# Small cabin off grid solar/battery/generator system?



## cbcansurvive

My wife and I will be looking for property in Maine very soon where we plan to build a small off grid cabin. I have been doing a lot of research over at the Outback Solar forums, but I thought I would post what I've learned over here and ask folks what they thought of my plans. 

The cabin itself
Basically we want to start with one main cabin with the intention of building two or three smaller cabins later on. The main cabin will have four rooms-three bedrooms and one kitchen/dining/common area. There will be one bathroom with a stall shower and flush toilet with an additional outside shower (like the ones you see at beach/lake houses) for summertime use. The main cabin would be where myself, my wife, and my children would sleep along with maybe one or two additional guests. It would also be where everyone ate meals, watched TV on rainy days, and would generally gather. The additional cabins would be very simple with disposable battery powered lighting (like touch lights) and no running water-those guests would need to come to the main house to use the bathroom. 

Total energy usage
Heat - Woodstove in the main house with smaller units in the guest cabins.

Hot water - Propane on demand HWH.

Refrigeration - Propane powered refrigerator. 

Cooking - Propane stove with pilot light/no electronics

Electricity - CFL lighting in each room at 15W per light, CFL floods outside at 26W per light, small TV, satellite box, modem, laptop, and of course the biggie-a deep well pump which will gobble up about 2000W. 

System 
All of this gives me a usage figure of about 3kWh per day. Based on that I was told that 1.5kW of solar panels in northern Maine will provide more than enough power during the summer months and slightly less than what I need during the winter which is where the generator would come in, but I'm getting ahead of myself. I was also told that I would need at least 375Ah of storage in order to be able to have 3 days of 3kWh on hand while only discharging the batteries 50% so as not to draw them down too far. This would all be tied together (including the generator) with an Outback FLEXpower ONE panel which includes the charge controller, "brain", inverter, etc...all in one package. Now to the generator itself-I was told to take my daily load, double it, and add 25%. This was to ensure that I would have the ability to power the cabin, charge the batteries, and still have some wiggle room if need be. It's certainly a situation I could get into especially when going up in November for deer season if we don't have clear skies. So here is the system in short:

1.5kW Solar array (8 220W panels)
4 12V 104Ah Absorbed Glass Mat batteries (48V)
FLEXpower ONE unit
8.5kW Kohler propane standby generator

I'm estimating all of this to come out between $15-16K including shipping costs, wiring, and other associated work (which I'll be doing myself). I'll be honest, its more than I want to spend to be able to run a three room cabin off-grid, but I also don't want to just run a generator constantly because it's noisy, inefficient, and will likely result in a dead generator after a few years. Does the system seem to meet my needs or is it overkill? In what ways could it be scaled down? Would it be possible to shave down my electrical needs even more in order to scale the system down?


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## wy_white_wolf

You sure like the idea of being tied to the propane grid! :bouncy: lol I just never could understand giving up one grid for another.

I would look into a cistern and do away with that big well pump. You could fill the cistern with a direct solar powered pump. Some fill cisterns with rainwater. 

If you do stay with the well pump I think your battery bank is a little small.


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## cbcansurvive

wy_white_wolf said:


> You sure like the idea of being tied to the propane grid! :bouncy: lol I just never could understand giving up one grid for another.


It makes sense for our application. We will only be there for three weeks at a time during the summer and a week or two in the winter. Our consumption between the generator, cooking, hot water, and refrigerator should be just under 9 gallons a day (likely much less in the summer since the generator shouldn't run much)-with two 1000 gallons tanks I'll be able to fill them after they're put in and probably not fill them again for another six years or so. 



wy_white_wolf said:


> I would look into a cistern and do away with that big well pump. You could fill the cistern with a direct solar powered pump. Some fill cisterns with rainwater.


I thought about that but what do I do when I'm up there deer hunting in November and the water starts to freeze before the tank is even half full? 



wy_white_wolf said:


> If you do stay with the well pump I think your battery bank is a little small.


How much larger should it be? 50% larger? Double?


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## Windy in Kansas

I tend to be opinionated and should keep my mouth shut but will give an opinion as well.

You really have a rather small usage for such a costly system to just set. I tend to think there would be theft risk to the PV panels. 

My thought would be to use a storage tank, perhaps a raised one with gravity flow system with it being filled via pump and generator. As the generator runs it could provide some of the battery bank charging. Depending upon pump capacity and well ability it would probably need to run longer just for charging needs. The generator exhaust gas could provide some heating of water in a tempering tank thus pre-warming the water going to the water heater. 
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My well puts out 35 gallons per minute so it would only take a few minutes to put enough water for each day of supply needs for several. Seems best just to fire up a generator each day for a few minutes rather than supply solar generated electricity.
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Just thinking out loud as to what I would do.


