is there a "gradual" way into battery banks?

al128 Solar Expert Posts: 65 ✭✭✭✭
Hi there,

I am still reading up a lot concerning PV's ... and a mayor hurdle to get into off-grid is the high cost of bat's.

what would/could one do to increase capacity over time?

I understand that it "should" be avoided, but assuming that I need to spread out of pocket expense out over a period of - say - 6 or 9 months ... what configuration would you advise?

here my basic numbers: daily consumption down to 4kw/h ... 2.3kw of PV's (nameplate) ... likely bat. AHourss of the bank (12v) somewhere between 1500-2000 ... (to get a 2 day coverage @ 33-50% DoD)

cheers al


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: is there a "gradual" way into battery banks?

    save your money. Batteries need to be installed in "batches" of like

    as batteries are used, they age, and degrade. A new battery introduced into an old pack, will quickly degrade to the age of the pack. Throw a new battery with some 4 year old ones, and you will quickly age the new battery, from what I hear. No easy way around it that I have heard of.

    Buy a cheap set of golf cart batteries for your first bank, use it, learn from it, and ruin it. (nearly everybody ruins their first set of batteries.)
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • Redford
    Redford Solar Expert Posts: 38 ✭✭
    Re: is there a "gradual" way into battery banks?

    I wish there were. Unfortunately due to the reasons mike listed, it is not advisable. I started out with just one circuit of lights, and two deep-cycle batteries which I manage to ruin in a short time. So I bought another set, of ones that were a little more expensive, which I'll try to take care of better. I am now running 4 circuits of lights off them and am learning a lot more everyday. Someday I'll buy some really good ones, but I still have a lot to learn.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,491 admin
    Re: is there a "gradual" way into battery banks?


    Since you are in Santiago Chile, and you are trying to build an "emergency" backup system for possible 2 hour daily grid power failures--perhaps you best bet it is get the batteries first with a good inverter, with integrated transfer switch and battery charger, so the system can behave as a "giant" ups.

    At this point, you don't really need solar panels as you have, I presume, reasonably priced grid power and, so far, there are no 24+ hour outages on the horizon--you just need to time shift your power because of "rolling" blackouts.

    And, if you do end up with few multi-day blackouts, a fuel powered backup generator would be a cost effective method to power through a few of these vs going the whole off-grid solar option...

    Since you don't use much power (4kWhrs per day or 120 kWhrs per month--congratulations on good conservation measures), one of the best small gasoline generators for the job would be a Honda eu2000i (1,600 watt inverter type). Very quiet and relatively fuel efficient even down to 25% load (fridge, freezer, a few lights and a radio/small TV). A couple gallons of gas/petrol per day would be all that is required to keep your home running (15 hours@1.1 gallons of fuel @ 400 watts, for 4 hours, 1.1 gallons, for 4 hours--basically 5+kWhrs per gallon). Yamaha and a few other off-brands of Inverter/generators are out there too if the Honda is not available or too expensive in Chile to justify.

    Don't buy the very cheap 5,000 watt generators unless you are on a farm (no neighbors) and have lots of gasoline storage--these things, running small loads (like your home) are way too noisy and consume many times the fuel (with small loads) as the eu2000i. The diesel gensets are more fuel efficient--but are usually much larger than 2,000 watts and more expensive. But if you can find one that fits your needs (and does not use too much fuel at light loads)--it might be an option.

    You can install all the batteries/inverter(s) you need, and a small generator for 50% of your "total costs"--and add solar panels/charge controllers as needed, and finances allow.


    PS: Conservation and choosing which loads you want electric backup power for will also reduce the loads on your battery bank... Things that need power are few (fridge, freezer, a few lights, radio). Other optional items, microwave oven, toaster, natural gas/propane powered appliances that use AC power to operate, forced air heating (unless winter) are easy to avoid during power cuts... A clothes washer does not use that much electricity (around 0.25 kWhrs per load. An electric drier would usually not be worth powering from battery).

    Myself, I have a camp stove and always have some stored fuel to operate during power failures (mine emergency would probably be earthquake related in California).

    In the end, off-grid solar, fuel driven generators, and such are very expensive ways to generate power... Using US numbers, those usually work out to more than $1.00 per kWhr--vs our electric costs of $0.10-$0.30 per kWhr. Even a generator is 5kWhrs per gallon--assuming $5.000 per gallon fuel is around $1.00 kWhr.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • adas
    adas Solar Expert Posts: 136 ✭✭✭✭✭
    Re: is there a "gradual" way into battery banks?

    aloha, most of you know my setup, using old electric forklift batterys. I got 8 free from a freight company and they all seem to work fine. They are huge, 14" deep, by 36" tall by 38" wide and 875 AmpHours. Forklift batteries are made to last 20 years and are made very rugged to withstand, fast charging, fast discharging, opportunity charging, bumpy riding forklifts, etc. But most companies get rid of them when they will not hold a charge for the whole day but may have plenty of life left. Mine were mostly neglected by needing 1-3 liters of water per cell, after I added it, all batteries came back to life, and after an EQ charge all are holding 2.09 to 2.12 per cell. Jury is still out as to the depth of charge, but so far it is doing its job. The company was almost willing to pay me to dispose of the batteries, but I took a chance.

  • SolarJohn
    SolarJohn Solar Expert Posts: 202 ✭✭
    Re: is there a "gradual" way into battery banks?

    My system is setup in such a way that it AUTOMATICALLY disconnects the battery from the load once the battery bank reaches a certain state of discharge. Since setting this up I have never ruined a battery. My batteries have never gone below 70% SOC. Considering the cost of batteries, I would advise others to do the same. How you do it is up to you, but I use a Morningstar Relay Driver (which is simply a voltage controlled switch), for this purpose. The relay removes the load when battery voltage declines to a certain point. I also use a delay so that a temporary voltage drop caused by a sudden power surge (like a compressor kicking in), doesn't prematurely trigger load disconnection.
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: is there a "gradual" way into battery banks?

    Simply no 2 your question but I bought 8 yr old batteries 3 yrs in with TLC going well,$2400 second hand $19,000 new if I get five years Im smiling and im saving for new cos I will have made corrected and eliminated most battery mistakes.

    Most people poo poo sh batteries but I like to think ruining $2400 is a lot smarter than killing $19,000 of lead. PS The only thing u can go on with sh batteries is provonence ie history ex bank, back up batteries 4 yrs old never been cycled other than test days is about is good as it gets if its true.:confused: