Off grid system for remote cabin

Caveman · October 2012

Hey all I'm a newbie here, my searching hasn't delivered the greatest results, so I'll start a new thread.

I am building a hunting cabin, my plan is to wire it with lights and plugs for AC, and also have some 12v lights. I would like to be able to use the system completely off solar panels, but have the ability to connect a generator to the system for poor weather or extended use. Right now the plan is that the cabin will only be used for a few days at a time, possibly a week, and mostly in the fall/winter. I would like to be able to use a microwave and a laptop if possible, among other things as well.
The more I learn, the more overwhelmed I feel. I don't know the first thing about solar. I need to know what brands to look out for, what size wiring for the 12v, how many watts of panels I'll need, etc. The cabin is 18 X 28. Are there any companies that I can talk to who can sell me a "tailor make" kit, so to speak? Should I buy it all separately? Like I said I don't know solar, but I'm pretty handy and want to learn.

Thanks in advance for any advice.

Cariboocoot · October 2012

Re: Off grid system for remote cabin

Actually what you need first is some power usage numbers. The best way to get these is to collect what you want to run at the cabin and run them at the house through a Kill-A-Watt meter. That way you'll know two vital things: the total Watts you'll use at any one time and the total Watt hours you'll use during a day. Without those numbers you are wandering aimless through a dark forest at night, and there are angry grizzly bears behind every tree.

If you have to, put the cabin wiring together first and run it off the generator to make your measurements. BTW, those little inverter-generators are your best bet. Especially as you can bring them back home with you when you're finished your expedition so they don't get stolen.

Beware of kits: they are out to sell you what they've got, which is not necessarily what you need.

If you're going to wire for 120 VAC anyway, skip the 12 VDC lights. The Voltage drop at 12 Volts is pretty heavy, so its not worth trying to get power from one end to the other. LED lights might be a good choice, albeit expensive.

You're microwave is going to draw over 1,000 Watts. That means you'd need an inverter capable of at least that much just for that. Such a size inverter will have a pretty healthy power draw for itself. You might be better off starting the gen for five minutes to warm up lunch. A small inverter (all you'd need for lights and laptop) will consume a lot less power on its own.

You've just been tossed into the tornado of solar power learning!

Caveman · October 2012

Re: Off grid system for remote cabin

Thanks for your informative post.
A few of questions;
how much does a "Kill-A-Watt" meter cost?
This inverter-generator you speak of sounds like exactly what I need, who sells them?
I can wire the cabin first, that sounds like a good plan. When I do, what is needed for the cable that the generator connects to, and does it need a disconnect when the inverter/battery system is in use? In other words, do I have to separate the solar power from the generator power?

westbranch · October 2012

Re: Off grid system for remote cabin

To add to 'Coots info, the Microwave is a tough one to manage on a 'small' PV system. without it a 'small' system is easily pulled together that will match all the other loads.

If you insist on the microwave, you should look for a genset that can handle that load and use it to 'bulk' charge your battery while it runs for an hour or so, charger or inverter-charger needed here...

hth

Caveman · October 2012

Re: Off grid system for remote cabin

hmmmm Might have to scratch the microwave. We'll see. Off I go to search "bulk charging" haha

Cariboocoot · October 2012

Re: Off grid system for remote cabin

I'll save you some trouble: here's a primer on deep cycle batteries; http://www.windsun.com/Batteries/Battery_FAQ.htm

BB. · October 2012

Re: Off grid system for remote cabin

Honda makes an euXXXXi family of inverter/generators... eu1000i (900 watt), eu2000i (1,600 watt), eu3000i (~2,800 watts, both rope pull and electric start versions are available--as I remember).

The eu2000i is similar to a standard 15 amp 120 VAC 60 Hz outlet. Very quiet (think Honda motor cycle idling) and pretty fuel efficient (eu2000i, 400 watts on 1.1 gallons of gas for ~9.5 hours; 1,600 watts on 1.1 gallons of gas for ~4 hours). A 5kW geneset may use ~1/2 gallon per hour of fuse for ~2.5kW or less loads.

My suggestion would be to get a Honda eu2000i (or eu1000i if you don't need much power), and get a big old 3.5w to 5kW noisy genset for running power tools/emergency backup).

A Kill-a-Watt type meter here (~$30) and you can usually get them at the local big box hardware store.

