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Thread: XW6048 for whole house battery backup

  1. #1

    Default XW6048 for whole house battery backup

    I'm looking for some advise on how to build a hybrid battery/generator backup system for my on-grid home. The goal is to coast through small (2 hours or less) grid outages on battery power with minimal disruption but to also use a generator to handle the longer outages. I'd like the system to be quiet, fuel efficient, and as automated as is reasonably possible.

    At first glance, the XW6048 seems to be just the ticket. I am sure that some of it's cost is due to also being able to support a PV array. While I am not planning for this as part of the initial project I do want to plan for it. I have 400sq of prime unshaded (though nearly flat) roof space and another 350sq of partially shaded in the morning and again in the late afternoon roof space that I'd like to press into service at a later date. Right now, the primary goal is just backup power.

    I'm thinking that the first phase will be to separate my breaker panel (200amp service) into loads that I want backed up, and those I dont. I currently have many loads that would would never make sense even on a generator. These include two zones of (rarely used) baseboard heat, oven, clothes dryer, pool pump, etc. I suspect that what remains could all be fed from a 60amp sub-panel.

    My current panel (30+ circuits) is monitored by 3 Brueltech 1240's. They give me 21 channels of monitoring so I have a pretty good idea of my loads. For any five minute period my total load rarely goes over 7kw and typical is far lower than that with an average under 30kwh/day. With the big loads out of the way, I would think the XW6048 would be just fine.

    Assuming the XW6048 is the way to go, the remaining questions have to do with the size and technology for both the generator and the battery bank. My (simple minded) analysis here is that I would need a minimum of 8-10kwh of capacity to get two hours of runtime assuming a 2kw average load for those 2 hours and a target of 50% discharge.

    My only experience with battery banks so far is with a large UPS in a data center where I hang out. It uses a two banks of 40 UB121000's and is designed to dump them all 80 in under an hour. So for my little project, it would seem that 8 would be able to handle my load and then some. Of course, Liebert doesnt expect that this system will be cycled continuously over the course of an extended outage. I'd guess they are making battery life trade offs that I dont understand. Regardless, they do expect the batteries to last 5 years in their intended role as a stand-by power source.

    In my hypothetical system, two hours into an outage my batteries are down to 50% then the XW6048 tells the generator to kick in and charge the batteries to 80%. Assuming 80% efficiency for the charge, this would be about 3kw for an hour, or a bit more than half what a 6kw generator could produce and would still leave enough head room for the 2kw (average) load. Another assumption I'm making here is that the remainder of the batteries would still available to the inverter to handle any surge or short term increase in the load while charging.

    I'm sure I've missed many details here, but if I am even close, it would seem that a 6kw generator and 8kwh of battery would give me somewhere around a 50% duty cycle (1 hour on 1 hour off) on the generator. While all that sounds great, I'd like to understand better the limits and factors that affect the generator's duty cycle.

    So my questions to the experts are: 1) how far off are my estimates? 2) would this line of thinking work with FLA batteries? 3) Does the XW6048 "clean up" the generator output or pass it through directly? and related, 4) would I need to use an "expensive" inverter based generator for any reason other than noise control? 5) When grid power is available will I notice the load associated with keeping the batteries topped off. 6) What have I missed?

    Thanks in advance for playing along.

  2. #2
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    Default Re: XW6048 for whole house battery backup

    the XW6048 has no solar provisions, other than it can run off a battery that is charged from PV panels, via a Charge Controller.

    It does not alter the input AC power, but does have "generator support" so if you are using the genset to run some loads, and charge via it's internal 240VAC charger, and you have a large surge, like a well pump engage, the inverter will "assist" the generator to keep the voltage stable.
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  3. #3

    Default Re: XW6048 for whole house battery backup

    Quote Originally Posted by dBeau View Post
    At first glance, the XW6048 seems to be just the ticket. I am sure that some of it's cost is due to also being able to support a PV array.
    The cost of the XW-series is due to it being 120/240 split phase, integral, without stacking inverters. And it is pretty much the "Cadillac" of residential battery-based inverters. It has three power inputs - DC from your battery bank, grid input, and gen input. It has no provision to directly support a PV array.

    When on gen power it's internal transfer switch switches all loads to to the gen input. It monitors the gen input voltage and frequency and if it goes out of range (such as a heavy surge load lugging the generator down) it will disconnect gen input and momentarily switch the load back to battery to meet the heavy surge load, then bring the generator back online to meet the continuous load. The XW6048 has roughly 2x the surge capacity of most 6 kW generators.

    Most of the description of your proposed system seems reasonable.

