[on-grid] Is small panel the same future-proof as large panel ?

[CostOptimizer]

Hi all, a question about an on-grid system here:

With a string inverter of 6 KW, I have now 2 choices on panel sizes & capacity, and I wonder which one is more future - proof ?
- the smaller (1.762 x 1,134, capacity around 450 Wp, N-type Topcon, efficiency 22-25%)
- the bigger (2.278 x 1.134, capacity around 580 Wp, N-type Topcon, efficiency 22-22.5%)

Imagine in 2027, when I want to add more panels (e.g. at least 3 Kw more), my choices are
- 1) Replace current 6 Kw string inverter by another 9 Kw String inverter, and sell / reuse the current 6 Kw else where. Would this be difficult if existing panels are 450 Wp when the new panels are 700 - 800 Wp ?
- 2) Add a separated 3 Kw system (add another 3 Kw string inverter with new panels). In this case any of current design is not relevant, right ?
Thanks

 

[chrisski]

Inverters likely need to be the same model and size to link together. I have an Outback Radian 8048 which is a 8 kW inverter and would need to upgrade with a second Outback 8048. Any other combination of inverters would not speak to each other to set the frequency match the AC with 60 HZ in phase. Each of the inverts can be hooked with 10 kW of panels. I have 10 kW of panels on inverter #1, I plan on getting 8 KW of panels on inverter #2, at which point, I am out of room for more panels.

Imagine in 2027, when I want to add more panels (e.g. at least 3 Kw more), my choices are

- 1) Replace current 6 Kw string inverter by another 9 Kw String inverter, and sell / reuse the current 6 Kw else where. Would this be difficult if existing panels are 450 Wp when the new panels are 700 - 800 Wp ?

Just buy the equipment you can upgrade now without selling the others. In America selling used equipment is not so great. Used equipment is not eligible for the 30% tax rebate, but the government will pay for 30% of your purchase for new equipment, so the used price would need to come way down.

- 2) Add a separated 3 Kw system (add another 3 Kw string inverter with new panels). In this case any of current design is not relevant, right ?
Thanks

I don't think you'll find a 3 kW inverter that will work together with the 6 Kw inverter you already purchased, but this is a better option if this new 3 Kw string inverter will match frequencies and work together.

- the smaller (1.176 x 1,134, capacity around 450 Wp, N-type Topcon, efficiency 22-25%)
- the bigger (2.278 x 1.134, capacity around 580 Wp, N-type Topcon, efficiency 22-22.5%)

I don't know what these panels are. One seems to be twice the size of the other with only 20% more output.

 

[OzSolar]

- 2) Add a separated 3 Kw system (add another 3 Kw string inverter with new panels). In this case any of current design is not relevant, right ?
Thanks

Ahh... I recognize my old nemesis "analysis paralysis". I think I get what you're trying to do.

Grid tied no batteries?

I've noticed that that the bigger the modules get the less flexibility you have for designs. EG: When you're building strings at 50 Voc or more at a time you can quickly run out of room on 500 Voc strings. 600 Voc strings are better.

I'd say design the best system for today and not worry to much about the future, plan on buying the right inverter then.

or (I just thought of this)

Option 3: 9.6 kW or more inverter today and choose one that has plenty of MPPT's. That way you can use whatever panel in the future. GOODWE and Solis both has 4 MPPT's models last I knew. Also remember that you can overpanel by 150% or more on most string inverters.

Did that help or did I completely miss your question?

 

[CostOptimizer]

I think I have partially found the answer:

- 1) If I add new panels to the existing inverter, then regardless of a parallel or series connection, the panels of year 2024 will always cause a loss in maximal production capacity of the new panels of 2027. The more difference in Wattage the higher the loss is.

- 2) If I add the new panels together with a new inverter --> I don't have the answer yet.

 

[CostOptimizer]

I don't know what these panels are. One seems to be twice the size of the other with only 20% more output.

My typo, sorry, meant to be 1.762 x 1.134 as the smaller panel

 

[CostOptimizer]

Grid tied no batteries?

On-grid, no batteries, yes

I've noticed that that the bigger the modules get the less flexibility you have for designs. EG: When you're building strings at 50 Voc or more at a time you can quickly run out of room on 500 Voc strings. 600 Voc strings are better.

Did you mean: a string inverter designed for 500 Voc will not be able to handle, e.g. more than 15 panels of 50 Voc each, in series connection, so having 10 panels of 50 Voc now and choosing vor an inverter of 500 Voc then my hands are tight and any meaningful addition of panels (normally more than 5 x 50 Voc) later will need buying another bigger inverter ?

Option 3: 9.6 kW or more inverter today and choose one that has plenty of MPPT's. That way you can use whatever panel in the future. GOODWE and Solis both has 4 MPPT's models last I knew. Also remember that you can overpanel by 150% or more on most string inverters.

Do I understand correctly that each MPPT can handle a series of panels ?

 

[OzSolar]

Did you mean: a string inverter designed for 500 Voc will not be able to handle, e.g. more than 15 panels of 50 Voc each, in series connection, so having 10 panels of 50 Voc now and choosing vor an inverter of 500 Voc then my hands are tight and any meaningful addition of panels (normally more than 5 x 50 Voc) later will need buying another bigger inverter ?

15? I mean 500v / 50v = 10 panels but you can't do that because the Voc rises as temp drops so 9 is all you could do.

Do I understand correctly that each MPPT can handle a series of panels ?

Exactly, each MPPT is it's own inverter per se, independent of the other. You just have to have a high enough Vmp to operate in the summer and low enough Voc to NOT blow up the inverter in the winter.

 

[CostOptimizer]

With a flat roof of 4,37 m x 10,37 m, here are my 4 options: green is small panels of around 450 W or big panel of 580 W.
In the champion of wattage: the panels seem to be off the edge, but in reality they will be put at the angle of around 20 degrees, which makes them "shorter" on 2D perspective.

Question: is the champion on the bottom-left (9,3 KW with 16 panels) the best possible setting ? in terms of (1) maximum Watt Peak, (2) allowing a bit of light to shine under the bifacial panels, (3) taking into account the East-West orientation to maximize production on weak sun seasons ?

 

[CostOptimizer]

Vertical on a wall

Big (blue) or small (green) panels ? This is a vertical wall facing South-east

 

[CostOptimizer]

Sloped roof: facing South-West: big (blue) or small (green) panels ?