Connecting XW6048 system output

Well, here I sit, going through a series of rolling blackouts to help keep the Texas grid from more serious shutdowns. No better time that I can think of to post here for the first time. Also no better time to count my blessings that I’m here in south central Texas instead of the upper midwest during this latest blizzard. I am of course a new guy, not even having built my system yet. I’d like to present here my plans and some questions for which I have yet to find suitable answers. I plan to build a grid-tied system that is also capable of operating off-grid indefinitely. Power is not particularly expensive here, compared to the rest of the country, but my plans are in keeping with my desires for preparedness. The system would more than cover all my use 7 out of 12 months (5 months of A/C, that I would forego when necessary). So here’s the layout…

20 acres. The 6.3KW array, ground mounted, with a shed on the north side housing 24-32 6V 395Ah batteries plus the XW 6048 inverter and other associated components, including a 7-8 KW gen set sitting outside the shed. Approx 170’ north is the power pole w/meter and service disconnect. I trenched the 180’ southeast from there to the house and the line runs underground from there to the distribution panel in the house. To complete the picture and show the triangle (PV-grid inlet-house) the house itself is about 270’ east of the PV array.

My question involves the power output from the inverter during a grid outage. Partly because of the distance from the array to the house and the distance between the service disconnect and the main panel, and partly because of my not wanting to split the distribution panel into an essential and non-essential panel (with the essential connected to the XW output), I’m having trouble figuring out how to connect the inverter output to the main line from the grid service disconnect to the house. It would have to include an automatic transfer switch after the meter, and the inverter output would have to remain disconnected at all times when the grid is up. I’ve considered a contactor, or SSR to connect the inverter output to the line after auto transfer, but would need to also disconnect prior to grid recovery. I’m just not sure any of this could be done automatically. Might end up being a manual setup. There are a number of reasons that I want to be able to power everything (except the obvious A/C, dryer, and other appliances I consider nonessential). I have two deep well submersible pumps, each 1 ½ hp, and would only need one at any time, but one is powered from the meter pole the other from the house. I need the flexibility to run either at my discretion. In other words, there are some times when one appliance is needed, and another time for some other appliance. I would have to keep in mind which could or could not be run in a given situation. I would much prefer this over an “essential power panel” that had no flexibility.

So with the way things would normally work with an automatic transfer switch, I haven’t come up with a solution for this to work automatically. The manual solution is easy.

The other question would be if one should periodically turn off the grid for, say a week, and “exercise” the PV system, rather than just leaving it tied to the grid all the time.

Hope the post wasn’t so long-winded that it completely tripped your interest breakers.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Connecting XW6048 system output

    Not a bad first post...

    Does your utility Net Metering (i.e., grid tied power and billing)?

    Your best use of power is to setup the Hybrid system to do Grid Tied when the power is up (you can power your home and sell excess to the utility). This will at least help the solar panel/system pay for itself a bit when the grid is up.

    Where to place your Hybrid Inverter--As close to the utility drop as you can. For your case, I would guess at your home service and run the 300-400 VDC from the solar array to your inverter / service.

    As background, the reason is your inverter will raise your local line voltage a little bit... If your line voltage is already high (~250-255+ volts), when the inverter runs in GT mode, it can raise the line voltage to ~260-264 which is the typical high line voltage setting for GT inverters.

    So, you may want to get a good quality AC volt meter and check your voltage at your home (a few different times during the day, and even seasonally) and make sure that you don't have any high/low line voltage problems.

    For a transfer switch (pumps, other stuff), you can get some pretty nice and relatively cheap Iota transfer relays intended to switch between line and gensets (these are not the expensive computer controlled ones with once per week exercising and line qualification circuitry). Use those to select between pumps when the power is out (put on a timer or something).

    My other warning is that solar PV systems are not cheap to operate. Batteries need replacement every 5-15 years, inverters/electronics about every 10 years or so, etc...

