Help designing a new system

NBDrancher · October 2010

I'm looking for any suggestions on what equipment I should start purchasing for building a new off-grid system for our ranch on the White Mtns. I have a small system already that makes about 1100 watts with 24 volts and 12 x 6v batteries. The inverter is an old Trace unit and the charge controller is a Xantrex C-40.
I figure my electrical needs will require a new system of somewhere around 4k-5k.

The new panel system/inverter/batteries will be fed through conduits from the pole-mounted PV panels into our new shop and branch off in two directions; one to the house and the other to the 240vac well. A 25KW diesel generator for back-up will feed through conduits also and will need connection with auto-start capability.

I want to start now on the interior of my building so I can get the pre-wiring, insulation, and drywall hung before it gets too cold up here. What size wiring do I need to run to the outside if the PV array is located 40 feet from the building? Any help would be appreciated.

Dave Angelini · October 2010

Re: Help designing a new system

Since you do not know the solar current that will drive the math in determining the wire gage, I would advise you to run 2 inch conduit and not worrry until you "get there" The 240VAC run will probably be 60A and you should use #6 wire or better if there is excessive voltage loss. Good Luck, the Whites are a nice place! Do you know a HAM up there named Brent who runs the Chubasco net?

mike95490 · October 2010

Re: Help designing a new system

Do you need only 120V, or 240V for any large motors/pumps ??

12, 6V batteries, and 1,100 watts seems like you are under charging.

NBDrancher · October 2010

Re: Help designing a new system

Mike:

Thanks for the reply. I will need 120vac for the general house circuits and 240vac for the future GFHP (ground source heat pump). The house is going to be approx. 100 feet from the shop. I will also need 240vac for the well (approx. 200 foot distance) and in the shop for my wire-feed MIG and air compressor. I contemplated an entire sub-system for the well but we will be irrigating over 80 acres of ground so I'm not sure how that will work.

I understand the "undercharging" fact but please realize this is only my existing system that came with the purchase of the ranch and rather than expand it, I want to move the entire system to another location and build it based on autonomy.

NBDrancher · October 2010

Re: Help designing a new system

Dave,

Thanks for the insight. From my own research I figured about 20-24 x 200 watt panels. I placed 2 : 1 and a-half inch conduit in the slab of my shop so that will probably work.

I don't have my HAM license although I've been studying and intend on taking the Tech test very soon.

mike95490 · October 2010

Re: Help designing a new system

I'd take a serious look at the system I threw together, and modify it to suit your needs.
my pump is about 300' from power shed, had to use #6 wire to supply it. House is 200' , and will be pulling #4 for it, as I don't want appliances resetting when the washer comes on, lights flickering.... There is a schematic on my page - http://tinyurl.com/LMR-Solar and the XW 6048 fires up the 1/2 hp pump fine. And I have room to add more gear in the power shed !
I time my pump run for daytime (10-2) with a intermatic clock timer, so i get some battery charge, then the pump kicks in, and runs off the solar, not the batteries, so I get better efficency for the big load. I store water 160' high on a hill, so I always have pressure from 3, 3000 gal tanks. (got the 3rd tank hooked up this weekend, and filled. 9,000 gal on tap.)

Ralph Day · October 2010

Re: Help designing a new system

Say Mike,
The fire insurance company must like that reservoir of water on hand...assuming you're not close to a hydrant.

Ralph

mike95490 · October 2010

Re: Help designing a new system

Ralph Day wrote: »

Say Mike,
The fire insurance company must like that reservoir of water on hand...assuming you're not close to a hydrant.

Ralph

Yep, to get permit, i had to install hydrant w/3000 gallons of storage. And I have a pond the local FD likes, they may plan to suck water out of it for choppers.
And fire hydrants are expensive !

NBDrancher · October 2010

Re: Help designing a new system

Mike,

Thanks for the great information. I am beginning to think we might build a separate power shed too and avoid some issues I had not considered.

mike95490 · October 2010

Re: Help designing a new system

I've got 2 sheds, about 6 ' apart, with metal roofs.

