Am I correct in understanding you already have a vacuum release valve on the solar system? I.e it allows air into the system so that's water can drain when the pump is off? This is an example of one:
Amazon.com: HELIOCOL 3/4" New Vacuum Relief Valve Pool Solar Panels - New White: Garden & Outdoor
If so, it should be able to bleed the air from the system as well IF it's properly installed. The relief valve needs to be at the highest point of the system and placed so that as water fills the panels (from bottom to top), air is bled slowly through the valve. Once water hits it, the valve is pushed closed.
Pictures of your setup will help a lot.