[RE-wrenches] Outback AC coupling Sunpower?
Eric.Bentsen at schneider-electric.com
Eric.Bentsen at schneider-electric.com
Wed Jul 31 13:53:52 PDT 2013
Hi Brian,
The issue is in backup mode, any grid tie source that exceeds the rating
of a single XW could potentially
overload the XW, because it will not necessarily split the power amongst
the other XW units.
You can certainly have separate single inverter AC coupled systems feeding
the same main panel.
Eric
_____________________________________________________________________________________
Eric Bentsen | Schneider Electric | Solar Business | UNITED
STATES | Technical Support Representative
Phone: +(650) 351-8237 ext. 001# |
Email: eric.bentsen at schneider-electric.com | Site:
www.schneider-electric.com/solar | Address: 250 South Vasco Rd.,
Livermore, CA 94551
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From:
Brian Teitelbaum <bteitelbaum at aeesolar.com>
To:
RE-wrenches <re-wrenches at lists.re-wrenches.org>
Date:
07/31/2013 01:18 PM
Subject:
Re: [RE-wrenches] Outback AC coupling Sunpower?
Sent by:
re-wrenches-bounces at lists.re-wrenches.org
Eric,
Can you expand on your “total kW of the grid-tie unit cannot exceed the
rating of a single XW, even in a multi-unit system” comment?
I assume that with multiple XW (or other battery-based) inverters, since
the AC is all coupled together, there is no way to prevent a pass-through
AC relay in one of the inverters from being potentially overloaded. Since
no two relays will have exactly the same resistance, and since the power
will always take the path of least resistance, it could cause the amperage
of the least resistive relay to exceed its rating.
Is this correct, and is this what you are referring to?
If so, I assume that you could use multiple XW inverters, as long as they
had separate GT inverters, with separate critical loads panels, installed.
They would essentially be separate back-up systems, each running different
loads, but all connected to the grid in the same Main panel.
Brian Teitelbaum
AEE Solar
From: re-wrenches-bounces at lists.re-wrenches.org [
mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of
Eric.Bentsen at schneider-electric.com
Sent: Wednesday, July 31, 2013 12:52 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Outback AC coupling Sunpower?
Hi,
That is correct...the XW does have a frequency shift (Batt V=Bulk) that
causes grid-tie inverter to disconnect. Remember, the
total kW of the grid-tie unit cannot exceed the rating of a single XW,
even in a multi-unit system.
Eric
_____________________________________________________________________________________
Eric Bentsen | Schneider Electric | Solar Business | UNITED
STATES | Technical Support Representative
Phone: +(650) 351-8237 ext. 001# |
Email: eric.bentsen at schneider-electric.com | Site:
www.schneider-electric.com/solar | Address: 250 South Vasco Rd.,
Livermore, CA 94551
*** Please consider the environment before printing this e-mail
From:
Ryan <ryan at kb1uas.com>
To:
re-wrenches at lists.re-wrenches.org
Date:
07/31/2013 11:16 AM
Subject:
Re: [RE-wrenches] Outback AC coupling Sunpower?
Sent by:
re-wrenches-bounces at lists.re-wrenches.org
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
kelly at whidbeysunwind.com
PH & FAX: 360.678.7131
On Jul 30, 2013, at 4:23 PM, Ray Walters <ray at solarray.com> wrote:
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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