    In my back of the envelop calculations, the rough range of power costs (before tax rebates and such):
    • Grid Tied (no battery backup) ~$0.15 to $0.30 per kWH
    • Hybrid (GT+Off-Grid backup) ~$0.45 per kWH (excluding power company charges)
    • Off-Grid (no utility power, genset backup) ~$1-$2+ per kWH
    Your system, would be generating, roughly as a Grid Connected system:

    Using PV Watts, 0.77 default efficiency for Grid Tied near Houston TX and a 6.3 kW fixed array:
    "Station Identification"
    "City:","Houston"
    "State:","Texas"
    "Lat (deg N):", 29.98
    "Long (deg W):", 95.37
    "Elev (m): ", 33
    "PV System Specifications"
    "DC Rating:"," 6.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 4.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.68, 503, 48.79
    2, 4.12, 502, 48.69
    3, 4.82, 642, 62.27
    4, 4.98, 629, 61.01
    5, 5.24, 670, 64.99
    6, 5.53, 673, 65.28
    7, 5.43, 677, 65.67
    8, 5.44, 685, 66.45
    9, 5.40, 664, 64.41
    10, 5.19, 667, 64.70
    11, 4.33, 555, 53.84
    12, 3.34, 453, 43.94
    "Year", 4.79, 7319, 709.94

    So, for Grid Tied, your system would generate (on average) around 453 to 685 kWH per month.

    When it is in off-grid mode, assuming 0.52 overall system derating:
    "Station Identification"
    "City:","Houston"
    "State:","Texas"
    "Lat (deg N):", 29.98
    "Long (deg W):", 95.37
    "Elev (m): ", 33
    "PV System Specifications"
    "DC Rating:"," 6.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 3.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.68, 330, 32.01
    2, 4.12, 329, 31.91
    3, 4.82, 423, 41.03
    4, 4.98, 413, 40.06
    5, 5.24, 440, 42.68
    6, 5.53, 441, 42.78
    7, 5.43, 443, 42.97
    8, 5.44, 449, 43.55
    9, 5.40, 438, 42.49
    10, 5.19, 442, 42.87
    11, 4.33, 366, 35.50
    12, 3.34, 296, 28.71
    "Year", 4.79, 4811, 466.67

    Your off system, when off grid, will generate around 296 to 449 kWH per month...

    Anyway, my two cents worth. Your comments?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Connecting XW6048 system output

    Evening, Bill,

    Yep, the co-op utility will swap out to a net meter, and they pay me same retail price they charge per kWh. I fully intend to sell any excess. I believe you’re right about the location of the inverters, etc. and the generator. I had figured it best to run the AC the 170’ or so from the inverter to the grid tie, but might as well run the high volt DC the 170’. I built this house in 2000, and did all the electric, not even considering solar at the time. I have measured the grid voltage a number of times and have never seen it below 242 or above 248.

    The co-op will require an auto transfer switch to disconnect from the grid during outages. and I don’t have any problems understanding that. It will be a 200A ATS, but I’ve not seen one that will complete the transfer without seeing the requisite voltage output from the backup system. If I have the generator controlled by the XW6048, I still need something to switch on the inverter outputs, and do it soon after the ATS disconnects the grid. The output from the XW6048 cannot be tied to the grid, so I’m looking for a way to have it connect its output to the main to the house after the transfer switch has dropped the grid offline.

    Concerning the well pumps, I normally have one or the other turned off all the time anyway, and in the case of being on inverter power, would definitely not need be concerned about switching them. I just like having the redundancy. Each pump serves my needs adequately on its own, each capable of 12 gal/min. The only reason I mentioned them was as an example of the flexibility I desire over use of the available wattage output of the inverter when off grid. It is that desire that makes it impractical to have a separate, distribution panel from the inverter output than the one I now use from the utility line. So instead of having the refrigerator, freezer, one well, the furnace fan, and a light or two as “essentials” on the distribution panel from the inverter, and everything else on another distribution panel from the grid, I’d leave the distibution panel as is and be judicious in my use of available inverter power. My problem is how to tie in the inverter output to the existing line to the house just downstream of the ATS. There may not be a way that I would feel safe with the ATS doing all the switching automatically. I sure don’t want the ATS switching back to the grid while the inverter output is still connected.

    Let me pose the question another way. If I understand the XW6048 setup, in the short time I’ve been looking at it, the AC1 line is connected to the grid (and would be required to be connected downstream from the ATS), AC2 to a generator (optional) and output to a separate distribution panel that would power those certain essential loads in the house. The selling to the grid is done via the AC1 tie. If this is the case, could the AC1 be used (in lieu of the “output”) to power the house after the ATS disconnected the load? I suspect not, and if not, then I need some way to disconnect the AC1 tie to the downstream side of the ATS and to connect in its place the output from the inverter, all after the ATS disconnects the grid. And undo all this in reverse order when grid power is restored. And that is what I can’t quite figure out how to do automatically. I’m intrigued by the whole thing at this point, so still search for that elusive “how-to”.

