Looking to DIY solar panel retrofit of a nearly 12 year old timber pergola facing 230º SW along with whatever I can get onto slate roof extension. Width is 16ft (488cm) and Length 12ft (366cm). I will be replacing the plastic sheets to be covered with all panels.

Solar PV dimensions are \~1762 × 1134 mm for a 480w 54 cell panel, so given the space I would be able to fit 8 on the pergola in portrait and 4 on the slate roof in portrait. There is occasional shading, particularly in winter and shoulder months from a chimney but by noon it typically clears up on the left most panels and in spring/summer/autumn it usually not an issue. 

The pergola has 7 rafters horizontally spaces 60cm between each and the first rafters is under the soffit of the roof. So the usable surface area is 12ft (366cm) so most likely \~300cm which would mean panels would have approx 22cm overhand of each side of the pergola, is this acceptable if it’s bolted down well?

I’d go with a 6kW hybrid inverter in that steel shed and wiring will be done by an electrician but the purchasing and mounting I would need to DIY. 

Is this even worth doing?

There are two skylights and how much margin do I need to keep?

Which mounting system would work best here?

Would pergola and slate roof be on the same string?

How do I keep the rain out underneath?

I’ve a steel shed in the back one facing north other south, I could get 2x700w larger cell panels onto them but not sure how they’d be handled, two separate strings?

Thanks in advance.

Is Solar pergola DIY viable here?