**5.1 PV module performance measured in mock-up model**

The total solar irradiance and power output of the PV module, depending on the inclined angle of double glazing, were monitored through the mock-up model for 9 months from November 2006 to August 2007. Data obtained from the mock-up was collected based on minute-averaged data, and the final data of 12,254,312 was statistically analyzed based on 56 variables. Firstly, daily data was rearranged into monthly data. Secondly, minute-based data was averaged and combined into an hourly data. Finally, each group was analyzed in terms of an arithmetic mean, standard deviation, minimum, and maximum value. The empirical data in this study was limited in DC output, which was obtained from the load using resistance without an inverter. Thus, it is assumed that there may be a number of differences between the data measured in this study and the empirical data controlled by maximum power peak tracking (MPPT) using an inverter.

Figure 6 shows the hourly data, which was yearly-averaged, of the intensity of solar irradiance and DC output depending on the inclined angle of the double glazed PV module. Based on the data measured at noon, the inclined slope of 30 º (SLOPE \_30) revealed an insolation of 528.4 W/m2, which shows a greater solar irradiation than that for the slopes of 0 º (SLOPE\_0, 459.6 W/m2) and 90 º (SLOPE\_90, 385.0 W/m2), as shown in Figure 6(a). Consequently, the average power output at noon also exhibited 19.9 W for SLOPE\_30, which was higher than that shown in the data for SLOPE\_0 (15.76 W) and SLOPE\_90 (8.6 W) (See Figure 6(b)).

Power Output Characteristics of Transparent a-Si BiPV Window Module 193

Fig. 6. Monitoring data of PV module depending on the slope through the mock-up model:

By observing the degree of scattering for each inclined PV module as shown in Figure 7, there was a higher density of power output distribution for SLOPE\_30 under the higher solar irradiance. On the other hand, the lowest distribution of power output was revealed for SLOPE\_90, even under the higher solar irradiance. The monthly-based analysis revealed that a double glazed PV module inclined at 30 º (SLOPE\_30) produced the greatest power output due to the acquisition of a higher solar irradiation. This result can also be achieved from a PV module with an incidence angle of 40.2 º, implying that it is more efficient to

In the case of SLOPE\_0, there were significant differences in power output with respect to solar irradiance depending on monthly variation (See Figure 7(a)). Specifically, the maximum solar irradiance in December is only 500 W/m2 resulting in a power output of 10 W. On the other hand, the maximum solar irradiance of 1,000 W/m2 with over 50 W power output was recorded for June. This high efficiency of power performance for SLOPE\_0 during the summer could be due to the incidence angle of 36.1 º, which was low enough to

The reverse tendency of power output for SLOPE\_0 was shown for SLOPE\_90, which was installed at the horizontal plane. Specifically, a maximum power output of above 30 W was observed. This was due to a quiet efficient solar irradiance with the maximum solar irradiation gain of over 900 W/m2 occurring in December. However, a lower solar irradiance of around 500 W/m2 with less than 10 W power output was observed during the summer months from June to August. This can be explained by the difference in the incidence angle of the PV module depending on the inclined slope, i.e., the lower incidence angle of 36.6 º for SLOPE\_90 was observed during the winter, particularly in January, while the higher value of 84.6 º was observed during the summer, especially in June. This implies that solar irradiation capable of producing a much higher power output can be easier to be

Figure 8 shows the amount of solar irradiation and power output accumulated for each month depending on the inclined angle of the PV module. A fairly effective solar irradiance

achieved with a lower incidence angle of solar radiation to the PV module.

**5.3 Monthly based analysis of power performance** 

hourly data averaged yearly: (a) solar irradiance and (b) power output.

acquire solar irradiation than any other factor (See Figure 7(b)).

absorb solar irradiation.

Fig. 5. Full-scale mock-up model: (a) a floor plan view, (b) a cross-sectional view, and (c) photographs of mock-up model.

#### **5.2 Effect of intensity of solar irradiance**

Figure 7 depicts the relationship between the solar irradiance taken from the PV module and the DC power output depending on the inclined angle of the module. For all PV modules, the power output increased with an increase in solar irradiance. While the increase rate of power output was particularly retarded under the lower solar irradiance, there was a very steep increase of power output under the higher solar irradiance (See Figure 7).

Fig. 5. Full-scale mock-up model: (a) a floor plan view, (b) a cross-sectional view, and (c)

Figure 7 depicts the relationship between the solar irradiance taken from the PV module and the DC power output depending on the inclined angle of the module. For all PV modules, the power output increased with an increase in solar irradiance. While the increase rate of power output was particularly retarded under the lower solar irradiance, there was a very

steep increase of power output under the higher solar irradiance (See Figure 7).

photographs of mock-up model.

