Building off grid cabin -- Can you provide input?

PorkChopsMmm · July 2010

This is my first post here and I am trying to be thorough, but please forgive any mistakes.

We recently purchased some acreage in Michigan and we are in the process of building a 1200 sqft off grid cabin. The contractor will "shell-in" the structure but I will be responsible for all insulation, electrical wiring, etc. The cabin will be completely off grid, well water w/ gravity fed water system, compost toilet, and minimal electricity needs provided by the solar solution detailed below. Can you help me think through my set up? I am currently testing this at my home and not at the acreage. I hope to move this out to a small storage shed close to the new cabin once the electrical wiring is completed. The goal of this solar solution is to provide electricity for the 1200 sqft cabin and in the future another 1200 sqft cabin with additional batteries and solar panels. Electricity needs are basic -- to help power the compost toilet fan (light load), power up to 10 LED light bulbs, a refrigerator, a freezer, 2 laptops, a few cellphone chargers, and a few ceiling fans in the summer. Heat, heating of hot water, and cooking duties will all go to a wood cook stove.

Below is my set up. I either bought these components barely used of off Craigslist, barely used from eBay, or received for free. For our purposes assume all of the below is working perfectly fine; I have tested everything including the batteries and everything checks out.
- Xantrex 2.5 2500 watt inverter/charger with 2 remote panels (one ACS and one basic control panel) wired to batteries with 1/0 wire with the the appropriate breaker on the negative line to the battery bank
- 7500 watt generator - plan on using for backup purposes only. Can charge batteries via the Xantrex inverter/charger or provide power for really large power tools, etc. May be overkill but it was free and basically brand new
- 3 240 watt Chinese solar panels (12 volt I believe but I forget the Amp rating on these)
- Outback FM-60 MPPT 60 amp charge controller (package arrived in the mail today)
- 8 Optima Yellow top 55 amp hour 12 volt batteries wired in parallel with 4 gauge wire (Method 2 from this website http://www.smartgauge.co.uk/batt_con.html)
- SquareD breaker box with 3 15 Amp breakers, one for each panel (similar to this http://www.freesunpower.com/project1.php)

My questions are...
1) I ordered 3 sets of 10 gauge wire with MC4 connections and bare wire to hook up all 3 of my solar panels in the combiner box. Is 10 gauge wire sufficient for each 240 watt panel going to the combiner box?

2) My plan was to wire the solar panels in a series into the combiner box. I have heard that running the solar panels into a higher voltage series will charge a 12 volt battery bank more effectively. I also read that it will allow you to use smaller size wiring from the combiner box to the charge controller. This interests me as the shed that will store the equipment (not the panels, they are on the roof of the main cabin) could be 50 ft away or so. I haven't found a good rule of thumb for what gauge wire I should use from the combiner box to the charge controller based on combined panel wattage-- any suggestions? My plan is to use 4 gauge wire from the charge controller to the bank of batteries. Is the gauge too small?

3) We are going to setup a gravity water system for indoor water supply, for water in the shower, sink faucets, etc, with heating of the water coming from the cook stove. This is still a work in progress. Based on my setup, do you think the system could handle a low flow water pump in addition to the other electrical needs? I would really prefer to not use the generator to refill our water reservoir daily. That would be loud and costly. I have been looking for an efficient pump to bring water up from out 20 foot well up to about 20 feet off of the ground (highest I could see a water tank being) but I can't seem to find a good solution. Any recommendations for a low power pump that would work?

4) For a cabin of this size, with minimal interior loads (no TV, DVD players, etc.) should I run DC outlets in addition to ~20 AC outlets I have planned? I would like to wire for future needs before I put up insulation and cover up the walls. I have seen DC appliances, fixtures, etc. cost quite a bit more than their AC components. Is there any benefit in my setup to go directly to DC and bypass the inverter? From what I can tell the inverter can more than handle the loads I will throw at it.

Thanks in advance! I have been lurking on the forums for a while before registering and I am thankful for what I have learned.

Kamala · July 2010

Re: Building off grid cabin -- Can you provide input?

I'm not going to offer a full analysis of your proposed system. Many others are better at that than I am. I will make two points that stand out to me.

1) Those who might offer a more detailed analysis will probably want to know with more certainty the specs of your panels. After all, they are the source of your energy.

2) The batteries. Eight batteries in parallel is not recommended. It is very difficult to insure that they are all dis/charged evenly. Four in parallel is considered a reasonable upper limit. You could achieve this if you used 110AH batteries instead of 55AHs. Also, I think the blue top Optima is more suited for RE applications than the yellow. IIRC, yellow is industrial/traction, but I'm uncertain.

