Ken – presumably your Owners Corporation (O/C) granted its consent prior to the installation of the solar array that’s now servicing your Lot, and that’s the same procedure that you may now use to obtain consent to the installation of your proposed hatch; that is by way of a special resolution taken at a General Meeting.
I should say however that notwithstanding the significant liability issues for your O/C arising from it permitting residents to wander around on the roof of its building, and the structural /waterproofing issues involved in installing an access way / hatch in the common property (roof), I wonder why you would want to clean your solar panels anyway, when there are contractors in the marketplace who provide that service, albeit of little benefit in my opinion.
My solar array has been in place since 2010, they’ve only ever been cleaned by nature, and the kW/h to the grid that they produce seasonally has not significantly varied over that time