**5.2 Effect of intensity of solar irradiance** 

Fig. 6. Monitoring data of PV module depending on the slope through the mock-up model: hourly data averaged yearly: (a) solar irradiance and (b) power output.

By observing the degree of scattering for each inclined PV module as shown in Figure 7, there was a higher density of power output distribution for SLOPE\_30 under the higher solar irradiance. On the other hand, the lowest distribution of power output was revealed for SLOPE\_90, even under the higher solar irradiance. The monthly-based analysis revealed that a double glazed PV module inclined at 30 º (SLOPE\_30) produced the greatest power output due to the acquisition of a higher solar irradiation. This result can also be achieved from a PV module with an incidence angle of 40.2 º, implying that it is more efficient to acquire solar irradiation than any other factor (See Figure 7(b)).

In the case of SLOPE\_0, there were significant differences in power output with respect to solar irradiance depending on monthly variation (See Figure 7(a)). Specifically, the maximum solar irradiance in December is only 500 W/m2 resulting in a power output of 10 W. On the other hand, the maximum solar irradiance of 1,000 W/m2 with over 50 W power output was recorded for June. This high efficiency of power performance for SLOPE\_0 during the summer could be due to the incidence angle of 36.1 º, which was low enough to absorb solar irradiation.

The reverse tendency of power output for SLOPE\_0 was shown for SLOPE\_90, which was installed at the horizontal plane. Specifically, a maximum power output of above 30 W was observed. This was due to a quiet efficient solar irradiance with the maximum solar irradiation gain of over 900 W/m2 occurring in December. However, a lower solar irradiance of around 500 W/m2 with less than 10 W power output was observed during the summer months from June to August. This can be explained by the difference in the incidence angle of the PV module depending on the inclined slope, i.e., the lower incidence angle of 36.6 º for SLOPE\_90 was observed during the winter, particularly in January, while the higher value of 84.6 º was observed during the summer, especially in June. This implies that solar irradiation capable of producing a much higher power output can be easier to be achieved with a lower incidence angle of solar radiation to the PV module.

#### **5.3 Monthly based analysis of power performance**

Figure 8 shows the amount of solar irradiation and power output accumulated for each month depending on the inclined angle of the PV module. A fairly effective solar irradiance

Power Output Characteristics of Transparent a-Si BiPV Window Module 195

of 147.7 kWh/m2 was obtained from SLOPE\_30 during May, and the lowest value of 75.3 kWh/m2 was obtained in December (See Figure 8(a)). The horizontal module of SLOPE\_0 resulted in the highest solar irradiance in June and the lowest value in January. On the other hand, the PV module installed at the vertical window exhibited the highest solar irradiance (115 kWh/m2) in January and the lowest (50.2 kWh/m2) in August. This can be explained by the highly effective solar irradiance of both of the PV modules that were installed horizontally (SLOPE\_0) and tilted at a slope of 30 º. This was due to the smaller incidence angle, defined as the angle between the incident solar ray and the normal line, close to the horizontal plane during the summer and related to the height of the sun, while the PV module installed vertically (SLOPE\_90) obtained an effective solar irradiance due to the

An analysis was also carried out on the monthly power performance depending on the inclined angle of the PV module, as shown in Figure 8(b). From the monthly data in Figure 8(b), it can be seen that the most effective power output during the summer, particularly for June, was obtained at SLOPE\_30 and SLOPE\_0. However, the highest power output was obtained at SLOPE\_90 for January. This could be due to the variation of solar irradiance from each PV module from the different incidence angles based on the height of the sun. In this study, the best power performance among all the tested PV modules was that obtained by the PV module tilted at an angle of 30 º (SLOPE\_30), comparing with those

Fig. 8. Monitoring data of PV module depending upon the slope through the mockup model: monthly accumulated data of (a) solar irradiance and (b) power output.

Figures 10~12 show the statistically analyzed monthly power generation data of PV module depending the inclined slope. The name of each part is provided for the better understanding in Figure 9. ■ sign in each box indicates Mean value, □ and ▨ signs indicate the range of Mean±S.D (Standard Deviation), Whisker Ⅰ sign indicates the range between maximum and minimum values. For example, in the first graph of Figure 10, the mean value at 12pm in January is approximately 20W, S.D. (Standard Deviation) is 5~30W, maximum value is 40W and the minimum value is 0W. The statistical data on how much power is generated in each hour can be easily understood with these graphs. Furthermore, the maximum and minimum ranges can also be easily analyzed, enabling the comparison of

smaller incidence angle during the winter.

installed horizontally (SLOPE\_0) and vertically (SLOPE\_90).

**5.4 Hourly based analysis of power performance** 

characteristic behaviors depending on the inclined angle.

Fig. 7. Power output data of PV modules based on monthly variation of solar irradiance measured in the mock-up model: (a) slope 0, (b) slope 30, and (c) slope 90, respectively.