Anyway, good luck and welcome.

K

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

Kamala wrote: »

I'm not going to offer a full analysis of your proposed system. Many others are better at that than I am. I will make two points that stand out to me.

1) Those who might offer a more detailed analysis will probably want to know with more certainty the specs of your panels. After all, they are the source of your energy.

2) The batteries. Eight batteries in parallel is not recommended. It is very difficult to insure that they are all dis/charged evenly. Four in parallel is considered a reasonable upper limit. You could achieve this if you used 110AH batteries instead of 55AHs. Also, I think the blue top Optima is more suited for RE applications than the yellow. IIRC, yellow is industrial/traction, but I'm uncertain.

Anyway, good luck and welcome.

K

Kamala, thanks for the quick reply. Here are my responses...

1) I will check the panels tonight and provide updates to the main thread

2) I wired them in parallel "Method 2" from this website http://www.smartgauge.co.uk/batt_con.html. For you or others out there -- would Method 3 or 4 allow me to run all 8 in parallel? I will update the main post to clarify how I have them wired. Hopefully I can get more feedback on the yellow top batteries. I bought the batteries and inverter as a set for very cheap off of CL. The solution was used for a short time and was installed by a professional electrical shop to provide off grid power. Hopefully I didn't hurt myself here.

Thank you for the help!

AntronX · July 2010

Re: Building off grid cabin -- Can you provide input?

You need another smaller inverter in 600W range to power your small constant on loads like lights, laptop, radio, TV. Use 2.5KW inverter for occasional big loads like water pump, coffee maker, microwave, then let it go into sleep mode. Most of the time, you will only draw 100 - 300W from your system, and 2.5KW inverter will be very inefficient at converting DC to AC at power levels that low. It will waste half of your solar panels harvest energy into low power conversion inefficiency alone. That is why myself, with only 520W of panels, I installed 600W inverter for always on small loads and ditched ProSine 2.0 inverter altogether.

You will need more solar panels, but later. You are limited to only 4 of your solar panels per FM-60 at 12V battery voltage. Similarly, 8 panels at 24V and 16 at 48V. If you plan for more solar panels running through same controller, change your battery system voltage to 48V now. This means replacing 12V Xantrex with 48V inverters. Added benefit is ability to connect up to 3 of your 230W panels in series, which save you a lot of energy loss in wire run from panels to controller, and keeps FM-60 operating efficiently.

You do not have enough batteries for storing enough electricity for cloudy days. Your setup will work for now, but you will quickly realize you need about 4 times more battery capacity.

edit: Consider also 24V system voltage. There are small and cheap inverters on the market for 24V, but 48V may be harder to find, or more expensive.

Kamala · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

... would Method 3 or 4 allow me to run all 8 in parallel?

I think you definitely need Method 3 or 4. Method 3 is probably easier and more intuitively understood than Method 4 but requires a larger "footprint" and more hardware.

PorkChopsMmm wrote: »

Hopefully I didn't hurt myself here.

I see that you are ready. I hope you have aimed before you fire.

n3qik · July 2010

Re: Building off grid cabin -- Can you provide input?

As for the batteries.

If you stay at 12 volts, go with method 3. This is what I am using with my 8 batteries in parallel.

I am also using yellow tops, 2 are from 2006, 6 from 2007. All are about 90% of capacity. The yellow top is a deep discharge/starting battery. I went with this type to handle the discharge and any surge from the inverter.

Photowhit · July 2010

Re: Building off grid cabin -- Can you provide input?

I too would suggest a 24 volt system, will this be a fair weather cabin? Many(most?) larger panels are 24 volt or odd 20V or 40V nominal for grid tie systems. (I suggest buying panels in pairs/even numbers as it often allows for easier changes to higher voltages)

Others here have DC run into their cabins/homes if your battery supply is 50 feet away, I wouldn't want to run DC since voltage drop would require some what heavy gauge wire.

Will water be stored indoors for your gravity fed system? Likely you'll want to be 48"+ to be below frost line. Fair weather, you'll want a hydrant type dump, so you can drain the lines, if you choose to be above frost.

Run times and sizes of fridge and freezer vary wildly and will be your greatest draw. doubt you have enought panels and storage for both in a warm summer, or for long in a mild spring or fall with lots of over cast skys, but I haven't looked into your area.

