Off grid system for remote cabin

BB.

Re: Off grid system for remote cabin

Caveman wrote: »

Just so I understand, in what kind of situation would I not have the option to control when loads are applied?What do you mean by that?

I am not sure I understand the context of the question--But it may be along the lines if you have a limited AC circuit or off grid power system--You either have to size the system as if all the loads could be turned on at the same time (fridge on, brewing coffee, and cooking in your hot pot)--Or, if you have options, you don't use the coffee maker and crock pot at the same time (simple example).

Sorry if that sounds like a dumb question, but i'm still groping.

By all means--Please ask questions if you are not sure of the answers... We are more than happy to clarify the answers. Many times we start "simple", and then add complexity once the basics are understood -- Or we correct our answers when we make mistakes (it happens ).

-Bill

Cariboocoot

Re: Off grid system for remote cabin

Caveman wrote: »

Thanks again for the help. Just so I understand, in what kind of situation would I not have the option to control when loads are applied? What do you mean by that? Sorry if that sounds like a dumb question, but i'm still groping.
Thanks again!

Opportunity loads: things you can choose to turn on when you know the batteries are full and the panels still able to produce more power.
I have my water pumps set up like this. They are off until I say otherwise. When the batteries are full and the sun is bright, switch on the pump and fill up the pressure tank. In six minutes I have enough water for the day. Likewise the septic pump gets turned on. These are both big loads and it would not be good to have them come on 'whenever'.

Things that have to be used at certain times of the day do not give you this option. You use lights at night when it's dark, not at noon! And meal prep is done at meal time. So some loads you can not shift to a more opportune time when you know the power will be coming from the sun and not the batteries. This is why over-all efficiency of off-grid systems is so poor; they can't make use of all the sun power potential, unlike grid-tie where there is always a place for any power produced to go.

Caveman

Re: Off grid system for remote cabin

Gotcha, makes perfect sense.
I think I’ll probably need to go with the second battery setup you mention, 2 strings of golf cart batteries for 440 amp hours @ 24 volts. How many batteries in each string? Is there somewhere on the forums or elsewhere where I can learn how to set up the batteries? Ill go searching anyway, but sometimes I’ll search for awhile before any success.

The Midnight Classic Lite charge controller you mention, why that particular one? It looks fine, and at this point I’m ready to just go buy everything you mentioned and be done with it, but my more sensible part of my brain want to actually understand why I am getting each component of this system if you know what I mean. I was looking at charge controllers online, man what a difference in prices for what look to be very similar equipment!

Same goes for the Solar World panels, why this particular one? Just wanna be sure. Looks like that Outback inverter is a true sine wave.
I can see 2 possible paths I can take here. 1: The setup I just described, 2: The same setup, but 12V with 1 string of batteries, right? The downside to the second system being I can’t run everything all at once.

Also, what would be an example of a "golf cart" battery, seems they're all called deep cycle, but I'm guessing some of them are golf cart batts.

Cariboocoot

Re: Off grid system for remote cabin

Why you'd choose one system Voltage over another: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
Differences in array design: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

Golf cart batteries are deep cycle: meant to be drawn down considerably and then recharged. The GC batteries are 'T105' size; 6 Volts @ 220-225 Amp hours. Because they are sold in such volume they are usually the cheapest choice on a per Amp hour basis. For 24 Volts you put four in series to get 220 Amp hours @ 24 Volts. Double the strings and you get 440 Amp hours @ 24 Volts.

The controller and panels I mentioned are only one option for achieving the results desired. The MidNite Classic controllers are the best on the market just now. For $5 more you can get an Outback FM60 with meter built-in. It too would handle the job just fine.

MidNite Controllers: http://www.solar-electric.com/misoclchco.html
Outback Controllers: http://www.solar-electric.com/ouchco.html

The SolarWorld panels I mentioned because they too are a bargain at $1.15 per Watt now. Panels: http://www.solar-electric.com/hiposopa.html

Brand-name (Crown) 'golf cart' batteries: http://www.solar-electric.com/cr225am6vode.html
You can sometimes get the generic equivalent of these from the big warehouse stores for <$100 each.

