How to prevent backfeed?

[cj3waker]

Hello, my name is Chris. I live up in northern NV and get to play with NV energy.

I have a single 100 amp service running to my house, this started as an attempt to increase my service amperage and I wanted to add solar down the road.

About 5 months ago I started the process with NV energy to upgrade my service, an upgrade to 330 amps was quoted around 6k, then came back as 30k+. I declined, and they told me a 220 amp service would only be a few thousand. I tried to move forward and waited for months for my project coordinator to complete a little MS paint drawing of the service upgrade so we could move forward. I finally got it, signed it all and went to move ahead. In the last bit of paperwork they sent me an easement application that they requested I have signed by the "responsible party" and notarized. Turns out the power lines that feed my house that run through a golf course aren't subject to any easement. And they basically pawned off the responsibility to get an easement to me, instead of their legal department or whatever. So I don't really have a feasible way to upgrade my service any longer, and the service that currently feeds my house isn't even on a legal easement. I am about fed up with NV energy.

So I'm thinking about going full retard and trying to build a massive system without any coordination with NV energy. I understand why this is frowned upon, but I'm pretty fed up. So before all the warnings or whatever, is there an iron clad way to prevent backfeed to the grid, in my ignorance it seems like a diode would do it? Or better does anyone have some resources on permitless grid tie?

So theoretically, in minecraft.. If you were dumb, and were going to try to build a big system while retaining the ability to feed from the grid, but without any agreements from your provider and really wanted to prevent backfeed, how would you do it?

 

[pollenface]

I think the safest way is to go off grid or partially off grid.

My eventual plan is to dedicate specific circuits in my house to run from battery/inverter power

 

[hwy17]

Most surefire way to prevent all backfeed, even momentary blips, is to use a double conversion system where the grid only inputs through a dedicated charger, such as a chargeverter.

 

[wdwtx2.0]

The absolute best way is to use an off grid inverter(s).
You can parallel stack as needed.
It is incapable of export.

 

[cj3waker]

That's simpler than I was thinking. I was thinking of adding some sort of diode (that I don't even think exists) between the meter and the inverter. I guess the inverter takes care of that functionality anyways. The EG4 18kpv seems pretty well recommended yeah?

On that model the max continuous AC current is 50A, but it mentions 200A of AC bypass. Does that mean that 200A line could run "through" the inverter to 200A of load downstream?

 

[MisterSandals]

but without any agreements from your provider and really wanted to prevent backfeed, how would you do it?

Are you worried about being detected or back feeding the grid if/when the grid goes down?

 

[hwy17]

I was thinking of adding some sort of diode

AC Diodes unfortunately can't exist.

All of the passthrough inverters including the 18kPV will be vulnerable to microexports, when a large load shuts off they just can't react in time before a few hz of export leaks out.

Normally the utility won't notice this but some smart meters can detect it.

 

[Q-Dog]

I too would just build an offgrid system. Use the existing grid to recharge the batteries during low sun times, and as backup if your offgrid system fails.

 

[murmeister]

All of the passthrough inverters including the 18kPV will be vulnerable to microexports, when a large load shuts off they just can't react in time before a few hz of export leaks out.

Normally the utility won't notice this but some smart meters can detect it.

I can confirm that the 18Kpv does, in fact, back feed (micro export), at various times. There is a "Zero export" option that you can set. I thought that would be sufficient. After a few days, I noticed I had exported 0.1kwh of power. Not significant, but also not zero.

There is also an "Off grid" setting that supposedly guarantees no export, but I never tried that. To my mind, that also means I don't import power, either - which is not what I want at this time.

 

[Hedges]

Ask if you can install a 200A or 225A service panel, simply so panel is allowed larger size PV breaker under the 120% rule, but without adding electrical loads. That should minimize their work and cost.

Previously I had requested reservation of a 15kW PV net metering system. Engineering review determined no utility transformer or wire upgrade needed, and I have the reservation.

I requested 200A service upgrade from 100A. I had to acknowledge a $3500 estimate. I listed some added loads to justify the upgrade (as I had to justify PV system size.) After PG&E inquiry, I said that there would not be added loads at this time. They determined their equipment didn't need to be upgraded, said to contact them again before adding major loads.

I'm ready to schedule their "Cut and swing" of overhead wires from old panel to new. I think they will keep their 2 awg (?) wires, crimp them onto my 3/0 wires. They came once before to do it, but rejected my "ringless" meter box so I've now replaced it with ring type.

