**4. Results and discussion**

Prior to presenting the results, it should be noted that all presented results are averaged over time. The change of the mean temperature of PV with wind direction is shown in **Figure 2**. It is seen that for both wind velocities of 2 and 5 m/s, the mean temperature of the PV is lower at angles below 90 degrees which is associated with higher surface heat transfer coefficients, as shown in **Figure 3**. Under these conditions, there is direct contact between the wind and module surfaces which contributes to forced convective cooling of the PV, thereby increasing the surface heat transfer coefficient, and decreasing the temperature of PV. At lower angles, the wind penetrates the gap between the PV and roof surface resulting in an increased heat transfer. In other words, the forced convective cooling effects on both sides (front and back) of the module are prominent at angles below 90 degrees. It is noticeable that by increasing the angle from 0 to 60 degrees, there is a slight decrease in the mean temperature of PV. This is mainly because, at angles higher than 0 degrees (and below 90 degrees), more airflow penetrates the gap between the PV and roof which in turn intensifies the convective cooling effects from the backside of the PV. **Figure 4** shows the schematic view of the airflow penetrating the gap between the PV module and roof for the wind angles of 0 and 60 degrees. As seen, when the wind angle is 0 degrees, the airflow mainly enters the gap from the bottom side. However, for the 60 degrees case, the

*Influence of Wind Incidence Angle on the Cooling of Rooftop-Mounted Solar Panels DOI: http://dx.doi.org/10.5772/intechopen.109610*

**Figure 2.** *Effects of wind angle on the mean temperature of PV.*

airflow enters the gaps mainly from both bottom and left side of the gap, thereby intensifying convective cooling effects.

It is worth noting that similar observations were reported by the experiments of Wen [10] who studied the cooling effects of wind direction on a PV panel whose surface was parallel to the wind and observed that the convective heat transfer coefficient reached a maximum value for the angles in the range of 60–120 degrees depending on the wind velocity. However, as will be discussed in the following, the HTC drops drastically in the current research for angles beyond 60 degrees due to the edges of the structure that act as a barrier.

**Figure 3.**

#### **Figure 4.**

*Schematic view of the airflow penetrating the gap between the PV and roof, left) 0 degrees and right) 60 degrees wind angle.*

*Influence of Wind Incidence Angle on the Cooling of Rooftop-Mounted Solar Panels DOI: http://dx.doi.org/10.5772/intechopen.109610*

**Figure 5.**

*Contours of mean static temperature of PV panel for free stream velocity of 5 m/s, top) 0 degrees, bottom) 180 degrees.*

By increasing the wind angle beyond 60 degrees, there is a sharp increase in the mean temperature and a decrease in the mean surface HTC of the PV, as shown in **Figures 2** and **3**, respectively. The reason behind this is that at higher angles, the

#### **Figure 6.**

*Flow streamlines for wind velocity of 5 m/s, top) 180 degrees, bottom) 0 degree.*

inclined roof and sidewalls of the structure act as a barrier between the module and wind, thereby decreasing the direct contact between the wind and module and consequently degrading the forced convective cooling effects.

**Figure 5** illustrates the temperature contours of the PV panel for wind angles of 0 and 180 degrees. As observed, PV experiences lower temperature due to higher cooling effects at zero wind angle. It is also observed in **Figures 2** and **3** that, as expected, mean HTC augments and mean temperature of PV decreases as the wind velocity increases due to the enhanced forced convective cooling effects.

To get a better understanding of the wind and structure interactions, **Figure 6** is presented showing the streamlines for the wind velocity of 5 m/s and angles of 0 and 180 degrees. As seen, for the wind angle of zero degrees, the wind flow approaching the PV is divided into two streams, one passing beneath the PV and the second passing over the surface of the PV resulting in convective cooling effects from both sides. A large vortex is being also generated behind the structure. However, at the angle of 180 degrees, the walls and edges of the structure result in the separation of flow and formation of a large vortex in the vicinity of PV which weakens the convective cooling rates.

*Influence of Wind Incidence Angle on the Cooling of Rooftop-Mounted Solar Panels DOI: http://dx.doi.org/10.5772/intechopen.109610*