You need to look over lots of choices before you pick one, so that you know the advantages and disadvantages of each. As it is you are at the 'threshold' for power use between 12 Volts and 24, and if you think there's likely to be further expansion (almost inevitable) going with 24 makes sense.

Photowhit

Re: Off grid system for remote cabin

Cariboocoot wrote: »

Brand-name (Crown) 'golf cart' batteries: http://www.solar-electric.com/cr225am6vode.html
You can sometimes get the generic equivalent of these from the big warehouse stores for <$100 each.

Batteries are big and heavy items which shipped together in a truck tend to be much cheaper thn sending out 4 to a home. Sam's Club and Costco are localish big box places that normally stock golf cart batteries for about $80 each, Sam's Club and (I hear) Costco require an exchange, but will take car batteries in exchange (without exchange add $15) I think the Energizer GC batteries I last bought at Sam's club were 215 AmpHour, but it's been 6 yrs.

Caveman

Re: Off grid system for remote cabin

So besides choosing a particular brand on the equipment mentioned, the only real decision here is whether to go 12V or 24V, right? Besides buying twice the amount of batteries, are there any cons to going 24V? I mean, regardless, I'm gonna want to get that charge controller, inverter, and panels you mentioned (not those specific ones, at least something comparable to it).

Cariboocoot

Re: Off grid system for remote cabin

Unless there is some pressing reason for going with 12 Volt (such as a mobile application or the need for 12VDC loads) there's no real downside to 24 Volt. It is slightly more expensive for the inverter, batteries, and some other pieces. You can't use 12 Volt auto fuses for instance. But the DC wiring does not need to be as large for the same Watts, and it is somewhat more efficient (less power going to heat as Amps).

Caveman

Re: Off grid system for remote cabin

Just thinking out loud here, do you think I need this much power? The cabin will probably only be used on weekends, and my gut tells me I could get away with a smaller system, but i just don't know. So far I've been describing a system like this:

2 strings of golf cart batteries (8 total) to provide 440 Amp hours @ 24 Volts
6 Panels to provide 1380 watts
Charge controller
Inverter

Everything I know about solar I have learned in the last few weeks, so I'm still pretty much an ignoramus, but I guess at the begining I wasn't thinking I would need 8 batteries and 6 panels. I do understand what you said about the greater demands due to it being completely off grid. Does this seem like a pretty standard system for a hunting cabin?

Photowhit

Re: Off grid system for remote cabin

A question only you (and your family) can answer.

I lived on 220 watt array for several years, light (once in a while 2), laptop, fans in the summer, TV, VCR a bit. Cooked with gas, used the comfort station for hot showers (have we asked about water, pumping, heating), took laundry down to the river and beat against rocks...lol.

If it's just you and your willing to heat water for coffee, and cook with gas, I might look at a smaller system. We've had some pretty good reports on a Xantrex 2000 (really 1800watt) 12 volt inverter which is pretty cheap at @$400, and if you can find cheap 12 volt (nominal) panels, you could go with a non MPPT inverter...

and of course if you want you could use a generator, and store a smaller amount of energy to get you through the night. Likely the cheapest in the long run.

... but loads grow and you would have to dump these things and switch if you need more energy. Something like a fridge puts you right back to a larger system.

Cariboocoot

Re: Off grid system for remote cabin

It comes down to how much power you need to supply, which is back where we started. If you need 2kW hours per day it doesn't matter if you only use it 2 days a week, month, or year. There's the rub.

If you can 'do without if need be' it's easy to reduce the system size. If you don't mind running the generator for recharging you can reduce the solar capacity to just enough to maintain the batteries when you are not there.

