Installation of solar panels on a flat roof
With the price of solar panels dropping, there are more offers to install them on flat roofs. Especially popular are the roofs of distribution centers, factory halls, megamarkets, warehouses, and cold stores. These are facilities that consume a large amount of electricity, so the economic profitability of this investment is unquestionable. The only question is: How to install solar panels to maximize your profits?
I have seen several types of panel installation, so I will analyze all cases with the SPAC application.
1. The building is ideally oriented: toward south-north
In this case, I will consider three variants, the last of which is only theoretical.
2.1 Classically placed panels as far as possible to the south
2.2 Panels are positioned on inclined supports with an east-west orientation.
2.3. Panels placed horizontally
2. The building is not ideally oriented.
In this case, I will consider:
2.1 classic south-facing panel setup.
2.2 horizontal panel setting.We will analyze Case 2 in detail in another article.
We will adopt a roof of random dimensions:
| Roof Dimensions | 60m X 80m |
| PV Module | Axitec 415 W |
| PV Module dimensions | Axitec 1172 mm X 1134mm |
| PV Module price: | Axitec $130 |
| Location: | Los Angeles, USA |
South-facing panel setting with gap due to shadow (ground standard)
The SPAC application automatically calculates the required distance between the panels due to shadow casting.
The length of the shadow varies according to the latitude.
On December 21, the shadow is at its most unfavorable, measuring 2.84 meters.
D = gap due to shadow = 2.84 meters.
At a distance of 60 m, the number of columns in an east-west direction is:
We calculate the number of rows according to the following formula:
N = (80 m / 1.722 m * cos(30)) : 2.84 m = 27
Now, by entering these parameters into the application, we can obtain the annual production of:
The panel settings on inverted "V" supports are aligned east - west
This setup is very popular due to the current drop in solar panel prices, and it attempts to get as much energy as possible from a rooftop installation.
We place the panels on isosceles triangular supports with two equal alpha angles and arrange them east-west, so that one side of the support receives sun exposure throughout the
day and both sides at noon.
With this shape, you should pay particular attention to the height of the triangle of the support, because the high height and the large alpha angle can cause the panels to cast
a shadow on each other.
The altitude angle must be greater than or equal to the panel’s inclination angle.
In order to find a compromise solution, one has to look at the altitude angle in the morning hours in December and January (when there is the biggest shadow) and possibly sacrifice
the energy gain in that month until 10 a.m. and after 2:30 p.m.In our calculations, we will use the angle alpha = 18.
The formula calculates the total length of one pair of panels on the support.
We count the total number of pairs of panels facing east to west (length 60 m)
The formula calculates the total number of panels in the south-north direction:
Compared to the first example, there are five times as many panels installed here:
We calculate the total energy according to the formula.
The power from panels facing east (before noon) is denoted as P-east. In the afternoon, panels facing west provide P-west power.
We assume that P east equals P west.
The parameters used in the P east calculation are
Panel tilt angle: 18 degrees
Facing south at 90 degrees
When we pass these parameters through the SPAC application, we get the following results:
Therefore, the total annual production is:
P anual = 2,140,8,706 kWh.
This considerably surpasses the traditional on ground configuration.
On the image above:
α: tilt angle on a V shape
β: altitude angle (It depends on the day of the year, time of day, and latitude.)