I would strongly advise if you are going to install on the front of a property you tell the client to get planning (OK it can take 8 weeks [17 months my longest]), there is a chance the others said don't bother, but if your client has it in written word it must be true and they will thank you for it.
I'd strongly advise the exact opposite unless there's a suitable alternative option, but the customer insists on putting it at the front.
If no other practicable option exists, then mounting on the front is permitted development, which specifically means it already has planning consent whether or not it has a separate piece of paper from the planning office stating this is the case. There's no point in us having a law stating it's permitted development if solar companies are going to ignore that law and advise their customers that they should be getting planning permission for it.
It does mean that you're in effect taking on part of the liability for that advice, but frankly IMO if you're not confident on the legal position on something as basic as this, and prepared to fight to preserve the permitted development rights if a council such as this one decides to challenge it, then you shouldn't be doing this. It took a good couple of decades of campaigning on this issue to get these permitted development rights granted, so please don't just give them away because you want to play it safe or some other rubbish reasoning - please take the time to understand properly what the law actually means in practice, advise your clients accordingly and make sure you have PI insurance to cover your advice in the unlikely event that there is a problem.
Aside from all that, there is a very good reason for not applying for planning when permitted development rights apply, which is essentially that in the act of applying for planning permission you're actually stating that you do not believe that permitted development rights should apply in that case, which should mean that there actually is an alternative practicable option available, or that there is some other reason that you want to deviate from the standard permitted development rules. To me all this is doing is flagging this up with the planning officers as a potentially problematic installation, which is fine when there is something potentially problematic about it, but not something you should be doing as standard IMO as it gives them carte blanche to use their personal judgement to decide on something that would otherwise have been permitted development.
Just my opinion mind, but this sort of advice really boils my ****, particularly as it has knock on affects for others as the council planning officers get it into their heads that all systems mounted on the front roofs should have planning permission because that's what company X are doing, then others who're operating entirely within the law will have to waste their time battling with these officials to get them to understand the actual law they're supposed to be operating under, instead of their assumptions on what it might mean.