Hi Guys

 

I am looking at a 8Kw sunsynk to replace my 5kw Growatt.

 

I currently have 12 x 315 Watt JA Mono Panels I want to keep these but also add 10 x JA 540/550 Watt Panels. So basically 12 on one input, and 10 new panels on the other input 

 

Will it be an issue to have different string sizes on different MPPTs ? I have done this before on a Mecer 10kw 3ph with no issues in service for 3 years now

 

Just wanted to if its recommended or not, if not will sell up the 12 panels and just get another 10 of the same

There's no issue with this. In fact it's the reason why there are two independant MPPTs

2 minutes ago, Speedster said:

There's no issue with this. In fact it's the reason why there are two independant MPPTs

Thanks been told differently, so thought I would check with the forum first, happy now! Thanks sir

2 minutes ago, Treschen said:

Thanks been told differently, so thought I would check with the forum first, happy now! Thanks sir

As long as each string is within the MPPT spec (450V Voc, 22A Isc) you're good to go. Also assuming you reach the minimum voltage but that shouldn't be an issue with the amount of panels you're looking at. 

2 hours ago, Treschen said:

Hi Guys

 

I am looking at a 8Kw sunsynk to replace my 5kw Growatt.

 

I currently have 12 x 315 Watt JA Mono Panels I want to keep these but also add 10 x JA 540/550 Watt Panels. So basically 12 on one input, and 10 new panels on the other input 

 

Will it be an issue to have different string sizes on different MPPTs ? I have done this before on a Mecer 10kw 3ph with no issues in service for 3 years now

 

Just wanted to if its recommended or not, if not will sell up the 12 panels and just get another 10 of the same

Just a warning. The JA 540W panels have a Voc of 49.6V at 25deg. This will already exceed the 450V input to the MPPT and can go higher at lower than 25deg on cold days.

I agree with @Scorp007, rather don't put 10 540W panels on one string, but 9x JA 540W panels, especially for cloud voltage spikes. This phenomenon happens when the sun moves past a cloud, and strikes the cold panels which produce a high voltage for a short time. Anything over 500V will blow the MPPT.

8 hours ago, TimCam said:

I agree with @Scorp007, rather don't put 10 540W panels on one string, but 9x JA 540W panels, especially for cloud voltage spikes. This phenomenon happens when the sun moves past a cloud, and strikes the cold panels which produce a high voltage for a short time. Anything over 500V will blow the MPPT.

Thanks makes sense, the JA panels are really efficient. 9 will have to do for now

8 hours ago, Scorp007 said:

Just a warning. The JA 540W panels have a Voc of 49.6V at 25deg. This will already exceed the 450V input to the MPPT and can go higher at lower than 25deg on cold days.

Noted sir thanks for bringing this up

4 hours ago, Treschen said:

Thanks makes sense, the JA panels are really efficient. 9 will have to do for now

I’m trying to do the same, I got a quote from solar and inverter warehouse for 18 x 545watt Jinko panels and the guy there told me 9x per string was to many. He said 8 is 400v and then you have to add 8-10% for safety which puts it to 450v. The manual of the 8kw sunsynk says max of 425v per mppt so you would be over 500v with the safety measure in place if you had 9 panels. I don’t know how true this is but I was going to buy 16 rather so I don’t stuff something up

13 hours ago, TimCam said:

I agree with @Scorp007, rather don't put 10 540W panels on one string, but 9x JA 540W panels, especially for cloud voltage spikes. This phenomenon happens when the sun moves past a cloud, and strikes the cold panels which produce a high voltage for a short time. Anything over 500V will blow the MPPT.

Just a slight correction as can be seen on the graphs. The voltage is higher when the panels are not producing power. The moment the sun comes out behind a cloud the voltage will drop and the panels produce high amps. At 10h08 the inverter was off thus the voltage is high. At 10h13 the inverter was on and producing power.

