Help with Battery Set Up for Off Grid Cabin

BobCobbBobCobb Registered Users Posts: 3
I have an off grid cabin that we are currently living in full time using only a pair of Honda EU2000i generators for power while we put the cash together for our actual solar set up. We have the cabin wired as a regular on the grid house would be wired and have a plug run to a shed outside where the Hondas are housed.

Up until a couple of weeks ago, we are able to use just one to power everything we use (small fridge, small freezer, lights and ceiling fans, etc.). We would run the generator for 6 or 7 hours in the morning, shut it down and run it for another 5 or so hours in the evening before bed, shut it down and start over again in the morning. It would run for a total of 10-12 hours a day using about 1 1/2 gallons of gas. This set up proved to be fine with maintaining temps in the fridge and freezer and all was well.

As the temperature has gotten hotter over the past few weeks, we have started using the parallel feature of the Hondas to run a small window unit AC to cool the house during the hottest part of the day. Again, this is working well.

Now we are finding we need the ceiling fans at night to stay cool so the one Honda is being run for over 20 hours a day. Alot of gas and wear on the unit.

I am looking for help in putting together a set up with batteries that will allow me to charge them during the day while the generator is running and use them at night to power the 2 fans we need to run.

The fans each use 72 watts on high speed and I expect to run them for 8 hours each night. This would be all we needed them for.

Can someone offer me some ideas on exactly what we would need to set this up as inexpensively as possible?

Thanks in advance.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    Welcome to the forum.

    What you propose to do is not difficult and quite a reasonable step towards full solar off-grid: batteries + inverter to run things, generator to recharge batteries until you can afford the solar. I actually ran my system like this for several months while waiting for a missing piece to arrive.

    First thing to do: get a Kill-A-Watt meter and measure all those loads you are now running off the generator. With those numbers you can get a reasonable approximation of daily Watt hours, which is the basis of sizing the battery bank.

    Forget the A/C: keep running that from the gen as-needed. To size a system to supply that as well will make for a very large and expensive system, and the power won't be needed most of the time.

    In fact this sounds like a very good application for an inverter that can provide generator support, but you may not have the budget for it (you'd be looking at fairly expensive units).

    To that end, just what is the budget? Chances are you will be laying out a couple of thousand at least for just the batteries and inverter. A more accurate number will come once the Watt hours have been determined.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    BobCobb wrote: »
    I am looking for help in putting together a set up with batteries that will allow me to charge them during the day while the generator is running and use them at night to power the 2 fans we need to run.

    Welcome to the forum.

    As Cariboocoot mentioned, knowing your loads is Everything! So I won't (in this post) answer your question. What I want to mention in this post is the Federal tax credits.

    When you commission your system, if you include solar panels you will be able to claim a federal tax credit of 30% of the entire system, excluding the generator. That means your batteries, surge protectors, inverters, solar panels, conduit, digging trenches, cables, charge controllers, solar panel mounts, circuit breakers, etc are all eligible for the credit. If you hire the work out, the credit includes labor. The credit you receive for just the battery and inverter might be enough to pay for the solar panels.

    If you start out with just the batteries, inverter, and associated wiring and circuit breakers (which is a very traditional way to homestead) you will lose the credit on those items.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ThomThom Solar Expert Posts: 189 ✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    At night we use a Ryobi 18v fan . Recharge the battery during the day .
    Thom
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator
  • BobCobbBobCobb Registered Users Posts: 3
    Re: Help with Battery Set Up for Off Grid Cabin
    Welcome to the forum.

    What you propose to do is not difficult and quite a reasonable step towards full solar off-grid: batteries + inverter to run things, generator to recharge batteries until you can afford the solar. I actually ran my system like this for several months while waiting for a missing piece to arrive.

    First thing to do: get a Kill-A-Watt meter and measure all those loads you are now running off the generator. With those numbers you can get a reasonable approximation of daily Watt hours, which is the basis of sizing the battery bank.

    Forget the A/C: keep running that from the gen as-needed. To size a system to supply that as well will make for a very large and expensive system, and the power won't be needed most of the time.

    In fact this sounds like a very good application for an inverter that can provide generator support, but you may not have the budget for it (you'd be looking at fairly expensive units).

    To that end, just what is the budget? Chances are you will be laying out a couple of thousand at least for just the batteries and inverter. A more accurate number will come once the Watt hours have been determined.

    Thanks for the welcome and the reply.

    Is it really necessary for me to measure all the loads the generator is currently running if all I want the bank for is to run the 2 ceiling fans at night?

