ambient temperature, wind speed, direct radiation, etc. [4].
In this work, there will be a study of the impact of these parameters on the performance of photovoltaic cells.

Effects of Environmental Factors on Photovoltaic Cell
In order to predict the energy production of photovoltaic cell, it is necessary to predict the cell temperature as a function of ambient temperature, wind speed, humidity and total irradiance.The success rate of the equation was 96.22% "depending on experimental results" as shown in fig. 1, which refers to the relation between success rate of equation and all values of residual cell temperatures predicted by the program.All factors in this equation are predicted depending on the P-Value in MINITAB program (Ranging of P-Value 0 to 0.05) and when the P-Value approach to zero that's mean the factor has a good effect in equation.The P-Value of ambient temperature, wind speed, humidity, radiation and constant was 0.000, 0.01, 0.005, 0.000 and 0.002 respectively.

Modeling of Photovoltaic Solar Cell Using Matlab/ Simulink Program
Mathematical model implemented in this work in order to study the effect of weather factors on power of PV module.Also, it's used for comparison between theoretical and experimental results.The main system of photovoltaic cell created as shown in fig. 2. The blocks of photovoltaic cell are designed for simulation system according to the inputs and outputs of photovoltaic cell.The main system can change very quickly and easily.The main system of photovoltaic cell with obtained mathematical model of photovoltaic cell is established.the current of a PV module can be expressed, as function of voltage [2].where parameters ISCS, VOCS, IMPPS and VMPPS are defined at standard conditions, STC (Gs=1000W/m 2 and Ts=25°C) and α and β are respectively the current and the voltage temperature coefficient; all the above parameters are provided by manufacturers on module datasheet.It is possible to note that the parameters referred to currents depends on module solar irradiance G and temperature T, while the voltage ones depends only on temperature [2].
To improve the accuracy of the model it is convenient to modify expressions ( 6) and ( 8

Experimental Works
The experimental work focused on the study the effect of weather factors on the performance of PV solar cell and modeling these results in MATLAB-SIMULINK.These tests were conducted at the environment of Baghdad city starting from Nov. 2015 up to Apr. 2016.The laboratory devices used through the experimental work was: • Monocrystalline solar module with maximum power: 30W, cell area: 0.282m 2 , open circuit voltage: 22V, short circuit current: 1.9Amp, voltage at maximum power: 17V, current at maximum power: 1.76Amp.A standard calibration procedure has been made to the monocrystalline PV solar cells according to standard procedure supplied by the manufacture

I-V and P-V Characteristic for Monocrystalline Solar Cell
The influence of cell temperature on the I-V and P-V characteristic curve of monocrystalline solar cell has been evaluated under three different radiations intensity 500,750 and 1000 W/m².Figures 4, 5 and 6 showing that the cell temperature has a strong influence on I-V and P-V characteristic of monocrystalline PV solar cell at constant radiation because its effect on open circuit voltage (VOC Whereas the best value of F.F achieved is 0.74, and the best value of efficiency was 10.25% on March.Also, noted that values of VMAX and VOC, and efficiency at radiation 1000W/m² less than the values at radiations 500, 750W/m² because the cell temperature was higher than cell temperature at radiations 500, 750W/m².The short circuit current (ISC) and maximum current (IMAX), increases with increasing radiation.These results matched with previously published data such as [4].

Effect of Ambient Temperature on Power of Monocrystalline PV Solar Cell
The influence of ambient temperature on the power of monocrystalline solar cell has been evaluated under three different radiations 500,750 and 1000 W/m². Figure 7 showing that the ambient temperature has a strong influence on power of PV solar cell, when the ambient temperature increases, the output power of the cell decrease due to increase cell temperature, therefore decreasing in voltage will occur, causing drop in the power of PV solar cell.This results matched with previously published data such as [5].

