Who needs 240v AC anyway?

2twisty2twisty Solar Expert Posts: 199 ✭✭✭
My wife and I are preparing for a major lifestyle change. WE currently live in southwest Ohio, and are consuming about 1100Kwh/mo. This is with electric water heat, electric stove, several computers and a window AC unit we use in the summer (gas furnace)

We plan to move out to the western Texas desert and go as off-grid as we possibly can.

I know I need to audit our energy use before I can design a system, but one question comes to mind:

Who needs 240v AC anyway?

Since we have no plans to run an electric stove or electric water heat, I don't see any advantage to building a system that can provide 240v. The only thing I could think of that I *might* want to have 240v for when I'm out in the middle of nowhere is for a welder, and well, it would seem really dumb to run that off a battery bank rather than a generator as needed.

So, this thread is to discuss why (or why not) I'd want to have a 240v inverter or a stacked set. I like the Magnum 4024PAE, but if 240v is not needed, why have an inverter that does it?

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Who needs 240v AC anyway?

    Every system must be designed to meet your needs. If you don't need it why buy it? Exception: sometimes you want to plan for expandability or future needs. If you need to transmit power for a great distance 240 volts is useful. How will you obtain water? If you have a submersible pump connected through hundreds of feet of cable, you will benefit from 240 volts.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • solar_davesolar_dave Solar Expert Posts: 2,381 ✭✭✭✭
    Re: Who needs 240v AC anyway?

    West Texas? You will want AC and probably larger than a 120v window unit. You should look at the mini split thread.
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    Re: Who needs 240v AC anyway?

    We are planning on not using AC except for the worst days out there.

    I don't anticipate needing to transmit power long distances, so it sounds like a 120v system with a genset that is 240v capable in the event that I want/need a welder for some project or another. I have a 110v welder, but it's got its limits.

    I was honestly thinking of using the AC in the battery shack to try to keep them cool. Also, thinking of (eventually) using earth (rammed earth or earthbag) to enclose the battery shack to provide thermal insulation from the sun out there.

    Stay tuned for more questions. I'm searching for my answers as much as possible, but it's sometimes difficult to weed through the loads of info here to get to the specific answer I'm looking for. I'll revive old threads if they're germane to my question, but if it's not directly related, I'll start a new thread.
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Who needs 240v AC anyway?

    Also, keep in mind that you can always use an autotransformer to run 240V loads from a 120V inverter.
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    Re: Who needs 240v AC anyway?

    So, this autotransformer -- can it provide split phase? (2 hots and a neutral)? What kind of efficiency losses? If it's only for occasional use, it's not that big a deal if it's lossy, but I'd want to know how much power I was losing...
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    Re: Who needs 240v AC anyway?

    Also, I forgot to mention that water will be in storage tanks on the surface. Trucked in from a local well I have access to. So, I plan to use a shurflo or possibly build a small water tower.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Who needs 240v AC anyway?

    Are you truly "going off grid" or are you using that as a metephor for reducing you need for power as much as possible?

    You ally should know, that if you have the grid available, off grid, battery based power is VERY expensive. Battery based systems tend to cost about twice as much per KW of PV capacity, delivering about half the out put compared to grid tied PV, leading to a KWH cost that is about 4 times as much.

    Especially in hot climates, batteries take a real hit. Before I spent a nickle building and buying anything, I would do some thorough research, understanding the issues. The bottom line is, off gird has severe limitations, both peak and daily loads, require aux charging sources, and do keep in mind that batteries have a (very) finite life spans, and ergo, you need to factor in on going replacement costs.

    Tony
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Who needs 240v AC anyway?
    2twisty wrote: »
    So, this autotransformer -- can it provide split phase? (2 hots and a neutral)? What kind of efficiency losses? If it's only for occasional use, it's not that big a deal if it's lossy, but I'd want to know how much power I was losing...

    It can indeed provide split phase. Going in, you have L1 and N, coming out you get L2 in addition. There is just a single winding with a center tap. You connect N to the center tap, L1 to one end and get L2 from the other end. The fact that there is only one winding is what makes it an autotransformer rather than an isolation transformer.

    At no load on its output, the autotransformer will be a nearly pure reactive load (VA but few watts). At full load, the losses are probably less than 5% for a good transformer. Probably almost as efficient as running a second inverter for the other phase.
    You can disconnect it to remove the VA load when you will not be using it for awhile.
    SMA SB 3000, old BP panels.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Who needs 240v AC anyway?
    inetdog wrote: »
    At full load, the losses are probably less than 5% for a good transformer. Probably almost as efficient as running a second inverter for the other phase.

    Recently in another thread ChrisOlsen reported that the transformer was much more efficient than running a second stacked inverter for 240 volts. Of course, that is for moderate loads. It would take a fairly large transformer to handle the the same power as two large inverters.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Who needs 240v AC anyway?

    Most of the systems I've dealt with are 120 VAC. My own has a transformer for running the one and only 240 VAC piece of equipment: a 1 HP digester pump for the septic system. No electric heating or heavy-duty pumps will eliminate the need for 240 VAC. No sense buying what you don't need.
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    Re: Who needs 240v AC anyway?
    icarus wrote: »
    Are you truly "going off grid" or are you using that as a metephor for reducing you need for power as much as possible?

    Both, actually. Where I'm headed, the grid is miles away, and where the grid is available, it's not terribly reliable. Either way, I'd want some sort of system to sustain me. Also, I want to be as self-sufficient as possible. I know that batteries do eventually wear out, but that is something that can be planned for.

    I plan to reduce my power use as much as possible. I am aware that this takes an enormous shift in thinking from what I'm accustomed to. However, that IS my goal.
  • PhotowhitPhotowhit Solar Expert Posts: 5,592 ✭✭✭✭✭
    Re: Who needs 240v AC anyway?

    I like the earth bag/sand bag idea, or a berm shelter, for keeping the batteries closer to the ground temps.

    If you need a welder you should look into underhood welders, which work off your truck motor. I found this for a friend who had heard of them and always needed the welder away from a plug... He has had several people(farmers) around here purchasing them.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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