2 Systems tying to one main panel: eg4 18k pv + IQ7+

[zanydroid]

I've said before, the best ROI is generally micro-inverters, no batteries, grid tie, minimal number of panels mitigating TOU or expensive power.

Line card: ~$120 per panel for micro-inverters. 12 panels, $1440 you just bought a 6000. Warranties are wonderful as long as you never have to use them. Add a battery to a micro-inverter setup and you can toss your ROI out the window. Thus it depends on your objective. Micro-inverters don't scale as well, simply because you have to keep buying them, and your not getting any inverter capacity along with it.

You’re sort of bouncing back and forth between different regulatory regimes here…

Setting aside balance of system differences:

16 panel Grid tie system

6000XP vs HMS2000
$1500 per inverter
$30 RSD per panel
~$2000
Vs
$385 for 4 ports (let’s round up to $400)
~$1600

(Growatt with HV batteries would be cheaper than the 6000XP)

Architecturally/COGS wise paying for inverters twice as AC coupling needs is going to double the cost of power electronics.

Now if you need to install today and pay market price (as opposed to cost to the manufacturer), and want to future proof to the highest regulatory standards you have to either buy a $6000 SolArk/18kpv with cheaper batteries or a $1500 hybrid with more expensive batteries. So today that redundant AC coupled inverter would be free! Due to the temporary high market price of UL9540 systems.

 

[Hedges]

Some people need to update their pricing cards. Microinverters are cheaper and have 2.5x longer warranties. Yes. It's more complex, but don't try to win the ROI war by arguing against micros.

Hybrids have 10 yr warranties, which makes them 2.5 less dependable than micros. Yes, we can debate the credibility of warranties, but 25 yr vs 10 yr warranties puts my mind and most customers minds at ease

Here's a hybrid with standard 10 year warranty, optional up to 25 year.

https://files.sma.de/downloads/SBSE-US-DS-en-23.pdf

Someone talked about the price-point of used microinverters. I've bought used and NOS Sunny Boys for $0.10/W. Some as little as $0.05/W.

RSD needs 5s minimum? Only if GT inverter supplies keep-alive. Some like SolArk simply close a relay or supply 12VDC for external keep-alive. Costs money, of course, cheaper to just be a software function (if volume is high enough, otherwise hardware would be cheaper.)

 

[zanydroid]

RSD needs 5s minimum? Only if GT inverter supplies keep-alive. Some like SolArk simply close a relay or supply 12VDC for external keep-alive. Costs money, of course, cheaper to just be a software function (if volume is high enough, otherwise hardware would be cheaper.)

I suspect you can make them work with lower, but I skimmed a bunch of SunSpec-compatible ones and they were around 5s or 6s minimum. I haven't found that much documentation about what guarantees you lose if you go below. I always assumed that the keep-alive doesn't care, and it's for providing emergency power. Haven't bench tested it & don't plan to.

You will violate the installation instructions, which is a technical code violation.

 

[ksmithaz1]

I'm a software engineer.

I've written extremely stable code in Z80 assembler, and some embarrassing stuff in BASIC. Today's stuff I find it stunning that someone could actually write stuff that awful and call it a finished product. It's all about time and effort. I was doing software since it was actually fun. Something about tapping hand assembled code in split octal on the front panel, and having it actually work is really rewarding. Self-modifying code is just genius I say.

Hybrids have 10 yr warranties, which makes them 2.5 less dependable than micros.

No it does not. A sorry-*ss lying MTBF number is more useful than a warranty. . . But let's say your right. So I have 40 micro-inverters vs two inverters. I have 20 times as many units a little over twice as reliable. Statistically , I am therfore seven times more likely to have a micro-inverter fail, than an inverter purely because of volume, not to mention that it's outside exposed to the elements, blah, blah. Now I have to pay someone to fix it, is the cost in the micro-inverter or the dude coming out to do the fixin'?

I've had similar arguments too many times, where people use irrelevant numbers to try and make a point. Several years back, hired out a cable run/trench across a large lot between buildings, spec'd fiber. "Fiber is way more expensive than copper, why don't you put in copper you'll save money". "Really? How much?" "Well the copper would run you about $500, the fiber around $2000." "Yea that's significant, how come the trenching & labor is so much less with copper?" "Oh, well that's just for the cable itself, the rest of it is about the same". "Ahh, indeed, so how much is the trenching and the mounting board in the back, and the ground rod?" "Oh that's about $5500". "Ahh so I can spend $6000 for copper wire that will be out of spec distance wise that needs special equipment to run a gig, or $7500 for fiber that I can run at 10G with an off-the-shelf optic."

So when you have a problem the cost is mostly in the technician who's going to come out, and or the labor to get it done. You wanna run a lot of micro-inverters your going to create a lot of extra work. But hey, if you want to bake in future labor for yourself it's a great idea. From a DIY perspective not so much mee thinks.

