Grid interactive 2kW Xantrex XW - with small genset and small battery bank

So here is my system I have been designing for about two years, and I think I have found all the right parts to make it happen. Here is my design basis:

Using Siemens generator-ready load center with MTS to split the buildings into grid and alternate energy systems.
Using the Xantrex XW 6048, with conduit box, and the XW-MPPT60-150 connected to around 2.5kW of PVs.
I don't have a PV panel product locked down yet, but these will be mounted on an out-building (a metal framed structure designed for PV panel roofing) in close proximity to the XW system (around 20' of DC cable). I will buy enough PV to fill my MPPT.
I have a really awesome 4kW air cooled diesel 1800RPM 240V genset electric start, that gets connected to AC2.
Use a small battery bank that has a primary function of peak load-shaving and short-term UPS hold-up for the XW inverter. 5kWh of SLA to start with.

Conditions in my area:
Frequent loss of power for several minutes during peak load periods.
Frequent brown-outs during peak load periods.
Once or twice a month several hour power outage from severe thunderstorms.
Infrequent one to two week outage from hurricane damage to distribution grid.

When the power is out:
Run on PV during sunlight, try to minimize consumption and maximize charging.
Run on generator at night, XW load-shaving to make a 4kW genset more useful.
Run generator on demand. 2-2.5 gallons for an overnight 10hr run. Can become automatic start.

When the power is on:
PV offsets consumption and will sell during the day, but not enough PV be a net exporter.

When the Alt-E system is down for service:
Throw the MTS on the Siemens load center and become a normal grid house again.


Thanks for your input!

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    well you haven't told us anything about the size and timing of your loads, we need these to fill out the picture. Especially why you have such a capable Inver/charger 6 KW
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    Loads ? Air Conditioning ? Electric heat ? If you want survival mode, you only need 1KW of PC, and can manually fire up the genset to to charge batteries.

    The inverter would "like" 600ah of batteries, because it uses the batteries as a capacitor to supply the AC peaks of the sine wave. too small of battery with near full loads, or load shaving, and you will vibrate your batteries to death at 120 hz, and heat up the fancy filter cap in the inverter.
    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 ,

  • solarcrawfishsolarcrawfish Registered Users Posts: 12
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    Sorry I neglected to mention loads. The loads are fairly significant actually, thus the Xantrex XW 6048 seemed attractive for this purpose.

    I have three buildings; a house, garage/apartment and a horse barn. The garage/apartment and the house nominally draw 500W during the day and without any appliances running.

    7 tons of central AC for the house, and electric DHW in both house and garage, no gas. Monthly use is around 1500kWh. All of these major appliances will be on the grid side of the Siemens generator ready load center(s).

    The apartment is 600sq ft with an inverter heat pump -12kBTU and 21SEER. This will be on the emergency power system.

    I read the:
    http://forum.solar-electric.com/showthread.php?15616-6048-reducing-sell-amps-because-of-a-small-battery-bank-will-it-work

    And it was extremely informative. It sounds like the XW just doesn't work as well is it says it does, with so many unexpected caveats that you can't read about in the operator manual.

    Is there another inverter that would work better for this application?
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    It sounds like the XW just doesn't work as well is it says it does, with so many unexpected caveats that you can't read about in the operator manual.

    It's in the manual, just needs to be read.
    While my house was being built, one day I noticed my batteries getting lower & lower, despite there being several sunny days in a row. I was horrified to discover the hardwood floor guy had opened up the main panel, and had clipped in the 240V 7.5KW floor sander, and had been sanding for 2 days. I have a single XW6048 and only 3KW of solar. My general had a 8KW generator that would not run the sander, so he thought his genset was bad, they finished the job with a 20Kw rental genset to run the sander. The 6048 is a tough awesome beast, if you feed it right. And when YOU are the power company, you have to read all the fine print under the fine print, in the back of the appendix.

    I think outback makes a 8KW house inverter - the Radian http://www.solar-electric.com/rasein.html
    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 ,

  • solarcrawfishsolarcrawfish Registered Users Posts: 12
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    So far I have identified Sunny Island, Outback, and Schnieder that make grid interactive battery backup systems in this "whole house" power class. Did I miss any?

    I did read the latest XW operator manual... I appreciate the reality check and I may grab some larger batteries.

    I have a 50kWh 48V battery bank from an old PBX sitting around on float charge with no loads... at work... I wish I could get it somehow...
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    mike95490 wrote: »
    I was horrified to discover the hardwood floor guy had opened up the main panel, and had clipped in the 240V 7.5KW floor sander, and had been sanding for 2 days. I have a single XW6048 and only 3KW of solar. My general had a 8KW generator that would not run the sander, so he thought his genset was bad, they finished the job with a 20Kw rental genset to run the sander.

