Question on how to power off-grid cabin

Barry Broome · June 18, 2012, 10:15:57 AM

I plan on starting my river cabin build this fall (occasional weekend getaway retreat). Due to being in a flood plain and a county that was hit hard by Hurricane katrina, I've decided to avoid building a septic system (use portable toilet) and perhaps even avoid traditional electric power. I believe I can cover my energy needs using 12v DC lights and a fan. I can use propane for heat in the winter. I found a small on demand propane water heater so we can have a hot shower.

I plan to haul in water to use while I'm there, then use a 12v water booster pump for water pressure.

I'm a bit ignorant when it comes to putting together a 12v DC power system. I'm hoping someone can give me some input.

Can I simply purchase a couple of rechargeable 12v batteries and use them to run my lights and water pump? Is it as simple as buying the battery and hooking the water pump and lights straight up to it?

Is there anything else I need to go between the battery and the pump/lights?

I thought I might also buy a solar panel and charging kit for the battery to help charge them during the day when I'm there.

Can anyone share their personal opinions with me on this matter? Our family is growing and we look forward to spending some time on the river.

NavyDave · June 18, 2012, 11:09:44 AM

I lived On a 32 foot sailboat for a couple years. Your electrical/plumbing systems of choice sound similar to what I had on the boat. With a strict off grid system like you are describing you have to really watch your electiciity and water usage (as some on here can tell you). You may want to check out some marine applications (just for ideas, marine stuff is pricey) to limit your use. For instance Maybe consider using a foot water pump for the kitchen or bath sink to minimize electrical draw. They also tend to conserve water too which would reduce the amount of trips bringing water in. You can find some fairly efficient lighting options also. Since you are designing your system yourself I'd suggest designing with conservation and efficiency in mind. This will save money by being able to use a smaller solar system (or even wind generator).

Didn't really answer any of your questions but I thought I might have sparked an idea for you. Look forward to seeing what you come up with.

June 18, 2012, 06:57:37 PM

A foot pump sounds interesting... however, considering that I'm already asking my wife to give up a well and a septic system... I really feel I must give her water pressure at her demand. At the end of the day it will still be a lot cheaper than paying a power bill every month.

Yes my setup will be a lot like the demands on a boat. I thought about having the local power Co. install a line to a meter so I could install a window-unit Air Conditioner. But after thinking it over.... the point in going to the river is to be outside, much like camping.... so I think we'll do good with the 12V system.

Thanks for your thoughts

alex trent · June 18, 2012, 07:04:36 PM

For you needs (and actually a lot more) a 12V system with a couple of batteries will work fine.

The 12v lights will run a log time...like a couple of nights worth without any problem (I assume 6 or so lights).

The little boat-type water pump will surlily pump all the water you need for a long weekend from the same batteries.

12V wiring is really simple and safe..direct to the battery.

You can also buy a small (200watt) inverter to power some AC stuff...like music or a computer.

When you go home, just pull the batteries and charge them at home off your line power.

It's a good system and no real hardship for the lights, pump, and some luxury items that take it a big notch up from camping.

CjAl · June 18, 2012, 08:54:35 PM

if you want to do 12v lights you can do LED's and they use almost no power. you can get round led tail lights for semi trucks that come in a metal housing. you can cut them right into the ceiling like pot lights.

June 18, 2012, 09:53:57 PM

Quote from: CjAl on June 18, 2012, 08:54:35 PM
if you want to do 12v lights you can do LED's and they use almost no power. you can get round led tail lights for semi trucks that come in a metal housing. you can cut them right into the ceiling like pot lights.

Pot lights.....

Is that like grow lights. Or sort of low key mood lights when passing a do-be ..... Okay, I'm sorry, just kidding ..... just could not help myself ..... but then I never inhaled ......

mgramann · June 19, 2012, 08:53:46 AM

One thing to keep in mind with the pump, is to get one with a pressure activated shutoff for when the taps are closed, or the pump will run until power is removed. If the pump doesn't have a pressure shutoff, a well pressure switch wired into the system will do the same thing. We did this with our very old camper that used to have a hand pump.

Barry Broome · June 19, 2012, 09:44:37 AM

I appreciate all the responses. I did see a small pump with a built in pressure switch to activate it when the faucet/shower was turned on.

The more I think about off-grid the more I like it. No power bills or anything to maintain. Just bring a couple of 12v batteries and 30 gallons of water,

My wife's parents have a cabin already in the same camp. They are tied into their cousins well and the water stinks so bad it is unusable. They shower using one of those Coleman portable shower bags. I might talk to him about hauling in water and getting a pump. They have electricity at their cabin so they're already set to go.

The only disadvantage with the 12v system is that I probably would not have a refrigerator or microwave. But considering we'd only be there for a couple of days I could make an ice run each morning and just fill up the cooler. And I could always get a small propane oven. I plan to use a charcoal grill when we cook dinner in the evenings.

