My new diagram. Please check.

[TheFlumph]

So after running into a roadblock with my 18kpv and backup plans with my utility (they require a separate production meter) Ive decided to go net metering only for now. Im gonna try to find two sunny boy 7.0 inverters (unfortunately just discontinued). They said I could keep my old plan and add a couple of inverters before the 18kpv and do ac coupled but thats just not in my budget so Im deleting the 18kpv and battery.

Please check my diagram. I think Ive got the DC side sorted here. What I need help with is combining AC after the inverters. Whats the best way to AC combine? A couple of 40a breakers going in and a 100a going out to the production meter? A bus bar coming in and a breaker going out?
also, please check my disconnect to line tap. What OCP do I need between the disconnect and tap, or should I just do a fused disconnect?

I know my meter/main breaker and main house panel is funky with the two neutral bonds. I can always run a ground from the outside meter and delete the neutral bond inside if the utility doesn't like it. No city/county inspections here. This is how they installed it 20 years ago.

I decided to go line tap because my panel bus bar is (I think)225a and ive got a 200a breaker in it. #30ax2x1.25 is 75a. I could only do max 70a backfeed breaker.

also, anyone with sunny boy experience, If i went with the 7.7kw model, could I limit them to be under 15kw together? My net metering agreement is for 15kw and under.

Thanks so much. This forum is wonderful.
will be limited to 15kw and below.

 

[mciholas]

So after running into a roadblock with my 18kpv and backup plans with my utility (they require a separate production meter) Ive decided to go net metering only for now.

Did you consider microinverters? If you are exclusively grid tie, that would seem to be the simplest system to build. It eliminates the PV isolators, the two string inverters, the AC combiner box, and the array AC output can go directly to the RGM. The microinverters, like Enphase, will give you rapid shutdown, optimization, and monitoring. I don't see rapid shutdown in your diagram and that is usually required by code, so there is usually SOME per panel box in this design. You have 60 panels which is a lot, maybe get higher power panels and fewer of them? This would cut down in the microinverter total cost.

Every box takes wires, conduit, fittings, mounting, wall space, etc. If you can design a system with minimal number of boxes, it usually is cheaper.

Personally, I'm leery of any system optimized around net metering rules. Those rules are changing all over the country. It is best to design a system which can adapt to new rules when it happens. That implies the option to add a battery to the system so you can use your energy locally (which is 100% value) versus pushing it back to the grid (which is heavily discounted). The battery also gives you backup capability, the value of which varies widely depending on your circumstances.

I know my meter/main breaker and main house panel is funky with the two neutral bonds.

I thought two neutral bonds was not allowed. I expect you will have to reduce this to one.

Mike C.

 

[TheFlumph]

Did you consider microinverters? If you are exclusively grid tie, that would seem to be the simplest system to build. It eliminates the PV isolators, the two string inverters, the AC combiner box, and the array AC output can go directly to the RGM. The microinverters, like Enphase, will give you rapid shutdown, optimization, and monitoring. I don't see rapid shutdown in your diagram and that is usually required by code, so there is usually SOME per panel box in this design. You have 60 panels which is a lot, maybe get higher power panels and fewer of them? This would cut down in the microinverter total cost.

Every box takes wires, conduit, fittings, mounting, wall space, etc. If you can design a system with minimal number of boxes, it usually is cheaper.

Personally, I'm leery of any system optimized around net metering rules. Those rules are changing all over the country. It is best to design a system which can adapt to new rules when it happens. That implies the option to add a battery to the system so you can use your energy locally (which is 100% value) versus pushing it back to the grid (which is heavily discounted). The battery also gives you backup capability, the value of which varies widely depending on your circumstances.


I thought two neutral bonds was not allowed. I expect you will have to reduce this to one.

Mike C.

I looked at the enphase, but for 60 panels it would cost me way too much. I already own the panels. Enphase would cost me almost 4x what sma string inverters would. I did look at the hoymiles 4 in 1 but I just dont know how reliable they would be. Those would be about $1000 more than the 2 sunny boys.

As for RSD, these arent going on my house, they will be ground mounted outside with tractor parking underneath. I think the DC disconnects should be acceptable?

I hear you on net metering. My state is very pro solar, and they mandate .20/kwh for net metering.

I appreciate your feedback. If I had fewer panels at higher wattage I think micro inverters would be a better option.

