Performance Analyses of 15 kW Grid-Tied Photo Voltaic Solar System Type under Baghdad city climate

The performance analyses of 15 kWp (kW peak) Grid -Tied solar PV system (that considered first of its type) implemented at the Training and Energy Research Center Subsidiary of Iraqi Ministry of Electricity in Baghdad city has been achieved. The system consists of 72 modules arranged in 6 strings were each string contains 12 modules connected in series to increase the voltage output while these strings connected in parallel to increase the current output. According to the observed duration, the reference daily yields, array daily yields and final daily yields of this system were (5.9, 4.56, 4.4) kWh/kWp/day respectively. The energy yield was 1585 kWh/kWp/year while the annual total solar irradiation received by solar array system was 1986.4kWh/m. The average power losses per day of array, system losses and overall losses were (1.38, 0.15, 1.53) kWh/kWp/day respectively. The average capacity factor and performance ratio per year were 18.4% and 75.5% respectively. These results highlighted the performance analyses of this PV solar system located in Baghdad city. The performance can be considered as good and significant comparing with other world PV solar stations.

. The merits of using PV technology are: low cost of electricity generation, simple installation and green energy production. In case of PV usage, the solar power plant is a non-polluted source of energy in contrast with traditional ones that produces environment pollution like greenhouse gases (Micheli, et al.,2014) Iraq is one of countries that severs environment pollution due to the use of conventional power plants as well as it possesses reduction in electricity generating especially in peak time demand during afternoon. Photo voltaic solar Grid -Tied power plant is an important application of electricity generation that can be used to reduce this problem and need no batteries to store energy making it very suitable to use. Many tapes of PV modules technology can be used in solar systems. The main types are crystalline silicon, thin film and novel technologies. The crystalline silicon has good efficiency with low degradation but it possesses high temperature loss coefficient compared with thin film technology (Raut, et al., 2017). Heterojunction with Intrinsic Thin-layer technology (HIT) solar module classified within novel technologies combines between the significant properties of crystalline silicon and thin film types. It has a good property of these two technologies of low degradation, high efficiency up to 21% with low temperature losses coefficient of 0.3%/°C (De Wolf, et al., 2012). Several papers were published worldwide investigating the performance analysis of On-grid Type systems. (Necaibia, et al.,2017) investigated the performance of 2.5 kWp PV solar implemented south of Algeria, they found that totally generated energy was in the spring season of 399.05 kWh, while the minimum generated energy was at autumn season with value of 328.23 kWh. The average yearly, performance ratio (PR) of the system was 73.82% while the annual average final yield of this system was (1737.28kWh/kWp/year). In the other hand, (Dobaria, et al., 2016) studied the performance analysis of Grid-Tied photo voltaic system with power of 5.05 kWp for three years. The system installed on the roof of Darshan Institute of Engineering and Technology building, Rajkot, India. They observed that the final yield, reference yield and performance ratio were (2.96 h/d -5.43 h/d), (4.22 h/d -7.29 h/d) and (68%-83%) respectively. The global horizontal solar radiation was 2212 kWh/m 2 /year. The energy yield was found to be 1636 kWh/kWp while the total estimated system losses were found 26%. Besides that, (Canete et al., 2014) studied four different panel technologies: Cadmium telluride (CdTe), micro crystalline silicon (μc-Si), poly crystalline silicon (pc-Si) and amorphous silicon (a-Si), with quantity of incident solar radiation for a 12 month in Spain. They found from the performance comparisons that the performance of thin film technology modules was better than that of pc-Si technology modules. However, CdTe and pc-Si modules achived the best performances during winter months with low total losses with high daily yield values. Kumar et al. (2019) studied the performance analysis of integrated building PV solar system. Thin-film cadmium telluride (CdTe) technology was used at their study. The Average yearly performance ratio was (7 kW flat roof, 2.3 kW facade in east and west, 5.5 kW facade in the north) are (76.26%, 71%, 70.53%) respectively and losses of energy were (−23.6%, −28.8%, −29.4%). The lowest performance in the system was recorded when it oriented northward.
The key target of the current research is to analysis the performance of PV solar system with 15kWp of power for a one-year period time under Baghdad climate conditions.

2.PV SOLAR SYSTEM DETAILS
The Grid-Tied PV solar system that used in the current study is installed at Training and Energy Research Center of Ministry of Electricity in Bagdad city at longitude 44.4°E, latitude 33.3°S and 41m above the sea level.  The experimental part was done by collecting the real data from sunny portal program which is the best PV monitoring system worldwide. The data had been recorded hourly, daily, monthly and even yearly in terms of AC and DC power and energy. For example, Fig.3 represents daily power output for the current PV system in 3/2/2017. The program belongs to SMA Company that manufactured the inverter system as shown figure.4. The inverter system is located indoor to avoid high temperature losses.

PERFORMANCE ANALYSIS
System parameters assessment includes the following items: yields (array, final and reference yield),energy output ,losses (system and array energy losses), inverter, total system and array efficiencies , capacity factor and performance ratio.