A warranty is great as long as you never have to use it. Something about a die hard battery with a lifetime warranty from sears comes to mind.

 

[zanydroid]

No it does not. A sorry-*ss lying MTBF number is more useful than a warranty. . . But let's say your right. So I have 40 micro-inverters vs two inverters. I have 20 times as many units a little over twice as reliable. Statistically , I am therfore seven times more likely to have a micro-inverter fail, than an inverter purely because of volume, not to mention that it's outside exposed to the elements, blah, blah.

It all depends on your operating model. I don't really buy the "uptime defined as 100% of panels available" rule.

Assuming independent probability of failures (which is a big assumption, I think some microinverters with inherent design flaws can die in correlated ways, heard some anecdotes of this)

The microinverters will still functional as they incrementally fail. I wouldn't be surprised if some utility scale microinverter systems just treat the loss of microinverters as cost of doing business. Or defer service calls until X% of the microinverters in a section of the farm break down, and have someone swap them all out at the same time for more labor efficiency.

The first string inverter failure will earlier than the first point failure of microinverters and take out maybe 2 dozen panels at a time.

You can probably also use less skilled labor / lower cost insurance if the service tech only has to work on AC (which can be fully de-energized) rather than DC (which cannot, unless you add RSD into the array)

On-Grid:
Microinverters deployed with no SPOF (IE, no battery) will require less careful planning / operation to achieve the same uptime as string inverters. Tesla forums are full of people whining about losing production $ for months because of their string inverters.

Off-grid:
However if we're talking about fully off-grid use, then microinverters will have a similar planning complexity to hybrid string inverters, since there is now either a SPOF at the battery, or the need to design redundancy at the battery / storage inverter side, same as hybrid inverters. Fully off-grid also likely needs a high overpaneling ratio to handle winter, which is an architectural weakness of microinverters.

 

[ksmithaz1]

Hello,

Long time reader, first time poster here....

I'm attempting to take the best parts of both microinverter and hybrid systems. Will the system I've designed in the picture work? I've seen some variations of this system discussed but nothing exactly...

I want all my home circuits (Main Panel) to take in power from 2 distinct and separated solar systems:

- 20 panel IQ7+ enphase microinverter system
- 30 panel eg4 18kw pv all-in-one hybrid inverter system

RE: Regulatory domains... Yea but we already stirred the pot by mixing a bunch of different tech, we want to tie it all together. With 50 panels, why would you even bother to tie to the grid at all? With 50 panels you must intend to have batteries, and/or the "regulatory domain" is going to be up your tush with 100A of back-feed capability, because it's about your capacity, not what you are actually sending them. If you are going to start breaking this up, feeding this panel here and that panel there, and this tie here so it can't back-feed, you might want some gift cards and a bottle for the inspector, cause he's not going to grok it.

Cryin out loud I run my whole house with something less than what we are proposing, though from a capacity standpoint roughly what I want, I just use a transfer switch to my 'secondary' panel which has everything in it, My grid fed panel has three breakers, The 150A main, 100A to the transfer switch, 50A to another transfer switch to an outside pedestal. The grid is my backup generator.

Curious to see how this pans out if we go this way. It's kind of a cool idea, but feels like a maintenance nightmare.

 

[Hedges]

The first string inverter failure will earlier than the first point failure of microinverters and take out maybe 2 dozen panels at a time.

You can probably also use less skilled labor / lower cost insurance if the service tech only has to work on AC (which can be fully de-energized) rather than DC (which cannot, unless you add RSD into the array)

Quality and MTBF will vary with brand, also environment.
From my experience operating up to 5 SWR2500U for 17 years with a couple failures, I calculated 32 years MTBF.
Quite sufficient for grid tie and offsetting power bill. Off-grid, have at least 2 so system keeps working with one down, or whatever number you need for minimum loads while waiting for repair/replacement.

For most people, having grid available is the way to get reliable power, because a crew will repair it and power is restored. Never want to be dependent on personalized service. Our equipment can further improve uptime. Offgrid, we need to provide redundancy.

I don't think one should depend on electronics (RSD) for human safety, ought to have an isolator switch.

My original string inverters were connected to PV array by external switch. One with fuses, you could open the fuse holders. Some of the later models came with DC disconnect attached; you could turn off the disconnect then remove wires from terminals to detach inverter.

Servicing on the ground rather than on the roof, middle of an array, is cost reduction and safety improvement.
Haven't heard yet about RSD reliability issues. (SolarEdge optimizers, certainly have.)

 

[zanydroid]

I don't think one should depend on electronics (RSD) for human safety, ought to have an isolator switch.