As far as the neutral bond thing, its wierd because there's no ground coming from the meter. Its how they used to do it here apparently. If I had a ground connecting the meter and breaker box I would definitely unbond the breaker box. Its stumped many electricians Ive talked to about it. I'm gonna give the utility the final say since there's no inspection oversight here other than the utility checking interconnection.

 

[TheFlumph]

Im also considering the Fronius primo 15kw if anyone has any experience with that one.

 

[TheFlumph]

bump please

 

[Norwasian]

As far as the neutral bond thing, its wierd because there's no ground coming from the meter. Its how they used to do it here apparently. If I had a ground connecting the meter and breaker box I would definitely unbond the breaker box. Its stumped many electricians Ive talked to about it. I'm gonna give the utility the final say since there's no inspection oversight here other than the utility checking interconnection.

This is just a side-note, perhaps, but personal experience seems to support two possible philosophies with respect to grounding. They are incompatible with each other, and most choose to ground the entire system. The opposite philosophy says it's best to ground nothing. I spent some years in Laos where the public utility would sometimes be mis-wired such that one of the three phases from the transformer was linked to ground, instead of the center/neutral tap. It was a nightmare. We had no idea what the problem was, but there were inconsistencies within our building as we had multiple meters (saved money on surcharges for higher usages) and multiple phases in the building--so we brought in an American electrician who we happened to know, who traced the problem right back to the utility's incorrect transformer configuration. Hah! Of course, there was little we could do about that--but everyone would get disconnected for a few hours each time a new building connection needed to be made (the entire subdistrict would be shut down for the utility workers to do their thing), and now and then the transformer's configuration would change! It was really quite a problem. All this to say that "ground" was not a very stable factor. Couple this with the fact that almost no building was ever grounded. Ground rods were not used, and electric plugs served only two prongs. Most of the buildings with the newer three-prong receptacles just facilitated the insertion of a grounded-type plug--they did not have the ground wire connected to anything.

Trying to do things right, I installed a ground rod at my home--a nice 2-meter-long copper-clad steel rod--and did so at a wet spot on the lower side of the house leading down toward a pond. Even in the poor conductivity of the clay, this rod was well grounded! I then hooked up my computer to a receptacle running off of batteries/inverter to which this ground was added. The very next lightning storm that we had knocked out my UPS, and my computer was worth so much that I was deeply afraid it might have been damaged as well. Fortunately, it wasn't--but I waited a month between sending the UPS back to the manufacturer for repairs and getting it back. My house was probably the only one grounded within a half-kilometer radius, and was made the more vulnerable to storm damage.

After this negative experience, I completely avoided grounding from then on. I had no further problems, and weathered many storms, safely isolated from ground.

 

[740GLE]

Solaredge offers a great design in many sizes.

They do recommend optimizers for any partial shading.

 

[TheFlumph]

Solaredge offers a great design in many sizes.

They do recommend optimizers for any partial shading.

I have heard bad things about solar edge inverter reliably. There was a link I saw in here that showed up to 30% failure. The. Then sent lawyers after the guy who was reviewing them.
Fortunately I don’t have shading. It’s a ground mount in a field.

 

[mciholas]

Given ground mount (removes RSD requirement) and no shading (removes optimizer utility), feels like the diagram you proposed generally works. Manual DC disconnect seems code compliant.

Note that the RGM doesn't measure the total SOLAR production, it measures the total INVERTER production. Not exactly the same thing. The inverters will also draw a little bit of power from the grid when the panels are dark, so there is some reverse flow. The SunnyBoy datasheet says this will be less than 5 watts, so you are burning under 10 watts in the dark.

Can you buy a RGM that only totals flow in one direction? If you can, then you can use one 18KPV and put that meter on the GRID line. When the flow is outbound (towards grid), the RGM totalizes your production. When the flow is inbound (towards inverter) the meter doesn't subtract that. You would have to not use the LOAD terminals on the 18KPV since that would be production you are not accounting for.

Mike C.

 

[TheFlumph]

Given ground mount (removes RSD requirement) and no shading (removes optimizer utility), feels like the diagram you proposed generally works. Manual DC disconnect seems code compliant.

Note that the RGM doesn't measure the total SOLAR production, it measures the total INVERTER production. Not exactly the same thing. The inverters will also draw a little bit of power from the grid when the panels are dark, so there is some reverse flow. The SunnyBoy datasheet says this will be less than 5 watts, so you are burning under 10 watts in the dark.

Can you buy a RGM that only totals flow in one direction? If you can, then you can use one 18KPV and put that meter on the GRID line. When the flow is outbound (towards grid), the RGM totalizes your production. When the flow is inbound (towards inverter) the meter doesn't subtract that. You would have to not use the LOAD terminals on the 18KPV since that would be production you are not accounting for.

