Is this basically what I'm looking at to combine the AC from all the inverters?
Can't say specifically about the firmware settings in USA but where I am the grid voltage dynamic power reduction (GVDPR) settings kick in above 253V, and gets pretty restrictive above 258V. Enough time above that and it will trip off. It's happened to me once a few weeks ago, I suffer from fairly high grid voltages where I am.Also, you should check the voltage in your home's breaker panel.. While the USA is generally 240, the fact is, 240 is almost never exactly 240 everywhere.. Reading internet forums, I've seen people with voltages as high as 245 and one guy, I think his was 247 volts, and that high voltage was causing his solar inverters to trip out because the inverter couldn't raise the voltage far enough to pump in enough juice.
The SMA units have a maximum MPPT input current of 10 amps, and considering most 350 to 400 watt panels are sitting right at that 10 amp limit, you can not parallel panel strings.Thanks. With the fronius units, I do not have to parallel them. They would just be individual series. If I did the sunny boys then I would have to parallel or the amount of runs back to the inverters would get a bit ridiculous at that length.
I have accounted for the cold weather on the voltage as well. My calculations say I could go up to 17 panels without exceeding 1000v and the fronius calculator has me at 16 panels.
I COULD consider doing the SMA units (6) and then run 3 strings in parallel. I think this would be less efficient and I would lose the possible effect of getting a bonus 10% ITC for 55% of the project being "made in the US" if that passes.
Just out of curiosity, if I did the SMA units and put 3 strings in parallel for 33A at 400v it would equate to just shy of 4% loss with 10 gauge copper wire.
I think I'm definitely going at this right with the fronius units, the longer run, larger array, US made potential savings, etc....
@MurphyGuy Thank you for confirming my belief. I am definitely no expert, but I'm accustomed to looking at things technically as I have an engineering background.
Is there any preference to having panels in portrait or landscape?
I'm going to do 48 panel arrays (3 x 16 series). I can do:
4 in landscape x 12 panels OR
2 portrait x 24 panels
The array, physically, is the just about the exact same either way. I was thinking portrait would be better because if you have to remove a panel then it would be much easier instead of it being "buried" in the middle somewhere and having to remove 1 or two other panels to get to it. I doubt I'll have to remove any panels, but it's about the only thing I can come up with other than the "route" that they will be wired in series. I could maybe come up with a more efficient way if they were in landscape that would use a little less wire.
What batteries do you use with your SMA off grid? I find that a limiting factor, as the SMA's need seperate everything, and specific batteries. $800 just for web connectivity? Midnight solar MPPT? Shunts? CT's? Why so complex?
Thank you for the tips! That's a fine look array!Panel orientation is a personal choice so far as I know. I think the only real consideration there is the physical height of the array as the higher it is, the more wind its going to catch. Other than that, I don't think it matters.
Over a 200 foot run, an extra 5 feet of wire at the array because you like one orientation over another, isn't going to mean squat.
As far as replacing a panel in the middle, the only real challenge is unscrewing the clamps because you have to get to those from the top. In my case, I have a farm tractor and I built a wood platform. My wife lays down on it with her head and shoulders hanging off the far end, and I can lift her up and drive her to the clamp screws.
I'll tell you something I noticed a year after I had the system.. we were gawking at internet pictures where storms would come through and destroy solar farms.. and I noticed something strange.. In many cases, the solar structures are mostly undamaged but the panels were blown away and all busted up. I thought that was a bit odd.
On a hunch, I took the torque wrench and socket back out to the array and started checking all the fasteners I could reach.. almost every single one of them was under-torqued by almost 50%.
I think that after a while, those fasteners loosen up due to the teeth on the clamps settling into place on the soft aluminium. Back onto the platform she went and re-torqued every clamp down to specs.
I checked them again in another year and they were all fine.. Lesson learned.. you need to go back to your array in a year and check them. And yes, make sure you use a torque wrench.. I bought a 1/4 drive unit from Home Depot, trained my 130lb wife how to use it, and then put her on the "platform of death" to go flying from bolt to bolt again.
Also, you're probably already doing it, but if not, make sure you reference the mounting instructions for your panels. There are specs for the rail spacing for both orientations. Its a pretty wide spec, but I suggest you do the math and hit it right in the middle.
Here's photo of the "Platform of death".. My wife still talks about her experience flying like Superwoman. LOL