Intriguing question - What happens when you hook an on-grid solar inverter to a portable power station in an off-grid situation?

[RockclimberKen]

Lets say you hook a 700W solar grid tie inverter into a powerstrip and then plug it into the AC output of a 600 W portable power station (Such as a BlueETTI EB3A). The 700W solar grid tie inverter has island protection, but detects the AC voltage of the 600 W portable power station, synchronizes with the AC wave, and becomes live.

1) If no other load on the power strip, would the output of the solar grid inverter backfeed into the portable power station and destroy it?
2) If load is applied to power strip, what would it be capable of (700W? 1300W?)
3) If only 400W load is applied to power strip, how much of it would come from portable power station / solar grid inverter?

I'm intrigued with the answers to these.... What is everyone's theory as to what would happen?

 

[Ampster]

1) If no other load on the power strip, would the output of the solar grid inverter backfeed into the portable power station and destroy it?

Yes. The grid tie inverter is designed to output all of its power regardless of load because the grid presents an infinite load. There is no way the power station could control the GT inverter unless it has AC coupling ability using frequency/Watt algorithms.

2) If load is applied to power strip, what would it be capable of (700W? 1300W?)

3) If only 400W load is applied to power strip, how much of it would come from portable power station / solar grid inverter?

The smoke would come out before any of these could be measured.

 

[Mattb4]

I would suspect the magic smoke will come pouring out. The inverter for the power pack is not designed to be in parallel with a solar grid tie inverter. But could be an interesting experiment if you keep a fire extinguisher handy and have money to spare.

 

[RockclimberKen]

Yes. The grid tie inverter is designed to output all of its power regardless of load because the grid presents an infinite load. There is no way the power station could control the GT inverter unless it has AC coupling ability using frequency/Watt algorithms.


The smoke would come out before any of these could be measured.

I was wondering about that. But there are grid-tie inverters that only supply power needed by the load. As an example:

https://www.amazon.com/gp/product/B07L5R4486/ref=ewc_pr_img_7?smid=A2L4N2PKBD1J75&th=1

In this situation, I could see the power station start supplying the current. The GT inverter then senses the load and it takes over from there. An issue I see is when the load reduces. There will be a latency of time the GT inverter will still send current before it recognizes the load reduction.

 

[Mattb4]

Interesting device. I suspect it is a code and utility co. violation in the US to use. I also suspect it has the lifespan of a few weeks or months at best.

 

[cs1234]

Interesting device. I suspect it is a code and utility co. violation in the US to use. I also suspect it has the lifespan of a few weeks or months at best.

Of course it is, almost everything seems to be, and this is certainly no exception to the general rule of everything needing a permit, inspection and UL listing.

Of course it has a short lifespan, it's even more poorly built than most of the stuff we see.

I've been following the device on a "private" facebook group (only real place I've found with stateside information). It does seem to work, but dies after a while from one particular piece of cheap innard. A higher quality version would be nice, but would still be an outlaw device that you can't use if you have anything to lose.

Solar Grid Tie Inverter with Limiter discussion

There is also a foreign facebook group that discusses it frequently, but I can't make much of it..

Foreign group discussing Grid Tie Inverter with limiter

 

[ncsolarelectric]

There are bi-directional off-grid inverters that can work that way, but you won't find them for these applications. When the grid-tied inverter pushes the power out, the bi-directional inverter uses that energy to charge the battery at first, then shifts the phase (frequency) so the output of the microinverters is reactive, not resistive. In the 1990's these were called a "line interactive UPS". I designed several bi-directional inverters, the Phoenix PowerVerter was the most popular one for Telecom at the time.

 

[Ampster]

I was wondering about that. But there are grid-tie inverters that only supply power needed by the load.

That is a grid tie inverter that uses current transformers to limit export. It won't work off grid and if you are lucky it would complete its power up test to see if the grid was present. If you are not lucky it wil force the smoke out of the power station.

As an example:

https://www.amazon.com/gp/product/B07L5R4486/ref=ewc_pr_img_7?smid=A2L4N2PKBD1J75&th=1
In this situation, I could see the power station start supplying the current. The GT inverter then senses the load and it takes over from there.

That does not make sense unless you mean the power station starts supplying the voltage and 60 Hz signal. In that case the two above scenerios would play out. If you don't mind blowing up your power station give it a try and report back to the team.

An issue I see is when the load reduces. There will be a latency of time the GT inverter will still send current before it recognizes the load reduction.