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## blufford

*QUOTE" but I also don't want to just run a generator constantly because it's noisy, inefficient, and will likely result in a dead generator after a few years."*

I would be afraid that the system might be stolen while I was gone. Thats a lot of loss.
Your only using your cabin 6 weeks out of the year. Maybe an RV approach would be better incorporating some of their energy producing plans (generators etc) for your cabins.

I live very near Dover Downs International Speedway where the RVs come in and park for the race sometimes for a whole week. Some of the generators can barley be heard.


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## mightybooboo

You are building far too much system for what you will use.Cut the panels in half (about 800 watts),get 8-12 batteries,8 minimum,cut the genny down to 5000 watts maximum,8000 watts to run a well pump and lights /tv is serious overkill unless thats one crazy well pump.

With the little time you are there,less charging,more storage of power is what I would do.For sure you have far too few batteries IMO.

With proper power use management that will be plenty with little need for running genny.I know someone running a freezer with that much system full time residence.Just upped his to add 1000 watts more panels (Yup,got those used panels on craigslist and couldnt pass up the price) so he can run 2 freezers and maybe change that to refer (from very wasteful propane refer,they are horrible energy hogs) and freezer in addition to house needs.Ran his genny twice last year.When weather is bad he doesnt use unnecessary energy,that simple.Doesnt watch TV (occ video's) but runs his heating pad a lot,rarely takes what he has now below 80% charged.Weather not as snowy as I imagine you are,but rather close.Last season was a LOT of rain and overcast.

Ever consider wood stove for heat and cooking and hot water,if you have a wood resource its a very nice system.

I too cant get excited over the propane setup.


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## wy_white_wolf

cbcansurvive said:


> ....How much larger should it be? 50% larger? Double?


3000Wh per day usage

your battery bank 104AH at 48V = 4992WH 

That doesn't even give you one days usage and stay about the 50% mark.

So 3000WH * 3 days / 50% = 18,000WH storage needed

Either cut you usage or get a bigger battery bank (3.5 times bigger).


Why would the cistern need to be outside? Keep it inside and mounted high it would pressurize your system. You could still keep the deepwell pump but only use the genny to run it. This could be done at the same time you are charging batteries with it.


BooBoo

I think he'll need at least that big of an array. Most of Maine only averages @1.5 hours of insolation a day in the winter.

pick you closest location for the numbers
http://www.gaisma.com/en/dir/us-me-country.html

"Solar energy and surface meteorology" chart near the bottom. may need to adjust settings.

WWW

(BTW - does your 3KWh number include system ineffecencies? If not add about another 33% to the battery bank and array size)


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## 12vman

LOL.. You guys in the sun belt don't realize the conditions up here. I couldn't rely on the sun to heat water for me in the winter. I need to use propane or take cold showers in the winter. Guess I could set up a system to heat my water with the wood burner but what about the days when it's too warm to fire it up?

As for powering a fridge, I'd have to increase my system times 3 to support one. I can afford $20/month for nice warm showers and ice cold beer. In the event that I couldn't get propane, then I'll rough it like I did when I first moved in here. I didn't forget how..

There's not many folks in this part of the country that can say they live comfortable year round with 512 watts of panel and $20 a month. (I have 2 fridges, btw..) I cook with it too..


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## Jim-mi

You must have good water pressure to run that "on demand" water heater.
So when you are there you will be using up a bunch of energy (batterys) so as to have warm water.


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## wy_white_wolf

12vman said:


> LOL.. You guys in the sun belt don't realize the conditions up here.....


I didn't realize Montana and Wyoming were in the sun belt. My winter numbers aren't much better than Maine. Solar showers in the summer and heated by the wood stove in the winter. 

Propane is only used for backup heat and refrigeration in the summer. Now that we have a a dual sorce frig (propane and 12v DC) at the cabin, I'm going to run it on solar as much as I can in the summer to use the extra power.

WWW


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## 12vman

I'm sure that you get many more clear sunny days out there compared to around here. Some months in the dead of winter, we're lucky to get maybe 6-8 "workable" sunny ones! I'm lucky to get a 5 amp charge some days. In the summer, it's a whole different situation.

IMO.. It would be great to have all of the added equipment to heat water with solar in the summer and with the wood burner in the winter but this sure adds to the list of things to maintain. If I wore the clothes of a younger man, it wouldn't be an issue. I have plenty of other things to do to keep things in order. The convenience certainly outweighs the effort and the extra costs for that matter. Looking at it from the carbon footprint point of view, my panels surely covers the amount of propane that I use.

If I had the resources to avoid using propane I would but the simplicity makes all of the difference. I totally understand the monthly burden of buying propane but the initital costs of the set up needed to be independent was out of my price range. I can always turn a wrench or something to make $20 a month for cold beer and warm showers. 

