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

[Travis Creswell]

Hi Kurt,

We've looked at the same thing several times and only came up with similar
"kluges" so we opted to power the pump with AC and get the largest pressure
tank the available space would hold.  80-120 gallons of reserve will get a
conserving house though a 24hr power outage.  The large spun fiberglass
pressure tanks are readily available for less then $500.

Don’t forget you can't guarantee the sun will be shining during the power
outage so you're still limited by the amount of water stored in the pressure
tank.

Travis Creswell
Ozark Energy Services


-----Original Message-----
From: Kurt Albershardt [mailto:info at es-ee.com] 
Sent: Sunday, June 17, 2007 2:01 PM
To: RE-wrenches at topica.com
Subject: Combining SQFlex PV direct with grid tie [RE-wrenches]


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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