Solar sunroof intermittent now not working

[HPsauce]

So it's not the relay. And I tested the socket while I had the relay out to swap, no voltage on the central 87A pin but 12V on 87 and the blower is working normally with either relay.
That 87A pin IIRC should carry whatever the solar panel is generating, in this case it was in full sun.
So there's a fault somewhere else, is there a fuse in the sunroof circuit? Edit, no!
Looking at photos of the wiring (saved from a8parts forum) it's a very simple circuit! Either a broken wire, loose plug at the sunroof or failed solar panel.

I did fully open the sunroof and close it again in case the contacts there were dirty, made no difference.
I don't normally ever open it so they should be OK and the ones I can see look clean, can't see the ones on the actual panel.

[HPsauce]

My suspicions are pointing towards the solar panel itself, is it a simple or complex job to just swap that over?

I tried taping some thin bare flex over the + and - contacts in the sunroof and closed it, didn't get any non-trivial voltage.
I'll try to get directly at the contacts on the panel itself another time to check, just need to work out how exactly.

[HPsauce]

My suspicions are pointing towards the solar panel itself, is it a simple or complex job to just swap that over?

And the answers are:
1. Solar panel is dead
2. Swapping looks to be quite easy.

With help (again) from Sean and rummage in Bentley manual I slid the sunroof headliner back. You open it partially and "spread" two hidden clips (one each side) on the front edge with your fingers and it slides back before closing the top panel. It's then just 3 bolts each side and it lifts off (not done that yet).

With the headliner back all the wiring is exposed and it's definitely NOT producing any voltage.
There's a central unit the wires converge on that has some capacitors on view so I suspect a failure in there.

[HPsauce]

Definitely the controller, made by Steca a German solar controller specialist. I got 14V off the panel earlier but zero output from the controller.
Took it out and had a look, no obvious visible signs of failure so investigated what if anything could do the job.
Seems I need a "DC-DC Buck Converter" and I found one on AliExpress for £7 delivered from China that seems to have the right spec: https://www.aliexpress.com/item/1005009349004307.html
Worth a punt at that price and simple enough to jury rig for testing or fit permanently, simple robust stuff with plenty of space.

The Chinese unit has a couple of heat sinks and different connectors:

AliExpress.png

but otherwise has significant similarities to the old German one:

Steca.jpeg