    For the generator, if you want one that is VERY quiet and fuel efficient, I can highly recommend the Generac EcoGen. It is designed for off-grid use and therefore comes configured for 120 volt output. For 240 split phase you have to purchase a field installable 240 kit on it. But if you intend to use it only to take over the inverter loads and charge batteries when the bank gets sacked, I think it would be the perfect unit. It has a low rpm (2900) engine and makes about as much noise as a central AC unit running. It's two-wire start system will work nicely with the Xantrex generator control.

    That all being said, the only real flaw in your plan is that it would be much cheaper to simply install a standby generator for two hour outages and forget the battery backup inverter. The only reason I would use the inverter is if you have loads that have to stay lit when the utility power fails, as the XW6048 will seamlessly switch over to battery power without the lights even flickering. It will take 10 seconds or better to bring a standby generator online. But from a cost standpoint, the standby generator makes more sense.

    If you plan to add a PV array and/or wind power, then the big Xantrex starts to make more sense.
    --
    Chris

  4. #4

    Default Re: XW6048 for whole house battery backup

    I have most of my 120 volt circuits on a separate panel, attached to a UPS (the few remaining 120 volt circuits are things like attic lights). When we are home and awake the continuous load is usually around 1500 watts, and it is less than 500 watts during sleep/away periods. This includes 2 fridges, 1 freezer, a whole-house air circulation unit, the blower on 1 of my 2 heating/cooling systems, TVs, lights, things charging, etc. I have a 22 kw battery bank and under normal loading - no conservation measures - it will last up to 17 hours.

    Bottom line, I don't think you need 10 kw of battery to last you 2 hours. I also agree with the suggestion that just for 2 hour outages you should stick with an automatic genset and put small UPSs on things like DVRs to carry over until the genset takes over. If you anticipate longer outages then a hybrid battery + genset system makes sense to improve efficiency since gensets run most efficiently near full load. This is the reason I added a battery + genset to my house, since we are on the edge of the distribution system and often get outages (neighbors have stories of being w/o power for 2 weeks after an ice storm...).
    12 kw Generac, Honda EU3000is, 4.2 kw APC UPS powered either by battery or a Prius. Really.

  5. #5

    Default Re: XW6048 for whole house battery backup

    Quote Originally Posted by ChrisOlson View Post
    For the generator, if you want one that is VERY quiet and fuel efficient, I can highly recommend the Generac EcoGen. It is designed for off-grid use and therefore comes configured for 120 volt output. For 240 split phase you have to purchase a field installable 240 kit on it. But if you intend to use it only to take over the inverter loads and charge batteries when the bank gets sacked, I think it would be the perfect unit. It has a low rpm (2900) engine and makes about as much noise as a central AC unit running. It's two-wire start system will work nicely with the Xantrex generator control.
    From the specs I was able to find, the EcoGen seems about right. Until you pointed it out I'd been considering the Honda EU6500is with a propane conversion. The EcoGen specs have it even quieter than the honda but fuel efficiency seems about the same. I do know that the honda will play nice with my home automation (computers, UPB light switches, etc). But heard some stories about other generacs not doing so well. With the honda, I'm still trying to figure out if it's remote start will play nice with the XW6048's generator control.

    Quote Originally Posted by ChrisOlson View Post
    That all being said, the only real flaw in your plan is that it would be much cheaper to simply install a standby generator for two hour outages and forget the battery backup inverter. The only reason I would use the inverter is if you have loads that have to stay lit when the utility power fails, as the XW6048 will seamlessly switch over to battery power without the lights even flickering. It will take 10 seconds or better to bring a standby generator online. But from a cost standpoint, the standby generator makes more sense.
    I'd love to say that cost is no object, but I cant. On the other hand, I am willing to spend a bit to eliminate the annoyance of short outages. I dont really expect to use the generator much at all as most of the outages are well under two hours. I just want to keep everything running without interruption. I'm already running about 3kwh of UPS battery and have been tempted to get a couple more small units. Instead, it looks like $10k (plus my labor) will get me a nice generator, inverter, and battery bank that will not only take care of the short outages but protect me from the kind of mess the northeast is dealing with right now (family and co-workers still have no power). From what I've seen with my collection of UPS, I'd expect that one large inverter will be more efficient than many small ones. My large 1000va unit uses 35 x 12v @ 5ah batteries at cost of $500 for replacement batteries alone! I'd rather not replace those batteries again.

