Thanks for the help - System status report

bentherebenthere Solar Expert Posts: 113 ✭✭✭
Thanks to your help, our off-grid PV system is a success.

Our system is:
9 Kyocera KD205 panels in 3 strings of 3.
8 Surrette S600 batteries in a string for 450AH at 48V.
Outback 3648 inverter.
Outback FM80 charge controller.

I had estimated our power requirements to be about 4KWH/day. That looks to be about accurate as it included a chest freezer we don't have and our usage runs a little over 2KWH/day. We've been line-drying clothes and conserving but not getting too crazy about it.

Today is the first day we didn't float the battery bank. It's been overcast all day and we only put 1.1KWH in. Usually we're floating by 10:15 or so.

Anyway; the system works, we're happy with it, and I appreciate the help received on this forum!

Comments

  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Thanks for the help - System status report

    What? No pictures?

    Oh well...congrats anyway. :D
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Thanks for the help - System status report

    make sure the batteries get the opportunity to get fully charged as riding a deficit will cause the batteries to start sulfating and lead them to an early demise.
  • bentherebenthere Solar Expert Posts: 113 ✭✭✭
    Re: Thanks for the help - System status report

    Niel,

    The batteries were floating when I got home from a bike ride at 11 this am. Are you suggesting that it's a mistake to let the batteries wait at say 95% charge for the next days solar input, and that you would use the generator in such a situation? Or that you wouldn't let them have too many days in a row like that?

    Thanks,
    Ben
  • icarusicarus Solar Expert Posts: 5,244 ✭✭✭✭
    Re: Thanks for the help - System status report

    Ben,


    You're doing just fine. If you are getting to float most days you are in great shape. Most people consider going more than ~3 days without getting close to a full charge is when you begin to run into trouble.

    I like you get to float by about noon every day. Makes me think of other loads I can run on my surplus.

    Tony
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Thanks for the help - System status report
    benthere wrote: »
    Niel,

    The batteries were floating when I got home from a bike ride at 11 this am. Are you suggesting that it's a mistake to let the batteries wait at say 95% charge for the next days solar input, and that you would use the generator in such a situation? Or that you wouldn't let them have too many days in a row like that?

    Thanks,
    Ben


    the latter, " Or that you wouldn't let them have too many days in a row like that?" a few days, no problem, but as i said too long can set up sulfation so if it's getting the charge it needs within a few days it won't be much to worry about. remember it was you who mentioned it not getting its charge and i wanted to remind you of sulfation and that if you run things the next day as per usual without making a bit more allowances for the previous deficit that could be trouble down the road.

    tony,
    thanks for answering, but i can talk for myself.
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Thanks for the help - System status report

    More or less, the rough decision point is around 75% state of charge--if it goes below that, then think about cranking up the genset for some bulk charging (at least) that morning--especially if no sun and/or heavy loads are planned. The longer (and deeper) the batteries stay below 75% -- the more sulfate hardening will occur (Battery FAQ). Degradation starts within hours--becomes a big issue after days/weeks of setting discharged.

    Since you are talking about 95% state of charge--You might have a battery monitor attached? If not, I would highly recommend. Continuous undercharging of batteries (deficit charging) and over charging (boiling dry with too high of charge voltage and/or not refilling with clean/distilled water as needed) probably combine for killing the most batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,665 ✭✭✭✭✭
    Re: Thanks for the help - System status report

    Obtain a decent meter to read specific gravity! It is the best way to know state of charge. The meter Outback provides is for indication only and even when recently calibrated is just an educated guess. If you set up a log and do what Surrette recommends you probably will have good luck for a decade.

    When you get some time you can start tweaking the setpoints to minimize water use. When it is right you should only be adding water every 3 months. Another reason to measure SG.....The worst newbie mistake that will do unrepairable battery damage is not setting the current limit for charging with a generator!

    Be Good!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • bentherebenthere Solar Expert Posts: 113 ✭✭✭
    Re: Thanks for the help - System status report
    remember it was you who mentioned it not getting its charge and i wanted to remind you of sulfation and that if you run things the next day as per usual without making a bit more allowances for the previous deficit that could be trouble down the road.

    It was my intention to indicate that this was the only day I have not received a full charge to date. Not that I am operating at nearly the system's capacity or having trouble getting a full charge on a regular basis.

