off grid appliances.. AC appliances vs DC appliances

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