    Quote Originally Posted by ChrisOlson View Post
    If you plan to add a PV array and/or wind power, then the big Xantrex starts to make more sense.
    With the right kind of planning I figure I can add 4kw of PV to the system for the price of a charge controller and the panels. I have a bit more usable roof space but due to shading issues, I suspect I'd have to go with micro-inverters to make the most of it. I'm pretty comfortable with the XW6048 as the heart of the system. It's all the details around the edges that have my head spinning.

  6. #6
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    Default Re: XW6048 for whole house battery backup

    Your thinking sounds reasonable. Most of my offgrid clients can afford the best and I certainly do not want to spend anymore time than I have to with equipment. Plug and play! Look at the XW-80 CC also! Really simple installation.
    http://members.sti.net/offgridsolar/
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  7. #7

    Default Re: XW6048 for whole house battery backup

    A downside to the Generac Eco is it can't idle down under a light load, where the Honda can. I have a Generac, but if I had to do it all over again I would have the Honda instead.

    No reason to replace your UPS batteries with another set of gel-cells. I bought my first UPS (see my signature) specficially to replace its batteries with standard flooded lead acids. Way more watts for the buck. Downside is the float voltage isn't optimal, but I compensate by manually charging occasionally. Larger APCs can be programmed to up their float voltage but I'm not sure about the smaller ones like yours.
    12 kw Generac, Honda EU3000is, 4.2 kw APC UPS powered either by battery or a Prius. Really.

  8. #8

    Default Re: XW6048 for whole house battery backup

    Quote Originally Posted by techntrek View Post
    A downside to the Generac Eco is it can't idle down under a light load, where the Honda can. I have a Generac, but if I had to do it all over again I would have the Honda instead.
    I'd think with the generator control of the XW6048, the EcoGen would only be running when the batteries need charging. But yeah, I guess if you wanted to top them off, the honda would be better.

    I am curious about the output of the EcoGen... how clean is it compared to that of the honda?


    Quote Originally Posted by techntrek View Post
    No reason to replace your UPS batteries with another set of gel-cells. I bought my first UPS (see my signature) specficially to replace its batteries with standard flooded lead acids. Way more watts for the buck. Downside is the float voltage isn't optimal, but I compensate by manually charging occasionally. Larger APCs can be programmed to up their float voltage but I'm not sure about the smaller ones like yours.
    When replacing those batteries I spent a bit of time trying to determine if the charger in the UPS could do the job. I never really got there but was willing to try. In the end, $500 was as cheap as I could go for the 2100AH. The problem came down to the 60v input. Ten golf cart batteries would have doubled the price and I couldnt find a large enough 12v for under $100/ea either.

  9. #9

    Default Re: XW6048 for whole house battery backup

    Quote Originally Posted by dBeau View Post
    I am curious about the output of the EcoGen... how clean is it compared to that of the honda?
    I guess HDTV's are supposed to be real sensitive? We have a big Toshiba HDTV and have never noticed any problems with it when the gen is running.

    The EcoGen has an electronic governor, and every time I check it with the inverter Control Module panels, the output is dead on 60 Hz and 121 volts per leg (we have the 240 split phase kit on ours).

    I have a friend about 30 miles away that has a Honda EU6500is and he has never gotten it to work with his Outback inverters for auto-start. It is not set up for remote one or two wire start (option not even available from Honda - all they have a remote wireless thing) and he always claims he's going to hack in to the controls on the generator to see if he can make it work, but never has. Our EcoGen is DEFINITELY quieter than the Honda. The EcoGen makes about as much noise as a residential central AC unit running when you're standing right by it.

    As far as the EcoThrottle on the Honda? It's totally useless for off-grid use. A properly set up off-grid system does not use the gen to "top off" batteries, and start and run the gen at partial loads. For off-grid you set up your inverters so when they bring the gen online, they warm it up for about 10 seconds, then take it to full load.
    --
    Chris

  10. #10

    Default Re: XW6048 for whole house battery backup

    Quote Originally Posted by ChrisOlson View Post
    As far as the EcoThrottle on the Honda? It's totally useless for off-grid use. A properly set up off-grid system does not use the gen to "top off" batteries, and start and run the gen at partial loads. For off-grid you set up your inverters so when they bring the gen online, they warm it up for about 10 seconds, then take it to full load.
    --
    Chris
    I disagree. I've logged thousands of hours on Hondas running off-grid using the eco-throttle. It works fine and saves gas. Loads are not constant, nor is charging. And sometimes the sun doesn't co-operate at all and you have to use the gen to do the whole charging process. Better to do that on eco-throttle than to waste the gas used by a fixed RPM gen.

    BTW you bring the little Hondas "on line" by pulling the rope and plugging them in; there is no auto gen start possible for these small units.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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