More or less, building a full off grid solar power system to supply most of your power (except during winter/bad weather), makes sense when you are occupying a cabin for ~9 months of the year (i.e., electric refrigerator, solar powered well pump, washing machine, laptop computer, etc.)... If this is a seasonal/weekend cabin, generally a "small solar system" with a Honda eu**** (or Yamaha, etc.) genset for running larger appliances/tools is a good compromise.

What is a small system..l. Say 2 or4 220 AH @ 6 volt golf cart batteries, 400-800 watts of solar panels, and a 300 Watt TSW MorningStar AC Inverter (600 watt 10 minute surge).

Such a system may provide around 832 Watt*Hours per day (400 watt array, 4 hours of sun per day, ~9 months of the year, excluding winter). A 800 watt array would supply 2x that amount.

Note that a standard energy start home refrigerator uses around 1,500 WH (1.5 kWH) of electricity by itself.

This is actually quite a capable system. We have folks here that live off grid in the far north on systems not much different that this (again, propane fridge, propane/wood heating, etc.).

-Bill

Caveman · October 2012

Re: Off grid system for remote cabin

Thanks guys, everyone has a piece of the puzzle for me.
What about the generator cable that powers the cabin? Does it need to have a disconnect? What should I be looking for with that. I'm thinking ill hook that up first.

niel · October 2012

Re: Off grid system for remote cabin

the part time worst time of the year for solar is what gets me here. this would be a very large system to insure power with solar during those times of the year.

i would say power things during the day with the inverter/generator(s) and these could also be used in conjunction with a good 3 stage charger to bring the battery bank up to full charge. solar can be used as an extra charge to the batteries and could maintain the batteries during times during the day of non-use of the generator or even the cabin itself. why still have batteries? because you don't want to run it at night if you could avoid it. this will reduce the gas costs some with the added solar and would reduce the solar system costs with requiring a solar setup to provide all of the required power.

the power requirements do sound like they will be large, but until you nail down the requirements better over the course of a day and the max power to be used during non generator times so as to determine the battery bank size, controller, pv w size, etc. some learning of conservation is very helpful too.

btw, i think radio shack still carries the killawatt meter.

as to a disconnect you should put a small electrical service box in complete with breakers and such to allow you to just flip either the breaker or master switch if it has one.

BB. · October 2012

Re: Off grid system for remote cabin

What you do not want to do is connect the generator output to the AC inverter's output (on or off). You will have some expensive smoke.

So, you could use a plug and cord (plug into the inverter or into the genset), or a manual transfer switch (you can find/make interlock sheet metal that connects normal AC breakers so that only one breaker set is on at a time), or even a simple/cheap automatic transfer switch (relay flips over to generator power after ~15 seconds to warm up/stabilize genset output).

Of course, there are many variations (auto start genest/transfer switch controllers, etc.). Depends what you are after (ease of use, automatic, manual, etc.).

Much of this goes back to loads--How big, how long... That will help in sizing the actual hardware needed.

-Bill

niel · October 2012

Re: Off grid system for remote cabin

good point bill. the thing is i often think in terms of what i already have as i was thinking of a inverter that has that ability to switch already there. of course some inverters such as my magnum also have the charger built in too. add a remote that has automatic generator start ability and he can cover the over use of the batteries by having the generator kick on when things go too low.

BB. · October 2012

Re: Off grid system for remote cabin

That is why it comes back to sizing for loads/battery bank... The smaller inverters are not (usually) going to have internal AC transfer switches or inverter/charger combination units, etc.

I sort of try to show all the "piece parts", then when all is "understood", we can talk about combination units 120/240 VAC outputs, etc...

Also, I like having discussions in the forum like this--Each person approaches a question from a different angle. Helps to have different views and points to ponder--And less likely some important "gotcha" sneaks through.

-Bill

Cariboocoot · October 2012

Re: Off grid system for remote cabin

If using a small inverter that does not have a built-in charger you do not necessarily need an AC transfer switch for the generator: you can have it power a separate outlet with a battery charger (which you'd need anyway) connected to the batteries. Generator powers charger, charger recharges battery, battery runs inverter. It would also be possible to use this outlet for the microwave. Not the most efficient set-up, but cheaper than buying a big inverter-charger.

Keeping the scale of the project small is an important point for a part-time application.

