Off grid system with very small grid assistance

maaddix · November 2016

Hello,

New to forum. Searched all over the net for my idea but can't seem to find someone who has tried it.

I've been off grid for 4 years and am happy with it, except for november till mid-january.
My workshop has the grid, about 500 meters from our house and my brothers.
I have a very small system, 530w PV and 200Ah batteries which are done.
In spring, I'll be renewing the batteries and I've been puzzled what to get.
If I'd buy for February till October, 200Ah be fine, but for those 3 months without generater backup (even then) I'd need 500Ah.

Here's my idea:
Run a 500 meter (about 1500 feet) 14 AWG cable with 240v grid power from my workshop to our houses so we can run a small
12 v 5A charger eaxh for both of our 12 v battery bank. That would be 0,25 A in 240v, which is not much explaning why we could use such small wire.
5A at 12v thats only 60w I know but after 24hours thats 1440w equivalent to 3 hours of sunlight on my PV
which is more then enough for my needs.

What do you think?

jonr · November 2016

You could even run a 20A charger with the 240VAC line at ~1 amp. Also consider using aluminum wire.

softdown · November 2016

What do I think? I might run 6awg to the house and re-install the solar on another project. This sound like a 1500' extension line.

As jonr mentioned, it may be possible to get similar capacity with aluminum while spending much less. Remember that heat effects aluminum a lot more than copper.

mike95490 · November 2016

For 3 winter months, just about any 2 wire cable larger than 14ga would work for the limited power you are thinking of.

BB. · November 2016

If you are going to trench for a cable... A 4/0 aluminum cable will carry about 30 amps @ 240 VAC with 3% drop at ~$2.09 per foot (US Home Depot prices--I guess you are in Canada?).

Power usage is a high personal set of choices--But if you trench for anything 1,500 meters--14 AWG vs 4/0 is about the same amount of work (do you run other things too--water, communications, etc. while the ground is open?).

You can keep a small battery+solar system if you have regular outages...

-Bill

softdown · November 2016

I must have well over 100 lbs of 4/0 aluminum. Too bad you are in Canada? Too bad that aluminum is frowned upon for battery cabling. Wish I could find a good use for the 4/0 Al.

4/0 Al is quite similar to 2/0 copper.

Like Bill is getting at.....220/240 has a lot going for it. Pretty sure that lowers the loss rate greatly. i think the US power companies are partial to 660 volts for going long distance. Wonder it they go higher than that at times?

maaddix · November 2016

Thank you for all replies.

Yes I am in Canada. Happy to see that my idea makes sence.
Will take all info into consideration and will post again when I get her done.

softdown said:

220/240 has a lot going for it. Pretty sure that lowers the loss rate greatly. i think the US power companies are partial to 660 volts for going long distance. Wonder it they go higher than that at times?

I know the sugar shack often go way higher but they get a special arrangement with the Utity.
However from what I heard, going higher the 480V is illegal pretty much everywheres.
Does someone have info on this?

mike95490 said:

For 3 winter months, just about any 2 wire cable larger than 14ga would work for the limited power you are thinking of.

You meain I don't need 3 phase? I can get by with 2 wires in the cable? Thought I needed 3 sealed connectors and one bare ground in cable for 240v.

mike95490 · November 2016

mike95490 said:

For 3 winter months, just about any 2 wire cable larger than 14ga would work for the limited power you are thinking of.

You meain I don't need 3 phase? I can get by with 2 wires in the cable? Thought I needed 3 sealed connectors and one bare ground in cable for 240v.

First I saw 3 ph, which is usually listed at 208V. I was thinking of 240V usa split phase, and thought you were using a matched pair of 12V chargers, which when in series (120-120), should be fine at 240V
A 3ph 12V charger is not my department.

BB. · November 2016

In North America, we have 120/240 split phase circuits which are L1+L2+Neutral+Green Wire safety ground.

To get 120/240 from the pole transformer, you need L1+L2+Neutral.

To get 240 VAC, you only need L1+L2...

However, there is safety. If you have a short from L1 to ground in the cabin (metal sink, electrical box), a green wire to a ground rod would not be enough to "trip" the breaker in the system.

So, you have one of two choices... use a 3 wire cable from your utility feed (L1+L2+Neutral), and bond the neutral+ground rod at the house (I believe this is legal--But I am not sure).

Another is to get a GFI (ground fault intrupt) breaker for 240 VAC and only run L1+L2, and green wire bond your electrical box/etc. to a ground rod.

https://www.amazon.com/Siemens-QF220-240-Volt-Circuit-Interrupter/dp/B0052ME2UK

If there is a short between Lx and ground, it will trip the breaker. This way you do not need a neutral for safety and can just run L1+L2 to your cabin (of course, you will only have 240 VAC at the cabin)..

http://forums.mikeholt.com/showthread.php?t=66292

-Bill

Off grid system with very small grid assistance

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