Water pumpimg AND Battery charging from same panels

Robert_WRobert_W Registered Users Posts: 10
Hello, first off thank you to this site and the folks here. There is a wealth of info, albeit some what daunting and a tad confusing to a novice.

Secondly, though the questions I have include water pumping in the system I believe I have a pretty good handle on the pumping side of things hence me posting this here and not in the pumping section. Hopefully that is OK. If not, please move it to the appropriate spot. I did see a similar questions asked a while back but there was never a definitive answer so I'm hoping to find one.

Our water system will be used for roughly 6 months out of the year to irrigate a small orchard and large garden. (1500 gallon tank gravity feed) Grundfos 11SQF-2 well pump, CU-200 controller with float switch and 3 - Suntech 190 watt solar panels. These are rated at 24 volts nominal each with an open circuit voltage of 45.2 and a short circuit Isc of 5.62 A each.

This leaves me with a dilemma. Most of the time the pump will not be running and that leaves me with an awful lot of power that I could be putting to use some where else. So I would like to utilize that excess.

Grundfos actually shows in one of their installation diagrams the use of battery back ups with a controller. But they do not list which controller...it's not one of theirs... and their wiring diagram seems counter intuitive. Also since I do not need battery back up on the pump, as we only need the water for irrigation when it's hot and sunny, this is a mute point.

I would like to be able to switch between pumping and charging a battery bank. But I can find no way of automatically switching from the

panels > combiner box > Grundfos CU-200 controller> pump
TO
panels > combiner box > separate 2nd charge controller > battery bank


It looks like I will need to do that manually. Which is no big deal really but I would prefer it if it was automatic. So if some one knows of a way please advise. My understanding is that since both the Grundfos and what ever controller I end up using for batteries will both be MPPT that I cannot put 2 controllers on the same set of panels. At least without a manual switch.

So on to a few questions.

The correct place to put a manual switch will be after the combiner / breaker box. One set of wires going to the the Grundfos controller and one set going to the charge controller for the batteries. Correct?

The panels will be wired in series because the pump needs a lot of voltage. This makes sense to me. Also I will need to run between 150 - 200 feet of wire from the panels to the second charge controller inside where the battery bank will be so having the higher volts for that long of run makes sense. What I'm not sure about is what gauge wire to use. If I'm correct three of these panels wired in series will run at 72 volts nominal with open circuit more like 135 volts and 5 amps. So...one of the guys at NAS says that 8 gauge wire is plenty. But that seems small to me. Is it really OK because of such high voltage? Or do I need to bury 6, 4 or 2 gauge? And will 8 gauge wire accommodate future upgrade? In other words if I want to add 3 more panels at a future date will 8 gauge handle this? That would mean 1140 watts roughly 11 amps with peak voltage of 135 or so. This seems OK but the trench is open now and I don't want to have to dig twice. (besides the fact that heavy gauge wire is STUPIDLY expensive)

Also I realize that I will need one heck of a charge controller for that much voltage but the new Outback Flexmaxs' look to be able to handle this. The plan is to set up a 24 volt 400 AH battery bank now and expand in the future.

Alright ....the parallel / series thing....and amps. Even after all the studying my brain is easily confused. Math was never my best subject. ;) So sorry for any stupid questions.

While I understand that series will add up voltage...and travel farther with less loss...and leave the amps the same....and parallel will add up amps but leave the volts the same....which is better for charging? Shouldn't more amps to the battery controller (parallel) allow the batteries to charge faster? Or does it not matter? Does the controller / charger some how make up the difference for less amps in series by having more voltage? There by allowing it to charge the batteries just as fast whether or not series or parallel? Sorry....some of these things still easily confuse.

I'm sure I'll have more questions as I go along but for now thank you for any answers. And any suggestions.....greatly appreciated.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Water pumpimg AND Battery charging from same panels

    I knew this issue had come up before. Have you looked at this thread: http://forum.solar-electric.com/showthread.php?t=10335
    I don't remember off the top of my head what the outcome was.

    You are correct about not feeding two controllers from one array, and where the switch-over needs to be. You may also need to consider using a Midnight Classic charge controller http://www.solar-electric.com/mnclassic.html which has very high input Voltage capability.

