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<p>I second the idea of just backing up one of the 200 A panels, and
moving critical loads there. The trouble I've seen with total
backup, is that the customers are not even aware that the grid
went down, and make no effort to curtail their usage. Then, once
the batteries are down, they are truly off line. I've had
customers even compliment our choice of circuits; they knew the
power was out because certain things went off, but still had a
very usable home. Also, on larger homes there are all sorts of
loads like steam showers, etc. that really don't need to be on,
but will drain the batteries quickly in an outage. <br>
</p>
<p>Finally, unless power outages are common, a GTB system can make
the power less reliable, not better. I quit doing them, unless
folks had numerous outages, like in Puerto Rico.<br>
</p>
<p>Ray Walters<br>
Remote Solar<br>
</p>
<div class="moz-cite-prefix">On 6/29/2025 12:35 PM, Jason Szumlanski
via RE-wrenches wrote:<br>
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<blockquote type="cite"
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<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">If you can
actually run the whole house on two Sol-Ark 15K (100A
combined output), realistically, they probably don't need
400A service. Have you done a load calc on the home? We
see lots of 400A services where they could have "gotten
away" with a 200A service. </div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">In these
cases, I always encourage the homeowner to just back up
one of the two 200A panels and move all critical loads to
that panel. If you need more spaces, add a subpanel. If
they have 400A service but only need 200A service
and demand truly whole-house backup, simply disconnect one
of the panels from the utility and instead feed it from
the backed up 200A panel as a subpanel. There's nothing
that says you can't have a 400A meter feeding a 200A main
panel protected by a 200A main breaker, and use the other
one as a subpanel, as long as the load calcs work out. You
will just have to separate neutrals and grounds and remove
the bonding jumper. Depending on the panel brand, you can
usually get a 200A breaker or feed-through kit that takes
up four spaces. </div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">Even if the
load calc for the home comes back over 200A, you can
probably easily get the backup panel under 200A of
calculated loads and just back that up. It makes no sense
to try to back up a whole home that needs over 200A
service unless you are installing a massive system, which
would be more than two Sol-Arks can handle. We encourage
people to choose non-critical loads to leave out, like
electric dryers, pool heaters, pool pumps (although this
is nice to have on a smart load), EV chargers, electric
ranges and cooktops, outdoor kitchens, hot tubs, electric
saunas, etc. This should easily get the backup panel under
200A. If you present it as a value engineering option,
it's relatively easy to get people to move away from their
"whole home or nothing" mentality.</div>
<br clear="all">
</div>
<div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">With that
said, if I am truly backing up a 400A service here in
Florida, I'm installing at least four 15K inverters, 35kW
of PV, and 120 kWh of battery capacity. And I'm
still dumping EV chargers and pool heaters during
a utility outage. I would put a 400A main service
disconnect ahead of the inverters and install a 400A DPDT
transfer switch for bypass purposes. Auxiliary generator
input goes directly to the Sol-Arks, unless the owner
wants to spring for another DPDT transfer switch to send
generator power directly to the house in the event of grid
and inverter failure.</div>
<br>
</div>
<div>
<div dir="ltr" class="gmail_signature">
<div dir="ltr"><br>
Jason Szumlanski
<div><span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Principal
Solar Designer | Florida Solar Design Group</span><br
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">NABCEP
Certified Solar Professional (PVIP)</span><br
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Florida
State Certified Solar Contractor CVC56956</span></div>
<div><font color="#333333"
face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif">Florida
Certified Electrical Contractor EC13013208</font></div>
</div>
</div>
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<br>
</div>
<br>
<div class="gmail_quote gmail_quote_container">
<div dir="ltr" class="gmail_attr">On Fri, Jun 27, 2025 at
3:06 PM scot.arey--- via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true" class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
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<blockquote class="gmail_quote"
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<div class="msg-1349004728057898872">
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<div
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Seeking your feedback and best practices.</div>
<div
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<br>
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<div
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<br>
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<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
We have a existing customer who wants to add ESS for
whole house backup. He has a 400-amp meter box with
two 200-amp panels on each side of the meter can. We
want to use Sol-Ark and HomeGrid which is our go-to
solution. Today, we have two 10KW ground mounts
feeding a grid-tied system with Fronius inverters
aggregated at the array with single set of conductors
back to the house and meter</div>
<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
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<div
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Option 1: Add a SolArk 15KW and HomeGrid '4-stack' per
each 200-amp panel and in essence have two separate
systems each backing up their own panelboard. Seems
easy but I know the panels are not totally balanced
and this seems like I'm having excess capacity at the
panel that powers circuits to run less than all the
time.</div>
<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
</div>
<div
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Brings me to option 2:</div>
<div
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<br>
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<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Install two <span style="font-size:16px">paralleled </span>SolArks
with two batteries again (and now a battery combiner)
and add a 400-amp transfer switch and take grid output
from meter and bring to ATS first. The GEN inputs on
ATS will be fed by aggregated LOAD outputs of the
SolArks so if grid fails, the ATS "sees" 240V and
transfers to the inverters only and opens circuit to
grid. When grid power is there, all is grid-tied and
bi-directional. I've done similar setup with Outback
Radian and ASCO 200A ATS for whole house backup.</div>
<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
</div>
<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
But this seems really complicated with lots of extra
boxes. </div>
<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
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<div
style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Take the simple-easy route even if one inverter is a
bit too much for one of the 200-amp panels? Ot
aggregate and use ATS so we can put two SolArks to
work together to address full load as one operating
output? Wall space for this is pretty good for both
options.</div>
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<b>Howard "Scot" Arey</b></div>
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<b>Owner, Solar CenTex</b></div>
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NABCEP PV Installation Professional</div>
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TECL 29755</div>
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254-300-1228 </div>
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