[RE-wrenches] AC Coupled Re-visited

Wed Oct 21 18:51:14 PDT 2009

So in essence, you had the PV's connected directly to the inverter's DC battery connection point. What did the MPPT charge controller do without the battery as a buffer? Did the efficiency go up on the system without batteries to keep charged?

Todd

On Wednesday, October 21, 2009 10:12am, "Darryl Thayer" <daryl_solar at yahoo.com> said:

> I have been quiet because i have not done SI but I have done several Outbacks. 
> One system is 12 OB GVFX 3648s on one battery bank of 600AH, the system will run
> with less batteries, in fact I left the battery off for a month and did not notice
> any loss of exported power to the grid. (this is 3 phase) (I had no grid shutdown
> and did not need critical power)  the system would start and run everyday without
> a battery.
> 
> On the other end of the scale I have a Standalone house, using 2 OBs and the
> battery bank is 48 volts 3500 AH
> 
> --- On Tue, 10/20/09, Glenn Burt <glenn.burt at glbcc.com> wrote:
> 
> > From: Glenn Burt <glenn.burt at glbcc.com>
> > Subject: Re: [RE-wrenches] AC Coupled Re-visited
> > To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
> > Date: Tuesday, October 20, 2009, 2:13 PM
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > SMA recently told me that the
> > recommended Ah of the battery bank
> > is related to the amount of PV and connected
> > inverters.
> >
> > They recommended a 500Ah bank
> > with a 5kW PV SB, and a 600Ah bank
> > with a 6kW PV SB.
> >
> > 100Ah to 10,000Ah are the
> > supported capacities.
> >
> >   
> >
> > I don’t believe you need
> > to have a separate battery bank
> > with two SI’s. I have been told they can share one.
> > One SI is programmed
> > as the master & of course they are data commed together
> > so they can talk.
> >
> >   
> >
> > -Glenn
> >
> >   
> >
> >
> >
> >
> >
> > From:
> > re-wrenches-bounces at lists.re-wrenches.org
> > [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
> > Behalf Of Mark
> > Frye
> >
> > Sent: Tuesday, October 20, 2009 2:42 PM
> >
> > To: 'RE-wrenches'
> >
> > Subject: Re: [RE-wrenches] AC Coupled
> > Re-visited
> >
> >
> >
> >
> >
> >   
> >
> > Thanks Kent. And so I understand
> > more clearly, in the case of 2 SIs
> > as you describe, each SI has it's own battery bank, and
> > the solar would be
> > split between the two.
> >
> >  
> >
> > Considering the charging capacity
> > of the SI, what would you say is
> > the largest battery bank size for each SI to insure an
> > effective "C"
> > value?
> >
> >  
> >
> > Mark Frye
> >
> >
> > Berkeley Solar
> > Electric Systems
> >
> > 303 Redbud Way
> >
> >
> > Nevada
> > City,  CA 95959
> >
> > (530) 401-8024
> >
> >
> > www.berkeleysolar.com 
> >
> >
> >
> >  
> >
> >
> >
> >   
> >
> >
> >
> >
> >
> >
> >
> > From: re-wrenches-bounces at lists.re-wrenches.org
> > [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
> > Behalf Of Kent
> > Osterberg
> >
> > Sent: Tuesday, October 20, 2009 11:10 AM
> >
> > To: glenn.burt at glbcc.com; RE-wrenches
> >
> > Subject: Re: [RE-wrenches] AC Coupled
> > Re-visited
> >
> > In off-grid mode the Sunny Island uses
> > frequency shift power
> > control to reduce the output of the Sunny Boy inverters and
> > thereby regulate
> > the battery voltage.  At some frequency shift (+1, or
> > 2, or 3 Hz, I'm not
> > sure) the output of the SB is reduced by 100%. 
> > It's proportional so that
> > 1/2 as much frequency shift gives a 50% reduction in the SB
> > output.  To
> > keep clocks accurate, the Sunny Island later shifts the
> > frequency a negative
> > amount, but the SB inverters ignore that.  For a grid
> > backup system, a
> > RS-485 cable is required so the Sunny Island can activate
> > (or deactivate) the
> > frequency shift power control capability of the SB.
