Redundant Xantrex PV system

Hello to all the years of experience on the board here. I am an electrical engineer, but I am new to PV power systems, so I hope you can bear with me and be gentle. I have a project to rebuild my garage to be more like a PV array with parking underneath. I have acquired 54 Sharp NT-175 panels for a really good price, delivered. I am planning on a Xantrex XW system, so I plan to split the panels into strings of 3 in series, and 6 strings in parallel per MPPT60-150 SCC, for 3 chargers (3.15 kW/charger). The original idea was to feed a single large bank of batteries at 48V then run 2 XW6048 inverters off the batteries to the house and grid, with a Xanbus connecting all 5 devices. But it occured to me that I could replace the 2 XW6048s with 3 XW4548 inverters, then split the battery bank into 3, each fed by one MPPT60. But all 3 inverters are tied to the same grid, same back-up generator, and same load. The idea is to implement 3 separate redundant subsystems, so that any one could be taken out of service with only a 33% degradation of capacity.

My question for the Xantrex pros is this: each inverter and charge controller can be tied together with a Xanbus, but when the inverters are tied together, what happens? The state of charge of each battery bank may vary, requiring different management by its SCC, and different sell back to the grid Can the inverters share a Xanbus together and still have an affinity for the charge controller that is tied to its DC bus? Do the inverters even need to talk to each other, other than the AC sync interface? If not, would that lead to 3 identically programmed inverters and 3 Xanbusses? Would there need to be 3 SCPs? And network gateways? That starts to get messy.

I have been looking at the MPPT80-600 but a pair of them doesn't have enough headroom for my comfort. This project is about a year out, depending on my architect's caffeine intake, so I have some time to refactor things.
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Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,353 ✭✭✭
    Re: Redundant Xantrex PV system

    The inverters will operate pretty much independently.

    The question I think you have is can a specific inverter talk only to a specific charge controller when all the equipment share the same network bus.

    I think the answer is yes but I don't have direct experience with shared network setup. Try looking at the bus interface spec for the hub controller. You only need one SCC.
  • Joe_BJoe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
    Re: Redundant Xantrex PV system

    You are most likely going to have issues with the CC on the same bus. The reason I say this is you cant tell the XW inverter which charge controller to follow. You will probably get all sorts of issues when they are in different states of charge. The only way to find out without trying it is to (cringe) call Schneider tech support and ask. If you can get a guy named Eric, he will be your best bet as to how the software works.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system

    Have you looked into "extreme" conservation yet?

    It is almost always cheaper to conserve power than to generate it.

    Do you have utility power (Grid Power) current available / connected? Going pure Grid Tied with some sort of Generator/smaller offgrid system as emergency backup would probably be more cost effective and less ongoing maintenance costs.

    That is a pretty large off-grid system. The XW Hybrid inverter system is nice--but you may be looking for a system designed for larger scale off grid systems for those power levels (Xantrex or others--I don't know).

    Normally, I would recommend running everything from one battery bank--balancing charging current/loads between two to three separate systems may leave you with an imbalance of charging vs loads (i.e., one unit lightly used, and another heavily used--how to pass energy from one to the other--hopefully automatically so you don't have to micro manage the system).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system

    I am hesitant to call Schneider from the horror stories I have read here and elsewhere. I am hoping that one of the experienced Xantrex professionals that wander through thiese fora might have some insights in this area.

    My thought was that I can't be the first person proposing a segmented, redundant architecture. Surely the bigger players don't put all their eggs into one basket?

    Most of the local solar Joes out here in the middle of the Pacific Ocean are, well, kinda hucksters; getting into PV from water heating if you're lucky. Very few have even heard of Xantrex: they want to push the micro-inverters du jour, for the price of what I paid for each panel. And that doesn't solve the bigger problem of my local power utility, which has third world reliability, first world costs, and no competition. Most PV installations are residential, and costs (shipping, material, and labor) out here are sky-high, so that tends to keep the systems smaller. My deal on the Sharp panels is due to them being older, MC-3 connectors. I have a (big) box full of the Shoals clamshell covers to bring them to code.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system

    From what I understand, schneider/xantrex have pretty good direct phone support. They probably cannot hold hands for an end customer, but should be able to provide guidance on the hardware and a knowledge retailer.

    You can try pm' ing xwguy (jeff) and see if he can give you some direction.

    I have designed redundant communication systems before. Many times, it is better to design a solid non-redundant system and have spares on the shelf.

    You could also do high reliability just for a few small critical loads and not burden every thing with the cost and complexity.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    BB. wrote: »
    Have you looked into "extreme" conservation yet?

    It is almost always cheaper to conserve power than to generate it.

    Do you have utility power (Grid Power) current available / connected? Going pure Grid Tied with some sort of Generator/smaller offgrid system as emergency backup would probably be more cost effective and less ongoing maintenance costs.

    Yes, it is a big system, but it is for a reasonable sized house. And it will be both grid-tied and with a back-up generator. I am having natural gas service brought to the house for the generator (and the grill) - unfortunately gas is expensive here. However, there is only so much conservation I can do. Due to circumstances beyond my control, I will be implementing a multi-zone heat pump system, which will be tied to a deep water cistern to make it GSHP. I also maintain a rack of servers and an electronics laboratory that needs a bit of power, as well as its own cooling & dehumidification. Most, if not all, of the interior lighting will be LED. And, depending on the my energy budget, I have plans for an electric vehicle, hopefully based on swappable batteries.