A very basic system would be like this:
Two 6 Volt 220 Amp hour batteries providing up to 1200 Watt hours AC per day. ($250)
20 Amp charge controller like this: http://www.solar-electric.com/ss-20l.html ($78 )
Two Kyocera KD140 panels: http://www.solar-electric.com/kykd140wasom1.html ($620)
Exeltech 2kW inverter: http://www.solar-electric.com/exxp1224vo20.html ($1,300)
Iota charger: http://www.solar-electric.com/ioen12vo15am.html ($137)
Honda EU2000i generator ($1,200 +/-)
Total of major components (no wiring, circuit protection, or mounting hardware): $3,585 or roughly $4,000.

If you needed more than the 1.2 kW max or the panels couldn't replace the 'used Amp hours' you'd run the generator for the loads and charge the batteries with the Iota.

Caveman

Re: Off grid system for remote cabin

Thank you guys for your patience and help. I have assumed too much in my life, sometimes regretting asking even what seems to be the obvious. That makes sense that it doesn't matter how often use use it, if you are gonna put a good load on it in even for one day it's gotta be up to the task.

This is what I'm looking at:

2 strings of golf cart batteries (8 total) to provide 440 Amp hours @ 24 Volts-

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$1,000
6 Panels to provide 1380 watts

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$1,600
Charge controller: http://www.solar-electric.com/misoclli150m.html

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$510
Inverter: http://www.solar-electric.com/fx2524t.html

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$1,800

Total not including cables, connections, fuses, etc.,

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$4,910
*prices are approximate.

Pretty close to the generator assisted system you laid out. I think I'll spring for the solar.

inetdog

Re: Off grid system for remote cabin

Caveman wrote: »

2 strings of golf cart batteries (8 total) to provide 440 Amp hours @ 24 Volts-

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$1,000

Pretty close to the generator assisted system you laid out. I think I'll spring for the solar.

In either case, don't forget that the batteries are a recurring expense. If you are fortunate only every two years with golf cart batteries that are actually being cycled.

Cariboocoot

Re: Off grid system for remote cabin

inetdog wrote: »

In either case, don't forget that the batteries are a recurring expense. If you are fortunate only every two years with golf cart batteries that are actually being cycled.

Two years? How deep do you plan on discharging them? Look after them and you'll get five years even from the 'cheap' ones (they're all basically the same inside).

Caveman

Re: Off grid system for remote cabin

Cariboocoot wrote: »

Two years? How deep do you plan on discharging them? Look after them and you'll get five years even from the 'cheap' ones (they're all basically the same inside).

You think there is an appreciable difference between the name brand and the economy batteries?

Cariboocoot

Re: Off grid system for remote cabin

Caveman wrote: »

You think there is an appreciable difference between the name brand and the economy batteries?

On a first set that is most likely to be over/under charged? Yes; the economy ones won't cost you as much if they fail prematurely.
Otherwise, since you inevitably have to replace batteries eventually, you might as well go for the bargain. Especially on a system that is not in full-time use.

Withing the name brands there are different levels too. Trojan has "ordinary" deep cycle batteries http://www.solar-electric.com/trgocarandot.html and "renewable energy" designated ones http://www.solar-electric.com/trdecysoba.html Likewise Crown has "standard" http://www.solar-electric.com/stdecyba.html and "renewable power" http://www.solar-electric.com/repose.html

These designations for RE are fairly new, and come from the battery industries response to renewable energy system needs. Exactly what changes are involved depends on the company. So far there aren't too many reports back on performance, but they are at least as good and probably better than the standard deep cycle. Worth the extra money? Perhaps on a full-time system, but not likely on an occasional weekend cabin set-up.

Cariboocoot

Re: Off grid system for remote cabin

BTW, I have to also mention that the 'low price' system I outlined can be further reduced in cost. You could by a cheap standard generator for $300 instead of a $1,200 Honda inverter-gen. The inverter only has to have enough capacity to run the maximum load. If you don't need pure sine for motors or other induction loads you could buy a less-expensive MSW inverter instead. There are even less expensive charge controllers available. Shop around, but be aware that bargains aren't always what they seem.

