Newbie needs help with cable sizing quote.

[Bullyf1]

Hi Guys, Im newly accredited and have got a pretty strange install to quote already.
The panels and inverters are fine but it's the cable size i’m getting different results with and none of them definite.
The array will be in a field on a frame, the house has a split supply (2 phase??) And the DNO have said 16A each is ok and another 16A to the cottage which belongs to the homeowner too.
The problem is that the customer wants it 200 meters away from the house.
4D4B in the 7671 says 50 mm cable will give 1.3% voltage drop and 70 mm will give 0.91% but Jesus that seems BIG. (And what about V gain back into inverter?)
This assumes that the inverter is in the field too so cable run is in A/C.
Any help/advice will be gratefully received. Walking away has been considered but seeing things are a bit quiet it’s do-able.
Cheers, Gary.

 

[moggy1968]

Nice first job! nothing like a steep learning curve!
I would run the DC back to the house then have the inverter there. If you double the voltage you 1/4 the cable size. Typically on a single string 16 panel system the voltage will be around 500V. I have just done a quote for a 300m run and it needed, from memory, a 120mm cable to run AC!! running DC instead it was a still considerable but rather more manageable 16mm.
You can use SWA to run DC. The array can be earthed in the field through a spike which then means you could use 4 core SWA to run 2 strings back to the house. More than 2 strings I would use seperate lengths of 2 core SWA.
If you use 50m SWA lengths it's more manageable and use resin filled joints to connect them underground (assuming your going underground)
As with you I thought about saying no thanks but as you say, times are tight! Build in a good FAF factor on your price though as on a job this size an unexpected problem can become quite expensive.