[RE-wrenches] AC Coupled Re-visited

Wed Oct 21 10:12:30 PDT 2009

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
> 
> 
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> 
> 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   
> 
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>   
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> 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
> 
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> 
> On Tue, Oct 20, 2009 at 9:21 AM, Jeff
> Yago <jryago at netscape.com>
> wrote: 
> 
> 
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> 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 
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> -----Inline Attachment Follows-----
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