Fig. 7. Power output data of PV modules based on monthly variation of solar irradiance measured in the mock-up model: (a) slope 0, (b) slope 30, and (c) slope 90, respectively.

of 147.7 kWh/m2 was obtained from SLOPE\_30 during May, and the lowest value of 75.3 kWh/m2 was obtained in December (See Figure 8(a)). The horizontal module of SLOPE\_0 resulted in the highest solar irradiance in June and the lowest value in January. On the other hand, the PV module installed at the vertical window exhibited the highest solar irradiance (115 kWh/m2) in January and the lowest (50.2 kWh/m2) in August. This can be explained by the highly effective solar irradiance of both of the PV modules that were installed horizontally (SLOPE\_0) and tilted at a slope of 30 º. This was due to the smaller incidence angle, defined as the angle between the incident solar ray and the normal line, close to the horizontal plane during the summer and related to the height of the sun, while the PV module installed vertically (SLOPE\_90) obtained an effective solar irradiance due to the smaller incidence angle during the winter.

An analysis was also carried out on the monthly power performance depending on the inclined angle of the PV module, as shown in Figure 8(b). From the monthly data in Figure 8(b), it can be seen that the most effective power output during the summer, particularly for June, was obtained at SLOPE\_30 and SLOPE\_0. However, the highest power output was obtained at SLOPE\_90 for January. This could be due to the variation of solar irradiance from each PV module from the different incidence angles based on the height of the sun.

In this study, the best power performance among all the tested PV modules was that obtained by the PV module tilted at an angle of 30 º (SLOPE\_30), comparing with those installed horizontally (SLOPE\_0) and vertically (SLOPE\_90).

Fig. 8. Monitoring data of PV module depending upon the slope through the mockup model: monthly accumulated data of (a) solar irradiance and (b) power output.

#### **5.4 Hourly based analysis of power performance**

Figures 10~12 show the statistically analyzed monthly power generation data of PV module depending the inclined slope. The name of each part is provided for the better understanding in Figure 9. ■ sign in each box indicates Mean value, □ and ▨ signs indicate the range of Mean±S.D (Standard Deviation), Whisker Ⅰ sign indicates the range between maximum and minimum values. For example, in the first graph of Figure 10, the mean value at 12pm in January is approximately 20W, S.D. (Standard Deviation) is 5~30W, maximum value is 40W and the minimum value is 0W. The statistical data on how much power is generated in each hour can be easily understood with these graphs. Furthermore, the maximum and minimum ranges can also be easily analyzed, enabling the comparison of characteristic behaviors depending on the inclined angle.

Power Output Characteristics of Transparent a-Si BiPV Window Module 197

 **Mean Mean±SD Min-Max** 

**Month:2**

**Month:6**

**Month:3**

**Month:7**

**Month:12**

**Month:3**

**Month:7**

**Month: 12**

 

 

 

 

 

 

 

 

 

 

 

 

**Time(H)**

 **Mean Mean±SD Min-Max** 

**Month:2**

**Month:6**

**Time(H)**

**Month: 11**

**Month:11**

Fig. 11. Power generation of SLOPE.\_30° in each timestep

**Month:1**

**Month:4**

**Month:8**

**Month:1**

**Month:4**

**Month:8**

**<sup>18</sup>**

**<sup>18</sup>**

**<sup>18</sup>**

**POWER(W)**

 

 

 

 

 

 

**POWER(W)**

Fig. 12. Power generation of SLOPE.\_0° in each timestep

Fig. 9. Explanation of Box-Whisker graph

Fig. 10. Power generation of SLOPE.\_90° in each timestep

In case of vertical PV module, the power generation turns out be significant in Janurary due to a farily effective solar irradiance. It showed the power generation of 20W on average at noon. On the other hand, in June when there is no high solar irradiance due to high incidence angle, the power generation was less then 10W on average at noon. The inclined slope of 30 º showed the best power generation during the measurement period. Especially the power generation was the greatest in June with 30W on average at noon.

Fig. 9. Explanation of Box-Whisker graph

**Month:1**

**Month:4**

**Month:8**

**POWER(W)**

 

 

 

Fig. 10. Power generation of SLOPE.\_90° in each timestep

In case of vertical PV module, the power generation turns out be significant in Janurary due to a farily effective solar irradiance. It showed the power generation of 20W on average at noon. On the other hand, in June when there is no high solar irradiance due to high incidence angle, the power generation was less then 10W on average at noon. The inclined slope of 30 º showed the best power generation during the measurement period. Especially

**Time(H)**

**Month:11**

**Month:2**

 **Mean Mean±SD Min-Max** 

**Month:6**

**Month:3**

**Month:7**

**Month:12**

 

 

 

 

 

 

the power generation was the greatest in June with 30W on average at noon.