    Grid power here is $0.25/kWhr. That makes a PV system very cost effective, even without the rebates and subsidies, if you can keep the installation costs under control. And the monopoly power utility here just doesn't give a damn. Their motto is "What are you going to do, go with the other guy?" We have had outages for hours and up to a day because they couldn't be bothered to build a reliable grid or treat outages as an emergency. I just put $500 into new SLAs for my UPSs because of recent outages. I see hiccups every single day, which a backup generator is completely useless to prevent. My goal is complete independence from my useless utility, who, by the way, places their power plants on the coast, where they will be swept away by the next tsunami. And we've had two close calls just this year.

    My goal is be able to go completely off grid when necessary, and I know that is going to take a huge battery array, but for the moment I'd like to be able to ride out 1 -2 hour outages without starting the generator, without ever noticing. Look, I'm not about to hunker down in a dark corner with just enough power to tune an AM radio and keep the ice cream from melting because some low effort slob can't be bothered to treat a power outage seriously.
  • mike95490mike95490 Solar Expert Posts: 9,320 ✭✭✭✭✭
    Re: Redundant Xantrex PV system

    For a 3 way redundant setup, just connect the Charge controller to it's own inverter. Each bank should function well on it's own. The inverters will all sync to the grid.

    You will have to use breakers or something to steer your backup genset to 1 inverter at a time.
    Maybe use inverter to generate AC2 for the other 2 ?

    You may need 3 Sys Control panels, or just move one back and forth to program each inverter (does the inverter remember the settings, or is it only loaded in the SCP ? )
    and keep the ice cream from melting because some low effort slob can't be bothered to treat a power outage seriously.
    Save The Ice Cream at all costs ! Morale is priceless !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    mike90045 wrote: »
    For a 3 way redundant setup, just connect the Charge controller to it's own inverter. Each bank should function well on it's own. The inverters will all sync to the grid.

    That was my first thought. But what happens when the grid is out? There is an AC sync interface for the inverters to share phase information - I think this is where "SplitPhMaster" and "SplitPhSlave" comes in. From the SCP, "Advanced Settings" --> "Multi-Unit Config" --> "Connections" --> "DCConn" it seems like each inverter can be tied to a named SCC? However, in the "Operation Guide" there is a note I just noticed on page 3-26 that states:
    Although the XW Power System does support multiple XW Inverter/Chargers connected
    to multiple battery banks, such configurations cannot be set using the System Control
    Panel. A special configuration application provided by Xantrex is required. To configure
    such a system, contact your installer or Xantrex.

    I guess that answers the question: "It depends." And "Call us."
    You will have to use breakers or something to steer your backup genset to 1 inverter at a time.
    Maybe use inverter to generate AC2 for the other 2 ?

    That is another conundrum. If I have a 6 kW backup generator, will an XW4548 be able to transfer the entire source? Can't all three inverter back-up inputs be tied together?
    You may need 3 Sys Control panels, or just move one back and forth to program each inverter (does the inverter remember the settings, or is it only loaded in the SCP ? )

    I believe the settings are stored in the inverter. However, the thought of managing 3 separate SCPs is not thrilling. And I was hoping to have a Gateway interface to the rest of the automation in the house, while the PV system is in the detached garage. However, I have recently found through comments on this forum that the Gateway is a failed orphan product. When the dust finally settles, I might take one apart and see what I can do to make it useful - my specialty is embedded systems, programming, and system development. Who knows, with any luck, I might be able to publish an open source interface and save Schneider the time & effort. They seem to be a top-heavy organization with very little agility - reminds me of my days as a project engineer in the USAF.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system

    Again, not complaining about your energy usage--We are just (over all) pretty cheap guys (and gals) here and want you to know your costs going in.

    There do seem to be "issues" with connecting multiple XW Hybrid inverters on one Xantrex Bus--From reports here, the XW inverters are pretty "chatty" and placing several inverters on the same bus may lead to bandwidth issues.

    We can do some quick estimates on system sizing based on how much power you use and where you live.

    If this is a Grid Tied System (assuming it is Legal in your area/utility). Using PV Watts for Honolulu HI. 9,450 watts of solar panels (9.45 kW) and 0.77 eff for GT and 0.52 derating for off grid system:
    "Station Identification"
    "City:","Honolulu"
    "State:","Hawaii"
    "Lat (deg N):", 21.33
    "Long (deg W):", 157.92
    "Elev (m): ", 5
    "PV System Specifications"
    "DC Rating:"," 9.4 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 7.3 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 21.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","18.1 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 5.01, 1027, 185.89
    2, 5.59, 1040, 188.24
    3, 5.89, 1208, 218.65
    4, 5.79, 1153, 208.69
    5, 6.00, 1231, 222.81
    6, 5.91, 1169, 211.59
    7, 6.02, 1228, 222.27
    8, 6.25, 1273, 230.41
    9, 6.41, 1262, 228.42
    10, 5.72, 1172, 212.13
    11, 5.16, 1026, 185.71
    12, 4.92, 1006, 182.09
    "Year", 5.72, 13796, 2497.08

    Or about 1,000 to 1,200 kWH per month for Grid Tied

    And for full off grid system:
    "Station Identification"
    "City:","Honolulu"
    "State:","Hawaii"
    "Lat (deg N):", 21.33
    "Long (deg W):", 157.92
    "Elev (m): ", 5
    "PV System Specifications"
    "DC Rating:"," 9.4 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 4.9 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 21.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","18.1 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 5.01, 677, 122.54
    2, 5.59, 690, 124.89
    3, 5.89, 799, 144.62
    4, 5.79, 760, 137.56
    5, 6.00, 811, 146.79
    6, 5.91, 769, 139.19
    7, 6.02, 809, 146.43
    8, 6.25, 840, 152.04
    9, 6.41, 834, 150.95
    10, 5.72, 775, 140.28
    11, 5.16, 677, 122.54
    12, 4.92, 663, 120.00
    "Year", 5.72, 9102, 1647.46

    Or around 700-800 kWH per month.

