Small Off Grid Cabin – looking for feedback

save_rka
save_rka Registered Users Posts: 5 ✭✭
I'm planning a small solar system to use with an existing generator
system and would like any comments you might have.
I don’t want to start into solar doing something dumb!:blush:


Load Analysis: 1000 Watt Hrs average needed per day. Load is mostly CF Lights and a TV. Assuming 80% DC to AC efficiency I’ll need 1200Watt hrs to the inverter ea. day

Inverter choice: Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC, turned off when not needed.

Charge Controller: Morningstar TriStar 45 amp MPPT solar charge controller, this way I can run a higher voltage (24v) array to feed the 12v battery bank. It will be mounted on a 125 Amp Midnitsolar Mini – DC Disconnect Power Center. and has a battery temp probe

Batteries: Concord Sun Xtender AGM, Start out with either 2ea- 12v 100ah or 2ea- 6v 300ah, drawing them down 40-50% or more if needed. If I end up needing more power I’m thinking I can increase the battery bank. We are using the cabin 6 to 8 weekends and 1 or 2 weeks or approximately 40 cycles per year. Batteries may end up on second floor (hotter location) due to space limitations.

Solar Panels
: Keocera, 2ea 130 watt panels, run in series to boost voltage. This should give me close to 800watt hrs per day in the summer. Solar panels mounted on roof of cabin.

Battery Charger: Iota Engineering 45 amp, 12 Volt charger wired to generator

Location: Mountains of Western Maine

Notes: I’m planning this system so that my batteries are charged up when I get to the cabin and I'll be staying 3 days. I’ll run my generator for 2 hours or so each morning while eating breakfast, taking showers etc. The generator is a Honda EU3000 rated at 2800w (with wireless remote nice!). Generator is used to power well pump, microwave, coffeepot, etc. Refrigerator is propane.

.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Small Off Grid Cabin – looking for feedback

    Using PV Watts for Caribou Maine, Start with 1,000 watts of panels (round number and program does not go lower than 1 kW), fixed array, 0.52 overall system efficiency for an off grid system with flooded cell batteries and an AC Inverter:
    "Station Identification"
    "City:","Caribou"
    "State:","Maine"
    "Lat (deg N):", 46.87
    "Long (deg W):", 68.02
    "Elev (m): ", 190
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 46.9"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","12.2 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.36, 58, 7.08
    2, 4.34, 67, 8.17
    3, 5.23, 86, 10.49
    4, 5.75, 89, 10.86
    5, 4.99, 74, 9.03
    6, 5.09, 71, 8.66
    7, 5.15, 73, 8.91
    8, 4.99, 72, 8.78
    9, 4.26, 61, 7.44
    10, 3.45, 53, 6.47
    11, 2.38, 35, 4.27
    12, 2.73, 46, 5.61
    "Year", 4.31, 784, 95.65

    You will generate (on average) from 35-89 kWHrs per month, of useful energy or per day:
    • 35 kWH per month / 30 days = 1.2 kWH or 1,200 Watt*Hours per 1,000 watts of panels in winter
    • 89 KWH / 30 days = 3 kWH or 3,000 WH per 1,000 watts of panels in summer
    You have 2x 130 Watt panels or ~260 watts:
    • 1,200 WH * 0.260 = 312 WH per day in November
    • 3,200 WH * 0.260 = 832 WH per day in April
    So, you will need the genset... However, you might not need to run it is as much as you are planning---That is a fairly large genset.

    If your loads are low, and you can live with pull start, you might look at an eu1000i or eu2000i if the fuel costs for the eu3000i get to be a burden.

    For the battery bank, I personally like to have batteries in series rather than parallel (no extra fusing per parallel string, fewer points to go wrong during charging/discharging/sharing of current). But either would work fine.

    The battery bank is probably sized fine for your current loads and with plans to use the generator much of the time when you are there.

    My 2 cents.;)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • save_rka
    save_rka Registered Users Posts: 5 ✭✭
    Re: Small Off Grid Cabin – looking for feedback

    Bill, thank you for the calculation and input.

    I like the Honda eu3000is due to it having an electric starter. With the wireless remote starter we leave the generator out by our shed and can just press the remote to turn it on/off. The problem we have it’s so quite we forget it’s running sometimes!

    We typically only use the place in the summer so looks like I’ll average somewhere near 800 watt hr on a good day.

    I agree with you on wiring the batteries in series. I was not aware that Concord made the SunXtender PVX-3050T until today so I’m leaning that way too.

    Anybody have any experience running the Iota Engineering DLS-45 45 Amp 12 Volt charger from a generator?

    Steve
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    hmmm. 1000wh/day and used for 3 days is 3000wh. dividing this by 12v = 250ah. assuming the use of the 300ah 6v batteries, 250ah/300ah capacity = 83.34% dod. this does necessitate the use of the generator while there as the pvs wouldn't likely keep pace with the loads while there and that's if the sun is out while there. if you want to not run the generator you would need at least 500ah of battery capacity to do it and that would need a minimum of 25a to charge at the 5% rate. in any case you can opt for a high rate of charge, and if your genny allows, for the batteries will take it.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Small Off Grid Cabin – looking for feedback

    Iota makes very good battery chargers (our host sells them too).

