Advice needed on commissioning of Infini Solar Super 4k

[SYC]

Hi Guyz,

Firstly thanks to all for the wealth of information provided on this forum.Keep up the good work

I presently have Axpert 5kva with 1x us3000 1xus2000 and 9x 325W canandian solar (3 in series and 3 parallel) working like a dream for 8 months now

I want to replace Axpert with Infini Super 4K FCS-InfiniSolar-Super-4KW-Broucher.pdf

So I have acquired 13x 335w Canadian Solar Panels 37.4v 8.94A (intend on disconnecting old panels and connecting new ones all in series)

By my calculations I'm within range for inverter specs 4355w ,486.2v and 8.94A to run the same load as below:

Please advice me if I'm wrong in calculation and intention to run as offgrid system like I have with Axpert?

 Intend on adding to day time load washing machine, tumble dryer, 2 x microwaves, 1 x kettle and 1 x 1800btu inverter split air-con unit as well

 

[Jaco De Jongh]

10 hours ago, sulyc said:

So I have acquired 13x 335w Canadian Solar Panels 37.4v 8.94A (intend on disconnecting old panels and connecting new ones all in series)

The recommendation for these units were done as follows. 

They used 72 Cell 250 watt panels with VMp = 36.7 Volt and IMP 6.81Amp .

The manufacturer recommended 12 in Series or 2 strings of 10 in series. They also recommend a nominal DC voltage as  360 VDC.

 

10 hours ago, sulyc said:

Intend on adding to day time load washing machine, tumble dryer, 2 x microwaves, 1 x kettle and 1 x 1800btu inverter split air-con unit as well

You might want to reconsider this. The chances of them all running at the same time is not that good, but still it can happen. Lets calculate. 

1. Washing Machine                 750 watts                    lets use  750w
2. Tumble drier, normally      2000 - 3000 watts         lets use 2200w              
3. 2 x Microwave                   600 - 1300 watt              lets use    800w x 2
4. 1 x Kettle                            1500 - 2200 watt            lets use 1800w
5. 18000BTU aircon              1800 watt                        lets use 1800w

                                                                                                    Total:  8150w        

Without some good load management, you can easily overload this unit.  

[SYC]

9 hours ago, Jaco de Jongh said:

The recommendation for these units were done as follows. 

They used 72 Cell 250 watt panels with VMp = 36.7 Volt and IMP 6.81Amp .

The manufacturer recommended 12 in Series or 2 strings of 10 in series. They also recommend a nominal DC voltage as  360 VDC.

Thank you for your valuable feedback but MPP Voltage Range 280 VDC ~ 500 VDC Number of MPP Trackers / Maximum Input Current 1 / 1 x 18 A and I'm at 486.2v  8.94A

Should I not be fine? 

Since I have already purchased and mounted panels on the roof please advise whether I should only use 9 panels in series thus dropping my watts to only 3015w ?

 

9 hours ago, Jaco de Jongh said:

You might want to reconsider this. The chances of them all running at the same time is not that good, but still it can happen. Lets calculate. 

1. Washing Machine                 750 watts                    lets use  750w
2. Tumble drier, normally      2000 - 3000 watts         lets use 2200w              
3. 2 x Microwave                   600 - 1300 watt              lets use    800w x 2
4. 1 x Kettle                            1500 - 2200 watt            lets use 1800w
5. 18000BTU aircon              1800 watt                        lets use 1800w

                                                                                                    Total:  8150w        

Without some good load management, you can easily overload this unit.  

With regards to adding on will definitely only add Washing machine and Tumble drier after I have measured the load

 

[Coulomb]

11 hours ago, sulyc said:

By my calculations I'm within range for inverter specs 4355w ,486.2v and 8.94A

Those are loaded voltages at 25°C. Open circuit you can expect about 45V @ 25°C, or about 49.5V @ 0°C. 13 x 49.5 = 644V, even 12 x 49.5 = 594. The inverter's maximum PV voltage rating is 580 V. You'll probably get away with the latter, but 13 panels is I believe too many.

