18KPV with no battery?

[mciholas]

For a grid tied EG4/Luxpower 18KPV, what happens if it has no battery attached?

There was some comment that the unit would not work properly in these circumstances, that is required a battery to be stable or operational. If so, this seems like a weakness since loss of the battery (for service, fault, or otherwise) would disable the unit and that seems operationally fragile.

If there is no battery and tied to the grid with no PV input, I'd hope the grid powers everything. If there is PV input and grid, the system would convert the PV input to AC which feeds local loads and the remainder back feeds the grid, or the shortfall is drawn from the grid.

What if there is no grid and PV input? Will the system try and make AC? What happens if that overloads (which could easily happen due to cloud)?

Also, if there is no grid, no PV, and no battery, the system is off. Then the sun rises. How do you dark start under these conditions? There is no way to generate the signal to the RSD devices on the panels to "open them up", so it feels like the system will stay dead until either there is grid or battery provided. Do you need some sort of kick start power to get things going?

I am exploring all the corner cases of operation before committing to the system and the manuals are totally useless for documenting these behaviors. The only way to know is to ask other owners to see how it actually operates. That's the engineering mindset, amateurs make things work, professionals make things not fail, and to do that, you have to look at all of the conditions.

I'm also open to knowing how other inverters in this class operate.

Mike C.

 

[EG4_Jared]

I've noticed several 18kPV systems configured without a battery, and they've all operated smoothly. If there's no battery or PV available, the inverter switches to AC bypass mode to power loads. However, if PV alone can't meet the load demand, the system may overload and shut down. As for the last scenario, I will have to get more information on this.

 

[mciholas]

I've noticed several 18kPV systems configured without a battery, and they've all operated smoothly.

Is no battery an officially supported operating mode? Is that written down somewhere?

This comment was made in another thread:

My new diagram. Please check.

So after running into a roadblock with my 18kpv and backup plans with my utility (they require a separate production meter) Ive decided to go net metering only for now. Im gonna try to find two sunny boy 7.0 inverters (unfortunately just discontinued). They said I could keep my old plan and add...

diysolarforum.com

"Apparently it’s not possible the moment for the 18kpv to function as a grid only inverter."

I'd like to confirm that information isn't correct.

As for the last scenario, I will have to get more information on this.

Please do and let me know.

To my knowledge, grid down, no battery, there would be no way to start the PV array due to lacking the RSD signals to open up the RSD devices on the panels. Therefore, no dark start capability. You would have to "bootstrap" it somehow in this mode.

Mike C.

 

[wpns]

Then the sun rises. How do you dark start under these conditions? There is no way to generate the signal to the RSD devices on the panels to "open them up"

RSD devices allow a volt or so per panel through, for a total of less than 30V but still enough to start.

The ‘panels but no grid or batteries’ thing is such a corner case you probably shouldn’t worry about it. No-one can even agree on how it should work (or fail) when the load exceeds solar input. Just don’t.

 

[DIYrich]

As long as it can push all the excess PV to the grid, it should work attached to the Grid without a Battery.

Grid down may be a problem.

See Section 3.1 System Diagrams of the manual. "C. On-Grid solar system without battery"

 

[mciholas]

Grid down may be a problem.

I'm willing to accept no grid, no battery, no output even with PV.

What I would like to work, though, is no grid, dead battery, PV charges battery to minimal SoC and then the system produces AC output.

This would be like an off grid system that gets depleted overnight. Surely that works?

See Section 3.1 System Diagrams of the manual. "C. On-Grid solar system without battery"

Interesting, says it also does EPS (emergency power system) without battery. So perhaps PV only does provide some power if you can manage not to overload it.

Mike C.

 

[wpns]

What I would like to work, though, is no grid, dead battery, PV charges battery to minimal SoC and then the system produces AC output.

Pretty sure this works just fine, why wouldn’t it?

 

[mciholas]

Pretty sure this works just fine, why wouldn’t it?

How does it activate RSD signals to open PV panels in the morning? There is no grid or battery to power anything.

Mike C.

 

[wpns]

How does it activate RSD signals to open PV panels in the morning? There is no grid or battery to power anything.

Mike C.

RSD merely guarantees under 30 volts (within 30 seconds) for fire safety, there’ll be enough power at the actual let-through voltage to power up the RSD transmitter and go from there

 

[wpns]

Interesting, says it also does EPS (emergency power system) without battery.

Indeed, because everyone is obsessed about the corner case. See “Just Don’t” above.

 

[mciholas]

RSD merely guarantees under 30 volts (within 30 seconds) for fire safety, there’ll be enough power at the actual let-through voltage to power up the RSD transmitter and go from there

Spec sheet on 18KPV says "Unit Startup Voltage" is 100 VDC on the PV inputs.

They do not list any sort of RSD minimum voltage spec to get the RSD signal active.

RSD devices allow a volt or so per panel through, for a total of less than 30V but still enough to start.

8 panels in series is only 8 volts.

The RSD devices (say Tigo TS4-A-F) don't know the entire array voltage, only the one panel they are connected to. So it is not like they can regulate the string to 30 volts.

Will an 18KPV dark start with no grid, no battery, with an 8 panel string on Tigo TS4-A-F RSD devices?

I remain skeptical of undocumented features until demonstrated. Assumed behavior often leads to disappointment.

Mike C.

 

[houseofancients]

For a grid tied EG4/Luxpower 18KPV, what happens if it has no battery attached?

There was some comment that the unit would not work properly in these circumstances, that is required a battery to be stable or operational. If so, this seems like a weakness since loss of the battery (for service, fault, or otherwise) would disable the unit and that seems operationally fragile.

