Heat Rise In Various Racking Methods
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 (T-rise) 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 T-rise equals approximately 29º C
- Ground Mount T-rise equals approximately 30º C
- Pitched Roof T-rise equals approximately 32º C
- Flat Roof T-rise 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.