    Depending on how much work you do yourself--A turnkey GT system is around $8 per Watt (maybe more for Hawaii--Something like $80k) and and full off grid system may run you $10-$20 per watt (DIY or turnkey install--$100k-$200k). (note I am not in the solar biz... Pricing is just for some back of the envelope calculations to level check some assumptions).

    Plus you will need to replace the electronics around every 10+ years, and the batteries every 7-20 years (depending on batteries chosen, how well they are treated, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system

    No offense taken Bill.

    The insolation numbers sound right - I'm working from an average value of 5.5 kWhr/m/day as measured at the UH Manoa campus (next door). But I don't know where the cost/kWhr are coming from. I wish we were paying $0.18/kWh! I just examined May bills, one very small, one very large, for two houses and after subtracting the fixed costs, I see $0.30/kWh for both. Of course, it's only going up because, well, there is no competition.

    The hardware is being assembled on the cheap. The Sharp panels are already purchased and delivered for the princely sum of $2/Watt. I'm expecting about another $1 to $1.5/Watt for the chargers and inverters, and $0.25 to $0.50/Watt for the batteries. Right there that's $3.25 to $4/Watt or $32K to $38K gross for a 9.5 kW system (nominally 52kWh/day) - see, I can be as cheap as they come! Derated by 0.77 that's $12/day and $365/month and energy independence.

    The installation will be bundled into the construction of the garage, which is being designed from the ground up to support the expected wind loads (quite high - I hope there is a egg beater wind turbine in the future). The roof will be oriented facing directly South, with a single slope at the angle of our latitude of 21.3 degrees (under the roof will be my workshop, and under the workshop will be a 2 car garage). I expect that the installation will be a wash after the tax incentives.

    I am aware that the batteries are a "consumable," but I hope to find good, deep cycle batteries and maintain them tenderly. One of the rationales for the redundant system is to be able to switch out a bank of batteries for maintenance without shutting down the system.

    I was not aware that the electronics were expected to wear out. What are the failure modes to be expected? Are the failures repairable? Is the standard LRU an entire box? Ouch! Again, this provides impetus to go with a redundant system that degrades gracefully.

    And I have read about the "chatty" nature of the XW inverters. I suspect that this is repairable with firmware upgrades. Eventually.

    Andrew
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system

    Andrew,

    Look for posts started by user "adas" here... He is also from Hawaii and setup his entire business (as I understand it) to run from solar + scrapped out forklift batteries. He also purchased used large MSW inverters and had very good luck with them to run his metal fabrication business (again, I think that is what he does--or at least related work).

    How long with the Electronics Last... More or less, these are the same components as in your typical tower computer case--Digital/Switching power supplies. Fans, large capacitors, and even digital components have a limited life--Frequently (from my point of view) a service life that is limited by the number of thermal cycles that the devices are subjected too (and how large a temperature band they are subjected too).

    The 10 year life--Again is my two cents guestimate of what I would use in a cost of power equation. Capacitors and power components are probably most likely to fail--but you can have other digital (cpu, memory, etc.) and analog components fail too...

    And, it is not necessarily that the product is "unrepairable" -- It is more the issue that any major components need to perform the repairs are not available any more.

    Many of these new designs are driven by the advances in consumer and other high volume electronics. And, after about 10 years--The ability to find spare parts in stock (and don't cost an arm and a leg) gets very difficult.

    And--so even if your device fails because of a 1 watt resistor failure--The chances are that the vendor has already stopped supporting the 10 year old Inverter/Charge Controller/Etc. because of the lack of other critical spare components. And even if your's is "repairable"--you will have a hard time finding somebody that will even bother trying (cost more to ship and debug than a new unit may cause).

    And, once you have to scrap your old unit--now you (or your installer) has to figure out how to wire up the 10-15 year newer unit into your existing setup.

    Not trying to scare of you off of even building your system out--Just want to make sure that everyone understand the issues behind trying to "run a power station" for 20-40 years.

    In a communications company I used to design product for--We were, many times, forced to design new generations of equipment because the old hardware was too costly to find/build out new systems. The old systems worked fine and did what the customers wanted--but we simply could not get Z80 processors and associated memory/PROMs/etc. in quantity at reasonable prices.

    Of course, with the new processors, more memory, etc.--we could upgrade our systems and their capabilities... But it was a lot of work to pick components that would be available for 5-10 years.

    Regarding redundancy--Not all it is cracked up to be... If you are not working on equipment that needs 99.999% uptime (something like 5 minutes a year down time)--Redundancy means 2x the amount of hardware, 2x the amount of things to go wrong, and the whole issue of testing standby hardware and knowing when the backup went down before the primary fails (very embarrassing to have your primary fail and then the backup fail to take over the load).

    If you have a few things that need 24x7 backup glitch free power--look at running a good quality UPS just for those loads (from your solar/grid/genset) and plan on manually fixing/rerouting if your other gear ever fails.

    Again--just a suggestion. I don't know your requirements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system

    Thanks Bill, I did check out adas's threads. He is the King of McGyver! I am trying to shy away from flooded batteries because my goal is an upfront investment in a system that manages itself without a lot of manual intervention. It's so easy to complicate life with technology that was supposed to make things easier.

