[RE-wrenches] Advice needed on upsizing a battery & grid interactive inverter stack

[Darryl Thayer]

Hi Doug
My 12 stack may not be in compliance today, it appeared to be in compliance when it was installed.  It works, but I do not wish to look to hard at it.  It involved extra and custom work by outback when it was installed.
Darryl

--- On Sun, 8/8/10, Doug Pratt <dmpratt at sbcglobal.net> wrote:


From: Doug Pratt <dmpratt at sbcglobal.net>
Subject: Re: [RE-wrenches] Advice needed on upsizing a battery & grid interactive inverter stack
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Date: Sunday, August 8, 2010, 11:43 AM








Hi Mick,
 
We’re increasingly running into this “how big can you go with battery-based grid-tie” question. Most of the hardware out there was designed with modest residential systems in mind.  
 
Outback is limited to 2 inverters max in grid-tie mode. 7.5kW. (I’m really curious what Darryl is doing with his 12-stack. I suspect it’s functional but not exactly in compliance with UL listings.)
 
With Xantrex we can get to 3 inverters, 18kW.
 
A Sunny Boy / Sunny Island stack can go to 4 Islands, 20kW.
 
Both Satcon and Princeton Inverters make 100kW battery-based, grid-tie capable inverters.  The Satcon runs a 240vdc battery pack…exciting!  Not sure about Princeton, but I believe it’s the same.  Prices for these large, more or less custom-built inverters is astronomical.  
 
And dammit, there’s nothing in between 20kW and 100kW! (A least that I’m aware of.) And we get requests in the 30-50kW range pretty regularly now.
 
The best advice I can offer:  First off, it’s just crazy to build such large battery packs for grid-tied systems.  Batteries have become very expensive over the past few years, and even the best aren’t going to last more than 15-20 years.  So build the client a modest 18-20kW battery backup system to cover the really important stuff. (Security system, critical lighting, communications, etc.) Put everything else on an auto-start backup generator.  The food isn’t going to spoil in the two minutes it takes the backup system to roll up to speed, and if the big screen goes blank for a couple minutes…well life is just tough sometimes.  I usually recommend propane as a backup fuel, it gets delivered and it doesn’t spoil or evaporate with age. But for something this big you’ll probably need to go to diesel.
 
Good Luck!
Doug Pratt
DC Power Systems  
 
 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mick Abraham
Sent: Friday, August 06, 2010 4:18 PM
To: RE-wrenches
Subject: [RE-wrenches] Advice needed on upsizing a battery & grid interactive inverter stack
 
Yo, Mechanics~

 

A client is considering a "biggest ever for me" battery based power system. They will probably scale down their ambitions once the cost realities settle in but for now they've asked me to look for battery based inverter systems which can scale bigger than a triple stack of Xantrex XW6048 inverters. Your advice would be welcomed. 

 

* The system must be split phase 120/240, not 3 phase. 

 

* Outback seems "out" because the inverter group should handle backup battery recharge using grid or generator AC...and we also want to sell excess PV power to the grid.

 

* No cobbled together AC coupled systems would be considered without a convincing way to feather the end of charge on the battery when the grid is down...float & all. I don't want to go back to the days of clunky, coarse battery "end of charge" care. 

 

* Sunny Island/Sunny Boy is in contention but I'm not keen on having to stack in pairs to maintain the 120/240 three wire architecture. A single Sunny Island failure would take down two of the yellow boxes. What is the limit on stack-ability for Sunny Island?

 

* A battery sales rep suggested Satcon brand but I think that's bogus advice. Satcon is pure grid intertie only, right?

 

***********************************************

 

So...there is your challenge de la semaine (challenge of the week). Who builds an inverter system with Xantrex XW-like features only bigger...much bigger? OR: who could supply the "Mother of Sunny Island/Sunny Boy" system? Replies would be welcomed on the  List or off.

 

The Wrench List is the Bomb!

 

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675
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