Fig. 11. Power generation of SLOPE.\_30° in each timestep

Fig. 12. Power generation of SLOPE.\_0° in each timestep

Power Output Characteristics of Transparent a-Si BiPV Window Module 199

Fig. 14. Power output data calibration by comparing the experimental data to the computed

Power performance analyses were performed of PV modules facing south (azimuth = 0 º) depending on the different inclined angles of 0 º, 10 º, 30 º, 50 º, 70 º, and 90 º. The data set consisted of the experimental data for 0 º, 30 º, and 90 º and the computed data for 10 º, 50 º, and 70 º. Figure 15 illustrates the monthly power output depending on the inclined angle ranging from 0 º to 90 º south (azimuth = 0 º). PV modules that were tilted at an angle below 30 º showed a relatively good power performance of over 6 kWh in the summer, while those with an inclined angle above 50 º demonstrated a power performance of less than 6 kWh. The most effective annual power output data of 977 kWh/kWp was obtained at an inclined angle of 30 º (SLOPE\_30), as shown in Figure 16. On the other hand, the lowest annual power output of 357 kWh/kWp was obtained from the PV module with a slope of 90 º (SLOPE\_90), which was 37 % of the annual power output of SLOPE\_30. From Figure 16, it can be seen that the annual power output performance was effective in the order of SLOPE\_10 (954 kWh/kWp), SLOPE\_0

The power generation performance depending on the angle of the azimuth was also estimated for PV modules with different inclined slopes, as shown in Figure 17. Similarly, a PV module inclined at an angle of 30 º showed the most effective power output data for all directions in terms of azimuth angles, and the lowest data was obtained from that with an inclined angle of 90 º. For the PV module inclined at an angle of 30 º, the best power performance among the analyzed PV modules facing various directions was obtained for the PV module that was installed to the south (azimuth = 0 º). It can be seen from Figure 17 that different azimuth angles affected the power performance of PV modules: that is, the power performance decreased as the direction of the PV module was changed from the south to the east and west, in comparison to the PV modules that were inclined at the slope

(890 kWh/kWp), SLOPE\_50 (860 kWh/kWp), and SLOPE\_70 (633 kWh/kWp).

data obtained from the simulation program (TRNSYS).

of 30 º, as listed in Table 2.

In case of horizontal PV module, it showed effective power generation performance in the summer similar to the case of the inclined slope of 30 º, showing more than 30W generation on average at noon. However, the generation barely exceeded 10W in December due to high incidence angle and low solar irradiance. The hourly average power generation depending on each inclined angle is illustrated in Figure 13. In case of inclined angle (SLOPE\_30), it showed power generation of 20W on average at noon, while the horizontal PV module showed 15W on average. Vertical PV (SLOPE\_90) showed the low generation performance of 8W on average. Table 5.5 summarizes the hourly average power generation, voltage and electric current.

Fig. 13. Annual hourly averaged power generation

#### **5.5 Analysis of power performance through simulation**

In this study, TRNSYS (Ver. 14.2, Solar Energy Laboratory, Univ. of Wisconsin, USA) was used as a simulation program to analyze the performance of power output for a double glazed PV module. Generally, TRNSYS has been widely used to compute the hourly data for power output, solar irradiance, temperature, and wind speed for both PV systems and solar heat energy systems [10]. From the simulation program, the relative error was verified, and a comparison was then made of the power output from the experimental and the computed data, as shown in Figure 14. In addition, the experimental data from the PV module with an inclined angle of 30 º (SLOPE\_30) was compared with the simulated data in terms of the annual power output: 1,060 kWh/kWp was obtained from the experiment and 977 kWh/kWp was estimated from the computational simulation. This computed data showed a relative error of 8.5 %, which is considered to be a reliable result within the error tolerance. Thus, the computational simulation was conducted to demonstrate the power output performance of a PV module installed at various inclined angles.

In case of horizontal PV module, it showed effective power generation performance in the summer similar to the case of the inclined slope of 30 º, showing more than 30W generation on average at noon. However, the generation barely exceeded 10W in December due to high incidence angle and low solar irradiance. The hourly average power generation depending on each inclined angle is illustrated in Figure 13. In case of inclined angle (SLOPE\_30), it showed power generation of 20W on average at noon, while the horizontal PV module showed 15W on average. Vertical PV (SLOPE\_90) showed the low generation performance of 8W on average. Table 5.5 summarizes the hourly average power generation, voltage and

electric current.

Fig. 13. Annual hourly averaged power generation

**0**

**10**

**20**

**30**

**40**

**POWER(W)**

**50**

**60**

**70**

**5.5 Analysis of power performance through simulation** 

performance of a PV module installed at various inclined angles.