The idea was in addition to an isolator. The idea is that you would have 600V or 1000V available at all times even when the isolator is off, so a multiple fault situation can be hazardous when moving panels or rewiring. With microinverters the maximum voltage is usually under 60 or 80 volts when isolated.

I wouldn’t be surprised if monitoring modules are added to single or pairs of panels in an array anyway. So adding shutdown does not require much in extra components.

After posting yesterday I realized RSD adds no advantages to swapping an inverter.

 

[the.shining]

Multi-port microinverters are NOT cheaper than the cheapest grid tie Growatts/etc with 1741SB, even with RSD added into the mix (and if it's a ground mount you don't need them). Assuming you can efficiently max out the grid tie inverter.

the cheaper inverters are cheaper, but the warranty isn't there. So if I have to replace an inverter 3 times in 25 years, then that needs to be priced in. And a vendor is less likely to balk on guarenteeing their warranty if it's a $100 micro to replace...vs a $5k hybrid to replace. Plus, iq7 vendor has testimonials of their warranties being honored.

let's say your right. So I have 40 micro-inverters vs two inverters. I have 20 times as many units a little over twice as reliable. Statistically , I am therfore seven times more likely to have a micro-inverter fail, than an inverter purely because of volume, not to mention that it's outside exposed to the elements, blah, blah. Now I have to pay someone to fix it, is the cost in the micro-inverter or the dude coming out to do the fixin'?

I'm not afraid of a $100 micro failure. I'm afraid of a $8k hybrid failure. the maintenance of a large micro system might be a concern for some, but to me it's a 30 minute to-do item if a micro manages to fail. If a $8k hybrid fails....

I've said before, the best ROI is generally micro-inverters, no batteries, grid tie, minimal number of panels mitigating TOU or expensive power.

this is true. but I'd rather have a 8% return on $30k than a 16% return on $5k.

RE: Regulatory domains... Yea but we already stirred the pot by mixing a bunch of different tech, we want to tie it all together. With 50 panels, why would you even bother to tie to the grid at all? With 50 panels you must intend to have batteries, and/or the "regulatory domain" is going to be up your tush with 100A of back-feed capability, because it's about your capacity, not what you are actually sending them. If you are going to start breaking this up, feeding this panel here and that panel there, and this tie here so it can't back-feed, you might want some gift cards and a bottle for the inspector, cause he's not going to grok it.

this is interesting. i hadn't heard this argument that the elec company cares about the total capacity of backfeed to the grid. My elec company caps at 10kwh, but I was going to circumvent that by getting permitted with the micros...then adding the hybrid/batteries after the inspector got back to his office. my system will be designed to not feed anything back to the grid, but i'm still curious why there'd be a concern with backfeeding 10 vs 100 amps to the grid. If I have 200 amps coming in, 100 amps going out shouldn't be a problem. Either way, I won't be sending out any amperage (beyond trace amounts)

 

[k490]

the cheaper inverters are cheaper, but the warranty isn't there. So if I have to replace an inverter 3 times in 25 years, then that needs to be priced in. And a vendor is less likely to balk on guarenteeing their warranty if it's a $100 micro to replace...vs a $5k hybrid to replace. Plus, iq7 vendor has testimonials of their warranties being honored.

I'm not afraid of a $100 micro failure. I'm afraid of a $8k hybrid failure. the maintenance of a large micro system might be a concern for some, but to me it's a 30 minute to-do item if a micro manages to fail. If a $8k hybrid fails....

this is true. but I'd rather have a 8% return on $30k than a 16% return on $5k.

this is interesting. i hadn't heard this argument that the elec company cares about the total capacity of backfeed to the grid. My elec company caps at 10kwh, but I was going to circumvent that by getting permitted with the micros...then adding the hybrid/batteries after the inspector got back to his office. my system will be designed to not feed anything back to the grid, but i'm still curious why there'd be a concern with backfeeding 10 vs 100 amps to the grid. If I have 200 amps coming in, 100 amps going out shouldn't be a problem. Either way, I won't be sending out any amperage (beyond trace amounts)

My utility used to have a limit how big of a system you could have based on amount of power you used. They gave that up when they got rid of the 1-1 Net Metering. Now they leave the limit to whatever the AHJ which means 120% rule. If you connect in on the line side between the meter and the first main breaker then only limited by the wire size usually big 4/0 wire can carry lot of current. You understand the 120% rule I'm assuming based on the amount of power your main busbar can handle.

 

[zanydroid]

this is true. but I'd rather have a 8% return on $30k than a 16% return on $5k.

This is confusing. I would say the following are slam dunks over 8% on $30K (unless that's blended and factoring in the 16% on $5K):

16% return on $5K and then diversify $25K elsewhere.

16% on $5K, and then $25K on 8% returning solar equipment.

 

[Danke]

New build totally off grid. Workshop/garage that is a separate building will have PV on the roof. Location does not require permits or inspection. What are the pros and cons of adding RSD units at the panel level?

