What is the temperature rise caused by various racking solutions?
I'm curious how various types of mounting methods impact the performance of solar panels.
Comments
The biggest factor in how well a PV module will perform is heat dissipation. The modules, just like inverters, do not like heat build up. This can greatly affect their overall performance in terms of output. You may be aware that temperatures above the standard test condition (STC) rating of the module (25º C, 77º F) have an inverse effect on the module output for every 1 degree, temperature rise (Trise) over the STC rating of the module. This can be calculated using the Pmax coefficient of the module which can be found on the datasheet. More on that here in this article.
Additionally, the manner in which these modules are mounted or their location can have a tremendous impact on how they will perform at higher temperatures. There are four mounting scenarios that I would like to mention to highlight what you can expect to see with various locations and racking solutions.
Pole Mount Trise equals approximately 29º C
Ground Mount Trise equals approximately 30º C
Pitched Roof Trise equals approximately 32º C
Flat Roof Trise equals approximately 36º C
From the bullet list above you can see the trend in temperature rise as modules are less able to lose heat. While sometimes unavoidable due to ground space, roof space or aesthetics, it is advisable to do whatever you can whenever possible to install the modules so that they can easily purge the heat.
One other way to determine delta-T is to use the data from a properly instrumented PV system; a thermometer on the back side of the module and an ambient sensor as well. The difference is also greatly dependent on the irradiance and wind speed. I find in Arizona that my delta-T is about 25C for ground mount and carports., and 30 C for roof mount on a standard pitched roof (at 1000Wm2). Another factor is the thickness of the glass and other aspects of the module (black, etc.). One way to compare this difference in the modules is to look at the NOCT values (at 800w/m2) in the data sheet. This is measured at 25C ambient.
Comments
The biggest factor in how well a PV module will perform is heat dissipation. The modules, just like inverters, do not like heat build up. This can greatly affect their overall performance in terms of output. You may be aware that temperatures above the standard test condition (STC) rating of the module (25º C, 77º F) have an inverse effect on the module output for every 1 degree, temperature rise (Trise) over the STC rating of the module. This can be calculated using the Pmax coefficient of the module which can be found on the datasheet. More on that here in this article.
Additionally, the manner in which these modules are mounted or their location can have a tremendous impact on how they will perform at higher temperatures. There are four mounting scenarios that I would like to mention to highlight what you can expect to see with various locations and racking solutions.
From the bullet list above you can see the trend in temperature rise as modules are less able to lose heat. While sometimes unavoidable due to ground space, roof space or aesthetics, it is advisable to do whatever you can whenever possible to install the modules so that they can easily purge the heat.