Would two inverters fight?

Reed_Richards

I already have solar PV with a 6.5 kWh battery.  But I've done a calculation that if I had another big battery, say a Frogstar 15.5 kWh one. then I could save about £400 per year purely by load shifting, charging the battery at night and using the electricity during the day.  That might be economically viable.

But my existing inverter can't cope with multiple different batteries and its maximum charging current is 50A, which works out at about 2.4 kW; too small.  So if I did get another big battery it would need a dedicated inverter.  But can two independent inverters work in concert or would they "fight"?       

Netexporter

I'm going to pair Frogstar batteries with an 8kW Sunsync hybrid inverter. The Sunsync has a connection for an existing PV inverter to plug into, as well as its own two MPPTs. It also has a signal connection to activate a contactor, in the case of mains failure, so you can go off-grid.

Heedtheadvice

To try and answer your question 

PV and generation side- but not definitively here as that really depends upon inverter design and grid voltage- they will not fight each other but will work independently.

Each inverter should just see the voltage in the property ( grid or grid+other generation) and generate it's own output accordingly. No inverter is aware of the voltage source.

There may be times when the 'grid' ( i.e. property) voltage is high and one or both inverters reach generation limits as they would under normal circumstances according to their max voltage setup.

Consider my own system PV with a Kaco inverter nominal 3.6kWp output,

Added lux inverter and batts another 3+kW,

Added a test system of E/W pv with 800Wp with Hoymiles four input inverter ( that could be augmented by more panels/inverters)

All different systems working seamlessly and outputs as expected.

There are of course inverters such as  lux ones that will work together as a single systems they communicate with each other.

Storage side.

It may well be from  the storage aspect that you need to make sure that monitoring and control is set up correctly as you would not want one charging the other much as that is inefficient.

I have not considered that in detail but the situation of two different storage units is very similar with two properties each having storage if the CTs are appropriately in place. Unless they communicate they will independently  charge and discharge

?

michaels

WE have an iboost export to hot water diverter and a V2H battery and PV. 

The V2H battery invertor tries to keep the house import between 50 and 100w.

The iboost tries to stop house export going above 50w.

Thus they play together nicely, battery addresses any import and also soaks up any pv generation until the battery is full at which point the iboost will then see some export and cut in.

Presumably you can configure two battery systems in a similar manner but it may mean that one system takes priority with the second one only cutting in when the draw goes above the first unit capacity or its battery is exhausted.

Solarchaser

Would they fight?
Maybe. 
I had a sofar me3000sp battery inverter and a growatt hybrid inverter and because they were timed very differently, they fought.
The sofar was much quicker to respond and so covered the load, then the growatt would join in, and the sofar would back off and start charging from the growatt. The growatt would still see load and would continue to flatten itself, charging the sofar.
Was not great.

I moved to 2 parallel lux acs and as they talk to each other there is no issue.

I've seen a few circuit diagrams that would theoretically work with dissimilar inverters in parallel,  but for me, it would have to be the same make as the response times would need to be the same.


These are two diagrams that in theory would work with two inverters.

Technically I have 5 inverters, 3 solar only and 2 battery only, the solar ones don't care,  they just produce what they can as they are old and dumb, and the battery ones are a bit more clever.

So you could say I have 5 inverters that work together, but that's not really true, I have 3 dumb ones that do their own thing and 2 that work together.