Is there a way to reduce Inrush Surge Current for efficient solar design?

Welcome to the forum SunnyFarmer,

What is the ballast for (green house HPS or Metal Halide or similar)?

One of the basic methods to limit surge current is to use NTCs (negative coefficient resistors). Basically, relatively high resistance when cold, and as they heat up over the first few seconds, their resistance falls and allows almost full voltage/current to the load:

https://amwei.com/ntc-thermistors/inrush-current-limit-surge-suppress-power-ntc-thermistors/
https://product.tdk.com/en/techlibrary/applicationnote/howto_ntc-limiter.html

This may be a bit more for an end user to attempt (picking the parts and building a surge suppressor module).

There are LED based greenhouse lighting... Should be much less surge.

And there are electronic ballasts---Here is one company that has less than 20 Amp surge:

https://www.umelighting.com/sale-13821946-265vac-hid-digital-greenhouse-ballast-ceramic-metal-halide-highbay-wave-electronic.html

Also--If you have multiple ballasts on a single solar inverter--You might look into sequencers... I.e., start first ballast, wait 5 seconds, then start the second, etc... Using time delay relays or other controller(s).

There are a few DC ballasts out there:

https://www.emergencylighting.com/productpdfs/d48tspec.pdf

But probably too small for your needs????

-Bill

Without knowing more about the electronic ballast design, it is difficult to make any educated guesses. One option would be to try their email addresses and ask them the question:

http://www.ebm-lighting.com/index.php?a=lists&catid=22

Many electronic power supplies have a (relatively) large capacitor on the input stage--And that would be what is charging. And doing some sort of soft start would not be a big issue. However, too slow of soft start and the unit may not "boot" correctly.

They may also have a "soft start" version available (no specs):

https://www.gold-agents.com/product.aspx?id=25245315

There are other designs that use Triacs instead:

https://neurochrome.com/pages/the-ultimate-guide-to-soft-start-design

NTCs are pretty cheap, and you can get "perf board" (fiberglass pre-drilled boards for proto-typing). NTCs are available from Amazon (US) if you want to try:

https://www.amazon.com/s?k=uxcell+NTC+Thermistor+Resistor+inrush&crid=3QKPG8Q67WOYU&sprefix=uxcell+ntc+thermistor+resistor+inrush

Maybe a 10 Ohm 2 Amp unit?

https://www.amazon.com/uxcell-Thermistor-Resistors-Current-Temperature/dp/B07L11VR22

But even then, it would limit surge current to (240 vAC / 10 amps = ) 24 Amps...
 
None of this stuff is that expensive (in parts). But if you hire an engineer to design and build--The costs will be a huge deal. And still do not know if this will work with your brand/model of ballast.

Sorry I cannot provide much more help here.

-Bill

You can try one (or more) solutions such as the NTC I linked to above (I guess you are in Australia--So what is available locally may be different).

I don't think it will damage anything--Just monitor the input voltage and make sure it is above ~216 volts (my suggestion) while the ballast and lamp are running (after a few seconds of "surge" suppression).

I don't think it will damage the ballast--If it does not "boot" within a few seconds of delay (over "normal boot time"), then turn off and try something else. With the NTC, you could bypass with a time delay relay ("shorts out the NTC" after a few seconds) and run "full power' to the ballast.

For example, an inexpensive HVAC delay relay:

https://www.amazon.com/EvertechPRO-Timers-Replacement-Universal-ICM105/dp/B08R31646Y/ref=sr_1_3?crid=3QDPKHW3L3FKS&keywords=time+delay+relay+240vac+20amp&qid=1655486959&sprefix=time+delay+relay+2,aps,944&sr=8-3

Just wire in parallel with the NTC so that after x seconds, the relay will "bypass" the NTC.

It appears that the ballasts are around USD$70 (plus shipping) here... You have to decide the "risk/reward" of doing your own testing.

I don't expect the NTC to "self destruct", but suggest that you put it in a metal junction box, or similar on an insulator/perf board just in case and mounting on an insulator with thru holes so that (for example) a solder joint comes loose and the exposed wiring shorts out.

"Off grid" power systems are a bit of "niche" market. And adding a few cents to a few dollars to a $70 high volume product that will rarely be used in an off grid setup is just a "loss of profit" for the mfg/seller.

Most of the operations around here are utility power or, for "other" remotely located grow-ops setups tend to use diesel gensets which can manage the extra surge current.

-Bill

Oops--My mistake--Yes the Evertech is not rated to drive an HVAC motor directly--Need to drive a separate relay... You need a heavier rated relay/TDR to ensure that the ballast does not overload the contactor (probably looking at >20 amps to ensure surge does not blow out the contacts). Anyway, you get the idea.

L1 ===+====NTC ===+=== Ballast=== L2
            |                        |
            +==contacts==+

That will ensure the NTC does not "restrict" the Ballast voltage/current, especially if the ballast is switched on/off with its "remote" control (draws something like 25 Watts when in "standby"?).

There are a lot of time delays out there--But finding one with a "high current" set of contacts included... I am not finding one quickly (I have to head out now).

That Evertech unit--The wrong choice here unless the "LOAD" is a separate 240 VAC contactor...

-Bill