WIND LOADS OF PHOTOVOLTAIC PANELS MOUNTED ON A HIP ROOF TO THE EDGE AND THEIR WIND-LOAD REDUCTION EFFECT ON ROOF CLADDING

Abstract

　The PV systems are generally designed based on JIS C 8955 in Japan. However, no provision is given to the PV panels installed in the edge zones. It is not recommended to install them in such zones, because very large suctions are induced by flow separation. When installing PV panels in such zones, we have to evaluate the wind force coefficients appropriately. Because it is difficult to make wind tunnel models of the PV panels with the same geometric scale as that for the building, we apply a numerical simulation to evaluate the net wind forces on the PV panels, where the pressures beneath the PV panels, called ‘layer pressures’, are numerically simulated using the unsteady Bernoulli equation together with the time history of external pressures on the roof measured in a wind tunnel. Furthermore, we propose to install the PV panels with small gaps between them, which may reduce the net wind forces acting on the PV panels due to pressure equalization. It is expected that the external pressures on the roofing are also reduced significantly.

　The present paper consists of six sections. Following the introduction, Section 2 illustrates the building models under consideration. Two models are used; one is a square-roof building with a square plan of 11 m × 11 m and the other is a hip-roof building with a rectangular plan of 18.6 m × 9.4 m. The ridge height and the roof slope are respectively 10.7m and approximately 25° in both models. Section 3 describes the experimental models and procedure used in the wind tunnel experiment. In the square-roof model case the PV panels installed on the roof are also modeled. The wind pressures at many locations on the top surface of PV panels as well as on the roof surface are measured in a wind tunnel, the results of which are used for validating the simulation method of layer pressures. The hip-roof model is not equipped with PV panels. The wind pressures measured on the roof are used for simulating the layer pressures. Section 4 first explains the method of simulation. The layer pressures are numerically simulated by using the unsteady Bernoulli equation together with the time history of external pressures on the roof. The net wind forces on the PV panels are provided by the difference between the wind pressure on the upper surface and the layer pressure. The simulation is verified by comparing the simulated results of the layer pressures with those obtained from the wind tunnel experiment for the square-roof model. Then, the simulation is applied to the hip-roof building model in Section 5. The wind force coefficients of PV panels installed all over the roof are evaluated. The results indicate that negative wind force coefficients large in magnitude are induced on the PV panels located near the roof corner. However, the magnitude of such negative wind force coefficients decreases with an increase in the gap between PV panels up to approximately 5 mm. When PV panels are installed on the roof, the external pressures on the roofing are equal to the layer pressures. It is found that the peak external pressures on the roofing are significantly reduced in magnitude by the PV panels. Finally, Section 6 summarizes the main conclusions obtained in the present study.