If your home meets the requirements, solar panel installation can fall under ‘permitted development laws’: you do not have to seek permission from your local authority. However, there are exceptions to the rule.
Installing solar panels onto a flat roof would require you to gain planning permission. For the sun to reach, the panels would need to be angled 0.2 metres above the slope: this breaks one of the central requirements for permitted development (‘the system cannot protrude more than 0.2 metres beyond the plane of the roof slope’).
Any dwelling considered a monument or a ‘listed building’ cannot have solar panels installed without planning permission. You would require both listed building permission and planning permission.
In conservation areas (places of architectural or historical interest), you may be able to install solar panels without planning permission. However, if you want to install them on a wall in front of a motorway, you must make an application.