Hi dcpjon
This is essentially a new variant on an old problem and what is appropriate might vary depending on whether you are looking at the scenario in the here and now, or perhaps with a client/designer eye to life cycle risks.
So, in the here and now it appears that you have full edge protection and you wouldn't expect the Contractors to be using harnesses when on the slopes of the roof UNLESS, possibly, due to fragile components ON the roof.
There might be existing fragile rooflights and it might be that the PV panels meet the general definition of "fragile" now (hope not if to appropriate design) or might become "fragile" in the future - just like many double skinned plastic roof lights were NOT fragile when first installed but became so when weathered and exposed to lots of UV light.
If you have any fragile components then it is time to decide what is reasonably practicable and that depends on how much people will be working near or over those components which is down to a mix of variables, but principally how much of the roof is fragile and how many people will be up there and for how long.
For what appears from your post to be a new installation, then if there are fragile components it is probably reasonably practicable to provide localised edge protection (as illustrated in the CITB document to which Roundtuit has referred) or covers.
However, for future short duration maintenance works then may be such localised protection might not be reasonably practicable and perhaps consideration should be given to fall arrest.
Which then gives the client/designers a headache. To install some permanent "Mansafe" lines or not?
If installed then the configuration needs to be such that someone can be attached to such a line at all times when in proximity of a fragile component - which might mean twin lanyards.
BUT, the bigger issue is the maintenance of the "Mansafe" system - you could end up putting those checking that the system remains fit for purpose at greater risk than those doing other maintenance on the roof.
....and if the client/designer decides NOT to install such a system, the next question is then where someone on the roof would attach to if working near any of the fragile components.
Ultimately there are numerous IFs, BUTs and MAYBEs so that there is no simple answer to your question.
What does the CDM Health and Safety File (or draft of same) have to say about THIS particular building?
What was said in the Pre Construction Information?