Connecting inverters

misbah711misbah711 Registered Users Posts: 4
I have installed two 1kva PWM-50AAttachment not found.Attachment not found. hybrid solar inverters. they are on-grid backup system. because we face load shedding. 200watt solar panels are installed on separate units. they are charging 100ah battery and some time run the load directly due to hybrid inverter when battery is fully charged.

1-Now my question is that how can I merge solar converted 230volts with grid 230volt and frequency.
2-Why I want to do this is that, as my load increase from the capacity of panels I want to run only the required amount of load from grid. Rather than totally switching away from solar to grid.
3-can this be done via some device already present in market. (I have worked on my own design for this scenario)

Thanks in advance.
Misbah Karim

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Connecting inverters

    Welcome to the forum Misbah.

    Let's straighten out some terminology first.

    You have solar panels connected to either charge controller that recharges batteries which power an inverter or;
    You have solar panels connected to a grid-tie inverter which sends power to the utility wiring.

    It sounds like you have the first scenario, but the charge controller is built-in to the inverter. This is referred to as an "all-in-one" and they aren't in common use in North America because the designs tend to be too limiting of the application.

    Now about the word "hybrid"; for our purposes this refers to a type of inverter which can connect to the utility grid but also has batteries which act as a back-up power for when the grid goes down. The diagrams you attach show what appears to be a hybrid all-in-one. It should have a manual and tell you which connectors are used to supply/feed the utility power. It will be something like AC IN or AC1 as opposed to AC OUT or AC LOADS.

    In some cases you are not allowed to back-feed the grid with your surplus power. In such an instance you should be able to program the inverter to turn 'SELL' (send power to utility when available) off.

    A good hybrid inverter should be able to do what you want. Without any details as to your specific inverter I can't advise further.
  • misbah711misbah711 Registered Users Posts: 4
    Re: Connecting inverters
    Welcome to the forum Misbah.

    Let's straighten out some terminology first.

    You have solar panels connected to either charge controller that recharges batteries which power an inverter or;
    You have solar panels connected to a grid-tie inverter which sends power to the utility wiring.

    It sounds like you have the first scenario, but the charge controller is built-in to the inverter. This is referred to as an "all-in-one" and they aren't in common use in North America because the designs tend to be too limiting of the application.

    Now about the word "hybrid"; for our purposes this refers to a type of inverter which can connect to the utility grid but also has batteries which act as a back-up power for when the grid goes down. The diagrams you attach show what appears to be a hybrid all-in-one. It should have a manual and tell you which connectors are used to supply/feed the utility power. It will be something like AC IN or AC1 as opposed to AC OUT or AC LOADS.

    In some cases you are not allowed to back-feed the grid with your surplus power. In such an instance you should be able to program the inverter to turn 'SELL' (send power to utility when available) off.

    A good hybrid inverter should be able to do what you want. Without any details as to your specific inverter I can't advise further.

    First Thanks for your reply!

    Details and images are below. Yes my system is hybrid, and works just like you are thinking. Plus we have to do new wiring in the whole house for hybrid inverter as low power equipment is on solar(image 1 will explain). Now when the load exceeds the limit of the solar panels this hybrid unit disconnects the solar and connects the grid to the load. As we don't have sell to the grid system ( feeding back to grid ); here is what I want
    For example:
    My Peak load is 400watt.
    Solar capacity is 300watt.
    Current running load is 350watt
    I want to run 300watt from solar and remaining 50watt from grid.


    But this hybrid inverter does not work like this, is there any module which can monitor the load and carry the phase & frequency matching to reduce electricity bills more. If no I guess I have to make it myself then.

    Details of the Inverter:
    Axpert KS-1kva-PWM
    Inverter Mode:
    DC i/p = 12vDC, 66.6A
    AC o/p = 230VAC, 50Hz, 4.3A
    AC Charger Mode:
    AC i/p = 230VAC, 50hz, 5.9A
    DC o/p = 13.5VDC, 20/10A
    AC o/p = 230VAC, 50Hz, 4.3A
    Solar Charger Mode:
    Rated Current: 50A
    System Voltage : 12VDC
    Min Solar Voltage: 9VDC
    Max Solar Voltage (VOC): 125VDC


    Current 1kva system:
    Image1:
    Attachment not found.

    Future planned 5kva System
    Image2:
    Attachment not found.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Connecting inverters
    misbah711 wrote: »
    First Thanks for your reply!

