Hi Team,

I was reading quite a bit around setup of the MUST inverters. I would like to ask some questions, maybe you can give me more light in to the darkness...

1. I want to have a SbU (1) - Solar/Battery/Utility setup

2. I like to use Solar power first on loads and after charging - LBU (5)

3. I want to charge the batteries only with solar power - OSO (10)

4. And if on top of the load and the battery charging I will have some energy left I want to send back to the grid - GRE (9)

For battery I have information from manufacturer LiON (14cellls - 3.3V cutoff and 4.1V max, 46.2V cutoff and 57.4V max)

My setup is: 17-57.3V, 18-57V, 19-46V, 20-47.5V, 21-54V

My issue is, when I set up GRE (9) -> it will check with LBU setup parameter 20 and if it is higher than 47.5V start to feed solar and battery power back to the grid. Which is not my intention to do.

Do you have any recommendation? Or any idea what could I set up differently(LBU/BLU)? Or maybe I'm completely wrong? Thank you!

According to your settings, its working correctly, as described in the manual.

I guess you could try setting #20 to a higher value, since in SBU/LBU configuration it seems to be relevant only when grid is available:

If grid is not available, the low voltage cutoff setting #19 will be relevant.

I do wish there was another option to never discharge to grid from the battery, but there isn't.

It does make some sense though: if solar is enough to power loads and battery is "full enough" then you benefit from putting some of that extra power into the grid. I guess you just need to have a high enough setting for #20 (like 80-90% SOC). It makes sense for OSO, where battery is charged only from solar, so basically you are maximizing your solar power (minus losses from DC to AC conversion).

Not ideal, but that's what it is...

Edited April 3, 20231 yr by meetyg

9 hours ago, bartalz said:

Hi Team,

I was reading quite a bit around setup of the MUST inverters. I would like to ask some questions, maybe you can give me more light in to the darkness...

1. I want to have a SbU (1) - Solar/Battery/Utility setup

2. I like to use Solar power first on loads and after charging - LBU (5)

3. I want to charge the batteries only with solar power - OSO (10)

4. And if on top of the load and the battery charging I will have some energy left I want to send back to the grid - GRE (9)

For battery I have information from manufacturer LiON (14cellls - 3.3V cutoff and 4.1V max, 46.2V cutoff and 57.4V max)

My setup is: 17-57.3V, 18-57V, 19-46V, 20-47.5V, 21-54V

My issue is, when I set up GRE (9) -> it will check with LBU setup parameter 20 and if it is higher than 47.5V start to feed solar and battery power back to the grid. Which is not my intention to do.

Do you have any recommendation? Or any idea what could I set up differently(LBU/BLU)? Or maybe I'm completely wrong? Thank you!

As @meetyg

suggested just set #20 as high as you want to keep the battery. As per #9 you enable exporting battery and PV to grid. It should keep the battery SOC high but export PV to the grid. 

As exporting to the grid is only allowed when you have grid it seems as #20 should work as you want it. 

Hi,

my issue with that is, than I can't use my battery energy at night, what was the intention. I want to have not a backup, however more island solution. If I will setup 80-90% SOC it would mean that I'm not using my battery power at al, while he will feed back in to the grid 10-20% and after in the night he will stop discharging while I have grid power. Or maybe I'm wrong?

4 hours ago, bartalz said:

Hi,

my issue with that is, than I can't use my battery energy at night, what was the intention. I want to have not a backup, however more island solution. If I will setup 80-90% SOC it would mean that I'm not using my battery power at al, while he will feed back in to the grid 10-20% and after in the night he will stop discharging while I have grid power. Or maybe I'm wrong?

But you decide if you want it 98% SOC then you only "loose" 100Wh. If you have a single cloud during the day you might "loose" 500Wh or more per cloud of PV-or on a bad day 10 times more. 

Sometimes equipment is designed in a way that does not suit all of us. 

Hi, thank you maybe in this case I need to try it, however if I have the setup what is above and I set up 20 for 90% SOC. For me it would mean:

1. Feed back 10% battery power to grid, at day time after you charged the battery (sunny day)

2. Do not use anything from 90% battery at night time, when I want to use battery power, while I have grid power and don't want to drain below 90%.

Is this assumption wrong? Inverter will use the 90% SOC at night with this setup? Thank  you for your feedback

1 hour ago, bartalz said:

Hi, thank you maybe in this case I need to try it, however if I have the setup what is above and I set up 20 for 90% SOC. For me it would mean:

1. Feed back 10% battery power to grid, at day time after you charged the battery (sunny day)

2. Do not use anything from 90% battery at night time, when I want to use battery power, while I have grid power and don't want to drain below 90%.