    My 95% figure was based on what the charge controller said it put in, an idea of what we typically put in each day, and the battery voltage. I don't have a battery monitor but it's on the shopping list.

    I do have a hydrometer, but won't be running out to use it every evening.

    I've not seen a suggestion on generator charging current, but am set to 12 amps (AC) on the inverter because that's the sweet-spot on my generator. What's the rule of thumb here?

    I've not seen a setting to cap the amps on the charge controller. My PV array can charge at a higher rate than my generator. Should I be looking for a setting like that?
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Thanks for the help - System status report

    For rates of charge (and voltages, etc.) follow the battery mfg. recommendations.

    For charging rates from your genset... probably somewhere between 50%-80% of rated load would be best. Most gensets, when the load fall below 50% of rated continuous load, there fuel flow stays around 50% -- so you are wasting fuel.

    A good way of running your genset is to fire it up early in the morning when the battery is below ~75% state of charge and run the genset until the battery is ~80-90% state of charge. Your genset charge controller will start tapering down anyway (from bulk to absorbe to float charge type)--and once the charge rate is lower--you can use the solar to finish the charging cycle off (quiet, no fuel usage).

    Depending on the make/model of charge controller--you can have an issue with Power Factor (PF)... Older charge controllers may have a PF of 0.6, newer ones may be very close to 1.0 -- which for the genset, means that a 0.6 PF charge controller increases current in the genset, but does not increase "real" power output:

    12 amps * 120 volts * 1.0 PF = 1,440 watts to be used by the charge controller
    12 amps * 120 volts * 0.6 PF = 864 watts to charge controller

    So, the generator wiring has to be sized to handle the higher currents required by power Power Factor... But it is not doing any useful work for that higher current (and wasting fuel as heat).

    In the end, the rough rule of thumb is between 5%-13% charging current (based on battery bank's 20 Hour rating).... The sum of the charging currents (solar + genset - loads) is really what you are aiming for.

    -Bill

    PS: If you have a Kill-a-Watt meter and your genset/charger is 120 VAC--it will report the PF / VA (volt*amps):

    Watts/PF = V*A
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Thanks for the help - System status report

    no problem then. hope your solar works out well and stays well.:D
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Thanks for the help - System status report

    Dave is referring to I think the possibility in some systems to be able to charge batteries at too high a current rate that would physically damage the battery.

    All batteries need to be charged in accordance with the battery manufaturers spec. This usually includes voltage settings for bulk,absorb,float and equalize if applicable .

    They also have a recomended maxcharge rate per battery capacity. 10% of capacity is a ball park figure but each battery chemistry is different and has different max ratings Im aware that some of the FLA batteries can be charge at around 15% of the A/hr capacity.

    So a system with a large AC genset and a High power Inverter Charger capable of delivering a large rate of current to a small battery bank capacity needs to be limited .

    Its usually never a problem as most people have generators smaller than the battery banks ability to accept charge and usually the current limiting facility on the inverter charger is adjusted to keep the generator happy.

    But it a real life senario with large genset and small capacity battery bank that you need to be aware of.

    Looking at your set up the max the OB inverter charger can supply is approx 10% of your battery capacity, so it shouldnt be a problem at all for you
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Thanks for the help - System status report

    And amps into the battery... Assuming an 80% efficient charge controller (if you don't have a DC amp meter handy):

    Watts * 0.80 * 1/bank voltage = charging current

    1,440 watts * 0.80 * 1/53 volts = 21.7 amps

    450 amp*hour battery bank:

    21.7/450 = 0.048 = 4.8% charge rate

    No danger of overcharging with the current setup.

    To charge your battery bank from 75% to 85%:

    (0.85-0.75% state of charge) / 0.048 charge rate = 2.1 hours of run time (assuming constant rate of charge during this period).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,665 ✭✭✭✭✭
    Re: Thanks for the help - System status report

    I or my customers check SG for each cell when new and when the days get longer in April. This allows you to lower absorb and float setpoints and use less water to get the same state of charge. Some of "my people" don't care and just put water in every 2 months. Certainly no one I know is rushing out and doing this every night.

    I only mention the limit charge because I never saw any gen set info and just wanted you to be aware. 450AH / 10% = 45 / 3.5 for 24V or / 1.75 for 48V
    This is what you should limit AC charge amps to on your inverter / charger. Pretty hard to damage with solar but I have seen it happen.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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