Off grid - generator and batteries to start

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  • jakenshake
    jakenshake Registered Users Posts: 14
    Re: Off grid - generator and batteries to start

    All those numbers I was slinging around were just practicing what Cariboocoot told me. In truth I'm only following a bit over half what is being discussed, so please bear with:

    BB
    I thought indicated that 57 volts is optimum output from panels to charge a 48V battery system. You disagree and say 70?

    Earlier I calculated 14 panels based on using 225 amp hour batteries, regardless of the number of batteries. So something must be wrong with my calculation because it does not consider AH x V x #Batteries = WH...which makes sense as the size of the 'gas tank'. (later in your post you seem to indicate that V x AH = WH?) To beat the dead carcass even further, if I had only one 225 amp hour battery, obviously 14 panels is too much. I searched everyone's response and can't seem to find where the number of batteries is taken into consideration when calculating number of panels.

    I plan to use Outback charge controller(s) which are MPPT according to their website. I take it that either type is fine as long as it is known up front.

    I scanned thru the thread you provided for the EU2000 charge controller. I understood that a charge controller was always placed between the panels and the batteries, and that only the inverter handled the gen charging of the batts. Maybe the terms are interchangeable? I plan to buy a 3048 or 3648 Outback FX or VFX. Maybe someone can confirm that the VFX is ideal for a protected interior installation.

    Techntrek
    I would think a charge controller for each battery would be extremely expensive. The outback charge controllers are about 5-600 dollars a pop. Maybe there is no need to spend that much? In my case, I won't need panels or charge controller(s) for a year or two because this year is just starting with the hondas, a bank of batteries, and the inverter wired into the AC panel.

    Cariboocoot
    You mentioned 50 amp hour batteries, but why not stick with 255? And again..I thought 3 x 17.7 = 53.1 was best for 48V?

    Maybe I'm biting off too much right now. I'm sold on future expandable 48V system, outback inverter and equipment in general, and this year only need 2000 watt hour per day and a 1500 watt maximum draw. All that along with the two EU2000i. Still a bit unsure as to what battery bank to start with.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off grid - generator and batteries to start

    Confused as I am, maybe I can clear up one or two issues for you.

    The panel Vmp is not the same as the charging Voltage. For a "12 Volt" system you would have a panel with a Vmp of 17.5, but the charging Voltage would be 14.2-14.8. The difference in Voltage is to make up for the inevitable losses from hot panels, length of wires, controller consumption.

    The other issue is that charging isn't a matter of just Voltage; you also have to have enough current to "push" the electrons back (boy, that is a terrible analogy). So for a 225 Amp hour 12 Volt battery you have to have 14.2 Volts minimum available at the battery and the potential for at least 11.25 Amps of current. Volts * Amps = Watts, so 159.75 Watts minimum - after losses. The array size minimum would be around 207 Watts. At least. For a "48 Volt" system you basically multiple Voltage (but not Amperage) by 4: at least 56.8 Volts and at least 11.25 Amps for 639 Watts after losses. The array size would be 830 Watts using the same loss allowances.

    Whereas you can recharge a 12 Volt battery with any Voltage above the 14.2 minimum (again, at the battery - not the same as Vmp of the panel(s)) by using an MPPT type controller to optimize output it can be somewhat more difficult to come up with the right size array for a higher Voltage system because not all panels have the right Vmp to add up to proper charging Voltage.

    Then you can run in to the other problem with higher Voltage arrays: too high a Voc for the charge controller to handle. Something like the MX60 can handle 150 Volts maximum, but when temperatures drop panel Voltage goes up so an array that looks like it's within specs at "room temperature" may cause the controller to shut down in Winter. Midnight Solar's new controller gets around this with an input max that's rated at Voltage plus battery Voltage, which gives a margin of error in case things get a bit too high.

    Clear as mud, ain't it? :p
  • jakenshake
    jakenshake Registered Users Posts: 14
    Re: Off grid - generator and batteries to start

    Mud? Try tar. So for a place in the frozen northwoods maybe I should go back to considering a 24V system? Can I build up a 24V system to someday handle 6000 w h/day and 4000 watt peak draw...bank and panels alone?

