How would you maximize solar input to inverter

[plympton]

I'm looking at this inverter: Growatt SPF 3000TL LVM-48P

It has a max Solar Input of 4500w. Check.
It can work with PV Input 30-115VDC. Check

So, 4500/115 = 39 AMPS!

So, I'd need 8awg cable to maximize solar input? Link says 55amps max. Bummer, I just ran 10awg cable. And just read that panels have 10awg cable. 10awg cable is rated at 30amps.

So, 30a * 115v = 3450w. Does that sound about right? And, in reality, you'd want to run 25a continuous, so 25a * 115v = 2875w, right?

HEY! I have 2 strings of 10awg wire, has a 37.07 * 3 = 111Voc, so I'm safe.

So, could I use these 30a combiners, with my existing wiring, and safely input my strings into an inverter like this? Mostly checking to see if I'm right. I honestly wonder what scenario could actually hit the 4500w solar input...

 

[registered-bum]

For VOC and the SCC max voltage, the spec sheet says "145VDC" ... so maybe you can have 3 panels ins series without exceeding max input to the Growatt.

What's the VOC - and the VOC temp coefficient for your panels?

 

[plympton]

For VOC and the SCC max voltage, the spec sheet says "145VDC" ... so maybe you can have 3 panels ins series without exceeding max input to the Growatt.

What's the VOC - and the VOC temp coefficient for your panels?

Voc is 37.07, and Voc Temp Coefficient is -0.304%/°C. I'm in Portland, OR.

 

[registered-bum]

If I get this wrong, one our regular solar nerds will be along to give me kick the arse ...

Think I saw where NOAA or other weather tracker reported coldest temp for Portland in recent years was 14dF (-10C, on December 08, 2013).

Ratings for solar panels reflect the "Standard Test Condition" or STC, which measures VOC at 25C. Beta reflects how voltsage output is changed by the temperature.

With the temperature differential is then 25-(-10) or 35C (delta T).
delta T times Beta => 35*(0.304) = 7.6v per panel.

We could then estimate VOC for a string of 3 in series as 3*(37.07 + 7.6) = 134v.

This leaves only a modest cushion if the temps actually do drop below that 14dF (-10C) : 145v-134v = 9v
This may be acceptable for many users, others may be more risk adverse - and willing to replace the 10AWG with 8AWG.

I'd use the 10AWG but I often take chances.

 

[MisterSandals]

With the temperature differential is then 25-(-10) or 35C (delta T).
delta T times Beta => 35*(0.304) = 7.6v per panel.

37.07V x 35 deg C x .00304 = 3.94V rise per panel

 

[plympton]

37.07V x 35 deg C x .00304 = 3.94V rise per panel

I had to double take the math, but I think I got it:

37.07V * (35 deg c) * (0.304%/deg c == 0.00304/deg c) = 3.94v rise per panel

so 37.07v + 3.94v = 41.01v * 3 (series panels) = 123.03v, which for a 150v MPPT is pretty good. Check!

 

[registered-bum]

Thanks for those corrections, Mr Sandals!

I'm still at the junior intern level ...