In this study, TRNSYS (Ver. 14.2, Solar Energy Laboratory, Univ. of Wisconsin, USA) was used as a simulation program to analyze the performance of power output for a double glazed PV module. Generally, TRNSYS has been widely used to compute the hourly data for power output, solar irradiance, temperature, and wind speed for both PV systems and solar heat energy systems [10]. From the simulation program, the relative error was verified, and a comparison was then made of the power output from the experimental and the computed data, as shown in Figure 14. In addition, the experimental data from the PV module with an inclined angle of 30 º (SLOPE\_30) was compared with the simulated data in terms of the annual power output: 1,060 kWh/kWp was obtained from the experiment and 977 kWh/kWp was estimated from the computational simulation. This computed data showed a relative error of 8.5 %, which is considered to be a reliable result within the error tolerance. Thus, the computational simulation was conducted to demonstrate the power output

**6 7 8 9 10 11 12 13 14 15 16 17 18 Time(H)**

**SLOPE\_90 SLOPE\_30 SLOPE\_ 0**

Fig. 14. Power output data calibration by comparing the experimental data to the computed data obtained from the simulation program (TRNSYS).

Power performance analyses were performed of PV modules facing south (azimuth = 0 º) depending on the different inclined angles of 0 º, 10 º, 30 º, 50 º, 70 º, and 90 º. The data set consisted of the experimental data for 0 º, 30 º, and 90 º and the computed data for 10 º, 50 º, and 70 º. Figure 15 illustrates the monthly power output depending on the inclined angle ranging from 0 º to 90 º south (azimuth = 0 º). PV modules that were tilted at an angle below 30 º showed a relatively good power performance of over 6 kWh in the summer, while those with an inclined angle above 50 º demonstrated a power performance of less than 6 kWh. The most effective annual power output data of 977 kWh/kWp was obtained at an inclined angle of 30 º (SLOPE\_30), as shown in Figure 16. On the other hand, the lowest annual power output of 357 kWh/kWp was obtained from the PV module with a slope of 90 º (SLOPE\_90), which was 37 % of the annual power output of SLOPE\_30. From Figure 16, it can be seen that the annual power output performance was effective in the order of SLOPE\_10 (954 kWh/kWp), SLOPE\_0 (890 kWh/kWp), SLOPE\_50 (860 kWh/kWp), and SLOPE\_70 (633 kWh/kWp).

The power generation performance depending on the angle of the azimuth was also estimated for PV modules with different inclined slopes, as shown in Figure 17. Similarly, a PV module inclined at an angle of 30 º showed the most effective power output data for all directions in terms of azimuth angles, and the lowest data was obtained from that with an inclined angle of 90 º. For the PV module inclined at an angle of 30 º, the best power performance among the analyzed PV modules facing various directions was obtained for the PV module that was installed to the south (azimuth = 0 º). It can be seen from Figure 17 that different azimuth angles affected the power performance of PV modules: that is, the power performance decreased as the direction of the PV module was changed from the south to the east and west, in comparison to the PV modules that were inclined at the slope of 30 º, as listed in Table 2.

Power Output Characteristics of Transparent a-Si BiPV Window Module 201

Fig. 17. Annual power production of PV modules with various slopes depending on the

South Azimuth 330 Azimuth 300 Azimuth 270 Azimuth 90 Azimuth 60 Azimuth 30

**Incidence Angle(Degrees)**

*0 10 30 50 70 90*

Angle of azimuth (º) Direction Power performance efficiencya (%)

a. Power performance efficiency was calculated from the percent of power output at each azimuth angle

It can be seen from Figure 17 that for the annual power performance of several PV modules, the power output increased with an increase of the inclined angle below 30 º, and decreased with an increase of the inclined angle above 30 º. In particular, at inclined slopes above 60 º there was a steep decline of power performance with the increase of the inclined slope, as shown in Figure 17. This could be due to the incidence angle modifier correlation (IAM) of glass attached to the PV module, which showed a similar tendency in IAM depending on the inclined angle [11], as can be seen in Figure 18. Actually, IAM should be computed as a function of incidence angle () when estimating the power output of the PV module, by

Table 2. Power performance efficiency of PV module with a slope of 308 depending on

angle of azimuth ranging from 0 to 90

**Power(kWh/kWp/year)**

using the following Equation (1) [11]:

azimuth angle

0 South 100 30 Southwest 30 º 99 60 Southwest 60 º 93 90 West 83 270 East 78 300 Southeast 60 º 88 330 Southeast 30 º 96

on the basis of the power output data of PV module to the south.

Fig. 15. Monthly power output data of PV module depending on the slope, and facing south (azimuth = 0).

Fig. 16. Annual power production of PV module depending on the slope, and facing south (azimuth = 0).

Fig. 15. Monthly power output data of PV module depending on the slope,

Fig. 16. Annual power production of PV module depending on the slope, and facing south

and facing south (azimuth = 0).

