[RE-wrenches] Grid tie with BB

[Rich Nicol]

Thanks Dan/Dick and Larry – 

My concern was too high a charge rate, particularly when the batteries are cycled during or after an outage when the controllers are delivering maximum current and the inverter is not selling, yet not wanting to limit the charge controllers when we’re back in grid tied mode. Outback noted that you can just limit the controllers during extended outages, but I would prefer that customers not have to make adjustments to the charge rates.

What I failed to consider is the particularly high charge rates that AGMs are able to withstand compared to FLAs. With a few tweaks to the system design we can easily hit a ~ .25C rate which is ideal for the batteries.

I like the perspective of the inverter as diversion controller when it’s in sell mode. 

Thanks again for your help!

Rich

 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of dan at foxfire-energy.com
Sent: Sunday, September 02, 2012 11:01 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Grid tie with BB

 

I'm with Dick. I liken grid tied inverters to diversion controllers. MPPT charge controllers (In Grid Tie Mode / talking to a HUB), pretty much just track a max power from the array. Good luck.

 

db

 


Dan Brown
Foxfire Energy Corp.
Renewable Energy Systems
(802)-483-2564
www.Foxfire-Energy.com
NABCEP #092907-44

 

-------- Original Message --------
Subject: Re: [RE-wrenches] Grid tie with BB
From: Richard.L.Ratico at VALLEY.NET (Richard L Ratico)
Date: Sun, September 02, 2012 9:16 am
To: re-wrenches at lists.re-wrenches.org

Rich,

If I understand your question, I think you're missing the functioning of the
inverter. Working independently of the charge controller, it will sell to
prevent overcharging the batteries. Correctly configuring the inverter's voltage
thresholds accomplishes this.

Dick Ratico


--- You wrote:
Wrenches,

I'm have a mental block with battery backup systems such as the Outback
Radian. Perhaps someone can help me get over it!

Essentially these systems sell back power off the top of the battery bank
and the array is maintaining the state of charge of the battery bank through
traditional charge controllers. If you have a modest battery bank sized for
limited use on critical circuits and a good size array for the benefit of
net metering I would think it would be necessary to limit the current the
charge controllers are capable of delivering to the battery bank to prevent
damage to the batteries when the controllers are Bulking or Absorbing, but
then it would seem that we limiting the utility of the larger array. If the
current from the controllers was not limited they will self-limit as voltage
rises, plus I suppose they will mostly be in float mode except when the
batteries are cycled but again it seems that we are limiting the capability
of the array compared to a straight grid tied system with a traditional grid
tied only inverter.

An example would be a 8000 watt array using a couple of flexmax80
controllers with a string of 8 - L16 AGMs feeding a Radian.

What am I missing here?

Thanks 

Rich
--- end of quote ---
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