Properly installed panels will not damage your roof. In fact, they can help save it from future damage and extend the life of the roof since they absorb the sun rays that would otherwise hit and cause the roof to deteriorate.

Typical solar panels weigh between 25-40 pounds each. They are generally installed (on pitched roofs) by attaching them to the rafters. Small holes are drilled and after the installation is complete, installers generally add sealants to fill any gaps between the fitting and the hole that was drilled. Most installers will also add flashing to further protect against the elements. If your roof is flat, most installers will secure the panels to ballasts, such as concrete blocks, so there are no holes drilled in the roof.

Since solar panels have long life spans, if your roof is in need of repair, it will be less costly to repair the roof prior to installation.

Your roof makes a difference in the installation of panels. A composite shingle roof is the easiest type of roof for installers to work on. Wood shake roofs and tile roofs can be difficult due to the splitting and breaking of tiles since these types of roofs are not made to be walked on. Slate roofs are generally not compatible with solar panel installation.

Sources:

http://www.energy.gov/eere/femp/downloads/solar-ready-buildings-planning-quide

http://www.solarenergyenvironments.com/faq.php#link24