    You can get an accurate sizing of wire using the Voltage drop calculator: www.solar-guppy.com/forum/download/voltage_drop_calculator.zip

    Whether series or parallel panel connections are better for charging is irrelevant. You're feeding an MPPT controller, so the output ends up the same. There may be slight variations between S/P depending on how the controller handles different Voltages. As in they tend to be slightly more efficient with array Voltage not too far above system Voltage (usually no more than 2X). On the whole, it is not a big issue. Select the arrangement according to what you need to get the power to the controller with minimal losses. That's what's important.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Water pumpimg AND Battery charging from same panels

    It is tough to do it nicely and in a cost effective manner...

    Basically adding a battery to a solar pumping system doubles the costs (batteries, controllers, wiring, and replacement batteries every 3-8 years or so) and can reduce available power by up to 1/2...

    Many times, it is best to keep the two systems separate unless your pumping power needs are small compared to the rest of the system power needs.

    Adding a manual transfer switch and appropriately configured controllers and PV Arrays can be done.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Robert_WRobert_W Registered Users Posts: 10
    Re: Water pumpimg AND Battery charging from same panels

    Cariboocoot- thanks for that calculator....much appreciated. I still have to research the controller options. That one looks good also. Right now my most important task is the wire. The trenches are dug already for fence posts and water. And yes, that other thread was one that I had referenced but it seems that the guy gave up trying to find an automatic solution. Guess I was hoping maybe some one had found one.

    BB- I am quickly discovering that the term "cost effective" and solar power don't really go together! ;) I do realize that it's more money. But we won't be using the batteries to power the pump and it won't be running the majority of the time. So it will drive both my wife and myself nuts if we have panels mounted close enough on our property to a building to utilize ...and NOT use them. If they were smaller panels and not so much power, maybe I wouldn't worry. But 3 -190 watt panels are an awful lot to have have mounted and not use them 365 day a year. And to add more in the future would be real easy....as long as I get the proper wire buried now.

    We have a small guest house that could easily be set up to use the extra power from these panels. A necessity? No. But worth doing for other reasons to us. Besides the more independence factor....this will also be a good intro and learning experience for me as we've always planned on taking the main house off the grid when $$ permits.

    Thank you.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Water pumpimg AND Battery charging from same panels

    Personally, I would bury some PVC Conduit (rated for the size wiring you may be installing, and add a size or too), plus I would bury a 3-6" Black ABS or other material pipe (use 2x 45 bends for soft corners and put some sort of pull rope in also, easier to pull cable later) in the open trenches so you can add the stuff when you have time to make the best decisions for your needs).

    I understand the desire to use the solar if you already have it... The issue becomes that, from the back of the envelope calculations I have done, just the batteries/inverter/chargers need to produce useful AC power comes out to a minimum of $0.45 per kWH (including battery bank replacement every 3-8+ years) just because batteries age as they cycle (looking at buying power at $0.09 per kWH at night instead of paying $0.27+ per kWH during summer afternoons for Time of Use billing).

    Anyway to cut it, putting a Grid Tied system in is just much more cost effective (around $0.15-$0.30 per kWH depending on where you live, local installation costs, local utility Net Metering Plans, etc.).

    Doing it with a manual transfer switch (Switch A on, pump gets power; Switch B on, battery bank gets power; Both A+B on--can't find interlock DC transfer switch--Priceless, i.e., cannot estimate the costs of repairs--:roll:Being 1/2 way funny here, but the shared power design does require serious thought and planning).

    Relays could be used--but they take 6-12 watts to latch, and you have to worry about what happens if they weld close or operate incorrectly. DC Relays have to be much larger/heftier than AC relays of similar ratings (DC really loves to sustain an arc and weld contacts).

    It can be done, most of it will revolve around trying to match the Vmp/Imp of the array vs your pump requirements, and your MPPT solar charge controller power requirements.

    There are some new controllers coming out that can operate with Vmp in the 250-600 VDC maximum input range (Vmp-array typical would be about 2/3rd of maximum controller rating) which make it much more possible that even a year ago.

