A few more gallons? [RE-wrenches]

[Gary Higbee]

Wrenches,

I installed a basic (SHURflo) submersible pump system for a client a while
back. The system fit their budget and has worked fine. Their garden and new
orchard is expanding, though, and we'd like to squeeze more water from the
system. I'm considering options for an economical solution.

Here's the current configuration: SHURflo 9300 submersible pump and
controller with low-water sensors, 2x75 watts PV modules, pump placement at
80 feet. Static level around 20 feet much of the year, dropping somewhat as
summer progresses. Well tested at 7gpm. We've got plenty of storage, just
not as much water out of the hole as we'll want in the summer.

I need to go up the mountain and stick my clamp meter on the pump wire, but
believe that in peak sun the pump is using reasonably less than the PV array
could provide. We may only be using around 1/2-2/3 of the peak PV potential,
since the static water level is fairly high until late summer (we've got a
nominal 150 watts and are likely using around 70). The idea here would be to
use a battery supplement to transfer the peak sun PV excess into later-day
pumping--essentially broadening out the pumping curve.

I'm contemplating adding deep-cycle batteries, a small charge controller,
and a low-voltage disconnect. It seems that in principle this idea should
work, though I know the system suddenly becomes more complex. It seems, too,
that the controller LCB wouldn't be doing anything, since the battery would
be the current source.

In this scheme I think the system would start pumping later in the day,
since we'd first be charging the battery. Then it should run at a fairly
uniform rate until the low-voltage cutoff turned things off. Since there
would be a lot of cycling in this I'd think we'd want to keep a relatively
high battery voltage. To reduce annual cycling I'd also probably set up
something to switch to normal PV-driven pumping in the many months when we
don't have the demand (taking care to float the batteries). I could also
consider adding a bit more PV.

Would this be worth it?

Any thoughts, suggestions, other ideas?


THANKS!

Gary

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
             Gary Higbee  (gary at windstreamsolar.com)
                     (541 )607-1818 (Eugene)
                        (541) 954-3881 (Cell)
Solar, wind, and hydro site analysis and system design
    Components dealer and installation assistance
                      ~WindStream Solar~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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