    Sounds like if they had just asked you, you might have done some quick research on generator support mode and gotten them through it just fine with only a minimal load on the Xantrex to backfill the generator during sander startup and carry a little bit extra while running.
    Truly an awesome beast.
    SMA SB 3000, old BP panels.
  • solarcrawfishsolarcrawfish Registered Users Posts: 12
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    Bump on the battery capacity area.

    600AH would be a massive battery bank for my application, but I understand the demand that the inverter's DC link and its amperage waveform will place on the batteries. The minimum recommendation was 100A in the XW manual, I was looking at using around 150-200AH for the XW6048.

    My intent is to keep a low load on the inverter while the engine generator is not running, and start the generator (which may be a 8 or 11kW Generac Guardian now). Load management is intrinsic to the system's design because of the split-interior load center (Siemens generator ready load center) that basically services as an emergency loads sub-panel.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    Bump on the battery capacity area.

    600AH would be a massive battery bank for my application, but I understand the demand that the inverter's DC link and its amperage waveform will place on the batteries. The minimum recommendation was 100A in the XW manual, I was looking at using around 150-200AH for the XW6048.

    My intent is to keep a low load on the inverter while the engine generator is not running, and start the generator (which may be a 8 or 11kW Generac Guardian now). Load management is intrinsic to the system's design because of the split-interior load center (Siemens generator ready load center) that basically services as an emergency loads sub-panel.

    Clarification: the Xantrex recommendation is 100 Amp hours per kW capacity of the inverter on a 48 Volt system.

    If you do not need a 6kW inverter you can use a smaller battery bank.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    600AH would be a massive battery bank for my application, but I understand the demand that the inverter's DC link and its amperage waveform will place on the batteries. The minimum recommendation was 100A in the XW manual, I was looking at using around 150-200AH for the XW6048.

    It has a huge ripple when working at full power. This may not be good for such a small bank. However, if you only use 30% capacity, it might be Ok. But in this case, you can buy a smaller inverter.
  • solarcrawfishsolarcrawfish Registered Users Posts: 12
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    Ultracapacitors might have an application here? I could downsize my inverter to the 4048 perhaps.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    Ultracapacitors might have an application here? I could downsize my inverter to the 4048 perhaps.

    No. The possibility of super capacitors on inverter input has been brought up several times on the forum. Short answer is it's a no go. You can search the forum for the term "super capacitor" and come up with some of the discussions on them and why they aren't suitable for this purpose.
  • solarcrawfishsolarcrawfish Registered Users Posts: 12
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank

    So the XW, like many inverters, have integral "smoothing caps" to reduce ripple current heating effects on batteries. At work I have VFDs and 224kVA UPSes with massive capacitor banks on the DC link to smooth ripple current effects on the rectifier section of the VFD or VRLA battery banks for the UPS. Has the XW undersized its smoothing capacitor section on the basis that you will use 100 Ah x instantaneous AC wattage no matter what your actual storage capacity requirements are?

    When one says "vibrate my batteries", I understood that I2r heating causing elevated battery temperature is the main enemy here. Is there another damaging force being exerted on the batteries outside of heating them with ripple current above their ideal specs?

    I did find a more detailed battery capacity guide with the Conext SW installation manual. The final element after estimating your kWh is to double the bank size. From my research on SLA/AGM battery life cycles, within the proper charge/discharge current and temperature specs, it is completely based on WH in and out of the batteries. Double your capacity and you double your bank life and cost.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid interactive 2kW Xantrex XW - with small genset and small battery bank
    So the XW, like many inverters, have integral "smoothing caps" to reduce ripple current heating effects on batteries. At work I have VFDs and 224kVA UPSes with massive capacitor banks on the DC link to smooth ripple current effects on the rectifier section of the VFD or VRLA battery banks for the UPS. Has the XW undersized its smoothing capacitor section on the basis that you will use 100 Ah x instantaneous AC wattage no matter what your actual storage capacity requirements are?

    The electrolytic capacitors inside inverters aren't "smoothing capacitors" for the batteries; they are there to stabilize Voltage for inverter function. By needs the current going to the batteries during charging is pulsed, which is a standard practice; that is how the Voltage is regulated. No capacitor will have as great an ability to do this as the battery itself, and the size of the battery bank directly relates to the size of the inverter for this reason.
    I did find a more detailed battery capacity guide with the Conext SW installation manual. The final element after estimating your kWh is to double the bank size. From my research on SLA/AGM battery life cycles, within the proper charge/discharge current and temperature specs, it is completely based on WH in and out of the batteries. Double your capacity and you double your bank life and cost.

    This is a comparison of Watt hours being used in the discharge cycle to maintaining a minimum 50% SOC to prevent premature failure of the battery bank. It is why we estimate Amp hour capacity and then double it or better yet quadruple it. To get a well-balanced system the short cuts of 25% average DOD and 10% peak charge current ability works about 90% of the time. The scale of 2X capacity = 2X lifespan and 2X cost is not entirely accurate, as the battery lifespan as a function of discharge depth & cycles is not linear nor are all batteries the same cost per Watt hour capacity.
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