Energy Output
The full energy output (product) is the magnitude of AC energy generated via solar system per specific duration (Adaramola et al., 2015).
The total monthly, daily and hourly power output can be calculated respectively as follows: Where: EACm is the monthly energy , EACd is the output daily energy , EACh is the hourly energy , EACt is the energy in minute and N represents number of days in a month. While AC symbol represents alternating current, for example EAC,t is AC energy product in minutes and so on.

System Yields
System yields include the array, final and reference yields. The PV solar array yield (YA) is the DC power output for an assumed duration per PV nominal power of the system, it denotes to the time measured in kWh/kWp (kilowatt hour/kilowatt peak) unit (Sidy et al.,2016), Array yield is given as follows: Where: EDC is DC (direct current) power produced by the PV modules of the system in kWh.

Journal of Engineering
Where, EAC is the altering current (AC) energy output in kWh The reference yield (YR) is the global solar irradiation in collimated surface over the reference irradiance. The reference irradiance is calculated at standard conditions and its value 1kWp/m 2 . The reference yield can be given by Equation 6: Where, HR is the reference solar irradiance in kW/m 2 and HT is the in collimated solar irradiance in kWh/m 2 .

Energy losses of Array and System
Array losses LA are the losses happened due to array performance indicating the incapability of the array to entirely convert the solar irradiance to electricity. The array capture losses given as (Wittkopf et al., 2013). Array losses can be happened due to dust accumulation (Hahsim and Hussien, 2016), or solar over heating of the solar module. The general module losses are given as: The system losses (LS) are the losses happened during the conversion of DC power to AC power by the inverter in PV solar system. It is given as:

System Efficiencies
The efficiency of PV solar system is divided into three types system efficiency, array efficiency and inverter efficiency (Vignola et al.,2008). These efficiencies are calculated on basis of annual, month, day, hour and instantaneous. The efficiency of system depends on AC energy output product, while the efficiency of array depends on the DC energy output product. While inverter efficiency depends on both DC and AC energy output. The array efficiency is given by Equation 9 : Where, Am is array area (m 2 ) and Ht is in collimated surface solar irradiation in W/m 2 .
Equation 10 gives the system efficiency of PV solar system as: While Equation 11 demonstrates the inverter efficiency as follows: ɳ = 100 * % (11)

5 Performance Ratio
Performance ratio (PR) is the proportion between the final yield to the reference yield. The Performance ratio value of any system shows how the PV solar system approaches the perfect performance through actual act. These values permit comparisons of PV systems depending on different variables; angle, installed location, tilt angle, orientation and their rated power capacity (Wittkopf et al., 2013). Performance ratio can be defined as: = % (12)

Capacity Factor
Capacity factor (CF) is applied to assessing the energy output generated by an electric power generating system (Adaramola et al.,2015). It is the ratio of AC energy generated by PV solar system per a specified duration (usually one year) to the system energy when it works at whole capacity (rated value) for the given period of time. The yearly CF of the PV solar system is represented by Equation 13: The comparison between capacity factors of different countries worldwide can be seen in Table 1.

RESULTS AND DISCUSSION
The monthly real and predict production of energy and in collimated surface global radiation can be seen in Figure 5.  The monthly average of daily yields for final array and reference yields were displayed in Figure 7, It had been found that the highest values were reported in August 2017 with values of 5.06 kWh/kWp/day, 4.88kWh/kWp/day, 7.04kWh/kWp/day respectively. The lowest values were reported in December as 4.32kWh/kWp/day, 3.7kWh/kWp/day and 3.58kWh/kWp/day, respectively. The yearly average of daily yields for entire months of 2017 year were 5.9kWh/kWp/day, 4.5kWh/kWp/day and4.4kWh/kWp/day, respectively. During months of the measurements, the differences between average array yield and system yield were constant. These differences were ascribed for the DC to AC conversion losses caused by the inverter. That means    8 illustrates the monthly average of daily yields of overall array and system losses ratio. The highest losses values in the array were found in July with a value of 2.2kWh/kWp/day. That can be ascribed to high ambient temperature. While in December, the minimum value of 0.6 kWh/kWp/day was recorded. These values coincided with 7% and 4.5% of monthly average of daily reference yield. System losses (represent by inverter losses) varies from 0.17 kWh/kWp/day in July to the value of 0.11 KWh/kWp/day in December. These values coincided with 7% and 4.3% of the respective monthly average of daily reference yield. Yearly average overall system, inverter losses, array losses were found to be 1.53 kWh/kWp/day, 0.15 kWh/kWp/day and 1.38 kWh/kWp/day respectively.   9 shows monthly average inverter ,system and array efficiencies during the observing duration. The annual average values were found to be 96.75% ,13.27% and 13.7 % respectively. In December, the maximum values of the inverter, system and array efficiencies were 96.80%, 14.8% and 15.2% respectively. In July, the minimum values were found to be 96.6%, 11.74% and 12.15% respectively.

CONCLUSIONS
: concluded had been the following conclusions In this study,  Baghdad city environment is suitable to install PV solar On-Grid system as performance analyses results indicated good and promising performance in spite of high ambient temperature. Rated power of PV system kW