I'm just in Missouri but have built with 6" thick walls, I would consider that a minimum in Michigan, I'd be sure you and the contractor for the weather in would be on the same page for insulating (12-14" in roof, water tank support, space for floor insulting as well.)

dwh · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

- Xantrex 2.5 2500 watt inverter/charger with 2 remote panels (one ACS and one basic control panel) wired to batteries with 1/0 wire with the the appropriate breaker on the negative line to the battery bank

Nope.

Breakers or fuses go in the positive side. Shunts for battery monitors go in the negative side.

dwh · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

4) For a cabin of this size, with minimal interior loads (no TV, DVD players, etc.) should I run DC outlets in addition to ~20 AC outlets I have planned?

I wouldn't. First of all, if you take the advice here, you'll end up changing your battery bank to some voltage higher than 12v anyway. Also, if you go ahead and wire the cabin(s) for 120v, then you won't have any worries if you end up needing to run them off the generator for some reason (hey, ya never know - might as well plan on having the ability even if you don't expect to need it).

Another thing to note is that according to some around here with experience (Icarus/Tony), composting toilets generally don't work well without a heat source. From what I understand, the liquids have to be evaporated so the bacteria can compost the solids, and "ventilation only" may not be (probably won't be) enough to get the job done.

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

Kamala wrote: »

I'm not going to offer a full analysis of your proposed system. Many others are better at that than I am. I will make two points that stand out to me.

1) Those who might offer a more detailed analysis will probably want to know with more certainty the specs of your panels. After all, they are the source of your energy.
K

Here are the specs from the back of the panels. I dont understand much of this:
Rated Power (Max) 240W
Tolerance +- 5%
Voltage at PMax (Vmp) 30.0V
Current at Pmax (Imp) 8.0 A
Open-Circuit Voltage (Voc) 36.0 V
Short-Circuit Current (Isc) 8.96 A
Nominal Operating Cell Temp (NOCT) 45 +- 2 degrees Celcius
Maximum System Voltage 600VDC
Maximum Series Fuse Rating 15A
Operating Temperature -40 to + 85 degrees Celcius
Fire Resistance Class C
Cell Technology Poly-Si

n3qik wrote: »

As for the batteries.

If you stay at 12 volts, go with method 3. This is what I am using with my 8 batteries in parallel.

I am also using yellow tops, 2 are from 2006, 6 from 2007. All are about 90% of capacity. The yellow top is a deep discharge/starting battery. I went with this type to handle the discharge and any surge from the inverter.

Glad to know these check out OK. Thanks for the feedback.

dwh wrote: »

I wouldn't. First of all, if you take the advice here, you'll end up changing your battery bank to some voltage higher than 12v anyway. Also, if you go ahead and wire the cabin(s) for 120v, then you won't have any worries if you end up needing to run them off the generator for some reason (hey, ya never know - might as well plan on having the ability even if you don't expect to need it).

Another thing to note is that according to some around here with experience (Icarus/Tony), composting toilets generally don't work well without a heat source. From what I understand, the liquids have to be evaporated so the bacteria can compost the solids, and "ventilation only" may not be (probably won't be) enough to get the job done.

Good call about keeping everything on AC for backup generator purposes, I didn't think about that. The generator is going to be tied into the inverter and turned on whenever the need arises. You are right about the composting toilet needing heat. Our composting toilet is a Biolet (www.biolet.com) and it has an adjustable heater built in to it that doesn't draw much power. So no worries there.

Thank you for all of the advice, it is much appreciated. Hopefully the panel info will help. I am confused though -- is each panel 36V and not 12V?

mike95490 · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

....Our composting toilet is a Biolet (www.biolet.com) and it has an adjustable heater built in to it that doesn't draw much power. So no worries there....

BIG WORRY

You do not have near enough power to serve the biolet. I'd strongly consider a "sawdust 5 gallon bucket toilet" . $15 luggable Loo.

Check the thread: http://forum.solar-electric.com/showthread.php?t=5999
scroll down to post #11, about a survey of compost toilet users

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

mike90045 wrote: »

BIG WORRY

You do not have near enough power to serve the biolet. I'd strongly consider a "sawdust 5 gallon bucket toilet" . $15 luggable Loo.

Check the thread: http://forum.solar-electric.com/showthread.php?t=5999
scroll down to post #11, about a survey of compost toilet users

I think we have more than enough power for the compost toilet. From the manufacturers site www.biolet.com ...