Fig. 7. Effect of ambient temperatures on power of monocrystalline PV solar cell at different radiation intensities.
At radiation intensity 500W/m², the best value of power was 15.95, 16.9 Watt experimentally and theoretically respectively when ambient temperature was 13.15°C in December.At radiation intensity 750W/m², the best value of power was 21.81, 26.76 watt experimentally and theoretically respectively where ambient temperature was 15.49°C in December.At radiation intensity 1000W/m², the best value of power was 28.82, 35.57watt experimentally and theoretically respectively where ambient temperature was 20.73°C in January.

Effect of Wind Speed on Power of Monocrystalline PV Solar Cell
The influence of wind speed on the power of monocrystalline solar cell has been evaluated under three different radiations 500,750 and 1000 W/m². Figure 8 showing that when the wind speed increase, the power of PV solar cell increase because of decreases the cell temperature due to increase wind speed.These results matched with previously published data such as [6].
At radiation intensity 500W/m², the best value of power was 15.95, 17 watt experimentally and theoretically respectively when the average wind speed was 0.73m/s in December.At radiation intensity 750W/m², the best value of power was 21.81, 24.74 watt experimentally and theoretically respectively when the average wind speed was 2.09 in December.At radiation intensity 1000W/m², the best value of power was 28.82, 32.67 watt experimentally and theoretically respectively when the average wind speed was 2.64m/s in January.

Effect of Humidity on Power of Monocrystalline PV Solar Cell
The influence of humidity on the power of monocrystalline solar cell has been evaluated under three different radiations 500,750 and 1000 W/m². Figure 9 showing that when relative humidity decreased the output power of PV solar cell increases when the humidity decreases.This results matched with previously published data such as [7].
At radiation intensity 500W/m², the best value of power was 15.95, 16.79 watt experimentally and theoretically respectively where the average humidity was 21 in December.At radiation intensity 750W/m², the best value of power was 21.81, 24.97 watt experimentally and theoretically respectively where the average humidity was 27 in December.

Conclusions
From the results obtained we can conclude the followings: • The cell temperature has a strong influence on performance of PV solar cells because its effect on open circuit voltage (VOC).Decreasing cell temperature, PV current decreases slightly while PV voltage increase clearly.Output power of photovoltaic module increases with decreasing cell temperature.• The ambient temperature has a strong influence on performance of PV solar cells when the ambient increase, the cell temperature increase, therefore decreasing in voltage will occur, causing drop in the power of PV solar cell.• The wind speed has influence on performance of PV solar cells because its decreases the cell temperature, therefore increasing in voltage will occur causing increases in the power of PV solar cell.• Low relative humidity increase in output current from solar panels.Voltage output also increased with decrease in relative humidity.Therefore the power of PV solar cell increases when humidity keeps at low values.• The decreasing of solar radiation has impact to the ISC and VOC.• Were these differences between the experimental results and theoretical results are because of the inaccuracy of equipment and environment interactions, therefore noted that the theoretical power of PV solar cells more than actual and practical power.After calculated error ratio according to relation between experimental and theoretical results as show in below: • Error (%) = (theoretical results -experimental results / experimental results) * 100 Error ratio was equal 6.88, 5.91 and 4.53 when the radiation intensity equal 500, 750 and 1000 W/m² respectively.
The cell temperature equation was determined by using MINITAB program.Minitab has all the tools needed to effectively analyze the data.By guiding to the right analysis and giving clear results, Minitab helps to create equation showing relationship between the cell temperature and all other factors by entering the experimental data in MINITAB program as below: Tcell = 1.4 Ta -0.566 W +13.97 H +0.01751 G -16

Fig. 2 .Fig. 3 .
Fig. 2. Simulink model of weather factors effect on performance of PV solar cell.

Fig. 8 .
Fig. 8. Effect of wind speed on power of monocrystalline PV solar cell at different radiation intensities.

Fig. 9 .
Fig. 9. Effect of humidity on power of monocrystalline PV solar cell at different radiation intensity.

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Prova 200 solar module analyzer used to measure output power, efficiency, fill factor (F.F), Vmax, and Imax of the solar module.