Solar Expert needed for correct sizing of inverter/optimizers/batteries that match qty of 30 REC 360w panels

[Tozlakes]

New to forum and solar but looking forward to learning and sharing in the future on a subject I am a bit green on.

My background is I just retired after 30 years of working overseas for ExxonMobil with a history of Mechanical/Electrical and Instrumentation on everything from GE and Solar dual fuel turbines to electrical distribution lines to large reciprocating compressors, pumps etc. Unfortunately no Solar background in all of those years but am excited to cram some knowledge about it into this overwhelmed brain.

In the process of installing 30 REC 360w solar panels in central California (Radiance value of 5.5)

My issue is ensuring the correct sizing of both the optimizers and the inverter for this grid tie in, non battery backup system. I have had some discussions and received quotes from a couple U.S. suppliers of SolarEdge inverters and optimizers but each came in with different suggestions along with crazy high quotes! The worst part is not being able to understand the conversation due to heavy accents causing even more frustration on my end hence the reason for me reaching out to the experts on this forum.

At this point I am looking for confirmation and feedback in compatibility of Inverter and optimizers below that I have been looking at.
SE7600H-US or SE10000H-US inverter? Must meet California Electric Rule 21 which I believe they all do now? (Spec sheet attached)
A quantity of 15 P860W, P960W or? SolarEdge Optimizers but would like some input on which for this system.
In “Series” or “Parallel” configuration or a combination of both.

Would also like the option to expand the system in the future in the case that demand for power becomes more than I anticipated.

My 30 installed panels are REC 360W (see attached spec sheet)
I believe that below calcs are correct but input if not would be appreciated.

30 panels X 360W = 10.8kw total system
33.9v = 1,017v in series
10.62a = 10.62a in series

33.9v = 33.9v in parallel
10.62a = 318a in parallel

Maybe a combination of both parallel and series as to match up with inverter?

I did receive a recommendation and quote from a company out of Florida that came back with SolarEdge P800 2X long optimizers (2X long is cable length?) and SolarEdge SE 7600N-USMNBBL ( not sure of the USMNBBL as it is not on my data sheet) but not sure if this will fit my need currently let alone for something along the lines of a 25% future expansion.

Currently going through the permit process but need to provide these components to both San Luis Obispo County building department and PG&E for approval.

In the future I am sure I will have many other questions on fuses, breakers, grid tie in, monitoring, wire sizing, expansion etc so please bare with me.

I know this is a lot of info and questions and will take time to go through but any help in confirming and ensuring a properly sized and designed system would be appreciated. If I missed any info needed please let me know and I will try and update this post.

Thanks in advance or the help. Tozlakes

 

[12VoltInstalls]

grid tie in, non battery backup system

Why no battery?
Even a ‘small’ battery bank has some benefits, and it’s even possible that ‘approved’ off-grid/grid-tie equipment not running microinverters might equal out $$$ with a battery setup. But my understanding is “that depends.”

any help in confirming and ensuring a properly sized and designed system would be appreciated

in my opinion I would suggest it being a reasonable idea to at least compare with a battery / non-microinverter system. You can still shave/share with your electric bill, but incorporate grid-down dependability. Especially in California where I think they only allow lettuce- or hemp-fueled backup generators.

 

[Tozlakes]

In my view I never thought about battery backup as in the 5 years I lived here I have yet to have the power from the grid go out a single time. In addition, at the 10 or so systems that I have looked at here locally not one of them had battery backups and likely due to the dependability of power in the area. Maybe something will drive to change my mind on batteries in the future,we’ll see.

 

[12VoltInstalls]

In my view I never thought about battery backup as in the 5 years I lived here I have yet to have the power from the grid go out a single time. In addition, at the 10 or so systems that I have looked at here locally not one of them had battery backups and likely due to the dependability of power in the area. Maybe something will drive to change my mind on batteries in the future,we’ll see.

There’s also the factor of using some of your own power overnight.
There are UL1741 units which can operate battery-less and are not microinverter-based. At least I’d explore the price for atypical.