    Do you know if there is any empirical data on charger and inverter longevity? As far as single point failures, I'm pretty handy with a soldering iron, and when I repair something, I tend to derate components like I'm still in aerospace. I put 15V electrolytic caps on 5V circuits, unless I have a tantalum on hand - that component will now be last to fail. That's why I have my electronics laboratory - I picked up a lot of good equipment from auctions during the post "dot com" busts in the Silicon Valley about 10 years ago.

    My goals with the system are two-fold: reliability, and maintainability. The "independent partitioning" supports both - perhaps "redundant" was the wrong word to use. When one charger, battery bank or inverter goes bad, the system stays up - with 1/3 degradation of capacity - but it remains up. The desired practical effect of the system is that we never notice when HECo fails, except that the streetlight in front of the house goes out. Computers, video, lighting, HVAC, kitchen, everything continues to work: no transients, not brown-outs, no flickering, no nothing - and no black magic that will annoy my better half.

    Andrew

    PS. I've got some Z80s for you. I even have a few 8080As, and a 4040 and a 4004, but you can't have them.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system

    Certainly, splitting the systems in 1/2 or 1/3rds will work....

    I am a bit concerned that you will need to "balance" charge between the various systems (system A has "extra" energy; and system "C" is running low because of HVAC operation in that wing of the home, etc.).

    Regarding life--Just that it is fairly likely after 5-7 years, there may be repairs, and after 10+ years, locating components and places that can program the hardware, etc. are going to be rare.

    There are some GT inverters (from reading here today) that are coming out with 25 year warranties (replacing electrolytic capacitors for example)--that should last longer.

    Will solar charge controllers and hybrid inverters follow suite--I really don't know.

    I expected my solar panels to last 25+ years--And I had to get them replaced after 5+ years. Luckily, my mfg. was still in business to replace them. And my inverter vendor replaced my GT inverter with a brand new unit--even though my was still working fine and it was already out of its 5 year warranty (I guess some early units had a manufacturing defect that limited the life of the inverter).

    I am not trying to predict your experience--just that you have the funding available to do anything that may be required in the future to keep your system operating.

    Off Grid / Hybrid solar power is not cheap... And we have had a few people here find out the hard way that Grid Power, if available, will probably continue to be less expensive than solar unless or until batteries make a huge change (not sure it will ever happen in my lifetime).

    You can do some quick calculations on cost for your system:
    • (capital costs + 20 year maintenance costs + Battery Replacement + etc.) / (20 years * kWH per year energy usage) = $$/kWH
    For the most part, a true Off Grid system probably will cost in the neighborhood of $1-$2+ per kWH vs the $0.30 per kWH you are paying today.

    But if the system gives you what you want--We are more than happy to help you towards that goal.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Redundant Xantrex PV system

    So I see you need to involve Schneider if you want to use 3 battery banks but tie the inverter outputs together. What about keeping them as 3 separate systems - each inverter powering its own panel? Then if you have a failure, as someone else suggested, you can then tie the panels together manually. Install a 50 amp split-phase locking outlet under each panel tied to a 50 amp breaker you usually will leave off (and build a male-male extension cord to connect them... yeah, I know, not to code but hopefully its never used either).

    I appreciate your needs, I have a similar problem since I'm on the edge of my utility's service area and I'm down winding country roads - with lots of trees. I get glitches and full outages all the time so I resorted to installing a double-conversion 6 kw UPS a few years ago with a 22 kw battery bank. I also have a 12 kw genset but if I had to do it all again I would have bought something with half that power now that I have the UPS, too.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    techntrek wrote: »
    So I see you need to involve Schneider if you want to use 3 battery banks but tie the inverter outputs together. What about keeping them as 3 separate systems - each inverter powering its own panel?

    There are two problems with this: (a) to be grid tied, all the inverters need to share at least the AC input so they may end up backfeeding each other and (b) load balancing becomes a real bitch.
    Then if you have a failure, as someone else suggested, you can then tie the panels together manually. Install a 50 amp split-phase locking outlet under each panel tied to a 50 amp breaker you usually will leave off (and build a male-male extension cord to connect them... yeah, I know, not to code but hopefully its never used either).

    You, sir, must give John Carpenter nightmares. Even if I was willing to jiggy around with 80 Amp cables and breakers, you definitely never want 10KW of short-circuit potential on the male end of anything. Sure I'm cheap, but I value my life.
    I appreciate your needs, I have a similar problem since I'm on the edge of my utility's service area and I'm down winding country roads - with lots of trees. I get glitches and full outages all the time so I resorted to installing a double-conversion 6 kw UPS a few years ago with a 22 kw battery bank. I also have a 12 kw genset but if I had to do it all again I would have bought something with half that power now that I have the UPS, too.

    All of Oahu seems to be at the edge of the service area. A 12 kW generator does sound like a bit of overkill - I was planning on a 4 kW unit myself. Can anyone tell me if the XW hybrid inverters will charge batteries from the generator? I have looked into the fuel efficiency of the smaller gensets and found that they are most fuel efficient near full load. So when on generator, can the XW chargers load it down to charge the batteries, then cycle to run off the batteries? Is this even a good idea because it will use up battery life?

    Andrew
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Redundant Xantrex PV system
    All of Oahu seems to be at the edge of the service area. A 12 kW generator does sound like a bit of overkill - I was planning on a 4 kW unit myself. Can anyone tell me if the XW hybrid inverters will charge batteries from the generator? I have looked into the fuel efficiency of the smaller gensets and found that they are most fuel efficient near full load. So when on generator, can the XW chargers load it down to charge the batteries, then cycle to run off the batteries? Is this even a good idea because it will use up battery life?