(azimuth = 0).

Fig. 17. Annual power production of PV modules with various slopes depending on the angle of azimuth ranging from 0 to 90


a. Power performance efficiency was calculated from the percent of power output at each azimuth angle on the basis of the power output data of PV module to the south.

Table 2. Power performance efficiency of PV module with a slope of 308 depending on azimuth angle

It can be seen from Figure 17 that for the annual power performance of several PV modules, the power output increased with an increase of the inclined angle below 30 º, and decreased with an increase of the inclined angle above 30 º. In particular, at inclined slopes above 60 º there was a steep decline of power performance with the increase of the inclined slope, as shown in Figure 17. This could be due to the incidence angle modifier correlation (IAM) of glass attached to the PV module, which showed a similar tendency in IAM depending on the inclined angle [11], as can be seen in Figure 18. Actually, IAM should be computed as a function of incidence angle () when estimating the power output of the PV module, by using the following Equation (1) [11]:

Power Output Characteristics of Transparent a-Si BiPV Window Module 203

PV (SLOPE\_90) showed the peak efficiency of 2.38% in February and lowest efficiency of 0.80% in June. The inclined slope of 30 º (SLOPE\_30) showed the greatest annual average power efficiency of 3.19%, followed by horizontal and vertical PV modules showing

> **SLOPE\_30 SLOPE\_90 SLOPE\_ 0**

efficiencies of 2.61% and 1.77%, respectively.

Fig. 19. Annual hourly averaged power efficiency

**0**

**1**

**2**

**3**

**4**

**PV\_Efficiency(%)**

**5**

**6**

**7**

**6.3 Power efficiency by the temperature variation** 

crystalline silicon solar cell (c-Si solar cell).

**6.2 Effect of power efficiency by the intensity of solar irradiance** 

Assuming the solar irradiance of 900 W/m2, the power efficiencies of the inclined slope of 30º and horizontal PV reached 5%, while the vertical PV partially exceeded 3%. The inclined slope of 30 º and horizontal PV showed relatively high power efficiency even under high solar irradiance conditions, while the efficiency of vertical PV significantly dropped after reaching 500W/m2. The inclined slope of 30 º and horizontal PV can obtain relatively uniform solar irradiance throughout the year and thus the high power efficiency can be achieved over the large range of solar irradiance, while the vertical PV absorb the low solar irradiance during the winter period and thus the power efficiency is reduced in those low irradiance conditions.

**5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Time(H)**

The correlation between the power efficiency and the PV surface temperature variation is illustrated. Under the low solar irradiance, the data is scattered and thus did not show the clear correlation. However, it showed the clear correlation between PV efficiency and the surface temperature under the solar irradiance higher than 600W/m2, i.e., the PV efficiency is improved at higher surface temperature. This is due to the fact that the higher surface temperature enhances the power efficiency in case of amorphous PV as opposed to

 IAM = 1 – (1.098×10-4) - (6.267×10-6) + (6.583×10-7) - ×10-8 (1)

Fig. 18. Correlation of incidence angle modifier given by King et al. (1994).

Accordingly, a characteristic of the glass attached to the PV module is considerably influential so that the solar transmittance (Tsol) remarkably decreases with an increase in the inclined slope of the PV module from the higher incidence angle. Therefore, the solar transmittance efficiency can significantly affect the power output of the PV module.

#### **6. Power efficiency of PV module**

#### **6.1 Hourly based analysis of the power efficiency**

The power efficiency can be calculated by multiplying total irradiation by the PV window area. Annual averaged power efficiency is illustrated in Fig. 19.

$$\eta\_{S,\mathbf{r}} = \begin{array}{c} E\_{\text{use,r}}\\ \hline A\_a \text{ X } H\_{\text{tr}} \end{array}$$

ηS,<sup>τ</sup> ; Power Efficiency

Euse,τ ; Power Output(Wh)

Aa ; PV windows area (m2)

Hτ ; Total irradiation on the PV windows

Annual average power efficiencies of the inclined slope of 30 º (SLOPE\_30), horizontal PV module (SLOPE\_0) and vertical PV module (SLOPE\_90) turned out to be 3.19%, 2.61% and 1.77%, respectively, indicating that the inclined slope of 30 º showed the greatest efficiency. On the other hand, the horizontal PV showed the highest instantaneous peak power efficiency of 6.0% followed by those of the inclined slope of 30 º (5.6%) and vertical PV (4.0%) angles. In terms of the monthly average power efficiency depending on each inclination angle, the inclined slope of 30 º (SLOPE\_30) showed 3.82% in June and the horizontal PV (SLOPE\_0) showed 3.63% in July. The inclined slope of 30 º showed 2.15 % of efficiency and the horizontal PV showed 0.81% in December. On the other hand, the vertical

Fig. 18. Correlation of incidence angle modifier given by King et al. (1994).

