Once permits have been approved and your installation is scheduled, the installation of the solar equipment itself is the quickest part of the process. Most solar installers can install a rooftop residential solar panel installation in one to three days, depending on how many panels you’re installing and how complicated the installation is. The process of installing a ground-mounted solar panel installation can take more time because of the additional work required; your installer will need to trench your land to run the wiring from your solar panel system to your building.