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SunSynk 8kW mpp voltage


RichardC

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It's been a while, but a brief update for anyone interested

I've ended up with the following setup:

  • MPPT 1 (Morning sun): 6x 380W panels
  • MPPT 2 (Evening sun): 6x 380W panels
  • MPPT 3 (Main sun direction): 9x 490W panels

Turns out that for this time of the year this is absolute overkill 😜 I've got 14kW of Pylons, deplete them on most nights to around 35% SOC (unless the kids are home and are playing PS5 in the eve...) - and by 10h30 in the morning they are fully charged again already. This is my chart from today:

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I would say that the addition of the string facing the morning sun (yellow below) has made the biggest difference - production starts a whole lot earlier and ramps up significantly quicker

PV.JPG.ba3fbef3949a54dbe4630a35e4020431.JPG

My main string (blue) never even reaches peak production... Evening string not included above. 

Will probably add another Pylon in the near future to cater for A/C during the night as well as kid's PS5. And won't hurt for winter days, when production days are shorter.

But overall really happy with the system 🙂 Total grid usage for Oct was 11kWh

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  • 3 months later...

Just a question. Due to a weird roof lay out I have 2 strings of 7 panels each ( 455w, Uoc 49.1v , Isc 11.53 A ), facing North west and 1 string of 4 panels( same size) facing North - North east. Do I put the 2 x 7 panels strings on the same MPPT and the 4 panels on the second MPPT ? Will the MPPT be able to handle the 23.06amps on a single MPPT ?

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  • 11 months later...

I planned to connect 10 x 550W panels to a 8kW Sunsynk inverter. One installer told me that this could shorten the life of the inverter due to the increased amperage and that I should rather use 12 x 460W panels. Is this a valid concern?

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The overall wattage of the two options will be similar - what your installer is probably alluding to is the fact that 10 of those panels on a single string will exceed the safe open circuit voltage of a string of panels connected in series (max would be 8-9 panels per string). That inverter has two independent MPPT inputs and could easily handle 10 of those panels, albeit across two MPPTs. However, the respective string voltages will then be on the low side (with around 250V Voc spec per string of 5 panels).  The amps aren't so much the issue as that panel's max amp rating is 14A and the MPPT can handle 22A (and would clip the amps otherwise). 

Not sure what the open circuit voltage of the smaller panels is (it also seems to be around 50V based on JA panel specs), meaning a 2 strings of 6 panels per string would have a Voc "spec" of around 300V, which is more optimal than the 250V that 5 units of 550W panels would have (spec).  I'm not sure whether the slightly more optimised string size of the smaller panels outweigh any disadvantages (eg more mounting infrastructure, space availability on roof, prospects also for future expansion, availability of that size panel in future, and so on). 

I'm guessing that the core argument of your installer evolves around getting each string closer to the optimum string voltage range which I believe is around 370V or so (?). If you added 2 more of the 550W panels you'd a similar amount of hardware (or less), yet be closer to the sweet spot, per string. Many other considerations obviously, like size and direction of roof, pitch, possible shading, etc. Sometimes smaller panels fit into certain spaces better, sometimes (as in my case - with plans for 550W panels) certain roof spaces will accommodate a vertically positioned row of panels, but not a second row - so it made more sense for me to go for the larger output panels while I'm at it. 

In summary, your optimal string size would probably be 8 panels (possibly 9). And if a second smaller string is also considered on the other MPPT, ensure that it gets well past the 150V minimum (I think that would mean 4+ panels, albeit not quite sure if one can risk going lower if there's a second larger active string delivering power to the inverter already). 

 

 

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1 hour ago, BenS said:

He claimed the total Amps of the 550W panels (split across 2 strings) would be too high and damage the inverter over time.

I sure do hope that this specific installer is not right about this - as I have a SS 8kw with 10 x 550 watt panels (string of 5 per MPPT) setup as per BenS' first post today. Kalahari Cruiser's explanation makes more sense to me as well. Although in my case it would be the preferred explanation 😉

For reference attached is screenshot of app, today was partly cloudy with full sun at times. At time of full sun one can see the amperage is high 17.x amps on both strings. And the voltage per string is lower than the sweet spot, but higher than the minimum +-150V. Not sure why the power of PV is more than 6300W+, it suppose to be max 5500W (but guess the readings is more an indication than exact and new panels might give higher yield in the beginning than its specified ratings, thumb sucking).

image.png.997a0c138f7b00a76547959c40e1f0a9.png

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2 hours ago, BenS said:

He claimed the total Amps of the 550W panels (split across 2 strings) would be too high

I think one worries primarily about volts and not amps - the MPPT clips the latter but can't do much about the former. Your panels in series shouldn't present any Amps problems, since Amps don't get added together when in series. Installer probably worried about excessive volts per string. Also remember that the SS 8KW inverter has two MPPT with 22A rating each. 10 (or 14) panels equally split across two strings in series wouldn't present any "max" issues either way. 

@jgdt Others are in a better position to comment but my understanding is as follows:

With your 10 panels across 2 strings you're nowhere near the upper limits of the inverter, if anything quite a bit closer to the lower limit. The Voc ratings are used to plan panel string sizes while the maximum power voltage of the panels is much lower - closer to 42V. Your readings seems to be in line with this. Many reports of panels delivering more than their rated power. No idea if this was sales talk or true, but an installer I spoke to recently mentioned that the power rating of one of the popular brands can be considered the minimum spec, whereas the same rating on the other major brand he found to be more of a "up to" power rating (hence he preferred the former brand). 

If the setup is fairly simple (i.e. 2 independent strings to 2 MPPT inputs) then I think one ideally wants to plan for a string Voc of 400-450V (i.e. 8-9 panels per string), and with a relatively constant price per watt, this is then sometimes achieved with a larger number of panels at lower watts per panel (bearing in mind the other issues to consider with this as mentioned earlier). So many different things to consider that are specific to a site and future expansion plans (and inverter size) that I guess it's difficult to generalise.

I've gone for 14 panels (@550W) consisting of 8+6 panel strings (with the roof-space with 8 maxed out, while the one with 6 could potentially get another 2 added to a nearby section at a later stage if needed). 

 

 

Edited by Kalahari Cruiser
clarification
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