Off grid power help????

GrandpaRedneck

Hi everyone,

My wife and I have been building an off grid cabin in northern NH, and the guy we were working with about our power plan is no longer available, so we are kind of left hanging with no where to go and not enough knowledge on our own to proceed with any amount of confidence, I remember a lot of what he said, and figured out a few things on my own but not enough, We really need help here.
The plan he had been making he called a hybrid system, a battery bank, with solar and generator
this is what we have so far for components,
we have 8 Trojan t-105 6 volt batteries
Champion 7000 watt generator, with remote start.
3 160 watt 12v solar panels
Go power 30 amp pwm controller
and a 3000 watt Aims pure sine inverter/charger

our 12 volt appliances are
all lights are 12 volt LED .5 amp draw each, 13 lights max
Unique UPG370-L1, 5.2 amp draw
water pump is a Seaflow 8L marine unit, with expansion tank, 17 amp draw
Water heater is a Precision temp 550 EC unit, propane on demand with 12 volt control, 3 amp draw
possibly adding a couple 12 volt fans for summer use
I use a c-pap machine, and had planned on getting the 12 volt adapter to run it
This was all of the original plan for needed power
In the last year my wife ended up needing night time oxygen and a c-pap
I purchased the 3000 watt aims after finding that out at Larry's suggestion , he said we could use the solar and battery bank with it to run the concentrator and connect the aims auto generator start circuit to our generator to keep the batteries from being drained too much until we could afford to add more solar panels and a better/larger charge controller.

Our 120 volt use is now 2 c-pap machines and an O2 concentrator for use at night,
power consumption according to a kilawat meter is 3.4 KWH over the 10.5 hr period the generator was running(o2 concentrator and c-paps only run at night)

We are hoping to start getting things powered up over our July vacation,( refrigerator functioning would be a HUGE plus)
We have an 8x10 shed 20 feet from the cabin that we plan to use to mount the solar on and house the battery bank, inverter, and generator. The plan was to use 2/0 welding cable to connect the battery bank to the 12v fuse panel in the cabin, and run the 120v power from the shed to the cabin breaker box too. the Aims instructions say to use 4/0 wire to connect it to the bank
should I use the 2/0 for connecting the batteries in series parallel also or use more of the 4/0?
what other fuses and components are we going to need to make it work? We want to make sure we have pretty much everything we need when we get started.
Also not sure if I should connect all the batteries in series parallel, or if making 4 sets of series 12 volts, then connect them to bus bars to make all connections to the 12 volt fuse panel, inverter, and charge controller

Thanks in advance for any and all help

Tecnodave

I think that for your needs a 12 volt system will prove inadequate and your inverter is way too big for a small system. A system redesign is in order

4 banks of batteries is a major fail point
Aims inverter is not very efficient and do you need 2000-3000 watts? Idle consumption will be too high, AIMS has a bad track record.
12 volt has too much wiring loss
your solar panels are way too small to support that large amount of batteries

Much better would be to have a 24 or 48 volt system in the shed with only the AC going to the cabin and a inverter no bigger than what your needs are. Look at Cotek for good quality at an affordable price. 
Solar array to support that battery bank at 10% rate of charge (minimum recommend charge current) 1200 watts
MPPT type of charge controller, at 48 volts the current is 1/4 that of 12 volts so the same 12 volt 400 watt controller can handle 800 watts at 24 volts or 1600 watts at 48 volts

BB.

Grandpa,

Welcome to the forum.

And, I suggest that you don't buy anything more until we get back to basics...

How much energy you need per day (Watt*Hours per day), peak Watts, how much sun you get, summer/weekend or 3-4 seasons full time, etc.

Solar power is not cheap, requires planning, engineering, and a good install with the proper equipment.

And adding generator auto start is not trivial either.

If you need that much power soon, and do not plan on having sufficient solar panels to run your system... I would suggest that you look at running your champion generator 24x7 for this family trip (and or a Honda eu3000i would probably be more fuel efficient and quieter). And bring 5-10 gallons or so of gasoline per day of fuel.

As this is your first install for a relatively large off grid power system in a short period of time, I fear that this is a bigger job (time, money, and experience) than could be pulled off without a lot of help.

I will be back home tomorrow and can help more, if needed, when not typing on my phone.