120Vac
275 Watts max
25 Watt fan (runs continuously)
25 Watt mixer (runs for 1 minute after each use)
225 Watt heaters (thermostatically controlled)

This is a newer brand compost toilet and we have been using it for a while at a small hunting cabin that already exists on the land. It has been working just fine. My main concern is figuring out how to hook the panels up to the combiner box, from the combiner box to the charge controller, and from the charge controller to the batteries. This is my first time doing anything with solar power and I was able to get this far with tutorials, this forum, etc. but I am finding this to be a grey area.

Cariboocoot · July 2010

Re: Building off grid cabin -- Can you provide input?

For what it's worth, quite a number of people on our lake have had composting toilets.
As far as I know, they've all been removed due to failure or dissatisfaction.
Be prepared for the contingency.

I am confused though -- is each panel 36V and not 12V?

They're neither. They're the slightly odd, not-quite-24-Volt panels that cause some planning problems for those who get them. With an MPPT controller (like your FM60) they'll be all right. You'd need to wire the three in series for a 24 Volt system, though, as at Vmp 30 there's not quite enough Voltage to charge a 24 Volt bank (they won't necessarily put out 30 V as sun conditions vary).

Personally, I'd not go for the Optimas as that's a lot of battery connection for a small bank. Some cheaper T105's might be a better choice - especially for starting out. They'll take more abuse - mistakes - and won't cost as much to replace should something go wrong.

But first you need to establish some load targets, as in Maximum Wattage used at any one time and daily total cumulative loads. Very important, that.

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

Cariboocoot wrote: »

For what it's worth, quite a number of people on our lake have had composting toilets.
As far as I know, they've all been removed due to failure or dissatisfaction.
Be prepared for the contingency.

They're neither. They're the slightly odd, not-quite-24-Volt panels that cause some planning problems for those who get them. With an MPPT controller (like your FM60) they'll be all right. You'd need to wire the three in series for a 24 Volt system, though, as at Vmp 30 there's not quite enough Voltage to charge a 24 Volt bank (they won't necessarily put out 30 V as sun conditions vary).

Personally, I'd not go for the Optimas as that's a lot of battery connection for a small bank. Some cheaper T105's might be a better choice - especially for starting out. They'll take more abuse - mistakes - and won't cost as much to replace should something go wrong.

But first you need to establish some load targets, as in Maximum Wattage used at any one time and daily total cumulative loads. Very important, that.

I will take the compost toilet concerns to heart. My buddy and I are setting this up and our wives will not be pleased if the bathroom is not in order. That's also the reason for the gravity water system. If it was just my buddy and myself we would be fine with a water pump outside. In the long term septic is a possibility.

Thanks for the info on the panels. Just so I know what I am missing, from what info listed did you get that they are not quite 24V panels? Also, could I wire the batteries up (from this site http://www.smartgauge.co.uk/batt_con.html) in configuration 3 as a 12 V bank and then have enough charging power from the panels to keep the batteries at 100%?

The batteries are already a done deal for now. The Optimas may not be perfect and may complicate my design but I paid so little for them that it is worth the extra effort to me. If they are that bad I can replace in a few years. I truly appreciate all of the feedback. Thanks again!

Cariboocoot · July 2010

Re: Building off grid cabin -- Can you provide input?

You have 3 30 Vmp panels. If you wire them in series you'll have a 90 Vmp array with a maximum Voc of 108. This would be fine on the FM 60 and would not require combining or even a fuse. It would supply enough to charge either 12V, 24V, or even a 48V system (albeit not a very big one; 720 Watts limits your max capacity). There would be less loss from wire length too, due to the higher array Voltage.

Given your batteries, I'd go with the 24V set-up; fewer parallel connections. With eight batteries you'd have four banks of 55 Amp/hrs for a total of 220 @ 24 Volts. The panels should produce enough to recharge this (720 W @ 80% = 576 / 28.4 = 20 Amps charging current). You'd still should connect the banks via method 3, with buss bars. Preferably with a fuse each. And don't forget the fuse for the charge controller!

I have a septic system at my cabin. Put it in myself (I know how). Expensive, but worth it. You need room to do it, however, and often a lot of permits and permission. Mine has to use a digester pump, which is 1 HP but not a big power concern as it only runs 30 seconds a day. It did require a large (3.5 kW) inverter to supply the power, though.

BB. · July 2010

Re: Building off grid cabin -- Can you provide input?