The more you use a system, the longer you intend to use it, the more sense it makes to put the $ into good equipment the first time, rather than buying it twice. The exception to this would be the batteries because they will need to be replaced at some time no matter what.

BB.

Re: Off grid system for remote cabin

A 440 AH @ 24 volt is a pretty large system--3/4's on the way to living at an off grid home with fridge/washer/well pump/laptop+cell phone power/some TV/etc...

Using our rules of thumb--5% to 13% rate of charge, the solar array would be around (for a 440 AH @ 24 volt battery bank):

• 29 volts charging * 440 AH * 1/0.77 panel+contorller derating * 0.05 rate of charge = 829 Watt array minimum
• 29 volts charging * 440 AH * 1/0.77 panel+contorller derating * 0.10 rate of charge = 1,657 Watt array nominal
• 29 volts charging * 440 AH * 1/0.77 panel+contorller derating * 0.13 rate of charge = 2,154 Watt array "cost effective maximum"

If you assume 4 hours of sun (on average) minimum for 9+ months a year (pretty sunny climate in North America--no coastal marine layer, etc.), such as system would generate around:

• 829 Watt array * 0.52 system efficiency * 4 hours minimum sun per day = 1,724 WH per day of 120 VAC power
• 1,657 Watt array * 0.52 system efficiency * 4 hours minimum sun per day = 3,447 WH per day
• 2,154 Watt array * 0.52 system efficiency * 4 hours minimum sun per day = 4,481 WH per day

More or less--I suggest around 3.3 kWH per day (or ~100 kWH per month) as the aim point for a very efficient off grid home with a refrigerator/etc. for loads...

This system and battery bank would certainly be capable of that.

Note, besides the actual amount of power you need per day (kWH per day)--There are peak loads too... For example, a 440 AH battery bank @ 24 volts would be able to source:

• 24 volts * 440 AH * 0.85 inverter efficiency * 1/8 hour discharge rate = 1,122 watt 120 VAC load max continuous (recommended)
• 24 volts * 440 AH * 0.85 inverter efficiency * 1/2.5 hour discharge rate = 3,590 watt 120 VAC load max surge (starting well pump, etc.)

For what you describe--You could look at a system that is much smaller and still meet your needs (assuming no fridge, limited amount of cooking/heating water/etc.).

Note--For your case, one of the drivers for battery bank capacity is the heavy load for making coffee/crock pot cooking...

If you like slow cooking--There is one alternative that I have used with good results... A cooking thermos. You fry/boil/sear the foods on the gas stove, pour in the liquids. Bring up to a boil and then place the whole "pot" into a thermos--And let sit for 4 hours (I will reheat once if needed for tough meat/etc.). Very fuel and cost effective solution. And popular with Asians (you should find the cooking thermos' in a good sized Asian market).

-Bill

Photowhit

Re: Off grid system for remote cabin

I have used the cheapest sam's club batteries and gotten 5 years out of them, abusing them in the summer time running an A/C and often drawing them down to 50% DOD. I do believe Trojan batteries are superior and most of the people who have gotten more than 5 years have been using Trojans, but they cost near 2X the cost. As others have said it's not uncommon to 'kill' your first set of batteries...

Also I don't think you need that large of an inverter, I might take a long hard look at the Exeltech 1100 at @$600 it's a quality inverter(made in USA) and often priced much higher! The PDF says it's UL listed, but I'm not sure if it's listed for home use, but it has all the properties, it has a cover for the battery cables so you can run them in conduit and the Ground bonding is a clip that can be removed at the connectors. FWIW The outback your looking at still needs a shroud(?) to cover the battery cables to meet code. If your coffee pot is 1100watts or less you should be fine a coffee pot is a resistance load and you should be able to run right up to the inverter rating.