 

[Sidewinder]

Those two panel's spec are as follows:

So, I would calculate the possibilities as follows:

Old Panels
9	panels	325	W	39	Voc	351	V	-0.29%/C	25.4475	V	376.4475	V	2925	W
New Panels
13	panels	335	W	39.4	Voc	512.2	V	-0.29%/C	37.1345	V	549.3345	V	4355	W
String 1																Min. Temp for Voc-max
1	panels	325	W	39	Voc	39	V	-0.29%/C	2.8275	V	41.8275	V	325	W		11.162	V	8.352	C
13	panels	335	W	39.4	Voc	512.2	V	-0.29%/C	37.1345	V	549.3345	V	4355	W
											591.162	V	4680	W
String 1
3	panels	325	W	39	Voc	117	V	-0.29%/C	8.4825	V	125.4825	V	975	W
+
5	panels	335	W	39.4	Voc	197	V	-0.29%/C	14.2825	V	211.2825	V	1675	W
Parallel with											336.765	W	2650	W
String 2
8	panels	335	W	39.4	Voc	315.2	V	-0.29%/C	22.852	V	338.052	V	2680	W
											338.052	V	5330	W

 

So in my opinion, you're best bet would be 2 parallel strings, String 1 made out of 3 x 325W + 5 x 335W and string 2 made out of 8 x 335W.

Then you will "match" the strings closely (within 1.3V over 338V, stay well below the Voc, and with losses, max out the 5000W PV your inverter can handle.

The calcs on the far right is the min. Temp in Celsius your location need to have, if you do 1 string of 1 x 325 + 13 x 335, as you have not set you location. In South Africa that would not be possible. Maybe in the Caribbean or closer to the Equator! 

Hope this makes sense, else bring me to sanity!

 

[SYC]

4 hours ago, Sidewinder said:

So in my opinion, you're best bet would be 2 parallel strings, String 1 made out of 3 x 325W + 5 x 335W and string 2 made out of 8 x 335W.

Then you will "match" the strings closely (within 1.3V over 338V, stay well below the Voc, and with losses, max out the 5000W PV your inverter can handle.

The calcs on the far right is the min. Temp in Celsius your location need to have, if you do 1 string of 1 x 325 + 13 x 335, as you have not set you location. In South Africa that would not be possible. Maybe in the Caribbean or closer to the Equator! 

Hope this makes sense, else bring me to sanity!

 

I am in South Africa and JHB South.

Makes total sense but inverter can only handle max 18A so going Parallel would be cutting it close or over am I correct?

Edited August 15, 2019 by sulyc

[Coulomb]

1 hour ago, sulyc said:

inverter can only handle max 18A so going Parallel would be cutting it close or over

Yes, good point. I wonder why the high voltage SCCs even give a maximum panel current; it seems unlikely that the transistors can't handle more than that. But maybe the high voltage transistors used really are rated at 20 A, and they want that 11% margin for safety. If the SCC was perfect, it would never draw more than rated power, and therefore the current would always be below 18 A. But of course, no SCC is perfect, and Axperts are known for their overshoots and undershoots, so I guess that's the reason.

It's really unfortunate that the SCCs were designed back when panel current limit of 18 A would easily accommodate two strings, but with today's typically much higher power panels, this is not the case.

In short, I think you're right: two strings would be pushing the SCC past its safety limit, so while you might get away with it for a some years, it may well have a shortened life, or might only last a few days.

[SYC]

Please render a verdict:

9 x 335W in series 3015W 354.6V and 8.94 should be safe within Inverter parameters ?

As I intend on commissioning this coming weekend.

Why do they overshoot with 5000W pv when it can't handle?

And so low current?

Honestly my intention is to save enough money so that when I'm a big boy I want to buy Victron system

Edited August 15, 2019 by sulyc

[Guest]

On 2019/08/14 at 8:30 PM, sulyc said:

Infini Super 4K FCS-InfiniSolar-Super-4KW-Broucher.pdf

1 hour ago, sulyc said:

I want to buy Victron system

May I ask. What does the Infini cost?

