Growatt 5000 ES in 2p4s with 400w panels

[Andy_Knowles]

Hi all,
I'm building my first system, and am just looking for advice really,
This is for a garden office, with a East/West roof - I want to put 4 panels on each side - so running 2 parallel sets of 4 in series.
I wanted to do them in two sets so that I won't get big losses in the morning and evening when the sun is low

I have sourced my panels which are 400w each (image shows details)
So i've read that the 5000ES can handle 22a, but the Voltage i'm a little concerned about -

Do i use the VOC voltage x 4, which would be 185.6v (Fine!)
or the Vm x 4 - which is 154.4v which is just above the start-up voltage? - Will this be fine?

I don't really want to have to buy two smaller inverters and end up with a more complicated system

Thanks in advance for help!

 

[sunshine_eggo]

You use Voc and you should be fine. Once started, Vmp needs to remain above 120V.

 

[Andy_Knowles]

You use Voc and you should be fine. Once started, Vmp needs to remain above 120V.

Ah, Thank you so much for this! I was so worried that I had made a complete mess of it all and ordered the wrong inverter!

185v is plenty over the 150 start voltage ??

 

[sunshine_eggo]

They put a tolerance on start up of ±10V, so I'd assume 160V. Even there, you should be good.

 

[Andy_Knowles]

Great stuff, so I think i've got my head around everything i need now,
Does this diagram all make sense? I think i've got it all in the right order

 

[sunshine_eggo]

Personally, I would just go 8S and call it good.

 

[Andy_Knowles]

The problem is having an East/West roof with a 22.5 degree angle,
Won't the shaded panels drag the output right down I. Morning and evening?

 

[sunshine_eggo]

The problem is having an East/West roof with a 22.5 degree angle,
Won't the shaded panels drag the output right down I. Morning and evening?

DOH!... insufficient coffee. Yes. 4S2P best in your situation.

FYI, blocking diodes are rarely needed. Even ambient light (shaded panels) can produce Voc or near Voc voltage.

Think of it this way: The presence of light gives voltage. The intensity of light gives amperage.

 

[Andy_Knowles]

Ahh cool, I'll stick with 4S2P

Ahh in that case I'll maybe just leave them out and then add them if needed.
I was under the impression that they were needed for parallel configurations, but I'm only just starting to get to grips with how this stuff works.

 

[sunshine_eggo]

Ahh cool, I'll stick with 4S2P

Ahh in that case I'll maybe just leave them out and then add them if needed.
I was under the impression that they were needed for parallel configurations, but I'm only just starting to get to grips with how this stuff works.

The only way they would be needed is if you completely obstructed one string - literally placed covers over them so they receive no light.

 

[Andy_Knowles]

Excellent, i'll just hang on to them maybe for a later project.
Out of interest, do you know what AWG the cables need to be from the panels through to the inverter?
I was thinking 30a (10awg would be enough?)
would it be the same for the Inverter to Battery? or thicker?

 

[sunshine_eggo]

10awg for 22A Isc from PV to MPPT is fine.

For inverter to battery:

5000W/48V/85% = 122A

1/0 awg for 75°C wire
2 awg for 90°C wire

What battery?

 

[Andy_Knowles]

Battery is likely to be a 48v Lifepo4 100a (potentially 150ah)

 

[sunshine_eggo]

That unit likely burns about 75W continuously just being on. That's 1.8kWh/day. A single 48V 100Ah is 5.12kWh, so the inverter will consume 1.8/5.12 = 35.2% of your battery capacity if you use no loads at all.

That will also consume 1800Wh/5h = 360W of your array, i.e., the energy produced by 360W of your array is powering the unit. In terms of usable power, your 3200W array is more like 2840W.

Folks don't always consider the high idle consumption of these cheaper units when sizing batteries/arrays. It's the hidden cost of the high idle consumption.

 

[Andy_Knowles]

So, best bet is go for a bigger battery?

 

[Andy_Knowles]

The Growatt has so much high praise for simplicity and efficiency, that's why I went with it. (The simple install)
I've read it's closer to 50w, but is that alot more than a separate charger, mppt and inverter would be?

 

[sunshine_eggo]

The Growatt has so much high praise for simplicity and efficiency, that's why I went with it. (The simple install)
I've read it's closer to 50w, but is that alot more than a separate charger, mppt and inverter would be?

40-50W/3000W inverter power is pretty typical. Any published draw is a minimum.

Inverter efficiency is a design/component quality issue. My 5kW Victron only burns 27W. Other Tier-1 hardware has similar consumption.

Voltronics/MPP solar/Growatt units are not designed for low consumption. Production batches are often made with different components depending on what's cheapest when circuity is ordered.

 

[Andy_Knowles]

Yeah that makes sense, happens across many parts of the electronics industry.
I think I'll try and push for a bigger battery

 

[Hedges]

As Sunshine said, any ambient light on a panel raises Voc enough it won't be a load on the 4s string which is in the sun. I've measured that for some I've got.

Current:
PV panel 10.97A Isc x 2 in parallel = 21.94A
You should see that on a cool day with sun directly overhead (if that ever happens.)

Wire ampacity and breaker rating should be 1.25x higher than max continuous current to avoid nuisance trips.
With PV as a source, should be another 1.25x higher, due to cloud edge effect (direct plus reflected light.)
1.25 x 1.25 = 1.56, which is NEC spec for sizing wires and breaker.

21.94 x 1.56 = 34A

Miniature circuit breaker rated 32A
(1000V and two poles in series is WAY above minimum requirement!)
Just under 34A "requirement". Probably close enough it will never be a problem.
Orientation of panels reduces peak current slightly, just enough. Cos(22.5 degrees) = 0.92
The 1.25x margin (continuous current 80% of rating) is for thermal breaker; if those are "magnetic-HYDRAULIC", may not need the margin.
Temperature coefficient of panels and ambient temperature of thermal breaker likely also prevents nuisance tripping.

15A DC isolator
This is below expected current flow. Any reason to have this at all, given breaker also isolates circuit?

 

[Andy_Knowles]

The isolator is just to have a switch to turn it all off - though i could just use the trip switch - I only added it because someone else said I needed one...

So the 4S2P should be fine to run the inverter and feed the battery ok?