solar backfed question

[Kaizen]

Just starting my research into setting up solar. Wanted to see what I could backfeed into my main panel using the 120 percent rule.
The main breaker is 200 amps. The box sticker says if backfed refer to main breaker. i don't see any busbar rating. Main breaker does not have any useful info that i see.
Are they just saying if main breaker is 200 amps then 40 amps is max backfeed?

 

[theoldwizard1]

Just starting my research into setting up solar.

Look at "grid tie micro inverters". Their output simply "plugs into" a standard 15A/20A duplex receptacle.

Although completely safe, most power companies won't let you use them (blame your local government) because any excess power you create would be sold back to them at "retail" rates and they buy power at "wholesale" rates.

 

[Kaizen]

I'm looking at using the eg4 18k hybrid inverter with some battery backup. The initial array will be about 10k. This inverter can take whatever i want and pump back into my panel and the rest to battery. but if i can only put 20 amps back into this panel thats not going to work too well. Initially i doubt i'd have excess power so my thought was to not go through the utilty with the net meter and inspections and just use it myself. I'd have to run a lot of wire for those microinverters as its a ground mount array about 50 feet from the house.
Any roof mount i'd most likely use those microinverters.
But i'm really a noob at all of this so maybe way off

 

[mm08822]

If the panel that the solar input connects to does not have a stated buss rating then it is rated for the size of the main cb.

So in your case, the max permitted backfeed is 40A.

 

[Mr onetwo]

The 18Kpv is UL 9540 listed as an ESS with the EG4 PowerPro 14.3Kw wall battery.I have one with a 6000XP for emergency...much better than a bunch of rack mount batteries.It is a nicely made piece. Go over to https://diysolarforum.com/ if you aren't already there.

 

[theoldwizard1]

I'm looking at using the eg4 18k hybrid inverter with some battery backup. The initial array will be about 10k. This inverter can take whatever i want and pump back into my panel and the rest to battery.

The whole point of a HYBRID PV system is to avoid (as much as possible) buy power from the PoCo.

To do this, you remove the feed from the meter to the main load center and connect it to the inverter/charger. The output of the inverter/charger now goes to the main load center.

On paper, this looks simple. In real life it is not ! Lots of heavy gauge wire, conduit, disconnects, etc. $,$$$ !

Some PoCos are now charging extra for peak usage times. If you have a big enough battery bank, you can "ride through" those times and even if you don't have sufficient solar power, you can (partially) recharge during "non-peak" hours.

 

[theoldwizard1]

Start small. Grid tie micro inverters. No batteries required. As I said, they simply plug into a 15A/20A receptacle. Don't tell the PoCo !

 

[Kaizen]

If the panel that the solar input connects to does not have a stated buss rating then it is rated for the size of the main cb.

So in your case, the max permitted backfeed is 40A.

Thanks for the confirmation. I'm showing about 9600 watts allowed.

 

[Kaizen]

The 18Kpv is UL 9540 listed as an ESS with the EG4 PowerPro 14.3Kw wall battery.I have one with a 6000XP for emergency...much better than a bunch of rack mount batteries.It is a nicely made piece. Go over to https://diysolarforum.com/ if you aren't already there.

Will do thanks

 

[Kaizen]

The whole point of a HYBRID PV system is to avoid (as much as possible) buy power from the PoCo.

To do this, you remove the feed from the meter to the main load center and connect it to the inverter/charger. The output of the inverter/charger now goes to the main load center.

On paper, this looks simple. In real life it is not ! Lots of heavy gauge wire, conduit, disconnects, etc. $,$$$ !

Some PoCos are now charging extra for peak usage times. If you have a big enough battery bank, you can "ride through" those times and even if you don't have sufficient solar power, you can (partially) recharge during "non-peak" hours.

That is one way to do it which I do not want to do. I am putting all of the equipment in a shed outside instead of the celler due to conditions and weight. So i'd have to run a lot of wire that way. This inverter can be set up so it only sends the needed amount of power to the backfed breaker while the grid supplies the rest. So if i'm making 10k and using 1k then it will send the rest to the battery or get clipped.
I'm most likely going to need a line side tap along with permits and inspections but around here that is 6 months minimum wait. Using the backfed breaker at least I can benefit through the summer.
I get what you are saying for the microinverter and might do that with some roof panels as i have an outlet right below it. But my first array is along a fence 50-60 feet from any plugs so i can't see running wire from each panel to a plug making financial sense.

 

[Mr onetwo]

Start small. Grid tie micro inverters. No batteries required. As I said, they simply plug into a 15A/20A receptacle. Don't tell the PoCo !

bad advice....do not do this

 

[walta]

If you can get a net metering agreement from your local utility it is a much better plan for you than buying and maintain batteries. The way I see it net metering provides you with a nearly perfect battery of unlimited capacity that you charge in the summer months with long days and discharge in the winter months when you have short days and higher demand at the measly cost of your connection fee.

