Large residential system [RE-wrenches]

[Gary Higbee]

Darryl, Jay, and Wrenches:

Thank you so much for the responses. It's always interesting to walk into a
system I did not design and attempt to make things right. If you haven't
been following the thread see the previous posts (saving bandwidth here...).

I have an appointment tomorrow morning with the owner to make a proposal,
and it will be something like:


INVERTER
Change out the two SW4024's for a stack of four VFX3648's, with a quad 100A
bypass on the AC end. The dramatically higher surge, 14kW operating, and
vastly higher battery charge rate would be a much better match for the needs
of this house, and for the (unfortunate) reality of the existing 40kW diesel
generator.

BATTERY BANK
Go with a an appropriate battery bank, giving the owner options. A 48-volt
string of the Surette 4KS-25P cells gives us around 1350 Ah (about 32kWh at
50% DOD). We'd be cycling like crazy with high loads, so I give the owner
the option of adding a second string OR running the generator when the loads
are extreme.

PV
The current 2500 watt array could be substantially increased in size, and
would scale well with summer A/C needs (I'll strongly push more passive
cooling, too!). Adding another 5-7.5kW of PV might almost eliminate the
substantial generator run time to feed the A/C on those hot SUNNY days.

Speaking of PV, the existing Outback MX60 was wired with the input of 15
Sharp 165's, set up as five strings of 3. Open-circuit is just under 130
volts, and I'm told this is fine (the spec has been raised). BUT whoever set
the thing up has the MX60 output into the 24-volt system. Hmm, just a quick
calc of 2475 watts/24 volts gives about 103 amps. Was anyone home?? Well, we
either must go to 48 volts, in which case we're fine, OR take the modules
up, rewire into two sub-arrays, run extra wires, and install a second MX60.
I vote we move forward to 48 volts.

GENERATOR
Keep the 40kW for now, unless a later study shows that we can make the fuel
economics pay off to change the unit out for something in the 20kW range.
With the Outback quad 100A bypass there will be plenty of fallback if
something fails. Who ever talked the owners into this monster...

HYDRO
Complete the Harris PM hydro. It looks like we'll push 500 watts or a bit
more, which should help a great deal when the seasonal water system is
running.


Any other thoughts?

Again, thank you Wrenches.

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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