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<div class="moz-cite-prefix">Hi Kelly;<br>
<br>
I agree the Radian system is appealing. Its basically uses a
circuit breaker that can be controlled like a relay as well, and
just disconnects the GT inverter.<br>
I'm going to offer a brief table of what I've found for my
choices:<br>
<br>
<table width="100%" border="1" cellpadding="2" cellspacing="2">
<tbody>
<tr>
<td valign="top">Brand<br>
</td>
<td valign="top">Control Method<br>
</td>
<td valign="top">Pros <br>
</td>
<td valign="top">Cons<br>
</td>
</tr>
<tr>
<td valign="top">SMA Sunny Island<br>
</td>
<td valign="top">Frequency shift to disconnect GT inverter<br>
</td>
<td valign="top">simplest wiring, Trusted GT industry player<br>
</td>
<td valign="top">most expensive, Freq shift can cause other
problems<br>
</td>
</tr>
<tr>
<td valign="top">Outback Radian<br>
</td>
<td valign="top">Remote controlled Circuit breaker
disconnects GT inverter<br>
</td>
<td valign="top">fairly simple wiring, relay and breaker
are combined, better control of battery charging<br>
</td>
<td valign="top">still expensive, not available in smaller
than 8 kw model<br>
</td>
</tr>
<tr>
<td valign="top">Magnum<br>
</td>
<td valign="top">Diversion load controls for battery
regulation (soon to offer AC load control)<br>
</td>
<td valign="top">lower cost, proven technology, freq shift
control offered as fail safe<br>
</td>
<td valign="top">most complicated wiring, diversion loads
not always reliable or available<br>
</td>
</tr>
<tr>
<td valign="top">Modsine Backup system<br>
</td>
<td valign="top">no AC coupling, just an old fashioned
backup system<br>
</td>
<td valign="top">low cost<br>
</td>
<td valign="top">complicated, needs customer interaction,
not as efficient, GT PV not used, dedicated PV modules
only charge backup system<br>
</td>
</tr>
<tr>
<td valign="top">Generator<br>
</td>
<td valign="top">No AC coupling, generator runs backup loads<br>
</td>
<td valign="top">lowest cost, backup power available for as
long as outage (no batteries)<br>
best for week long outages that only occur every few years<br>
</td>
<td valign="top">Not Renewable, fuel storage issues, doesn't
switch fast enough to maintain computers, etc.</td>
</tr>
</tbody>
</table>
<br>
<br>
I'm still pricing out the options, but the SI and Radian seem a
bit overkill for smaller systems. Backup inverter power of just a
couple thousand watts is all that most people need. The Magnum is
appealing, but I have quite a bit of experience with load
diversion controls from wind and Hydro systems, and I really feel
that its overly complicated for the less than 1% of the time that
the grid is out. Keeping the battery from being damaged is what's
important, but maintaining full 3 stage charging for a couple of
days a year is not. The batteries can be properly charged once
the grid returns. May be able to use Outback's ROCB with the
Magnum? That might get the best of both worlds.<br>
If I was building the entire system to start, I'd just use a
single Outback GVFX with its own PV array, and add GT inverters
and array that were independent for the rest of the GT
requirements. This project however is retrofitting an existing GT
system. <br>
I've done many backup systems in the days before Grid Tie, and
they work fairly well. Basically either the modules are not used
much of the time, or the customer has a few circuits that are on
the backup system (off grid) all the time. They operate it just
like an off grid system, the only difference is that when its time
to run a generator, they can just switch to the grid. These are
not for your average customer, but can work well for someone that
likes to save money and tinker.<br>
Another consideration is that if the battery bank is large enough
relative to the array, over charging becomes less of an issue;
especially with flooded cells that can stand a bit of over
charging ("equalization") every now and then. However, I can see
that the average small sealed battery bank hooked up to several
KWs of PV could get ruined in a day.<br>
I'll close with a quote from Joe Swartz in his 2012 Solar pro
magazine article : <br>
<br>
"AC coupling is still the Wild West of renewable energy
applications"<br>
