Re: [RE-wrenches] AC Coupled Re-visited
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_so...@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.b...@glbcc.com wrote: From: Glenn Burt glenn.b...@glbcc.com Subject: Re: [RE-wrenches] AC Coupled Re-visited To: 'RE-wrenches' re-wrenches@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-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 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
Re: [RE-wrenches] AC Coupled Re-visited
Jeff, How would the battery based inverter control the charge? Most modern control algorithms are based around some version of pulse width modulation -- PWM. You open the circuit for a tiny fraction of a second, and as the battery voltage rises the open (off) pulses get wider, and the closed (on) times get shorter. To those of us living in meat time, it looks like the current is magically tapering. However, the GT inverter isn't a generator that can have loads unplugged and plugged back in -- it's a current source. *If *you could open the circuit for a millisecond without tripping the anti-islanding protection, the voltage on its output terminals would begin to rise as the BB inverter tapered the current. You may have seen a similar reaction if you've ever measured the voltage on the PV side of an old-fashioned PWM charge controller when the batteries near full and the charge controller begins to regulate -- the voltage on the PV side begins to drift towards module open circuit voltage. Once the voltage on the GT inverter's output terminals rose to the UL1741/IEEE high limit, the inverter would trip offline. Therefore, the only practical way to regulate the charge is to either tell the GT inverter to stop making power (ie, shut it down by forcing a blackout), tell the GT to throttle back power output via communication (ala Sunnyboy/Sunny Island RS485 and frequency shifts), or to divert that power and absorb it doing some other work. Per my other post, I now think this latter solution is the better idea if you're going to mix brands. Allan asked what would I recommend to accomplish this. There's a couple ways. 1. DC diversion, using standard PWM controller and DC resistance load. Advantages: temperature compensated PWM charge regulation. Disadvantages: difficult to source and size diversion load, and you need to ensure the regulation voltages don't interfere with normal charging and sell back voltages. I can share a good technical bulletin written by Morningstar on sizing DC diversion loads, if you contact me off-list. No magic bullet on keeping regulation voltage out of the way of charging voltages -- it's probably the one aspect that you will spend the most time getting right. 2. AC diversion, using relays driven by Aux Outputs and AC resistance heaters. I believe this is the most practical solution available today for grid tie applications. It's not PWM, but it's far more stable than 5 minute off cycles. Depending upon the brains driving your aux output, it's probably temperature compensated. AC heaters are commonly available in a range of wattages and voltages, and they're dirt cheap. Besides, it's AC power that you're trying to absorb, so why make your BB inverter go through the stress of having to convert that AC power to DC just to send it off to a heating element? If you want to get fancy and have multiple inverters (therefore multiple aux outputs) in the system, you can do staged diversion (1,000 watts of load come on at one voltage, an additional 2,000 watts comes on .2v higher, etc). Same complication of ensuring regulation voltage doesn't interfere with normal charging and sell back voltages apply, however. 3. Christmas Wish-list solution: I've been trying to talk the guys at Outback into creating a Diversion controller that can talk to the rest of the system, provide temperature compensated PWM control of energy flow to a diversion load, but most importantly know when grid power is present and then stay out of the way. That would ensure that there is no time where you're buying AC power from the grid and dumping it to the heater, and it eliminates all the gyrations of staggering voltage setpoints and hoping that the multiple temperature sensors and devices will all play nicely under all conditions. Bonus points if it can work with AC or DC. Extra bonus points if it can work with any brand of equipment (wind or hydro, anyone?). However, I'm just one voice in the wilderness -- if you would like to see a solution such as this come to market, send Outback an email. Let them know Phil sent you ;-) I think there is a lot of opportunity to add power reliability and stability to traditional grid tie systems -- what we need is a way to do it easily and effectively. Here's to looking for a way! Phil Undercuffler Conergy -- Forwarded message -- From: Jeff Yago jry...@netscape.com To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Wed, 21 Oct 2009 19:53:11 -0700 Subject: Re: [RE-wrenches] AC Coupled Re-visited There have been some good advice related to battery bank sizing and a better description of how Sunny Islands work with SunnyBoys, but I am afraid we are getting away from my original post that started this and that was: Since a battery based inverter has a battery charging section and all kinds of software control over the charging process when connected to the grid, why does the battery charging process go wild when the grid