Mike C.

That’s a great point about the 18k. I messaged eg4 the other day with just that question. I wasn’t sure about the Gen outbound and load terminals being used.
The utility supplies the meter. I’ll need to check with them.

 

[mciholas]

That’s a great point about the 18k.

if you don't use the LOAD connection, then the 18KPV does basically the same thing as the two inverters in your diagram. The key advantage is that you can reconfigure the 18KPV to due backup (add batteries, and it will work with the grid). When (not if) your utility stops net metering, then the 18KPV is adaptable to load shaving and having your energy used locally.

In the coming age of no net metering, grid tie without storage is not going to work very well.

Mike C.

 

[740GLE]

I have heard bad things about solar edge inverter reliably. There was a link I saw in here that showed up to 30% failure. The. Then sent lawyers after the guy who was reviewing them.
Fortunately I don’t have shading. It’s a ground mount in a field.

I hadn’t heard of this, bummer. A while ago they were the go to for string inverters for installers in our region.

 

[TheFlumph]

if you don't use the LOAD connection, then the 18KPV does basically the same thing as the two inverters in your diagram. The key advantage is that you can reconfigure the 18KPV to due backup (add batteries, and it will work with the grid). When (not if) your utility stops net metering, then the 18KPV is adaptable to load shaving and having your energy used locally.

In the coming age of no net metering, grid tie without storage is not going to work very well.

Mike C.

I hear back from signature solar about this.
Apparently it’s not possible the moment for the 18kpv to function as a grid only inverter.

“the 18k does not currently function as a "grid tie only" inverter. It seems this is the only application in which the EG4 18kPV does not operate well. There's something about the lack of batteries that causes relays in the 18k to fluctuate on and off, back and forth, and does not export to the grid properly. It's possible EG4 may do something to fix this in the future.”

 

[mciholas]

Apparently it’s not possible the moment for the 18kpv to function as a grid only inverter.

I find it really upsetting when such limitations are not CLEARLY defined in the manual.

It leaves you wondering what other gotchas are lurking in the system.

What this means is that if your batteries are down due to fault, maintenance, replacement, whatever, you've lost you solar system entirely. Yuck.

I was wondering how the 18KPV would handle a dark start with no battery and no grid, where did the power come from to activate the RSD to turn the panels on. Now I know it won't work at all without battery. This kind of makes the 18KPV not really a true "hybrid" inverter.

This really fracks with my plans. Oh well.

Are there any hybrid (grid tie and off grid) inverters that work grid tied without batteries properly? Sol Ark maybe?

Mike C.

 

[BKY2003]

I noticed the new yellow/ black 18Kpv has a selection for no battery. But probably just used for off grid.

 

[Oldphile]

I

Are there any hybrid (grid tie and off grid) inverters that work grid tied without batteries properly? Sol Ark maybe?

Mike C.

Yes, Sol-Ark. I don't have batteries.

 

[mciholas]

I noticed the new yellow/ black 18Kpv has a selection for no battery. But probably just used for off grid.

New yellow/black?

Have you tried it without the battery attached? Does it work?

(Maybe this needs to be a separate thread?)

Mike C.

 

[TheFlumph]

New yellow/black?

Have you tried it without the battery attached? Does it work?

(Maybe this needs to be a separate thread?)

Mike C.

I don’t mind this thread getting bumped honestly. I never got help about my ac combiner question. lol.

 

[TheFlumph]

I find it really upsetting when such limitations are not CLEARLY defined in the manual.

It leaves you wondering what other gotchas are lurking in the system.

What this means is that if your batteries are down due to fault, maintenance, replacement, whatever, you've lost you solar system entirely. Yuck.

I was wondering how the 18KPV would handle a dark start with no battery and no grid, where did the power come from to activate the RSD to turn the panels on. Now I know it won't work at all without battery. This kind of makes the 18KPV not really a true "hybrid" inverter.

This really fracks with my plans. Oh well.

Are there any hybrid (grid tie and off grid) inverters that work grid tied without batteries properly? Sol Ark maybe?

Mike C.

Ya I’m hoping this helps my return go easier and my restock fee to get waived.

 

[BKY2003]

If i went with the 7.7kw model, could I limit them to be under 15kw together? I don't think you can limit them. My manual says 7680 watts max each. 15,360 watts total, so that might force you down to the SB7.0. But maybe your Power company would let it slide?