Combining SQFlex PV direct with grid tie [RE-wrenches]

[Kurt Albershardt]

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I've thought about this type of application for awhile and it appears we now have a project that needs it:

900-1000W PV array feeding an SQFlex with DC.  When the pressure tank is full, the PV is switches over over to a small grid-tie inverter (SB1100?) to sell power.  This way, there is always water pressure even when the grid goes down (several times per year out there) and water pumping takes priority over selling power.  I figured a DPDT Pumptrol would do the trick but I haven't located one of those just yet.  More complex control arrangements are possible of course, but would involve grid 
powered relay coils and extra parts.  We could AC power the pump, eat the inverter losses, and provide a manual changeover (double throw safety switch) but it seems there ought to make this work correctly by default.

Anyone tried this?  Possible AHJ issues as well, but those can be worked around sometimes.










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