Others here should be able to get the conversation going on the basics...

Bill

Tecnodave

Grampa 

It's good that BB Bill chimed in here, he will lay out all the numbers for you in a way that is easy to understand, he will be a huge help!

and thanx BB for just BBing...

mike95490

With 2 CPAP & an O2 machine, you need a reliable system, and it's not going to be cheap.     Sure you can limp along, maybe for a year, but after 1 winter, those parallel battery banks are going to be soft and die some night.

You really need to carefully plan your loads, how many watts per hour, and how many hours.

An energy star fridge will consume (roughly) 1kwh daily., but you will need much more solar than your system was built with.

Having 8ea, 6v  batteries, puts you in line for a 48V system, which even for modest needs, is the smallest I'd design for a house.

Will you live year round in the house ?    Do you get snow ?   Can you access the generator, fuel and oil in snow or bad weather ?

Estragon

Not sure I'd be so set on 48v in this application.  Most loads runs 12vdc.  With a 12v fridge already, an ac fridge likely isn't in the immediate future.  The only ac loads mentioned are for the medical devices, apparently running average ~350watts for 10 night-time hours.  Unless device(s) have a huge startup surge requirement, the 3kw inverter is definitely overkill.  It should be turned off when not in use.

A few numbers to get started:

Battery bank is 4 strings of 2x6v GC, ~225ah@12v x 4 = 10800 watt-hours capacity, of which maximum 50% should be actually used (for best battery life vs cost), so ~5kwh useable.

The dc fridge might use 500wh/day, ac loads ~3.5kwh, lights etc maybe another 500wh, so say 4.5kwh/day.

Although what you have may not be ideal, it is what it is.  IMHO, it's reasonable to use what you have for now.  Once you've occupied the cabin for a while, you'll have a better handle on what loads actually are, and may find there are things you would really like but haven't included.  I like toast, for example, and making it on a campstove rack got pretty old.

For the time being, I'd plan on using the generator to charge the batteries up to about 75-80% full every morning.  If the batteries are ~60% full from overnight loads, s this would take roughly 2 hours.  3 x 160w panels well tilted should put out roughly 350w .  Using Lancaster NH, pvwatts.nrel.gov shows nearly 6hrs of full sun equivalent in July, so you might average ~350 x 6hrs = 2100 wh/day.  This will offset daytime loads, and bring batteries to full or nearly so on sunny days.  In Dec, average sun is < 2hrs/day average though, so you'll need to run the generator for an extra hour or two to charge.

With 4 strings of batteries, each string of 2 x 6v batteries should be fused (on the positve wire from string to buss bar near the battery post.  If using 2/0 for interconnects and to busses, size fuses accordingly (NEC is ~175a, depending on insulation type, etc).  The positive buss to inverter should have a breaker sized per inverter max.  4/0 wire is rated for ~230a per NEC, but the inverter could put out ~3000w ÷ 10.5v = 286a.  This is one reason not to use a big inverter on a 12v system.

With 3 solar panels, each should really be fused before the parallel connection.  This would normally be done using breakers in a combiner box.  Given you'll likely want to add panels fairly soon, either get a combiner with lots of extra space, or take a bit of a risk and skip the panel fusing for now.  After the parallel connection, run heavier wire (say 4awg) to the controller with breaker on positive sized per controller spec.  On the controller to positive buss (also ~4awg), another breaker also per controller spec.

The DC wire from busses to DC fuse panel should have a DC breaker.  2/0 might be a bit big for your loads and a 20' run, but won't hurt and would keep voltage drop down.

Other stuff you'll want:
- a digital multimeter
- a DC clamp current meter (note AC meters generally don't work) to check current per battery string under load.
- a hydrometer to check battery specific gravity
- box(es) to hold DC breakers
- some sort of racking for solar panels.  Being able to set vertically in winter to shed snow may be helpful.
- possibly MC4 extention cables depending on combiner box location
- crimping big (eg 4/0) wire is hard to do properly. Premade is preferable, but if doing on site, borrow or rent a good crimper?
- high output (>90a) hardwired AC battery charger(s) with appropriate wire and breaker(s).  A couple of 45a iotas, for example.
- some sort of no-ox goo for battery terminal connections.
- tape and/or rubber gloves, old rubber hose or whatever to cover metal tools used to work around batteries.  Dropping an unprotected socket wrench across battery terminals can make for a bad day.
- distilled water and a small funnel for watering batteries.
- baking soda to make a neutralizing solution in case of battery acid spillage.