> >
> >
> >
> > You need to stack two SI inverters to get 240-vac, but that
> > will allow you to
> > have a 10-kW of grid backup power with up to 12-kW of
> > solar.  If you need
> > more, you can stack four of SI inverters.
> >
> >
> >
> > Kent Osterberg
> >
> > Blue Mountain Solar, Inc.
> >
> >
> >
> >
> >
> > Glenn Burt wrote:
> >
> > Our installations of Sunny
> > Islands (SI) with Sunny Boys (SB)
> > have always used the recommended RS-485 communications
> > between all units
> > involved. This with reprogramming the SB’s to be able
> > to switch to
> > off-grid mode per the SI instructions allows a more
> > integrated system.
> >
> > We have had problems with the
> > OB PSX-240 and stepping up the 120
> > to 240 for the crit load panel (where the SB’s
> > connect) when the site has
> > slightly high AC voltages. The SB pushes the existing ACV
> > higher, then it goes
> > out of UL spec & disconnects. Also the SB is now
> > sensitive to imbalance on
> > L1 & L2 because of the neutral sensing – we had a
> > customer where the
> > SB was disconnecting due to this as well…
> >
> > I thought the freq shifting was
> > to allow other non-SMA inverters
> > to be controlled when batteries were full?
> >
> > Where is the SMA rep on this
> > list?
> >
> > -Glenn
> >
> >
> >
> > From: re-wrenches-bounces at lists.re-wrenches.org
> > [mailto:re-wrenches-bounces at lists.re-wrenches.org]
> > On Behalf Of Kirpal Khalsa
> >
> > Sent: Tuesday, October 20, 2009 12:05 PM
> >
> > To: RE-wrenches
> >
> > Subject: Re: [RE-wrenches] AC Coupled
> > Re-visited
> >
> >
> >
> > Greetings......it is my understanding
> > that the Sunny Island
> > coupled with Sunny Boys is able to taper charge in an AC
> > coupled system as the
> > 2 inverters are able to communicate with each other and the
> > Sunny Island alters
> > the frequency input of the Sunny Boys and lowers the total
> > output of the Sunny
> > Boys to match the needs of the battery bank....this is
> > SMA's method of not
> > using their "charger"....they simply alter the
> > amount of available AC
> > input into the AC to DC converter present in the Sunny
> > Island.....This logic is
> > what encouraged me to select SMA's for an AC coupled
> > design rather than mixing
> > brands of battery-less and battery based inverters.....in a
> > mixed brand
> > scenario there is no communication other than an on/off
> > command so no
> > regulation is available.....My understanding may be
> > flawed--please correct me
> > if so....
> >
> > Another way for mixed brands to AC couple and provide some
> > charge
> > "control" would be to have an AC dumpload on the
> > AC input side of the
> > battery based inverter to suck up some of the excess power
> > from the GT
> > inverters so not as much power is available for battery
> > charging.....This
> > dumpload would be voltage based and in a mixed brand system
> > would add more
> > relays to the mix...in many cases there may not be that
> > many auxillary outputs
> > available to connect relays to.....
> >
> > I would like to see more GT inverter companies make
> > compatible battery based
> > inverters......One idea is for micro inverters to be paired
> > with the battery
> > based inverters and when less power was needed to
> > facilitate a taper charge one
> > solar panel at a time could be switched
> > off......effectively providing a
> > smaller available charge current to help with the taper
> > charging.....
> >
> >
> >
> > --
> >
> > Sunny Regards,
> >
> > Kirpal Khalsa
> >
> > NABCEP Certified Solar PV Installer
> >
> > Renewable Energy Systems
> >
> > www.oregonsolarworks.com
> >
> > 541-218-0201 m
> >
> > 541-592-3958 o
> >
> >
> >
> >
> >
> > On Tue, Oct 20, 2009 at 8:34 AM, Mick Abraham <mick at abrahamsolar.com>
> > wrote:
> >
> > Hi,
> > All~
> >
> >
> >
