[RE-wrenches] Grid-Tied, PV by AC or DC

Mon Mar 5 06:17:41 PST 2012

As I understand it, the SI to SB connection works slightly differently than
described below, and this is borne out by my experience, and a lot of
re-reading the SMA literature;

Grid goes away – SI shifts to a voltage source for the SB

SI communicates with SB and tells it to operate in off-grid mode, widening
its voltage window outside of the UL 1741 usual values

Batteries full & no loads, SI shifts the frequency of its micro grid
slightly and SB will eventually drop off line. This is why it also works
with other manufacturers inverters because it does not rely on the SMA
proprietary data comms to make this happen.

SI continues to monitor its loads and the grid and during the night it will
shift the freq of its micro grid slightly in the opposite direction to ‘make
up’ for the period it used this to remove the SB, allowing things like
clocks that use the 60Hz of the grid to regain time.

SI detects return of grid – communicates with SB and returns it to normal UL
1741 mode

Glenn Burt

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry Brown
Sent: Sunday, March 04, 2012 11:13 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Grid-Tied, PV by AC or DC

Jay,

We have installed a number of AC Coupled systems using Sunny Boys and Sunny
Islands.  One important consideration in this approach is to connect the
inverters (Sunny Boys and Sunny Islands) together with a communication cable
and Communication Cards and to upload new software into the Sunny Boys that
let them know when the grid is down to operate in off grid mode. In this way
when the grid is down the Sunny islands can limit the output of the Sunny
Boys to meet the demand of the loads in the protected loads sub panel.
Without the communication between the inverters, if the grid is down and the
output of the Sunny Boys exceeds the demand of the loads in the protected
load sub panel, then the Sunny Island will phase shift and the Sunny Boys
will completely disconnect and then wait five minutes to try and connect
again and will continue to do this until the output of the Sunny Boys does
not exceed the demand of the loads.   So it is all or nothing without
communication between the inverters.  This would seem to hold true as well
for Sunny Islands mixed with any other Grid Tied inverters that are not of
the SMA family and can not effectively talk to each other.

Larry

Larry Brown

Sun Mountain

NABCEP Certified PV Installer

On Mar 4, 2012, at 10:25 AM, jay peltz wrote:

HI Darryl,

Is this a UL listed application for the Radian/Outback?

And in following this thread about AC coupled:

Given the higher efficiency of the batteryless inverter and fantastic MPP,
vs the relatively high losses with the 600v xantrex or standard CC/inverter
losses, I would use the AC couple technique.

Jay

peltz power

On Mar 3, 2012, at 8:06 AM, Darryl Thayer wrote:

A few years back I made some year long measurements on an outback GVFX and a
sunny boy for net energy to the grid I got only a few percentages not 10%  I
think one of the problems is the battery selection, these new batteries from
Outback seem to have very low self discharge so very little energy should be
expended to keep them charged.  I am trying to close on a system where the
distance from the solar array to the house is far, so I am planning to AC
couple to a Radian to the grid, and I have been sucessful with AC coupleing
on GVFXs and Outback assures me it will workas well with theRradian.  This
install is very sensitive to LOL (loss of load) and has the generator ready
to go, but for the short outages that he has it is a hassel.  (he has worn
out one generator all ready, it was a construction grade genny)  

I am hoping if this system is a go to consider a Xantrex 600 volt charge
controller, but it depends upon the customer

thanks for the patence 

Darryl

From: Drake <drake.chamberlin at redwoodalliance.org>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org> 
Sent: Friday, March 2, 2012 9:31 AM
Subject: Re: [RE-wrenches] Grid-Tied, PV by AC or DC

I think the AC coupled approach would be the best.  For the 10KW system, a
pair of Sunny Islands fed by Sunny Boys would make an efficient system.
Since there is no generator, the system should be fairly straight forward. 

At 02:06 AM 3/2/2012, you wrote:

i think mark was asking more about ac coupling to get away from the horrible
inefficiencies of battery based, grid-tied inverters.

as an experiment, i have been thinking about ac coupling one (or more) of my
arrays on my outback system to gain 10% over having the gvfx do the selling.

stc to ptc usually costs about 20%, then losing another 10% in the inverter
is a real performance hit. i advise customers about phantom loads and
conservation, when actually the battery based inverter is itself the big
lump under the carpet!

todd

On Thursday, March 1, 2012 7:07pm, "Maverick Brown [Maverick Solar]"
<maverick at mavericksolar.com> said:

My two cents:
"battery-based inverter w/ PV on the DC side via charge controllers"
Simply replace the GT inverter with a Xantrex 600V Charge Controller plus
the 48V Grid Interactive Inverter of your choice and added battery bank,
etc.
Until the market is saturated with unneeded GT Inverters, you will be ok.
;-)
Try your best to provide enough battery for at least 24 hours of outage at
50% DOD. You may have add a Sub-Panel or Manual Transfer Switch.
Thanks
Maverick
Maverick Brown
BSEET, NABCEP Certified Solar PV Installer Â® # 091209-26
President & CEO
Maverick Solar Enterprises, Inc.
Billing:  PO BOX 1229, Dripping Springs, TX 78620
Office:       512-919-4493
Fax:           512-607-6398
Cell:          512-460-9825
Corporate: http://www.mavericksolarenterprises.com/

From: re-wrenches-bounces at lists.re-wrenches.org [
mailto:re-wrenches-bounces at lists.re-wrenches.org
<mailto:re-wrenches-bounces at lists.re-wrenches.org> ] On Behalf Of
toddcory at finestplanet.com
Sent: Thursday, March 01, 2012 5:46 PM
To: RE-wrenches
Cc: 'RE-wrenches'
Subject: Re: [RE-wrenches] Grid-Tied, PV by AC or DC

excellent question mark... and one which has been on my mind as well, being
most of my work is bbgt.

todd

On Thursday, March 1, 2012 11:37am, "Mark Frye" <markf at berkeleysolar.com>
said:

Folks,

I have a residential grid-tied customer in a net metered utility with a
favorable TOU rate.

They could use about 10 kW of PV to offset 100% of their usage.

But, they also complain about regular power outages in their neigborhood.
They don't want a generator.

With reliable AC coupling now available, do we yet know which is the more
advantagous architecture; grid-tied, battery-based inverter w/ PV on the DC
side via charge controllers, or grid-tied, battery-based inverter w/ PV AC
coupled via grid-tied, utility-based inverter?

Your thoughts? 

Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
www.berkeleysolar.com <http://www.berkeleysolar.com/>  

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Drake Chamberlin          
ATHENS ELECTRIC LLC
OH License 44810         
CO license 3773
NABCEP Certified PV

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