    The batteries that I plan to use would be 24 6v 395Ah Crowns, 8 in series for 48v. I expect to have to replace them (hoping for the high side of your 5-15 year projected life), but I was surprised by your estimation of the XW system lifespan. This may figure into my consideration on whether to go forward with this idea. I have never expected that this setup would ever pay for itself in my lifetime (I’m 64 shortly) but that wasn’t really part of the equation anyway. I’m just one of those “preparedness” nuts, who hopes for the best, but long ago decided not to expect it. So along with my 1000 gal propane tank that lasts me 3 years without consciously conserving, I look for something to replace the electic utility should the need arise.

    My PV production figures are a bit better than you presented, BTW, since I live far to the west of Houston. I’m much closer to San Angelo (110 miles SE) and slightly higher than San Angelo’s elevation (2000’ vs 1900’)

    By PV Array’s calculator:

    Grid-tied

    "Station Identification"
    "City:","San_Angelo"
    "State:","Texas"
    "Lat (deg N):", 31.37
    "Long (deg W):", 100.50
    "Elev (m): ", 582
    "PV System Specifications"
    "DC Rating:"," 6.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 4.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 31.4"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.4 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.87, 689, 57.88
    2, 5.40, 679, 57.04
    3, 5.92, 800, 67.20
    4, 6.09, 779, 65.44
    5, 5.91, 756, 63.50
    6, 6.06, 738, 61.99
    7, 6.23, 770, 64.68
    8, 6.34, 792, 66.53
    9, 6.01, 750, 63.00
    10, 5.91, 780, 65.52
    11, 4.69, 611, 51.32
    12, 4.54, 637, 53.51
    "Year", 5.66, 8780, 737.52


    Off-grid:

    "Station Identification"
    "City:","San_Angelo"
    "State:","Texas"
    "Lat (deg N):", 31.37
    "Long (deg W):", 100.50
    "Elev (m): ", 582
    "PV System Specifications"
    "DC Rating:"," 6.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 3.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 31.4"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.4 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.87, 457, 38.39
    2, 5.40, 452, 37.97
    3, 5.92, 533, 44.77
    4, 6.09, 517, 43.43
    5, 5.91, 500, 42.00
    6, 6.06, 487, 40.91
    7, 6.23, 507, 42.59
    8, 6.34, 523, 43.93
    9, 6.01, 495, 41.58
    10, 5.91, 516, 43.34
    11, 4.69, 404, 33.94
    12, 4.54, 423, 35.53
    "Year", 5.66, 5814, 488.38



    Thanks for your input, Bill. This is going to be interesting…..fun, too!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Connecting XW6048 system output
    Harper wrote: »
    The co-op will require an auto transfer switch to disconnect from the grid during outages. and I don’t have any problems understanding that. It will be a 200A ATS, but I’ve not seen one that will complete the transfer without seeing the requisite voltage output from the backup system. If I have the generator controlled by the XW6048, I still need something to switch on the inverter outputs, and do it soon after the ATS disconnects the grid. The output from the XW6048 cannot be tied to the grid, so I’m looking for a way to have it connect its output to the main to the house after the transfer switch has dropped the grid offline.
    As far as I understand, the X6048 includes the ATS required to interface to the grid, to the genset, and to the loads...

    The XW hybrid inverter is capable of both Grid Tied (tied directly to the grid) and Off-Grid (open the ATS and operate as an Off-Grid inverter).

    With the Genset, the Generator can both charge the battery bank and operate your AC Loads.

    I did talk with one installer about an XW installation that had manual transfer switches (really bypass breakers) to allow the home to have power when the inverter system was being serviced... Apparently, the interlock hardware (sheet metal?) that prohibited having both the inverter on and the grid directly connected together was missing--and the two sets of breakers were turned on at the same time--Not a good thing. :cry:
    Concerning the well pumps, I normally have one or the other turned off all the time anyway, and in the case of being on inverter power, would definitely not need be concerned about switching them. I just like having the redundancy. Each pump serves my needs adequately on its own, each capable of 12 gal/min. The only reason I mentioned them was as an example of the flexibility I desire over use of the available wattage output of the inverter when off grid.
    You have several ways of addressing the pump issue...
    • Large inverter to power through the surge current required to start the pumps
    • Use a VFD (Variable Frequency Drive) to ramp up and control the pump power/speed. Depends on the pump type if you can use VFD (three phase pumps or one phase pump with starting cap at well head are OK. Pumps with cap in well cannot be run from VFD--as I understand)
    • Install an AC/DC pump in well (like Grundfos or others). Works from solar panels, battery, or AC genset. Of course, way less water flow. You need either a cistern on the surface or several pressure tanks to store water for use.
    It is that desire that makes it impractical to have a separate, distribution panel from the inverter output than the one I now use from the utility line. So instead of having the refrigerator, freezer, one well, the furnace fan, and a light or two as “essentials” on the distribution panel from the inverter, and everything else on another distribution panel from the grid, I’d leave the distribution panel as is and be judicious in my use of available inverter power.
    Practically, speaking, you probably will need two panels... Main AC panel (pump, AC system, drier, etc.) that are for grid use only. And the protected panel for loads that you want to operate from backup power.
    My problem is how to tie in the inverter output to the existing line to the house just downstream of the ATS. There may not be a way that I would feel safe with the ATS doing all the switching automatically. I sure don’t want the ATS switching back to the grid while the inverter output is still connected.

