Solis Hybrid Inverter : Operation of backup circuit

I've just had my solis hybrid inverter installed RHI-6k-48ES-5G, but am still waiting for my batteries to arrive (September I hope !)
I have installed a lighting circuit and fridge freezer on the AC back-up circuit which should operate from the battery when the grid is down to provide some power to the house on this circuit during a power cut.

I was surprised last night to find that the inverter switched off completely when it went dark, taking with it the back-up circuit and fridge freezer. No response from the inverter front panel. Thought the inverter was defective as the electrician had literally only turned it on a few hours previously, only to find that it was back alive in the morning .
After some head scratching it seems that this is the correct operation for the inverter. If there is no DC solar, or DC battery it will turn itself off, but taking with it the AC back-up circuit !
I find that really surprising as I would have expected that if the grid is still on then the AC back-up circuit would just be grid powered ?

It also implies that when my batteries arrive, if I have any battery problem then the AC back-up circuit will die at night. That seems far more likely than a grid outage in the UK and defeats the point of using AC-backup !
I can't seem to find any option on the inverter panel which would fix this, but quite frankly the manual is a hard read !

Is anyone familiar with this inverter and can confirm if I am missing something or this is indeed the intended operation ?
Thanks in advance.

Doesn’t sound like it’s configured correctly. It should route the AC grid to the critical AC output when the grid is present but the solar isn’t.

Pure speculation, in many power transfer operations, there is an intentional delay from when one source of power goes out to when its fed from another source. When the grid goes away, the inverter has to create its own frequency and that frequency is probably not in phase with utility frequency, it the switch was instantaneous any motorized electric loads could be trashed if the phase angle is wrong. So called "bumpless" transfer with no interruption can be done but its far more complex operation.

In order for the inverter to manage a transition it has to have constant source of power, without that source it is going to go dark in safe mode. My guess is once you have a battery in the system, the inverter will get backup power and ride through the event. On large industrial systems, the switchgear has its own separate dedicated back up power supply(batteries) to manage these transitions.

You might check to see if it has a No Battery mode selection. Just glancing through a pdf copy of the manual it mentions it. BTW that is a pretty impressive hybrid inverter. I'll have to look to see if a comparable one is availble for the US.

Mattb4 said:

You might check to see if it has a No Battery mode selection. Just glancing through a pdf copy of the manual it mentions it.

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Thanks for the reply. Inverter is set up in "No Battery" mode already, otherwise it alarms "No CAN" so unfortunately that is not it.

Sounds like it requires battery/solar to power the inverter operation. With neither availble it does not turn on so no AC bypass. One way you could work around for your critical load panel is to run a circuit from your main connected to a transfer switch. Your Solis would be also connected to this transfer switch and from there it feeds the load panel. If you go with a ATS it would do the transfer upon loss of power from the Solis.

Solis can only power backup loads if there is a battery present, no if/butts about this.

The reason for this is when the Solar goes below 75V and there is no battery, the units electronics no longer have a power source. I believe this logic is from carried over from the gridtie units to have no tar loads at night and I have back and forth with them about this, Solis stance is it works as documented.

What Solis recommends is an external bypass which for the US units is built into the auto-transformer, for the UK you would need an external bypass

Solar Guppy said:

Solis can only power backup loads if there is a battery present, no if/butts about this.

Click to expand...

Yikes .
Wish I'd known this before the install as it was quite a bit of effort to configure and would have saved me quite a few pounds on the install.
Disappointing that this is not clearly described in the manual !
Thanks for the confirmation @Solar Guppy, and hope this post helps anyone considering the RHI series solis inverter, and maybe not bother with the back-up circuit !

marky0 said:

Yikes .
Wish I'd known this before the install as it was quite a bit of effort to configure and would have saved me quite a few pounds on the install.
Disappointing that this is not clearly described in the manual !
Thanks for the confirmation @Solar Guppy, and hope this post helps anyone considering the RHI series solis inverter, and maybe not bother with the back-up circuit !