<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 7/30/2013 11:37 PM, Kelly Keilwitz, Whidbey Sun & Wind
wrote:<br>
</div>
<blockquote
cite="mid:B906C0AF-0199-44BB-A98E-6D2164CF4660@whidbeysunwind.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
Ray,
<div>The battery-based inverter in an AC-coupled system should not
be grid-interactive. The grid passes through the BB inverter to
the grid-direct inverter(s). The BB inverter is there to create
a stable grid-like signal for the grid-direct inverters when the
grid is not present, and to manage the batteries. Thus, the
pass-through AC capability of the BB inverters normally (there
is a complicated work-around) must be able to handle all of the
PV AC output, when loads are low.</div>
<div>You probably are aware, but to make it clear in this thread:
the system needs to have some method to protect the batteries
from overcharging, as a result of the grid-direct inverter
output when the grid is down and loads can't use all the solar
energy available. With the Sunny Islands it's done by a signal
that reduces output from the Sunny Boys without disconnecting
them. With Outback and others it's done with a
installer-designed relay that disconnects the grid-direct
inverter when the battery voltage gets to a set point. We
haven't done an AC-coupled system with the Radian, yet. Sounds
like the remote controlled breaker is Outback's approved and
listed way to do it. About time.</div>
<div><br>
</div>
<div>-Kelly <br>
<div apple-content-edited="true">
<span class="Apple-style-span" style="border-collapse:
separate; color: rgb(0, 0, 0); font-family: Helvetica;
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-webkit-text-size-adjust: auto; -webkit-text-stroke-width:
0px; font-size: medium; "><font class="Apple-style-span"
size="2"><br class="Apple-interchange-newline">
Kelly Keilwitz, P.E. <br>
Principal<br>
Whidbey Sun & Wind<br>
Renewable Energy Systems<br>
NABCEP PV Installation Professional<br>
WA Electrical Administrator<br>
<a moz-do-not-send="true"
href="mailto:kelly@whidbeysunwind.com">kelly@whidbeysunwind.com</a><br>
PH & FAX: 360.678.7131<br>
</font><br>
<br>
</span>
</div>
<br>
<div>
<div>On Jul 30, 2013, at 4:23 PM, Ray Walters <<a
moz-do-not-send="true" href="mailto:ray@solarray.com">ray@solarray.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">The Outback rep got me some good info,
and I'm liking the Radian with the Remote controlled breaker
to control the GT inverter when the grid is out. I've heard
of quite a few problems related to the Sunny Island
frequency controlled system.<br>
My question is can off grid inverters like the Magnum be AC
coupled? I'm trying to get the price down, and still handle
the 240 vac input from the GT inverter.<br>
I penciled out the Radian and I was topping $10k before
installation. This customer is hoping for a solution under
$10k, and closer to $5k if possible. I think an elegant
lower cost solution for Grid tie with battery back up is in
order. A Radian Lite?<br>
For backup, it could even be mod sine, as it wouldn't be
much worse than generator power or the average UPS setup.<br>
<br>
<br>
R.Ray Walters<br>
CTO, Solarray, Inc<br>
Nabcep Certified PV Installer,<br>
Licensed Master Electrician<br>
Solar Design Engineer<br>
303 505-8760<br>
<br>
On 7/30/2013 2:59 PM, Ray Walters wrote:<br>
<blockquote type="cite">Hi All;<br>
<br>
I know AC coupled systems have been covered before, but I
have a new issue: positive grounding. A customer with an
existing 8kw Sunpower system wants to add backup. He was
put off by the high cost the Sunny Island, so I was
steering him towards a single Outback VFX coupled to just
one of his 3 inverters. The issue is how will the VFX
work with positive grounded inverters. I'm assuming that
since the two inverters will only be connected by AC, that
the positive vs negative grounding of their separate DC
systems will not matter. Any experience with this
particular scenario: Sunpower system AC coupled to an
Outback?<br>
Also, would I even need a GVFX, since the inverter would
only be used during outages (which might allow a
generator to be used later as well) A VFX should still AC
couple to the GT inverter during an outage, right?<br>
<br>
Thanks as always,<br>
<br>
</blockquote>
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