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mark-m avatar image
mark-m asked

Maths on mixed solar panels

New to the forum and after some advice on my maths on a possible solar set up on my upcoming camper build. Due to roof size I’m looking at mixing panels. Plan is for Victron blue solar mono panels using two 175w and two 55w. The mppt will be feeding into a 48/5000/70 Multiplus-2 and 9.6 kWh pylontech battery bank.


2 x 115w in series = 38.8v @ 9.03a

IMPP 9.03a

VMPP 19.4v

VOC 23.7v

ISC 9.89a


2 x 55w in series = 37.6 @ 2.94a

IMMP 2.94a

VMPP 18.8a

VOC 22.9v

ISC 3.22a


Then wired in parallel coming out to 37.6v @ 11.97 = 450w (a loss of only 10w)


Is this maths correct or have I missed something?


Then as to which MPPT -


2 x 55w panel ISC 3.22a

2x 175w panel 9.89a

+20% =31.36a


2 x 55w panel VOC 23.7v

2x 175w VOC 22.9v

+3.5% =96.46v


So a Smart solar 100/50 will be correct?


Looking forward to any advice, help.

Thanks

Mark





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4 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Your maths is bad.

Pylontech batteries are 48v?

You have chosen an Mppt that is only capable of 24v battery.

Your pv array is unsuitable for a 48v battery system.

For such a large inverter and battery, you would be better off with a much larger pv array.

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mark-m avatar image mark-m commented ·

Hadn’t realised I’d chosen one of the few smart solar controllers not able to charge at 48v. Thanks for pointing that out. And yes the pylontech us2000 are 48v. The size of the solar array is unfortunately dictated by availability of roof space but a portable auxiliary panel to supplement is probably on the cards.
if you could point out where the maths went wrong, it would really help with any further calculations I try to do. Cheers Mark

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klim8skeptic avatar image klim8skeptic ♦ mark-m commented ·

In all reality's a 460Wp solar array would take 18 hours under full sun to charge your 48v-180Ah battery from flat.

Perhaps you are not in reality expecting much of a load on your system..

Perhaps you are expecting to be plugged into mains or a generator for 4 hours each day..?

What exactly do you expect your daily loads to be?

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mark-m avatar image mark-m klim8skeptic ♦ commented ·

Around 2.5kwh. Biggest consumers being hot water (not always on but if used 48v 1500w for 1hr a day) and stove (2000w for probably 1/2 an hour). The dc to dc is a 3000w buck boost system which should charge the system quite quickly when engine running but I’d like to be able to go at least a week or more without starting the van. Mains hook up is a last resort. And the efficiency of the buck boost should negate the need for a generator.

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Ulrich avatar image
Ulrich answered ·

Hi Mark,

if I know correctly, then you cannot combine different modules with one another.

If the voltages are different, the MPPT controller cannot find the optimal operating point. If the currents are different, the modules with less current flow are short-circuited and thus their voltage breaks down.

I can't tell you exactly how the MPPT solar charge controller works. Perhaps you can first set up your system for a test to see whether you still need a second MPPT solar charge controller, or whether one is enough.

There is an MPPT calculator on the Victron site (https://www.victronenergy.com/mppt-calculator). Here you can enter all the data and you will be shown the appropriate MPPT solar charge controller.

I hope I could you help a bit.

greetings

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mark-m avatar image mark-m commented ·

Thanks. I was under the assumption that using panels of the same make and series of voltages were similar I might have been able to mix.I did play with the MPPT calculator but couldn’t get it to work with multiple strings(think that’s the terminology) of different panels, and that’s probably because you’re right in saying that it’s not possible. Thanks for the response and help.

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mark-m avatar image
mark-m answered ·

Using the MPPT calculator it looks like 4 x115w panels and a SmartSolar MPPT 150/35 would be the best option. Guess I was just trying to be too cute mixing panel sizes.

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myhomebuzz avatar image
myhomebuzz answered ·

mark-m

The parallel setting of solar panels must have the same voltage and always with diodes, otherwise: fire.

In your case, the parallelization of this small world will not work.

Better to put in series. You can watch these videos very well explained in French, but in English translation possible.

In parallel : Parallel

In serial : Serial


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