Honestly I’m really not much help for your questions. I’m really not familiar enough with microinverter solar aka solar that isn’t battery-based, and - no criticism- I have no concept of being completely grid dependent anyway.
Long before I embarked on solar I’ve always (not always) had some ‘alternate’ power for whatever situations arose. I bought my first inverter back in the nineties and have had something 12V-based for lighting and at least a propane camping stove longer than that, too.

But I’ll be intrigued to read along as your solution develops.

 

[Tozlakes]

Besides a suggestion of adding batteries to our new system does anyone have any input to my questions about inverter and optimizer sizes above?

 

[zanydroid]

Are you on NEM2 or NEM3? If on NEM3 it is very difficult to have an economical system without batteries. Since this is a new project I’m 99.9% it is NEM3 because you would have answered these questions in March 2023 and had an application in around that time. For all ROI calculations you MUST use more recent California specific advice.

Before diving into the inverter question I think we tend to want to confirm that optimizers are needed for your case. SolarEdge is proprietary so you are stuck with their inverters “forever” unless you rip off the optimizers. Also if you add battery you will pay extra with solar edge one way or another . Solar edge native batteries are $$$ and if you want to use other batteries you have to AC couple them, which is fine technically but adds cost bc there’s more power conversion hardware

 

[zanydroid]

Anyway big picture out of the way. If the optimizers are compatible with parallel of two panels connected then that would be better for shading. I thought the ones that can connect two tended to be designed for 2S. Also I believe those require the 2S Voc to be under 80V in rooftop installs to be rapid shutdown compliant

Happy to dig into the specs once big picture questions of direction are addressed

 

[Tozlakes]

Thanks for the feedback Zanydroid.
Unfortunately after further investigation we do fall under NEW3 whereas batteries may now make a lot more sense as I read into the ill effects of the new net metering plan.
Bad timing for us I suppose.
As for optimizers, in my mind and understanding I was thinking of a single panel degradation dragging down the output of the other panels. There is no chance of shading outside of clouds temporarily passing over portions of the panels as they are installed on the ground with no trees or buildings anywhere around them.
Maybe it makes sense to put the money spent on optimizers into battery backup instead? I also am not stuck on using SolarEdge just was somewhat impressed with the feedback I’ve read online about their line of products.
What brand and sizing of battery system and inverter would you suggest that is more reasonably priced than SolarEdge yet still perform at a high level?
As I stated above, I have next to zero knowledge at this point about solar systems but am excited about learning as this process moves forward.

 

[zanydroid]

As for optimizers, in my mind and understanding I was thinking of a single panel degradation dragging down the output of the other panels. There is no chance of shading outside of clouds temporarily passing over portions of the panels as they are installed on the ground with no trees or buildings anywhere around them.

There are many parts of the world where they don't use optimizers, and clouds are the same everywhere. My view on clouds is, they move so quickly that the edge across your panel will not last long. Minimum speed is a couple MPH, it'll cross your array in minutes, if even that.

Optimizers are a little janky from an ecosystem & compatibility angle. The most (and only) vendor neutral optimizer right now is TIGO. It is cheaper than SolarEdge. If it's a roof mount then there is a smaller cost increase to go to Optimizers vs RSD (rapid shutdown) only modules.

SolarEdge isn't that popular on this DIY (off grid biased) forum b/c of the high extra cost of their native batteries. They're probably reasonably popular for turnkey. If you don't want to use their batteries, then you need to buy a higher end battery inverter with "AC Coupling" capability. In this mode, the battery inverter and solar string inverter are connected via AC. The inverter will form a grid when the grid goes down, in a manner that is compatibility with activating the string inverter off-grid in a safe manner. It needs to defeat the anti-islanding detection on the grid tie inverter, as well as absorb all power the grid tie inverter seeks to push out. (Grid Tie inverters are designed to push out as much power as possible into the grid, raising their voltage etc as needed to achieve the output power. If they cannot push out all the power, they'll likely cause damage or shutdown).

DC coupling is more popular in DIY b/c it's historically been cheaper (since AC coupling has only been widespread in DIY hardware for 1-2 years). In a fundamental technical sense, it will cost more because the AC output of the grid tie inverter has to be absorbed by an AC charger before it can go into the battery, which is an extra power conversion stage. On a hybrid inverter like EG4 18kpv or SolArk 15k, one box can connect to a commodity 48V battery as well as the solar panels, and there is very little, if any, extra hardware needed to invert or charge the battery. There are schematics floating around the forum showing how the power architecture works.