> > On an AC coupled system as Jeff describes, the
> > "battery charge
> > circuitry" on the battery based inverter is not even
> > participating.
> >
> >
> >
> > A straight pure sine inverter...with no charger function
> > built in...would also
> > "charge" the battery if AC coupled to a SunnyBoy
> > with no grid
> > available. The "charge" is just the
> > inverter's way of dealing with
> > back EMF.
> >
> >
> >
> > I agree that better control over that "recharge"
> > is an important
> > area; I hope somebody is working on that. It's true
> > that the "wild card
> > recharge" only occurs if grid goes away but as Jeff
> > mentions, it only
> > takes a few times of crummy end of charge management to
> > ruin a nice set of
> > sealed batteries.
> >
> >
> >
> > Mick Abraham, Proprietor
> >
> > www.abrahamsolar.com
> >
> >
> >
> > Voice: 970-731-4675
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > On Tue, Oct 20, 2009 at 9:21 AM, Jeff
> > Yago <jryago at netscape.com>
> > wrote:
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > We have
> > completed several totally different AC coupled systems
> > using different inverters,
> > due to large ground mounted arrays that had to be located a
> > great distance from
> > inverter-battery-generator-grid BAS, which are working just
> > fine even with the
> > mis-match of inverter brands.  The SunnyBoy seems to
> > not care what its
> > connected to or how, as it just keeps doing what it does
> > and if a relay cuts
> > off its connection to the grid when the battery voltage
> > goes high then it just
> > waits and re-connects when the grid is back or the battery
> > voltage drops.
> >
> >
> >
> >
> >
> > What
> > I am bothered by is the need to custom design a power
> > relay circuit on
> > each project which takes lots of fine-tuning of
> > setpoints to get
> > everything to work correctly.  If you have not done
> > one the problem is
> > simple - when you backfeed the AC output from a remote
> > grid-tie inverter "through"
> > the AC side of a battery based inverter, everything works
> > great and the solar
> > AC just passes straight through the sub-panel, back
> > throught the battery
> > inverter, back into the grid.  However, when
> > the grid is down and the
> > battery-inverter is no longer receiving (or sending) power
> > from the grid, for
> > some reason I cannot begin to understand, any AC being fed
> > from the solar
> > inverter goes straight into battery charging with
> > absolutely no limit on charge
> > rate or charge limit, and if you do not add a relay to
> > dis-connect or shut-down
> > the solar inverter you can quickly destroy a bank of AGM
> > batteries if there are
> > no major system loads as it just keeps charging and
> > charging.
> >
> >
> >
> >
> >
> > I
> > am not an electronics engineer, but if the battery is being
> > charged by the
> > battery charger built into the inverter, I just do not see
> > why the same battery
> > charger suddenly has no clue that the battery is being
> > overcharged when its now
> > receiving AC power from a different source.  I think
> > with larger and
> > larger arrays being installed as module costs fall, higher
> > DC array string
> > voltges to reduce wire costs, and more people worried about
> > grid reliability,
> > there would be a good market niche for an inverter that can
> > properly charge a
> > battery bank regardless of which way the AC power comes
> > into the charger section. 
> > Whats the problem?
> >
> >
> >
> >
> >
> > Jeff
> > Yago
> >
> >
> >
> >
> >
> > DTI
> > Solar
> >
> >
> >
> >
> >
> >  
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >   
> >
> >
> >
> >
> >
> >
> >
> > -----Inline Attachment Follows-----
> >
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> 
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