Caveman · October 2012

Re: Off grid system for remote cabin

That battery FAQ was great, read all of it and now have a much better understanding of batteries, thank you Cariboocoot.

Caveman · October 2012

Re: Off grid system for remote cabin

Okay, just so I can get off the ground, I'd like to go ahead and get this system up and running with the generator. Right now I've got the cabin wired for lights and plugs like a typical house going back to a 70A circuit breaker in the wall like this.
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=100176423&storeId=10051&langId=-1&catalogId=10053&ci_sku=100176423&ci_kw={keyword}&kwd={keyword}&cm_mmc=shopping-_-googleads-_-pla-_-100176423&ci_gpa=pla#.UIavUYHaGSo

I was planning on running a cable down through the wall to a shore type setup outside the building. With that in place, I can then calculate the kilowatt hours.
I actually like your idea of having a separate outlet for the microwave and/or battery charger.

Caveman · October 2012

Re: Off grid system for remote cabin

Okay, my link looks like it didn't work, here it is again,

http://www.simsupply.com/p-10887-70a-main-lug-load-center.aspx

Also interesting to note BB, the automatic transfer switch is cheaper than the manual one.

Based on what I've been reading, seems like this is the battery to get.

http://www.solar-electric.com/sunxtenagmse.html

Cariboocoot · October 2012

Re: Off grid system for remote cabin

Whoa. Time to slow down again. At this point you do not know what battery to get because the loads have not been determined. Not sure why you'd pick an AGM either; more money for the capacity than an FLA and somewhat less forgiving of mistakes.

In this case I think you can scrimp on PV a bit and just get enough to 'finish charge' the batteries (whatever they may be) and keep it charged while you're not there. Bulk charging with the generator every day may be a pain, but it will be a lot cheaper.

Considering the size of this installation, one 15 Amp breaker is probably all you need. When powered by the inverter, the inverter will fault before the breaker trips. The generator will have its own breaker built-in.

Wire it up the way you want it, run everything to the generator, monitor through a Kill-A-Watt, then you can plan the solar aspect accurately.

niel · October 2012

Re: Off grid system for remote cabin

i have to ask if a refrigerator will be among the other things at the cabin? i know it will be winter there and you could put things outside, but some, ok most, of us like the convenience of having it indoors with a controlled temp. anyhow, we need to get a better idea of the power consumption you will encounter over the course of a day with the items you intend to run. we can't speculate on more specific scenarios until we know more closely what will be required.

i will also note that you can keep all lighting as typical 120v ac as it is cheaper and easier to accommodate for even though it is another step in conversion affecting the overall efficiency, but make sure you have a dc light near the breakers, inverters, etc. just in case of a failure. this failure could be a tripped breaker to a total inverter failure and with the dc light there you can discern better what the problem is. btw fusing of the dc should be as close to the battery as possible.

coot is thinking like me to have most of the power requirements fulfilled by the generator and only some by the pvs. the pvs could also be added to in the future if planned rightly to get closer to the goal of solar primary and generator secondary.

inetdog · October 2012

Re: Off grid system for remote cabin

BB. wrote: »

What you do not want to do is connect the generator output to the AC inverter's output (on or off). You will have some expensive smoke.

So, you could use a plug and cord (plug into the inverter or into the genset), or a manual transfer switch (you can find/make interlock sheet metal that connects normal AC breakers so that only one breaker set is on at a time), or even a simple/cheap automatic transfer switch (relay flips over to generator power after ~15 seconds to warm up/stabilize genset output).

Of course, there are many variations (auto start genest/transfer switch controllers, etc.). Depends what you are after (ease of use, automatic, manual, etc.).

The variation that I like (which I have not seen discussed before) is to buy two suitable sized Air Conditioner Disconnects, the kind which has a pull out switch/jumper block which you put back in upside down to keep the load disconnected. Wire one to the generator output, and one to the inverter output, with the other side (the load side) of both going to your distribution system.
Now remove and hide one of the two blocks. The only potential downside that I have seen is that the load side of both disconnects will be live if either of them is on. That could trip up a person who is trying to work on the disconnects themselves, so put a sign on them!

The result is that you have to disconnect one before you can connect the other. It costs far less than any transfer switch that I have seen, either manual or automatic, and it is easy to implement up to about 60 Amps 220 volt. Beyond that point it gets hard to find cheap disconnects of that type.