(SolarEdge is also a single box but the battery is proprietary)

(AC coupling turns out to be valuable/scalable in other situations but we can set that aside for now, as it's still early in adoption in DIY solar)

There are a few hybrid or storage inverters people talk a lot about:

Grid-tie compliant in California:

• Schneider XW
• SolArk 15K
• EG4 18kpv
• (Outback is too, I haven't heard much about them lately, could be I just ignore the threads)

Not grid tie compliant in California, probably not permittable:

• MidNite inverters (bleeding edge IMO, the company has a great reputation but I don't get their product strategy at all)
• Victron
• SRNE 10K (sold under many names)
• EG4 6000XP

 

[zanydroid]

Couple more details about your hardware that you had found on your own.

Those SolarEdge inverters are designed to take the solar panels in 2P. You have just about the highest current solar panels that they're supposed to take (constrained by Isc limit)

SolarEdge inverters have a published maximum series count of optimizers. They do some magic to park the total voltage exactly at 600V (or some other constant voltage). They have built-in MPPT for each panel (solar panels are current sources, they need to be operated at the correct voltage/current for the amount of sun hitting them) and a DC-DC boost/buck converter for matching current and voltage. So at a first order safety/equipment protection thing you don't really have to calculate the string voltage, as long as you stay under the limit. (There are some issues with the min/max output voltage and current limits that will need to be accounted for too, you can either do this manually or use design tools. The high power optimizers you are looking at probably have more quirks than standard single input optimizers).

(TIGOs only have a buck converter for dropping voltage)

 

[Hedges]

I would avoid optimizers and I would avoid Solar Edge.

If this is rooftop, RSD will required (unless you use microinverters like Enphase.) for a bit more than RSD, you can get optimizers and panel level modeling.

What I will be installing for myself, family and friends (we got NEM 2.0 reservation) is Sunny Boy Smart Energy and PV panels, with RSD. There is an RSD endorsed or sold by SMA, so I will use those (but Tigo for myself, because I already bought them.)

The SMA optionally works with a battery. We will not use one initially, but might add one for backup for one of the people. BYD LiFePO4 HV battery, costs 2x what Server Rack or EG4 PowerPro does.

For you, you can get a GT PV string inverter, or you can get something like SolArk which is also batteries optional but takes a 48V battery. I think EG4 18kPV is also batteries optional, and is UL listed ESS with PowerPro.

There are cheap brands and there are quality. Responsiveness of support also varies widely.

Current Connected is a vendor we are hearing many, virtually all, customers are happy with.

 

[Tozlakes]

Thanks for the replies guys.
I am now researching all the details to try and fully understand it all so may take some time before I come back with many more questions I’m sure. THX JG

 

[400bird]

Tigo and Solar Edge optimizers operate in two different ways and aren't really comparable.

Tigo is limited to 25% output difference between panels. This limit doesn't apply to Solar Edge.

Solar Edge optimizers only work with Solar Edge inverters. Tigo is inverter agnostic.

Tigo you need to do the math and stay under the inverter's max voltage rating. Solar Edge can buck/boost the output voltage to hold the string to their desired voltage, mine sits at about 380 vdc constantly. They can also do weird stuff like allowing an 8s and 12s string to run in parallel with no performance hit.

You'll need RSD in the panels, as noted. But without shade, optimizers may not be needed.
However, panel level monitoring is a nice feature to have. I had a solar panel partially fail. It lost a significant portion of it's output power. However, in the entire string it was just a few percent, I would have never noticed.

However, the solar edge panel level monitoring caught it and sent me an automated email about it. I literally would have never noticed without panel level monitoring.

I diy'd a solar edge install here in the California Central Valley in 2018, it was easy and has been pretty well trouble free other than the one solar panel failure. In 2022, I added 4 more panels to the solar edge string taking it to 2 parallel strings of 12.

One issue is battery, as othera have mentioned, your not in quite the same spot I was. I got in on NEM2, not whatever the current deal is called.