Re: [RE-wrenches] AC Coupled Re-visited
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.b...@glbcc.com wrote: From: Glenn Burt glenn.b...@glbcc.com Subject: Re: [RE-wrenches] AC Coupled Re-visited To: 'RE-wrenches' re-wrenches@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-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 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 bankthis is SMA's method of not using their chargerthey simply alter the amount of available AC input into the AC to DC converter present in the Sunny Island.This logic is what
Re: [RE-wrenches] AC Coupled Re-visited
There have been some good advice related to battery bank sizing and a better description of how Sunny Islands work with SunnyBoys, but I am afraid we are getting away from my original post that started this and that was: Since a battery based inverter has a battery charging section and all kinds of software control over the charging process when connected to the grid, why does the battery charging process go wild when the grid is down and the AC power is being backfed from a separate AC coupled inverter. Also, why do we keep having to field wire and program an added power relay or a separate diversion load relay to prevent over-charging and destroying an AGM battery bank because the battery charging process suddenly has no clue how to charge the battery bank. Yes, the Sunny Island varies frequency which will cause an AC coupled SunnyBoy to be faked out and drop off line to avoid overcharging the battery bank, but it seems to me this is all just software programming, so why can't any inverter manufacturer simply control battery charging no matter where the AC power is coming from? Why can't grid tie inverters used in an AC coupled application have the software to recognize a full battery condition and stop charging without having to drop off line on an out of limit grid condition and then cycle through the 5 minute wait? I am not an electronics engineer, but I don't see where any hardware changes are required, just some added software to select during initial setup. Many of you may not deal with battery based systems, but half of our systems are and AC coupled is a great way to avoid long low voltage DC wire run losses. We select generator type from a setup menu, how about Press 1 for standard inverter setup, press 2 for AC coupling. Jeff Yago _ Netscape. Just the Net You Need. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] AC Coupled Re-visited
Jeff Yago wrote: There have been some good advice related to battery bank sizing and a better description of how Sunny Islands work with SunnyBoys, but I am afraid we are getting away from my original post that started this and that was: Since a battery based inverter has a battery charging section and all kinds of software control over the charging process when connected to the grid, why does the battery charging process go wild when the grid is down and the AC power is being backfed from a separate AC coupled inverter. Also, why do we keep having to field wire and program an added power relay or a separate diversion load relay to prevent over-charging and destroying an AGM battery bank because the battery charging process suddenly has no clue how to charge the battery bank. Because, people are using these inverters in ways they were not really meant to be used. It can be made to work, but the inverter is not aware of the battery voltage in this mode of operation Actually, another way to look at this is to put the onus on the grid tie inverter rather than the battery based inverter, providing the reference grid, to be able to easily turn its power level down. SMA just happens to have a way to do this in a pretty slick way. The regular battery based inverter, like the FX or Magnum, etc, is bidirectional. When the grid-tie inverters voltage gets pushed up because the battery based inverter has nowhere to put that energy, the AC voltage rises and so the DC battery voltage side must rise as well. That is, unless some inverter like the SI tells the grid tie inverter to lower its output power, the grid tie inverters' voltage will try to rise to try and sell more power to the grid.But there is no grid when the batteries are full, so the grid tie inverters' AC voltage goes out of UL range, and goes off line. Yes, the Sunny Island varies frequency which will cause an AC coupled SunnyBoy to be faked out and drop off line to avoid overcharging the battery bank, but it seems to me this is all just software programming, so why can't any inverter manufacturer simply control battery charging no matter where the