Looks like a nice cabin.  Be sure to consider changing seasonal shade angles from the trees when locating shed and panels.

mcgivor

There is a point where 12V has its limitations, it's fine for small systems like a RV or small occasional use cabin. For larger applications it's better, in my opinion, to use domestic 120V appliances supplied by an inverter, preferably a quality inverter charger, this allows longer wiring runs which limit the cost effectiveness of 12V. Having a dual voltage system when an inverter is already in use renders the 12V superfluous.

Carefully calculate loads liberally, a conservative approach can lead to dissapointment, most with any off grid experience will attest to this, a few lousy weather days can take many more to recover from such an event. Generators are very useful to subsidize periodic solar shortcomings but regular use usually indicates shortcomings in the design of the solar. Additionally generator charging is not the most efficient, there is labor involved and noise, auto generator start can reduce the labor albeit at the expense of reliability.

My advice, for what it's worth, is build it right the first time, finances permitting of course, because when medical requirements are involved shortcuts could slow you down, literally.

All opinions are based on full time useage, living rather than camping.

Estragon

@mcgivor - I'd normally agree, but in this instance OP already has the main components, and wants to organize for July installation.  I think for now we can be more helpful in assisting with making the best of what they have.

mcgivor

In normal circumstances, without medical reliance perhaps yes, make do with what's available, however it's my humble opinion thet it's wiser to engineer a reliable system to support requirements when ones life depends on it, if the lights go out, no big deal, if it's your lights that go out, it's a big deal.

NANOcontrol

I think you re way under paneled. Most people in solar are batterycentric. I'm up in your general area and all my panels are under trees.  I can operate in the rain without relying on that much battery. You still have to live and recover your batteries. I'm off grid with PV hot water, dishwasher with heated dry and something that keeps me alive at night.  I have five times the panels you have and it is the cheapest investment you can make. Grid tie panels are less than 50 cents a watt delivered.

arilans

 Oh my God I can’t believe I finally am able to post. I’ve been trying to make a post for so long. I need some help with my solar system I am .  I can’t find anyone to ask a question to and I’m getting really frustrated. I need you very simply one question answered. I have a 12 V 200 amp power mighty Max battery and I need to know  The vaulted voltage amounts where I turn it off and I need the voltage amount where I need to stop using it. No one can give me a straight answer this is crazy please someone help 

GrandpaRedneck

Estragon said:

Not sure I'd be so set on 48v in this application.  Most loads runs 12vdc.  With a 12v fridge already, an ac fridge likely isn't in the immediate future.  The only ac loads mentioned are for the medical devices, apparently running average ~350watts for 10 night-time hours.  Unless device(s) have a huge startup surge requirement, the 3kw inverter is definitely overkill.  It should be turned off when not in use.

A few numbers to get started:

Battery bank is 4 strings of 2x6v GC, ~225ah@12v x 4 = 10800 watt-hours capacity, of which maximum 50% should be actually used (for best battery life vs cost), so ~5kwh useable.

The dc fridge might use 500wh/day, ac loads ~3.5kwh, lights etc maybe another 500wh, so say 4.5kwh/day.

Although what you have may not be ideal, it is what it is.  IMHO, it's reasonable to use what you have for now.  Once you've occupied the cabin for a while, you'll have a better handle on what loads actually are, and may find there are things you would really like but haven't included.  I like toast, for example, and making it on a campstove rack got pretty old.

For the time being, I'd plan on using the generator to charge the batteries up to about 75-80% full every morning.  If the batteries are ~60% full from overnight loads, s this would take roughly 2 hours.  3 x 160w panels well tilted should put out roughly 350w .  Using Lancaster NH, pvwatts.nrel.gov shows nearly 6hrs of full sun equivalent in July, so you might average ~350 x 6hrs = 2100 wh/day.  This will offset daytime loads, and bring batteries to full or nearly so on sunny days.  In Dec, average sun is < 2hrs/day average though, so you'll need to run the generator for an extra hour or two to charge.

