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# Front and back spacing design of photovoltaic array

View: 9402020/12/29
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Shadow occlusion will seriously affect power generation. Although the shadow only covers 1/10, it may reduce the power generation by more than 90%!

Therefore, in distributed projects, especially household projects, there are two problems that plague many installation teams:

1) What is the distance between the front and rear of the photovoltaic array to ensure that it does not affect the power generation?

2) When there is an obstacle (such as a parapet) in front of the photovoltaic array, how much space should be kept to ensure that it is not blocked?

In household projects, due to the lack of technical strength of the installation team, a large number of front and rear rows are blocked due to insufficient front and rear spacing, which seriously affects the power generation. As shown below.

How reasonable is the spacing between the front and rear rows?

According to the "Specifications for Design of Photovoltaic Power Stations (GB 50797-2012)":

It is necessary to ensure that the front, back, left, and right are not blocked from each other during the period from 9:00 to 15:00 (local true solar time) throughout the year, that is, the front and back are not blocked from each other during the period of 9:00 to 15:00 on the winter solstice day.

At this time, the calculation method of the distance between the front and rear of the array is as follows:

If the height of the photovoltaic array in front (height of the obstruction) is H, H can be actually measured; keep the distance between the front and back of the winter solstice 9:00-15:00 (local true solar time) unobstructed as D, which can be calculated by H , The calculation method is as follows.

Sun altitude sinα=sinφsinδ+cosφcosδcosω;

Azimuth angle of the sun cosγ=(sinαsinφ-sinδ)/ (cosαcosφ)

Array spacing D=Hcosγ/tanα

φ: latitude, δ: declination angle, ω: hour angle

The above formula is relatively complicated, and it is difficult for general household installers to calculate. However, we can find that the ratio of D to H is a fixed value, which is only related to the latitude of the project site.

D/H=τ=cosγ/tanα

τ is called the shadow magnification of the project site

For the convenience of query, Tables 1 to 5 list the shadow magnification when the latitude of the project site is 10°~55°.

For example, if the latitude of a place is 25°, according to Table 2, its shadow magnification is 1.5124. After measurement, the height of the front array/blocking object is 2m, then the front-to-back distance D=2m×1.5124=3.0248m, and the actual project can be taken up to 3.1m. If the latitude of a place is 35.7°, according to Table 3, the shadow magnifications at 35° and 36° are 2.3028 and 2.4174, respectively, and the shadow magnifications at 35.7° calculated by interpolation are 2.383. After measurement, the height of the front array/blocking object is 1.4m, then the front-to-rear distance D=1.4m×2.383=3.336m, and the actual project can take 3.4m upwards.

Table 1: Shadow magnification when the latitude of the project site is 10°～19°

 Latitude 10° 11° 12° 13° 14° 15° 16° 17° 18° 19° Shadow magnification 0.8856 0.9172 0.9499 0.9836 1.0186 1.0548 1.0923 1.1314 1.1720 1.2143

Table 2: Shadow magnification when the latitude of the project site is 20°～29°

 Latitude 20° 21° 22° 23° 24° 25° 26° 27° 28° 29° Shadow magnification 1.2584 1.3045 1.3528 1.4033 1.4565 1.5124 1.5713 1.6336 1.6695 1.7694

Table 3: Shadow magnification when the latitude of the project site is 30°～39°

 Latitude 30° 31° 32° 33° 34° 35° 36° 37° 38° 39° Shadow magnification 1.8438 1.9232 2.0081 2.0991 2.1970 2.3028 2.4174 2.5422 2.6785 2.8282

Table 4: Shadow magnification when the latitude of the project site is 40°～49°

 Latitude 40° 41° 42° 43° 44° 45° 46° 47° 48° 49° Shadow magnification 2.9934 3.1768 3.3818 3.6125 3.8743 4.1740 4.5208 4.9271 5.4098 5.9932

Table 5: Shadow magnification when the latitude of the project site is 50°～55°

 Latitude 50° 51° 52° 53° 54° 55° Shadow magnification 6.7128 7.6236 8.8139 10.4371 12.7834 16.4776

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