[RE-wrenches] Off-Grid to Grid-Connected -essential loads

Sat May 5 12:36:25 PDT 2012

Dan, I agree, the batteries are a major factor here and as usual much can get lost in translation when details are left out.  My bad, I'll try to bridge the gap a bit...
What we have here is a complete up and running off-grid system; -the batteries are Surrette 2YS31P (2V each x 24 = 48V system) ~one year old-there are two FM80's and a FM60 with a combined 8435 W of PV -currently there are two VFX3648's (series stack) and there are two GVFX3648's waiting to be swapped in when the grid connection happens.-back-up 12kW gen
Welcoming neighbours into the area who are not as open to the limits and responsibilities of off-grid living, this system owner has agreed to help with the cost of bringing the grid into the area.
 So working with the set-up we have, what i'm thinking (hoping) is that the system will continue to run off the batteries and the PV will continue to keep the batteries full and running all the loads and the inverters will be set to only "buy" from the grid when the PV is not able to maintain a predetermined battery voltage. Essentially the grid will become the "back-up generator", and the existing back-up gen will not be seeing any action unless there is no sun and the grid is down.  It appears that this is programmable via the HBX mode from the Mate.  Am i missing any critical points here? 
Currently the main distribution panelboard, which feeds everything (the house and shop loads) is supplied from the AC-Out bus in the Outback FW-AC, which is supplied from the VFXs output and when in by-pass mode, from the generator, and since the (battery) system was originally designed to supply all the loads I see no reason/purpose to dedicate certain loads to a separate "essential loads" panelboard, which is what i was getting at with my original post.  
Thanks,benn
DayStar Renewable Energy Inc. www.daystarsolar.ca780-906-7807 Certified Construction Electrician Solar Photovoltaic Systems CertifiedCertificate # 0007SHAVE A SUNNY DAY

From: dan at foxfire-energy.com
To: re-wrenches at lists.re-wrenches.org
Date: Fri, 4 May 2012 18:23:33 -0700
Subject: Re: [RE-wrenches] Off-Grid to Grid-Connected -essential loads

IMHO, the batteries are the real skeleton in the closet here. Sooner or later they're gonna poop. at 2400 Ah you're likely running a multi string set up, so it's likely someone's number is already on the board. Even if you set the FX down to a trickle charge or use some kind of contactor to fake the FX into thinking the grid is really a gen set, sooner or later the batteries will fail. Better to design for it now.. Besides, Rather than regulating solar input to protect batteries, You're better off selling (Storing) power on the grid. Depending on the age of the batteries or the competence of the operator (Home Owner), I'd either swap out the FXs for a GVFX  (and down size the batteries when they puke), or loose the current setup all together and go for a batteryless Grid Tie inverter. (and maybe keep the current setup as a whole house UPS.. until the batteries poop). Again, depending on the customer, you might milk these batteries by setting up individual strings on an isolation switch (like in the marine industry), at least this way you can referee. 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-wrenches] Off-Grid to Grid-Connected -essential loads

From: benn kilburn <benn at daystarsolar.ca>

Date: Fri, May 04, 2012 5:08 pm

To: Wrenches <re-wrenches at lists.re-wrenches.org>

    Wrenches,I have an off-grid client who is going to be connecting to the grid.  Since the system (~9 kW of PV and ~2400 Ah battery) is already well suited for the loads, I am wondering about the necessity of an essential loads panelboard.  I'm not sure if I see the need since the battery is already sized for all the existing loads.
The intent is to continue running all the loads from the battery and have the (Outback) settings so that the grid is only used when the PV isn't able to maintain a particular battery voltage setting.  
Comments, insights into this type of set-up?
Thanks,benn
DayStar Renewable Energy Inc. www.daystarsolar.ca780-906-7807 Certified Construction Electrician Solar Photovoltaic Systems CertifiedCertificate # 0007SHAVE A SUNNY DAY  _______________________________________________

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