Excellent input, as usual. Thanks to all. *******************************************************
My original drawing showed three triple-stacks of Xantrex XW6048 inverters...with the note that three may not be enough. That XW architecture would require splitting up the downstream loads. Just the main house would require more than one of those triple-stacks. If a separate battery were devoted to each stack...that's more batteries to monitor for state of charge, state of health, etc. If one giant battery were devoted to the entire group, the fact that one trio can't know what the other trios are doing may cause recharge problems. Bob's thought about blending grid-tie type Outback inverters with off-grid type inverters would still require that the loads for one type be kept separate from the loads for the other type. I didn't realize that Daryl's jumbo Outback stack was marginal for compliance. I'll ask my Outback contacts about a big stack but I'll leave your name out of it, Daryl. Those giant inverters mentioned by Doug might be just the thing, but a 240 volt battery bank would require special dispensation from the inspector because of the NEC 50 volt limit. A high voltage battery makes perfect sense when considering giant inverting but those are obviously intended for "behind the fence" utility scale operations only. One of my early questions for the client was if they had 3 phase power to the site because that would allow for 30kW in a Sunny Island 3 X 2 stack. Alas... ************************************************************ Side note: This discussion may be moot as regard my present client. Prospects often start out with high "renewable ambitions" then scale back on the dream when the dollar amounts become evident. Nevertheless, the discussion may prove instructive and helpful down the road. There are some billionaires out there; I just don't get much chance to count them as my clients. Caution: a long discourse follows and maybe I'm going crazy or getting too caught up in the moment. List participants, you are forewarned... ************************************************************ The point about going back to the load & reducing the load always reasserts itself, doesn't it? The problem there is that the average homeowner doesn't want to cross off certain loads as "non-critical"...at least not in a rigid fashion as when we split up the wiring with no simple recourse to those decisions. The typical client wouldn't mind having to conserve in event of a crisis or power blackout but they'd rather do that by switching off the individual loads themselves instead of having entire circuits go black. Considering the SunnyIsland/SunnyBoy architecture...and thinking outside the box as Daryl suggests...in sunny times, the SunnyBoy's would augment the SunnyIsland wattage, while reducing the need for the loads to be split up. What's the limit? 1000 watts of SunnyBoy/PV power for every 1000 watts of SunnyIsland rating? If that 1:1 ratio is true...and assuming a utility blackout, the grouped together loads could enjoy 40 kW of available power...about half of that courtesy of the sunshine and the other half courtesy of the battery bank. Of course there is the nighttime problem when that SunnyBoy augmentation goes away. OK, so what if we had fueled grid-tie type generators which are AC coupled to the load side of the battery based inverter stack. That same wattage augmentation would occur but could also continue in the nighttime...provided that there's plenty of fuel. Last summer I saw the EcoPower micro "combined heat & power" CHP machine in operation in Wisconsin. www.marathonengine.com has impressive engine longevity technology, and the technology is not even new/unproven. Their engine gets its first oil change when other machines are at end of lifetime. The 7,500 watt EcoPower unit is designed to synchronize with the grid and spin the meter backwards...just as a SunnyBoy inverter might. EcoPower could therefore "AC couple" to a battery based inverter stack and lift some of the loads off that stack. Marathon has never tried an AC coupling of their machine to the load side of an inverter. They have some ideas for off-grid operation but those are quite different and to me, less elegant. Some bold solar guy in the MidWest might help us prove that the synchronization would occur with no surprises. That's step one. Step two is that any installation must have a beneficial way to use the heat coming off the CHP machine...such as a swimming pool or maybe to drive chillers for air conditioning purposes. (The system then would be know as CHPC: combined heat, power, and cooling.) Step three is most intimidating to me: We need a way to control 240 volt AC heating elements in a fine pulse width modulated PWM fashion, to protect the battery from destructive overcharge in event of a utility blackout. I say 240 volt AC because the amperage goes off the chart if trying to divert big energy from a 48 volt battery. Mr. Ohm would tell us that it's better to use a higher voltage/lower amperage, and on/off control is less sparky with alternating current. Morningstar makes their Relay Driver which can follow the PWM signals of a Tri-Star controller. One of the mfrs of solid state relays told me that their unit could flicker very quickly if the input signal to the virtual "coil" was also flickering quickly, so...a DC signal chopped into pulses via the Morningstar components could drive the solid state relay which could turn the AC heating element on & off quickly. OR: if I recall correctly, the Outback system can also deliver a PWM output which may be able to drive the diversion loads. If an Outback grid tie type inverter...stacked big as with Daryl's setup...could be AC coupled to one or more synchronizing type of generator as described above, that's a way to use a fueled generator to drive battery recharge through the GT inverter...but the "step three" control issue must be solved. I only know enough to be dangerous in these areas, but I keep thinking that our industry needs this type of big diversion capability. Who could build a control to do this...preferably a control that could be listed or at least would be assembled from all listed components? The same assembly would need good cooling of the switching components and would need some circuit breakers plus a fail safe mechanism to break the AC coupling if the battery voltage rises too high. Maybe I'm the only one who would buy such an item and maybe if it's all custom/not mass producible the cost would be so high that even I wouldn't buy it. OR: maybe not. Who can bell the cat? Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 On Sun, Aug 8, 2010 at 10:51 AM, Darryl Thayer <daryl_so...@yahoo.com>wrote: > Hi Doug > My 12 stack may not be in compliance today, it appeared to be in compliance > when it was installed. It works, but I do not wish to look to hard at it. > It involved extra and custom work by outback when it was installed. > Darryl > > --- On *Sun, 8/8/10, Doug Pratt <dmpr...@sbcglobal.net>* wrote: > > > From: Doug Pratt <dmpr...@sbcglobal.net> > > Subject: Re: [RE-wrenches] Advice needed on upsizing a battery & grid > interactive inverter stack > To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> > Date: Sunday, August 8, 2010, 11:43 AM > > Hi Mick, > > > > We’re increasingly running into this “how big can you go with battery-based > grid-tie” question. Most of the hardware out there was designed with modest > residential systems in mind. > > > > Outback is limited to 2 inverters max in grid-tie mode. 7.5kW. (I’m really > curious what Darryl is doing with his 12-stack. I suspect it’s functional > but not exactly in compliance with UL listings.) > > > > With Xantrex we can get to 3 inverters, 18kW. > > > > A Sunny Boy / Sunny Island stack can go to 4 Islands, 20kW. > > > > Both Satcon and Princeton Inverters make 100kW battery-based, grid-tie > capable inverters. The Satcon runs a 240vdc battery pack…exciting! Not > sure about Princeton, but I believe it’s the same. Prices for these large, > more or less custom-built inverters is astronomical. > > > > And dammit, there’s nothing in between 20kW and 100kW! (A least that I’m > aware of.) And we get requests in the 30-50kW range pretty regularly now. > > > > The best advice I can offer: First off, it’s just crazy to build such > large battery packs for grid-tied systems. Batteries have become very > expensive over the past few years, and even the best aren’t going to last > more than 15-20 years. So build the client a modest 18-20kW battery backup > system to cover the really important stuff. (Security system, critical > lighting, communications, etc.) Put everything else on an auto-start backup > generator. The food isn’t going to spoil in the two minutes it takes the > backup system to roll up to speed, and if the big screen goes blank for a > couple minutes…well life is just tough sometimes. I usually recommend > propane as a backup fuel, it gets delivered and it doesn’t spoil or > evaporate with age. But for something this big you’ll probably need to go to > diesel. > > > > Good Luck! > > Doug Pratt > > DC Power Systems > > > > > > *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: > re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Mick Abraham > *Sent:* Friday, August 06, 2010 4:18 PM > *To:* RE-wrenches > *Subject:* [RE-wrenches] Advice needed on upsizing a battery & grid > interactive inverter stack > > > > Yo, Mechanics~ > > > > A client is considering a "biggest ever for me" battery based power system. > They will probably scale down their ambitions once the cost realities settle > in but for now they've asked me to look for battery based inverter systems > which can scale bigger than a triple stack of Xantrex XW6048 inverters. Your > advice would be welcomed. > > > > * The system must be split phase 120/240, not 3 phase. > > > > * Outback seems "out" because the inverter group should handle backup > battery recharge using grid or generator AC...and we also want to sell > excess PV power to the grid. > > > > * No cobbled together AC coupled systems would be considered without a > convincing way to feather the end of charge on the battery when the grid is > down...float & all. I don't want to go back to the days of clunky, coarse > battery "end of charge" care. > > > > * Sunny Island/Sunny Boy is in contention but I'm not keen on having to > stack in pairs to maintain the 120/240 three wire architecture. A single > Sunny Island failure would take down two of the yellow boxes. What is the > limit on stack-ability for Sunny Island? > > > > * A battery sales rep suggested Satcon brand but I think that's bogus > advice. Satcon is pure grid intertie only, right? > > > > *********************************************** > > > > So...there is your challenge de la semaine (challenge of the week). Who > builds an inverter system with Xantrex XW-like features only bigger...much > bigger? OR: who could supply the "Mother of Sunny Island/Sunny Boy" > system? Replies would be welcomed on the List or off. > > > > The Wrench List is the Bomb! > > > > Mick Abraham, Proprietor > www.abrahamsolar.com > > Voice: 970-731-4675 > > -----Inline Attachment Follows----- > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: > RE-wrenches@lists.re-wrenches.org<http://us.mc519.mail.yahoo.com/mc/compose?to=re-wrenc...@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 > > >
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