Some of those 12 volt/propane fridges require ~400 watts to operate. That's quite a load! I looked into that myself. Again, the costs of building my array to cover that load alone would be as bad as operating a conventional fridge.

cbcansurvive.. I would suggest that you keep anything you can operate direct from your battery, especially lighting. Larger, short term loads could be operated from a generator, like your well pump. Smaller loads can operate with an inverter. Your modem, laptop can be converted to operate directly from the battery. Not sure about the satellite box. You might consider a sawdust bathroom system to keep the water usage down and to avoid the cost of putting in a septic. Just a few thoughts..


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## Harry Chickpea

I would approach the problem entirely differently.

You have building(s) that will be empty and subject to vandalism for most of the year, and you plan on putting a lot of expensive stuff in and on them. That makes absolutely no sense to me, and reminds me of the line "I have ALWAYS depended on the kindness of strangers."

I would buy a used decent travel trailer that could be placed on the property during the time of occupation and trailed home after I was through. However, if you want the cabin experience...

This all assumes your property isn't subject to a lot of building codes and regulations. I would built a simple bunkhouse/cabin with a fireplace, water tank and hand pump. Nobody can steal a fireplace, and loss of a tank and hand pump is nothing. Outhouses are still legal in some locations, otherwise whatever would pass inspection - destroylet, chemical toilet, whatever is cheap.

Then I would buy a junker travel trailer that could be stripped for parts - furnace, stove, ac, microwave, kitchen sink, toilet, shower, AC unit, etc.. Make a small module of the kitchen/bathroom/shower area that can literally be transported in a cargo trailer and slid into the cabin on casters and locked down to prevent it from rolling around. 

The small honda and honda clone generators are FAR less expensive than your system, are extremely quiet (they have to be to allow for use in RV parks), and supply reliable clean power. You might even luck onto an old RV that has a good quiet generator on board. Cost of running a generator would be comparable to the cost of replacement batteries - you are going to totally trash your batteries at least once a year with that type of usage. I would have a battery inverter set for overnight use, recharged by the generator.

One other chuckle I got was the use of a tv on rainy days. Reminds me of that cartoon in an old TMEN, where a camper is parked at night in front of a gorgeous lake and mountainfront view, with light coming out of the windows and the caption "Heeeeeeres JOHNNY!" It amazes me how far we get away from "camping."


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## mightybooboo

WWW,Bangor Maine and Eureka Ca come in just about same for winter numbers.So what Bud does,and the OP,are going to be close.I would bet he might even be worse than Eureka.

I think OP needs to scale back expectations for a 6 week visit yearly in 2 week periods.Think his usage too high personally.But if pockets deep enough go for more even.

If I did my numbers right....197 hours used 2.67 kw/h for my refer conversion from chest freezer,its 325 watt/hrs daily.

800 watts panels X 1.5 hrs/day = 1200watt/hrs a day?

Get a decent battery supply he should be amply endowed for a 2 week dead of winter visit along with his genny with minimal usage? I could do it,Bud DOES do it.

BUT,Im not a numbers guy on this,only reporting what Ive seen done,and what its doing,I could be all wet.

As for leaving the system alone,unattended,nope,I wouldnt.I'd come up with a portable solar system myself,a power trailer or somesuch.Leaving 15,000 sitting alone,isolated....bad idea IMO.Too many tweakers in this world to do that.

They do ,or did,make a 12 volt sat box,but price was crazy high.

Wood stove is a year round proposition for Bud,cooking,so hot water is year round too.He can see 90 in summer and is working on a solar hot water system in addition to stove for just that reason.Sometimes does propane cooking if just too hot for woodstove.But is actively working away from the propane as much as possible,and doing it on a retirees budget,ie,not much.He is NOT a happy camper when the propane guy shows up,being on a fixed income.

I think he has the right idea,pay the costs up front,get realistic on power usage and use power related to weather.To each his own,eh?

Maybe WWW has the answer,give OP everything he wants,and at the costs it will entail.If OP can swallow that,then thats the answer.All up to OP's bank acct,he may have a pretty good one to play with.


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## artificer

I've been thinking about this for a few day, and this is the design I came up with. Get batteries and inverter that can handle the electrical loads minus the well pump. Size the battery bank to last at least 3 days, but the solar can be modest in size. Get a good generator like the Honda inverters, probably the EU3000I. The generator is to pump water and charge the batteries.

For water, get the largest pressure/holding tank you can find. Design the plumping so everything is easily drained/blown out during winter visits. Put a storage tank in the highest insulated space. Size the tank to last a day or two of normal water usage. Fire up the generator, fill the pressure holding tank and the storage tank. Use a 12V RV pump to keep the pressure tank charged from the storage tank. Make sure your flush toilet is the lowest water using kind, or better yet, go with a composting/sawdust/outhouse toilet.

