Yikes! Solar panels and Inverter/Battery Backfeed Into Duplex Receptacle!

[electrofelon]

So you're going to convert the entire house to DC?

No, why would I do that?

 

[480sparky]

No, why would I do that?

You do understand Alternating Current, don't you?

 

[jaggedben]

The problems I see with the way they are presenting this are:

1) As GoldDigger noted, you can't plug a power source into to an ordinary branch circuit receptacle without defeating the branch circuit overcurrent device. This is why 705.12 has required the power source to have a dedicated OCPD since forever, and why UL (to my knowledge) won't list this type of plug and play inverter.

2) They try to claim that you don't need an electrician. But they clearly show a power meter using CTs installed inside a load center. While many DIYers will be fine doing that, it's not for the typical layperson, and they shouldn't be claiming you don't need an electrician. The money they show pledged in their fundraiser so far won't cover the first lawsuit from someone who gets electrocuted.

3) They don't get to be the ones who say that you don't need some kind of permit or permission for this.

In short, this is a gadget. Apartment dwellers who want to be serious about 'participating in the renewable energy revolution' should do community solar or advocate for it where it isn't legal yet.

 

[jaggedben]

You do understand Alternating Current, don't you?

You must realize how condescending you're being.

Metering AC power flow at an import/export location and telling a load side power source to throttle to prevent backfeed is a concept I'm sure you can wrap your head around. Moreover, there's already a bunch of widely installed products that do it, such as Powerwall, Enphase Ensemble, Solaredge inverters, etc.

 

[jaggedben]

All it has to do is prevent reverse energy flow on the incoming mains. That is easy.

To be clear, it's easy to engineer a product that does that when it will be installed by a professional. But it's not easy to do as a 'plug and play' product that Joe Apartment-Dweller can just buy and use. You need a meter somewhere. (Or you would need the battery and solar inverter to plug into the same outlet and never backfeed it, but that doesn't look like their approach.)

 

[480sparky]

You must realize how condescending you're being.

Metering AC power flow at an import/export location and telling a load side power source to throttle to prevent backfeed is a concept I'm sure you can wrap your head around. Moreover, there's already a bunch of widely installed products that do it, such as Powerwall, Enphase Ensemble, Solaredge inverters, etc.

No. I can't understand how combining two power sources on one circuit can be separated by some snap-on device somewhere else on the circuit.

You have utility power coming in from the street on a conductor. On that same conductor, MORE power is being added by the inverter of this system.

Explain to me this process of preventing the current provided by the inverter from being sent back out the circuit to the utility's transformer.

 

[ramsy]

Explain to me this process of preventing the current provided by the inverter from being sent back out the circuit to the utility's transformer.

I am having visions of a CT metering total solar production, the other CT for total building load.

When production exceeds load some kind of switching takes place.

 

[electrofelon]

Explain to me this process of preventing the current provided by the inverter from being sent back out the circuit to the utility's transformer.

Very easy. You have CT's on the "mains" and they send a signal to the inverter and/or battery so that the inverter can throttle down and/or the battery can uptake the energy if local loads stop using the power. I'm really not sure why this is so difficult to understand, its done all the time. There are also reverse power relays, very common (although that isnt specifically how this company is doing it).

Its easy to prevent reverse energy flow on the mains, what is harder is preventing an overload on the connected branch circuit from the two sources (mentioned by jaggedben).

Im not endorsing all aspects of this product, just saying prevent energy backflow to the utility is easy, and it is an interesting discussion as to whether that precludes the requirement for an interconnect agreement.

 

[mikeames]

Explain to me this process of preventing the current provided by the inverter from being sent back out the circuit to the utility's transformer.

You can algorithmically. Take an initial current reading on the service. If its greater that the total output capability the 300 watt solar product then its safe for it to turn on. It must then monitor the current and if it drops to or through zero, it must turn off.

I don't support this product, and it would need an electrician to put the CTs on but its could possibly be done but like someone already said. This is a lot of overhead for 300 watts at best.

 

[480sparky]

Very easy. You have CT's on the "mains" and they send a signal to the inverter and/or battery so that the inverter can throttle down and/or the battery can uptake the energy if local loads stop using the power. I'm really not sure why this is so difficult to understand, its done all the time. There are also reverse power relays, very common (although that isnt specifically how this company is doing it).

Its easy to prevent reverse energy flow on the mains, what is harder is preventing an overload on the connected branch circuit from the two sources (mentioned by jaggedben).

Im not endorsing all aspects of this product, just saying prevent energy backflow to the utility is easy, and it is an interesting discussion as to whether that precludes the requirement for an interconnect agreement.

Egads, there's millions of solar generators out there that do the exact same thing except they're not connected to anyone's house wiring. Boondockers and off-gridders use solar and batteries and inverters all the time. Heck I've even got a similar system in my house. But I cannot back-feed the utility unless I start rewiring things. But take that same system referenced here, wire it up to a simple dwelling system, and suddenly you've got huge back-feed problems when the utility goes out?

So in other words, this system does ZERO in terms of energy production if the utility power is on? Than what good is it? I'm not really sure why this is so difficult to understand.

No thanks. I doubt anything like that could even get an recognized listing.