    I found a licensed electrician familiar with PV systems to help me install everything. Now just have to figure out enough to feel comfortable laying down 5 or 6G on the right starting equipment.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Off grid - generator and batteries to start

    jakenshake, you'll still need AC-based charge controller(s) when running your genset, you just don't need solar charge controllers yet. Using 12 volt charge controllers is often cheaper because so many companies make them for the average Joe consumer. You can go to Wal-Mart and pick up a good 3 stage 12 volt charger for under $50.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off grid - generator and batteries to start
    jakenshake wrote: »
    Mud? Try tar. So for a place in the frozen northwoods maybe I should go back to considering a 24V system? Can I build up a 24V system to someday handle 6000 w h/day and 4000 watt peak draw...bank and panels alone?

    I found a licensed electrician familiar with PV systems to help me install everything. Now just have to figure out enough to feel comfortable laying down 5 or 6G on the right starting equipment.

    6000 Watt hours is about 250 Amp hours on a 24 Volt system: 500 Amp hour battery bank minimum. Entirely possible. Outback's largest single inverter is 3.6 kW, but you can double them up if needed. On the other hand Magnum and Xantrex both make 4 kW 24 V inverters.

    One configuration I had in the frozen Cariboo had three "24 Volt" panels in series. The Voc should have been "within specs" for a MX 60, but the -40 Winter temps pushed it way over and it had to be reconfigured.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off grid - generator and batteries to start
    jakenshake wrote: »
    BB
    I thought indicated that 57 volts is optimum output from panels to charge a 48V battery system. You disagree and say 70?
    As Marc says--yes, you only need around 57 volts at the 48 volt battery for proper charging... But the Vmp (and Voc) rating is based on ~75F solar cell temperature...
    I.e., in the lab/factory, they shine a bright light for a few seconds to "characterize the panel" at ~1,000 Watts/sq.meter intensity.

    Solar panels, roughly, for a Kyocera 135 watt solar panel (PDF) has an output voltage drop of -0.08 Volts per degree C---For a solar panel, they can be ~35C over ambient temperature. Say you are running a 40C day (104F), that means:
    • Cell temp = 40C + 35C = 85C
    • Voltage Drop = 85C-20C lap = 65C rise over STC (standard test conditions)
    • -0.08 volts * 65C rise = -5.2 volt drop
    • 17.7 volts Vmp - 5.2 volt drop = 12.5 volt Vmp worst case
    So--you can see on a very hot day with poor air circulation, your 17.7 Vmp panels can be ~12.5 volts--not even enough voltage to fully charge a battery bank... You can probably see +10% from the array (13.75 volts) which is slowly charging the battery bank (high float charging voltage) due to the fact that the Pmp power curve is fairly flat and you do not loose that much current at +10% Vmp.

    Realistically, from my array--I would see the rough equivalent of ~15.2 volts on a warm day (80's).
    Earlier I calculated 14 panels based on using 225 amp hour batteries, regardless of the number of batteries. So something must be wrong with my calculation because it does not consider AH x V x #Batteries = WH...which makes sense as the size of the 'gas tank'. (later in your post you seem to indicate that V x AH = WH?) To beat the dead carcass even further, if I had only one 225 amp hour battery, obviously 14 panels is too much. I searched everyone's response and can't seem to find where the number of batteries is taken into consideration when calculating number of panels.
    That VxAH is where the number of batteries is taken into account... Remember, voltage goes up if the batteries are added in series. And AH goes up if the batteries are added in parallel... Let's take the 8x batteries and add them up into 12 volt arrays:
    • 2 series batteries * 6 volt battery * 4 parallel strings * 255 AH = 12,240 WH @ 12 volt bank (1,020 AH)
    • 4 series batteries * 6 volt battery * 2 parallel strings * 255 AH = 12,240 WH @ 24 volt bank (510 AH)
    • 8 series batteries * 6 volt battery * 1 parallel strings * 255 AH = 12,240 WH @ 48 volt bank (255 AH)
    Notice that the storage energy (Watt*Hours) is the same for all configurations. However, if you only look at AH--the same number of batteries produces more AH of storage at 12 volts and less AH of storage at 48 volts.... That is why looking at AH only gets kind of confusing.