Yes that is the issue in AC coupling and why an elaborate algorithm, batteries and an integral battery charger that can use the batteries for the buffer are what makes it work. Your Power Station does not have that algorithm or the power switching capability to make it work. AC coupling is not trivial and it is is not a simple just tricking a GT inverter to think it is connected to the grid.

 

[DThames]

Lets say you hook a 700W solar grid tie inverter into a powerstrip and then plug it into the AC output of a 600 W portable power station (Such as a BlueETTI EB3A). The 700W solar grid tie inverter has island protection, but detects the AC voltage of the 600 W portable power station, synchronizes with the AC wave, and becomes live.

1) If no other load on the power strip, would the output of the solar grid inverter backfeed into the portable power station and destroy it?
2) If load is applied to power strip, what would it be capable of (700W? 1300W?)
3) If only 400W load is applied to power strip, how much of it would come from portable power station / solar grid inverter?

I'm intrigued with the answers to these.... What is everyone's theory as to what would happen?

The grid tied (if UL-1741) will test the impedance of the grid and not turn on because it will see it is not a stiff power source. End of story....nothing would be what I expect. Maybe a blinking red light.

 

[ncsolarelectric]

Of course it is, almost everything seems to be, and this is certainly no exception to the general rule of everything needing a permit, inspection and UL listing.

Of course it has a short lifespan, it's even more poorly built than most of the stuff we see.

I've been following the device on a "private" facebook group (only real place I've found with stateside information). It does seem to work, but dies after a while from one particular piece of cheap innard. A higher quality version would be nice, but would still be an outlaw device that you can't use if you have anything to lose.

Solar Grid Tie Inverter with Limiter discussion

There is also a foreign facebook group that discusses it frequently, but I can't make much of it..

Foreign group discussing Grid Tie Inverter with limiter

A Hoymiles microinverter with the CSS WattNode Meter on a RS485 + Wifi network with the Hoymiles DTU Pro can provide a zero-export feature. If this is connected to the output of the off-grid inverter, it should be able to prevent the grid-tied microinverter from backfeeding into the off-grid inverter. Then it should work. I am going to do this experiment. In fact, I've already run the HM microinverter in parallel with my Enphase microgrid and it worked fine. See my video on YT, the Solar Power DIY Helpdesk. T

 

[cs1234]

I was wondering about that. But there are grid-tie inverters that only supply power needed by the load. As an example:

https://www.amazon.com/gp/product/B07L5R4486/ref=ewc_pr_img_7?smid=A2L4N2PKBD1J75&th=1

In this situation, I could see the power station start supplying the current. The GT inverter then senses the load and it takes over from there. An issue I see is when the load reduces. There will be a latency of time the GT inverter will still send current before it recognizes the load reduction.

It would be interesting to see if it responds fast enough to not blow up an inverter supplying it with the originating supply voltage. Somebody needs to get one for science and find out, it's pretty cheap. Give it a huge load, shut off huge load once it shows it is supplying it, see what happens. For extra fun, make the inverter originally supplying the electricity a small one that normally can't handle much load.

 

[stienman]

Lets say you hook a 700W solar grid tie inverter into a powerstrip and then plug it into the AC output of a 600 W portable power station (Such as a BlueETTI EB3A). The 700W solar grid tie inverter has island protection, but detects the AC voltage of the 600 W portable power station, synchronizes with the AC wave, and becomes live.

1) If no other load on the power strip, would the output of the solar grid inverter backfeed into the portable power station and destroy it?
2) If load is applied to power strip, what would it be capable of (700W? 1300W?)
3) If only 400W load is applied to power strip, how much of it would come from portable power station / solar grid inverter?

I'm intrigued with the answers to these.... What is everyone's theory as to what would happen?

The manufacturers don't support it, so you're not going to get any useful answers except through testing.

1) Probably, but some hybrid and off-grid inverters (ie, standalone, or "micro-grid" inverters) will take the excess power and charge their batteries while they try to maintain the grid voltage and frequency. For instance, the Growatt SPF6000 exhibits this behavior, and I did this for a time until I found that the growatt doesn't limit battery voltage or current in that mode, and you could destroy batteries through overvoltage when the batteries are full, and the grid-tie inverter is putting out more power than the loads are consuming. The growatt inverter is fine, at least for the several months I ran it that way with a SolarCity grid tie (Delta H6) attached.

2) As long as the grid tie inverter and the off-grid inverter play nice, then they would each contribute their maximum output to the load, so you should be able to run a 1.3kW load. I doubt inverters that small will place nicely with each other, though.

