Ray
You did not mention the XW, it frequency dithers so it is a pretty
straight forward setup. It also comes in 4, 4.5 and 6KW
Ryan
On 7/31/2013 2:04 PM, Ray Walters
wrote:
Hi Kelly;
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.
I'm going to offer a brief table of what I've found for my
choices:
Brand
|
Control Method
|
Pros
|
Cons
|
SMA Sunny Island
|
Frequency shift to disconnect GT inverter
|
simplest wiring, Trusted GT industry
player
|
most expensive, Freq shift can cause
other problems
|
Outback Radian
|
Remote controlled Circuit breaker
disconnects GT inverter
|
fairly simple wiring, relay and breaker
are combined, better control of battery charging
|
still expensive, not available in smaller
than 8 kw model
|
Magnum
|
Diversion load controls for battery
regulation (soon to offer AC load control)
|
lower cost, proven technology, freq shift
control offered as fail safe
|
most complicated wiring, diversion loads
not always reliable or available
|
Modsine Backup system
|
no AC coupling, just an old fashioned
backup system
|
low cost
|
complicated, needs customer interaction,
not as efficient, GT PV not used, dedicated PV modules
only charge backup system
|
Generator
|
No AC coupling, generator runs backup
loads
|
lowest cost, backup power available for
as long as outage (no batteries)
best for week long outages that only occur every few
years
|
Not Renewable, fuel storage issues,
doesn't switch fast enough to maintain computers, etc. |
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.
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.
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.
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.
I'll close with a quote from Joe Swartz in his 2012 Solar pro
magazine article :
"AC coupling is still the Wild West of renewable energy
applications"
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 7/30/2013 11:37 PM, Kelly Keilwitz, Whidbey Sun & Wind
wrote:
Ray,
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.
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.
-Kelly
Kelly Keilwitz, P.E.
Principal
Whidbey Sun & Wind
Renewable Energy Systems
NABCEP PV Installation Professional
WA Electrical Administrator
ke...@whidbeysunwind.com
PH & FAX: 360.678.7131
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.
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.
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?
For backup, it could even be mod sine, as it wouldn't be
much worse than generator power or the average UPS setup.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 7/30/2013 2:59 PM, Ray Walters wrote:
Hi All;
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?
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?
Thanks as always,
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