Click to expand...

My thoughts on this: if the grid is down at night & your battery would be needed to manage the base load, then it would make sense for the inverter to be reliant on its power. (or am I missing something obvious here?)

I have a 3.6k solis hybrid inverter and a fox ess lv5200 lithium battery. I remember being a bit amused that you need two power sources for the inverter to wake up, as in DC from PV and grid, I first powered it on before my battery arrived, it was night time and I though the unit was dead….
So with a battery it all makes more sense, the panel is always accessible, it stays connected to solis cloud and my home assistant install 24*7. Ac backup I have to a double socket as I don’t really have an issue with grid ever going down.

This Ac backup circuit seems perfect so long as you have a battery? Loads of options for times and priorities for ensuring your battery has juice for an grid failure situation if you want that?

treveansalt said:

I have a 3.6k solis hybrid inverter and a fox ess lv5200 lithium battery. I remember being a bit amused that you need two power sources for the inverter to wake up, as in DC from PV and grid, I first powered it on before my battery arrived, it was night time and I though the unit was dead….
So with a battery it all makes more sense, the panel is always accessible, it stays connected to solis cloud and my home assistant install 24*7. Ac backup I have to a double socket as I don’t really have an issue with grid ever going down.

This Ac backup circuit seems perfect so long as you have a battery? Loads of options for times and priorities for ensuring your battery has juice for an grid failure situation if you want that?

Click to expand...

Any ideas if your panels will still charge your battery if the grid fails?

mybigwhy said:

Any ideas if your panels will still charge your battery if the grid fails

Click to expand...

I’m pretty sure it would, I’m the inverter wants to see two power sources. It would have PV and battery, obviously the ac backup circuit runs if enabled when grid goes down so yes it must do!? I’ll flick the power off to the inverter when I get a chance in the daytime to test it!

mybigwhy said:

Any ideas if your panels will still charge your battery if the grid fails?

Click to expand...

If it helps I've just fitted my 5kw Solis to a battery and PV only and it's charging. Sad I cannot suss how to get some AC out of it though :-/

This has bit me in the ass today and I'm not happy. I just finished wiring in the backup AC circuit to my burglar alarm and internet routers etc, everything was working until the sun went down. Then the inverter went completely off and my 'critical loads' then shut down.

Anyway - the manual clearly states (typed verbatim):
Scenario 2: When the PV power is not enough or no PV power is generated (at night), P(PV)-p(Critical Loads)-p(Non-Critical Loads) <0,
battery power will be used to support the loads and if the battery power is not enough, grid will be used to support the loads as well.

(My emphasis).

It does not make sense that at night, your batteries are meant to power your critical loads, even when you have grid. This means you've gotta run your refrigerator, computers, routers, security system, etc, from battery, EVERY NIGHT?

My battery was already at 15% (low threshold)... we have had hardly any sun here recently so it hasn't had a chance to charge.

Does not compute.

Coda said:

It does not make sense that at night, your batteries are meant to power your critical loads, even when you have grid. This means you've gotta run your refrigerator, computers, routers, security system, etc, from battery, EVERY NIGHT?

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No,

The grid is directly connected to the load / backup port by a relay and as long as there is battery voltage, that relay stays engaged.

What runs the battery down ( when operating mode is backup mode ), is batteries have balancers active when the battery is below 20% or above 80% of SOC, at least it is with the BYD batteries.

Solar Guppy said:

No,

The grid is directly connected to the load / backup port by a relay and as long as there is battery voltage, that relay stays engaged.

What runs the battery down ( when operating mode is backup mode ), is batteries have balancers active when the battery is below 20% or above 80% of SOC, at least it is with the BYD batteries.

Click to expand...

Thanks for your input.

Something is misconfigured then...

The inverter is in AUTO mode which should work as the manual describes under Scenario 2 which I copied above.