3) This will depend on inverter specifics, such as settings and component variations. If one inverter tries to keep the line voltage at 120VAC and the other at 110VAC, then the inverter with the higher voltage output will supply the greater share of the power. The frequency of each inverter will also affect the sharing. Even if both are set to 120VAC at 60Hz, individual variations in components will generally cause one to be slightly higher than the other. Perfect 50% - 50% sharing is unlikely.

 

[cs1234]

I was wondering about that. But there are grid-tie inverters that only supply power needed by the load. As an example:

https://www.amazon.com/gp/product/B07L5R4486/ref=ewc_pr_img_7?smid=A2L4N2PKBD1J75&th=1

In this situation, I could see the power station start supplying the current. The GT inverter then senses the load and it takes over from there. An issue I see is when the load reduces. There will be a latency of time the GT inverter will still send current before it recognizes the load reduction.

Potentially just as junky, but maybe less junky, would be the Legion Solar kit with panel level microinverters. I seriously doubt one could get it approved by an inspector of course, and good luck with your homeowners insurance. It claims to be able to do zero export. They are of course full of it with their claims you don't need permits, etc.. The equipment itself doesn't necessarily look terrible though.

Legion Solar Starter Kit

@ncsolarelectric I'm curious how it compares in price to your Hoymiles setup for zero export? They both use a box that can monitor usage with current clamps for zero export and can use individual panel microinverters. The Hoymiles stuff looks nice, but it doesn't look like they sell direct to DIYers.

 

[ncsolarelectric]

Potentially just as junky, but maybe less junky, would be the Legion Solar kit with panel level microinverters. I seriously doubt one could get it approved by an inspector of course, and good luck with your homeowners insurance. It claims to be able to do zero export. They are of course full of it with their claims you don't need permits, etc.. The equipment itself doesn't necessarily look terrible though.

Legion Solar Starter Kit

@ncsolarelectric I'm curious how it compares in price to your Hoymiles setup for zero export? They both use a box that can monitor usage with current clamps for zero export and can use individual panel microinverters. The Hoymiles stuff looks nice, but it doesn't look like they sell direct to DIYers.

The CSS WattNode meter alone costs more than that.

 

[cs1234]

The CSS Wattson meter alone costs more than that.

I'm having trouble finding a CSS Wattson online.

Is it one of these?
Maybe a CSS Wattson?

 

[ncsolarelectric]

I'm having trouble finding a CSS Wattson online.

Is it one of these?
Maybe a CSS Wattson?

This one.

 

[cs1234]

Thanks @ncsolarelectric . Those certainly don't look like a cheap item. They look much more configurable and reliable than the cheap grid tied inverter or the legion solar stuff probably is.

 

[RockclimberKen]

The grid tied (if UL-1741) will test the impedance of the grid and not turn on because it will see it is not a stiff power source. End of story....nothing would be what I expect. Maybe a blinking red light.

That's a great point, and I do believe even the GT inverter I mentioned follows UL-1741 as the video for it shows the slow ramp up of power to the grid (following the UL-1741 spec). BUT.... I also think it goes by sequence of how you power everything on. For instance:

Portable power station has power strip with a 100W light bulb plugged in. Light bulb is on and is getting power supplied to it by power station. Then the GT inverter with a 80W solar panel is plugged in to the same power strip. It tests the impedance successfully and then matches voltage and frequency. It then ramps up power to supplement the portable power station. At the conclusion of the test, the power strip is removed from the power station. Island protection causes the GT inverter to stop supplying power and the light bulb goes off. Very simple test, and I'm not seeing magic smoke. This is all theory and I am just having fun with the thought. What do you think?

 

[ncsolarelectric]

Thanks @ncsolarelectric . Those certainly don't look like a cheap item. They look much more configurable and reliable than the cheap grid tied inverter or the legion solar stuff probably is.

They have to be, it's intended for commercial and utility-scale applications, not off-grid residential, but we can use it.

 

[cs1234]

They have to be, it's intended for commercial and utility-scale applications, not off-grid residential, but we can use it.

It certainly looks it, but if something is commercial and utility-scale, it is going to cost accordingly, which will price it out of range to encourage even more residential solar adoption. I'm looking for budget friendly, approved solutions that can be spread to everybody. I want to spread our solar panel love to everybody, and that means the cost has to stay down while hopefully keeping the fires to a bare minimum.