    I already know they power usage...72 watts each. I already know how much usage I need the bank to supply...8 hrs a night each.

    I know that the bank must allow enough hours to not discharge more than 40% each night before recharging.

    Is this not enough information to know what I need for the system?

    Thanks again.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    BobCobb wrote: »
    Thanks for the welcome and the reply.

    Is it really necessary for me to measure all the loads the generator is currently running if all I want the bank for is to run the 2 ceiling fans at night?

    I already know they power usage...72 watts each. I already know how much usage I need the bank to supply...8 hrs a night each.

    I know that the bank must allow enough hours to not discharge more than 40% each night before recharging.

    Is this not enough information to know what I need for the system?

    Thanks again.

    If all you want to run are the fans then that's all you need the power info for. But I think you'll find that you can improve the efficiency of your existing system by going the "gen charges batteries" route.

    72 Watts each * 2 fans = 144 Watts * 8 hours = 1152 Watt hours
    But just because the fans are rated as "72 Watts" doesn't mean they actually use 72 Watts, and with things that have motors there's this nasty little surprise called "power factor" which can cause the real power ("Volt Amps" or "VA" - the actual rating used on inverter output) to be higher than expected.

    So here's the thing: for just the fans you could use a 12 Volt system, small pure sine inverter (the loads being <200 Watts), and enough battery for 1200 Watt hours +/- (a pair of "golf cart" batteries). Pretty inexpensive, including the battery charger.
    Example:
    Two Crown batteries http://www.solar-electric.com/cr225am6vode.html (you can probably find the equivalent locally and possibly for less if you get "warehouse" brand units) $240
    Small pure sine inverter http://www.solar-electric.com/sa300wa12vos.html $150
    Battery charger http://www.solar-electric.com/ioen12vo15am.html $95

    Or about $500 total (misc. wiring bits not included).

    But if you shift your sights towards running the whole place off batteries/solar you would want quite a different system, and starting out with this small sort of set-up will prove to be a waste of money.

    In case you are wondering, your generator can probably put out enough power in a couple of hours to run the place for a whole day. How do I know? I have a Honda EU2000i that is my "cloudy day" supply for my system which runs electric 'frige, water system, comp & satellite set-up, et cetera. There is 232 Amp hours of 24 Volt battery and 700 Watts of panel that does for the power normally, but when the sun isn't present the Honda can bulk up the batteries in a couple of hours. I do not, however, have any A/C unit.

    Something to think about anyway.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    I think Coot has told you right. Having two Hondas is a huge plus, but you need to be able to use and store all the power they can produce. The reason you have to run them 20 hrs a day is storage. Running every thing you mentioned in your first post is no problem to run all night if you have the ability to store the energy. A setup to do that would take 6-8 golf cart batteries and at least a 2000 w Inverter / Charger. Two ceiling fans is a piece of cake $ 500-600. A/C, refrigerators, freezers is another issue and would require a $2,000 +/- investment.
  • BobCobbBobCobb Registered Users Posts: 3
    Re: Help with Battery Set Up for Off Grid Cabin
    enough battery for 1200 Amp hours +/- (a pair of "golf cart" batteries)

    Is this right? That seems like alot of amp hours for just the fans...

    Otherwise it seems like just what I am looking for.

    I have another question on using the inverter to feed the main breaker box.

    I currently run a line straight from a 30 amp breaker in my main 100 amp box to my Honda to power the house and love the set up.

    Can I do the same with this inverter? Just run wire from the inverter directly to a breaker in the main box to control the power. When we are shutting down the generator for the day, we would turn the breaker for the generator off and turn the breaker to the inverter on to utilize the batteries during the night and reverse the process in the morning.

    Will this work?

    Thanks again.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    Depends on the inverter you buy. If the Inverter you get has a transfer switch, it is between the generator and the panel. When you shut the generator off the Inverter automatically picks up the loads, things like your refrigerator never shuts off. A Inverter / Charger takes the incoming power and divides between loads and charging. " Generator Support " is a different, it takes the incoming power and divides it and can also combine the power of the Inverter and the generator to power larger loads. There is a lot of difference between a $100 and a $1,200 inverter, it's called features.

    I think the 1200 amp hrs is a error.
  • solar_davesolar_dave Solar Expert Posts: 2,343 ✭✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    Bob I think what everyone here is trying to say is that if you size the batteries for the whole place and use the generator to charge the batteries (maybe minus the AC unit or while using the AC unit) you have done half the battle for a solar setup and the generator run times will be much less and with the charger be at a more efficient load profile for the generator, ultimately saving you fuel and run-time on the generator.

