[RE-wrenches] Outback AC coupling Sunpower?

[Kelly Keilwitz, Whidbey Sun & Wind]

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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