    The standard 120/240 VAC XW will charge from a 120/240 VAC genset. It also can be programmed to limit maximum current from the genset to XX amps--And share the generator power between charging and loads. Also, if the loads exceed generator capacity, the Inverter can actually support the AC loads too.

    And, if you only need 120 VAC (generator and mains), you can reconfigure the unit to run at full wattage on 120 VAC (may need firmware change too).

    For the most part, it will cost you more money (reduced battery life) if you cycle the batteries daily instead of using grid power.

    Does your utility support Net Metering (Grid Tie) power?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    BB. wrote: »
    The standard 120/240 VAC XW will charge from a 120/240 VAC genset. It also can be programmed to limit maximum current from the genset to XX amps--And share the generator power between charging and loads. Also, if the loads exceed generator capacity, the Inverter can actually support the AC loads too.

    Excellent, that's what I was hoping for. This would only be necessary for an extended outage, like say, another tsunami or a hurricane. Which are not unheard of in these parts.
    Does your utility support Net Metering (Grid Tie) power?

    Most reluctantly. HECo is a public company that despises their customers and views us as cash-filled piñatas to be beaten with sticks until all the money falls out (read: "shareholder value"). They see no advantage to themselves for supporting solar (much less infrastructure investment), so, as I understand it, it took an act of the legislature to finally force net-metering upon them. In fact, HECo is the only utility in the island that stubbornly refuses to go to remote meter reading, so they demand an easement on every property to access their meter. And in the process, employ hundreds of otherwise unemployable, who wander in and out of your yard on a monthly basis. Yeah, that's certainly a warm feeling. But of course there is no free lunch: they have to charge you for that privilege.

    It has always been my plan to be grid tied, for the time being. But I have yet to enter the ring with HECo on this project, and I suspect that it will be a knock down, drag out affair. To sweeten the pot, the city & county has all manner of intrusive and unreasonable demands of its own. From my reading of the Revised Ordinances of Honolulu, it is a misdemeanor to build a solar PV system and not inform the planning department. It is similarly a misdemeanor to disconnect such a system, or to sell or buy the property with the system, and not inform the planning department. To think, you could go to jail because you bought a house with a PV system, and in the middle of up-ending your life and moving your possessions, pets and loved ones, you don't stop to take the time out to inform some petty bureaucrat - barely awake, in a comfy air-conditioned office - that you now own a PV system that was installed on the property at some earlier time. It's genius.

    That's part of the price of living in paradise: the state and city & county government is exceptionally obstructive and useless. But they provide nearly a quarter of all employment. To those unqualified to read meters.

    Andrew
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Redundant Xantrex PV system
    There are two problems with this: (a) to be grid tied, all the inverters need to share at least the AC input so they may end up backfeeding each other and (b) load balancing becomes a real bitch.

    No, if the grid goes down they will all drop off the grid. No backfeeding is possible. Otherwise you and a neighbor with a grid-tied PV system could backfeed each other, anti-islanding would always be a problem and grid-tie PV systems would be illegal.

    Load balancing is extremely easy when you do it before installing the circuits in the panels. Add up your loads, divide them by 3. With 3 separate systems you can also plan for a "clean" system and a "dirty" system - put your computers on one system and put your motor loads (fridges, hvac) on another so their startup surges don't affect the computers. Put your lighting, tvs, etc on the 3rd system, again so the startup surges from the motor loads don't give you flickering lights. With my system that's my biggest problem - every time one of the fridges or freezer kicks on my tube flourescents in my kitchen dim for a second. I can't see it on my CFLs because they have such a wide voltage operating range, but I think your LEDs would have that problem since LED light output is so sensitive to input voltage. If you use ultra-efficient mini-split hvac systems flickering won't be a problem with them since they soft-start the compressors, so you could mingle some of those loads on your lighting system. I plan on converting to them soon.
    You, sir, must give John Carpenter nightmares. Even if I was willing to jiggy around with 80 Amp cables and breakers, you definitely never want 10KW of short-circuit potential on the male end of anything. Sure I'm cheap, but I value my life.

    I was going to suggest using service-rated manual transfer switches, each one set up to switch between utility input or one of the other panels. But that would require 6 of them, lots of spaghetti wiring, a major pain making sure you keep your phases straight, and probably ten thousand in extra cost. Even then I don't think it would pass code or at the very least you would have to hand-hold the code inspector. Weighing cost to benefit, having one of the systems go down is very small, so no matter how you look at it its a non-starter all around. Add in what happens when you sell the place and/or you die tomorrow and whoever comes after will have a mental breakdown understanding the system or why it was ever done that way.

    Then there is adding three 50 amp double-pole breakers, and three twist-lock 50 amp split-phase outlets. Plus building one 50-amp male-male extension cord long enough to reach between the farthest two outlets. No code issues during inspection (as long as you keep the extension cord out of sight), simple to understand (anyone else might wonder about the extension cord and then throw it in the trash, but the outlets are just... outlets). You can also re-use the outlets for high-amperage loads like powering an electric car's charger. As for a short, you MIGHT use this once in 20 years, maybe twice. You turn off the main breakers on both panels you need to bridge, turn off the breakers feeding the outlets, plug it in on both ends, and turn on all breakers except the main breaker leading back to the dead inverter. No shocks possible, especially since these are twist-locks that won't just pull out of the wall. I only suggest this because you don't sound like a newbie. This is also far safer than you opening up panels and stringing wires between them with covers off because you didn't design in a safe bridge. Or pulling individual circuits and rerouting them to another panel, just as fast as you can, in the dark... THAT is putting your life at risk.