AC power is coming from? Other's could do this too, if they know what Grid-tie inverter is that they are tied to and how to control it (like varying frequency). SMOP Simple Matter Of Programming as they say. That is, ~IF~ the grid-tie inverter can be turned down. This is the best way. The battery based inverter can not use the energy. It can't just keep the AC voltage at 120V and the battery voltage down if the grid tie inverter is trying to raise that AC voltage by trying to sell to it. Otherwise, all the battery based inverter can do is to turn off. Then, of course, the reference for the grid tie inverter goes off, and it must wait another 5 minutes after the battery based inverter starts inverting again. Why can't grid tie inverters used in an AC coupled application have the software to recognize a full battery condition and stop charging without having to drop off line on an out of limit grid condition and then cycle through the 5 minute wait? It's because it's not a charger at this point... It's a bi-directional inverter. I am not an electronics engineer, but I don't see where any hardware changes are required, just some added software to select during initial setup. Many of you may not deal with battery based systems, but half of our systems are and AC coupled is a great way to avoid long low voltage DC wire run losses. We select generator type from a setup menu, how about Press 1 for standard inverter setup, press 2 for AC coupling. It's kind of like when your stomach is full, you have to stop being fed, otherwise you get real sick. (sort of) boB Jeff Yago _ Netscape. Just the Net You Need. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] AC Coupled Re-visited
Wehave 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 botheredby is the need to custom design a power relay circuit on each project whichtakes 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 thegrid 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 SolarNetscape. Just the Net You Need.___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] AC Coupled Re-visited
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 -- Netscape. Just the Net You Need. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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 bankthis is SMA's method of not using their chargerthey 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 -- Netscape. Just the Net You Need.
Re: [RE-wrenches] AC Coupled Re-visited
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 Kirpal Khalsa - Yes, if we usea Sunny Island AC coupled with a SunnyBoy we would not have the batterycharging problem, but remember, the SunnyBoy is 240 VAC and the Sunny Island is 120VAC which I also find is just has expensive to match up by having to installan external step-down transformer so I still feel inverter manufacturers are missing an opportunity to provide a needed product feature that nobody is providing.. Jeff Yago DTI SolarNetscape. Just the Net You Need. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] AC Coupled Re-visited
Kirpal, You’ve got it summed up pretty well, although I would add that you need to use RS485 cards and cabling between the SBs and the SI Master to get regulated charging – the comm. allows the SI to send a handshake to the SB, telling the SB to go into “off grid” mode and accept wider voltage and frequency swings whenever the grid is not present. Kent sums up this control mechanism very succinctly below. The biggest challenge when mixing brands is dealing with the 300 second timeout after grid disturbance (what I call 5 minute PWM) make for less than ideal system operation. There needs to be a better way to regulate power than kicking the string inverter offline. Imagine, say, a 7kW array pumping energy into the home on a beautiful sunny day. The grid goes down, but the battery based inverter (BB) picks up the slack and the grid-tied batteryless inverter (GT) stays online. Home is drawing less power than the array’s output (~6kW worth), and the batteries are full. Battery voltage hits the regulation voltage, and the BB inverter (or the voltage controlled switch) activates a relay to open the circuit to the GT inverter, effecting a blackout on that circuit. Suddenly the BB inverter and the battery bank is hit with the full 6kW of load. The batteries are a little undersized because that was the easiest portion of the system to cut costs on, and they’re a little old and dried out from years of sitting in an uncooled garage, so their voltage sags under the load. The voltage controlled switch senses the drop, and closes the relay to the GT. However, the GT has to stay offline for another 299 seconds and the battery voltage continues to fall….. I’ve been worried about just this scenario for some time, especially as systems age. Therefore, I’ve been suggesting to anyone interested in using mixed brands of inverters (or those who don’t want to use RS485 communications with SB/SI combos) that they strongly consider installing a