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bladerunnervf asked

Choosing between Victron 250/85, 250/100, 450/100 for East-West facing ~8.5kWp system 48V

I was trying to choose between different MPPTs, comparing victron 250/85, 250/100, 450/100, for a set-up of trying to get 10or11 panels on one roof and 10 on the other for an East-West PV system.

My conclusion was that the 250/100 will handle the most PV panels in parallel and input power, the 450/100 will handle more panels as a single string but less input PV power than the 250/100.

I would choose two 250/100s ?


In particular does the Pmpp variation with temperature dictate the power handling capability of the victron MPPT? e.g. if Pmpp < victron MPPT level at -10C and +40C then all is good?


Have I got it right? Please could someone cast an eye over the method for calculating string voltage and powers for different victron charge controllers please and let me know if I've made any howlers?


Thanks for taking a look


[Edit: I know there's an MPPT calculator on the victron site but you can't select one product and try different panel combinations on it !]



Panels 405W Qcell

https://midsummerwholesale.co.uk/pdfs/qcells-data-sheet-q.peak-duo-m-g11-series-390-410-30t-2022-06-rev02-en.pdf

I think:-

1) The 250/85 will take 6 panels in a string, or 2x5 in parallel, or 5panels into MPPT1 and 5panels into MPPT2


2) The 250/100 will take 6 panels in a string, or 2x6 in parallel, or 6panels into MPPT1 and 6panels into MPPT2, as it will cope with more PV power than the /85 model


3) The 450/100 will take 10 panels in a string, or 5panels into MPPT1 and 5panels into MPPT2,

It cannot be used for two strings in parallel due to PVmax of 18Amps

The Voc max is limited by the battery float voltage [Edit: to 8 x float voltage, which means it can be less than 450V]


String voltage at -10degC example calc, using STC of 25degC

e.g. Voc + Voc*((-0.27/100)*(-10-25))

e.g. 37.18 + 37.18*((-0.27/100)*(-10-25)) = 37.18+3.51 =40.69V


For the power limit then the panel's Pmpp and it's variation vs temperature is what to watch ?

Power at -10degC example calc

e.g. Pmpp + Pmpp*((-0.34/100)*(-10-25))

e.g. 405 + 405*((-0.34/100)*(-10-25)) = 405+48.195 =453.2W


A) Victron 250/85:-

MPPT 250/85, 3x MPPT trackers

PV max power 4900W, Vmax 250V

70A max PV short circuit current, 30A per MPPT

https://www.victronenergy.com/uploa...oller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf


1684017888147.png


B) Victron 250/100:-

MPPT 250/100, 3x MPPT trackers

PV max power 5800W, Vmax 250V,

70A max PV short circuit current, 30A per MPPT

https://www.victronenergy.com/uploa...oller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf


1684018186862.png

C) Victron 450/100:-

RS MPPT 450/100, 2xMPPT trackers

PV max power 5000W, Vmax 450V, 30A per MPPT

https://www.victronenergy.com/solar-charge-controllers/smartsolar-mppt-rs-450-tr

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-MPPT-RS-EN-.pdf



MPPT ControllersMultiPlus Quattro Inverter Chargermppt calculator
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Michelle Konzack avatar image Michelle Konzack commented ·
With the QCells 410Wp I get a maximum Voltage of 248V with 6 modules in series.

I have cooked my SmartSolar MPPT 250/100 with 6 Winaico 410Wp modules because I used the 0,28% from the Vmpp.


If I would have used the Voc then the damage could have been avoided.


My 6 panels delivered 270V @-25°C


Chears!


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bladerunnervf avatar image
bladerunnervf answered ·

Excel for the 450/100...

1684683328486.png


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cacer avatar image
cacer answered ·

The 250/xx have only one tracker.

Just more Inputs, if i am right.

So you can only put east and West in parallel, or use two of them.

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bladerunnervf avatar image
bladerunnervf answered ·

Hi cacer, thanks very much for taking a look :-)


Yes I would use one 250/xx for East roof, and a second 250/xx for West roof, if I understand correctly.


I had thought from the spec that there were three MPPT trackers?

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf

1684699202440.png

but now I look more closely at 3), it says

1684699262082.png


What does this mean for the case of 10 PV panels?

MC4 Connector1 3panels

MC4 Connector2 3panels

MC4 Connector3 4panels

So they are in parallel into the one MPPT tracker ?


