What battery for best long term usage

Joesouth75Joesouth75 Registered Users Posts: 30 ✭✭
Hello All,
From my previous posts many of you know my set-up. Six 320v panels, 2 strings of 4 t-105's in a 24v configuration.
My question is are these the right batteries? I have a composting toilet that runs a fan and heating element, along with lights, charging phones, tv, etc. Keeping these going throughout the night is challenging. Not to mention my friends breathing machine.
Do I need more amp hours? More strings of batteries? Larger batteries? Any advice is appreciated. Thanks in advance.


  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    edited September 12 #2
    The composting toilet with the heater (and depending on the fan size), is probably your biggest killer.

    You really need to measure the current/Wattage/AH/WH of your loads and see what is happening.

    A Kill-a-Watt meter works well for 120 VAC loads... There are DC versions that do WH/AH too.


    And there are battery monitors that can tell you what the battery bank is supplying (and how well it is getting recharged):


    And lastly, you can measure AC or DC current (amps) and estimate how many hours a day they are used (the "hours" in Amp*hours):


    Lots of choices out there, and lots of different ways of accomplishing the energy usage estimates... What looks interesting to you (I have only provided a few links--There are many more choices out there).

    I don't remember where you are at--But a rough guess:

    Wausau Wisconsin
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 45° angle:
    (For best year-round performance)

    Here we are in the middle of September... Guessing 4.27 hours of sun per day, your array could produce an average of:
    • 6 * 320 [corrected] watt panels * 0.52 off grid AC system eff * 0.65 max suggested usage per day * 4.27 hours of sun (sept) = 2,771 WH per average September day (recommended "base load")
    And then there is the battery bank:
    • 6 volt * 225 AH * 8 batteries * 1/2 days storage * 0.50 max discharge * 0.85 AC inverter eff = 2,295 WH per day typical discharge of battery bank
    So--If this was a weekend place, you could take ~2,295 WH per day (2 days of poor weather) from battery bank. And, an average useful energy from your array of 2,771 WH (assuming 65% base load) without using a genset.

    Depending on your loads, they sound like the loads are are simply more than your system can supply on a continuous basis--As a guess--Need "real numbers" to be sure. And there are unknowns (AC inverters draw 6-20+ Watts just being turned on--20 Watts * 24 hours per day = ~480 WH per day just to run the inverter without any loads--~20% of your daily base production).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novakbill von novak Solar Expert Posts: 814 ✭✭✭✭
    Hello All,
    From my previous posts many of you know my set-up. Six 320v panels, 2 strings of 4 t-105's in a 24v configuration.
    My question is are these the right batteries? I have a composting toilet that runs a fan and heating element, along with lights, charging phones, tv, etc. Keeping these going throughout the night is challenging. Not to mention my friends breathing machine.
    Do I need more amp hours? More strings of batteries? Larger batteries? Any advice is appreciated. Thanks in advance.
    First off turn off loads you don't need during the night.  The composting toilet can probably live without the heater at night.  The breathing machine (I assume oxygen concentrator) is a killer - switch to bottled O2 at night.  It will be a lot cheaper in the long run.

    As the other Bill mentioned, figure out loads first, then decide what to do.  Minimizing loads is always cheaper than adding panels and batteries.
  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    Corrected a couple numbers in my above post...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 706jim706jim Solar Expert Posts: 217 ✭✭✭
    Disconnect the compost toilet. In my opinion, the heater does little but kill your batteries with little effect on the consistency of the compost. If you had more panels and more batteries it might be practical but even then a few days of cloud and your batteries will take a beating.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 26th year.
  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    If O2 concentrator, find a very energy efficient version (they have battery powered prorat portable units wit which should use less power).

    If a CPAP machine, some use a hot plate to increase humidity which increases energy usage. Again a battery powered portable system should use less power.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Joesouth75Joesouth75 Registered Users Posts: 30 ✭✭
    Yes it's a cpap. I'm thinking maybe taking 2 panels and dedicating them to the composting toilet with the existing battery banks. Then getting a few SIND model trojan batteries for the rest of the cabin. Unless anyone can recommend another battery brand.
  • EstragonEstragon Registered Users Posts: 3,043 ✭✭✭✭✭
    Before buying anything, I'd highly recommend following Bill's advice to measure your loads. The bank should be sized to support the loads for a desired time (days of gloomy weather before starting a generator), and charging sources are sized to properly charge the bank. Without a reasonably accurate estimate of loads, the chances of getting a system that works as expected are much reduced.

    For the composting toilet, have you considered ways of storing heat (eg thermal mass like stone or water) rather than storing watts? If it's doable, you could use "excess" pv available when the batteries are in absorb and/or float to heat the mass.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Solar Expert Posts: 8,030 ✭✭✭✭
    .... I have a composting toilet that runs a fan and heating element, along with lights, charging phones, tv, etc..
    Going to have to get rid of that heater.  No way can you harvest enough sun to run that heater day and night.    I looked into composting toilets, and the heater is used to boil off urine, so if you can get 50% of the population to use a tree outside, you are half way there.

    Heat is used to remedy poor compost practice - good compost generates heat via microbiological action.  Also look into the variations of a 5 gallon bucket (loveable Loo)

    I'll repost a 2010 informal survey I did when I was researching.    I ended up with a "throne room privy" for a year, using a bucket and peat moss (no wood ash), and built my house with conventional septic with 2 chamber tank.


    What I arrived at, was that the Loveable Loo style, seems to be as useful as any of the other mega-priced gadgets.  Do you turn a crank, and work some levers and hope the $$ innards stay intact, or carry a bucket outside between rainstorms ?


    1) ALL low-power composting toilets have problems with liquids, and require a urine drain or tank or a tank that must be emptied somewhere.

