Glenn:
This is correct on the battery bank separation. You don't split out the battery banks until you reach a "cluster". For example, one three phase setup is a cluster. If you have two, three-phase setups - you have two clusters - and two battery banks. And.I think if you check through the charging parameters, you will find that the ratio of 10 to 1 as you have below is very conservative for PVkw versus battery Ah. We have gone with 10KW PV vs 1800 Ah with no problem. I think maybe what they may mean is that the 10 to 1 ratio is for what you intend to CHARGE in the battery bank. So - if you are planning on a 50% DOD every day, then maybe the 10 to 1 would work well, for that 50%. Walt From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Glenn Burt Sent: Tuesday, October 20, 2009 12:14 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] AC Coupled Re-visited 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-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@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 <http://www.berkeleysolar.com/> www.berkeleysolar.com _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Kent Osterberg Sent: Tuesday, October 20, 2009 11:10 AM To: glenn.b...@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-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@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 <m...@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 <jry...@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 _____
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