The array’s tilt is the angle in degrees from horizontal. A flat roof has 0 degree tilt and a vertical wall mount has a 90 degrees tilt angle. Whether you are installing solar panel on a flat roof or a pitched roof, the output of the solar PV system would be increased by optimizing the tilt angle.
One can ask the question, how much would the energy output change in a case where the array is tilted 30 degrees instead of 10 degrees? To answer this question; we must initially be aware of the following;
- The Latitude
The sun, at noon time, is not always directly on top of us. The sun will be slightly to your south throughout the year, if your location is in the north of 30th latitude in the Northern Hemisphere. (That is approximately the border of Mexico and USA)
The array output is highest, if the array faces directly to the sun at all times. Since the location of the sun moves throughout the day, it is not possible to face directly to the sun unless we use 2-axis solar tracker. Yet, it’s possible to optimize the output by tilting the array at a correct angle.
- The Shade of the Tilted Array
A tilted array on a flat roof means an obstacle for other modules in the same roof. We don’t want any shade on any modules at any time. Therefore, there should be enough clearance between the rows of the array.
Here is the answer to my previous question;
how much would the energy output change in different tilt angles?
I’ve run a simple calculation on the free software SAM (System Advisor Model) that is provided by NREL (National Renewable Energy Laboratory). The sample 3.4 kW system, consists of 16x Sanyo HIT-N215A modules and is assumed to be located in Phoenix, AZ and Portland, OR.
|Array Tilt Angle|
|Phoenix, AZ (33 North)||Portland, OR (45 North)|
|0 - flat||5,723||0||3,624||0|
|90 - vertical||3,966||-31%||2,967||-20%|
This example shows that the solar array tilt angle of 20 to 30 degrees would significantly increase the energy output of the system. The positive effect of the array tilt angle is higher in the northern cities than in the cities closer to the equator.
I am going to post an article about "The effect of Azimuth Angle on Solar Energy Output", which is a related topic to what we've discussed in this article.
Here are some links that I recommend for using in similar calculations: