Sharing water pump PV with house PV

azrcazrc Solar Expert Posts: 43
If I go with a DC BEC water pump (seems to be the prevailing wisdom), but do not need continuous daylight pumping, what is the best way to share panels with the house electrical system?

MPPT charge controllers seem to max out around 150c while the pumps seem to like upwards of 180v. Can I have two separate wiring systems separated by a switch or breaker of some type? If I am not pumping water, I would like to divert more power to the batteries.

I have not seen a breaker that seems to have been made for this purpose.

tia

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Sharing water pump PV with house PV

    There's no simple solution here, for just the reasons you've noted.
    The water pump wants a dedicated high-Voltage PV array it can draw from whenever there's enough current to accomplish anything. No charge controller, no batteries.
    The battery-based system requires lower array Voltage and a controller to keep Voltages in-line.
    You'd have to have a switch set up that could "rewire" the pump array into something more suitable for a charge controller to take, and possibly another controller if the resultant re-worked array wasn't compatible with the existing battery array.
    And then you'd have to switch it back when you wanted water.
    So double the wires coming down from the "water pump array", a two-pole switch to change out the middle from series to parallel with the ends, different fusing to make sure the new circuit was properly protected, and another switch to change the resulting "half Voltage" version of the "pump array" from the pump to the battery controller (or a separate, second one if the Voltage is too high).

    On the other hand, diverting a "battery array" to another task once the batteries are fully charged is easy.

    The idea behind the "continuous daylight pumping" is to store up enough water for those times when the daylight isn't there or isn't very strong. It's another one of those "predict the future and balance the system" things.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Sharing water pump PV with house PV

    Why not just use an AC pump instead? Less efficient, but would easily solve your problem. And possibly cheaper too - so you can reinvest the savings into buying more panels.
  • azrcazrc Solar Expert Posts: 43
    Re: Sharing water pump PV with house PV
    stephendv wrote: »
    Why not just use an AC pump instead? Less efficient, but would easily solve your problem. And possibly cheaper too - so you can reinvest the savings into buying more panels.

    I had the same idea, but most people recommended against this largely due to the stress put on the inverter. Another option maybe would be to use an AC input into the DC pump controller which it looks like is an option (?)with the grundfos pumps at least, but don't know.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Sharing water pump PV with house PV

    Yep you could do that. The problem with starting motors, especially submersible pumps is the high in rush current, which means that a pump rated at say 1kW could use 2-3 times that in the first few split seconds. Usually this means you need an inverter that can cope with the extra power draw.

    So you probably have a few options:
    - DC pump with dedicated solar array = waste lots of panels when you're not pumping
    - DC pump with AC input (Grundfos sqflex only AFAIK) = expensive and a waste of most of the pump controller since you're not using the solar MPPT features
    - Single phase AC pump = could work if your inverter can handle the inrush current
    - Variable Frequency Drive connected to a 3 phase pump = less efficient, but no inrush current; more reliable 3 phase motor; gentle startup

    The last option is what I went for for 130m, 3hp pump. I've only run it from the generator, because I don't have solar yet, but my ammeter shows a gradual current increase from 0 to 7A over a period of 10 seconds (configurable in the VFD). The VFD also has some free inputs to connect sensors - I connected a float switch to mine so that it shuts down when the well is dry. VFD's have been discussed here before, try a search for "variable frequency drive".
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: Sharing water pump PV with house PV

    I looks like you can also put a VFD on a three wire single phase pump too (run / starting windings).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • azrcazrc Solar Expert Posts: 43
    Re: Sharing water pump PV with house PV
    stephendv wrote: »
    So you probably have a few options:
    - DC pump with AC input (Grundfos sqflex only AFAIK) = expensive and a waste of most of the pump controller since you're not using the solar MPPT features

    VFD's have been discussed here before, try a search for "variable frequency drive".

    Thanks, I'll search for the VFDs.

    Connecting a DC pump to AC would still go through an MPPT, so your (additional) losses would only be in the inverter. Does anyone make a DC pump that will run from 48v?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Sharing water pump PV with house PV

    Some links for you to check out:

    Sun Pumps infor & equipment (note some of the controllers say "45-90" Volts, etc)
    http://store.solar-electric.com/sun-pumps.html

    Choosing an inverter for water pumps (if you go that way)
    http://lib.store.yahoo.net/lib/wind-sun/Pump-Inverter.pdf
  • wild01wild01 Solar Expert Posts: 97 ✭✭✭
    Re: Sharing water pump PV with house PV

    If you go the ac route on the pump you can put in a grundfos SQ not an SQFlex which is a pump for dc use

    a grundfos sq has zero start surge and can be picked up for less than $600

    I used to have a nightmare dc pump holding tank system on my house (which seems to be the traditional wisdom in solar even though they never work right)and finally got sick of messing with it, I replaced it with an sq plumbed directly into the house with an 80 gallon pressure tank. the pump pulls 750 watts at startup and 1000watts at full flow, this is because grundfos uses a microprocessor in the pump itself which starts the pump slowly and brings it up to full speed over the course of several seconds.

    my pump is a Grundfos 10SQ05-160 1/2 HP 115V 3" Well Pump and I run a 20/40psi pressure switch. I shopped around and ended up paying less than 500 for it delivered. when I think about how much time I spent trying to make the other system work I figure that breaks down to about $.50 an hour

    make sure you get the right pump model for your well depth and you will never look back

    oh and grundfos even advertises it as safe for msw
    I have briefly run it on a old trace 2012 while I was changing my system over from 12 volt to 36 (sold my 12 volt psw b4 the 36 volt one came in) and it did fine.

    I can now wash clothes while running the dishwasher while showering w/o a noticeable pressure drop.
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: Sharing water pump PV with house PV

    Moved additional questions from Tulumtam to own thread here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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