[Coulomb]

5 hours ago, sulyc said:

9 x 335W in series 3015W 354.6V and 8.94 should be safe within Inverter parameters ?

Yes. But actually, now that I see your actual panel specifications, I see that 13 panels in series will also be safe, down to 0°C.

Voc @ 25°C = 39.4 V. Temperature coefficient for Voc is -0.29%/°C, so at 0°C the factor is 1 + (25 x 0.29%) = 1.0725. So Voc @ 0°C for each panel is 39.4 x 1.0725 = 42.26 V. Times 13 panels is 549 V, which is under the 580 V rating.

The Vmp is also well within range. Sorry for being lazy and not looking up your actual panel specs, but I get tired of doing this for every person that requests help. If you just post all the relevant data with the query, it makes life so much easier.

 

5 hours ago, sulyc said:

Why do they overshoot with 5000W pv when it can't handle?

I'm just guessing that they suffer from the same overshoots as the Axperts. Some inverters, Plonkster has mentioned Fronius I believe, do a much better job at minimising the overshoots.

5 hours ago, sulyc said:

And so low current?

As I speculated earlier, they designed these things when panels were typically much lower power. They just haven't bothered updating the specs to handle two strings of modern panels. With a hybrid inverter, every design change seems to require re-certification, which is an expensive process, especially when the different markets require different certifications. 

[SYC]

3 hours ago, Coulomb said:

The Vmp is also well within range. Sorry for being lazy and not looking up your actual panel specs, but I get tired of doing this for every person that requests help. If you just post all the relevant data with the query, it makes life so much easier.

My apologies for not providing all the relevant info

[SYC]

3 hours ago, Coulomb said:

Voc @ 25°C = 39.4 V. Temperature coefficient for Voc is -0.29%/°C, so at 0°C the factor is 1 + (25 x 0.29%) = 1.0725. So Voc @ 0°C for each panel is 39.4 x 1.0725 = 42.26 V. Times 13 panels is 549 V, which is under the 580 V rating.

That was my thinking exactly. See below

On 2019/08/14 at 10:17 PM, Jaco de Jongh said:

The recommendation for these units were done as follows. 

They used 72 Cell 250 watt panels with VMp = 36.7 Volt and IMP 6.81Amp .

The manufacturer recommended 12 in Series or 2 strings of 10 in series. They also recommend a nominal DC voltage as  360 VDC.

What do I do?

Don't want to blow inverter up and neither do i want under feed 

My thoughts on swapping units was that I will have more daytime solar watts and can increase the load a bit thus saving on the electricity bill

Connecting 9 in series gives me what I have presently

The load I can manage

Edited August 16, 2019 by sulyc

[SYC]

My Axpert spec max 3000w pv and max 4000w load an old one bought 5yrs or so ago, only commissioned last December was building system as finances afforded

But now I've become a solar junky I want more and more and more

[Jaco De Jongh]

29 minutes ago, sulyc said:

What do I do?

I am to afraid to make an recommendation because I know those units and dont want to be the cause that it blow up. 

If i had your panels, the biggest risk I would take, is 2 parallel strings of 6 in series. 

 

[Jaco De Jongh]

9 hours ago, sulyc said:

Honestly my intention is to save enough money so that when I'm a big boy I want to buy Victron system

You will never look back after that day. 

[SYC]

 

17 minutes ago, Jaco de Jongh said:

If i had your panels, the biggest risk I would take, is 2 parallel strings of 6 in series

 

16 hours ago, Coulomb said:

 I think you're right: two strings would be pushing the SCC past its safety limit, so while you might get away with it for a some years, it may well have a shortened life, or might only last a few days.

[Jaco De Jongh]

2 minutes ago, sulyc said:

20 minutes ago, Jaco de Jongh said:

If i had your panels, the biggest risk I would take, is 2 parallel strings of 6 in series

 

16 hours ago, Coulomb said:

 I think you're right: two strings would be pushing the SCC past its safety limit, so while you might get away with it for a some years, it may well have a shortened life, or might only last a few days.

Then I guess 9 is the limit. 

Unless you have smaller panels.