Squirl · June 19, 2012, 10:25:41 AM

Navy dave makes a good point. For weekend cabin trips look into cruising and boat magazines and books. You will find more on low wattage 12v systems than many of the 24v and 48v systems listed in off grid living guides.

From the boating world on the refrigeration. Blocks of ice last longer than cubes (less surface area). Air is a worse transferrer of thermal energy than water. So keeping the ice out of water helps it last longer. Small older cruising boats are usually fitted with a chest ice box (cold air falls) with a small hole and tube at the bottom to drain the melted water away. Freezing a large block of ice at home should probably last you the whole weekend. A dollar store plastic shoe container or an old Tupperware container makes a good ice block mold.

With the batteries, the deeper the cycle the longer they will last. 12v deep cycles should probably be fine for weekend use. 6v golf cart batteries are better if you have them locally at a good price.

June 19, 2012, 10:33:41 AM

This may sound like a dumb questions.... but.... if I use (2) 6-volt batteries in series will I have a 12v system?

Squirl · June 19, 2012, 10:38:12 AM

Yes.

mgramann · June 19, 2012, 10:39:11 AM

Yes-in series they will give you 12v.

You may want to look into an RV refrigerator-as they can run on LP. They also make 12v coolers. They may use more power, but you could setup your system to charge from your vehicle should you ever get in a pinch. You could setup a quick connect that would charge your batteries when you drive to town.

Barry Broome · June 19, 2012, 10:41:36 AM

I have considered getting the propane refrigerator but they are priced very high. A good ice chest with a block of ice might be the ticket.

mgramann · June 19, 2012, 11:14:55 AM

I was thinking used. Lots of people scrap out RV's so you may find a deal.

June 19, 2012, 11:40:02 AM

That would be great if I could find a used one at a good price. I'm wondering if a 40 lb propane tank maintains enough pressure to fire a frig and wall heater? I might need to buy a 100 lb tank? I tried hooking a 20 gallon tank up to a large propane heater at home and it wouldn't work. I could get a pilot flame but that was all.

I think that covers most of my questions. Here's my list so far....

Energy Needs

1) 2 deep cycle 6v batteries w/ charge guage
2) 1 Solar panel for keeping the batteries charged
3) some 12v led lights
4) 12v light switches
5) 12v bilge pump with pressure switch like this one http://www.westmarine.com/webapp/wcs/stores/servlet/Product2_11151_10001_14751_-1____ProductDisplayErrorView#.T-CoGLV5GSo

6) 12v fan

7) 40 lb propane tank

on demand propane tankless hot water heater
9) propane heater
10) propane burners for cooking

11) solar charger controller

Septic System

1) portable toilet or use plastic bags/kitty litter and incinerate when I get home

2) pipe system for catching grey water from shower and sink (gonna catch in container and dispose of back home)

***I figure by packing out all of our waste water the county will ease my permits/requirements for building the structure.

I read on the Pearl River County website that if you live in a flood plain you have to hire an engineer to to design your septic system and then the county has to approve it.

I think the only permit I'll need will just be a building permit for the construction of the cabin.

Squirl · June 19, 2012, 11:50:18 AM

You might also consider a charge controller so you don't overcharge your batteries.

Barry Broome · June 19, 2012, 11:52:47 AM

Ok thank you

Wal-mart has one in stock

http://www.walmart.com/ip/Coleman-30A-Digital-Solar-Charge-Controller/15063162?ci_src=14110944&ci_sku=15063162&sourceid=1500000000000003260430&veh=cse

UK4X4 · June 19, 2012, 02:29:22 PM

Things to concider

water for some reason we seem to use more than we should- on a 3 week trip to our property staying in our trailer
we used 300gal of water for the three of us the shower did not work that well the first week thats about 14gal /day

water weighs a kilo for every ltr so transporting it is heavy work............especially as when you filled up your 150gal tank, arrive at the trailer only to find the fill is higher than the back of the pickup.....100ft of hose later and driving the pickup up the bank the other side of the road solved that one....then I bought a pump for the following week !

weight wise......strap that tank down well, I changed the shape of my pickup bed last time out

Solar wise yep two 6's in series gives you 12V but the amp hours stays the same.

Costco/sams club golf cart batteries are aprox 220amp/hrs each

2 gives you 12V 220amp/hrs----ie if you have a load of 1 amp you can run it for 110hrs before you get to 50% discharge
if your load is 5 amps it will run for 2 hrs before you hit that 50% deep cycle

So to check your batteries are the right size- you need to calculate the usage first.