If there is no battery and tied to the grid with no PV input, I'd hope the grid powers everything. If there is PV input and grid, the system would convert the PV input to AC which feeds local loads and the remainder back feeds the grid, or the shortfall is drawn from the grid.

What if there is no grid and PV input? Will the system try and make AC? What happens if that overloads (which could easily happen due to cloud)?

Also, if there is no grid, no PV, and no battery, the system is off. Then the sun rises. How do you dark start under these conditions? There is no way to generate the signal to the RSD devices on the panels to "open them up", so it feels like the system will stay dead until either there is grid or battery provided. Do you need some sort of kick start power to get things going?

I am exploring all the corner cases of operation before committing to the system and the manuals are totally useless for documenting these behaviors. The only way to know is to ask other owners to see how it actually operates. That's the engineering mindset, amateurs make things work, professionals make things not fail, and to do that, you have to look at all of the conditions.

I'm also open to knowing how other inverters in this class operate.

Mike C.

Why would you run a very expensive hybrid inverter if you simply are looking for a (much cheaper) grid-tie inverter ?

 

[DIYrich]

RSD merely guarantees under 30 volts (within 30 seconds) for fire safety, there’ll be enough power at the actual let-through voltage to power up the RSD transmitter and go from there

"guarantees under 30 volts". It doesn't guarantee there is 30v "to power up the RSD transmitter". An RSD could drop the voltage to 1v until allowed to let through power.

 

[DIYrich]

Will an 18KPV dark start with no grid, no battery, with an 8 panel string on Tigo TS4-A-F RSD devices?

Yes. With no power to the Tigo RSD controller, the Tigo RSD will not allow power through. With no power to the 18kpv (no grid, no battery, no PV), it will not do anything.

The AIO recover from dark start by reserving some battery power. Once an hour, it powers up the RSD to see if there is enough PV being generated. If not, it sleeps another hour.

You could have one under 30v panel that powers the RSD controller. It would not need an RSD. It would be in parallel with a 20v power supply, so the power supply could keep the RSD controller alive if the panel gets shaded.

 

[mciholas]

Why would you run a very expensive hybrid inverter if you simply are looking for a (much cheaper) grid-tie inverter ?

I'm looking for a hybrid inverter to grid tie excess, work when grid is down for an extended period, and cover nuisance trips.

I want it to be adaptable and work with various configurations. One of those is no battery, which may be how it gets approved initially, or may occur during battery servicing of fault. Another might be no PV but with battery, which serves as a whole house UPS.

Proper engineering of a system means exploring how it works when things go wrong, not just making sure it works when all things are right.

Mike C.

 

[mciholas]

Yes. With no power to the Tigo RSD controller, the Tigo RSD will not allow power through. With no power to the 18kpv (no grid, no battery, no PV), it will not do anything.

Now there's a useful and clear answer. The 18KPV has its own RSD transmitter for the TS4-A-F RSD modules (over PV powerline). For the TS4-A-S or O modules, you do need the CCA and TAP units to do that.

The AIO recover from dark start by reserving some battery power. Once an hour, it powers up the RSD to see if there is enough PV being generated. If not, it sleeps another hour.

Got it. The inverter will stop using the battery before the battery BMS will shut it off, then it goes into a kind of hibernation testing for PV input periodically. The battery, even at low SoC, ill have enough energy to do this for a very long time. But you need a battery to make this work.

You could have one under 30v panel that powers the RSD controller. It would not need an RSD. It would be in parallel with a 20v power supply, so the power supply could keep the RSD controller alive if the panel gets shaded.

Or I can have some sort of jump start system. If I use the TS4-A-S or O which has the CCA and TAP, then I can inject 12 volts into that to wake up the panels. Then the PV wakes up the inverter proper.

This should be a rare case, grid out, battery off/gone. But I like to know how things operate in these corner cases should they occur.

How I wish UL 3741 was available in some way. Then we could avoid all the stupid RSD devices per panel. They cost money and lower reliability.

Mike C.

 

[zanydroid]

RSD devices allow a volt or so per panel through, for a total of less than 30V but still enough to start.

Yes, that's how the RSDs are supposed to help.

But I've never seen a post on this forum confirming that it actually works. It involves some magic on the transmitter too.

CCA is poster child for something unlikely to work given how thirsty it is for power.

Why would you run a very expensive hybrid inverter if you simply are looking for a (much cheaper) grid-tie inverter ?

I thought it was (eventually) clear that this thread was about dark start of system.

Or I can have some sort of jump start system. If I use the TS4-A-S or O which has the CCA and TAP, then I can inject 12 volts into that to wake up the panels. Then the PV wakes up the inverter proper.

There's a thread around here of a pretty sweet build for this kind of dark start. They used a backup battery and inverter.

For SunSpec (or the TIGO RSD only wannabe with a slightly different transmitter) you can likely just loop a second set of transmitter coils, hooked up to a transmitter that you use to power up the panels.

 

[zanydroid]

Here is the not-at-all-overkill dark start build thread.

My experiences finding the right black-start UPS for an off-grid solar system

I would like to share my experiences in finding the right black/dark start UPS for a solar system. It might be helpful for someone to avoid making the same mistakes as me. First, you only need to take care about a dark-start situation if you have some sort of emergency shutdown relays or...

diysolarforum.com

 

[zanydroid]

There are a lot of dark start game plans on other threads too.

Another one is to have V2L or generator into a chargeverter. This will be my second backup plan, eventually.