    In the above cases--since all 3 configurations all store the same amount of energy--then all would use the same size solar array based on our 5-13% rule of thumb (with a 0.77 derating factor because solar panels get hot, and loose power under full summer sun).
    I plan to use Outback charge controller(s) which are MPPT according to their website. I take it that either type is fine as long as it is known up front.
    MPPT controllers are typically more complex, have more options/functions, and are more expensive. Typically, MPPT are a good deal for >400 watt arrays and PWM are better for <200 watt solar arrays (cost and efficiency).
    I scanned thru the thread you provided for the EU2000 charge controller. I understood that a charge controller was always placed between the panels and the batteries, and that only the inverter handled the gen charging of the batts. Maybe the terms are interchangeable? I plan to buy a 3048 or 3648 Outback FX or VFX. Maybe someone can confirm that the VFX is ideal for a protected interior installation.

    There are Inverters (DC to AC), Battery Chargers (AC to DC, or even DC to DC), and Inverter/Chargers (can take AC to DC; DC to AC; and AC to AC pass through).

    The Inverter/Chargers are usually the "high tech" units. And can work like a UPS for your home--Just attach AC power, generator backup AC power, and a battery bank, and you are ready to go (after reading the "War and Peace" programming manual, and purchasing the $XXX external programming display/keyboard/computer dongle).

    The Inverters themselves can be simple or fairly complex.

    The Battery Chargers seem to be the step child of the solar RE industry. Typically simple and pretty rugged. However, not always very efficient and usually lack programmability/reconfigurability to optimize the AC Battery Chargers for the installation (limited generator capacity, remote battery temperature correction, etc.).

    There are some very nice combination Inverter/Chargers out there. You can find very efficient Inverter/chargers (high power factor and high efficiency, some even have programmable support for sizing generator inputs, etc.).

    Others folks like the separate units--if one fails, you do not loose everything (AC battery charger fails, you still have solar panels and AC inverter, etc.).

    The Honda eu2000i generator thread was because that person wanted the "ideal" separate AC Battery Charger that worked best with a small (1,600 watt) Honda genset.

    Personally, I like the idea of small loads (conservation) and small gensets (fuel efficient, not too expensive to purchase and maintain, etc.).

    If you have a large genset (to run your shop, for instance)--Then a larger "simple" battery charger is not an issue for your installation.
    Techntrek
    I would think a charge controller for each battery would be extremely expensive. The outback charge controllers are about 5-600 dollars a pop. Maybe there is no need to spend that much? In my case, I won't need panels or charge controller(s) for a year or two because this year is just starting with the hondas, a bank of batteries, and the inverter wired into the AC panel.
    As long as you run the batteries as a unified bank (i.e., 24 volt or 48 volt) and don't pull 12 volts from a couple batteries to run 12 volt loads--then you can run one charge controller across the whole 12/24/48 volt string.

    Note that the typical large charge controller is rated for maximum current regardless of 12/24/48 volts... So--the charger can manage a 4x larger wattage solar array at 48 volts than on a 12 volt battery bank.
    Cariboocoot
    You mentioned 50 amp hour batteries, but why not stick with 255? And again..I thought 3 x 17.7 = 53.1 was best for 48V?

    In the end, we like to measure/estimate the loads, then design the Battery bank. With the Loads+Battery Bank--then the rest of the system (solar panels, charge controllers, genset, AC battery charger) sizing/design works from those first decisions.
    Maybe I'm biting off too much right now. I'm sold on future expandable 48V system, outback inverter and equipment in general, and this year only need 2000 watt hour per day and a 1500 watt maximum draw. All that along with the two EU2000i. Still a bit unsure as to what battery bank to start with.
    Unless you have a need to power 12 volt DC loads--you are right on the edge of designing a 24 volt battery bank (to support the 1,500 watt peak loads).

    If you do have native 12 volt loads (say car radio, RV lighting, 12 VDC pumps, etc.)--then it may be worth going with a 12 volt bank (assuming your loads are pretty close to the battery bank).

    If this is mostly inverter loads, and/or the loads are spread around (well pump away from house, etc.)--then 24 or 48 volt may make more sense (or even driving the remote loads directly with a 120 VAC inverter or even a 120/240 VAC split phase inverter).