Accordingly, a characteristic of the glass attached to the PV module is considerably influential so that the solar transmittance (Tsol) remarkably decreases with an increase in the inclined slope of the PV module from the higher incidence angle. Therefore, the solar

The power efficiency can be calculated by multiplying total irradiation by the PV window

�� <sup>=</sup> ������

Annual average power efficiencies of the inclined slope of 30 º (SLOPE\_30), horizontal PV module (SLOPE\_0) and vertical PV module (SLOPE\_90) turned out to be 3.19%, 2.61% and 1.77%, respectively, indicating that the inclined slope of 30 º showed the greatest efficiency. On the other hand, the horizontal PV showed the highest instantaneous peak power efficiency of 6.0% followed by those of the inclined slope of 30 º (5.6%) and vertical PV (4.0%) angles. In terms of the monthly average power efficiency depending on each inclination angle, the inclined slope of 30 º (SLOPE\_30) showed 3.82% in June and the horizontal PV (SLOPE\_0) showed 3.63% in July. The inclined slope of 30 º showed 2.15 % of efficiency and the horizontal PV showed 0.81% in December. On the other hand, the vertical

�� � ��

transmittance efficiency can significantly affect the power output of the PV module.

+ (6.583×10-7)


IAM = 1 – (1.098×10-4) - (6.267×10-6)

**6. Power efficiency of PV module** 

Hτ ; Total irradiation on the PV windows

ηS,<sup>τ</sup> ; Power Efficiency Euse,τ ; Power Output(Wh) Aa ; PV windows area (m2)

**6.1 Hourly based analysis of the power efficiency** 

area. Annual averaged power efficiency is illustrated in Fig. 19.

PV (SLOPE\_90) showed the peak efficiency of 2.38% in February and lowest efficiency of 0.80% in June. The inclined slope of 30 º (SLOPE\_30) showed the greatest annual average power efficiency of 3.19%, followed by horizontal and vertical PV modules showing efficiencies of 2.61% and 1.77%, respectively.

Fig. 19. Annual hourly averaged power efficiency

### **6.2 Effect of power efficiency by the intensity of solar irradiance**

Assuming the solar irradiance of 900 W/m2, the power efficiencies of the inclined slope of 30º and horizontal PV reached 5%, while the vertical PV partially exceeded 3%. The inclined slope of 30 º and horizontal PV showed relatively high power efficiency even under high solar irradiance conditions, while the efficiency of vertical PV significantly dropped after reaching 500W/m2. The inclined slope of 30 º and horizontal PV can obtain relatively uniform solar irradiance throughout the year and thus the high power efficiency can be achieved over the large range of solar irradiance, while the vertical PV absorb the low solar irradiance during the winter period and thus the power efficiency is reduced in those low irradiance conditions.

### **6.3 Power efficiency by the temperature variation**

The correlation between the power efficiency and the PV surface temperature variation is illustrated. Under the low solar irradiance, the data is scattered and thus did not show the clear correlation. However, it showed the clear correlation between PV efficiency and the surface temperature under the solar irradiance higher than 600W/m2, i.e., the PV efficiency is improved at higher surface temperature. This is due to the fact that the higher surface temperature enhances the power efficiency in case of amorphous PV as opposed to crystalline silicon solar cell (c-Si solar cell).

Power Output Characteristics of Transparent a-Si BiPV Window Module 205

Fig. 22. Correlation between the surface temperature and power efficiency (SLOPE\_30°)

Fig. 23. Correlation between the surface temperature and power efficiency (SLOPE\_0°)

Fig. 20. Correlation between solar insolation and power efficiency (SLOPE\_90°, SLOPE\_30°, SLOPE\_0°)

Fig. 21. Correlation between the surface temperature and power efficiency (SLOPE\_90°)

Fig. 20. Correlation between solar insolation and power efficiency (SLOPE\_90°, SLOPE\_30°,

Fig. 21. Correlation between the surface temperature and power efficiency (SLOPE\_90°)

SLOPE\_0°)

Fig. 22. Correlation between the surface temperature and power efficiency (SLOPE\_30°)

Fig. 23. Correlation between the surface temperature and power efficiency (SLOPE\_0°)

Power Output Characteristics of Transparent a-Si BiPV Window Module 207

Fig. 25. PV module power efficiency vs. solar incidence angle (SLOPE\_30°)

Fig. 26. PV module power efficiency vs. solar incidence angle (SLOPE\_0°)

#### **6.4 Power efficiency by the solar incidence angle**

The PV efficiencies of each inclination angle under different solar incidence angle and solar irradiance are illustrated in the figures below. In case of vertical PV module (SLOPE\_90), the power efficiency showed constant value until the solar incidence angle of 65° and it started to rapidly drop after 65°. These characteristics are considered to be the effect of absorbed solar insolation (incident angle modifier) depending on the solar incidence angle reaching the PV module glass wall. This phenomenon did not take place in case of the inclined slope of 30 º (SLOPE\_30) due to the low PV efficiency at the solar incidence angle higher than 65°. Likewise, the horizontal PV module was not affected by incident angle modifier as well in most of the solar radiation conditions except for the high solar incidence angle of greater than 65° and the low solar insolation of less than 400W/m2 where the efficiency was rather decreased.

