How to prevent backfeed?

[cj3waker]

Depending on what I have running I am already flirting with my 100A Load. I have turned everything in my house on and measured over 100A at the main, luckily this doesn't seem to trigger the breaker, and I have never triggered my main from too much draw. But I am planning on adding and will be drawing much more than 100A - which was the reason for the service upgrade.

So at a minimum my ideal setup would be my 100A service ----> Inverter that can utilize all 100A from the grid without backfeeding -----> 100A load on subpanels

That doesn't help me with the additional service hopes that kicked all this off... so

Pipe dream would be an inverter than can output ~200A of 240v AC. Obviously it would be great if that was solely supplied from the solar/batteries, but I would have no problem if during high load demands 100A was still coming from the grid

I do have a smart meter

 

[Hedges]

SolArk has 100A pass through, can invert I think 12kW or 15kW from battery, 18kW from PV.

2x of my Sunny Island can pass through 13kW, invert 12kW. 4x about double that (supports your 100A pass through.) However, total output current allowed won't exceed your 100A by much.

What you want is 200A pass-through. Schneider can do that with external relay.

What should also work is AC coupled battery. Something like Tesla Powerwall + PV or Sunny Boy Storage + Sunny Boy. Not necessarily for backup during power failures, but just to monitor grid connection with CT and add power, or charge battery.

Sunny Boy Storage discontinued, but Sunny Boy Smart Energy should do it. However, both use expensive battery. Some of the other brands should be more economical. Many that use CT at grid connection should support. Ask Current Connected about using SolArk or EG4 18kpv for this application.

 

[SupraSPL]

You can go partially off grid this way. Wiring is easy/legal and no risk of backfeeding

 

[Texas-Mark]

Has anybody here heard of anybody being detected/caught?

I backed less than 100 watts for maybe 15 minutes and got a call.

 

[SSC00]

It seems to me the only way that you can have a hybrid system without back feeding to the grid would be to have the grid connected to the battery with a separate mppt charge controller that can accept charging from two different sources and then connect the solar to one connection and then run the grid AC power through an AC to DC converter then to the second connection at the MPPT charge controller then connect the battery to the inverter serving the whole house. Sound like a set up that would prevent any back flow to the grid?

At that point, you really only need the grid to charge your battery. Then just enroll in your utility's time of use program and you should save a little more too. lol

 

[hwy17]

It seems to me the only way that you can have a hybrid system without back feeding to the grid would be to have the grid connected to the battery with a separate mppt charge controller that can accept charging from two different sources and then connect the solar to one connection and then run the grid AC power through an AC to DC converter then to the second connection at the MPPT charge controller then connect the battery to the inverter serving the whole house. Sound like a set up that would prevent any back flow to the grid?

At that point, you really only need the grid to charge your battery. Then just enroll in your utility's time of use program and you should save a little more too. lol

Yes, but you don't have to use an mppt. You can just use and ac to dc charger or power supply.

 

[SSC00]

Yes, but you don't have to use an mppt. You can just use and ac to dc charger or power supply.

oh ok. So you could have an AIO and only connect the AC to DC charger to the battery? That kind of makes it simpler

 

[hwy17]

oh ok. So you could have an AIO and only connect the AC to DC charger to the battery? That kind of makes it simpler

The charger just has to be separate from the inverter. It can be done with or without an AIO. It would broadly be called "double conversion" since all your grid power is going AC-DC and then DC-AC.

The most commonly recommended product for is the Chargeverter. But we also have a thread on the DIY Chargenectifier which uses server power supplies. I use a 2300w Meanwell power supply.

 

[Bluedog225]

Putting current on someone else’s property without their permission seems wrong and unsafe. In addition to being trespass, I’d be surprised if it does not violate the agreement you have with the utility to provide service. We should honor the agreements we make in life. I think it’s good that you are being careful.

 

[Skypower]

I can attest that the “Voltronic family 6548” sold under a multitude of paint colors and names, all clones have zero export (no back feed/ no micro export). They are discontinued under the MPP and Eg4 brands but seem to live on in several lesser brands. They have different variants which is primarily the mpp voltage rating. When they are connected to the grid they always pull some small operating current from the grid regardless of mode. As a general rule of thumb, the higher the mpp voltage rating the higher the operating current/standby current. If the grid is not available, then of course this load would be taken from solar/batteries. The earliest version had a maximum PV OCV of 250 thou this is low, they are also the least problematic. These very economical priced for performance and probably should be considered disposable so if you need two get three (running spare) because they may not be able in a year. Here’s the latest flavor and package deal, strangely they have the lower mpp OCV rating which to me is intriguing;
https://a.co/d/bXRfge5

https://a.co/d/1yJwf5x

 

[Skypower]

I want to add that they are a bit noisy and do generate heat under load or making power

 

[SSC00]

The charger just has to be separate from the inverter. It can be done with or without an AIO. It would broadly be called "double conversion" since all your grid power is going AC-DC and then DC-AC.

The most commonly recommended product for is the Chargeverter. But we also have a thread on the DIY Chargenectifier which uses server power supplies. I use a 2300w Meanwell power supply.

Ok. interesting. I will look into chargeverters

 

[cs1234]

Putting current on someone else’s property without their permission seems wrong and unsafe. In addition to being trespass, I’d be surprised if it does not violate the agreement you have with the utility to provide service. We should honor the agreements we make in life. I think it’s good that you are being careful.