 

[zanydroid]

New build totally off grid. Workshop/garage that is a separate building will have PV on the roof. Location does not require permits or inspection. What are the pros and cons of adding RSD units at the panel level?

Pros:
Save money. Fewer points of failuire.

Cons:
VS crime scene investigation / firefighters getting upset at you b/c they wasted time looking for a shutdown, or you didn't have a system map placard in standard format.

 

[Danke]

Pros:
Save money. Fewer points of failuire.

Cons:
VS crime scene investigation / firefighters getting upset at you b/c they wasted time looking for a shutdown, or you didn't have a system map placard in standard format.

If there’s a fire, place would be so far gone by the time the fire department got there, I don’t think they’d be crawling on the roof.

Is there a greater fire hazard at the panel level if I don’t have an RSD device?

 

[zanydroid]

Is there a greater fire hazard at the panel level if I don’t have an RSD device?

RSD is not for preventing fires. It’s for protecting firefighters from HVDC when they start swinging axes.

MPPT Arc fault detection/interruption does prevent fires and that is not available in a fair chunk of off grid equipment.

EDIT: it is required for installation on most structures, but not for basic UL1741. For instance I don’t believe those EG4/Deye hybrid heat pumps have it. I was considering it for an ADU but this was a dealbreaker.

 

[Hedges]

I think if AFCI triggers RSD, that is more likely to prevent a fire than AFCI alone.

Twice as many connections that could cause a fire, and if they are interspecies then much more likely.

 

[zanydroid]

I think if AFCI triggers RSD, that is more likely to prevent a fire than AFCI alone.

Twice as many connections that could cause a fire, and if they are interspecies then much more likely.

I am not sure how to tie the two together. Haven’t seen it in a manual. I assume AFCI will stop MPPT. Might need an integrated RSD transmitter to configure also triggering a RSD.

Stopping MPPT I think would be good for series arc. RSD would help for both.

 

[Hedges]

Yes, AFCI stops current draw of MPPT. Where AFCI and RSD are both integrated into inverter, it might also turn off keep-alive, but only if the design spec or firmware coders happened to address that. Probably not an NEC requirement, so I'm not confident. Maybe this can be tested.

I picked up a couple Sensata AFCI modules, also Tigo keep-alive transmitter. If I do move my legacy system to roof I want to try using those together, and could have the AFCI signal cut AC to inverter, also cut keep-alive.

AFCI came before RSD, more likely to be in an older inverter. I think that is the case with SolArk as well. If an inverter had an error status output for AFCI, that could disable RSD.

 

[zanydroid]

I picked up a couple Sensata AFCI modules

How do these work? I assume they’re some kind of standalone AFCI.

AFCI came before RSD

(I assume you know this, just repeating it for others on the thread)

What I was getting at was that AFCI is often dropped (just as RSD is) esp for equipment designed for overseas, and this is a problem for inspections even if one chooses a UL1741 off grid inverter (just because it has the listing, does not guarantee it has the necessary features to pass in all possible installation scenarios).

 

[the.shining]

This is confusing. I would say the following are slam dunks over 8% on $30K (unless that's blended and factoring in the 16% on $5K):

16% return on $5K and then diversify $25K elsewhere.

16% on $5K, and then $25K on 8% returning solar equipment.

Yes, its blended. I'm factoring in the high initial roi (16%) prior to battery. Once battery gets involves, roi suffers, but emergency off grid backup power is a nice tradeoff for the lower roi.

Can't get better than an 8% return though for the manageable risk. T bills at 5.5%, but doubt that will last. Stock mkts only avg 7% over time, so 8% is as good as it gets.

 

[Hedges]

How do these work? I assume they’re some kind of standalone AFCI.

Stand alone, I don't think on the market anymore, now that inverters integrate that.

Haven't tried them yet, but PV wires pass through inductive pickup. 24VDC is fed to the module. It has a relay output. So I would use it to trip a power relay and cut AC to inverter. Also to keep-alive.

(I assume you know this, just repeating it for others on the thread)

What I was getting at was that AFCI is often dropped (just as RSD is) esp for equipment designed for overseas, and this is a problem for inspections even if one chooses a UL1741 off grid inverter (just because it has the listing, does not guarantee it has the necessary features to pass in all possible installation scenarios).

UL1741 was good enough years ago.
SMA SWR 2500U was UL1741 (anti-islanding) and has a 1A fuse for ground fault detection.
The 5000US I'm now using I think are the same, except maybe ground fault doesn't use fuse.
10000TL-US-12 I used for a while has AFCI.
TriPower 30000TL-US does not have RSD keep-alive, but it does have capacitor discharge.
SB 7.0 -41, which I picked up and will install later, has keep-alive for RSD, also capacitor discharge.