 

[wwhitney]

I don't think you're following the idea. The CTs on the service conductors (necessarily coupled with a voltage measurement, I think) can quantitatively determine the net power flow, from the grid or to the grid. So the control system can use a feedback loop to ensure there is never net flow to the grid. [On a time scale longer than the response time of the control system.]

E.g. Say the PV/batteries are off, and the house load is 200W. The control system tells the inverter to make up to maybe 150W (for a 50W margin of safety). The inverter says it can make up to 250W in the current conditions? Tell the batteries to charge at 100W, and increase PV production to 250W. The house load increases so the net flow jumps from 50W to 200W? Tell the batteries to stop charging. The net grid flow drops below 50W? Tell the inverter to throttle production. Etc.

Cheers, Wayne

 

[480sparky]

I don't think you're following the idea. The CTs on the service conductors (necessarily coupled with a voltage measurement, I think) can quantitatively determine the net power flow, from the grid or to the grid. So the control system can use a feedback loop to ensure there is never net flow to the grid. [On a time scale longer than the response time of the control system.]

E.g. Say the PV/batteries are off, and the house load is 200W. The control system tells the inverter to make up to maybe 150W (for a 50W margin of safety). The inverter says it can make up to 250W in the current conditions? Tell the batteries to charge at 100W, and increase PV production to 250W. The house load increases so the net flow jumps from 50W to 200W? Tell the batteries to stop charging. The net grid flow drops below 50W? Tell the inverter to throttle production. Etc.

Cheers, Wayne

I don't think you're following the idea.

So......... what happens when the utility power goes out? Does the system simply shut down completely to prevent back-feeding the service?

 

[wwhitney]

I don't think you're following the idea.

Was there a typo when you wrote "ZERO in terms of energy production if the utility power is on"? If you meant "off", then I understand your concern.

Obviously without a disconnect switch (microgrid interconnect device), the system has to stop producing when the grid is out. So like any usual grid-tie system, it is only useful for offsetting grid usage. The battery component is to avoid production loss that would otherwise be required to avoid grid backfeed, and can not provide backup power.

Cheers, Wayne

 

[electrofelon]

But take that same system referenced here, wire it up to a simple dwelling system, and suddenly you've got huge back-feed problems when the utility goes out?

I assume the inverter has anti-islanding protocols equivalent to UL1741.

So in other words, this system does ZERO in terms of energy production if the utility power is on?

When the grid is off it produces no energy (or maybe it disconnects from the grid and charges the battery, I didnt look closely enough at it). When the grid is on, it supplies energy, but no energy is sent to the utility. It does not feed energy into the grid even if all local loads are turned off.

So......... what happens when the utility power goes out? Does the system simply shut down completely to prevent back-feeding the service?

Most grid tied systems do. This one may be able to keep charging that battery, again, i didnt look real close at it.

 

[ramsy]

So in other words, this system does ZERO in terms of energy production..

When California burns every summer, the grid shuts down, along with everyone's grid tied solar arrays.

Interactive inverters able to switch to battery during blackouts is something new. Tesla power wall may have started this emerging development, but I don't hear much about that anymore.

 

[jaggedben]

...

Interactive inverters able to switch to battery during blackouts is something new. Tesla power wall may have started this emerging development, but I don't hear much about that anymore.

It's not really that new (Trace and Outback and SMA were making systems that 'island' many years ago). But it has been swiftly changing in the last five years. And I'm not sure why you would've stopped hearing about Powerwall because that market has only gotten bigger recently, and with more players involved.

 

[GoldDigger]

I assume the inverter has anti-islanding protocols equivalent to UL1741.



When the grid is off it produces no energy (or maybe it disconnects from the grid and charges the battery, I didnt look closely enough at it). When the grid is on, it supplies energy, but no energy is sent to the utility. It does not feed energy into the grid even if all local loads are turned off.


Most grid tied systems do. This one may be able to keep charging that battery, again, i didnt look real close at it.

With a completely electrician free installation, the only possible way to go to island mode is for the owner to manually open the main breaker. Since there is no interlock, I guess they are counting on backfeed sensor to turn off island mode if the main breaker is reclosed.

 

[pv_n00b]

I see these come and go. I think the first one I saw was maybe 10 or 15 years ago at a home show. Someone had grafted an early microinverter to a module and spliced a plug onto the microinverter AC conductor. These come and go, I've never seen one actually for sale, they always seem to be in the preorder make a deposit phase. I have never heard from someone who bought one and used it at home.

 

[tortuga]

I bought a cheap one of these inverters off ebay a few years ago and set it up to a bunch of damaged panels I had salvaged right before an after work social . A POCO engineer and a solar guy came over also, It blew their minds, I ended up giving it to them because they could not believe it worked. The POCO had an extensive meeting about these, and concluded they do in fact shutdown when the grid does.

 

[jaggedben]

I bought a cheap one of these inverters off ebay a few years ago and set it up to a bunch of damaged panels I had salvaged right before an after work social . A POCO engineer and a solar guy came over also, It blew their minds, I ended up giving it to them because they could not believe it worked. The POCO had an extensive meeting about these, and concluded they do in fact shutdown when the grid does.

I never really doubted that those cheap eBay grid-tie inverters worked, I've just doubted how long they would work for.