Is this assumption wrong? Inverter will use the 90% SOC at night with this setup? Thank  you for your feedback

When at 90% at sunset you can set priority to SBU so that you can use the battery power during the night. Next day PV will charge battery back if set to charge only from solar. All extra solar when battery is at 90% or whatever you set it to will be exported and battery kept at 90%. 

Here you have to decide to export solar or use some yourself for standing loads during the day. 

1 hour ago, Scorp007 said:

When at 90% at sunset you can set priority to SBU so that you can use the battery power during the night. Next day PV will charge battery back if set to charge only from solar. All extra solar when battery is at 90% or whatever you set it to will be exported and battery kept at 90%. 

Here you have to decide to export solar or use some yourself for standing loads during the day. 

Thank you I will check that!

To summarize for the the people who want to have similar setup (basically it works based on documentation):

1. With SBU/LBU/OSO setup it is not possible to feed just solar energy back to the grid. It will take/drain also the batteries.

2. In SUB/LBU/OSO it is possible to feed back just the solar power, however in this setup the battery is just active when utility power is not available

3. in SOL mode you can't use setup 9 feed back to grid, more island solution, with bypass possibility.

I tested out all of this options. Thank you for your comments.

I know this is an old thread. But as I just recently connected my PV to the MUST (used as grid UPS till now), I'm starting to get frustrated.

I purposely got the "true" hybrid because I wanted to maximize PV production with my little system (5kwh of storage, 1.2 kwp of solar).

It seems grid-feedback logic is simply stupid/wrong.

There is a hidden setting of "max discharge to grid", which is not mentioned in the manual or visible in the inverter menus but available via Solarpowermonitor or SolarAssistant.

This setting seems to affect how much power will be pulled from battery to grid when in SBU mode, or how much PV+battery power will be available to loads when in SUB mode (the rest will come from grid).

Another observation that I noticed with this setting is that it also limits charge from grid to battery! So even if you have "grid charging" amperage set to say 40 amps (DC), and this setting to lower wattage (AC amps x AC voltage), it will only allow to charge battery up to this lower wattage.

In short, all of this is very confusing and not working as expected. I would expect/like the inverter to work in more logical manner:

If I have SUB/SBU mode with BLU setting, PV power should first go to charge the battery, any excess to power loads, and any remaining power to feedback to the grid.

So for example if I have 1000w PV power, 500w should go to charge battery (according to "max charge setting") until full, 200w to current loads (let say that's what we are using at the moment) and all the remaining 300w go to grid.

But all this voltage based logic is not only confusing, it simply isn't working as expected. I think it should all be current or power based, not voltage based. 

I can't get it to work this way. I find that "Solar output priority" isn't really a priority, but rather which voltage to consider (setting #20/#21).

If any of you have successfully figured this out, I'd be pleased to hear.

 

Edited May 13, 2024May 13 by meetyg

Hi, I fully agree with you about the logic or wrong logic of the inverter setup. I'm managing all the settings with Home Assistant integration. It means I'm using automation in Home assistant to keep it doing what I want. I'm changing "Inverter Discharger To Grid Enable" switch and "Energy Use Mode" switch together. I need to use HA while you need to change more values based on sensor data...

I worked also with SolarAssistant team they were very helpful to connect Inverter and that time made a change in system to be able to see the back feed to the grid, however I was not able to set up automation which would work with the logic of the MUST inverter.

Thanks. I could use some external automation to achieve what I want, but I'm reluctant to change settings automatically. My worry is that when you change settings, it's saved to the internal EEPROM memory chip of the inverter. These chips have a finite number of write cycles, so I don't want to wear mine out. 

It might be far fetched, but still, these Chinese inverters use mediocre components and I want to prolong the lifespan of mine.

I also just noticed a strange issue when back feeding: I have an RCD on the output of the inverter. In normal conditions everything works fine.

But if I turn off the input MCB (going to AC IN of the inverter), simulating a power outage, if makes the output RCD trip! This only happens when actively backfeeding. If I disable grid feedback, I can cutoff power to the inverter and everything continues to work fine.

So I may just give up on backfeeding for now. I'm seriously considering getting a different inverter, but am afraid I will meet similar or other oddities with another model too.

Unfortunately, most reviews don't go into the intricate details or workings of these inverters.