It turns out that the power efficiency of PV module is largely affected by the solar incidence angle, solar azimuth and altitude. Furthermore, the rapid decrease in the PV efficiency during the summer period is due to the reduced solar transmittance through the window system at the solar incidence angle higher than 70°, showing the impact of the front glass of PV module on the power efficiency.

Fig. 24. PV module power efficiency vs. solar incidence angle (SLOPE\_90°)

The PV efficiencies of each inclination angle under different solar incidence angle and solar irradiance are illustrated in the figures below. In case of vertical PV module (SLOPE\_90), the power efficiency showed constant value until the solar incidence angle of 65° and it started to rapidly drop after 65°. These characteristics are considered to be the effect of absorbed solar insolation (incident angle modifier) depending on the solar incidence angle reaching the PV module glass wall. This phenomenon did not take place in case of the inclined slope of 30 º (SLOPE\_30) due to the low PV efficiency at the solar incidence angle higher than 65°. Likewise, the horizontal PV module was not affected by incident angle modifier as well in most of the solar radiation conditions except for the high solar incidence angle of greater than 65° and the low solar insolation of less than 400W/m2 where the efficiency was rather

It turns out that the power efficiency of PV module is largely affected by the solar incidence angle, solar azimuth and altitude. Furthermore, the rapid decrease in the PV efficiency during the summer period is due to the reduced solar transmittance through the window system at the solar incidence angle higher than 70°, showing the impact of the front glass of

Fig. 24. PV module power efficiency vs. solar incidence angle (SLOPE\_90°)

**6.4 Power efficiency by the solar incidence angle** 

decreased.

PV module on the power efficiency.

Fig. 25. PV module power efficiency vs. solar incidence angle (SLOPE\_30°)

Fig. 26. PV module power efficiency vs. solar incidence angle (SLOPE\_0°)

**10** 

*1,2Italy 3Cuba* 

*1IMEM-CNR, Parma* 

*Univ. of Havana, La Habana* 

*2Thifilab, University of Parma, Parma* 

**Influence of Post-Deposition Thermal** 

**of Materials for CdTe/CdS Solar Cells** 

*3Lab. of Semicond. and Solar Cells, Inst. of Sci. and Tech. of Mat.,* 

**Treatment on the Opto-Electronic Properties** 

Nicola Armani1, Samantha Mazzamuto2 and Lidice Vaillant-Roca3

Thin film solar cells based on polycrystalline Cadmium Telluride (CdTe) reached a record efficiencies of 16.5% (Wu et al. 2001a) for laboratory scale device and of 10.9% for terrestrial module (Cunningham, 2000) about ten years ago. CdTe-based modules production companies have already made the transition from pilot scale development to large manufacturing facilities. This success is attributable to the peculiar physical properties of CdTe which make it ideal for converting solar energy into useful electricity at an efficiency level comparable to silicon, but by consuming only about 1% of the semiconductor material required by Si solar cells. Because of the easy up-scaling to an industrial production as well as the low cost achieved in the recent years by the manufacturers, the CdTe technology has carved out a remarkable part of the photovoltaic market. Up to now two companies (Antec Solar and First Solar) have a noticeable production of CdTe based modules, which are

assessed as the best efficiency/cost ratio among all the photovoltaic technologies.

characteristics and the factors limiting the efficiency of the devices.

Since the record efficiency of such type solar cells is considerably lower than the theoretical limit of 28-30% (Sze, 1981), the performance of the modules, through new advances in fundamental material science and engineering, and device processing can be improved. Further studies are required to reveal the physical processes determining the photoelectric

The turning point for obtaining the aforementioned high efficiency values was the application of a Cl-based thermal treatment to the structures after depositing the CdTe layer (Birkmire & Meyers, 1994; McCandless & Birkmire, 1991). The device performance improvement is due to a combined beneficial effect on the materials properties and on the pn junction characteristics. CdTe grain size increase (Enriquez & Mathew, 2004; Luschitz et al., 2009), texture properties variations (Moutinho et al., 1998), grain boundary passivation, as well as strain reduction due to S diffusion from CdS to the CdTe layer and recrystallization mechanism (McCandless et al., 1997) are the common observed effects.

**1. Introduction**