    I really like Power Factor Corrected (reduces AC current) and temperature corrected (remote battery temperature sensor; hot batteries need lower charging temperatures and cold batteries need higher voltage--plus AGM's are very sensitive to over charging)....

    Xantrex made a TC 20 and 40 amp series power supply... And they have a new TC-2 version that looks very nice also (includes PFC, RBTS--but so far has been difficult to get. You might ask NAWS (our host out of Arizona) or look around to see if you can find one (they have the 20 amp, but no 40 amp yet).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    Just FYi, we live off grid, use ~600 wh/day. No TV, no toaster, no microwave, but we pump our water with the solar, propane fridge(s). We have a very nice balance with ~400 watts of panel, 450 ah of battery (12 volt). This gives up a daily discharge of ~15%, a three day discharge of about 40% max, and we can recharge that 40% in one good day. (Almost, but I never let the battery go below ~75% just to preserve longevity.

    We supplement charging with a Honda Eu 1000i, running a Xantrex TC-20 charger.

    This set up works perfect for us. If you are nearer 1kwh/day, I would consider another 100 watts or so of panels. The nice thing about the Eu 1000 is that it is very fuel efficient and quiet. I wouldn't worry too much about the rope start. (although the remote is nice) The rope start Hondas are VERY easy to pull and they start on the first or second pull nearly every time!

    Tony
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    We use about 4X what Tony does. This includes electric 'frige, microwave (used sparingly and only under full charge - a whopping 1050 Watts), "full size" water pump (1/3 HP - about 850 Watts for 6 minutes per day), and digester pump (around 1000 Watts for less than 1 minute).

    Other equipment includes desktop computer & satellite Internet/phone unit, various lights, radio, occasional power tools, vacuum cleaner, et cetera. Pretty much typical household usage except no hair dryers, electric coffee pots, or big screen TV.

    System produces about 2.4 KW hours per day. We have long Summer days (up to 16 hours so 'harvest' is greater than the typical 4 hours) and uselessly short Winter ones (6 hours - barely enough sun to keep the batteries up with zero use).

    Just to give you some idea of another set-up.
  • save_rka
    save_rka Registered Users Posts: 5 ✭✭
    Re: Small Off Grid Cabin – looking for feedback

    Tony, the TV is for the kids, I don’t usually watch it even at home. My load is an estimate with lots of room for the inevitable growth once power is available at night with the generator off.

    Our well pump surges to 24a at 120v on start up, then drops to 12a running. That surge current means I need the eu3000is to start my well. With the auto idle on the Honda I’m not using much gasoline, so I’m very happy with the generator. Plus with the wireless remote I can pump water without leaving the cabin. It does start very well with the rope as well (like when I forget to turn the key off and leave for 3 weeks).

    My thought on the Iota Engineering DLS-45 45 Amp 12 Volt charger is it will be charging the batteries at a good rate while the generator is running.

    Bill, I’m planning on buying most of my solar equipment from our host (I just think it’s the right thing to do)

    Steve
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    Don't misunderstand,, I am not editorializing about TV,, we just choose not to bother, nor the generator for that matter, I am only commenting on my situation.

    My neighbour has an IOTA and is very happy with it.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Small Off Grid Cabin – looking for feedback

    Regarding generator use---For the inverter/generators (Honda, Yamaha, etc.) you can probably load them with only 25% of rated load and get pretty good fuel economy.

    With standard gensets, they use just about 50% fuel flow for 0-50% electrical loading--So folks with large gensets and "small" electrical loads tend to spend a lot more on gasoline that they really need to...

    I would suggest a Watt*Hour meter (old utility meter) and/or kill-a-watt type meter to log how many kWHrs per gallon of fuel you are getting... An efficient genset (seems from my little bit of research) to get 5kWH-6kWH per gallon of fuel when running efficiently... If an installation is getting less than 2.5 kWH per gallon of fuel, I would review the setup and see if things can be changed to increase efficiency (either a smaller genset and/or more electrical load). [fuel=gasoline in this comment]

    The general idea is to run the genset in the morning and bulk charge the battery set--and once the current tapers down (~80-85% state of charge), cut the genset and let the solar finish charging for the rest of the day.

    -Bill

    PS: For example a 45 amp Iota charging a 14.4 volt battery with 80% efficiency:
    • 45A * 14.4V * 1/0.80 eff = 810 watts under full current...
    So, a 1,600 standard or inverter/genset to possibly a 3,200 Watt Inverter/Genset might be the best fit.

    And to only run the generator until the current charging current falls off (by a factor of 2 or more????).

    my 2 cents worth of engineering...

