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

Mon Apr 16 13:51:01 CDT 2007

I guess my vote would be with Corwyn, skip the battery maintenance
headache and tolerate the 2-8 hours per year your grid will be offline.

Or a compromise case - install battery backup for a few key circuits -
computers, say, with a small, non-grid-tie battery backed inverter
system and a battery charger, and grid-tie the rest batteryless.  

The decision really comes down to - how reliable is your utility?  How
costly is an outage?  If outages are rare (as on a campus utility) and
don't cost much, then grid tie.  If outages are more frequent (as on a
rural utilty) and cost a lot, then put in batteries.  

For a small home system, the hybrid tie/battery system might make sense
- battery backup for your computer, a few lights, your freezer and your
heat.  The rest can go down if the utility is down.  A small, cheaper
inverter might handle some of these loads, in an isolated circuit not
connected to the utility, whereas the bulk of the power is grid tied and
vulnerable to an occasional outage.  I can't envision a scenario where
the hybrid would make much sense for a commercial building, but your
mileage will vary

Lawrence Lile, P.E., LEED AP

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Drew A.
Gillett, P.E.
Sent: Monday, April 16, 2007 9:27 AM
To: wmdorsett at sbcglobal.net; Greenbuilder list; hseia at topica.com
Cc: Vandermark Henry
Subject: [BULK] Re: [Greenbuilding] Current thoughts on Batteries in
grid connected PVsystems?
Importance: Low

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_S
olutions/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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