You will be very surprised to see how quickly power usage adds up... Taking some guesses (say heater runs a 30% duty cycle):

225 watts * 0.3 * 24 hours per day = 1,620 watt*hours per day
25 watts * 24 hours per day = 600 watt*hours per day
Total for composter = 1,820 WH per day

For example, around Chicago, solar varies between 2.25 and 6 hours per day (winter/summer). Using our typical derating of 0.52 for a flooded cell off-grid system with an inverter, your 720 watts of panels will generate around:

2.25 hours of sun * 720 watts = 842 WH per day in dead of winter
6 hours of sun * 720 watts = 2,246 WH per day in summer

So--guess guessing--it is possible that your composter will use more power than you have available most of the year and will either have to run off of the genset or sit not composting correctly.

The numbers I have given are long term averages and stretches of bad weather will reduce your output. And the 0.52 derating gives a "maximum average" amount of power you can pull... Obviously, there are day to day variations--some days more and some days less... But to expect to pull 100% useful power 100% of the time is not practical either.

-Bill

icarus · July 2010

Re: Building off grid cabin -- Can you provide input?

I have been away so I missed the earlier parts of this thread.

I will only add a vehement suggestion that you stay away from composting toilets! (Unless they will only be used rarely).

The issue is that the "compost" need heat in order to properly digest. The heating element will make using them effectively from a battery system, nearly impossible. (I have built a propane heater for a composting toilet, but the amount of propane required was silly.)

Given the headaches, and they are indeed headaches IMHO I strongly suggest that you consider a well designed, well built outhouse. I know that there is a social stigma about outhouses, but a well designed and built one will not stink, will not pollute water, and will not attract flies.

In any case, be careful with any manufacturers claim that their product will work with out at the very least a 24/7 vent fan, and without heat.

Tony

PS. I build a bush camp for some folks, and they insisted on composting toilets. (Against my advice, as they had several outhouse that were ideal!) Of the 6 we installed, only 3 are still in use, and these require that the genny be run ~7 hours a day, only to power the fans and the heaters. Even at that, they are only marginally satisfactory.

dwh · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

- SquareD breaker box with 3 15 Amp breakers, one for each panel (similar to this http://www.freesunpower.com/project1.php)

I meant to mention this before and forgot...

If you are planning to use that box as a combiner, the breakers have to be rated for DC. Typical breakers, such as Square D Homeline are normally only rated for 120/240vac.

That setup on that page you linked to is wrong in a few ways.

* He's using AC rated breakers instead of DC rated.
* It's an indoor box that he's using outdoors - silicone around the seams just don't cut it.
* You DON'T run wires through holes in sheet metal without something to protect them especially low-voltage high-amperage DC. Talk about welding.

If you wire the panels in series (which is better since you have MPPT), then you won't need a combiner anyway unless you add another series string and then you'd have to combine the two strings.

I guess the way I would probably plan this would be to have a "power shack". Panels to the charge controller to the batteries to the inverter, then run AC from the inverter to a breaker box then from that to the cabin(s).

Add the generator wherever it seems best - to the inverter if it's designed for a gen hookup, or to a transfer switch to the breaker box in the power shack if not. I would probably also plan a way to hook the generator up to the breaker box in the power shack anyway - just in case the inverter breaks down.

icarus · July 2010

Re: Building off grid cabin -- Can you provide input?

Square D QO series breakers are DC rated to 48 vdc.

Tony

Photowhit · July 2010

Re: Building off grid cabin -- Can you provide input?

It should be a single string, so a combiner box shouldn't be needed, but, strain reliefs are available at any electrical suppy (for the pass through steel box. A minimal weather proof structure can be built or used inside a shed.

I will state as firmly as you think you have "...more than enough power" you might for the toilet, but not for your demands. ...fridge, freezer, 2 laptops and a composting toilet...

I would suggest running the tiolet heater on a timer for a couple hours during your peak charging. this should incourage composting while not drawing down your battery. The composting will help maintain heat, watch your liquids, a male urinal/rock pit will help. Adding peat after each use will also.

Looks like your invested, if you don't have an inverter, I'd highly recomend switching to a 24 volt system. Reguardless if your using used batteries, precharge/top off all the batteries before you put them back in service!

Still don't know if this is a fair weather cabin or a hunting/fishing shack or year round residence...

Good Luck!

stephendv · July 2010

Re: Building off grid cabin -- Can you provide input?