My guess is if you divide the cost of the preposes battery by your monthly connection fee. The resulting number is likely to be much larger than the life expectancy of the battery.

I encourage you to follow your utilities rules and get all the required permits and agreements.

I don’t see why a micro inverter setup would need any more or larger wires.





Walta

 

[theoldwizard1]

This inverter can be set up so it only sends the needed amount of power to the backfeed breaker while the grid supplies the rest. So if i'm making 10k and using 1k then it will send the rest to the battery or get clipped.

Never heard of this. So on sunny days and light load (no one home, no A/C), you get fully charged batteries ? Will you have enough battery capacity to run all night when you are home ?

I'm most likely going to need a line side tap along with permits and inspections but around here that is 6 months minimum wait. Using the backfeed breaker at least I can benefit through the summer.

I hope that inverter has a good "Anti-Islanding"

But my first array is along a fence 50-60 feet from any plugs so i can't see running wire from each panel to a plug making financial sense.

Where will your solar shed be in relationship to the array ? Wire your solar panels for the highest voltage the inverter/charger can handle.

You can "backfeed" as much as that inverter can output. use the same size breaker in you load center as is on the inverter.

FYI - Install a Micro-Air EasyStart on your A/C (unless it has an inverter drive for the compressor motor).

 

[WisJim]

You can back feed up to 20% of the rating of your main breaker, per NEC.
All UL listed grid tie inverters have anti-islanding as an integral part of their design.

 

[mm08822]

You can back feed up to 20% of the rating of your main breaker, per NEC.
All UL listed grid tie inverters have anti-islanding as an integral part of their design.

 

[mm08822]

The backfed cb rating can be 20%. The wiring and cb has to be at 125% for cont load. So a 40a cb/wiring can only receive a max inverter output of 32a.

If the main cb can be changed out to a lower value, e.g. - 150/175a then the 40a limit can increased.

 

[RPH]

Just looked at diysolar.com. First opened and a bunch of complaints about the eg4 inverters. I suggest strongly you review the information.
Let the buyer beware!
Not to rain on the parade.

 

[theoldwizard1]

You can back feed up to 20% of the rating of your main breaker, per NEC.

A question that can not be answered. It a load center has a 200A main breaker and allows 100A load side breakers, why would the NEC limit backfeed breakers to 40A ? Your statement would also apply to interlocked generator inputs.

All UL listed grid tie inverters have anti-islanding as an integral part of their design.

Not all inverters are UL rated.

 

[Git]

Speaking of a line side tap - have you ever seen a 'meter adapter'?

 

[dave*99]

deleted

 

[mm08822]

A question that can not be answered. It a load center has a 200A main breaker and allows 100A load side breakers, why would the NEC limit backfeed breakers to 40A ? Your statement would also apply to interlocked generator inputs.

If there were no limitation on the total simultaneous power fed into a panel, the buss could easily be overloaded at various locations along its length.

Without such a requirement, any clown could easily buy the smallest rated panel and load it up with backfed cbs.

What do generator interlocks have to do with this thread?

 

[Kezorm]

If there were no limitation on the total simultaneous power fed into a panel, the buss could easily be overloaded at various locations along its length.

This. The bus bars have a limit. Can’t feed unlimited current through the bus. Note that for the 120% rule to apply, the backfed breaker also needs to be at opposite end of the bus from the main.

 

[Kezorm]

The bus rating is right there on the label in the first picture. 200A maximum.
The backfed language on the label has nothing to do with the main breaker. It states that backfed breaker requires hold down kit.

 

[WisJim]

Not all inverters are UL rated.

Two things: UL lists items, they don't "rate" them. And if they aren't UL listed or listed by an equivalent agency, they can't be legally connected to a utility grid.

 

[dave*99]

Your statement would also apply to interlocked generator inputs.

An interlocked generator input supplies current in place of current entering through the main breaker

A breaker backfed from an inverter can be additive to power supplied through the main breaker.

If there were sufficient load the bus could see current levels above its rating.

 

[wyliesdiesels]

Your statement would also apply to interlocked generator inputs.

What? You wouldnt have a generator and the grid feeding the panel at the same time.

 

[Mr onetwo]

Just looked at diysolar.com. First opened and a bunch of complaints about the eg4 inverters. I suggest strongly you review the information.
Let the buyer beware!
Not to rain on the parade.

False news......That was for the discontinued "voltronics" produced inverters.They are NLA. The EG4 18Kpv and the EG4 6000XP are produced by LuxPower and are well proven and ROCK solid

 

[Mr onetwo]

The equivalent agency is called an NRTL. https://www.osha.gov/nationally-recognized-testing-laboratory-program

 

[Kaizen]

Speaking of a line side tap - have you ever seen a 'meter adapter'?

from the research i've done so far it seems most electric companies are not wanting their meter box touched. I still need to dig into what my local one does.

 

[Kaizen]

The bus rating is right there on the label in the first picture. 200A maximum.
The backfed language on the label has nothing to do with the main breaker. It states that backfed breaker requires hold down kit.

