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

[Kurt Albershardt]

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Great idea, but unfortunately there's no space for a cistern on this one.  Just fitting a properly size pressure tank is going to be a challenge.





--On Wednesday, June 20, 2007 1:16 PM -0700 Matt Tritt <solarone at charter.net> wrote:
>
> Hi Travis and Kurt,
>
> Wouldn't a better method be to use a smallish battery bank with a grid-tied OB? That way you could use a DC pressure pump to draw from a cistern into your PT and not have to be concerned with loss of water pressure.
>
> Matt T
>
> Travis Creswell wrote:
>
>> 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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