Left one is closed up, and has inverters and batteries, right side has genset and 6" rafters for genset hoist. (hope facebook photo link works)
I rolled the tarpaper over the roofs after the inspector left, so I have a great covered storage space between them.

Dave Angelini · October 2010

Re: Help designing a new system

I have to give some balance here (because I can) and I don't want to spoil the party (but I might) but I have to say, that most of the problems I have had over the years with 42 systems now, are from power sheds. Just an FYI, if you have a choice, and are in a climate with extremes in temperature, it is just better for many reasons to keep all this gear close to the dwelling.

sub3marathonman · October 2010

Re: Help designing a new system

Dave Sparks wrote: »

Since you do not know the solar current that will drive the math in determining the wire gage, I would advise you to run 2 inch conduit and not worrry until you "get there" The 240VAC run will probably be 60A and you should use #6 wire or better if there is excessive voltage loss.

As a non-expert, I would definitely agree with that advice.

I ran 1 1/4" conduit, which seemed huge to me. Well, a miscalculation with the EGC wire, which I thought would not be necessary if you used the conduit as the grounding but which didn't go over with the local authorities, and I was stuck needing bigger than 1 1/4" conduit. :grr But, it really did have a happy ending, because I then ran another conduit, keeping each set of PV panels in its own conduit and then the main electrical panel and the subpanel connections to the inverter in their own conduit, and upsized the wire to #2. Even then, the electricians pulling the wire had a difficult time.

One electrician I had talked to when I was working on the project told me "use the biggest conduit, and the largest wire you can." He said that if all these houses had oversized wiring the savings would be gigantic. And using the #2 wire will soon pay for itself in reduced losses. And, if you are off-grid and count "lost PV generating capacity," which is very expensive, in the equation, it pays for itself even sooner.

mike95490 · October 2010

Re: Help designing a new system

Dave Sparks wrote: »

I have to give some balance here (because I can) and I don't want to spoil the party (but I might) but I have to say, that most of the problems I have had over the years with 42 systems now, are from power sheds. Just an FYI, if you have a choice, and are in a climate with extremes in temperature, it is just better for many reasons to keep all this gear close to the dwelling.

Thanks for the heads up. Gotta do it this way though, I've got no house to hang it all on, and the sheds are structural, plywood inside, sheathing outside, and seldom below frost at my zipcode. Sheds and electrical has been inspected. House will come along in a year or so.

BB. · October 2010

Re: Help designing a new system

And just a reminder--Plan for fire safety--especially around the genset (at least one poor soul here lost the entire solar PV system--arrays, batteries, controllers, inverters, etc.--when the genset caught fire).

-Bill

Dave Angelini · October 2010

Re: Help designing a new system

mike90045 wrote: »

Thanks for the heads up. Gotta do it this way though, I've got no house to hang it all on, and the sheds are structural, plywood inside, sheathing outside, and seldom below frost at my zipcode. Sheds and electrical has been inspected. House will come along in a year or so.

And you live in a place that will not be really hard on the battery in summer!

NBDrancher · October 2010

Re: Help designing a new system

mike90045 wrote: »

I've got 2 sheds, about 6 ' apart, with metal roofs.

Left one is closed up, and has inverters and batteries, right side has genset and 6" rafters for genset hoist. (hope facebook photo link works)
I rolled the tarpaper over the roofs after the inspector left, so I have a great covered storage space between them.

Your Facebook page has some great photos Mike, thanks for the info.

NBDrancher · October 2010

Re: Help designing a new system

So, obviously Dave you are a wealth of knowledge with different configurations. I can appreciate the idea of keeping things close to the dwelling. I am going to see if I can improve on my design because the most important concepts to me are; 1)Safety, 2)Limit current losses to the home, and 3) temp-friendly battery storage.

Help designing a new system

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