wire size from solar panel to controler

[buckshot]

Hello everyone !! I am new here and to the off grid world.  I will give u a little info on my project. I am installing a system {solar] at my cabin. I prob should and would hire someone but it is so remote no one wants to go that far to work.
I have purchased a system _  3 250w panels 24v in series  72v dc output, 60amp xantrex charge cont, magnum 4024 pae , e panel, combiner box and mag advanced remote and 8 surrette s-530 6v.
A midnite solar prewired i guess , because it all came in midnite packaging!     Dont let me fool you,  i bought it all as a pkg from a supplier, i trust or at least still do.
The big ? what size of wire do i need to run from my panels to my controler?  It is approx 30' from my panels {roof} to the controler. I would like some room for expansion should i decide to add more panels.
I have got it sized locally by 3 diff people with 3 diff answers from  #12 wire  to #2 wire. 
any suggestions?

[cpm]

Need to know a few more factors.

In great big round back-of-a-napkin-guesstimates, I'll call your 30' run 50' to cover what we don't know. 12awg will give you about 3.6% voltage drop, 2awg will give you .4% drop.

I have no idea what your situation is, but if you can, I'd try to co-locate your power equipment to the panels to the best of your ability. Keep those runs short.

what are the specs of the panels Voc, Pmax, etc.
Are you using conduit? if so, what type?
what are the environmental factors, free air, on the roof, max and minimum annual temps, etc.

and I'm kinda confused, that's a *lot* of battery for those panels.

The s-530 is a 400ah battery (in big round numbers), you have 8 for a 24v system, so that's 2x4 grid battery bank,
for 800ah @24v. 10% of 800 is 80amps, which again, in great-big-guesstimated-average-rule-of-thumb-don't-know-all-the-details-back-of-a-napkin-making-it-up-as-I-go numbers is what will be needed to keep the battery bank happily conditioned from time to time, and your system will only be able to put out 30 or so amps under ideal conditions. Unless you've got a beefy genset to use to do conditioning charge cycles.

Cut the battery bank by half, or double the number of panels, then you'll be a lot closer, though still not ideal.

I've not really had my coffee yet, and others here are smarter than I am, but that's my take without knowing more.

[buckshot]

thanks for the input  CPM
the panels are solarworld 250w   i am installing them on a south facing roof 8/12 pitch 2 storey building and about 6" above the shingles. using unistrut channel and feet etc.
in winter it can go as low as -40 but -20 is common and in the summer 80"s F is common with a few 90 + days
I am presently ussing a 5000w gen to power the cabin and it is being connected to the system {no auto start]
the idea behind the big battery and small panel is that this is a weekend place only and it was sized that i could have 3-4 days of power with no sun and the system would have a week to recharge. It is beiing hooked up as 240v. i may add a sec set of panels someday {on a budget} that is why i wanted the wire from the combiner to control sized for expansion.
as for conduit < prob pvc or poly pipe, or is there a better choice ?  I assumed the combiner box would be as close to the panels as possible so i was going to install it on the exterior wall near the peak of the roof> straight down from there and into the bsmt to my control centre would be 30 ft max 1 way.

[Westbranch]

it was sized that i could have 3-4 days of power with no sun and the system would have a week to recharge.

his is 'old thinking' wrt to PV  vs batteries, mainly changed by the recent drop in PV prices, used to be PV was very pricey and batteries cheap (relatively).  Now batteries are very expensive and PV is dirt cheap, so to speak...

Look to the Classic wizard as it has a wire sizing section too.

I assume you have been to Solarworlds site, they have a design tool posted right at the top of the page...http://www.solardesigntool.com/components/module-panel-solar/Solar%20World/SW-250-mono/specification-data-sheet.html;jsessionid=FB659F9291306714757547CA740DEAF8

[Vern Faulkner]

This link will send you to a well-designed spreadsheet to aid in calculating voltage drop, wire size, etc. etc... I found it quite instructional.

http://www.solar-guppy.com/download/voltage_drop_calculator.zip