    Then once you get enough $$$ together you can add solar panels for charging and relegate the generator to low sun periods.

    The key to sizing the battery bank is knowing all the loads.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: Help with Battery Set Up for Off Grid Cabin

    I think Marc intended 1,200 Watt*Hour load:
    72 Watts each * 2 fans = 144 Watts * 8 hours = 1152 Watt hours

    So, a 12 volt battery bank sized for 2 days of storage and 50% maximum discharge would be:
    • 1,200 watt*Hours * 1/12 volt battery bank * 1/0.85 inverter efficiency * 2 days * 1/0.50 max discharge = 340 AH @ 12 bolt battery bank

    That would be ~4 golf cart batteries (4*6 volt @ 220 AH batteries would give you a 12 volt @ 440 AH battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Battery Set Up for Off Grid Cabin

    Yes, I meant 1200 Watt hours. :blush: (If they'd give me something that kills the pain instead of the brain this would be easier.)

    As for the AC wiring side, it would be a bad idea to connect the inverter to the main panel just to run the fans. Inevitably it would end up being connected to everything and one wrong breaker flip could make fireworks. If the inverter is going to be for "fans only" the wiring should be entirely isolated from the rest of the AC connections.
  • PanamretireePanamretiree Solar Expert Posts: 278 ✭✭✭✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    BobCobb wrote: »
    I already know they power usage...72 watts each. I already know how much usage I need the bank to supply...8 hrs a night

    Without getting into the load or solar aspect, we have purchased our fans here in Panama. They are the Casablanca model "Panama DC". They are expensive at $459.00 each, but it is extremely quiet and looks good. Installed one in our rental place to check out the performance - there are 6 speed settings and with the fan on "2" (1 being the lowest) the air flow matches the other fans that are operating on high. The specs are:

    Low - 2895 CFM @ 6W
    Med - 4662 CFM @ 14W
    High - 6675 CFM @ 32W

    The only other ceiling fans that I have seen with better specs are the eco fans from Emerson. Considering that good ceiling fans have a longevity of over 10 years, these are a good investment for us and an off-grid system. Amortized over 10 years gives $90.00 per year. I would think the savings in fuel alone would pay for new ceiling fans.

    Using the numbers above and putting a "fudge factor" for power in of say 3W, then on medium you would be using 17W and having extra air flow of 1600 CFM (most residential ceiling fans on high are ~3000 CFM - some more some less). This would give you 17W*8*2=272 Wh instead of 72*8*2=1152 Wh, a savings of 880 Wh per day. Even using the "Panama DC" on high is a 50% savings.

    When you get into the Energy Star rated ceiling fans, the fans are rated by CFM (still power hungry), or a combination of CFM and Wattage. Seen both down here since we have been looking for options.

    Tried my clamp meter on the wires to the fan today and did not get a reading. Wanted the real skinny on these "Panama DC" ceiling fans. Have to investigate this.

    Just MHO and $0.02 worth.

    Cheers

    Ernest
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    Tried my clamp meter on the wires to the fan today and did not get a reading. Wanted the real skinny on these "Panama DC" ceiling fans. Have to investigate this.

    The clamp meter has to go one one wire; if it is against both wires it will read zero (current traveling in one side cancels current traveling out the other).
  • Coach DadCoach Dad Solar Expert Posts: 148 ✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    BobCobb wrote: »
    Thanks for the welcome and the reply.

    Is it really necessary for me to measure all the loads the generator is currently running if all I want the bank for is to run the 2 ceiling fans at night?

    I already know they power usage...72 watts each. I already know how much usage I need the bank to supply...8 hrs a night each.

    I know that the bank must allow enough hours to not discharge more than 40% each night before recharging.

    Is this not enough information to know what I need for the system?

    Thanks again.

    BobCob-
    Does it make sense to size up your batteries, inverter and charger for just the fans today,,,,, and then throw everything away when you what to connect the rest of the cabin?
    You have gone through the trouble of wiring the cabin like a conventional house, so do yourself a favor and measure all of your loads before buying anything.

    I agree with Coot,,, forget the Air Conditioner but include everything else... What about your well pump and refrigerator?
  • PanamretireePanamretiree Solar Expert Posts: 278 ✭✭✭✭✭✭
    Re: Help with Battery Set Up for Off Grid Cabin
    The clamp meter has to go one one wire; if it is against both wires it will read zero (current traveling in one side cancels current traveling out the other).

    Will give it another go.
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