question

peternielsen avatar image
peternielsen asked

What is the reasoning mixing panels West and East on same MPPT ?

Hi,

I have two sided of roof, one pointing almost West, one almost East, (20 degree turned towards east) (location is Denmark) see picture here :

1606384912969.png1606384930400.png

My plan was : 3,7Kw array on West and 2,8Kw on east, my reasoning was that we consume more energy towards the end of the day than in the morning. I am planning doing a DC and AC coupled system using Multiplus II, Fronius and a Victron MPPT.

My plan was to have one side on the Fronius and one side on the MPPT but somebody suggested to different.

He suggested take half East to Fronius MPPT1, half West to Fronius MPPT2 and the rest from West and East in parallel to the Victron MPPT. He said it's better to do this because the MP2 can only charge with 1.5kw on the battery from AC (if there is surplus from Fronius).

Why is that a good idea ?


Here is a full diagramsplit-array.jpg

MPPT ControllersMultiPlus Quattro Inverter ChargerFronius
1606384912969.png (259.4 KiB)
1606384930400.png (242.9 KiB)
split-array.jpg (1.7 MiB)
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4 Answers
Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

As you pointed out elsewhere, Fronius have a paper from 2013 pointing out that East/West banks on a single Fronius MPPT are only marginally less productive than split on two MPPTs and the cost saving of the single MPPT outweighs the production benefit:

1606414651944.png

SE_TA_Efficient_East_West_orientated_PV_systems_with_one_MPP_Tracker_EN.pdf

However, this is for Fronius. The Victron team have yet to address this question to my knowledge and it should be determined first whether the Victron MPPT handles to two conflicting IV curves efficiently.


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peternielsen avatar image
peternielsen answered ·

@warwick thank you, @Guy Stewart (Victron Community Manager) do you have a comment on this?

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peternielsen avatar image
peternielsen answered ·

@warwick if i put the east side on a MPPT 150/45 what would i miss ? If it worked with both sides on same MPPT why is it a good idea to do this ? I didnt understand his reasonings about the MP2 1,5kw charger ? Is it because i can’t charge battery quick enough or ?

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

I’m not sure what the person was getting at but the MP2 3KVA charges at about 1500W but AC to DC losses are, say, 10%. So it is more efficient to charge DC solar to DC battery.

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peternielsen avatar image peternielsen Warwick Bruce Chapman commented ·

@warwick The idea was that when sun comes up and lights up all the panels on the east side then if i had all of them on the Victron MPPT then the MP2 would have to provide for the load in the house e.g power from PV which means it will run at full throttle and the efficiency in the MP2 is not good when it runs at 100% so he said that it's better to split the load so that when sun comes on east both the MPPT and the Fronius MPPT get's sun so the Victron MPPT can charge battery and Fronius which is more efficient making AC can provide battery and the same when the sun comes from the West, that way the battery charges slowly and is full towards the end of the day, does that makes sense ?

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman peternielsen commented ·

Sounds fine to me.

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Trina avatar image
Trina answered ·

wUnless you are dirt poor in ghetto or 3rd world economy the need is better served with 2 separate controllers. Here is why...

1. You MUST have a controller that can handle the voltage of ALL your PV's at ANY given time of day -regardless of amps, the voltage (1st stage in MPPT controller) need to be met or you have limits and complete losses of anything else attached (at best)-negating any gains you hoped to have cutting costs here.

2. You MUST address the possible best solar condition or you will FRY your MPPT at some point -destroying it, and ALL initial cost savings you were attempting to reduce -to the sum of needing to have bought now THREE separate controllers; the 1st (now toast) and two new ones to avoid frying even more.

3. A MPPT (by anyone) large enough to handle all the above will be significantly more expensive than TWO smaller ones which, once you factor in the difference in prices works out to be very minimal in cost vs efficiency! Remember it's not the cost of one huge controller but only that cost vs two smaller ones adequately sized -because you STILL need to have the system PV size needs met.

So if you really can NOT afford that then you bought or got too many PV's and didn't budget -and hence design- correctly IMHO. It is a beginner"s mistake to invest in top notch or new PV's and run out of money when the most important thinga are (in order) - your battery system, monitors, wiring, fuses, controllers and inverters, and lastly the PV's!

I.E. Used grade-b panels can still harvest plenty of voltage and be obtained dirt cheap if you dig around in a modern culture (where you are) -which if you are efficiency and budget conscious might have been the better direction to go in. But since we all make mistakes and this is the most common one for solar (not budgeting correctly for a system's needs) then there are solutions.

A. Go with what you can afford to hook up with correctly sized controller and wiring -morning vs afternoon having best light will depend on your exact area and common weather patterns (where I used to live the clouds would roll in off the ocean in the afternoons most days of the year but where I am now the fog is common until noon so a morning array here is a luxury).

Now if it really is a matter of the budget and unforseen by anyone hurdles and you find you need to somehow finish a system bought or designed out of order then Traces/EPEVER (China) makes an excellent MPPT that can suffice efficiently when you can't afford to get the two MPPT's from Victron! The BN-series can handle the voltage and amps needs and be sized correctly without needing budget problems solved getting similar sized units from Victron.

I have used both and there are a lot of pros on the Tracer-BN series but the biggest con is it is not Victron networking -which is huge for me. The biggest plus is big lugs and higher amps per cost capable.

If this is just theoretical than budget and costs are irrelevant and you would be better served with a MPPT for every series of panels and huge single-roof sized panels that have super high voltage. So aim for THAT everytime!

:D



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peternielsen avatar image peternielsen commented ·

@Trina thank you for your reply,


So first let's get some facts on the table, i have 3 MPPT, 2 in Fronius and one Victron MPPT. I could decide do what i put on the diagram,

East side on the 150/45 (the array is a little bigger than 150/45 but that's ok, it will cap a bit).

West side on the 2 x Fronius MPPT.

The reason i got not to do this is that the loss running a part west and part of east on same MPPT would outweigh the loss of the MP2 (efficiency) when it has run at full throttle, MP2 has heat dissipation of 400W at 3kw !!. The article that Fronius made is here, please do read https://www.fronius.com/~/downloads/Solar%20Energy/Technical%20Articles/SE_TA_Efficient_East_West_orientated_PV_systems_with_one_MPP_Tracker_EN.pdf. , i don't know if this practice can be used here. I have yet to hear from Victron about this.

Regarding burning MPPT i don't see how that's possible when strings are equal e.g you don't mix 3 in serial with 2 in serial. This is not the case discussed here. Here we discuss same voltage east/west, in my case 3s2p west and 3s east, the voltage will never be higher than 120V so no problem.

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