With 4 strings of batteries, each string of 2 x 6v batteries should be fused (on the positve wire from string to buss bar near the battery post.  If using 2/0 for interconnects and to busses, size fuses accordingly (NEC is ~175a, depending on insulation type, etc).  The positive buss to inverter should have a breaker sized per inverter max.  4/0 wire is rated for ~230a per NEC, but the inverter could put out ~3000w ÷ 10.5v = 286a.  This is one reason not to use a big inverter on a 12v system.

With 3 solar panels, each should really be fused before the parallel connection.  This would normally be done using breakers in a combiner box.  Given you'll likely want to add panels fairly soon, either get a combiner with lots of extra space, or take a bit of a risk and skip the panel fusing for now.  After the parallel connection, run heavier wire (say 4awg) to the controller with breaker on positive sized per controller spec.  On the controller to positive buss (also ~4awg), another breaker also per controller spec.

The DC wire from busses to DC fuse panel should have a DC breaker.  2/0 might be a bit big for your loads and a 20' run, but won't hurt and would keep voltage drop down.

Other stuff you'll want:
- a digital multimeter
- a DC clamp current meter (note AC meters generally don't work) to check current per battery string under load.
- a hydrometer to check battery specific gravity
- box(es) to hold DC breakers
- some sort of racking for solar panels.  Being able to set vertically in winter to shed snow may be helpful.
- possibly MC4 extention cables depending on combiner box location
- crimping big (eg 4/0) wire is hard to do properly. Premade is preferable, but if doing on site, borrow or rent a good crimper?
- high output (>90a) hardwired AC battery charger(s) with appropriate wire and breaker(s).  A couple of 45a iotas, for example.
- some sort of no-ox goo for battery terminal connections.
- tape and/or rubber gloves, old rubber hose or whatever to cover metal tools used to work around batteries.  Dropping an unprotected socket wrench across battery terminals can make for a bad day.
- distilled water and a small funnel for watering batteries.
- baking soda to make a neutralizing solution in case of battery acid spillage.

Looks like a nice cabin.  Be sure to consider changing seasonal shade angles from the trees when locating shed and panels.

Thanks, I am mechanically inclined, and as a former auto mechanic I completely understand the dangers of a short across battery posts. The components I have I purchased over the last 3 years. The cabin is for weekend use and a couple weeks of vacation in the summer. We have been on the property for going on our 4th summer now. The original thought was for only 12V appliances / system along the lines of the camper we used for the first three years. (that is why the 12V panels, and all 12v appliances) Larry had suggested around 500 watts of panels, and 4 6v batteries. He had me buy the major components, and we had planned for him to do the install and supply the smaller components when the time came. When we found out my wife needed the O2 concentrator I asked Larry what his thoughts were for moving forward,(I knew that was a big curve ball from the original plan) he said to double the battery bank to 8 and add a 2000 Watt or larger inverter/charger with auto gen start capabilities. He said we could use the gen to help charge the bank until we could afford more panels and a bigger/better charge controller.
When we had the camper we went up every weekend May through late October(couldn't keep it at a comfortable temp through the winter), now that we have the cabin we have been going up almost every weekend all winter too, It stays very comfortable even at temps below 0. We currently run the gen all night to keep the O2 and c-paps going, and don't shut it off in the morning until after brewing a pot of coffee and making the toast(did the same with the camper). We actually have 2 generators on site, as we figured a back up was a necessity, and if for some unforeseeable reason both quit at once we would just pack up and head home.
At this point I was hoping to at least get the 12 volt part of system up and running to run the lights, fridge, water pump, and water heater, if we need to continue to use the gen at night for the O2 and c-paps we are OK with that for now, and I am assuming while running at night it would be charging the battery bank too?
Shade consideration was the reason for locating the shed 20 feet from the cabin.
Another question I have thought of is would it make any sense to use the 12v system for the 12v loads only and in the future design and build a larger stand alone system to run the 120v loads?
Thanks for the comments and suggestions.

GrandpaRedneck

mike95490 said:

With 2 CPAP & an O2 machine, you need a reliable system, and it's not going to be cheap.     Sure you can limp along, maybe for a year, but after 1 winter, those parallel battery banks are going to be soft and die some night.

You really need to carefully plan your loads, how many watts per hour, and how many hours.