    2) All require carbonaceous material to be added (sawdust, peatmoss or "magic mix powder $")

    And now the details:

    Q.  Anyone off grid with composting toilets, that have a real winner, or are they all losers? I'm wondering if any are worth the $1,700 price tag, or is a "throne & bucket of peat moss" the better way to go?.

    I have had an very expensive sunmar and it was the worst "investment" ever made.
    I have 5 other friends with SunMars that are very unhappy with them, for smell and inability to compost.
    You basically wind up scooping raw poop out.
    We now do the 5 gallon bucket Humanure thing and we love it.
    We're making lots of compost for the orchard and our toilet cost less than $20 to build.
    Good luck to you!

    Mike, been using a mid line sun-mar for 4 years and have nothing but good things to say about it.  I think it went for ~$1100 and it has paid for itself in water, power and personal responsibility enhancement.  Needs a light dimmer to cut down the noise and power consumption and could use a little higher seat - which is a standard mounting item.  I would go to the larger unit if more people or money allowed.

    I have an envirolet composting toilet. It is  low water flush. If I had known what I know now I would have bought a toilet  and done the composting part myself with a 50 gal drum and small gravel leach area. Save the money and do it yourself.... speaking from experience. let me know if you have any questions...

    We have a rotating drum composting toilet.  It is a real pain in the xxx
    to clean out.  And the stuff isn't really composted no matter how much
    moldy bread, peat moss or green stuff you add. If I had it to do over, I
    would get a hospital-type potty chair, put a bucket under it, and use
    peat moss, saw dust or kitty litter.  Then, if using peat moss or saw
    dust, dump it out in a safe place to compost for a few years. Use to
    dress ornamental plantings.  If using kitty litter, line your bucket
    with a plastic bag first, then throw the thing in the garbage when it's

    I never had one myself, but a couple of folks I know got the factory units, and it seems like a lot of money for little real advantage. The compost method works fine with proper attention. I have one that's been going strong for almost 30 years - pretty much just a standard outhouse built on top of a concrete double-bin. The bucket & peat moss thing is effective, but requires a little more fussing. You can do it.

    if you are interested I have a new one that you might buy for $840... I hardly ever need it, so when using the cabin, we just take the shovel... my property is steep, so hurling it down the hill, seems to be good enough, every now & again.
    re composting toilets, I'd have it outside in a separate little closet type room, only use for # 2 and use Kombutcha & baking yeast w the peat moss. Burn the paper in a coffee can, after each use, and the small room takes on the odor of the burnt paper, highly preferable smell.

    ok  so heres my feedback
    after the bucket & ashes/sawdust mess in the 70’s, my 3 grown boys still talk about the out house days to friends, its like a badge of accomplishment, I moved up the hill to a real house w/ a sunmar, non electric throne. it had the drum that got turned & emptied into a drawer which we dumped in a compost bin w/ 2 compartments. we would fill one side & then let it sit for 6 months to break down while we used the other side, back & forth. the aged compost we spread out over flowers & trees & forest land. (did the same when we emptied bucket in the ‘old days’. ) there was just 2 of us using the sun mar throne, & the tp got burned, & we had a separate pee pot. (a bar sink w/ toilet seat, w/ spray wand for ‘flushing’.) the boys, my kids & male grandkids I asked to pee outside when they visited. I did find that peat moss is a much better mix for covering poop. .unless its aged sawdust the breaking down of it depletes the nitrogen & it hangs out
    instead of breaking down. peat moss also better for smell & finished product. so the throne lasted for 22 years, 2 breakdowns & more fruit flies than I ever want to see again. I used diatomaceous earth & lime to control fruit flies in cold weather. the throne did not have a heat unit (off grid) or fan to keep condensation down. it was also in a almost detached small room w/ out heat cept what came fm water heater that shared the room w/ a little sink. also when the it got too wet w/ too much use it did get fruit fly problems. the last breakdown came when I could not handle another yr of ff & I wanted to rent a room in the house so I had lots of incentive to upgrade. It needed a new gear thing to turn the drum. so I let it dry out, emptied it & moved it outside w/ the intention of using it at the barn when it gets fixed. new part no problem fm company. used a bucket till I invested in the sun mar centrex 2000 ac/dc. I did a lot of investigating & asking
    around. the main thing was to get a low flush toilet inside & the compost unit outside. it has some draw backs, some points I can & will fix to make it possible to maintain it. 1) I don’t have the dc fan in flue to facilitate the drying out of condensation, pee, water. 2) it is too flat so it does not drain in a timely manner so the compost stays too wet for breaking down rapidly. 3) I was limited to where I could put it so it is not real easy to turn the drum or empty. since I have since moved to an other little house on my land w/ a regular septic system (all to code, 1st time since I bought this forest in 73.) & rented it to a person who did not want to do the drum turning or let me know when all was not well…it has suffered. the renter is gone & I wont rent it again till I get the fan in, the drum set right & a willing renter. but it is so nice to have the regular toilet when my family comes to visit. I don’t mind fooling w/ it cus its an
    upgrade for me. I also don’t use peat moss anymore cuz it not p.c.  coconut fiber is the new thing, it works great, is cheep, & smells nice. I would encourage the inside flush & outside drum depending on your willingness to maintain & do all that is called for. my finished compost from drum still goes into the same compost 2 sided bins outside. oh, the only time it has the electric fan going is when I have the genny on to charge my batteries. its not often enough cuz I have a decent solar set up. but I intend to set up dc fan. all of this new stuff was pricey but after all my experiences its going to be the best under the circumstances. no way could I get a septic set up on this hill…..however….i did set up a backwoods septic on a little trailer im renting. let me know if you want to know about that.

    h)  peatmoss bucket, and then fling it over the hill and down the cliff

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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