Best way to run AC power 500 ft from array to cabin

[AlaskanNoob]

Hello DIY Solar folks,

I'm MrsAlaskanNoob, borrowing his account. You may be familiar with AlaskanNoob's trials and tribulations trying to plan our system here:

About to spend a lot of money tomorrow on this system (am I making a mistake?)

Planning on buying the bolded * items tomorrow for our completely off grid homestead. Big purchase for us! Just posting this in case somebody sees something glaring with our mix of components who might sound the alarm and prevent me from making a costly mistake. I'm showing the 22KW ground...

diysolarforum.com

Before we go with some really high number of wires, in a system that is getting crazy expensive, I'd like to reopen the design and make sure we're thinking through this correctly. We have been so grateful for the info folks on this forum have provided, given that we know very little about what we are doing. (Yes, I recognize that is not ideal). Thank you in advance for any thoughts you may be able to share on this question: If the solar array is 500 feet from the house, and we choose to place the inverter at the solar array, how can we best do that in a way that avoids (or mitigates) a crazy expensive wire cost? Details about constraints and design follow.

The following items are un-changeble constraints (because of reality on the ground/things we've already bought):

1. Panels are 50 x LG440N2T-E6 Bifacial Solar Panels (https://s3.amazonaws.com/ecodirect_docs/LG/2021/LG440N2T-E6/LG440N2T-E6-DataSheet.pdf)
Nominally a 22KW array
Based on my understanding of what we've learned from this forum (thank you!) volt/amp specs per panel are: 46 Voc (56.58 temp corrected) and 10.23 Isc

2. Distance from array to cabin is 500 feet. Can't be helped.

3. Batteries are 8 x Pylontech US5000 48V/100AH LifePo4 batteries

4. Generator for backup power is Honda eu7000is

5. At the cabin, overall demand assuming a bunch of things on at one time is maybe about 15.2kw (heat pump and water heater are largest components of this). We need at least one 240v circuit for the ground source heat pump (3kw demand) and another one for associated water heater (1.6kw demand from the heat pump and 4.5kw max demand for aux heat). Possibly a third 240v circuit for an appliance (e.g., combined/washer dryer) (say 2kw demand). If I had my druthers, there'd also be an oven (also 240v, 2.5kw) but the reality is we're probably getting beyond what we could do, and likely wouldn't be using these things at same time (save for the heat pump/water heater). In future, possibly a fourth 240v circuit for charging electric ATVs. Everything else on 110/120v.

AlaskanNoob had planned everything with Victron inverter and charge controllers, etc., but I'm reopening that. How we wire the panels together (e.g., how many per string) is also open to change. Assume we have decided to put the batteries, charge controllers, inverter etc. near the panels, and are running AC power the 500 feet between that location and the cabin. I gather with a 'normal' split phase inverter, such as we might have if the panels were right next to the cabin, the output of the inverter would be 2 live 120v wires, a neutral, and a ground. But if we put such an inverter 500 ft away, I think the (relatively) low voltage on each of those two lines would drive extremely big (expensive) wires. So the question is, any thoughts on equipment/design to run AC power across that distance? Invert it to single-phase 240v and step it up to 480 before running it (meaning one live wire and a neutral?) the distance, then step it back down to 240 and split it to two 120v lines plus neutral by the cabin? Other approaches?

(I recognize running DC power from the solar array all the way to the cabin and then putting batteries/charge controller/inverter/etc at the cabin is an alternate approach, but I'm trying to figure out what an AC solution might look like, because having the equipment at the array will make it easier for us to distribute power to other parts of the property in future).

Thank you for any guidance!

 

[Warpspeed]

Golly, that amount of power at 220v would require copper wires as thick as a garden hose over that distance.
Only one solution is really possible, do what the power utilities do.

You might get lucky and be able to pick up a couple of "pole pig" transformers for scrap value. These step down from several thousand volts to 220v and usually sit up high on a power pole. Use one to step up your inverter voltage at the source, and the other to step the voltage back down to 220/110v at your home.

You can then string some pretty thin bare copper (or maybe even steel) wires between suitably high poles.

 

[AlaskanNoob]

Wow, that transformer seems really intense for a newbie... good to know what kind of machinery we might be dealing with.

