Sunday, July 24, 2011

Off-grid folks....your opinions please!

I posted this over on a forum I frequent but want to throw it out there for random readers here to opine on.

The Soldier and myself have thought long and hard about building plans and whatnot...and this one is attractive to us both (though in stick form since Soldier isn't hay bale friendly).

Now for the mass tied in solar system or small kits for each?  We're talking LED lights, possible radiant heat (do check that link...I'm really digging the system), the chest fridge and a small deep freeze for the kitchen and well pump will all be on electric via solar.  Range/stove and possibly a tankless water heater (still being debated) on propane.

So preach to me the pros and cons of small individual systems and/or on mass tied system.


tweell said...

What region of the country is this for? Solar can be very good or not so good depending on climate and where situated. You may want a windmill as well - often if there's no sun, there's wind. In any case, you should calculate a 'power budget'. This is figuring out how much power you are going to use. After you have that WAG, you add in the losses. Lead-acid batteries, for example, have a power factor of .6 - you can count on only 60% of the power out that you put in (until they are fully charged, then it's nothing after that). How many days without sunshine can you expect? Calculate your power storage accordingly.

Individual systems are generally less efficient. The way to make them more efficient is for the individual system to be running DC. You would purchase lights and appliances for an RV made to run off of 12v or 24v DC, and size the individual systems according to the loads on them. I wouldn't try to have small AC systems, a small inverter can lose 20-30% of the power going to AC. Low voltage DC has high transmission losses, so you would need to minimize the power draw. A small IR heater still draws 400 watts or more, that is 33+ amps at 12v and would require 12g copper wire (I would be running 10g for safety). Individual systems add redundancy, if one room is busted, go to another until you can fix it.

A single system handling all the load is generally more efficient. You can set up the panels to do a limited amount of moving with the sun, this increases efficiency but can get rather expensive if there's a bunch of individual panels to set up this way. A windmill can be plugged into a main system. Inverters to change DC to AC get more efficient as their size increases. AC has lower line losses, that's why we generally use AC everywhere but vehicles. As noted, those fancy IR heaters would put a hurting on individual room systems.

Honestly, I prefer to burn stuff for heat versus using electricity. A small woodstove can put out a lot of heat for hours with a chunk of wood or tightly compacted junk mail. Even an efficient electric heater costs more by a factor of 3-5. Another issue is that heaters are used in the winter, when solar is at minimum efficiency.

Jess (Ozark Momma) said...

Thanks twell! We've done a bit of tinkering and I think the Soldier is now set on a single building vs a compound style setup (I'm good either way).

We're heading to Nevada (Northeast), so sun times won't be too much of an issue...I hope! Wind backup is a definite as is a generator (most likely diesel, though I've also been pricing propane).

tweell said...

Sun is definitely good for that location. There is a major wind project going in on the NE Nevada border, so wind is viable too. Since it's high desert, there's no real biomass to use. Perhaps you can get your name on a bunch of mailing lists and burn catalogs for heat. That's only half in jest, solar electric is a very expensive way to heat. I would be looking at house designs optimized for passive solar heating, it's much cheaper and more efficient as well.
A single building is a more efficient use of materials, and you can make a compound later as time and resources permit, so I'd agree with the Soldier.
With a single building, it makes sense to have a single power system as well, so that's settled.
As far as generators go, there's always tradeoffs. Propane is quiet, has very little smell and the generator requires less maintenance. The fuel will not go bad if not used. Since you are planning to cook and heat water with propane, it would be simpler to just use propane for everything.
Diesel generators are more efficient and will last longer with proper maintenance. My uncle has a 20KW diesel generator that's 50 years old and still going strong (I replaced the voltage regulator on it this year, but that was a $50 fix).

The true danger is when liberty is nibbled away, for expedience, and by parts. --Edmund Burke