A composite or asphalt shingle roof is one of the easier and most painless installs for a solar system.
Quite simply, your installer will be able to slide the footings under the shingles, then secure them to the rafters. From there, your installer will install the array on the racking system.
Since composite shingle is not overly expensive, if you have an older composite shingle roof, you should re-roof before going solar. Not only is it more expensive to remove panels to re-roof, you can claim the 30% federal tax credit on the portion of the roof that has solar if you replace your roof in order to go solar.