Cariboocoot

Re: Off grid system for remote cabin

Actually the Outback's shroud comes with it.
Take a look at the picture here: http://www.solar-electric.com/ouin.html (Middle pics)
The red and black are plastic covers over the connections, the black thing shown separately at the bottom fastens over top of it all with four screws. Very safe and secure.

Photowhit

Re: Off grid system for remote cabin

The cables still just come out of the unit, to meet code you have to have This thingy .

Maybe you need this thingy for the AC side of things too? But I thought they had a conduit out for AC...

Cariboocoot

Re: Off grid system for remote cabin

Photowhit wrote: »

The cables still just come out of the unit, to meet code you have to have This thingy .

Thank you for reinforcing my belief that much of the NEC is a load of dingos' kidneys.

Photowhit

Re: Off grid system for remote cabin

Cariboocoot wrote: »

Thank you for reinforcing my belief that much of the NEC is a load of dingos' kidneys.

I'm right there with you... My Prosine has UL 1741(?) home use, but has no provision for battery cables in conduit, I think they are used in some stair lifts in homes (or use to) so perhaps they were totally enclosed in a UL case? Who knows... other than that one guy... Glad to live in Missouri where I'm not likely to see an inspection until the grid runs dry...

Caveman

Re: Off grid system for remote cabin

I noticed you added a battery charger in the scaled down version. Why is that?
You know the more I thing about it, I think a generator assisted system will suit me better. Maybe I can just run the lights and a radio of the solar and use the generator to charge the batteries and use the higher demand appliances.

Cariboocoot

Re: Off grid system for remote cabin

Caveman wrote: »

I noticed you added a battery charger in the scaled down version. Why is that?
You know the more I thing about it, I think a generator assisted system will suit me better. Maybe I can just run the lights and a radio of the solar and use the generator to charge the batteries and use the higher demand appliances.

There are inverters like the Outback that have a built-in charger (actually uses the inverter circuitry backwards) and then there are less expensive inverters that do not have a built-in charger. If you use one of the latter and want to charge from an AC source like a generator you need a stand-alone battery charger.

Caveman

Re: Off grid system for remote cabin

Ok, thanks. Would it be a good idea to get one of those multi-stage chargers?

Cariboocoot

Re: Off grid system for remote cabin

Caveman wrote: »

Ok, thanks. Would it be a good idea to get one of those multi-stage chargers?

Yes; they don't perfectly duplicate the solar charging but they are a lot closer to it than a standard automotive charger.
However, if the budget is a concern and you understand the automotive charger will not bring the Voltage up to Absorb level (much less hold it there or drop back to Float) they can be used to Bulk the batteries so that they won't be below 70% and sulphate too quickly. (Gets a bit tricky using them above 12 Volt systems as you either have to use multiple chargers at once or do a messy swap-around.)

westbranch

Re: Off grid system for remote cabin

here is a thread about chargers and a small Inverter type genset full of good info.8)

http://forum.solar-electric.com/showthread.php?10123-Question-about-battery-charger-selection-with-EU2000-generator

Caveman

Re: Off grid system for remote cabin

Well now I need help installing it. What things do I need to buy in addition to the main components? Any instillation tips?

Photowhit

Re: Off grid system for remote cabin

Lots of fusing and code things...

A fuse on each string if you have more than 1 string of batteries, and a combiner box with fuses or breakers if you have more than 2 strings of panels.

Also you will want a DC breaker sized for you inverter and may want an array disconnect/breaker.

Midnite makes some E-Panels and DC disconnect boxes that help people meet code and/or ease instalation.

Caveman

Re: Off grid system for remote cabin

I almost always build to code because there are good reasons for those codes to exist. That being said, there are no codes out here, so I won't have any local guidance. Is there somewhere on this site or elsewhere that details how to set up some of the more technical aspects of a system?