The Northern Alberta Institute of Technology (NAIT) reference array has been designed to provide solar designers, installers and the general public with site-specific information to address questions regarding the impact of array tilt angles and snow accumulation on overall solar system production.
Situated on the roof of the NAIT is a solar photovoltaic array consisting of six pairs of solar modules. NAIT’s main campus is located at 11762 106 Street NW, Edmonton, Alberta.
Reference array details:
Four of the angles were chosen because they are the most common roofing angles (14°, 18°, 27°, 45°). In addition, the angle of 53° was chosen because it is Edmonton’s latitude and 90° was chosen to represent a wall mount installation.
The reference array design including angles in degrees and in roofing terms.
Since 2012, snow-clearing maintenance has occurred an average of 24 times on the West side modules, during each winter season. A 2-meter long automotive brush and scraper has proven to be the best tool for cleaning the modules. The extendable brush dismisses the need for ladders and ensures a safe environment.
Prior to being cleaned.
After a snow cleaning event.
See latest attached report for the latest data
The following conclusions are drawn from the six possible angles set points of the reference array. Actual optimum angles would likely fall between these numbers.
The snow naturally slides off as the tilt angle increases. At a tilt angle of 90°, there was no snow accumulation for 99.5% of the winter. As the module angle decreased from 53° to 14° a greater difference in energy output occurred between the cleared module and the unmaintained module.
The reference array demonstrated that clearing your modules offers a gain of 0.85%-5.31% more energy depending on the module tilt angle.
In general, individuals with on-grid systems do not clear their modules throughout the winter. It does vary for the type of system; a ground mount array would be easier to clean than an array that necessitates climbing onto the roof. Off-grid systems owners generally do clear the snow regularly, but it is a judgement that solar system owners have to make for themselves.
|Month||Optimum Angle (°)|
|Month||Optimum Angle (°)|
With off-grid systems it is in the best interest of the owner to change the angle of the array twice a year at spring and autumn equinox. It is a judgement that solar system owners have to make for themselves.
|Angle (°)||Increase when cleared (%)|
There are additional factors to consider:
The NAIT reference array recorded a 17% difference in total output between the first and second winters. This demonstrates that system production can vary significantly year to year. This project will be able to provide more and more reliable information as additional years of data are accumulated.
For more information, see the attached Northern Alberta Institute of Technology Solar Photovoltaic Reference Array Report – March 31, 2015. Project funded by NAIT and the City of Edmonton.
For more information about the NAIT Alternative Energy Technology Program go to: http://www.nait.ca/program_home_76007.htm
Reference: Northern Institute of Technology (Tim Matthews). (2014). Solar photovoltaic reference array report. Alternative Energy Program. Last update: August 18, 2015