Loads and Loading Cases

The tracker is equipped with a PV panel with a surface 1.48×0.67 m2, approx. 1 m2. The maximum wind speed for the Bra§ov region is 30 m/s resulting a maximum wind force on the panel Wmax = 580 N for a maximum wind pressure pm = 580 N/m2 [3]. The wind direction can be considered towards the front of the panel (fig. 2, a.. .c) or towards the back of the panel (fig. 2, d.. .f). Different assumptions can be considered on the distribution of the wind pressure on the panels: uniform pressure [4], resulting bigger wind force (fig. 2, a, d); trapezoidal distribution, approximating the distribution presented in [5], reversed for opposite wind direction (fig. 2, b, e); triangular distribution [6], reversed for opposite wind direction (fig. 2, c, f). For all six wind load cases presented in fig. 2, the load can be reduced to a single wind force W and a moment M, placed on the axis of the panel, with values according to Table 1.

Подпись: pm pm pm pm pm/2 a b c d e f image018pm pm

image019

Wind

Fig. 2. Wind load (a — wind case 1; b — wind case 2; c — wind case 3; d — wind case 4; e — wind case 5; f —

wind case 6).

Table 1. Wind loads for wind pressure distribution cases.

Wind direction towards front of panel

Wind direction towards back of panel

M

W

Wind case 1

Wind

case 2

Wind case 3

Wind case 4

Wind case 5

Wind

case 6

W

W

max

Iw

2 max

3W

4 max

Wmax

— IW

2 max

—W

4 max

M

0

—W l

12 max

—W l

24 max

0

—W l

12 max

—W l

24 max

The only weight that is considered for preliminary design is G = 250N, the weight of the panel together with all the parts (frame) directly attached to it.

Table 2 presents the loading cases given by the extreme positions of the tracking system.

Table 2. Loading cases.

1 — Winter solstice sunrise

2 — Winter solstice sunset

3 — Winter solstice noon

4 — Summer solstice sunrise

5 — Summer solstice sunset

6 — Summer solstice noon

Y *= 55°; P*= +48°

Y*= 55°; P*= -48°

Y*= 67°; P*= 0°

Y*= 0°; P*= +65°

Y*= 0°; P*=-65°

Y*= 23°;

P*= 0°