diversion load and controller capable of absorbing at least the majority of the expected surplus energy. A blackout relay can be used as a secondary control mechanism. I think that this is going to provide the most reliable operation, ultimately. To answer the question about number of inverters, the SMA 5048U supports parallel operation of up to 4 inverters on a single phase system, up to 4 inverters on a split-phase system, or three inverters on a 3-phase system -- all connected to one battery bank. The PV can come through any number of SB inverters, but they would all be connected to the same protected load panel served by the SI. This is one cluster. The rule of thumb John Berdner passed along years ago was up to 2kW of PV for every 1kW of SI. If you can break the load into multiple clusters, the system can be any size -- you just run multiple clusters side by side independently. If the loads can't be separated, then you need to look at using the Multi-cluster box, but that's not yet Listed or even technically available in the US. But if the job is *really *that big, you're playing in a whole 'nother ballpark. Definitely not the job to take on for your first battery based project. Phil Undercuffler Director, Battery-based and Off-grid Distribution Sales Group *Conergy* *Our World Is Full of Energy* 1730 Camino Carlos Rey Suite 103 Santa Fe, NM 87507 p.undercuff...@conergy.us Direct | 505.216.3841 Toll Free | 888.396.6611 x4841 Fax | 505.473.3830 www.conergy.us Phil Undercuffler On Tue, Oct 20, 2009 at 1:38 PM, re-wrenches-requ...@lists.re-wrenches.orgwrote: Send RE-wrenches mailing list submissions to re-wrenches@lists.re-wrenches.org To subscribe or unsubscribe via the World Wide Web, visit http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org or, via email, send a message with subject or body 'help' to re-wrenches-requ...@lists.re-wrenches.org You can reach the person managing the list at re-wrenches-ow...@lists.re-wrenches.org When replying, please edit your Subject line so it is more specific than Re: Contents of RE-wrenches digest... When responding to posts within the Digest, be sure to restore the Subject: line to the original, and please edit out any extraneous lines from the quoted message. Today's Topics: 1. Re: AC Coupled Re-visited (Walt Ratterman) -- Forwarded message -- From: Walt Ratterman wratter...@sunenergypower.com To: glenn.b...@glbcc.com, 'RE-wrenches' re-wrenches@lists.re-wrenches.org Date: Tue, 20 Oct 2009 12:37:04 -0700 Subject: Re: [RE-wrenches] AC Coupled Re-visited 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
Re: [RE-wrenches] AC Coupled Re-visited
Phil, Good advice. Assuming 48V and a large system, what would you use as a diversion load and controller in this application? As I understand it, this would be a DC diversion load, such as a wind gennie air heater, that would be gradual, resistive, and noncritical for occasional use in this rare scenario. Thank you. Allan Sindelar al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.PositiveEnergySolar.com http://www.positiveenergysolar.com/ Kirpal, The biggest challenge when mixing brands is dealing with the 300 second timeout after grid disturbance (what I call 5 minute PWM) make for less than ideal system operation. There needs to be a better way to regulate power than kicking the string inverter offline. Imagine, say, a 7kW array pumping energy into the home on a beautiful sunny day. The grid goes down, but the battery based inverter (BB) picks up the slack and the grid-tied batteryless inverter (GT) stays online. Home is drawing less power than the array's output (~6kW worth), and the batteries are full. Battery voltage hits the regulation voltage, and the BB inverter (or the voltage controlled switch) activates a relay to open the circuit to the GT inverter, effecting a blackout on that circuit. Suddenly the BB inverter and the battery bank is hit with the full 6kW of load. The batteries are a little undersized because that was the easiest portion of the system to cut costs on, and they're a little old and dried out from years of sitting in an uncooled garage, so their voltage sags under the load. The voltage controlled switch senses the drop, and closes the relay to the GT. However, the GT has to stay offline for another 299 seconds and the battery voltage continues to fall... I've been worried about just this scenario for some time, especially as systems age. Therefore, I've been suggesting to anyone interested in using mixed brands of inverters (or those who don't want to use RS485 communications with SB/SI combos) that they strongly consider installing a diversion load and controller capable of absorbing at least the majority of the expected surplus energy. A blackout relay can be used as a secondary control mechanism. I think that this is going to provide the most reliable operation, ultimately. Phil Undercuffler Director, Battery-based and Off-grid Distribution Sales Group Conergy ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