Thanks. I was under the impression there was a seperate "bus bar rating" that was supposed to be listed.

 

[Kaizen]

The backfed cb rating can be 20%. The wiring and cb has to be at 125% for cont load. So a 40a cb/wiring can only receive a max inverter output of 32a.

If the main cb can be changed out to a lower value, e.g. - 150/175a then the 40a limit can increased.

I have this 200 amp panel and a 125 sub panel off of it so i don't want to try and derate the main. Probably could be done but easier to do a line side tap someplace.

 

[Git]

Agree - but that is the power company that put out that video - SDGE (San Diego Gas & Electric)

Sure makes things a lot simpler/easier/cheaper by using that adapter

 

[Kaizen]

Never heard of this. So on sunny days and light load (no one home, no A/C), you get fully charged batteries ? Will you have enough battery capacity to run all night when you are home ?

I hope that inverter has a good "Anti-Islanding"

Where will your solar shed be in relationship to the array ? Wire your solar panels for the highest voltage the inverter/charger can handle.

You can "backfeed" as much as that inverter can output. use the same size breaker in you load center as is on the inverter.

FYI - Install a Micro-Air EasyStart on your A/C (unless it has an inverter drive for the compressor motor).

I believe this system needs some kind of a battery to run/start. Might be wrong but I at least want to have some battery power even if i'm on a net meter. Never made any sense to do all of this and not have some power in a black out.
The panels shed and house/meter are in an L shape with the panels running 65 feet or so along the long leg, shed at corner, and meter at short leg of L. I'm leaning at this point to a shut off and line side tap at the meter outside so I can expand later.
The inverter takes in 18k of pv and outputs 12k plus i think over the 12k to battery. So you can see the inverter far exceeds the 40amps i could probably back feed. I havent read through the whole manual yet but here is the unit.

EG4 18KPV Hybrid Inverter | All-In-One Solar Inverter | 18000W PV Input | 12000W Output | 48V 120/240V Split Phase | EG4 18KPV-12LV

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

 

[Kaizen]

Agree - but that is the power company that put out that video - SDGE (San Diego Gas & Electric)

Sure makes things a lot simpler/easier/cheaper by using that adapter

I work with electric utilities across the country daily and you'd think when one would allow it would flow but it takes a lot of pushing for most to change. I'm sure san diego has had 100 times the installs that the utilites in New Hampshire has seen. Maybe i'll be the first!

 

[dcg9381]

The whole point of a HYBRID PV system is to avoid (as much as possible) buy power from the PoCo.

To my "hybrid" means a system with a battery.
I've got regular old "grid tie" solar, based on what I see, when we are producing PV, we're using almost all of it, I believe it comes in at slightly over grid voltage, so you "should" (in theory) be using the power you produce first with any grid tie system.

To do this, you remove the feed from the meter to the main load center and connect it to the inverter/charger. The output of the inverter/charger now goes to the main load center.

From experience, a hybrid system that is PV solar and grid tie does "switching". PV solar is not really that stable, it just takes a cloud to massively alter your current output. When this happens the hybrid inverter will switch to grid (or to battery).

Regular PV grid tie will work just as well, no switching. Your PV power is just a little "hotter" than grid, so you'll pull that first.

What's cool about true hybrid is that you can store excess (if you have it and if your grid provider pays a crappy rate for any back-fed power). So you can do time of use storage and discharge in many cases.

Batteries are expensive. Expect 100% or more cost.

Doing a "in the middle" switching inverter at household scale of 200A capable inverter - that's really expensive. It's also unnecessary unless you want a backup option with battery.

On paper, this looks simple. In real life it is not ! Lots of heavy gauge wire, conduit, disconnects, etc. $,$$$ !

Yes, to push 13KW from 48V batteries we're using 2/0 gauge copper with two inverters and two battery banks. That's about 25% of your basic residential 200A.

Some PoCos are now charging extra for peak usage times. If you have a big enough battery bank, you can "ride through" those times and even if you don't have sufficient solar power, you can (partially) recharge during "non-peak" hours.

This is where hybrid makes sense. Charge at low costs (solar or grid) and discharge at peak. 100%.

 

[ipgenie]

The backfed cb rating can be 20%. The wiring and cb has to be at 125% for cont load. So a 40a cb/wiring can only receive a max inverter output of 32a.

If the main cb can be changed out to a lower value, e.g. - 150/175a then the 40a limit can increased.

When I installed my system, I had the option of replacing the main breaker with a smaller one to increase available bus capacity for the solar feed, or replace the main panel with one that has a higher rated bus. Connecting to a sub panel was not permitted.

Depending on your load calculation, replacing the main breaker could be a fairly cheap option. The only other option they gave me was to use a line tap prior to the bus but I didn't look into that so I don't know what the pros/cons are.

I replaced the whole meter base and main panel, primarily to allow for additional capacity because I've switched my primary heat source to electricity, purchased an electric car and installed AC in the house and soon in the shop and I didn't want to reduce my main breaker to 125A.