Can Solar Panels Be Installed on Flat Roof - Flat roof solar

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.
1.1 Classically placed panels as far as possible to the south
1.2 Panels are positioned on inclined supports with an east-west orientation
1.3 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:

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 m.

D = gap due to shadow = 2.84 m

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:

Now, by entering these parameters into the application, we can obtain the annual production of:

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 α 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 high height and a large α 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 α = 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:

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.

Parameters used:
- Panel tilt angle: 18°
- Facing direction: East / West

Results from the SPAC application:

Therefore, the total annual production is:
P_annual = 2,140,706 kWh

This considerably surpasses the traditional ground-style setup.

On the image above:
α: tilt angle on a V shape
β: altitude angle (depends on the day of the year, time of day, and latitude)

I have not seen this case in practice, probably due to problems with drainage or removing accumulated snow, but I will analyze it for comparison with the previous two.

First Option

Summary: 52 x 46 = 2392 panels

Second Option

After all calculations with the SPAC application, we get the following comparative results. To simplify the analysis, I will divide the energy gain by the total investment ($) to get a clear picture of kWh per invested dollar:

Conclusions:

• For the first case, the best yield per dollar is 5.17 kWh/$ per year.
• The second case yields the highest total energy output.
• The second and third cases are virtually identical in terms of invested dollars per generated kilowatt.
• In areas without heavy snow or rain, the third case shouldn't be completely ignored.