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

Matt Tritt solarone at charter.net
Wed Jun 20 22:56:39 PDT 2007


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Oh well. No chance for a buried cistern then?

Matt

Kurt Albershardt wrote:

>
> 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.
>
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>
>
>
> --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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