Off-grid pumps [RE-wrenches]

[Kelly Keilwitz]

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Pump Wrenches,

We have an off-grid customer living on an island in Puget Sound who needs
pumps for his well and storage tank. We don't have a lot of experience with
pumping and would appreciate any suggestions.

It's a small home (~800sf) that will be used part-time for probably several
years before going full-time. The well is 151' deep, with a static water
level at 138' and a reported water column of just under 13'. The well report
says 6 gpm production. But, as this is a salt water intrusion area, we want
to pump at no more than 3 gpm. There is an existing 1000 gal concrete
storage tank in the ground about 20 feet from the well head (no elev
change). Considerations are low-water sensor shut off and, probably
grit-tolerance of the pump (or some way to keep grit out), as the pump will
have to be located close to the bottom of the well.

The power system is not in-place, or even designed yet. But we're
contemplating an Outback PS-2 system starting with one FX2548 inverter. The
batteries (48V) and inverter will be about 50 feet from the well head.

I'm trying to weigh the pros and cons of either using a more expensive
battery-based, more efficient positive displacement (?) well pump or a less
expensive, but more power hungry soft-start 120V AC pump running off of the
inverter. If the energy savings of a more efficient pump (and keeping the
inverter off) can reduce the needed PV array size, then it will be a good
thing, as the PV array will probably live in a tree.

I've only considered the Grundfos SQ Flex, so far, as I'm not up on other
currently available pumps. The differences in cost between the 120V
soft-start pump and the SQ flex seem to be around $1000, not considering
larger wire sizing for the DC. I don't see the power needs of this place
needing more than one inverter, even using the AC pump - but have been
surprised before. 

This customer also needs a pressurizing pump from the storage tank. There is
less than 10 feet suction head from the bottom of the storage tank to the
power house, where the pump will be located.

I would appreciate any suggestions and recommendations.
Thanks,
-Kelly


Kelly Keilwitz, P.E.
Whidbey Sun & Wind, LLC
Renewable Energy Systems
NABCEP Certified PV Installer
987 Wanamaker Rd, 
Coupeville, WA 98239
PH & FAX 360-678-7131
sunwind at whidbeysunwind.com
 


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