It looks like they will not actually charge me that $3500.



Does net metering offer decent terms?

 

[cj3waker]

Are you worried about being detected or back feeding the grid if/when the grid goes down?

yes

 

[cj3waker]

Ask if you can install a 200A or 225A service panel, simply so panel is allowed larger size PV breaker under the 120% rule, but without adding electrical loads. That should minimize their work and cost.

Previously I had requested reservation of a 15kW PV net metering system. Engineering review determined no utility transformer or wire upgrade needed, and I have the reservation.

I requested 200A service upgrade from 100A. I had to acknowledge a $3500 estimate. I listed some added loads to justify the upgrade (as I had to justify PV system size.) After PG&E inquiry, I said that there would not be added loads at this time. They determined their equipment didn't need to be upgraded, said to contact them again before adding major loads.

I'm ready to schedule their "Cut and swing" of overhead wires from old panel to new. I think they will keep their 2 awg (?) wires, crimp them onto my 3/0 wires. They came once before to do it, but rejected my "ringless" meter box so I've now replaced it with ring type.

It looks like they will not actually charge me that $3500.



Does net metering offer decent terms?

Panel size must match service size, and It doesn't look like any changes to my service are ever going to be made considering they don't even have an easement for the current lines that supply me

 

[MisterSandals]

yes

Personally I would be wildly surprised if they detected tiny amounts back fed into the grid.

Has anybody here heard of anybody being detected/caught?

Regarding energizing a downed grid so as to not kill any linesman, most systems strictly prevent this already. If not, rapid shut down devices are readily available.

 

[wpns]

Either setting up for zero export (the EG4 18Kpv also has a fast response zero export function.) should do it, but worst case get an EG4 ESS and a ChargeVerter or two and you can guarantee that power will only flow in one direction. Then you can as as much solar as you want to keep your batteries charged for free and only buy the amount of power you want to.

 

[Batronca]

Hybird inverter (Sol-Ark,EG4 18kpv, Sky Box Outback.....), set zero Expot and set 50 or more, the inveter will always draw 50W from grid.

 

[RCinFLA]

Existing hybrid inverters that can do load shaving can do what you want.

You are more likely to find a LF inverter that does this properly.

Preventing back feed is easy. Load shaving requires instant supplementing by inverter which is easier to achieve with LF inverters that are inherently bi-directional in power transfer to or from battery. They can instantly go from charging battery to sourcing battery power to AC output on the fly and vice-versa direction.

 

[millsan1]

I have heard of a guy who ran his 18 as zero export, for 6 months, and it never was true zero, but also was never noticed by his utility company, most likely because of the insignificant amount of backfeed, less than .2kw per day, at worst.

YMMV

 

[Hedges]

Panel size must match service size, and It doesn't look like any changes to my service are ever going to be made considering they don't even have an easement for the current lines that supply me

Which makes sense. I was surprised I'm allowed to have 200A breaker when PG&E isn't upgrading lines to match its rating. Not sure, but I suspect even their pole pig can't deliver that.

To support PV, consider a 200A (or 225A) breaker panel with 100A main breaker (125 if allowed). That OCP matches service size. The panel can then be backfed by up to 100A or so PV breaker. And if utility ever upgrades it will be ready to accept other breakers.

Alternatively, a PV-ready panel, or line side tap, or like I did "load side tap" after a main breaker only panel. I got a 200A one. Maybe there is a 100A one. There are 100A visible blade knife switches which can be service disconnect. Then fan out to existing loads panel and your PV system.

I have a single 100 amp service running to my house, this started as an attempt to increase my service amperage and I wanted to add solar down the road.

Do you need more than 80A continuous draw?

See if you can find service disconnect with magnetic-hydraulic breaker. Those should work up to 95% continuous or 100% continuous.

See if a modest 125A upgrade would be allowed.

Finally, an inverter supporting "additional local consumption" would blend power from PV/battery with grid power, limiting grid current to a target like 80A max. You'll want a way to shed loads if the inverter can't keep up.

 

[hwy17]

Has anybody here heard of anybody being detected/caught?

There was a guy posted a little while ago in Florida about his utility contacted him about micro exports.

 

[SparkyJJO]

There was a guy posted a little while ago in Florida about his utility contacted him about micro exports.

But I'm willing to bet that the OP's old feed is not supported by any fancy hardware remotely capable of detecting anything.

 

[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