Are there devices besides inverters that will sometimes spuriously backfeed current onto the utilities lines? Certain types of motors spinning up / down?

 

[SSC00]

Like this? @hwy17

 

[hwy17]

View attachment 206811

Like this? @hwy17

Yup, that's it. Guaranteed no backfeed. Then the tricky part is automating the charger's operation. New chargeverters have an RS485 port. Maybe they will automate with EG4 inverters in the future.

I use a dry contact relay from my BMS that closes when battery SOC is below a certain percent, and my Meanwell charger has a two wire on/off control.

You could also just let the Chargeverter float the batteries all the time, but that way doesn't leave room in the battery bank to put away any excess solar power.

 

[SSC00]

Yup, that's it. Guaranteed no backfeed. Then the tricky part is automating the charger's operation. New chargeverters have an RS485 port. Maybe they will automate with EG4 inverters in the future.

I use a dry contact relay from my BMS that closes when battery SOC is below a certain percent, and my Meanwell charger has a two wire on/off control.

You could also just let the Chargeverter float the batteries all the time, but that way doesn't leave room in the battery bank to put away any excess solar power.

yeah. that's a good point. maybe an EG4 person could shed light on that at some point. I think the next stage of development would be to have more DC appliances available. As more DC appliances become available, the need for a large inverter decreases. Honestly would be worth our while to start pressuring more companies to start making DC appliance options now that batteries are becoming cheaper.

 

[hwy17]

yeah. that's a good point. maybe an EG4 person could shed light on that at some point. I think the next stage of development would be to have more DC appliances available. As more DC appliances become available, the need for a large inverter decreases. Honestly would be worth our while to start pressuring more companies to start making DC appliance options now that batteries are becoming cheaper.

Back before rural electrification, fancy farmhouses used to use "Delco light plants" with a 32v lead acid bank and an auto run generator. There was a whole market for 32v DC appliances and power tools to run off these systems.

I don't think it will happen again. Too much copper required to run 48v around a house.

 

[SSC00]

Back before rural electrification, fancy farmhouses used to use "Delco light plants" with a 32v lead acid bank and an auto run generator. There was a whole market for 32v DC appliances and power tools to run off these systems.

I don't think it will happen again. Too much copper required to run 48v around a house.

well, true. unless you step up voltage for the really big loads. I have no idea how efficient a dc to dc converter is.

Wait. Maybe that is the case. Just depends on distance away from batteries. If you can cite the batteries right by the heat pump power connection and same with water heater, it shouldn't be too big of a deal. it seems like it only becomes a big problem when you get more than 50 ft away from the batteries and 50 feet is quite a distance within a home.

 

[cj3waker]

So... An update. After a bunch of back and forth and filing a complaint with the public utility commission, it was determined that it was not my responsibility to gain a 10ft wide nearly unlimited easement for hundreds of feet of power lines that already exist and are not on my property. I got a 3ft easement for "Scope of the project." At this point I don't really know or care about the legalities of the rest of the run (and I'm assuming no one else does either)

It still gets dumber though. The entire plan was changed on what was required to put some power in the ground, probably because I had pissed off NV energy at this point. I had to put in a 48-60" x 24" trench, 3" conduit, and a 17x30 concrete pull box, for a run that is less than 70 feet.

Absolutely insanity, but I had already made a $2700 nonrefundable payment for the service upgrade, so I went ahead and chiseled through rock last week to make it happen. So I will be getting 225A of grid power, which is what I wanted in the first place.

But I'm also done giving those dickheads any more money. So I will 100% be adding a solar system once this stage is done. And I don't want to backfeed or have issues with NV energy, but also.... I've become more than a bit jaded towards NV Energy throughout this entire process, so I'm a little more open to the idea of minimal/probabably won't get caught backfeed, vs absolutely zero backfeed

What I want to do is run primarily off solar with minimal battery backup and utilize the grid as my secondary feed, the caveat being I'd like whatever system I set up to still allow me to utilize all 225A (or 200A...whatever) of grid power if necessary

It seems like an EG4 AIO between my service panel and my loads would allow for this? The only question I have is if that thing can passthrough 200A of grid power, it seems to me like it does, but I'm hoping for clarification. This also seems like a better way to go to either have no batteries, minimal batteries, or being able to put off the purchase of batteries. With a no export option the EG4 shouldn't backfeed during outages, correct?

The other option seems to be the chargeverter to completely isolate grid backfeed. This seems more battery intensive, and a high amperage grid draw would be running both into, and out of the batteries - right? It seems like if I had amperage periods off grid/battery power I would be giving those batteries a pretty rough life, and I would need batteries that could support a full 200A/240V discharge which seems insane in general, and especially over any given length of time.

Something like an EG4 AIO is where my head is at right now, I'm just hoping has some insight on how much grid power in can passthrough, and some more info on no export. Or if I'm just an idiot or if you guys have any other ideas I'm all ears

 

[hwy17]

This seems more battery intensive, and a high amperage grid draw would be running both into, and out of the batteries - right?

Power can flow from the AC/DC supply, over the DC bus, past the battery, and straight into the inverter.

But you're right that double conversion is just more intensive all around, and you lose like 20% or more efficiency on all the grid imports. And the whole DC bus has to be ready to carry all those amps all the time.

Good work on the trench. Seems like you're definitely capable of dealing with them when they get demandy, so you can probably stand the battle if they ever do notice export blips. Probably not.