    You have stated that providing backup power to your loads in the event of an inverter failure is a system requirement, and these are your options. You have completely safe but insanely expensive and hard to understand (and possibly not allowed anyway) - 6 service-rated transfer switches. Mostly safe with common sense, plus very cheap and easy to understand - 3 outlets and 3 double-pole breakers. Or stupidly unsafe and dirt cheap - stringing wires between open panels. Your choice.
    All of Oahu seems to be at the edge of the service area. A 12 kW generator does sound like a bit of overkill - I was planning on a 4 kW unit myself. Can anyone tell me if the XW hybrid inverters will charge batteries from the generator? I have looked into the fuel efficiency of the smaller gensets and found that they are most fuel efficient near full load. So when on generator, can the XW chargers load it down to charge the batteries, then cycle to run off the batteries? Is this even a good idea because it will use up battery life?

    Yes, you want to load a genset to its max, de-rated for altitude and highest possible air temperature for your location. You get your lowest cost per KW. Only consider diesel gensets if you have a base load above the minimum load specified for that genset to prevent wet-stacking. That's usually easy in commercial situations, and usually a problem for residential loads which often are only a few hundred watts for 3/4 of the day. In your case you have many loads that resemble commercial ones - steady computer loads going 24/7 - plus battery charging will be a known load and fairly steady since you'll only want to bring the batteries through the bulk charge state (to 80% SOC) during a long outage. So you might consider diesel instead of NG. You will only be cycling the batteries very shallowly for day-to-day glitches and an hour outage here and there, and only deeply every month or three so don't worry about longevity. You won't be using them like an off-grid system, cycling them deeply every day.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    techntrek wrote: »
    No, if the grid goes down they will all drop off the grid. No backfeeding is possible. Otherwise you and a neighbor with a grid-tied PV system could backfeed each other, anti-islanding would always be a problem and grid-tie PV systems would be illegal.

    I was contemplating the situation when the grid was up, and one inverter might be in sell back or load shave and one might be in charge. But I think that I'll go with the design from the Xantrex installation manual, but separate the DC busses from each charger and battery bank. This will entail the "special configuration program" from Schneider. I have time - my architect tells me that he should be able to begin planning Phase 3 this week. Battery Bill is going to be delighted when it's time to buy batteries.

    I plan to go with an NG generator for several reasons: fuel availability, and concern about the need to stock liquid fuel, concern about it going stale, and replenishment. NG is available from an underground line in front of the house, and can also be delivered, both for domestic usage and powering the generator. In addition, I plan to program an automatic genset start monthly for some short time like 15 minutes, after sunset, to keep the motor lubricated and head off a failure when I really need it. I am assuming that the AC2 inputs of multiple XW inverters can be tied in parallel to a single split phase genset.

    Andrew
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Redundant Xantrex PV system

    One thing to consider with NG units, is your local earthquake activity. Think about the California quake in '89 and all the NG fireballs all over the place from broken lines. A 500 gallon LPG tank gives you many of the same benefits as NG (burns clean, stores indefinitely) and will most likely be available after a big quake.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Les NagyLes Nagy Solar Expert Posts: 121 ✭✭
    Re: Redundant Xantrex PV system
    But I think that I'll go with the design from the Xantrex installation manual, but separate the DC busses from each charger and battery bank. This will entail the "special configuration program" from Schneider. I have time - my architect tells me that he should be able to begin planning Phase 3 this week. Battery Bill is going to be delighted when it's time to buy batteries.

    There is no special configuration software. You only need to use XWConfig and/or Caltool. Referring to my thread: http://forum.solar-electric.com/showthread.php?t=11094
    You can see that in my last post the procedure to make it work is as follows:
    "When hooking two inverters in parallel but with separate battery banks, the output voltages of the two inverters must be finely tuned so that they "see" the same voltage. It is not merely a matter of setting the voltages in XW Config to the same value as the XW inverters do not have very accurate outputs according to the setting. I had to set one inverter to 218V and the other to 224 volts for them to be in balance. Otherwise, the one that is in reality higher in output voltage will push its power into the other's battery bank through AC coupling.

    The best way to set this IMHO at this point is with XW Caltool which allows much finer control over the output values and a better balance."


    I am assuming that the AC2 inputs of multiple XW inverters can be tied in parallel to a single split phase genset.

    Yes, but when using XWs in parallel, and one is acting master, both inverters need to qualify the generator before either can use it.
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    techntrek wrote: »
    One thing to consider with NG units, is your local earthquake activity. Think about the California quake in '89 and all the NG fireballs all over the place from broken lines. A 500 gallon LPG tank gives you many of the same benefits as NG (burns clean, stores indefinitely) and will most likely be available after a big quake.

    Great, something else to worry about! Actually, there is little I can do about the existing infrastructure. On my side, however, I will be running flexible HDPE lines inside of 2" schedule 40 conduit from the curb to a manifold and then to each destination. This should leave room for a significant amount of ground movement. I am leaving the option of an NG tank open by bringing the gas to a manifold at the rear of the house before splitting it out, so the gas source can be easily switched from underground to tank and back. This is driven more from a supply price/diversity perspective rather than an Armageddon scenario. Oddly enough, sitting on the Pacific's Ring of Fire, we have surprisingly little earthquake activity.
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    Les Nagy wrote: »
    There is no special configuration software. You only need to use XWConfig and/or Caltool. Referring to my thread: http://forum.solar-electric.com/showthread.php?t=11094

    You, sir, are the man. This is exactly the information I needed. I was unaware of the XWConfig S/W or the USB-Xanbus (CANbus) interface. I can only locate information about XWConfig - can you tell me more about Caltool?

