Designing a small off-grid system, 225' from array

[Tobit]

I have a 5-acre mostly wooded mountain parcel I will be moving to in the near future and will be building a permanent cabin to live my preferred hermit lifestyle.  It is on a south facing slope and already has a  natural clearing that will be perfect for locating my array, I just need to clear a few trees to the south for even better exposure.

My problem is, I want to locate my cabin 225' from the array to maximize shading, for my comfort, during the long hot summer months.  How would I best locate the charge controller and batteries?  Do I do a long run from the combiner near the panels to the MidNite controller?  Also, when combining, what would be the best serial/parallel ratio to go with based on 16 panels? 8x2, 4x4, ??

I've been playing around with MidNite's calculator and reading the Classic manual along with a few other documents so I know a few things already.  I think I want to use a MidNite Classic 250 Lite and MNPV6-250 combiner.  I also want to use 16x 100W panels as they are easiest to install by myself.  1600W is a bit more than I need so I already have some fudge factor planned in.  I plan on a 48V battery bank.  I have the 250 Classic planned based on what I read in the manual for long distance runs where it stated to go with a 250 for 180' or longer runs.  Is this based on the distance between the combined array and the controller?

Here's a screen capture from the tool based on an 8x2 string.  I greatly appreciate the help.  Thanks!

[ClassicCrazy]

This calculator may be helpful in your designing of system  in case  you haven't seen it yet.
http://www.solar-guppy.com/download/voltage_drop_calculator.zip

[Vic]

Hi Tobit,

A few quick thoughts;

The great exposure for the proposed PV array site might be a bit too warm for the batteries and electronics on Summer afternoons.   Although,  wherever your batteries wind up,  consider a Root Cellar for them.  Perhaps this could be on a north-facing slope,  allowing easy transport and access,  yet be closely-coupled to the earth for coolness.

Know that you really like 100 watt PVs,   BUT,  they will be more expensive in several ways than will be 60 cell  GT type PVs  with 250 or so Watt ratings and a Vmp of about 30-31 V.

Customers always pay for "free shipping" anyway,  and,  ten or so PVs on a pallet might only cost $200 - 300  in freight.   If you have a Pickup,  this is an easy transport,  and you really need do this only once in 20 or 30 years.  Even an old guy like me can handle 270 watt SolarWorld PVs ( 40" X 66"  and less than 50 Lbs).

If you can run your string Vmp at about 180 - 200 V,  the 225 foot one-way run to the rest of the system would not be too bad.   BUT,  use the MidNite String Sizer,  as you have been doing,  and keep a close eye on the Voc.   You need to find the coldest recorded low temperature for a site close to yours to get a good idea of just what the cold temperature's effect on the Voc that the CC will see.

You will need to size the strings based on the Voc of the PVs that you are considering,  as your "mountain" location may we a bit cool at times.   This will really govern the number of PVs per string,  and the total number of PVs you need to buy.

Good to plan for some future expansion of the PVs now,  so that there will be fewer things needing replacing when you expand,  as most of do from time to time.

More later,  Have Fun,    Vic

[Tobit]

The great exposure for the proposed PV array site might be a bit too warm for the batteries and electronics on Summer afternoons.

That's why I was asking if I could put the electronics and batteries up to 225' away from the array at the cabin site.

Thanks for your thoughts.

[Tobit]

I should add that my land is in the Missori Ozarks so the mountain location would be a foothill location to others.  LOL.  Not too worried about the cold temps, rarely does it get below 0F in the winters and, if it does, it's not for more than a day or two.

[Halfcrazy]

Yes I would put the batteries and electronics in the cabin 225 feet away. You could work on  away to keep all of that at the array but I prefer to have it where I can keep an eye on it. 225ft is not bad at all. I like the strings of 8 into a Classic 250 as it is now. I do also agree that if you can find a way to wrangle the 250 watt panels you will probably save a bunch of coin

[Tobit]

The SW160 panels do look nice, they are $1.05/watt before freight.  The 100W panel I brought down to my land when I first visited is $1.50/watt delivered.   

In the MNPV combiner manual, I like what Larry did with the GFP breaker on the output.  With the MNPV6-250, would there be room for 3 strings plus the 300V GFP breaker?  I will be digging a trench in very rocky ground as Larry did. 

[Bob D]

My system is similar, with the array around 200'from the cottage, where I located the controller, battery, etc.
12 panels @ 215W, Vmp = 29V, Voc @ -40 deg = 42.7V, Imp = 7.4A.
I connected them in 4 banks of three, so the nominal voltage is 87, and the current is about 30 amps.
Since the max Voc is 127V or so, I used a Classic 150.
From the combiner box at the array to the Classic 150 I buried standard USEI-90 service cable, 3 conductor #2 aluminum.  This provided about 1.5% voltage drop, using two conductors on the positive, and the other conductor and the ground for negative.
My system design is such that I separately ground the array at the combiner box, and the rest of the system at the cottage.
I have a bit more array than I need so I wasn't too concerned about the power loss, and the aluminum cable, since it is a standard house service cable, is pretty inexpensive.  Just buy the correct lugs and the anticorrosion compound.

[Tobit]

Hey Bob, thanks for the reply.. I appreciate it. 

[Vic]

Hi Tobit,

Not to harp too much on the larger GT PVs,  but this is a table of PV Modules  stocked by a very reputable company ...  know that they are not too close to you,  but  this is a handy reference,   and this company has been in biz for decades,  no seconds on blems here ...   FWIW -- I have no relationship with this company,  just a happy,  repeat customer:

http://www.solar-electric.com/hiposopa.html

Good Luck,   Vic