    If you put in a "primary" ATS switch--I assume that would be AC Main / AC Genset switching which would allow you to run your whole home (Air Conditioning, drier, etc.) from the genset (and your backup loads through the XW).

    I am not sure this is a good way to do it or not... I am not sure what the XW would do with gen power on AC1. There is the issue of frequency stability and the Grid Tied function (XW should not Grid Tie power the genset).
    Let me pose the question another way. If I understand the XW6048 setup, in the short time I’ve been looking at it, the AC1 line is connected to the grid (and would be required to be connected downstream from the ATS), AC2 to a generator (optional) and output to a separate distribution panel that would power those certain essential loads in the house. The selling to the grid is done via the AC1 tie. If this is the case, could the AC1 be used (in lieu of the “output”) to power the house after the ATS disconnected the load? I suspect not, and if not, then I need some way to disconnect the AC1 tie to the downstream side of the ATS and to connect in its place the output from the inverter, all after the ATS disconnects the grid. And undo all this in reverse order when grid power is restored. And that is what I can’t quite figure out how to do automatically. I’m intrigued by the whole thing at this point, so still search for that elusive “how-to”.

    The XW has AC1 In and AC2 In and AC Out... It should manage all of those automagically.
    The batteries that I plan to use would be 24 6v 395Ah Crowns, 8 in series for 48v. I expect to have to replace them (hoping for the high side of your 5-15 year projected life), but I was surprised by your estimation of the XW system lifespan.

    Good batteries, with good maintenance, can last 15-20 years... There are a few people with lots of battery experience here that can probably help you with the details and the best choices for you.

    The 10 years on the inverter--That is just my experience with any digital electronics/power systems out there...

    It is sort of the nature of the commercial electronics market now. More than likely, there is something repairable (FETs, processor, IC's, Capacitors, etc.)--But the problem is that after 10 years, the majority of the "High Tech" electronics are no longer available (at least at reasonable prices and volume) as they have been replaced by some new whiz-bang electronics... So, personally, I would plan on saving money to pay for replacement hardware after ten years because, most likely, there will not be anybody able to service it.
    This may figure into my consideration on whether to go forward with this idea. I have never expected that this setup would ever pay for itself in my lifetime (I’m 64 shortly) but that wasn’t really part of the equation anyway. I’m just one of those “preparedness” nuts, who hopes for the best, but long ago decided not to expect it. So along with my 1000 gal propane tank that lasts me 3 years without consciously conserving, I look for something to replace the electric utility should the need arise.

    Yea--Making your own Off-Grid power station is not cheap up front and comes with DIY maintenance issues too.

    Many times, for short term outages, your genset and and 1,000 gallons of propane is hard to beat. Going Off-Grid is hard to do unless you really are going to conserve/cut back on power usage. Large Off-Grid Solar PV systems are tough to justify.
    My PV production figures are a bit better than you presented, BTW, since I live far to the west of Houston. I’m much closer to San Angelo (110 miles SE) and slightly higher than San Angelo’s elevation (2000’ vs 1900’)

    You are out of the marine layer effects of the Gulf?

    I have a 1,000' coastal mountain range between me and the Pacific Ocean---It is a night and day difference in weather and sun.

    Again--I would not suggest that I make the decisions for you--but we are all here to help you gain the knowledge so you make educated choices.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Connecting XW6048 system output

    Yeah, to answer your last question, I'm about 100 north and west of San Antonio. But most of the gulf influence goes up east of I-35 (San Antonio-Austin and north). I lived many years in Albuquerque, and our climate is much closer to that of Albuquerque than it is to that of San Antonio. Largely enfluenced by the Chihuahuan Desert.

    As far as the rest of your last post, I'll chew on it awhile. I am aware of about everything you wrote, but it's late and I don't think I've communicated my intention all that well. I do appreciate your comments. I'll be around.