Friday, July 15, 2016

Roof mounted solar panels cool inside the building

I was looking up at my solar panels on a very hot sunny day recently.  I noticed that they were shading the roof and wondered if they were having a cooling effect and thus reducing the air-conditioning load in my office below.  So I set up 4 temperature sensors connected to my data logger to look at a days worth of data on a clear sunny day when the ambient temperatures peaked at around 100°F in the shade.
Click image to enlarge
As you can see, the shaded roof temperature averaged about 10°F cooler than the exposed roof.  I expected the solar panel surface temperature to be significantly hotter, but it was only about 10°F above ambient.  I'm not certain that my methodology was perfect.  All I did was tape a sensor onto the back of the solar panel and secure the others to the roof with duct tape.  The ambient temperature sensor was in the shade away from the roof.

The take away here is that solar panels do have a cooling effect when covering an asphalt roof.  This is clearly an advantage when the rooms below that roof require air conditioning in the summer.

Another way to reduce air conditioning costs is to install a solar powered ventilation fan in the attic.
I installed a SunRise Solar Attic Fan many years ago and it reduced my attic temperature by up to 60°F.  These clever designs use a 10 W solar panel directly connected to a fan.  You can add a thermostat to ensure that it is not running when the attic is cool.

So one can definitely say that solar panels are cool!