off grid appliances.. AC appliances vs DC appliances

iyotankaiyotanka Registered Users Posts: 3
Sorry if any of this has been asked before hand.

I'm beginning the process of picking up materials for an off the grid setup for camping to semi permanent housing.

So i have a couple questions, that i haven't been able to answer on my own yet.

I plan on..
going with a 24v or 48v setup, not sure which yet
running 12v batteries in series/parallel
running all my lighting at 12/24v
running my hvac at 12/24v



to the questions
is it more efficient to run 12/24v refrigerators & freezers, rather than 120v systems?

also anyone have any efficient ways for water from a well, rather than converting to 220v for a pump?

one last thing, I understand that 24v to 120v is more efficient than 12v to 120v, if this is the case, why isn't everyone just going to 120v dc and converting it to ac?


thanks.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: off grid appliances.. AC appliances vs DC appliances

    Welcome to the forum.

    The question of which is more efficient, AC or DC, really depends on what power source you have. There was a recent announcement of a DC A/C unit for the home based on what truckers use, this being its claim to efficiency. However, the DC unit is only efficient for truckers because they have a DC power source to begin with! Converting from one form to another in either direction reduces efficiency.

    In your case you may be able to find 12 VDC and even 24 VDC lights/appliances, but how many and will they cover all your needs? At what cost? If you end up needing an inverter anyway it is often simpler, more economical, and yes more efficient to go with all 120 VAC equipment. Especially (and this is important) if there are going to be long wire runs between the power source and any given load: higher Voltage will 'travel better' than lower.

    A 12 VDC refrigerator usually costs more than a 120 VAC one, especially on a per cubic foot capacity basis.

    As for the well pump, it would depend on how deep the well is and what amount of flow & pressure you require.

    Personally I favour going 120 VAC on a 24 VDC inverter to trying to run everything off 12 VDC or 24 VDC. The more stuff you want to use, the easier (and more practical) it is to go AC. You can get all the components 'off the shelf' at just about any hardware rather than having to search all over to find something that will work.

    Maybe I'm just getting lazy after all these years.
  • iyotankaiyotanka Registered Users Posts: 3
    Re: off grid appliances.. AC appliances vs DC appliances

    thanks for a quick reply. appreciate the help
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: off grid appliances.. AC appliances vs DC appliances
    iyotanka wrote: »
    Sorry if any of this has been asked before hand.

    Don't worry--All of us here where new at this--one time or another. We try to never tell you to "go search" on a topic.
    I'm beginning the process of picking up materials for an off the grid setup for camping to semi permanent housing.

    In general, it is very difficult to start with a small/camping type power system and "cost effectively" grow the system to cabin size, then to full time home with A/C.

    The best thing, start with measuring/estimating your loads. A Kill-a-Watt type meter for AC loads, a DC AH/WH meter for DC loads, a DC Current Clamp Meter (this is also a full function AC/DC multi-meter), etc. are all good places to start.

    But it is difficult--The "name plate" ratings on appliances (and if you can even find one on a DC unit) are almost useless when applied to sizing an off grid power system. Actual measurements are the best place to start.
    I plan on..
    going with a 24v or 48v setup, not sure which yet

    Smaller systems, a 12 VDC setup can work well and be very cost effective. Basically, under ~1,200 watt average loads.

    A 24 VDC system is nice for 1,200 to 2,400 watt average loads.

    And a 48 VDC system for >2,400 watt loads.
    running 12v batteries in series/parallel

    Paralleling battery strings is something I would recommend avoiding if you can. There are lots of options out there today where you can get high AH rated 12/6/4/2 volt batteries and avoid the costs/mess/maintenance issues of paralleling batteries (poor current sharing, difficult to debug battery problems, more cells to check water levels on, really should use a fuse/breaker per battery string--adds costs, etc.).
    running all my lighting at 12/24v

    These days, you can get very efficient 120/240 VAC lighting (CFL, LED) that will meet most of your needs at a fraction of the costs of 12/24 volt DC lighting. Also--Sending "low voltage/high current" DC power longer distances requires heavy/costly copper wiring, and larger DC rated fuses/breakers/switches (depending on actual power used, etc.).

    If you can justify it--I would just "eat" the ~15% losses of an AC inverter and go 100% AC for all the wiring unless you have something very specific (12 volt car radio, HAM equipment, etc. that works well on DC).
    running my hvac at 12/24v

    The best systems out there right now are the Mini-Split AC/Heat pump units. There are a couple 120 VAC units, but most are now 240 VAC (Sanyo made a very nice smaller unit, but Panasonic appears to have taken those off the market).

