Can I use an old patio door thermal pane as the cover for a solar air heater?
I will probably build a solar panel with layers of black screen. My question is, I have a patio door with a thermal pane in it. Could this be used for the glass cover of the collector?
For a DIY solar air heater that sounds like it would work fine. It may help you even more than a single pane of glass as a thermal pane will keep even more heat inside the box, not to mention that using reclaimed building materials saves money and saves useable materials from ending up in a landfill. See here for more on how to build solar air heaters -
DIY solar air heater instructional video
So if I understand correctly you are using the layered screen technique to build your panel?
The only downside that we find with solar air heaters is storing the heat. If you incorporate thermal mass into it you can get more production from your solar panel, as it will act as a thermal battery. here you can see how we installed a solar air heated floor using air tubes to ward concrete for radiant heat delivery.
Since you are building this yourself I assume you have building skills and ingenuity, so I just wanted to pitch you the idea of somehow incorporating mass (stone or brick perhaps) to increase your comfort and efficiency. You may have seen them already, but below are a few pages about solar air heaters and storing heat that may be of value to you.