    Also, I was thinking about an idea of sending part of the PV array output through an MPPT, batteries and one or two XW hybrid inverter/chargers. The other part would be directly grid tied through one or more GT inverters in a "mini-grid" configuration mentioned in Schnieder's "3268.0.ac-coupling-app-note(976-0240-01-01_rev-a).pdf". In this "mini-grid" configuration, the GT inverter(s) is tied to the output side of the XW hybrid charger/inverter. However, the way the XW controls the GT is by slipping AC frequency until the GT finds it out of spec, and shuts down, which seems awful primitive to me. According to GT 3.3/3.8/4.0/5.0 spec sheets, they includes both RS232 and Xanbus interfaces. Is the XW Hybrid firmware unable to communicate with the GT inverters? The approach in the application note seems kind of clunky, including the possibility that the GT inverter is upset at the transient when the XW hybrid switches from AC1 to AC2 when the grid fails, so the GT will drop offline for 5 minutes. Has anyone tried this "mini-grid" approach?

    Andrew
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Redundant Xantrex PV system

    If you want to do that I think you'll do better looking at the Sunny Boy and Sunny Island line. The SB 6000 has 95.5% CEC efficiency @240 volts, XW 6048 is 92.5% CEC. Other SB models get even better efficiency, I grabbed the numbers for the 6000 so you could directly compare to the XW 6048. Just a few percentage points over the lifetime of the system can literally mean the equvalent of an extra year's output for free by end-of-life.

    The SB will control the SI using frequency control, supplying the SI via AC for loads and battery charging.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Les NagyLes Nagy Solar Expert Posts: 121 ✭✭
    Re: Redundant Xantrex PV system
    This is exactly the information I needed. I was unaware of the XWConfig S/W or the USB-Xanbus (CANbus) interface. I can only locate information about XWConfig - can you tell me more about Caltool?

    Caltool is a program that Xantrex only gives out to you if you really need to adjust something for a specific reason. It allows you to adjust the calibration references inside the equipment. Doing this incorrectly can destroy things so they seem to be careful about releasing it.

    The best way to get both programs is to phone Schneider/Xantrex and explain what you want to do and they should email you the files you need. Also keep in mind that when you have two separate systems running, they can be run in master slave mode, or in simple synchronous mode.

    In master/slave mode, if the master goes down for any reason, they slave shuts off. If the slave goes down, the master will/can continue to operate. So in this case, it is not truly redundant.

    If you connect both inverter outputs together in soley AC synchronous mode, then things can be a little messy, but I have not tried this setup yet.
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    techntrek wrote: »
    If you want to do that I think you'll do better looking at the Sunny Boy and Sunny Island line. The SB 6000 has 95.5% CEC efficiency @240 volts, XW 6048 is 92.5% CEC. Other SB models get even better efficiency, I grabbed the numbers for the 6000 so you could directly compare to the XW 6048. Just a few percentage points over the lifetime of the system can literally mean the equvalent of an extra year's output for free by end-of-life.

    The SB will control the SI using frequency control, supplying the SI via AC for loads and battery charging.

    Thank you for that suggestion. I've begun to look at Sunnyboy products, and they do look interesting, and expensive. I couldn't figure out if they make solar charge controllers - they show them as a blue box in some diagrams, but they seem to specialize in battery inverters and solar/wind inverters. And I could find little information about any kind of C3 interface for individual units to communicate or coordinate. Is "funging with AC mains frequency" the standard method of communicating between inverters? Aside from how it may impact other devices that rely on a stable AC frequency (clocks), it just seems so primitive - like sticks and sharp stones. We live in a world of gigabit home networks! The Xanbus CANBus seems like a step towards the future, though it sounds like they have a long way to go. It does appear there is a "communications option" that may be added to select Sunny units - RS232 or RS485 - relying on a Windows PC host. I haven't figured out if it is for data collection only or allows for real time control. Most of the documentation on the SMA web site seems to be limited to marketing collateral and the few tech docs are nearly a decade old. The logging functions appear rudimentary, requiring Windows 95, and storing the data as comma delimited ASCII text in predetermined files on your "C:" drive.

    Andrew
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    Les Nagy wrote: »
    Caltool is a program that Xantrex only gives out to you if you really need to adjust something for a specific reason. It allows you to adjust the calibration references inside the equipment. Doing this incorrectly can destroy things so they seem to be careful about releasing it.

    The best way to get both programs is to phone Schneider/Xantrex and explain what you want to do and they should email you the files you need. Also keep in mind that when you have two separate systems running, they can be run in master slave mode, or in simple synchronous mode.

    In master/slave mode, if the master goes down for any reason, they slave shuts off. If the slave goes down, the master will/can continue to operate. So in this case, it is not truly redundant.

    If you connect both inverter outputs together in soley AC synchronous mode, then things can be a little messy, but I have not tried this setup yet.

    Thank you for that information. I had noticed the master/slave architecture and it had me wondering what happens in the event of a fault, or when the master needs to be taken offline. In the my heart of hearts, I had hoped that the Xanbus protocol and firmware would allow for the graceful recovery from the loss of the "master" with the election of another master. Instead, the implementation appears to be designed to magnify a single point failure to system wide failure, negating any kind of redundancy. In the communications and networking world, failover is quite common, if not required outright, to minimize downtime.

    Can you explain the difference between the master/slave mode and synchronous mode? My guess is that parallel inverters need the AC Sync ports tied together, so they don't backfeed each other, which would be "synchronous mode". When the units are also tied together via the Xanbus, there must be one firmware making the decisions about DC load, AC load, and time based power profiles. Hence the master/slave relationship. In synchronous mode, the time based decisions become dicey if the internal clocks are not initialized identically.

