How to have off grid inverter supply power only if able to?

[hidegety]

Transfer time for UPS is up to 12ms. There are 120 peaks per second in a 60hz wave form for a rectifier to convert the AC to DC. Anything greater than 4ms risks missing one of the peaks. I have no idea how many peaks it can miss before causing a problem. What is the transfer time of your ATS?

According to documentation 8-12ms typical, with 18 max guaranteed (for 50Hz).

In any case, a few transfers per day is not an issue. The problem is when your system is hovering around transfer state. It could cycle every few seconds. That is hard on your switch and equipment.

True, the switching must be done above the boundary, with enough reserve so that it doesnt come to that. All question of properly seting switch limit voltages.

 

[DIYrich]

All question of properly seting switch limit vovoltages.

I don't think that is easy to do without a battery.

 

[hidegety]

I don't think that is easy to do without a battery.

Oh, I see. Battery would drop the solar voltage down to its voltage, as opposed to solar panels solo - where it is more current that fluctuates (only losing voltage if heavily shaded).

So, If the system is [panels / battery / inverter+mmpt] then voltage is a good indicator of the off grid system ability to fully power the load.
Without batteries - can I set inverter so, that it powers the output only in case, it is able to supply some min load (min watts)?

And extension of that question: can I somehow signalize inverter what is ATM current expected load (load it must support).

Which brings us neatly to the beginning of the thread: How does off grid inverter know if it is capable to support the load (that for sake of the argument is currently powered by diesel generator)? Or am I beating a dead horse here?

 

[DIYrich]

Oh, I see. Battery would drop the solar voltage down to its voltage, as opposed to solar panels solo - where it is more current that fluctuates (only losing voltage if heavily shaded).

Charge controller or Inverter drops the Solar voltage to Battery voltage.

So, If the system is [panels / battery / inverter+mmpt] then voltage is a good indicator of the off grid system ability to fully power the load.
Without batteries - can I set inverter so, that it powers the output only in case, it is able to supply some min load (min watts)?

Battery voltage is a good indicator of whether there is enough battery power to let the inverter provide maximum output. When Solar charges up to that minimum level, then inverter turns on. It will continue to run as long as there is enough PV to keep the batteries charged, or until the batteries drain down to the cutoff point.

And extension of that question: can I somehow signalize inverter what is ATM current expected load (load it must support).

Only if the inverter has the ability to connect to CT's.

Which brings us neatly to the beginning of the thread: How does off grid inverter know if it is capable to support the load (that for sake of the argument is currently powered by diesel generator)? Or am I beating a dead horse here?

You size the inverter for your needs. It is your responsibility to ensure that you do not overload the inverter. There are Load Management devices that can turn on/off individual circuits to avoid overloading the inverter.

 

[hidegety]

Thank you all very much for your patience and suggestions. I think I now have clearer understanding of what needs to be done in order to bring this setup to fruition.
The realization will take me couple of months, I will post some results and experiences once it is done - just in case someone else comes across this issue.