An energy star fridge will consume (roughly) 1kwh daily., but you will need much more solar than your system was built with.

Having 8ea, 6v  batteries, puts you in line for a 48V system, which even for modest needs, is the smallest I'd design for a house.

Will you live year round in the house ?    Do you get snow ?   Can you access the generator, fuel and oil in snow or bad weather ?

Hi mike, we will only be there on weekends year round and a couple weeks for vacation in the summer for now, maybe for all summer when we hit retirement, but even then likely only weekends in the winter.
Yes we get a LOT of snow, and yes we can get to the gens in the winter, even this last winter when they were not in a shed. I had them under a tarp that was tented between 2 trees, I would clear the snow off the tarp when we arrived on Friday nights, and fire the gen up. In a shed It will be a lot easier.

littleharbor2

GrandpaRedneck said:

Another question I have thought of is would it make any sense to use the 12v system for the 12v loads only and in the future design and build a larger stand alone system to run the 120v loads?
Thanks for the comments and suggestions.

That's the way I have my vacation home set up. Matter of fact I have two separate 12 volt set ups for running my water pumps and VHF radios in the main house and detached garage.  With AGM batteries they are really no maintenance. Going strong for 5 years now.

mike95490

Estragon said:

@mcgivor - I'd normally agree, but in this instance OP already has the main components, and wants to organize for July installation.  I think for now we can be more helpful in assisting with making the best of what they have.

I call it limping along, and I guess we'll disagree.   I don't like using what I call a weekend system, for full time.

If having to stay at 12V , then at least get a morningstar suresine 300 inverter to run the medical loads

https://www.morningstarcorp.com/products/suresine/

and leave the big honking inverter off as much as possible.

And then there is the issue of wiring the house for 12VDC  AND 120VAC.  Which outlet is which?  Where do you get 12VDC wall switches?  What is the expense of the #8 wire to carry the loads to the other end of the house?

I "managed" for half a year, using a jump start pack for my CPAP.  Cheap is cheap.

wellbuilt

  Hi GP The CPAC And air concentrator doesn’t use much power at all . 
  I have run both of them off a. 300 watt Morningstar sure sine inverter with 2 6v GC 215 battery’s . 
    My son uses the air  concentrator turned way up and it uses 25watts the CPAC uses 20watts . 
 I powered my cabin first with a 200$ 1800 watt generator  run 24 hrs a day .
 Then I used the morning star 300 watt inverter  with 3 295 watt solar panels and 2 6 volt go 215 battery’s . 
 I could run a 50”
’tv a bunch of led recessed lights 12 volt rv water pump radio small fan and CPAC over night .
 Now I have a out back power system up and running (thanks to these guys on the forum ) 
   I tried to cobble a system together on my own but ended up with this set up that I bought thru our host it came pre wired and I screwed it to the wall  and had it running in a few hours with 8 6v batterys and champion generator for charging . 
 Then it took a few hours a day for 4/5 weekends to get it all  permanently wired and Solar Panels mounted . I had to ask a lot of questions here to get every thing hooked up . 
  I ended up buying my solar panels and racking  thru a place in Vermont not far from NH I bought them thru a Electrical supply house I do business with in New York and there was no shipping fee . 
  The Engineer there was very helpful with hooking everything up , he pretty much thru everything on the truck that I needed and sent me a bill 🤣  I  laid  out the parts and call him in Vermont and he walked me thru the system  hook up .

 AWS is very help full with the out back equipment , you can call them and get a lot of tec advice from whoever picks up the phone.
  There sales guys know the outback systems .  
 I would also Recommend running the house with ac power it’s very easy , my Electrical inspector  totally shot down any 12 V DC power run thru the walls , and I was not in any  position to argue with him  , all in all it worked out well .  
           PS great cabin .  John 
  

GrandpaRedneck

mike95490 said:

Estragon said:

@mcgivor - I'd normally agree, but in this instance OP already has the main components, and wants to organize for July installation.  I think for now we can be more helpful in assisting with making the best of what they have.

I call it limping along, and I guess we'll disagree.   I don't like using what I call a weekend system, for full time.

If having to stay at 12V , then at least get a morningstar suresine 300 inverter to run the medical loads

https://www.morningstarcorp.com/products/suresine/

and leave the big honking inverter off as much as possible.