BB. · October 2012

Re: Off grid system for remote cabin

You can buy or build an Interlock (kit) for many standard circuit breaker panels.

Attachment not found.

Generally some form of sliding/toggle lever that prevents two circuit breakers from being turned on at the same time.

Note that interlocks may not be acceptable to building inspectors (especially if you make your own). Also, people "forget" to install the interlocks or something falls off--I know one large XW 6kW system that smoked because the "service bypass" interlocks where not installed (somebody probably saw the bits of sheet-metal and screws and said "what the heck is this" and forgot about them)--And at some point the owner or installer/service person just "flipped all the breakers on".

I am sure it was an expensive repair.

-Bill

vtmaps · October 2012

Re: Off grid system for remote cabin

BB. wrote: »

Generally some form of sliding/toggle lever that prevents two circuit breakers from being turned on at the same time.

Midnite makes such a device. Its part of their ePanel. I can't seem to find it as a stand-alone part on their web site, but if you call them I'm sure they can tell you about it. It has been mentioned on this forum: http://forum.solar-electric.com/showthread.php?p=93579#post93579

--vtMaps

inetdog · October 2012

Re: Off grid system for remote cabin

BB. wrote: »

You can buy or build an Interlock (kit) for many standard circuit breaker panels.

Generally some form of sliding/toggle lever that prevents two circuit breakers from being turned on at the same time.
... (especially if you make your own).

In the US at least, to be code compliant the interlocks have to attach to the base structure of the breakers and box, so that removing the cover plate does not remove the interlock. I suspect that the one shown in your picture does not meet that requirement.
At some point, somebody will have the cover off and "just flip all the breakers", even if they should have all power off to the panel before removing the cover.

BB. · October 2012

Re: Off grid system for remote cabin

I agree, there is a big difference in designing something that is fool resistant vs fool proof.

The code compliant interlocks appear to cost well north of $70 for this "simple bits" of sheet metal.

-Bill

inetdog · October 2012

Re: Off grid system for remote cabin

BB. wrote: »

I agree, there is a big difference in designing something that is fool resistant vs fool proof.

The code compliant interlocks appear to cost well north of $70 for this "simple bits" of sheet metal.

-Bill

You can make anything foolproof, and most things engineer proof, but never physicist proof. :-)

Caveman · October 2012

Re: Off grid system for remote cabin

Okay, been real busy the last couple of days. I really appreciate all the input guys. I really want this system to be fully functional without a generator, so without getting ridiculous, I'm not too concerned about cost. To keep things simple, lets forget about the microwave and fridge. Here's what I want to be able to use out there:

Radio
Coffee maker
Crock pot
Cell phone charger(s)
a couple of lamps
Possibly a blender
and of course the light in the ceiling that's been hard wired.

Now can someone explain to me why I need to plug everything in and measure the killowatts that way. Why can't I just look at the power usage on the appliance itself? Just asking....

I should add that other people besides me will be using this cabin, so if possible I would like it to be simple enough that someone without the intimate knowledge of it that I will have can still use it. I know sometimes when you get into homemade/custom modifications, others may not understand their importance, as BB already mentioned.

inetdog · October 2012

Re: Off grid system for remote cabin

Caveman wrote: »

Now can someone explain to me why I need to plug everything in and measure the killowatts that way. Why can't I just look at the power usage on the appliance itself? Just asking....

The most important reason is that the coffee maker (for sure) and maybe the crock pot have a thermostat which turns the heating element on and off.
You can get out your stopwatch and check how long the coffee maker takes to go from startup with cold water to the point where it goes into keep-warm mode and multiply that by the nameplate wattage. And maybe see how much power it uses for keep-warm once it is finished brewing. Or you can just plug it into the KAW for day and it will keep track of how many pots of coffee you brew.

A secondary, concern is that the nameplate rating is correct only at one line voltage and depending on whether you actually have 110 volt or 120 volt of 125 volt that actual power consumption may vary.

Similarly you can look at the rated current of the lights (if you can trust it) and keep track of every time you turn the light on and off OR you can just leave it plugged into the KAW for a couple of days and know the real numbers.

The blender will probably not count for much anyway, but the power it draws will depend on the speed you set it at.