Regarding the composting toilet, I don't have any experience with them, but am also planning to install one so have done some research, there are a few basic types:

In toilet composters - are the most advertised type where the composting happens inside the toilet itself in a heated compartment. People have reported that because there is such a small space for the composting and there's no additional organic matter, that the composting process is very sensitive. So you have to get the moisture levels and the heat just right for it to work properly.
Urine separating composters - The toilet contains a urine separating system so that liquids and solids are separated, you can use the urine for fertilizer and the solids compost better because you don't have to also dry them as much.
A popular choice here is the Separette: http://www.separett.ca/ it only needs a fan to work, but the composting doesn't happen in the toilet, you need to use an outside external composter and empty the toilet periodically. The advantage is it's simple, and if the composting process isn't working 100%, that's not so bad, because the smelly mess is outside and not in your bathroom.
Dry composting using central system - composting happens in a tank in your basement or outhouse, you might still need a heater for it. See: http://www.clivusmultrum.com/
Central Liquid separation - I only know of one product here, and it's the Aquatron separator: http://www.aquatron.se/index-2.php A central composting system, that includes a central liquid separator. Your toilets can then be normal flush toilets, and the aquatron will take care of separating water from the solids. You will have to treat the runoff water as blackwater though!

For cabin use, I'm leaning towards the Separette. It's simple and the composting process doesn't have to work properly, I can simply keep the waste in a container for over a year and it will be reduced to fertilizer no matter the temperature. There's no need to treat blackwater, because there isn't any and I can collect urine for use as fertilizer.

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

Photowhit wrote: »

It should be a single string, so a combiner box shouldn't be needed, but, strain reliefs are available at any electrical suppy (for the pass through steel box. A minimal weather proof structure can be built or used inside a shed.

I will state as firmly as you think you have "...more than enough power" you might for the toilet, but not for your demands. ...fridge, freezer, 2 laptops and a composting toilet...

I would suggest running the tiolet heater on a timer for a couple hours during your peak charging. this should incourage composting while not drawing down your battery. The composting will help maintain heat, watch your liquids, a male urinal/rock pit will help. Adding peat after each use will also.

Looks like your invested, if you don't have an inverter, I'd highly recomend switching to a 24 volt system. Reguardless if your using used batteries, precharge/top off all the batteries before you put them back in service!

Still don't know if this is a fair weather cabin or a hunting/fishing shack or year round residence...

Good Luck!

Sorry for not directly addressing the uses of the cabin. For the first year or so it will only be a weekend or short week vacation get-a-way. After a year our plan is to move out there full time and homestead. We are gung-ho on the idea of using less electricity in general and not trying to replace what we use now. If needed, and it sounds like it will, I foresee us growing this solar solution after the first year. For now it is a sort of "test bed" for solar up at our land.

I don't think I can do a 24V battery bank since my Xantrex inverter is 12V.

Last question...
Once I wire my solar panels up in a series what gauge wire will I need to run the positive and negative back to the charge controller assuming the solar panels are 50 feet away from the charge controller? I keep reading that wiring the solar panels in a series will allow you to use cheaper wire but I don't see any reference to *what* gauge is appropriate. Thanks!

mike95490 · July 2010

Re: Building off grid cabin -- Can you provide input?

There is a new one on the market, called Natures head. originally designed for boaters, but the RE/off grid has picked up on it. Article about it
http://www.green-trust.org/wordpress/2009/02/25/installing-the-natures-head-composting-toilet/
it's also a urine separating system, and has a simple mixing system.

Cariboocoot · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

Sorry for not directly addressing the uses of the cabin. For the first year or so it will only be a weekend or short week vacation get-a-way. After a year our plan is to move out there full time and homestead. We are gung-ho on the idea of using less electricity in general and not trying to replace what we use now. If needed, and it sounds like it will, I foresee us growing this solar solution after the first year. For now it is a sort of "test bed" for solar up at our land.

I don't think I can do a 24V battery bank since my Xantrex inverter is 12V.

Last question...
Once I wire my solar panels up in a series what gauge wire will I need to run the positive and negative back to the charge controller assuming the solar panels are 50 feet away from the charge controller? I keep reading that wiring the solar panels in a series will allow you to use cheaper wire but I don't see any reference to *what* gauge is appropriate. Thanks!

Wire size calculator: http://forum.solar-electric.com/showthread.php?t=29
Since the answer varies with the installation there's no set answer. The series-vs.-parallel issue is one of upping the Voltage to reduce the current, thus allowing smaller gauge (and therefor less expensive) wire. The only caveat is to be sure the array Voc doesn't exceed the charge controller's maximum, remembering that certain conditions can send the Voltage above the panels' rating.

