If the panels for a household collector unit contain a heat transfer liquid, and you believe the liquid contains antifreeze, then drain the antifreeze and bring it to a household hazardous waste collection site for free.
If the heat transfer liquid is a salt solution, you may drain that and dispose of the liquid down a sanitary sewer connection (e.g, toilet or laundry tub drain), followed by lots of water. If you are not sure what type of heat transfer liquid is used, drain liquid into a closed container and bring it to a household hazardous waste collection site.
Place drained solar panels in the trash or bring them to one of the disposal companies listed below. Call to verify items accepted, hours and fees.