    As you add solar panels+batteries, even heat pump water heaters are starting to look very promising vs propane/cutting wood for hot water.
    to the questions
    is it more efficient to run 12/24v refrigerators & freezers, rather than 120v systems?

    Some of the modern Energy Star fridge/freezers are approaching or virtually equivalent to the power usage of DC/off grid appliances--At 1/3rd the cost (put that into your inverter/battery bank). And the Off Grid appliances can be difficult/expensive to repair or replace...
    also anyone have any efficient ways for water from a well, rather than converting to 220v for a pump?

    Like the rest of my hand waving answers--Really need to start with your needs (2 cuft freezer, 20 cuft frostless fridge/freezer, 5 GPM 30' well vs 10 GPM 300' well, etc.). Define your needs, then start looking at solutions for each need. Perhaps you start with a chest freezer and a 35 degree thermostat--That can use 1/4 the power of a standard refrigerator for your "camp" mode design. Use a Honda eu2000i (1,600 watt inverter/generator for ~4-9+ hours of run time per gallon of fuel for camp/cabin mode) for larger loads, perhaps a cheap 3.5-5kW genset for running the power tools/saws during construction.

    Later, you will be building a permanent home and designing/building a now solar system to support those needs.
    one last thing, I understand that 24v to 120v is more efficient than 12v to 120v, if this is the case, why isn't everyone just going to 120v dc and converting it to ac?

    There is probably lots of long answers on that one... A few I can give are:

    1) The various safety codes define ~42-60 volts as the maximum "touch safe" voltage for untrained people to use. Above that voltage level, you need to treat power as if it is 120-600 VAC--Metal cabinets behind locked doors, etc.... Also, the Batteries (cases, posts, wiring, etc.) would have to be rated to >600 VAC (>849 volts DC) if the battery bus voltage was >60 volts (if I read current code correctly). Not a common rating at this time.

    2) Batteries are able to supply scary amounts of peak current... 1,000's to 10,000's + amps into a dead short. That is as much, or more current than available from a Pole transformer supplying your home. Arc Flash (shorts with high current feeds) are very dangerous for fires and dangers to people working on the systems. 120 VDC and 10,000 amp current--Is very scary amount of power (note that DC also is very good at sustaining arcs--Much more so than AC--So DC rated switches/breakers/fuses/etc. have to be physically larger and designed to interrupt DC current and not simply ARC into a pile of molten plastic and metal.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: off grid appliances.. AC appliances vs DC appliances

    After a number of years basically living off grid, I agree with others, the best way to go is with a GOOD inverter and 120 VAC high efficiency EnergyStar appliances. SO easy to add or exchange appliances, and they are usually far less costly than DC units.
    One red light went on however when I read you're intention to go with a 24 or 48 volt system - - but using 12 / 24 volts for your lighting. Is that what you intended to say? If so, what is your plan for reducing the 24 or 48 volts to 12 or 24 volts for the lighting?
  • iyotankaiyotanka Registered Users Posts: 3
    Re: off grid appliances.. AC appliances vs DC appliances
    One red light went on however when I read you're intention to go with a 24 or 48 volt system - - but using 12 / 24 volts for your lighting. Is that what you intended to say? If so, what is your plan for reducing the 24 or 48 volts to 12 or 24 volts for the lighting?

    I plan on have more than one solution to obtaining green energy. wind, water, and solar.

    let me back up a bit. I used to work at a camping resort, that recently went under. my reward for many years faithful service, they let have boxes and boxes of lighting, which most are 12/24v. I also have what feels like miles of varying lengths and gauge copper and aluminium cable. most is #2 copper..

    I also have many new to used hvac setups from 12/24 rental cabins, I've had one running off of a electrolysis machine for about 6 months with no issues(knock on wood).

    so my whole reasoning for wanting to go 12/24v is the amount of supplies i already have.

    I was just concerned about the major appliances, tv, fridge, freeze, etc.

    Great info in the replies, i really appreciate them all :)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: off grid appliances.. AC appliances vs DC appliances

    As I said I'm old and lazy; I'd sell off the stuff to some experimenters and buy exactly what I need to do the job, rather than try to make less-than-ideal equipment do.

    Which comes to the issue of defining what that job is. There's a lot of variables in an off-grid power situation, not the least of which is "How critical is the need?"
    Now, if you're okay with the prospect that something might go "pfft" (or other cartoon noise of your choice) and you have no power that's one thing. If you're going to be running a refrigerator with hundreds of dollars worth of food stored up for an extended stay miles and miles away from civilization, that's another.

