## 3 Results
### Parametric Analysis of the PV
On the other hand, the PCM PV had a different behavior and was the less efficient choice in the case of low ambient temperatures and the most efficient one in the case of high ambient temperatures. In any case, there were no huge deviations among the examined PVs because the impact of the cell temperature on the results was relatively restricted. Figure 12: Cell temperature variation of the examined PVs for different ambient temperatures and low incident irradiation level at 400 \(\mathrm{W/m^{2}}\). Figure 13: PV efficiency variation of the examined PVs for different ambient temperatures and low incident irradiation level at 400 \(\mathrm{W/m^{2}}\). production per m\({}^{2}\) and the cumulative electricity production per m\({}^{2}\). The maximum obtained specific electricity production was 185 W/m\({}^{2}\), while the cumulative yearly electricity production was about 352 kWh/m\({}^{2}\). The results indicate that higher production existed during the summer because the production lines were denser and the cumulative curve had a higher slope during the summer. Figure 17 depicts the cell temperature variation of the simple PV for the location of Athens. The maximum cell temperature obtained was 66.2 \({}^{\circ}\)C during the summer which is a great temperature level. Hence, there is potential for reducing this temperature level by applying the proper cell cooling techniques. Figure 16: Yearly variation in specific electricity production for the simple PV in Athens and cumulative specific electricity production. Figure 17: Yearly variation in cell temperature for the simple PV in Athens. Figures 18 and 19 illustrate the yearly variation of the BIPV production and the BIPV cell temperatures for the case of Athens. Figure 18 investigates the hourly variation of the specific electricity production of the BIPVs which were mounted on the south side of the building. The maximum specific BIPV production was about 48 W/m\({}^{2}\), significantly lower than the maximum produced value of the simple PV. This lower value is explained by the significantly lower reference temperature of the BIPV module compared to the simple PV. The cumulative specific electricity production was found at 49 kWh/m\({}^{2}\), which is lower than the respective for the simple PV for two reasons: the first one is the lower reference efficiency of the BIPV and the second is the lower incident solar potential in the south wall compared to the optimally inclined PV in the roof. Also, the BIPV electricity production was not maximized in the summer because during this period, the solar position was high during the noon and so the solar rays reach the south vertical wall with great incident angle. Figure 19 illustrates the BIPV cell temperature variation during the year. The maximum obtained value was around 65.1 \({}^{\circ}\)C, which is similar to the respective maximum value of the simple PV cell temperature. Figure 18: Yearly variation in specific electricity production for the BIPV in Athens and cumulative specific electricity production. In the last part of this section, the summary results for eight studied buildings are given in Figures 20 and 21, as well as Table 7. The yearly total electricity demand, the simple PV production, the BIPV production and the electricity surplus with the combination of simple PV and BIPV are depicted in Figure 20. In all the cases, the buildings were positive by the combination of BIPV and simple PV. The use of BIPV was needed for having an electricity surplus in the B1 building in the locations of Munich and Stockholm. The highest electricity surpluses were found for the B2 building, while the B1 building had lower electricity surplus values. Moreover, it is interesting to state that the electricity production with simple PV was significantly higher compared to the BIPV production. The PV production was significantly higher in the warmer climates, while the increase in BIPV production in the warm climates was not so intense compared to the coldest climates.