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Infinisolar 3K tie-in issues.


Soltra_1
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Hi.
I have had some experience installing several Infinisolar 3K units.  I have always assumed that the load output (AC Output) of these units is limited to the 3 kW capacity of the internal inverter.

So I have analysed the household circuits and divided these up into "essential" and "non-essential" circuits.  The essential circuits are driven by the inverter AC output and typically include lights, burglar alarm, electric fence, TV, DSTV and one or 2 other appliances which the owner would like to use in conditions of power failure.  I have assumed that in total they should not exceed 3 kW at any time so as not to overload the inverter.

The non-essential circuits run directly from the mains and are not available during power outages.

In addition, the AC input to the Infini is fed from a new 20A circuit breaker in the DB (also fed directly from mains). 

Although this has worked well, when the essential circuits are drawing a minimum load during the sunny hours, the PV output can often exceed the essential load.

If grid feed-in is enabled, this surplus energy is pushed back down the AC input(Utility) connection from the Infini back into the DB.  From there, it helps to power whaterver non-essential loads fed from the DB which may be on at the time.  

If the PV output exceeds the combined essential and non-essential loads,  there is excess power which would feed into the grid.  Grid feed-in is problematic in many cases.  The only way to prevent this is to disable this feature at the inverter which means no power leaves the inverter via the AC input.

This resolves the grid feed-in issue, but typically throttles the PV output significantly, reducing the benefit of the system.

Recently, I became aware that a Modbus card and Energy Meter are available for the Infini which can be used to help with this situation. When configured, it will cause the feed-in to only start throttling when the total PV power exceeds the combined load (no unnecessary throttling).

I am seeking feedback from anyone who has implemented this solution.

However, more important is what I found out today.  Apparently, when correctly configured, the Infini can drive much more than 3 KW of load from the AC output.  Supposedly, when the load exceeds the capacity of the internal inverter, the Infini supplies additional mains power to the AC output to assist with the overall load (similar to Victron Mains Assist).  Provided the mains is available, the inverter does not overlaod.

This feature potentially makes connecting the Infini much simpler.  One no longer has to "split the DB"  into essential and non-essential loads.

True, you have to ensure that when the mains fails, the load does not exceed 3 kW.  But this can be achieved by installing a contactor which falls away when the mains fails.  All essential circuits are fed by the inverter output directly and all non-essential circuits are fed by the inverter output via this contactor.

This makes for a much simpler tie-in scenario, with less disruption in the DB. 

However, although I have studied the Infini manuals, I cannot find an explicit explanation of this behaviour.  I do not know if the Infini should be set up in Grid-Tie with Backup or Offgrid Mode.  I also do not know what the limit of this "mains assist" feature is  e.g  could one have a load of 10 kW of which 3 kW is supplied by the inverter (using PV power)and the remaining 7 kW is being supplied by mains ?

If anyone has hands-on experience on the Modbus meter feature or the "mains assist" feature, I would be grateful to hear from you.

Thanks.


 

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3 hours ago, Soltra_1 said:

I am seeking feedback from anyone who has implemented this solution.

I've done it with a different kind of inverter: A Victron Multiplus.

@Wetkit has done it too, with an Infini, but his prepaid meter is particularly sensitive and it keeps tripping whenever small bits slip back into the grid (because the control loop adjusts quite slowly when using the external mater).

3 hours ago, Soltra_1 said:

One no longer has to "split the DB"  into essential and non-essential loads.

Well, depends on what you mean by "essential". Normally that means "I want this to continue working if the grid fails", and by that definition, you still want to split it. You can only push power out on the input when the grid is up. When the grid goes down the inverter only powers loads on the output.

But it does make things a lot simpler, I will definitely concede that.

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