Assuming we step it up to 480, I'm trying to see where that gets us for wire size. Using this calculator:

Voltage Drop Calculator For Solar Electric Systems

Use this voltage drop calculator to help determine proper wire size for an electrical circuit based on voltage drop and current carrying capacity.

unboundsolar.com

Am I right that the inputs are copper, 1-phase-2 wire (live and neutral?), 500 ft for one-way circuit length, and 31.7 amps (15.2kw/480volts)? That would mean a 3/0 AWG to keep voltage drop less than 3% (based on this calculator, anyway). Does the neutral wire have to be the same size as the live wire? I confess I don't understand the purpose of the neutral wire.

Stepping it up more would allow us to use smaller/cheaper wire, but presumably the more you step it up, the more expensive the transformer, so not sure how that balances out, cost-wise (or energy-loss wise).

 

[Warpspeed]

Yes I was assuming about 3% loss or 6.6v drop at 220v. That's roughly 0.1 ohm for 1,000 feet of wire.
A bit of rough calculation, about 53mm square cable. Rather like fat battery jumper, or welding cables. Very spendy !!
For the length you require, no real option but buying brand new wire, and burying it. That can be a problem too in rocky ground or permafrost prone areas.

Not 480v, but maybe say 6Kv. That drops the current from about 68 amps at 220v (15Kw) down to only 2.5 amps.
Then you can run bare steel fencing wire which costs almost nothing. Easy to fix too if it blows down in a storm.

Going overhead on tall poles will be a lot simpler than buried cable.
The trick will be sourcing some suitable transformers. These often must be upgraded by power utilities as loads never seem to get smaller. The power utilities do not like reusing very old transformers, so they frequently get junked.

Five hundred feet is not that far, and the whole thing hinges on scoring some low cost transformers from a junk yard or scrap metal dealer.
If it was a quarter of a mile mile or more, there would not be any other practical way to do it.

 

[WYtreasure]

Howdy Mrs,
You folks may have something like this nearby.

Surplus & Sales of Nebraska

Where the hard to find electronic parts are found and onhand. Great selection and prices on motors, transformers, capacitors, resistors, switches, power supplies, cases, and more for the hobbyist, makers, builders, scientists, ham radio enthusiast. New old stock and manufacturer overstock.

www.surplussales.com

 

[sunshine]

If the solar array is 500 feet from the house, and we choose to place the inverter at the solar array, how can we best do that in a way that avoids (or mitigates) a crazy expensive wire cost?

Maybe rethink this strategy by running DC to the house by going with a inverter with the highest PV V input. AC and DC losses are similar....22kw @700v dc is only 35amps. Keep most of the components in, or near, the house.

 

[AlaskanNoob]

Maybe rethink this strategy by running DC to the house by going with a inverter with the highest PV V input. AC and DC losses are similar....22kw @700v dc is only 35amps.

Thanks. AlaskanNoob is running down the DC option (I'm MrsAlaskanNoob - but waiting for account to be approved), so I'm trying to focus on AC here. Will post this idea in the other thread and respond there.

About to spend a lot of money tomorrow on this system (am I making a mistake?)

Planning on buying the bolded * items tomorrow for our completely off grid homestead. Big purchase for us! Just posting this in case somebody sees something glaring with our mix of components who might sound the alarm and prevent me from making a costly mistake. I'm showing the 22KW ground...

diysolarforum.com

 

[MrsAlaskanNoob]

So the question is, any thoughts on equipment/design to run AC power across that distance? Invert it to single-phase 240v and step it up to 480 before running it (meaning one live wire and a neutral?) the distance, then step it back down to 240 and split it to two 120v lines plus neutral by the cabin? Other approaches?

I have now learned that a single-phase 240v run would mean 3 wires (one live wire, one neutral, and one ground), and that the neutral has to be the same size as the live wire, but the ground can be a bit smaller. So I now understand that the AC option would take a 3-wire run over the 500 feet.

 

[MrsAlaskanNoob]

Invert it to single-phase 240v and step it up to 480 before running it

As for the possibility of step-up & step-down transformers, I'm trying to price out a 240-960 single phase step up transformer.

