The effect of an array's tilt angle on solar PV energy output may be up to 20% compared to that of flat installations. A comparison of data in two US cities has been completed to exhibit the importance of a solar PV arrray's tilt angle.
As a general rule of thumb, energy output can be optimized by adding 15 degrees to a site's latitude in the winter and subtracting 15 degrees to a site's latitude in the summer.
The array’s tilt is the angle in degrees from horizontal. A flat roof has a 0-degree tilt and a vertical wall mount has a 90-degree tilt angle. Whether you are installing a 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 noontime, is not always directly on top of us. The sun will be slightly to your south throughout the year if your location is north of 30 degrees latitude in the Northern Hemisphere (approximately the border of Mexico and the 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 a system uses a 2-axis solar tracker. Yet, it is possible to maximize the output by tilting the array at an optimal angle.
- The Shade of the Tilted Array
A tilted array on a flat roof means an obstacle for other modules in the same roof. The goal is to eliminate shade on any modules at any time. Therefore, there should be enough clearance between the rows of the array.
So how much would the energy output change with different tilt angles?
Completing a simple calculation on the free software SAM (System Advisor Model) provided by NREL (National Renewable Energy Laboratory), the sample 3.4 kW systems consist of 16x Sanyo HIT-N215A modules and are assumed to be located in both Phoenix, AZ and in 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 northern cities than in the cities closer to the equator.