The idea is to have a system that can be drained during the winter when heat is out. When you get there for hunting, you fire up the generator to charge the batteries and fill the tanks. As long as the interior of the cabin is above freezing there should be no problems. When you're done with that trip, you drain the tanks and lines so they don't freeze. During the summer, you just use the system as is. You might drain the storage tank to get fresh water each time you go out, however.

For the electrical system, you would need the batteries, inverter/charger, generator, solar panels, charge controller. I can't see spending thousands of dollars on solar panels that will sit unused for most of the year. Just run the generator (Honda's are quiet) for 3 hours a day. The generator should last years at that usage.

For hot water I would just get a propane powered tank heater. If you can live with the on-demand water heater, go with it. I don't know how well they drain, and fill, which will be an important feature of your plumping system. About the only drawback to the tank I can see is the time it takes to get up to temp the first time, unless you use a LOT of hot water. 

If you get extra batteries and larger inverter, you could use an electric refrigerator/freezer. They will cool faster, and work better. Only problem is the increase in electrical usage. The generator can handle the power needs, so if you swap getting solar panels for more batteries, you would have enough power. Propane refrigerator is fine, as long as you know their limitations.

I don't see a problem with "the propane grid." This is a leisure cabin. If the propane grid goes down, do you really think you're going to be out there? If you want to design the system around something that probably will not happen, you can spend the money. Personally, I wouldn't.

Depending on the parts you buy, I can see the electrical system costing around $5,000-$6,000.

Michael

Edit: did you know the Honda generators can be converted to run on propane as well?


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## jwal10

I built our off grid cabin in 1994, 380 sq ft, with 2 small solar panels, 2-12 volt batteries and THE tiny Harbor Freight generator for backup, even wired a seperate 110 volt outlet in the livingroom, kitchen, bathroom and bedroom for emergencies. We have gravity fed water. I used the generator 3 times in 16 years on weekend stays, maybe 20 times on full week winter stays and this is OREGON. We moved here full time in March, I put in a small 24 volt, 2 nozzle hydro generator in the spring of 2009 (run off the gravity waterline) that I picked up for 25 dollars at a junk store (he didn't know what it was). Added 4-12 volt batteries to the 2 we had for the original 12 volt system, wired in series to make 24 volts. I added a 6'x15' sun/therapy/bathroom with a flush toilet, 4' clawfoot tub, even a small hydrotherapy tub for my wife's bad neck (car accident). I added a solar water heat system on the south facing roof to preheat the water for the cabin. We have a 24 volt water heater when the solar heater isn't enough. We run it all off the "system". We have a wood stove for heat, hot water and for baking in the winter The rest of the time we use small 12 volt appliances. Haven't used the generator yet. It has been an unusually cool spring and summer so we have used the wood stove more than a usual year. We have "roughed" it for a week at a time to check out the "system". Only thing I had to do was heat 3 gallons of water on the stove when I wanted to take a bath one night right after the wife took one. We watch the time of use to spread out big power use times. We are very happy with it. We don't HAVE to live "this way" but we see little difference than when we lived in our 900 sq ft 3 bedroom solar mansion in town. It is just the wife and I now instead of with our 2 kids there, lol. We even have a 12 volt TV. My wife uses netflix and watches the movies on a 7" 12 volt player. I use a cell phone to check in here. All is good....James


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## Qhorseman

I have been homesteading since 1991, began building my hybrid home then. I heat with a woodstove, use propane to cook with. I have grid power available, I do use it for high consumption appliances, like the air conditioner and the 16Kw on-demand hotwater heater. All other electric loads are supplied by my solar array, I Have 4 123 watt modules, 12 trojan T-105 batterys in series/parallel. All of the lighting in the house is either CFL or LED. I have a small pure sine-wave inverter that powers the computer/entertainment system. My well system is independant on a PV direct system feeding a 500 gallon tank behind the shed. The pressure pump for the house is a 12 volt with 2 RV/Marine batterys and a 5 watt solar panel.

This system has evolved over 19 years to suit me and my budget. Had a propane refridgerator for awhile, then the price of propane got to high for my tastes and I went to a 10 cu.ft fridge, 120 volt. It is doing just fine on my present array. During the summer months I get along just fine on solar to keep the battery's charged up. During the winter months I need to use the grid on occasion to keep the batterys at optimum charge. My bill for the grid power stays very low, less than $50 a month, and $25 of that is their stupid availability charge and taxes. Plan on adding a wind generator this fall to make up capacity this fall.

For the fella that began this thread, I bought the solar system from Real Goods as a package, modules, charge controller, DC load center, panel mounts, PV combiner. I think it is like $3500 in todays catalog. Buy your batterys locally to save the shipping fee. I cover my solar equipment on my homeowners insurance. Like the other I guy I don't have to live like this, I choose too.


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