I found this 240 to 480 step up single-phase transformer, rated for 52 amps at 480V (more than we need, but the version one-size smaller is a smidge too small) for $1684. Wondering if a 240-960 would be roughly twice as expensive, but haven't found one of those yet..

240 X 480-120/240 Volt 1 Phase Transformers

Install our 3 kVA, 5 kVA, 7.5 kVA, 10 kVA, 15 kVA, 25 kVA, and 37.5 kVA single phase transformers. These 240 X 480-120/240-Volt units are energy test efficient.

www.northamericaphaseconverters.com

 

[Warpspeed]

Power rating will influence the price far more than voltage.
Double the voltage just means twice as many turns of wire at half the thickness.
Same physical size, same amount of copper and steel, very similar cost.

If you do decide to go with transformers, go for a much higher voltage.
It does not make sense to spend two to three grand on transformers and still have to use fairly thick expensive cables.
Ten times the voltage makes sense, merely doubling the voltage hardly worth the trouble.

 

[Don B. Cilly]

Maybe rethink this strategy by running DC to the house

OK, you can tell me to go take a hike, but I honestly think that the strategy that needs revising is the energy usage.
What you're planning seems - to me - utterly ludicrous.

I have a 70 sqm. house. Middle of nowhere. I have a fridge, a washing machine, computers... everything.
I have 5kW of (LFP) batteries. 1kW of panels. It's January, they never discharge over 50%. On subsequent cloudy days, I help them a little bit with the generator.

But then, I don't use electricity for cooking (you can't cook anything decently with it anyway), or water heating. I use (butane) gas for those.
I don't use it for heating - I use wood - see my signature for some ideas.
I dry clothes in the sun and wind. Light-duty power tools I run off the batteries. Heavy-duty ones, off the generator.

In short, I don't have to generate or store a lot of energy because I simply don't use a lot of it.
It's not difficult. It just takes a bit of practice and the proper mindset.
-

 

[AlaskanNoob]

OK, you can tell me to go take a hike, but I honestly think that the strategy that needs revising is the energy usage.
What you're planning seems - to me - utterly ludicrous.

I have a 70 sqm. house. Middle of nowhere. I have a fridge, a washing machine, computers... everything.
I have 5kW of (LFP) batteries. 1kW of panels. It's January, they never discharge over 50%. On subsequent cloudy days, I help them a little bit with the generator.

But then, I don't use electricity for cooking (you can't cook anything decently with it anyway), or water heating. I use (butane) gas for those.
I don't use it for heating - I use wood - see my signature for some ideas.
I dry clothes in the sun and wind. Light-duty power tools I run off the batteries. Heavy-duty ones, off the generator.

In short, I don't have to generate or store a lot of energy because I simply don't use a lot of it.
It's not difficult. It just takes a bit of practice and the proper mindset.
-

There is no question we could use power in a different way (as we have been doing) and keep hauling up propane on our two mile ATV trail in our conditions, and keeping hauling up gas and oil to fill chainsaws, keep cutting down our trees and hauling them over our terrain with the ATV, and using that to heat with, but that's not what we want to do.

What we want to do is use our sun power to power as much as we can. That is our mindset and it's proper for us. Whether or not it's doable is another question hence the thread. We also don't live in Ibiza, Spain so our differing conditions and needs no doubt drive a different mindset.

 

[Don B. Cilly]

Maybe a bit of a compromise? :·)
Propane, you can get a big tank, wood you can buy - should be cheap enough up there - and the ATV trail should be easy (doable?) enough to make passable for lorries. That might be the crux of the issue, but it's probably the best investment.
And electricity is useless for cooking anyway ;·)
-

 

[Warpspeed]

I am in much the same boat.
In this part of the world natural gas is dirt cheap, I use it for cooking, space heating, and hot water, its also a warm climate.
So I get away with 5Kw solar, 5Kwh battery, and 5Kw inverter.
Then someone pointed out, natural gas may be cheap, but its not free and never will be.
He has a point....
If I size up a bit, maybe gradually, I can use less natural gas, and maybe eventually none at all.
There is no single correct answer to any of this.