    Pretty much, pencil out your pump needs (optimal array watts, Vmp, Imp) then try to look at existing/new solar charge controllers that will operate within those limits (or you reconfigure the array from Vmp=120 VDC on pump to 60 VDC on Battery, etc.).

    The options are out there--just need to get into the details to figure out a safe way of doing it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 7,288 ✭✭✭✭
    Re: Water pumpimg AND Battery charging from same panels

    if you haven't already bought pumps and panels yet, my solution was to use a small, generic well pump wired for 240VAC, and ran it off my main inverter and battery bank.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Water pumpimg AND Battery charging from same panels

    You could also look at a 3 wire (well head capacitor) or a 3 phase 120/240 VAC pump running off a VFD (variable frequency drive)... It is supposed to be real sweet (efficient, low starting surge, variable frequency based on needed rate of flow and pressure, etc.).

    One or two people are already using them here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Robert_WRobert_W Registered Users Posts: 10
    Re: Water pumpimg AND Battery charging from same panels

    Thanks guys, appreciate the feedback.

    I will at a minimum bury some conduit with some pull rope. That is probably the best thing to do for now. It will always be better than direct bury any way. Then worry about the rest once the panels and pump are installed. First things first. Sure would be nice to get any wire though before copper goes up any more.

    But I'm pretty sold on this Grundfos system. Don't think I've read anything bad about them yet and I sure do like the convenience of the controller, pump and float already being designed to work together. I realize this can be done for less with other pumps and parts, but this seems prudent at the moment. If any one knows anything negative about them I'd sure like to know.

    I do have another question though.

    On the system quote from these folks they speced it out with a fuse holder and fuse in the combiner box instead of a breaker? Seems a bit old school. Is there a reason for this or is it just a simplicity / cheaper thing to do. I would rather use what is best.

    So....fuse of breaker?

    Thanks
  • mike95490mike95490 Solar Expert Posts: 7,288 ✭✭✭✭
    Re: Water pumpimg AND Battery charging from same panels
    Robert_W wrote: »
    this Grundfos system. Don't think I've read anything bad about them yet and I sure do like the convenience of the controller, pump and float already being designed to work together. I realize this can be done for less with other pumps and parts, but this seems prudent at the moment. If any one knows anything negative about them I'd sure like to know...

    When something fails, how long does it take to get parts? That was the 2nd reason I went with conventional well pump, contactors, float switches, motors, all are in shops all over the place. I need 2,000 gal daily for orchard drip system, so mine has to keep going.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • DaveRDaveR Registered Users Posts: 5
    Re: Water pumpimg AND Battery charging from same panels

    I have an off-grid system with eight ~200-watt panels. Two strings of two panels (nominal 60 v) are dedicated to battery charging, but the other 4 panels can be switched between that same configuration (for additional battery charging) or reconfigured to a single string of four panels (with a nominal voltage of 120 v) for water pumping. To switch between these 2 configurations, I use a pair of Magnecraft DPDT power relays (W199 series with magnetic blowouts). For double-break circuits, these relays are rated 20 amps at 110 vdc, 15 amps at 144 vdc, or 8 amps at 220 vdc. I'm not an electronics engineer, so use at your own risk.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Water pumpimg AND Battery charging from same panels

    I think this is the relay family you are using?:

    http://www.serelays.com/library/section6/105A_199.pdf

    What are you using for the coil? AC or DC? powered by one of the local panels?

    Neat idea to use a permanent magnet to "blow out" the DC arc in the contacts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DaveRDaveR Registered Users Posts: 5
    Re: Water pumpimg AND Battery charging from same panels
    BB. wrote: »
    I think this is the relay family you are using?:

    http://www.serelays.com/library/section6/105A_199.pdf

    What are you using for the coil? AC or DC? powered by one of the local panels?

    Neat idea to use a permanent magnet to "blow out" the DC arc in the contacts.

    -Bill

    Yes, that is the family of relays. I use 24 volts DC (from the main bank of batteries). The relays are for 12 volts, so I run the 24 volts through the coils of the two relays in series. I added a resistor in series so the voltage drop across each coil doesn't exceed the coil rating (110% of the nominal 12 volts).
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