    There is no right or wrong answer--but getting this stuff all figured out on paper first before you start buying equipment will probably make your spouse much happier. ;)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jakenshake
    jakenshake Registered Users Posts: 14
    Re: Off grid - generator and batteries to start

    Still scratching my chin reading your posts about the panels...and my wife isn't happy about me buying any of this stuff. If it was up to her we would just hardwire the generator into panel and let it run all day.

    Future expandability is my main concern. Decided on Outback VFX 3648 inverter along with the Honda 2000s and all that on the way. Considering (4) 225ah 12V instead of (8) 6V. Can always add a row of (8) 6V in the future? Do you see any downside to the 12V batteries to start? I'd prefer to put the $ saved into some panels this year.

    Speaking of panels, any specific recommendations to charge a 48V bank in the upper midwest (type and number)? I know getting specific recommendations from you guys is like pulling teeth.

    Also, I spoke to a tech rep today who told me that as long as air is moving through my battery closet, it's not necessary to vent my batteries to outside the camp. I'm told the H gas wouldn't be enough to cause a problem as long as the air is kept moving into the main room with a fan during charging. I'm thinking a vent to the outside would freeze/reduce efficiency of the batteries anways. Comments?
  • jakenshake
    jakenshake Registered Users Posts: 14
    Re: Off grid - generator and batteries to start

    for some reason my eights were replaced by smiley faces in post below...
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off grid - generator and batteries to start

    8) eight right parenthesis becomes a smiley.

    You can click (disable similes) below, like I did here. Or use 8 ) eight space right paren to skip smiley conversion.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off grid - generator and batteries to start
    jakenshake wrote: »
    Still scratching my chin reading your posts about the panels...and my wife isn't happy about me buying any of this stuff. If it was up to her we would just hardwire the generator into panel and let it run all day.

    Your wife is stone deaf and has stock in Exxon-Mobil? :p
    Future expandability is my main concern. Decided on Outback VFX 3648 inverter along with the Honda 2000s and all that on the way. Considering (4) 225ah 12V instead of (8) 6V. Can always add a row of (8) 6V in the future? Do you see any downside to the 12V batteries to start? I'd prefer to put the $ saved into some panels this year.

    No downside to using 48V worth of 12 Volts as opposed to 6 Volts. But do you mean 225 Amp hour? That's the rating for a 6V T105 Trojan. If I were you I'd go for the best deal possible on the batteries, because you already know you want to expand in future (old and new batteries do not mix well) and it is very easy to make a mistake with the first set of batteries and shorten their lifespan considerably.
    Speaking of panels, any specific recommendations to charge a 48V bank in the upper midwest (type and number)? I know getting specific recommendations from you guys is like pulling teeth.

    That's because all panels perform about the same, so it mostly comes down to what good brand can you get where you are for a good price per Watt.
    Also, I spoke to a tech rep today who told me that as long as air is moving through my battery closet, it's not necessary to vent my batteries to outside the camp. I'm told the H gas wouldn't be enough to cause a problem as long as the air is kept moving into the main room with a fan during charging. I'm thinking a vent to the outside would freeze/reduce efficiency of the batteries anways. Comments?

    I disagree on all counts. Hydrogen gas in even a semi-enclosed space can ignite, if not explode. It rises up and will collect inside the battery compartment or at the ceiling. Doesn't take much of a spark to ignite it - especially since oxygen is the other gas that will spew forth.

    Charged batteries don't freeze unless you're in Baffin, or some other Northern settlement (-70C Winters are NOT fun). Kept charged, the batteries will have a certain amount of residual heat and will not suffer in performance from cooler temps.
  • Lois
    Lois Registered Users Posts: 7 ✭✭
    is this thread still active?
    If so can anyone explain how I could charge 6 - 6 volt batteries with a propane 6000 w generator.?
    Our situation is such that we loose power due to downed trees.  He have a golf cart with batteries we could use to run our wasser boiler pumps and controller.  so we could continue to heat our home. there are 5 pumps .9 amp and the controller that we would like to keep running. folks near us have been without power since Dec 31- 6 days now. what would I need buy to to connect the batteries to the pumps while charging the with a generator when they get low.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Welcome to the forum @Lois

    It would be better to start a new discussion relevant to your requirements rather than piggybacking on an old thread. Include details such as the pump voltage, run time etcetera to allow others to provide information.

    Are the batteries all the same age/condition ? 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.