 

[AlaskanNoob]

Maybe a bit of a compromise? :·)
Propane, you can get a big tank, wood you can buy - should be cheap enough up there - and the ATV trail should be easy (doable?) enough to make passable for lorries. That might be the crux of the issue, but it's probably the best investment.
And electricity is useless for cooking anyway ;·)
-

What you're envisioning is not our reality.

Our commute is a two mile ATV trail that goes a thousand feet up and requires a tracked ATV due to mud or snow. We have thought about our requirements which is why we're investigating solar.

 

[Rednecktek]

What you're envisioning is not our reality.

Stupid reality! Getting in the way of all my hopes and dreams!

I getcha. Some thoughts to throw out there though:

What about a solar water heater, the tubes-sitting-in-the-sun type, not the electric type. If you can pre-heat most of your hot water via free solar then you could save a butt-ton of energy on the heating elements. My dad made one when I was a kid out of an old hot water tank spray painted flat black, some of the mylar coated insulation foam, a plywood box, and a sheet of plexiglass. No need to fork out big moneys that might be spent better elsewhere.

I don't think you can take 2 120v lines, combine them to a 220v for the transformer, bump them up to ZOMGVolts, then split them back out to dual lines again on the other end. You'll have to have a transformer with coils for all 3 wires separately, but most commercially available split phase transformers should have lugs for all those.

Something to factor in also is that unless you track down the special high-voltage wire, almost all of your commercially available wire is only rated for 600v, so strapping that to a 900v transformer will not end well.

Doing the step-up makes sense logically, you just need to figure out if the cost of the fatter wire for 220v is more expensive than 2 transformers (one for either end).

 

[noenegdod]

(I recognize running DC power from the solar array all the way to the cabin and then putting batteries/charge controller/inverter/etc at the cabin is an alternate approach, but I'm trying to figure out what an AC solution might look like, because having the equipment at the array will make it easier for us to distribute power to other parts of the property in future).

Thank you for any guidance!

Dont take this personally.

You are suffering from target fixation and possibly working in the wrong direction. Everything is just math and money.

If you are trying to future proof and consider future distribution that is another layer of complexity that shrinks options.

AC distribution makes no sense to me in what I have read. Your actual loads can not tolerate voltage drop, You have to do what is required to maintain their supplied voltage. Line losses in lower voltage DC are even greater but you can suck that up with no issues. If you have the skills available you can go above ground with a solid conductor that is far cheaper if you dont mind the aesthetic. Yes the system is less efficient but is more affordable in the short term. You will have to install a few more panels or run the the generator more often. Just do the math, pick a direction, pay the money.

 

[efficientPV]

If it was me, I'd be running lower current 24 hours a day instead of a few hours at peak current. Then, I don't do anything the way other people do here.

 

[A.Justice]

If that were my system, I would definitely be working on running high voltage DC to the house. Instead of a bunch of transformers, and added industrial equipment, I would stack the panels voltage up, and run it into a high voltage solar charge controller at the house.

The only two viable options that I can see are either very large transformers, or a high voltage DC configuration.

 

[BobK53]

Stupid reality! Getting in the way of all my hopes and dreams!

I getcha. Some thoughts to throw out there though:

What about a solar water heater, the tubes-sitting-in-the-sun type, not the electric type. If you can pre-heat most of your hot water via free solar then you could save a butt-ton of energy on the heating elements. My dad made one when I was a kid out of an old hot water tank spray painted flat black, some of the mylar coated insulation foam, a plywood box, and a sheet of plexiglass. No need to fork out big moneys that might be spent better elsewhere.

I don't think you can take 2 120v lines, combine them to a 220v for the transformer, bump them up to ZOMGVolts, then split them back out to dual lines again on the other end. You'll have to have a transformer with coils for all 3 wires separately, but most commercially available split phase transformers should have lugs for all those.

Something to factor in also is that unless you track down the special high-voltage wire, almost all of your commercially available wire is only rated for 600v, so strapping that to a 900v transformer will not end well.

Doing the step-up makes sense logically, you just need to figure out if the cost of the fatter wire for 220v is more expensive than 2 transformers (one for either end).

For a lot of very useful information on solar water heating (not using electricity) go to
https://www.builditsolar.com
BobK53