Inverter too big for array?

[Jeroen1000]

Dear non-beginners

I'm having trouble figuring this out. I am (at last) putting 12 panels 400 Wp. In theory the 5.0 model should more than suffice and I could even go for the 4.0 model. Alass
I would really like the Fronius Symo Gen 24 6.0 model as it can work off grid temporarily. I was trying to figure out the downsides of getting a too big inverter. There a no graphs for the 4.0 and 4.5 models in the specifications but I would like to ask some q's nonetheless.

Curiously, the sweet spot operating voltage (nominal input voltage) is the same for the 3.0 model all the way up to the 10.0 model: namely 610v. This does not make sense to me as getting to 610v with the smaller models probably requires a too large amount of panels for the inverted rated performance. Moreover, looking at the efficiency curves, the 6.0 model seems to be more efficient accross the board than the 3.0 model.

Can someone tell me if there are notable downside of selecting an oversized Fornius and maybe explain what "Normalised output power PAC/PAC,R" means?

 

[12VoltInstalls]

First I think you are overthinking this with too little knowledge. Not a mean statement or criticism, just an observation.

there are notable downside of selecting an oversized Fornius

Whether big (“oversized”) or small (with appropriately limited overpanelling up to the mfgr instruction manual) a device will only use the available solar panel output up to the amount of load presented and up to but not over the designed output limits of the device regardless of brand.
So unless you plan to add panel capacity in the future the only practical downside is spending extra money.

efficiency curves, the 6.0 model seems to be more efficient accross the board than the 3.0 model.

Efficiency is a funny idea. Some people get all concerned about efficiency while others just select components that provide the output they require- which often/usually just means an additional panel or two. Some are concerned about ‘wasted’ watts, but the reality is that they aren’t wasted- slight efficiency “losses” cost no money on an ongoing basis. Just maybe in up-front cost.
Select the unit that produces what you need keeping in mind any possible future upgrading. Or maybe upgrading is not a concern to you.

it can work off grid temporarily

I didn’t look it up but apparently this is a batteryless model? That does load sharing but goes ‘dark’ with sunset?
I personally would always incorporate some battery capacity. Since I’m general grid power is ‘cheaper’ than solar; producing power that cannot be stored for passing clouds, at least some load support overnight, and having grid-down power at night does not make sense to me. The battery bank is an expense that affects ROI by extending it a bit, but it also sheds some monthly billing that over time can help the battery to ‘pay its own way.’
A properly designed and purchased diy system will have a break even point where it generates a ‘profit’ in its lifespan- often in just a few years, but even 4-8 years is tolerable imho on a system that will have at least a 10, or 12, or 15+ year lifespan.

getting to 610v with the smaller models probably requires a too large amount of panels for the inverted rated performance

So 12 panels at 400W is what VOC for you panels? Let’s wildhat guess 56VOC or say “50V Imp” for easy figuring. Series string that’s 600V. Whatever ‘sweet spot’ the efficiency difference is likely in the low single digit percentage.
In practical terms a nonproblem imho.

It’s good to study up and make a plan, it’s good to know where you’re headed, but don’t get stressed out over a few watts difference here and there. What’s important is does it work and is it reliable? The ancillary ‘efficiency losses’ on good equipment are not the most important factor. Just like with a certain amount of ‘food waste’ running a restaurant or packaging costs for a small farm producer are just the cost of doing business, so are the acceptable efficiency losses just a cost of powering your electrical needs with solar.

 

[Jeroen1000]

First I think you are overthinking this with too little knowledge. Not a mean statement or criticism, just an observation.

@12VoltInstalls I have this occupational habbit (annoyance if you will) trying to get to the bottom of things

. But your observation is accurate. I will be upgrading (or maybe I'll do it in one go if I can afford it) to 18 panels thus 7200Wp.

I didn’t look it up but apparently this is a batteryless model? That does load sharing but goes ‘dark’ with sunset?
I personally would always incorporate some battery capacity. Since I’m general grid power is ‘cheaper’ than solar; producing power that cannot be stored for passing clouds, at least some load support overnight, and having grid-down power at night does not make sense to me. The battery bank is an expense that affects ROI by extending it a bit, but it also sheds some monthly billing that over time can help the battery to ‘pay its own way.’
A properly designed and purchased diy system will have a break even point where it generates a ‘profit’ in its lifespan- often in just a few years, but even 4-8 years is tolerable imho on a system that will have at least a 10, or 12, or 15+ year lifespan.

It has a double socket that would indeed go dark with sunset. It can provide 3Kw (if there is enough PV production for that at any given time). It can also accomodate a battery and then it can do failover for the whole house with a higher power budget. See my nifty attachment.
A battery is too expensive right now but some day...

So 12 panels at 400W is what VOC for you panels? Let’s wildhat guess 56VOC or say “50V Imp” for easy figuring. Series string that’s 600V. Whatever ‘sweet spot’ the efficiency difference is likely in the low single digit percentage.
In practical terms a nonproblem imho.

This is the Open Circuit Voltage right. In that case: STC VOC: 36,9. NOTC VOC: 35

It’s good to study up and make a plan, it’s good to know where you’re headed, but don’t get stressed out over a few watts difference here and there. What’s important is does it work and is it reliable? The ancillary ‘efficiency losses’ on good equipment are not the most important factor. Just like with a certain amount of ‘food waste’ running a restaurant or packaging costs for a small farm producer are just the cost of doing business, so are the acceptable efficiency losses just a cost of powering your electrical needs with solar.

So putting it in perspective using your knowledge. Just get the 6 kW inverter (rated output)? I will be overpanneling with the 6.0 one to 7200 - 7800 Wp but the inverter can take 50% extra.