Re: the composting toilets. Remember that they use the heaters to maintain a temperature in the composting compartment. They have to have power available whenever they need it. If you turn it on and off as available they won't work right. And they cost a lot of money. For weekending, a good outhouse is a better solution. Used one for 20+ years with no trouble at all. In fact it's still there and still viable.

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

Cariboocoot wrote: »

Wire size calculator: http://forum.solar-electric.com/showthread.php?t=29
Since the answer varies with the installation there's no set answer. The series-vs.-parallel issue is one of upping the Voltage to reduce the current, thus allowing smaller gauge (and therefor less expensive) wire. The only caveat is to be sure the array Voc doesn't exceed the charge controller's maximum, remembering that certain conditions can send the Voltage above the panels' rating.

Re: the composting toilets. Remember that they use the heaters to maintain a temperature in the composting compartment. They have to have power available whenever they need it. If you turn it on and off as available they won't work right. And they cost a lot of money. For weekending, a good outhouse is a better solution. Used one for 20+ years with no trouble at all. In fact it's still there and still viable.

Thank you, that calculator is invaluable. I was trying to use a web based tool before and it wasn't helping. This is perfect.

Photowhit · July 2010

Re: Building off grid cabin -- Can you provide input?

I think we've had several long discussions about composting toilets, or perhaps just one here and one on every solar/off grid forum I've been at...

The need is to kill bacteria and pathagines(?) As I recall it's a time temp thing with 140 degrees for 18-20 hours being a minimum. I'm sure I'm way off! Also I think the Biolet requires "finishing" in an outdoor compose pile. I think only multi tray can finish in unit. I have a book some where, "Humanure"? that talks about the assorted methods, and I think they stated a 2 hole, 2 chamber, shovel out outhouse works as well as any... use one side for a year, and switch, let the first side 'season' for a year...

If you have codes, and sanitation codes are the most prevelent, you'll want toilets that meet NSF (National Sanataion Federation?) standards, there are just a few, and I don't believe the Biolet is one of them. Here in rural Missouri, I can run 24 volts at 60 amps through a 24 gauge phone wire and no one will come out to check, but I can have someone come out to check if I'm peeing in the yard...

As to wire gauge, typically your looking for less than 2% loss across the entire run so there and back again is 100 feet + 10-25 feet for connecting in series and the height adjustments, my guess is you will be around this for 90 volt nominal, with 10 gauge wire, might have to factor in 12 feet of 12 gauge wire if thats what the panels use. Someone has already provided a link to a calculator.

Check into the fridge and freezers if your thinking about putting them in unheated space, I recall reading that some modern fridges and freezers have issues when outside temps aproach freezing.

niel · July 2010

Re: Building off grid cabin -- Can you provide input?

humanure? you know i think that i know some of those people.:p
yes, i changed it to peeing in your post.
they check if you pee in your yard?

are they also distinguishing between human and animal pee? and how long afterward can they do this as most of it will wash away or go deep into the soil? you don't want fined because jethro got drunk many times and relieved himself out there long before you lived there.

niel · July 2010

Re: Building off grid cabin -- Can you provide input?

ok i got the point, but refrain from bible quotes here as religion is not in the scope of this forum. i just want women and children to be able to read this without any swearing, savvy?

solorone · July 2010

Re: Building off grid cabin -- Can you provide input?

I have scanned over the thread, think I have the jest of the facts.

I am not up on new things, and that seems to have been addressed here.

I do agree that the 225 resistive load will end up being more that you can handle, especially in a Michigan winter.

All I can add is my experience dealing with change. Change to your family's needs and wants, change due to new electrical toys.

We have been off grid for 28 years, pre inverter, at least a practical efficient inverter. So change was a big factor in our lives and home.

Accept that you will be using more power. You already have an inverter, but it is best to buy a large one the first time, rather than buying twice.

You say your going to grow the system, so plan for future loads. Run conduit in hard to get to areas and put in wiring, or conduit, for 220, maybe a future well, there is no problem with throwing extra lines in the access spaces and wireing them in later as needed.

I would plumb the house for a future pressured system, if not for you, then for resale value. If you run water under concrete, then throw in another line or two and cap off, this will be a great asset if you develop a leak. I wonder how you would fight a fire with a gravity system. Yes I have had a couple of those. As I write this, I can see two fire extinguishers, and there is one in the battery house.