    PPS: "Fuel" above is gasoline---Diesel can do much better, and propane will be less (due to amount of energy per unit of between different types of fuel).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • save_rka
    save_rka Registered Users Posts: 5 ✭✭
    Re: Small Off Grid Cabin – looking for feedback

    Tony, I didn’t think you were trying to educate me on the virtues of TV :) I have formed many of my thoughts and methods for this project by looking at your and others posts in this forum. Thanks for the feedback on the Iota.

    “The general idea is to run the genset in the morning and bulk charge the battery set--and once the current tapers down (~80-85% state of charge), cut the genset and let the solar finish charging for the rest of the day.”

    Bill, that sounds like a good plan, would some kind of battery meter be my best bet for monitoring this?


    Steve
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    I think one could also make a case for running the generator at night. (if one is willing to listen to it). Assuming the gennie is big enough to power the charge and much of the expected loads, you could serve two function, add bulk charge to the batteries at a time when there is obviously no sun, but perhaps more importantly you could reduce you battery loads and ergo how much you need to charge.

    Let's assume for the sake of argument that you need to charge with the gennie 1 hour/day because your system can't keep up. 1 hour @ 40 amps (Iota) would put ~40 ah into the battery. (simple math here, no calcs for loses etc.) At the same time, let say you use (from the gennie) X number of watt hours that would other wise have to have come from the battery. The net effect is that using the gennie is ~25% more efficient simply because you are not having to replace ah into it.

    It is in essence, like the load shifting we do by pumping water in the daylight.

    All that said, many off grid cabin owners have gone solar simply to not have to hear the gennie on quiet evening, although Eu series gennies have largely changed that equation as well. The reality is, if you use X wh/day, every wh not used from the battery is ~1.25 wh you don't have to generate one way or another.

    Tony

    I don't think the above is very well written, but I think you get the idea.

    T
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Small Off Grid Cabin – looking for feedback

    I really like Battery Monitors to watch charging levels. You can scroll through and check current flow too. However, they are not cheap...

    Battery Monitors (Trimetric is a good, lower cost unit. Tony/Icarus use this one, IIRC)
    Victron Battery monitors (a couple others have recommended here too)

    Like any device, they have their limitations but they are very easy to use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback
    save_rka wrote: »
    Bill, I’m planning on buying most of my solar equipment from our host (I just think it’s the right thing to do)

    Steve

    Also a smart thing as you get great service. I just went thru a nightmare for a customer who insisted on "buying at the May sale at Sun in Miami.... Is that place one of the most F'd up organizations in the world or what.

    The charging methods the guy's posted here are all just strategies for you as the system grows and changes. When you eventually have a robust charge source/refined design life will be so much better for your family. It will be as simple as just checking that you completed charge or looking out the window at the weather. Good Luck!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • save_rka
    save_rka Registered Users Posts: 5 ✭✭
    Re: Small Off Grid Cabin – looking for feedback
    icarus wrote: »

    All that said, many off grid cabin owners have gone solar simply to not have to hear the gennie on quiet evening,

    That is exactly why I want to add some solar to my system.


    Steve
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Small Off Grid Cabin – looking for feedback

    i might add that you will also have charging losses, but maybe go forth with your plans and with upping the battery capacity as i mentioned to better accommodate your needs now and without being drawn down below 50%. the genny can only output what it outputs and your current loads on it will probably not allow simultaneous charging of a high capacity battery bank so genny charge times may be separate. to charge at a high rate with the genny may mean more than one charger like the iota to pump the current into the batteries in a shorter time frame as normal charge rates are long term. solar will help, but as you said only in the final stages of charge with a few pvs if the sun is out so you are still highly reliant on the genny while there. for stop gap charging you don't really want to be below 3% of the battery capacity for charging and this smaller rate also dictates a longer time to reach full charge as it is a 33 and a 3rd hr rate. do you think you'll get that much in full sun hours to achieve that between visits as most do not get more than 5 full sun hrs in a day even in the summer? i mention this only due to my recommending higher battery capacities as you may go under 3% with a bank at around 500ah. higher charge rates in general regardless of the source of the current will yield shorter charge times.
    if the genny runtime is too much for you to bear then maybe a 2nd genny running to charge the batteries with as the noise you want confined in a certain timeframe. the 1st genny may run the pumps, microwave, etc. while the other runs the charger circuits. it does sound easy to answer to you, but there's allot of in and outs with ifs, ands, and buts so it may need fine tuned by you later with maybe more pvs or another charger to shorten the runtime. remember the genny must supply all of the power for the chargers and with power factor involved it could almost double the power needed. example- 12v charger rated at 25a and pf of 69% would be 12x25=375w/.69=543.5w. taking it more seriously with 2 heavy chargers at say 45a could reflect 90a x 12v = 1080w/.69=1565w. the 69% power factor is a guess and you'd need to know that % for a particular charger you get.
    that 90a example for 2 hrs would only supply 180ah and if a 500ah battery represents 36% of the capacity. if you drained to 50% you may need another hour.
    i am only working through examples to show you a more reasonable approach to solving your problem yourself. i think it's doable, but it's hard to say exactly what will suffice for you. also remember what may work now may not work in the future if your loads increase.