**5. Conclusion**

454 Solar Cells – Thin-Film Technologies

very high temperature (indicated by trend 2), while the rest of the days would be for typical winter season, normally characterized by mostly low temperature. In both cases, a negative WUF temperature coefficient is observed, with trend 1 being -0.001/oC and for trend 2 being

The same procedure was also used to find the effect of temperature on WUF for summer

Interesting to note from figure 12 is that the spectral effect temperature coefficient for summer period is the same as the one obtained during winter, clear sky (trend 2) although for summer the highest temperature reached was above 60oC while for trend 2 (figure 11), the highest was less than 60oC. From the two figures, it has been shown that temperature coefficient due to spectral effect (WUFβ) can be obtained once the outdoor spectrum data for a device is correctly calculated using the Weighted Useful Fraction (WUF) concept. Like other performance parameters, whose temperature coefficients are equally important in PV characterization and system design, the WUF should be also be considered as this might help to minimize some of the system sizing errors, which in most instances lead to under

> 10 20 30 40 50 60 70 **Tmod (o C)**

Fig. 12. Relationship between the outdoor WUF and back of module temperature of the CIS

y = -4E-05x + 0.9805 R2 = 0.6894

months of CIS module. Figure 12 shows the WUF versus temperature relationship.

performance, unreliable and financial repercussions.


0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1.00

module during summer period.

**WUF**

The outdoor spectral effects using the Weighted Useful Fraction (WUF) of CIS module was analyzed. Observed was a 17% decrease in the device short - circuit (Isc) current attributed due to a change in season. The change in season (summer/winter) result in the outdoor spectrum to vary by ΔWUF = 1.5%, result in the decrease in the device Isc. From the analysis done, it was concluded that a small percentage change in ΔWUF resulted in large % difference of the module's Isc as the outdoor spectrum changed during the course of the day, which confirmed that the 17% decrease in Isc was due to a ΔWUF of 1.5 %. A strong correlation between FF and the WUF exists for CIS module. It is observed that the FF increases by 6.5% as WUF increases. The temperature coefficient of a device is one of the important concepts for characterizing device performance parameter. A close correlation between WUF and temperature was established. Temperature coefficients for spectral induced effect (WUF) were found to be -0.001/oC for winter period and -4×10-5/oC for summer seasons. This difference in WUFβ for summer and winter indicated that the temperature coefficients obtained in controlled environment (indoor procedure) can not be truly dependable for modeling purposes or system sizing since the outdoor conditions has an effect also. It should also be noted that the temperature coefficient for spectral effect is indeed an important parameter to consider.

#### **6. References**


silicon photovoltaic devices. *Measurement Science and Technology*, vol.15, pg 460- 466.

M Simon and E.L Meyer (2010). The effects of spectral evaluation for c-Si modules", *Progress in Photovoltaic: Research and Application,* DOI:10.1002/pip.973.

M Simon and E.L Meyer (2010). The effects of spectral evaluation for c-Si modules", *Progress in Photovoltaic: Research and Application,* DOI:10.1002/pip.973.

466.

silicon photovoltaic devices. *Measurement Science and Technology*, vol.15, pg 460-