    In the meantime, I wonder if there is enough flexibility in the Xanbus protocol to allow an external device to handle the master failover, and source & load management, among other things? I can dream, I suppose.

    Andrew
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Redundant Xantrex PV system

    I suppose if you ran all components in a star-hub configuration, with your "external device" in the middle, and did some reprogramming of the varioius devices to accept some new commands (like "hey inverter 2, inverter 1 is dead, you are now the master"), that would be possible. For existing components using your theoretical brain device. If the system was designed correctly star-hub and your device shouldn't be necessary.

    I agree with you that systems today should be way more advanced. From a functional standpoint the XW line is very advanced compared to other offerings, but Xanbus is not. The fact that some XW components can overload the bus with status updates is insane - obviously they haven't hired a good networking engineer to help tweak it. Your brain device could help correct this, filtering out redundant data. How many thousands of times a second does the inverter really need to tell everything else that its input voltage is good? :-)
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: Redundant Xantrex PV system
    techntrek wrote: »
    I suppose if you ran all components in a star-hub configuration, with your "external device" in the middle, and did some reprogramming of the varioius devices to accept some new commands (like "hey inverter 2, inverter 1 is dead, you are now the master"), that would be possible. For existing components using your theoretical brain device. If the system was designed correctly star-hub and your device shouldn't be necessary.

    I agree with you that systems today should be way more advanced. From a functional standpoint the XW line is very advanced compared to other offerings, but Xanbus is not. The fact that some XW components can overload the bus with status updates is insane - obviously they haven't hired a good networking engineer to help tweak it. Your brain device could help correct this, filtering out redundant data. How many thousands of times a second does the inverter really need to tell everything else that its input voltage is good? :-)

    I have read up on Modbus, which is the underlying API layer, ontop of CANbus, that defines Xanbus. Modbus was developed by Modicon in 1979, to address the needs of the Programmable Logic Controller market of the last century. Some time in the last 30+ years, Schnieder bought Modicon. While the Modbus is a publicly published standard of the Modbus Organization, it seems to be primarily controlled by Schneider, who also maintains a proprietary version called "Modbus+" or "Modbus Plus".

    The idea for Modbus back when the days of bell-bottoms and "Funky Town" was that one master controller would supervise a number of slave devices. It was advanced for its time, and supported point-to-point/star topology with a RS232 PHY, and multidrop with RS485. It eschews bus arbitration questions by declaring a single master as the only initiator of bus transactions. Hence, in order for the master to know what's going on with a slave is to poll it, regularly. I suspect that this is the cause for all the hybrid inverter traffic from the master to all the slaves, the cause for the complete reliance on the master, and system failure when the master disappears.

    This implementation for a power subsystem is plainly inadequate. There is no support for dynamic network configuration as devices are added, removed, or fail. There is no mechanism for devices to discover dependencies, failover, and vote for leadership. The Modbus was a fine solution to the PLC problems of the late 20th century, but is plainly inadequate for the power systems of the 21st.

    As far as the Xanbus implementation goes, it scales very poorly and is demonstrably fragile. Each subsystem's firmware must necessarily incorporate all knowledge required for it to become a network master over heterogeneous devices, should someone architect a topology place it as a master. It is too late to use the native features of CANbus - including higher speed - without new firmware from Schneider for every device. The other option is to implement a dedicated controller. The usual, (and poorest) choice is some clunky Windows white box, that will irregularly blue screen, taking down the system. Either it is used as a desktop and is rebooted frequently (upsetting the control system) or it will sit in a corner and acquire viruses as it is unlikely to be patched and loaded with recent AV software. The other option is a dedicated, and very expensive, custom controller box, only available from the vendor, with an unconscionable service contract befitting the vendor lock-in.

    The Gateway, or a similar small, embedded Linux box like a WRT54G or Chumby, would make a fine system controller, and network interface. The Xanbus could continue to be used with all the devices as Modbus slaves. Now you have a single piece of open source firmware that can be updated as necessary to support new devices - not necessarily all Xantrex either (now that I have discovered that SMA and others support Modbus). It may also be updated without going offline. Basically, it is Dan Lennox's PowerDashboard but without MS Windows, and a little more intelligence. One of the prime, but not obvious, functions of this firmware will be security: data logging is low security, but device configuration & control is must be highly secured. Outside control could be limited to just a few pre-configured enumerated options, e.g. "On Grid," "Off Grid," "On Back Up Generator," and "Off".

    This is just a seed of an idea in my head at the moment: decomposing a power system from the top down, into replicable blocks with specifiable inputs & outputs that can be organized graphically... I hope this doesn't sound too crazy.

    Andrew
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Redundant Xantrex PV system

    Crazy? It sounds awesome :D For off-grid systems I think an intelligent brain type system could make a few clever decisions like managing optional loads and generator starting. The kinds of functions I'd like to see in a such a device would be:
    • If the generator is on, and the load is less than 50%, then turn my well pump on.
    • If the batteries are at 60% State of charge and the weather forecast is for clouds all day, then turn the generator on early in the morning.
    • If the batteries are in float and there's surplus solar power, turn the well pump on
    • Reprogram my morningstar MPPT to perform a short charge to reach 2.65V for 5 minutes after being in absorb for 3 hours, every 2 days.

    For the SMA kit, they've released an open source API for windows and linux called YASDI, which can be downloaded from http://www.sma.de/en/products/software/yasdi.html with it, you can talk to every SMA device.
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