Large residential system [RE-wrenches]

[Gary Higbee]

Wrenches,

I've taken on straightening out a residential system I did not design or
install, and would appreciate your thoughts. The key thing here is not money
so much as very solid performance. The owners want a hands-off system and it
must be very reliable. Show up, turn everything on, and no problems. Sure,
there can be maintenance contracts, but we want things to work very well.

THE HOUSE
This is a high-end off-grid place on a square mile of land in a warmish part
of the Cascade range in Oregon. The house is periodically visited, and when
the owners are there the loads can be very high--they occasionally entertain
dozens to hundreds of guests. Cooking and water heating are propane, but
there's a 5 ton heat pump that is run in the summer, the well pump, a hot
tub circulating system, sewage pump, and plenty of assorted house
loads--lots of CF lights (yea!), TV's, satellite internet, radio telephone,
computer and such.

THE EXISTING SYSTEM
Currently there are two SW4024's, a pitifully small (400 Ah) and fried
battery bank, a 40kW (gasp, gross overkill) diesel generator, 2.5kW of PV,
and an incomplete Harris PM unit.

LOADS
Other than not running the heat pump do any of you know how to reduce the
startup surge of the thing? I did measurements yesterday, and had a start
surge of 55 amps per leg and 20 amps per leg running. I know we're starting
a compressor here, so maybe there's not a whole lot that can be done to
soften the start...

BATTERIES
We do plan to install a much larger battery bank. It appears that
maintenance-free is quite important (unless these folks want to contract
someone to check and fill flooded cells). OK, so what is the best large
sealed cell we can get? I don't want a bunch of parallel strings, so we need
big or low-voltage cells. This is a big one, as I've got to get this
component ordered in the next few days--in preparation for a several-hundred
person gathering in a couple weeks.

INVERTERS
Though the loads are generally fairly low, when the owners are at the house
they can skyrocket. There are two separate AC load panels, and currently the
dual SW inverters feed both. We have separate feeds from the power shed to
each panel. I contemplate adding another two SW's and breaking out the main
panels so we feed each panel from each set of two SW's. In this
configuration we'd be running two stacked sets of SW's (a total of four
SW's) from the same large battery bank. Conversely we could dump the current
SW's and go with a large Outback system, or use the existing SW's and add a
set of the new SW plus units.We could also keep the existing SW's, and add
four Outback units for the second panel, though I'm concerned about mixing
inverters on the same battery bank. Thoughts?

GENERATOR CONTROL
We're using what I think is a repackaged GenMate, that used to be sold by
Wrico (a manufacturer of generator systems). Currently the unit has
intermittent reset problems, which means that if the generator does not
start on the first round the controller doesn't respond to the inverter's
request to give it another go. I have verified that the restart command is
making it out of the SW, and that the controller is not responding to a
second try some of the time. I'm told that this unit is no longer
manufactured, and that it is also very reliable. The contractor here tells
me to "just fix it." I have other generator control units out there on the
same brand of generator, and they work fine. I also have several Wrico
generators without the control units (i.e., directly inverter-driven), and
they work fine, too. Any particulars on generator control units?

GENERATOR
I'd love to see the 40kW diesel unit leave, and be replaced by something
that makes sense for this system--maybe in the 12kW range. This big machine
seems very out of line. Any of you in the West have a commercial prospect
that could use such a generator? This is a longer-term issue, as the above
are critical items to the operation of the house.

SUMMARY
This is an interesting system, which I have inherited. I want so much for
things to work well, and greatly appreciate and value your wisdom.

Thank you!

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
 Energy Trust of Oregon contracted system inspector
 ~ WindStream Solar (www.windstreamsolar.com) ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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