In Scenario 1 of AUTO mode, PV supports normal loads, the excess solar charges the battery, and if theres more excess still, that goes to the grid. This has been working exactly like that, during the last 6 months or so - i.e. batteries charge during the day, and when there's no PV, the batteries support loads in the house. At the moment, the batteries are off because they are below threshold, so the inverter is off. However, if the battery was above 15% and the inverter would be on, AC backup would be supplied from Grid, but the batteries would still be being drained to power the normal loads, which means they would shortly be dead again and the inverter would go off.

What am I missing?

Coda said:

Thanks for your input.

Something is misconfigured then...

The inverter is in AUTO mode which should work as the manual describes under Scenario 2 which I copied above.

In Scenario 1 of AUTO mode, PV supports normal loads, the excess solar charges the battery, and if theres more excess still, that goes to the grid. This has been working exactly like that, during the last 6 months or so - i.e. batteries charge during the day, and when there's no PV, the batteries support loads in the house. At the moment, the batteries are off because they are below threshold, so the inverter is off. However, if the battery was above 15% and the inverter would be on, AC backup would be supplied from Grid, but the batteries would still be being drained to power the normal loads, which means they would shortly be dead again and the inverter would go off.

What am I missing?

Click to expand...

I have never heard of auto mode.

The Solis storage inverters I know of have four storage modes of:

Self use
Feed in priority
Backup
Offgrid

Here is a write up I made for myself after many hours of the poor descriptions from the Solis documentation. Attached is the document I created for my own use, it may or may not help , no warranties provided.

treveansalt said:

I have a 3.6k solis hybrid inverter and a fox ess lv5200 lithium battery. I remember being a bit amused that you need two power sources for the inverter to wake up, as in DC from PV and grid, I first powered it on before my battery arrived, it was night time and I though the unit was dead….
So with a battery it all makes more sense, the panel is always accessible, it stays connected to solis cloud and my home assistant install 24*7. Ac backup I have to a double socket as I don’t really have an issue with grid ever going down.

This Ac backup circuit seems perfect so long as you have a battery? Loads of options for times and priorities for ensuring your battery has juice for an grid failure situation if you want that?

Click to expand...

Hi,

Really sorry to jump in on a old thread but struggling here.
Just added 5kwh pylontech batteries to a new 5G Solis hybrid. (I swapped out a non-hybrid inverter)

You mention of "Loads of options for times and priorities for ensuring your battery has juice for an grid failure situation if you want that?"

I would like to charge cheap rate 2:00 to 6:00, I can set that, OK.
zero discharge, OK

However business use & when cold heating can be drawing 2wkw - 10kw or more & would have drained the battery by 8 or 9am.

Ideally I would like to have the battery at 100% at 10am.
At that point either a bit of sun, less heating but also more of a chance to manage power issues.

Would keeping the charge times to 9.30 or 10am avoid this, keeps it topped up, any later and imagine perhaps a waste as if sunny its competing to top up the battery from the grid?

Leads me to the 2nd & main problem.
I had originally thought to keep SOC high e.g. 30% so if grid failure, then have 10% or so to run computers etc for a hour or hopefully longer if some daylight but then of course I realized that below the SOC it will stop powering the backup circuit.

I wanted this to be automatic but the only way I can think is to show my staff how to change the SOC, down to 20% or lower in these emergency situations as should be rare.

Is there a clever way to get around this, Can I use charge from grid somehow, want to make sure of the solar as much as possible to save money but prepared to loose some benefit for backup.


SOLVED the earthing issue :
Not had much time with the wiring and stupidly not looked at the diagram carefully enough, Had put a proper tester on for the earth readings so was not about to use it dangerously but is poor to be honest.
Meant to connect the earth from the inverter in the backup cable with the mains socket earth that already has the TT connection, so it provides the earth for the inverter when grid failure. get loop impedance of 3 Ohms on backup power where my normal TT is 83 Ohms to confirm.


Don't often have power failure but when it does so inconvenient for my staff. OK'ish if I am around but difficult otherwise.