And then there is the issue of wiring the house for 12VDC  AND 120VAC.  Which outlet is which?  Where do you get 12VDC wall switches?  What is the expense of the #8 wire to carry the loads to the other end of the house?

I "managed" for half a year, using a jump start pack for my CPAP.  Cheap is cheap.

@mike94590 This is a small 18x24 cabin, we will use it weekends year round, and a couple weeks of vacation in the summer, not full time.
As far as switches go, 12V switches are easily available thru RV/marine, and even automotive suppliers. And I may be an old redneck grampa, But I ain't a damn fool, I am not foolish enough to be using standard 120v outlets for 12v connections, all 12v loads, with the exception of the fridge are going to be hard wired in with a switch, and fused too, the fridge came with its own unique 12v plug set up, and I will use that. If I do eventually set up for a couple of 12v fans I would use an automotive style of plug, possibly a simple trailer connector set up, I really hate the little cigarette lighter plugs, but those would be a possibility too.
The heaviest 12v load is the water pump at 17 amps, it will be located within 10 feet of where the 12v fuse panel will be, calculator said 12 gage, I used 8.  Next heaviest is the fridge at 5.2 amps, and that is going to be directly above the 12 volt fuse panel, about 3 1/2 foot run of wire, I had enough 8 left over I used it there too. All lights are wired 2 or 3 lights per circuit for a total of 1 or 1.5 amp circuits. short runs were 3 lights longer runs were 2, I used 12 gage wire for the lights, even though the wire gage calculator said 18 gage was sufficient.
I hope this puts some of your concerns at rest.

Wheelman55

Grandpa. I’ve had good luck with these ARB plugs and sockets. 

https://www.youtube.com/watch?v=p_SzIY05bYY

Estragon

+1 on using a little Morningstar 300w inverter overnight if it will run the medical gear.  They have very low standby loss.

The batteries will charge with generator power, assuming you have an AC battery charger hooked up.  A solar charge controller generally won't use AC power though.

I run two separate systems, but there are pros and cons to this approach.  What tipped it for me was at the time, there wasn't much available in decent, small 48v inverters.  There are some now, so would likely stick to a single voltage if setting up today. 

The limiting factor for 12v systems is larger loads like 240v pumps.  The current for big loads just gets unwieldy at 12v.  Running things like standard AC fridges, it generally makes sense to go to at least 24v.  Bigger pumps etc means 48v. 

GrandpaRedneck

@estragon
Thanks again,  I appreciate your input. We don't have any need for a large water pump, we have a spring fed well on the property that will gravity feed 2 55 gallon food grade  drums in the basement, and then the 12v marine pump will put out plenty of pressure pulling from the tanks. We could even gravity feed to the kitchen and bathroom and not use a pump  but it wouldn't be much pressure.

BB.

You can get pretty cheap RV type pumps in 24 VDC too..

https://www.solar-electric.com/residential/solar-water-pumping/surface-pumps.html?nav_pump_voltage=453

-Bill

Estragon

I gravity feed toilets from a cistern I fill using extra available solar (batteries often get to float around noon).  It doesn't take much pressure to fill the toilet tanks, and it saves battery power, filter changes, and late night pump noise.  There's a x-connect valve so toilets use the pressure system during "hard water" season (I'm in Canada).

icarus

Remember that roof mounted PV will need to be shoveled or swept in snow season, maybe problematic for an occasional use cabin.  If you have lots of snow, and you are away for any length of time, your batteries will receive no charge current, and if there are full time loads like fridges they may well be discharged or dead after a few snow events.  I always install PV on walls, (hinged to fold them flat when un attended) so that they never get snow covered, in buildings that are likely to be unattended during snow season.

Tony

Estragon

I learned that the hard way.  Just charge controller self-consumption nearly killed the banks with snow covered main arrays, so I now have small vertical arrays and controllers to be sure they float unattended in winter.

Thom

I just wired 120vac like a regular house with a 300 w inverter and a switch to run off generator to pump water or vacuuming ,power tools.  12v wiring cost more and less convenient.  I have 12v to charge phones and iPad ,DSL. I turn on the inverter when I need it a few hours a day. Propane refrigerator.

thom