Then size the panel to how much power you need and then the controler

Note the panels on that wally world link are rather expencive- I'm looking at a sharp panel for my trailer 220watt for 370usd

The charge controller is also not a good quality one- if your going to invest in a decent system you may want to concider something like a Blue Sky SB2512i

25amps but 30% more efficient charging algorythems- mppt chargers giving you the best results from a panel although with a slight cost increase

Gas wise my trailer uses 40lbs tanks for the fridge and heat- but really the tank size should not make a diference - but the regulator will.....some are higher flow rates and pressures- some are not.

Usage on the fridge and a liitle heat plus daily hot water was less than 80lbs for the three weeks

POOP wise- the trailer is basicly parked and we don't have septic- we just use a portable dump tank.

Thetford smart tote 35gal

The RV camp closest charges me 5usd to dump it and 10usd to fill my water tank

The tank size holds a weeks worth of deposits and a grey water flush.

First time out was a bit like Robbin williams in the RV movie as I'd left the dump tank valves open and when you crack that cover - watch out !

I've since upgraded the cap to one with a window valve and hose connection for those little whoops days.

This way I leave the poop tank at the property rather than cart in backwards and forwards to home

Grey water wise we use biodegradable soap and a filter for the food waste and dump into a ditch on the land

flyingvan · June 19, 2012, 03:01:59 PM

Actually, regardless of what somebody told you, size matters----Propane tank-wise, at least.
The availability of the propane gas evaporating out of the liquid in the tank is a function of pressure, temperature, and surface area. Pressure is going to be around 100-200 psi. Temperature will be around ambient---but drop very quickly in a small tank with usage, and slower the bigger you go. The big factor is the surface area of the liquid propane, which is why your house furnace wouldn't run off a portable cylinder, just the pilot.
A disadvantage to a DC system is how much drop you get in voltage in a length of wire (so the shorter run from your batteries, the better)

Calculation of the voltage drop is given by the formula below
Voltage Drop (Volt) = [(mV/Am)/1000] * I * l

Where mV/Am = millivolt drop per meter per ampere of the cable
(this information is given in the table based on IEE Wiring Regulation)
I = Current in the cable (in Ampere)
l = Distance of cable (in Metre)

gibby · June 19, 2012, 03:10:31 PM

Quote from: Weasel on June 19, 2012, 10:41:36 AM
I have considered getting the propane refrigerator but they are priced very high. A good ice chest with a block of ice might be the ticket.

You may know this, but put a pound of dry ice at the bottom of the ice chest, and then pour a bag or two of ice over it. It'll stay frozen for days. Works well as a temporary fridge.

June 19, 2012, 03:13:16 PM

The charge controller should work, but will be higher than you may need. It allows up to 360 watts.

Barry Broome · June 20, 2012, 10:14:12 PM

I really appreciate all the information that others have shared with me. Yesterday, I spent a good bit of time looking over Mountain Don's cabin build in the Jemez Mountains.

http://countryplans.com/smf/index.php?topic=2335.0

He had a lot of good information about off-grid power while he was constructing the cabin... and also provided a lot of references to other sources.

That being said I'll likely contact a local Solar Provider to get specific details about the system I plan to build. There's no advice better than those who've built these systems themselves.

I also took some time to review the permit regulations for Pearl River County. It turns out I can get a power pole permit if we plan on bringing in a RV.... and it turns out that my wifes parents have an RV just sitting in their driveway not being used. However, if I don't need power, and I have no plans for a well or septic system... then really all I need is a permit for building a structure/utility building.

All I have to give the county are 2 copies of the plans... that's all. And it turns out the River we are on is considered a 'stream' by the State of Mississippi and the state doesn't consider the Wolf River a threat to the local population. So things are looking good for us!!!

There's just a certain amount of freedom that comes with having a cabin that is not dependent on the utility grid to make life bearable.

MountainDon · June 21, 2012, 02:21:00 PM

Propane and portable cylinders (what flyingvan said)......

http://countryplans.com/smf/index.php?topic=10186.msg130016#msg130016

Barry Broome · June 21, 2012, 08:45:32 PM

Wow what a wealth of information.

Thanks MtNDon!!!

ColchesterCabin · June 22, 2012, 02:35:25 PM

What I plan on doing for my build project as RV and marine applications can be pricey is using craigs list or the local classifieds and pick up a older camper and stripe the stuff out of it. Around here you can find one for less then $1000 which would get you a stove, fridge, oven(if equiped), Water Pump, and in my case the matresses need for the bunk beds I'm building for my loft, plus and again around here I can strip it and haul it back for scrap and still get close to $200 back for the steel and aluminum.remeber RV's have LP and 12V switching to their systems so if you run out of LP as long as you have juice in your batteries your laughing. Here at the local hardware shops you can get a small solar battery charger for cars/rv's you can mount on the outside to charge the battery when your not there, hell, even if you are there for $30 or so.