You don't need planning permission providing that your 'permitted development' rights have not been removed by a condition on a previous planning permission.
Bye-laws note: you don't need building bye-law permission to install solar panels. You will however need building bye-law permission to install any hot water storage system provided in connection with solar panels except where the work is undertaken by an approved competent person and the department is notified of the works within 30 days of completion.