Ground mounted solar arrays are fantastic when there is available land near the home. They often can be faced at the optimal azimuth (south). They stay cooler as they don’t have a hot roof underneath which leads to greater performance. They are also simple to wash off during periods of extended dry weather.
The biggest considerations are the distance to the point of interconnection (where the solar ties into an electrical panel). Most building departments require a minimum of 18″ from the top of the conduit to the surface of the ground. Trenching is not allowed to go through leach fields and septic tanks. Existing utilities require hand digging. If any warranty work is required, the ground mount is easier to work on.
There are two common installation types on membrane roofs. If the roof is flat and not in area with seismic requirements, ballasted mounting systems can be used. These type of systems do not penetrate the roof and use weighted blocks to meet the structural requirements of the area (wind, snow, weight).
When there are seismic requirements or the roof is not flat, then there are special attachments used to hold the racking system to the roof, requiring a penetration. The membrane specific attachments require a boot to be installed around them and sealed appropriately to the roof.