Handling long distances from inverter to AC load center

How do most intallers handle off grid installations where the inverter is a long distance from the house. I want to put all my equipment in a separate building. (It is necessary in order to keep my array close to the batteries and limit the DC voltage losses). The conduit run will be 400' long. I will have one 3648 inverter.

I want to keep my voltage drop no more than 2%.

At a 30a max load, I would need a 1/0 wire

I calculate only a 20a simulateous load 98% of the time. So could I size the VDrop to that? At 20a the cable size is #2.

Are transformers a better option? or is there too much loss involved with them? Do I need an isolation xformer because I am supplying a separate building?

I am confused on the VFX3640 bypass. If a generator is able to supply the full 60a to the bypass, is the current split internally so you have no more than 30a to the charger and 30a to the AC output? or will the AC output supply more than 30a if it encounters a larger load during bypass?

Comments

  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Handling long distances from inverter to AC load center

    Have you thought about using 240V AC inverter with step down transformer at the house? This way you can meet your 2% loss goal using 4 AWG wire at 20A for that distance. 240V x 20A = 4,800 W

    I assume you wanted to run 120V AC at 20A most of the time. At 240V AC to carry same power you would have 10A. At that current 6 AWG wire would get you 1.6% loss at 400 feet.

    Keep in mind, that step down transformer will have loss too, probably 1 - 2 % and magnetizing loss while energized and not used.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Handling long distances from inverter to AC load center

    unfortunately there is also a loss in stepping the power up to 240vac as well as down so double those losses. with the costs of those transformers he might as well put that extra money straight into larger wires. there's just no getting around the inefficiencies and losses of running power long distances without investing bigger money to try to keep it efficient.
  • BB.BB. Super Moderators, Administrators Posts: 29,981 admin
    Re: Handling long distances from inverter to AC load center

    Also, you can send split phase 120/240 VAC (Xantrex XW Hybrid Inverter supports split phase right out of the box--no extra hardware)--costs you just one more wire... Assuming you can spread your loads across several 120 VAC circuits (and can support 240 VAC loads too).

    What does your load profile look like? Do you have some loads 24x7--or can the inverter be shut down/search mode and only turn when a load needs power (remote on/off for inverter or run inverter in search mode for > 8 watt loads)?

    I would suggest giving Midnite Solar a call--I think their new solar charge controller (due out anytime now :roll:) may have a 250 volt Voc solar array input option... You could run Vmp of the array at ~165 volts or so (depending on how cold it gets in your area)... The difference between 165 and 240 VAC is not as bad as a lower voltage array would be for voltage drop/power losses.

    It would be nice if you could put the batteries/controllers/shed next to the point of use and remote site the solar array.

    -Bill

    Depending on how big the array is--this almost looks like a possible candidate for the mythical AC coupled GT inverter back-driving an off-grid inverter to charge the battery bank. Run high voltage transformers (if more than 240 VAC is needed) for the long distance link.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Handling long distances from inverter to AC load center

    Also,

    Depending on how big your solar array is, it may be better to run DC from the panels to your house, instead of AC from inverter. If you have 1 KW of PV wired for highest safe voltage your charge controller will handle, lets say 104 Vstc. 1000W / 104V = 9.6A. That's 3.55% loss at 400' using 6 AWG. This way no need to get another inverter, no transformer and you can power lighting and other loads straight from 48V DC battery bank.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Handling long distances from inverter to AC load center
    AntronX wrote: »
    Also,

    Depending on how big your solar array is, it may be better to run DC from the panels to your house, instead of AC from inverter. If you have 1 KW of PV wired for highest safe voltage your charge controller will handle, lets say 104 Vstc. 1000W / 104V = 9.6A. That's 3.55% loss at 400' using 6 AWG. This way no need to get another inverter, no transformer and you can power lighting and other loads straight from 48V DC battery bank.

    antronx,
    would he not be better off just inverting it right at the pvs as the inverted voltage would be 120vac and that would translate like 1000w/120v=8.34a? that would show a vdrop of 2.8%. of course this is only an example following your example as he intends much higher wattage and current levels seeing as the ability of the inverter is much more than 1kw.

    bill,
    the split phase would do nicely for him, but again it boils down to investing in more wire as i said for that would pose an extra wire in the run.
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Handling long distances from inverter to AC load center
    niel wrote: »
    antronx,
    would he not be better off just inverting it right at the pvs as the inverted voltage would be 120vac and that would translate like 1000w/120v=8.34a? that would show a vdrop of 2.8%.

    Sure, but we know maximum AC current will be 30A. But we don't know how much PV there is. I need more info.
  • farmerjohnazfarmerjohnaz Registered Users Posts: 7
    Re: Handling long distances from inverter to AC load center

    I sort of figured the larger wire would be the solution. Just wanted to know if there was anything new on the market. The transformer losses and cost of xformers would more than offset cost of wire. I have no room for batteries or equipment in my house, so even if a higher capacity charge controller were avaiable, I do not want to go that route.

    The 2nd part of my question on the generator bypass. Can the bypass technically supply up to 60a if there is a load that large at the house? What does it do, cut out the battery charger as the house load increases?
  • BB.BB. Super Moderators, Administrators Posts: 29,981 admin
    Re: Handling long distances from inverter to AC load center

    Yes, the inverter/chargers will (should?) cut down the battery charger current if the house current goes up (I think most units let you program the maximum draw from the genset).

    I don't know much Outback product--but check on the AC generator input specifications for the unit you are looking at--I seem to remember that some of the inverters were designed to operate on Utility Grid Systems and did not really like the frequency drift that off-grid generators typically have (1% frequency drift for grid vs 10% for geneset).

    The Xantrex XW hybrid inverter (GT and off-grid support) had a wider generator frequency acceptance range than the Inverters that were designed for utility grid connections.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Handling long distances from inverter to AC load center

    I'd put my vote with BB and split the power into two runs through the conduit. Yes you'll have to buy twice as much of a smaller gauge wire, but won't you have the option of having 240v at the house if you need it?

    A bigger plus is that you'd have a second wire in the conduit in case years from now when you are troubleshooting and want to eliminate the 400' run as a possibility it'll be easy.

    I ran two power wires when I installed our conduit a couple of decades ago -- one for the inverter and one for the genset. Now both wires come off of separate inverters, but it was an easy change since the wires were already there.

    Will you also be putting other wires in that conduit? I also ran a 6 wire cable in the conduit even though I only needed 2, for remote generator start. Years later I used two more of those wires for a digital voltmeter in the kitchen so we can tell at an instant the condition of the battery voltage (we just have to add 3/10th V mentally to know what the bank is actually reading).

    And don't forget to run a strong cord through it too, so years from now when you think of some other thing you need, it'll be easier to add more.

    Phil
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: Handling long distances from inverter to AC load center

    Sounds like them new Midnight solar charge controlers will be just the bee,s knee,s for this problem. Wonder how much they will cost. S:Dlarvic
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