The cell phone chargers will draw a different amount of power depending on whether the phone is fully charged or not. And the KAW will show you how much the phone charger, radio, etc use when they are nominally turned off. That way you can decide whether to unplug them (or plug them into a power strip with a switch) to save the wasted energy.

Surfpath · October 2012

Re: Off grid system for remote cabin

Caveman wrote: »

forget about the microwave and fridge. Here's what I want to be able to use out there:
Radio
Coffee maker
Crock pot
Cell phone charger(s)
a couple of lamps
Possibly a blender
and of course the light in the ceiling that's been hard wired.

Now can someone explain to me why I need to plug everything in and measure the killowatts that way. Why can't I just look at the power usage on the appliance itself? Just asking....
.

Caveman, in my experience a lot of appliance labels (especially with the higher power consumption items) are not accurate. Also you want to record your average daily energy use. The killowatt meter will help you do that. Those labels can't.

Looking at your list, the outlier I see there is your coffee maker. Since it has to (essentially) boil water using a heating element it will probably pull 1000 to 1500 watts (think electric kettle). Also, those coffee makers often have digital timers, and might also use energy just on idle. We make do with an insulated french press and boil our water using gas. No watts used there, pretty good coffee.

This link for typical appliance energy use may be useful
Cheers,
Surfpath

Caveman · November 2012

Re: Off grid system for remote cabin

Been real busy, finally getting back to this project. Couldn't find the Kill-A-Watt locally, so I ordered it. Was wondering why I hadn’t received it yet until I found out that FedEx put it in my trash box out in the driveway. FedEx.....grrr
Anyway, been plugging things in and getting some numbers, Here's what I've got so far:
Radio

Plugged in for a couple hours and KWH was still at zero
Coffee Maker

.33 KWH, Plugged in 3 hrs 23 min
Crock Pot

1.68 KWH Forgot to write down the time, but it was several hours.
Cell phone Charger

0.0 KWH Plugged in for 1hr 33min
Blender

.01 KWH----6min
Combined Lights total

.09 KWH----4.54 total

Total KWH

2.11

What do I do now?

Cariboocoot · November 2012

Re: Off grid system for remote cabin

You're halfway there.

You now know you need to supply about 2kW hours per day, if that was typical use. The other number will be the maximum Watts. I suspect the coffeemaker is the big consumer there: probably 1500 Watts to 'brew up' then a regulated lower Wattage to keep warm.

These numbers are right on the 12/24 Volt system threshold. I would favour 24 as you probably want a tad more load capacity even if you never use it. And if the major load is 1500 Watts, that's 125 Amps on 12 Volt or 62.5 on 24 (roughly speaking).

So let's say you need 2kW hours on 24 Volts, plus the power to run the inverter; about 2.4 kW hours per day. (Yes I'm cheating so I can do the math in my head.) That's 100 Amp hours. If you go for 25% DOD that's a 400 Amp hour battery bank. You could do this on one string of golf cart batteries at 220 Amp hours, providing you can use power when the sun is shining. if you don't have the option to control when loads are applied you need to have the capacity available at all times. That would be two strings of golf cart batteries for 440 Amp hours @ 24 Volts. Or you can find some other battery configuration which meets this power need and suits your budget.

From there its fairly easy to plan panels & controller to recharge the batteries. Use the 10% peak charge current with 25% DOD and you get 44 Amps (so the controller must be able to handle at least that) @ 24 Volts (1056 Watts) / typical efficiency 77% = 1371 Watt array. Naturally arrays don't come made-to-order, so you find the nearest available that comes closest to that. A little more is usually preferable to a little less, but not if it's going to cost a lot more.

One example: six of these SolarWorld panels: http://www.solar-electric.com/sosu230wapo.html
That's 1380 Watts for about $1600 (not incl. taxes and shipping). Coupled with a MidNite Classic Lite for $510. You could use an Outback FX2524T as the inverter.

Again, that's just an example not a specific recommendation. Your budget has to be taken into account of course.

Caveman · November 2012

Re: Off grid system for remote cabin

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!

Photowhit · November 2012

Re: Off grid system for remote cabin

That Crock pot must be something special, I'd check out others, I had one 2 quart(?) that drew 50 watts max on low and the thermostat would shut it down a good bit, You can also discover how simple things like leaving a hand towl on top of the crock pot lid can reduce you usage.

Off grid system for remote cabin

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