    And there is absolutely no reason why you can't have the wonderful redundancy of two systems, with dedicated 12 Volt lighting and a 24 Volt AC inverter to run the big stuff.

    In any case I would definitely skip on the DC appliances unless you already have them. Lots of money and they aren't any more efficient than the AC stuff.
  • MarkPMarkP Registered Users Posts: 50 ✭✭
    Re: off grid appliances.. AC appliances vs DC appliances

    I like my 48 volt system. It is as high as you can go and still call it low voltage. Well, I qualify that. It sometimes sees voltage up to 60 during equalization but I am pretty sure that the codes treat it according to the nominal voltage of 48. Hard to get switches and fuses since most are rated at 32 vdc.

    For lights I would double or quadruple identical fixtures in series to get 24 or 48 volts and so reap the benefits of higher battery bank voltage while still using what you've got in stock. It does make sense to use the DC fixtures for lighting since you've got them as long as you have the wire to carry all that current.

    All that being said I am in the camp of those that say go with 120 vac appliances and use the money saved during the initial purchase to buy more panels and batteries.
    15 Panels (about 3,000 watts), Schneider Conext 60-150 MPPT Charge Controller, Schneider Conext 4048 Inverter, 8 x 6-volt Costco GC-2 Batteries.
  • thehardwaythehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: off grid appliances.. AC appliances vs DC appliances
    iyotanka wrote: »

    also anyone have any efficient ways for water from a well, rather than converting to 220v for a pump? ,,,thanks.

    Iyo,

    How deep is your well, what is the distance to your point of use from the well and is it up or down hill from there? how much water do you need to pump each day? How much water do you need at peak demand? These are all questions you will need to answer to resolve your problem.

    They make DC powered pumps for solar or wind power. They also make manual pumps that maybe sufficient for semi-permanent use if the static water level in your well is not too deep (less than 200')
  • dnicholsundnicholsun Registered Users Posts: 1
    Re: off grid appliances.. AC appliances vs DC appliances

    If you don't have already have120/240V AC wiring does it make sense to instal less expensive 12/24 DC wiring and use the savings on your PV system. This assumes that you can find DC appliances that satisfy your needs at a reasonable price. It also assumes that the local building code will allow you to not wire for 120/240V AC.
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: off grid appliances.. AC appliances vs DC appliances

    It really matters what your loads are... If they are small (less than ~100 amps @ 12 volts), not on too long during the day, and the distances you have to send the power is not far--You can use 12 volt DC appliances (or 24 volt for larger/marine/etc. DC loads).

    However--If you need any 120 VAC, or need to send "substantial" amounts of power any distance--In my humble opinion, 120 VAC ends up being pretty competitve. You can use 120 VAC outlets/appliances, simple extention cords/standard AC wiring, and get 120 VAC appliances that have similar power usage as their DC counter parts, many times, for less money.

    In the end, after you figure out your loads--You design your system, one AC and one DC and see which works out best for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: off grid appliances.. AC appliances vs DC appliances
    dnicholsun wrote: »
    If you don't have already have120/240V AC wiring does it make sense to instal less expensive 12/24 DC wiring and use the savings on your PV system. This assumes that you can find DC appliances that satisfy your needs at a reasonable price. It also assumes that the local building code will allow you to not wire for 120/240V AC.

    Welcome to the forum,

    I usually think of low voltage DC wiring as MORE expensive because you need more copper to carry the higher current. If the wiring is cheaper, it may be because the insulation is thinner. Usually when folks try too hard to save money, it comes back to bite them.

    One other consideration that hasn't been mentioned yet in this thread is the variable DC voltage... a 12 volt system varies between 11 and 15.5 volts depending on where you are in the charge/discharge cycle. Not all 12 volt lights and appliances appreciate this wide range of voltages. A small sine wave inverter will provide more uniform power than the power company.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: off grid appliances.. AC appliances vs DC appliances

    DC distribution has a place, you just need to understand what it is.

    - you have short distances, ie cabin, rv, boat
    - your system is small, ie inverter idle losses bite too hard
    - you like DC, have lots of dc stuff etc, can do dc conversion easily for specific needs

    If one or more of those dont match, then id be with the others. However here we run a 60m2 house on DC lighting, refridgeration, computer gear etc, The inverter is used for appliances only, and only on during dayight hours. An inverter uses roughly as much as a fridge, in terms of its idle losses. Hence reducing the role of the inverter allows to run an overall smaller system. However remember that with system costs reducing now, thats not so much a benefit as it once was.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


Sign In or Register to comment.