Put in plenty of AC outlets, you can never have enough, even if your loads are limited, believe me, I wish I had put in AT LEAST ONE 110 outlet for every 12V outlet:D

I am a life long commercial builder, here we rarely build in wood, but when it happens, 6" walls are the minimum, I would think 8" up there would give a big payback.

Cellulose sprayed insulation is the best economical bet, but sprayed foam is tops.

Tyvek house wrap is a must, the other stuff, if you look close, will say it is water repellent, when burned it disappears like a plastic bag, Tyvek leaves the fiber, it sheds water and breathes. Worth every dollar, seal the windows with a proper tape to produce a water proof plane from gable to foundation.

I have often wondered what it is like to build in such a cold climate, here we only need a footing's top to be 8" below grade.

Good luck.

PorkChopsMmm · July 2010

Re: Building off grid cabin -- Can you provide input?

solorone wrote: »

I have scanned over the thread, think I have the jest of the facts.

I am not up on new things, and that seems to have been addressed here.

I do agree that the 225 resistive load will end up being more that you can handle, especially in a Michigan winter.

All I can add is my experience dealing with change. Change to your family's needs and wants, change due to new electrical toys.

We have been off grid for 28 years, pre inverter, at least a practical efficient inverter. So change was a big factor in our lives and home.

Accept that you will be using more power. You already have an inverter, but it is best to buy a large one the first time, rather than buying twice.

You say your going to grow the system, so plan for future loads. Run conduit in hard to get to areas and put in wiring, or conduit, for 220, maybe a future well, there is no problem with throwing extra lines in the access spaces and wireing them in later as needed.

I would plumb the house for a future pressured system, if not for you, then for resale value. If you run water under concrete, then throw in another line or two and cap off, this will be a great asset if you develop a leak. I wonder how you would fight a fire with a gravity system. Yes I have had a couple of those. As I write this, I can see two fire extinguishers, and there is one in the battery house.

Put in plenty of AC outlets, you can never have enough, even if your loads are limited, believe me, I wish I had put in AT LEAST ONE 110 outlet for every 12V outlet:D

I am a life long commercial builder, here we rarely build in wood, but when it happens, 6" walls are the minimum, I would think 8" up there would give a big payback.

Cellulose sprayed insulation is the best economical bet, but sprayed foam is tops.

Tyvek house wrap is a must, the other stuff, if you look close, will say it is water repellent, when burned it disappears like a plastic bag, Tyvek leaves the fiber, it sheds water and breathes. Worth every dollar, seal the windows with a proper tape to produce a water proof plane from gable to foundation.

I have often wondered what it is like to build in such a cold climate, here we only need a footing's top to be 8" below grade.

Good luck.

Solorone, all great information and feedback, thank you. My plan was to wire the entire cabin, each room, with a bunch of AC outlets. My Father-in-law usually gives good advice and he says to double whatever number of outlets you think you need in a room. Is there a point where the number of AC outlets draws too much power from your solar set up? After counting outlets I think I am in the area of 20 to 25 going back to the electrical panel.

Good point on a fire. There is a small off-grid hunting cabin up there now and we have extinguishers all over the place. We would do the same thing in this new cabin, especially in the kitchen and wood stove area.

We are contracting out the build so I don't know the exact thickness of the walls. It is a traditionally built structure but with quarter log siding on the exterior for looks which will add a couple of inches to the wall thickness. My plan was to use R19 in the walls and R30 in the ceiling but I have been told that spray insulation, even with the contractor to spray it, isn't too expensive so I may go that route. The cabin contractor is from the immediate are and he is building this structure the same way he built his own house (which I have seen and toured) so hopefully it will come out alright. The floors will be insulated as well and with a vapor barrier. The whole structure is going to be wrapped in tyvek in and out.

Thanks for all of the feedback. I am waiting on a few more pieces in the mail and then I will do a test run with the solar panels hooked up. Currently the inverter/charger is just tending the battery bank.

dwh · July 2010

Re: Building off grid cabin -- Can you provide input?

PorkChopsMmm wrote: »

Is there a point where the number of AC outlets draws too much power from your solar set up?

Nope. Receptacles don't draw any power - it's what you have plugged into them that draws power. You can install as many as you want - you just can't plug in and turn on more loads than the power you have available.

I.e., say you had 12 duplex receptacles on a 20 a circuit. You could plug in 24 microwave ovens but you just can't use them all at once - you might be able to run three at once, but when you fired up that 4th one the breaker is going to trip.

Building off grid cabin -- Can you provide input?

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