So if the MPPT is to work correctly all three MC4 connectors would need 3 panels so that each MC4 connector can be at the same Vmpp for the tracker to work properly?


Thanks



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cacer avatar image
cacer answered ·

it schuld be possible to use one 250/xx

If there is no shadow on both sides it can work good.

East: 5 in series with 5 in series parallel with y connector (mc4 max 30A) into one input on the 250/xx

The same for the westside.

If curent in parallel connection of each side stays under 30A (because of the connectors)


If you got shadows, i would go with 2x 250/xx.

Then no y-connectors needet.


But that is expensive.

Bretter choice could be the 450/100


Sorry for my bad english ;)

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kevgermany avatar image
kevgermany answered ·

With panels with different alignments to the sun, use one MPPT/tracker per set.

Input power is, generalising, not an issue, MPPT will draw what it can handle.

Do not exceed input Isc limits.

As you're aware, do not exceed input voltage limits, especially at low temps.

MC4 connectors are max 30A.

Keep panel inputs to a tracker/MPPT equal in pairs/strings. E.g. 3 in series is ok, but 2 in series plus a single in parallel is not.

With a big, high voltage system like this it's essential to get professionals in for design and installation. You risk expensive mistakes and serious safety problems otherwise.


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bladerunnervf avatar image bladerunnervf commented ·

Thanks kevgermany

interesting to hear MPPT will draw what it can handle,

I was concerned that if I put more PV power in than the PV power limit quoted on the datasheet then it would make the warranty void.

OK as suspected, keep panel inputs equal sized if in parallel, so 3s3p good, 3s2p+2s1p not good (3s2p = 3 in a string, with 2 parallel strings) Other wise the max power point would be odd.

If significant shading then consider additional MPPTs

Yes I would be getting the installers in, if I can actually find any in my area that is!

I'm just trying to understand things as well as I can in advance so I don't make an expensive mistake at purchase time

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seb71 avatar image
seb71 answered ·

Since you must split the PV panels/ PV modules in at least two PV arrays anyway (at least one East facing PV array and one West facing PV array), I would go for separate MPPTs.

One reason is redundancy, the other is lower PV arrays voltages.


Make sure you also include a GX device (such as Cerbo GX) in your system.

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bladerunnervf avatar image bladerunnervf commented ·
Thanks seb71.

Yes at least 2x MPPTs. The original thought was East roof 1x (250/100) and West roof 1x(250/100)

The GX device is for monitoring ?

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bladerunnervf avatar image
bladerunnervf answered ·

Hmmm food for thought. thanks everyone.


Is there any benefit in winter to having

a) 5s2p (5 in a string, with two parallel strings) into a 250/100 with one MPPT OR

b) 6s1p and 4s1p into a 450/100 with two MPPT

it's about the same volts into each MPPT?


For my East roof I think the panels would be arranged like this

PP W PPP

PP S PPP

where P = PV Panel, W= window, S= soil stack

So I had been thinking 4s1p, 6s1p, or possibly 4s1p, 3s2p,

or even 4s1p, 3s1p (upper), 3s1p (lower)


In winter, for East roof, I think the left side panels get sun earlier than right side

LL W RRR

LL S RRR

where L = Left, R = Right


So a 450/100 on East side ? (4s1p, 6s1p) but was concerned in winter that the 4s1p might not reach start-up voltage


For my West roof I think the panels would be arranged like this

PPPPPPP (6 or 7 panels on top row)

PPPP ^^ x

where P = PV panel, ^^ = dormer window with pitched roof, x = narrow gap, not enough space for a panel

There will be some shading from trees in autumn/winter which is very variable as the sun moves behind the trees around 15.00 to 16.00. but they lose their leaves so early winter slightly better than late autumn. The shade affect the left side of the roof first, moving across to the right.

A bit like this at worst for about an hour

ssPPPPP

sssP ^^ x

Rest of the year is good, no shading


I had been thinking 7s1p, 4s1p, in an upper / lower split, or

1112222

1112 ^^ x

where 1 = MPPT #1, 2 = MPPT #2


So a 2nd 450/100 on West side?


I also have a shed which could in principle take two large panels (~600Wp each), flat on the roof. So that would be 5 x MPPT trackers needed ? Not convinced it's worth the extra expense of another PV inverter.


So, in principle, East ~4000 to 4250 Wp, West ~4000 to 4700 Wp, shed 800 - 1200 Wp. South is the gable end wall of the house.

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