Grunfos SQF and charge controller possible from same array?

cruiser guy
cruiser guy Solar Expert Posts: 87 ✭✭✭✭
We are getting ready to open a clinic in what will eventually be a community hospital in a remote village in Sierra Leone. I have 12 – 90 watt panels powering our Grunfos SQF pump. I have only ever seen it draw about 350 – 400 watts according to the CU-200 controller display. Of course it only draws power when it needs to pump water and the rest of the time the panels are not serving any useful purpose. I’d like to make them work to the maximum possible potential thus the following question! Our Grunfos pump has the CU-200 controller and an IO-101 switch box hard wired to the breaker panel to allow us to run the pump if the panels have power either from a generator or inverter. Naturally it only makes sense to run the pump from the solar panels direct and not through an inverter.

Is it possible to connect the panels to a charge controller and battery bank at the same time as they are connected to the pump? How would one wire it to give preference to the pump when the pump needs to run?

Is there any special things I need to do to make sure this all works? The biggest problem I see is finding a charge controller that can take the fairly high voltages that the Grunfos pump requires and using that to charge a battery bank. Alternatively I run the panels in a parallel/series configuration with a lower maximum voltage, live with the lower pump capacity which of course means the pump runs longer and I am not able to get as much power into the batteries because of the pump inefficiencies due to running at reduced voltage. I’ve found Su-Kam controllers out of India that will charge 96, 110, 120 and 240v battery banks but I have no information on cost or quality. I have a Su-Kam 1400w sine wave inverter in my house for the 230vAC 50Hz duties and so far it is working great for the last 10 months.

What is the highest voltage a standard MPPT charge controller can take and charge say a standard 24vDC or 48vDC battery bank? I assume they take the voltage/amperage coming in and transform it down to what is needed/usable to charge the batteries. Are there reasonably priced charge controllers and inverters that work with higher voltages, say 96v or more other than the Su-Kam controllers? Does a higher voltage battery bank cause me other problems if one of the batteries starts to go bad? Are there 230v 50Hz chargers available to charge these higher voltage battery banks if the generator needs to be run for other purposes?

The final icing on the cake is I’d like for all of this to be upgradeable as the clinic moves from merely a clinic for minor ailments to a more full service hospital. It is planned that eventually it will have operating room capabilities. This means that at some point we’ll likely want to go to a three phase system rather than single phase (our panels are three phase with all phases tied together right now).

Here we are also dealing with running both 230vAC 50Hz and 120vAC 60Hz meaning two separate inverters. We have medical equipment from the US running on 120vAC 60Hz and the country runs on 230vAC 50Hz.

This could provide the needed power for the clinic without needing to resort to a generator and fuel and maintenance and all that is involved with that. We’ll still need the generator but hopefully not as much and only when the sun isn’t out for a few days.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grunfos SQF and charge controller possible from same array?

    In general, it is not a good idea to connect one solar array to two or more MPPT charge controllers. MPPT controllers "search" the array to find Pmp=Vmp*Imp by changing the current through the array. With several MPPT controllers attached (the Grundfos pump has an internal MPPT controller), they will confuse each other.

    I would try taking panels from the array and see if the smaller array still supplies enough water/pressure for your needs.

    Otherwise, you could install a 2 pole relay/transfer switch to switch both leads from the pump (when no needed/running) to a another charge controller. And when the pump is required, switch the relay back to the pump. I am not sure I would do this--I am worried about surge current during switching causing reduced life of the pump/charge controllers--But it should work.

    Typical high end MPPT charge controllers have around 140-150 VDC as the maximum input voltage. There are a few controllers (Midnite is one) that can operate at higher voltages (Midnite has 250 VDC maximum).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Grunfos SQF and charge controller possible from same array?
    We are getting ready to open a clinic in what will eventually be a community hospital in a remote village in Sierra Leone.

    The final icing on the cake is I’d like for all of this to be upgradeable as the clinic moves from merely a clinic for minor ailments to a more full service hospital. It is planned that eventually it will have operating room capabilities. This means that at some point we’ll likely want to go to a three phase system rather than single phase (our panels are three phase with all phases tied together right now).

    Here we are also dealing with running both 230vAC 50Hz and 120vAC 60Hz meaning two separate inverters. We have medical equipment from the US running on 120vAC 60Hz and the country runs on 230vAC 50Hz.

    This could provide the needed power for the clinic without needing to resort to a generator and fuel and maintenance and all that is involved with that.

    sounds like you need to look towards a 48V system or higher...
     
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  • cruiser guy
    cruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Grunfos SQF and charge controller possible from same array?

    So would I be better suited to run the Grunfos SQF pump straight from the battery pack and leave the charge controller to charge everything? I'd expect a loss of efficiency in doing that but it may still be worth it to harvest the power that is otherwise lost.
    If I were to run the pump straight off the battery bank I'd like to set it up in such a way that the pump is disabled from running off the batteries when there is no solar input. Having showers in the evening and that sort of thing means that the most likely time the float switch will call for the pump to run is in the evening after showers and the like. Our tank capacity is such that I'm not worried about lack of water in the evening. However I would be concerned about drawing the batteries down too far by running the pump at times of no solar power. Is there a relay or charge controller capable of operating a relay of sufficient amperage rating that could perform such a function?
    On another note, with the IO-101 switch box, I have this hard-wired into the AC panel. Is there a means to have this permanently connected yet only live when it sees the generator? I could always simply leave the breaker off but I'd like something totally automatic so if I am not here it still works.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grunfos SQF and charge controller possible from same array?

    As I recall, the SQF is more efficient above something like 60 VDC--So a 48 volt vs a 120/240 VAC inverter will probably have roughly the same efficiency at the pump (you will need to look at the specifications closely for the pump).

    The other issue is simply how far you will be sending the power--240 VAC is a lot easier to send long distances vs 48 Volts (a lot less copper in the cable).

    The Grundfos controllers have a tank full / well empty switch--You might be able to add a low power relay in one of those circuits.

    And it is easy enough to find a relay (even electronic relay) that will switch 240 VAC (note, some folks here find that the electronic relays can fail easily--so make sure you have a good sized metal heat sink and a spare relay in case something goes wrong).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guy
    cruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Grunfos SQF and charge controller possible from same array?

    Yes, the SQF is more efficient at higher voltages. According to the data I have here I loose 20% efficiency at 36v, 10% at 60v, 5% at 90v and above 120v is best.

    The "well empty" sensor is on the pump and Grunfos uses the power line for communication as well so that is out but I could hook something to the float switch line.

    Do the charge controllers generally have a set of contacts that would be capable of operating a relay when there is no solar? The Xantrex XW-MPPT60 talks about a "Configurable Auxiliary Output" but it doesn't tell me what it can be configured for.

    How much of a surge is there in the Grunfos SQF since it has a "soft start" feature. I'll need to know if I'm going to try to run this from an inverter.
  • cruiser guy
    cruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Grunfos SQF and charge controller possible from same array?

    Is there any possibility of using a current sensor of some sort so that when it senses that the pump is drawing power it cuts out the charge controller and then when the pump drops out the charge controller is active again?