If or when there is a benefit in having Micro Inverters in an off grid system?

[SparkyGage]

I understand the purpose in dealing with the shading problem and single panel failure, but the only time I see Micro Inverters (or MIs) talked about is on grid-tie systems. Is there a use case for MIs in an Off Grid system with batteries?

 

[LydMekk]

If you have shading on your panels.
Otherwize, no.

 

[sunshine_eggo]

I understand the purpose in dealing with the shading problem and single panel failure, but the only time I see Micro Inverters (or MIs) talked about is on grid-tie systems. Is there a use case for MIs in an Off Grid system with batteries?

Almost never.

Allegedly, optimizers give comparable benefit as microinverters.

Grid tie systems require connection to an "infinite grid" where they can continuously output maximum available power. You need an AC coupled inverter of equal power to handle the input from the GT system. When the battery hits absorption voltage, the off-grid inverter will move its frequency off of the nominal 50/60Hz to force the GT inverter to disconnect. This can create rapid cycling as battery voltage oscillates around absorption.

If you also have DC PV, this may be sufficient to keep the battery at absorption and avoid the connect/reconnect behavior.

Additionally, some systems are designed to work together. Example: Victron and Fronius string inverter - Victron ESS can control a Fronius inverter to force it to regulate its output.

I'm not aware of any means of regulation between an AC coupled off-grid inverter and microinverter system. That doens't mean there is one.

One case I can see is if you have strictly daytime loads that exceed your off-grid inverter capacity; however the on/off nature of the connection could cause unreliable operation in certain conditions.

 

[SparkyJJO]

If I was strictly off grid I wouldn't even think of it. They're more of a pain to control output because they're meant to push power at the max they can do all the time. Frequency shifting can be used to control them in a grid down situation, but that requires a hybrid inverter than can do that sort of thing, and it is just more complicated and limits your options more.

 

[SparkyGage]

Thanks for the clarification guys!

 

[Ellcon123]

I run a 300W micro through a smart plug and shut it down at a set battery voltage. Panels are in a poor location so not the best production but it is simple to implement. Running about 6 months now and just wanted to see if it would work.

 

[Bluedog225]

I believe they reduce the fire danger on a roof, provide redundancy, and allow greater use of reliable customary AC systems and equipment. I don’t often see support for this position.

 

[Ellcon123]

Mine's an off-grid system and specific advantage was just having to run AC wiring at low current. Wouldn't put the micro near the house though.

 

[Consumerbot3418]

I'm not aware of any means of regulation between an AC coupled off-grid inverter and microinverter system. That doens't mean there is one.

One case I can see is if you have strictly daytime loads that exceed your off-grid inverter capacity; however the on/off nature of the connection could cause unreliable operation in certain conditions.

Well, I guess I'm a bit of a unicorn? I've got a completely off-grid solar setup with both AC and DC-coupled solar, and it seems to work just fine. AC coupled PV provided by Sunny Boy and IQ7s. SB is set to "SMA Island" mode, and IQ7s have an off-grid profile loaded. Both smoothly dial back their output as the Sunny Island units shift the frequency away from 60Hz, ie CA Rule 21/UL1741SA. The AC coupling adds to the inverters' max output, as you mentioned.

I've seen that Victron inverters handle both AC and DC coupled PV, but I'm struggling to determine if they can implement the above-described frequency shifting here in the US. It appears the answer is "no", because of the lack of grid code. Not even for off-grid use... I've had a pair of Multis in series with the Sunny Islands, and using ESS to charge an LFP battery bank, then give the power back. Be nice if I could still use my AC-coupled PV with them, in the event the Sunny Islands quit working. Makes me wonder how the Multis would respond to backfeeding on the AC output, if there was no AC input connected!

Mine's an off-grid system and specific advantage was just having to run AC wiring at low current. Wouldn't put the micro near the house though.

Funny you should mention that. I'm about to add panels to my house, and am presently conflicted as to whether I should buy some TS4-A-F modules, or use the IQ7s I have on-hand. Why no micro near the house?

 

[Ellcon123]

It's a cheap Chinese 300W GTI. It can burn the chook shed down but I wouldn't trust it on the house. It runs hot and shuts down regularly on over temp so I've fitted a CPU fan to stop this. The GTI was only done for proof of concept.

 

[DIYrich]

Is there a use case for MIs in an Off Grid system with batteries?

You max out your inverter production, and you want a little more peak power during sunny days.

Might be cheaper to add a few micros than parallel a 2nd inverter.

 

[Consumerbot3418]

It's a cheap Chinese 300W GTI. It can burn the chook shed down but I wouldn't trust it on the house. It runs hot and shuts down regularly on over temp so I've fitted a CPU fan to stop this. The GTI was only done for proof of concept.

Oh, yeah, gotcha! I picked up one of these Vevor 600W micros, but ended up returning it when I found out it couldn't even output half its rated power on a summer day due to overheating, which changed the value calculation drastically. Combined with lack of Rule 21, it just wasn't worth messing with. The IQ7s, on the other hand, seem to reliably operate cool, even at their rated power output.