[Greenbuilding] Current thoughts on Batteries in grid connected PVsystems?

[Drew A. Gillett, P.E.]

yeah, agm  have been  a nightmare.  but good charging control by outback 
should remedy the prob.   unlike offgrid where the battery is indeeded 
cycled a lot daily and has extended seasonal lows, the use by your client is 
trickle charging most of the time with very occasional short outages and the 
occasional long outage with immediate recharging.

best and cheapest with flooded lead acid and a good maintenance program  or 
the agm if you must..

it has little to do with the 6 volt vs 600 volt issue.

the only "reason" why there are fewer battery backup systems is mnfrs are 
concentrating on lucrative utility tie (and die) systems.  this trend will 
reverse as more customers wise up as your client and architect have .  when 
they realize that their expensive pv system is useless without the utility , 
they begin to see the value of battery backup.

the inverter mnfr.  fail to consider the large enhanced value to the 
customer of battery backup. many customers (even residential ) will pay 
thouands of dollars for backup power usually in the form of a generator. 
line tie with automatic battery backup of 4-24 hours is a better way to go 
with a smaller generator for longer periods.

this was discussed in detail at www.beo7.org  you might contact the chair or 
presenters and ask them this question.  over 4 of the atendees had the exact 
same question. 
http://buildingenergy.nesea.org/documents/Thursday/Track5-Clean_Energy_Solutions/Sess6-Inverters/Inverters_Worden.pdf

a friend of mine hkv at solarwave.com has just installed a dual 3.5 kw outback 
with agm line tied with battery backup system in cambridge ma . nabcep 
certified installer was rich gottlieb at sunnysidesolar. utility has 
approved.

----- Original Message ----- 
From: <wmdorsett at sbcglobal.net>
To: "Greenbuilder list" <greenbuilding at listserv.repp.org>; 
<hseia at topica.com>
Sent: Sunday, April 15, 2007 5:33 PM
Subject: [Greenbuilding] Current thoughts on Batteries in grid connected 
PVsystems?


>   I have a client who wants to put a couple thousand Wp grid-connected
> PV system on an educational building in town and the architect is
> wanting to put an Outback inverter with a battery backup. He is
> proposing Concord AGM batteries and I'm concerned that we are adding to
> our complications of meeting all the requirements of an antagonistic
> utility and inexperienced inspection office.
>
>   In order to get approval by Westar to tie into their lines, we need
> to have engineering drawings and meet a long list of specs. I think
> those systems designed to pass the California Energy Commission's
> requirements have already plowed the way and we can probably boiler
> plate plans from any of their suppliers. The fact that of 154 approved
> inverters, only four are designed with battery backup says a lot about
> the idea. And the one from Xantrex (SW series) is being discontinued. I
> suspect that part of the reason for this is that there is a mismatch
> between 6VDC of typical deep cycle batteries and the input voltage of
> most current  inverters. This would mean a long series string for the
> input voltages of up to 400 VDC.
>    My experience tells me that batteries are a pain if you can do
> without them (and doubly so if you are relying on uninformed volunteers
> to maintain them.) . Maintenance free batteries still need terminals
> cleaned, and from my past understanding, the plates are made with
> calcium instead of antimony to reduce their need for additional water.
> This also makes them more vulnerable to over-discharging and
> over-charging so you can only cycle them down to average of 75% of their
> nominal capacity. And they die quicker because they can't be equalized
> as you would a flooded deep cycle bank.
>
> Questions: Is my reasoning obsolete with Concord AGM batteries and what
> other explanation do you have for the trend away from  battery backup
> systems?
>
> Thanks for your thoughts
> Bill Dorsett
> Sunwrights
> Manhattan, KS
>
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