I did add battery storage in 2021 by adding a separate battery inverter, but that's more complex. It did allow me to skip the expensive Solar Edge batteries.

 

[zanydroid]

TIGO you need to do the math and stay under the inverter's max voltage rating.

Thanks for the writeup.

TIGO is buck only. Theoretically it might drop below start voltage but I’ve not seen people complain or talk about this.

You can do parallel string matching with Tigo as well but I’m not sold on allocating the 25% limit for it (and they don’t explain the consequences clearly in their documentation, the limited matching budget surely has consequences like not being able to handle as much shade).

With Tigo at some point all the limits (25%, no per panel MPPT) adds complexity to designing properly.

 

[400bird]

Sure, Tigo is going to buck the individual panel voltage lower to increase the current on the single panel and keep the current up for the rest of the string.
You still need to calculate max open circuit voltage for the string and protect the inverter.

Solar Edge mostly had min/max number of optimizers/panels in series, no need to calculate open circuit voltage for the string.

I'm not advocating that Solar Edge is, or isn't, the right choice for this application, just wanted to make sure the OP understands how it works compared to Tigo optimizers.

 

[zanydroid]

Interesting thing to think about is. If optimizers are so good, why are there only two choices still in 2024Q1? The ecosystem didn’t get any major new entrants. While there are a ton of microinverters.

Now there is a pretty reasonable argument that RSD mandate + hybrid inverters together might encourage more entrants (and there are a few that were supposed to come out around now), but they are still early adopter/vaporware.

 

[400bird]

Micro inverters are still easier for installers (and likely easier for manufacturers). No DC, no arc fault, no (or maybe less?) requirements around running conduit inside the house.

Plus, I'm pretty sure the optimizer+inverter is more expensive than micro inverters until you get into large systems (but I haven't done the math)

Again, I'm not saying this is the right situation for the OP. In their shoes I'd probably go with a DC string/battery inverter or Enphase micro inverters.

 

[zanydroid]

Micro inverters are still easier for installers (and likely easier for manufacturers). No DC, no arc fault, no (or maybe less?) requirements around running conduit inside the house.

Yeah, they are way easier. Don’t need conduit for microinverters.

I was under the impression that SolarEdge had to compete on price with Enphase for turnkey installs here. There was no marketing extolling technical benefits of either approach the last time I got quotes.

 

[Nevada Solar Designs]

invest a bit more in a compliant hybrid inverter maximizing system design capacity with #BigGrid interoperability today and future expansion

 

[Tozlakes]

OK I think I am heading down the right path after a month of investigating, discussing and finally going with the EG4-18kPV and because of the NEM3 net metering requirements, three of the EG4 PowerPro 14.3 kWh wall mount batteries, all compliant with California BS requirements.

-The Hybrid EG4 18kPV impressed me with all of the integrated components it offered. More or less all in one instead of scattered components.
-The noise level at full load vs others was much less through my investigations.
-The ease of installation with the matching batteries was a big plus. Batteries include conduit boxes and all paralleling cables.
-Both the inverter and the batteries are designed for outdoor applications. This allowed me to install on exterior of garage saving my precious room inside. With that said I will be fabricating a shelter to still protect the components and screens.
-No RSS as this is a ground array and not required in Cali.
-No optimizers as the extra cost at this time does not make sense. No chance of shading outside of clouds.
-Cost was much more reasonable yet still had similar warrantees when comparing to the likes of SolarEdge, Sol-Ark, Fortress and LG home. Also was able to negotiate the price down and get free shipping through Signature Solar.
-3 strings of 10 panels each coming from array.

Worked with GreenLancer on the drawings for submitting to SLO County Building department and PG&E. This was a relatively painless process as I also needed to receive the Electrical Engineering stamps through them.

In addition, was able to design my ground array through the Iron Ridge website whereas I also was able to download the required Structural Engineering stamps for submittal to SLO County.

Not sure the timeline for County approval, once drawings are submitted, but will likely start on the outdoor concrete pad for inverter and batteries along with stabbing poles into the ground for the array. Will keep all posted with pics as the project moves along.

I’ve attached the drawing below for feedback from all in the case I am missing something that needs attention early on.

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