Ac coupling additional benefits?

animattanimatt Solar Expert Posts: 295 ✭✭✭
Does having a gridtie inverter pumping power into an offgrid system increase the maximum power system can power.  Assuming power coming from grid tie inverter obviously. [Opportunity loading]

I am building a small building that will be located roughly 150 meters from main house and it's power source.

Was thinking of using out building and putting solar panels on it.  Something along the lines of 2kw. So this power needs to get back to main house.

At the same time was thinkin of having some basic electricity in the out building. 

So kind of tempted in using a small gridtie inverter at the out building.  Then just running L1,N,L2 back to main house.

Some older small gridtie units seem fairly inexpensive. 

My inverter is a magnum pae 4448.

I was wondering if I was getting 2000w from the gridtie inverter would that allow an increase in ac load support?

I have plenty of headroom in my system right now.  But see an increase ac capacity via gridie inverter as useful.

Matthew wright 


  • BB.BB. Super Moderators, Administrators Posts: 30,490 admin
    The answer, in its most simple form, is yes... Your load could be what the GT inverter outputs + that available from the off grid inverter (your micro grid).

    In practice, the answer will likely be no--It will not "reliably" supply "extra" load capability to your micro grid.

    There are several issues. One is the hardware you are looking at. As far as I know, if you have a typical GT and OG (capable of being connected to a GT inverter and backfeeding power to charge the battery bank) is that the way they manage charging the battery bank. The GT inverter has two modes--One is feeding as much power backwards from the solar array to the OG Inverter + Battery bank, and the second is off--Typically the OG inverter, when the battery bank is full, will shift the frequency by +/- 1.0 Hz or so--This is enough to knock the GT Inverter off line for ~5 minutes before the GT inverter will attempt to restart.

    The second is that you would have to schedule your loads when the sun is out and shining brightly. If a cloud goes by (or even a bird flies by/lands on a panel in the array--The GT inverter output will fall and stop supporting your loads.

    The two factors above, I would suggest, make "reliable use" of the GT+OG inverters' combined output as more trouble than it is worth.

    There are (at least one) GT + OG inverters that are designed to work together in a micro-grid situation. The SMA family has the ability, through the use of varying the 60 Hz base frequency (or 50 Hz for non-north America) for the OG inverter to signal the GT inverter to throttle back on the GT inverter's output (not just 100% or Zero). It should be possible for the system to work and (possibly) add the two outputs together to give you a somewhat better ability to share total output power (assuming the sun+bird issues are not a limiting factor for you).

    You are still left with the issues of what kind of load can take an AC power cut "gracefully" when the sun goes away. And any inductive motor load (water/air pump/etc.) that has high surge current demands (GT inverters are not capable of surge current beyond the steady state solar panel output).

    Could you or somebody make a system that does this shared output function--Probably (and SMA, to a degree does that already). It it worth it to many people? That I am not so sure about.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,178 ✭✭✭✭✭
    edited November 2016 #3
    I am not sure either. If it were a Scneider or Outback system they have known solutiions to doing this and software to make it work, within reason. Maybe Magnum has something, maybe not. Almost all of the AC coupling solutions I have seen are based on the SMA (TL series) GT inverters.
     For a 150 meters run my take is dig the trench and run an extra set of #2 wiring (should run a 60A max load with some loss) and decide later. Avoid headaches and keep it simple.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    I kinda of figured as much.  Thanks for the confirmation.
    With my limited knowledge it appears that magnum kind of has something that deals with this. I really have not looked at it but appears to be some more sophisticated diversion control which uses/burns of excess power. Rather than sma way of producing just what is needed.

    I figured also it would not just be strictly plug and play and that I am fine with. As it is for my property if does not work as expected not the end of the world.
    I totally understand if doing this for a living of taking all variable out of it and keeping it simple.

    To be clear I would try/expirement with this If I pick up a gridtie inverter for cheap.
    Something 2.5kw in size for $200-$300 dollars.

    I just see extra capacity would be good for opportunity loads. Obviously  if clouds pass by the system would need to support load via battery and inverter limited surge capacity. Until sun comes back.

    Also could not have a massively oversized gridtie system. But with moderate gridtie I am tempted to try.

    As for trench it will have conduit in the ground.  I am thinking of just having 3  8awg wires to supply power to outbuilding.  The same 3 wires could send power other direcruin easy enough.

    Thanks again.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,178 ✭✭✭✭✭
    If you try it, make sure the inverter can be driven off or on frequency by the magnum for AC coupling. Many used inverters are old enough that they do not support AC coupling well. I certainly am not an expert with grid-tie but have been to the training.

    In a trench, always add extra wires and do the math that they can do what you want without too much loss. This is really important for grid tie where a long run might have too much drop to operate the AC coupling correctly. 

    When in doubt, do the testing on the bench first! Just like the pros do! 
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 30,490 admin
    As long as the GT inverter is less than 10-15 years old--You probably will be OK to try.

    Big thing to watch for is that the OG inverter does shift frequency correctly and you do not over charge your battery bank ($$$ mistake and possibly worse if you boil dry/melt down the bank).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    Yeah. I saw a post on here with recommended gridtie inverters specifically to work with the magnum OG inverter.
    I just need to wait until one surfaced and the price is right.  But not in a rush.

    I will definitely post update if/when I do something. 

    Thanks again.

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,178 ✭✭✭✭✭
    There were only 2 models I remember at the training session that worked with a Schneider XW or SW and were "known" to work without problems. I heard the same for but maybe one more on Outback.  They also were doing zero export for places like Austrailia/Hawaii where the eletricity is really expensive and no credit for sell. The self consumption was maxed during the day and batteries at night with the grid for stormy weather only.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    edited November 2016 #9
    i did a little more investigating of the magnum acld-40 .  A load controller on the ac side of this.  It can controller 2 diversion loads. a primary and a secondary.  If i read correctly both driven by PWM.   it networks to the magnum pae inverters and monitors battery voltages and uses the inverters charge settings to apply 3 stage charging. pulsing the outputs to control battery charging.

    a quick read of the manual and it appears their implementation at least in theory should provide a fairly robust system. definately something to consider if adapting a gridtie system to have some offgrid capacities.

    I have seen posted by someone else that Magnum works with several grid tie inverters .  And several specifically that it does not work with.

    The main ones I remember in the not work category were Aurora Power one, and Fronius. 

    The main working ones were Sma inverters, Xantrex , and Solectria.  There were a few others i believe.  I will see if i can get a link back to the other thread.

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