    Details and images are below. Yes my system is hybrid, and works just like you are thinking. Plus we have to do new wiring in the whole house for hybrid inverter as low power equipment is on solar(image 1 will explain). Now when the load exceeds the limit of the solar panels this hybrid unit disconnects the solar and connects the grid to the load. As we don't have sell to the grid system ( feeding back to grid ); here is what I want

    If this is how the inverter is working it is a strange animal indeed.
    A true hybrid inverter outputs whatever power it can; any deficiencies for the loads attached to it are made up by the grid. It does not stop producing just because the loads require more power than it can supply.

    So what we would expect is:

    Inverter capacity 1000 Watts
    Load demand 1500 Watts
    Grid supplies 500 Watts of the load demand, inverter supplies 1000 Watts

    Note that the inverter's output is not limited by the PV but by its rating because it can draw from the batteries as needed. If the battery bank and PV are undersized then the inverter will drop out because the Voltage on its input will sag too much under load. I suspect this is what is happening here.

    It appears the nominal DC Voltage of this inverter is 12, which is not desirable unless there are specific reasons for 12 VDC. In a house system it makes no sense. As it is, a 1kW 12 Volt GT inverter (which would never be allowed over here btw) would require 400 Amp hours of battery minimum. Plus it would want at least 600 Watts of PV to recharge it, and 1000+ Watts would be better (to allow charging and load supply at the same time).

    With a couple of clamp-on AC Ammeters you can measure the current from the grid to the inverter and from the inverter to the loads at the same time and see if the inverter is actually dropping out because it can't keep up with the demand. Measuring the DC input Voltage at the inverter would be a good idea too.

    Otherwise there is no way for an inverter to inject power to a system only for loads: if its output exceeds household demand the surplus will go to the grid, which is not allowed in your case. (The true hybrid inverter, when SELL is turned off, only allows power in from the grid connection and will not send any out.)

    As for your planned 5kVA system ... I would not be wanting to parallel up several of these units. I'm not impressed by the operational parameters. You would be better off looking at getting a single inverter capable of doing the whole thing at once, with proper sized battery bank and PV array.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Connecting inverters

    The closest thing to what the OP seems to be describing is an off-grid inverter with an internal transfer switch which, instead of connecting the load to the inverter when the grid drops out, is transferring the load to the grid whenever the inverter cannot handle it exclusively.
    That said, I have not seen such a unit advertised with enough detail to convince me that is how it is working.
    Presumably the inverter would continue to monitor the load current from the grid to see when it would be OK to switch back to the inverter. That circuitry could also allow the inverter to synchronize to the grid before transferring back.
    The method used by the hybrid inverters that we know of, as you stated, will generate as much power as possible, up to but not exceeding the load demand when sell if turned off.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Connecting inverters
    inetdog wrote: »
    The closest thing to what the OP seems to be describing is an off-grid inverter with an internal transfer switch which, instead of connecting the load to the inverter when the grid drops out, is transferring the load to the grid whenever the inverter cannot handle it exclusively.
    That said, I have not seen such a unit advertised with enough detail to convince me that is how it is working.
    Presumably the inverter would continue to monitor the load current from the grid to see when it would be OK to switch back to the inverter. That circuitry could also allow the inverter to synchronize to the grid before transferring back.
    The method used by the hybrid inverters that we know of, as you stated, will generate as much power as possible, up to but not exceeding the load demand when sell if turned off.

    Except that a typical off-grid inverter-charger will switch to generator (or grid in this case) any time power is detected on the AC IN. I don't know of any that will invert first and pick up external power if the load demands. That would be like "reverse gen support", which again would be found on a hybrid inverter with bi-direction AC connection.

    Not knowing the details of just what this all-in-one is we can't really say how it is or should be working.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Connecting inverters

    I don't know enough about how it works or is employed to talk about it, but I think this how Outbacks " Grid-Zero " works with the Radian hybrid Inverter / Charger. Of course different Manufacturers will have all kinds of variation's to the same concept.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Connecting inverters
    I don't know enough about how it works or is employed to talk about it, but I think this how Outbacks " Grid-Zero " works with the Radian hybrid Inverter / Charger. Of course different Manufacturers will have all kinds of variation's to the same concept.

    Again that is basically a GT hybrid inverter, design to synchronize with the utility power. The function is more than just turning off "SELL" it actually gives load priority to the inverter. And yes I had to go look that up because the Radian is so new and there are very few that have been brought to my attention so far.

    Not sure if the OP's unit works like that; from his post I would say not. Trying to get an off-grid inverter to synchronize (parallel) to the grid is as close to impossible as can be; they just aren't meant for it.
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