4 hours ago, Derek Ramos said:

I’m trying to do the same, I got a quote from solar and inverter warehouse for 18 x 545watt Jinko panels and the guy there told me 9x per string was to many. He said 8 is 400v and then you have to add 8-10% for safety which puts it to 450v. The manual of the 8kw sunsynk says max of 425v per mppt so you would be over 500v with the safety measure in place if you had 9 panels. I don’t know how true this is but I was going to buy 16 rather so I don’t stuff something up

Yeah I see what you mean even at 9 you literally on 450v, I might need to sell up the JAs, and do 16 as well to be on the safe side. This is an expensive inverter so don't want it to be on its limits in any case will stay within limits always. Just the insane price of panels at the moment is something that my sway my decision 

How the sun can overshoot the voltage as it peek's out from the clouds, and energises your cold solar panels.

 

The MPPT's will Track the Maximum  Peak Power  available from your solar panels by adjusting the resistance in-line with the panels. This is also dependant on load, and if load is low, the MPPT's are dialled back by also increasing the resistance. MPPT's are not instantaneous circuits, but have hysteresis as they find the Maximum  Peak Power. This hysteresis can be seen when the inverter has no Eskom input during load-shedding, and is working on Solar during the day. If you switch the kettle on, the inverter will draw power from the battery for a second or two, while the MPPT's adjust to the new load.

 

Understanding MPPT's (29 Sept 2020)

https://www.youtube.com/watch?v=C1lNAuUhlnk

 

On a cloudy day, as the sun peek's out from the clouds and energises your cold solar panels, the photons will dislodge masses of electrons which will increase the current instantaneously, but the resistance hasn't changed yet by the MPPT, this causes a large potential difference (Voltage), as the MPPT adjusts the resistance to find the Maximum  Peak Power. This is the dangerous voltage spike that can overshoot the MAX MPPT voltage, and damage the MPPT circuitry.

 

Hope this make sense.

4 minutes ago, TimCam said:

This is also dependant on load, and if load is low, the MPPT's are dialled back by also increasing the resistance.

What your graphs above are showing is the relationship between load and voltage on the MPPT input. As the resistance in the MPPT increases, the potential difference (Voltage) also increases. As the Load increases, the MPPT will lower the Resistance, therefore lowering the potential difference (Voltage). 👍

2 hours ago, TimCam said:

What your graphs above are showing is the relationship between load and voltage on the MPPT input. As the resistance in the MPPT increases, the potential difference (Voltage) also increases. As the Load increases, the MPPT will lower the Resistance, therefore lowering the potential difference (Voltage). 👍

THANKS. I thought with the inverter off it just measured the panel voltage without trying to add or remove resistance as it was not in a position to produce power via the MPPT.

I've never switched my machine off with the DC switch still on to see what happens, interesting. 🤔

I know with the battery connected and on, and machine switched off, it still powers up internally and the display is on. As for the MPPT's, with your observation it appears they too are powered up and operational, but with no load the Voltage and resistance is high.

Lovely and amazing machines.

So been watching some videos, I see Keith from Sunsynk saying not to exceed 450v on the MPPT side, so assuming that if the VOC is 450v with 9 panels one should be fine, he also goes on to say the absolute maximum the inverter will take is 520v

 

 

1 hour ago, Treschen said:

So been watching some videos, I see Keith from Sunsynk saying not to exceed 450v on the MPPT side, so assuming that if the VOC is 450v with 9 panels one should be fine, he also goes on to say the absolute maximum the inverter will take is 520v

 

 

It depends how much of a chance of frying your inverter you want to take, remembering that cold panels can have voltage quite a bit higher than their spec. 

Edited July 10, 20223 yr by Speedster

50 minutes ago, Speedster said:

It depends how much of a chance of frying your inverter you want to take, remembering that cold panels can have voltage quite a bit higher than their spec. 

After looking at my own Voc over 3yrs and during cold spells like the recent minus 4 my panels did not even reach the Voc as per 25deg spec. Based on the 450-520V safety margin I do belief its not something that will easily happen but NEVER is a long time. 

It will be interesting to see members Voc during cold periods vs the spec at 25deg.