Problems getting a 4kw array with growatt spf 3000tl lvm es

[mcmullen7242]

I have the inverter stated in my title and trying to get solar panels that will allow me to get close to the 4kw allowed by this inverter. My problem is the 18A limit on the pv array. I am looking at these panels as the had the lowest amps I’ve seen while still producing a high amount of watts. I was thinking of buying 9 of these and putting them in sets of 3 in series and have 3 strings paralleled using a 3 to 1 mc4 adapter.
I believe I should be at 218.7V (under my 250v limit) and 17.1 amps (under my 18a limit stated in manual). Any input or advice would be greatly appreciated! I really want to be in the 3.5-4kw range with my array

 

[sunshine_eggo]

Welcome to the joy that is the 250V inverters. It's pretty much impossible to get an array up to the power limit, but yours is the closest I've ever seen. Nicely done.

You're technically over 18A as you use the Isc value in that computation; however most MPPT are tolerant of a little over-current on the input as they just ignore anything above that limit.

IMHO, you have a winner provided you don't get much below freezing in your area.

Make sure you have a 20A fuse/breaker on each string before you parallel them.

 

[mcmullen7242]

Thanks, I will get those panels and do I still need a fuse or breaker if the panels are going to a 1000v 30A solar disconnect? Also was I correct about the voltage? Definitely has been a challenge to find these haha

 

[sunshine_eggo]

Thanks, I will get those panels and do I still need a fuse or breaker if the panels are going to a 1000v 30A solar disconnect? Also was I correct about the voltage? Definitely has been a challenge to find these haha

You need a 20A max fuse/breaker on EACH 3S string. You could go as low as 10A. When you have 3 or more strings in parallel, each string must have over-current protection (OCP) - either fuse or breaker.

Voltage is correct provided it doesn't get too cold. Running a quick approximation, your 219Voc should be good down to about -7°C.

 

[mcmullen7242]

Ok I’ll definitely do that thanks. And the open circuit voltage is 85.7v is that a problem with three together at 257.1? Or does it go by just the voltage of the panels as I thought?

 

[sunshine_eggo]

Ok I’ll definitely do that thanks. And the open circuit voltage is 85.7v is that a problem with three together at 257.1? Or does it go by just the voltage of the panels as I thought?

CRAP!

Yes. That's too high. I though Voc was 72.9V. Sorry. You can't 3S those panels on that system.

 

[mcmullen7242]

Ahh damn, no problem thanks for your help though! Looks like I’ll be searching Facebook marketplace and google for something else.

 

[sunshine_eggo]

Seek 60 cell panels with Voc around 36V. 6S should put you around 220Voc. Wattage 250-300, should be around 9A, could go 6S2P.

 

[mcmullen7242]

I was told by watts 247 that I could still use these panels if I did 3s3p to a 4-1 combiner box. I’ve never looked into a combiner box because my system was so small before. Does that sound right to you? And if so do you have any recommendations on a combiner box?

 

[sunshine_eggo]

I was told by watts 247 that I could still use these panels if I did 3s3p to a 4-1 combiner box. I’ve never looked into a combiner box because my system was so small before. Does that sound right to you? And if so do you have any recommendations on a combiner box?

Is Ian aware that the Voc at 77°F is 257V? If so, I'm at a loss. That's shocking.

 

[mcmullen7242]

I think he’s mistaken and probably didn’t take a close look at what I sent. I think I’ve found some candidates for other panels that I was thinking of doing 6s2p with, I’ll attatch the photos

 

[sunshine_eggo]

Unfortunately, those are all 235-240Voc or so. If you NEVER get below 15°C, you're fine, but even Phoenix, AZ easily gets that chilly in winter.

 

[mcmullen7242]

If my limit is 250v on the inverter why would being in the 220-240 be a problem? Does voltage increase that much in the cold?

 

[sunshine_eggo]

If my limit is 250v on the inverter why would being in the 220-240 be a problem? Does voltage increase that much in the cold?

Yes. Voc raises about 4% for every 10°C drop below 25°C. Some panels may be less than this, so if you can find a Voc temperature coefficient for that model panel, you might get a little more wiggle room.

220V would be good as that would get you down to about -9°C.

 

[mcmullen7242]

Thanks for the help! I really wish I knew this prior to buying this growatt, do you know of any all in one unit that accepts a high voltage and higher amps? I won’t need more than 3kw of inverter power but could go to 5kw. Might just sell this and upgrade as I need to get my array up to at least 3.5kw

 

[sunshine_eggo]

Do you actually need 250V? Do you have a very long cable run from the panels to the MPPT?

The 145-150V units can accept much more PV input current. With any of those ~39Voc panels, you could easily put 3 in series and parallel several of them. A 3S4P or 3S5P array would work out nicely.

 

[mcmullen7242]

My panels are about 100ft from my inverter and batteries, I figured it would save on cable prices but not totally set on that. I was mainly trying to dodge costs of a big combiner box but I’m really a beginner on all this but have been reading and watching videos for a while

 

[mcmullen7242]

Growatt 48V SPF 3000TL LVM – 3kW 120Vac Stackable Inverter 4.5kW MPPT Charge Controller Split Phase 120V/240V capable with two or more units + free wifi – Watts247 Wholesale

watts247.com

With this inverter how many amps could my array be? I couldn’t find it under the pv array stats.

 

[sunshine_eggo]

My panels are about 100ft from my inverter and batteries, I figured it would save on cable prices but not totally set on that. I was mainly trying to dodge costs of a big combiner box but I’m really a beginner on all this but have been reading and watching videos for a while

100' is significant. With 8awg cabling and the 3S5P array I mentioned, you'd have a voltage drop of about 6%

With 5S2P, you'd have about 1.3% drop.

Growatt 48V SPF 3000TL LVM – 3kW 120Vac Stackable Inverter 4.5kW MPPT Charge Controller Split Phase 120V/240V capable with two or more units + free wifi – Watts247 Wholesale

watts247.com

With this inverter how many amps could my array be? I couldn’t find it under the pv array stats.

When a limit isn't listed, it is presumed to be the same as the output. In practical terms, since your PV voltage will always be notably higher than your battery voltage, your input current can never be as high as the output.

The proposed 3S5P array will have < 50A PV input current.

Even with the additional wiring losses, you have the ability to hang a larger array to capture all the available PV charging power. Attaining 4000W+ will be pretty easy.

 

[mcmullen7242]

I really appreciate your help, saved me a lot of research time! I will definitely look into that as buying any panel on Facebook and that inverter would actually be cheaper than finding specific panels to work with my inverter, so I believe that’s what I’ll do. I’m gonna be busy today but will run all the numbers tonight. Would the pv array input on the growatt inverters be big enough to fit 8 awg in there?