PV Throttling

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mauromartini asked Mar 9, '20

PV Throttling

Hello community,

I need some help please!

I have just installed my system:

1 x Multiplus 48/5000

1 x SmartSolar MPPT 15/70-TR

1 x Venus GX

1 x PylonTech US2000B 2.4kw

12 x 350w Canadian Solar

ESS is installed in 'Keep Batteries Charged'

DVCC -ON

My PV is peaking out at about 3350W. It seems that something is throttling the system.
I have followed the setup recommendation for the Victron/Pylontech setup.

System has been running for 2 days. When I first set up it would not work on ESS 'Optimised without Battery Life'. PV was on and then off, on and then off. I then setup as 'Keep Batteries Charged' and PV worked fine. End of the day, still on 'Keep Batteries Charged' the system went crazy again with PV on, off, on off, on off. I looked closer and it seems liked the 'State' on the MPPT was ESS/Fault.

I then reset as much as I could and everything started working again today. My PV is still peaking out at about 3350W.

Surely I should be getting at least 3800w out of the max 4200w? Is there anything I am missing?

Does this have anything to do with the jumpers on the underside of the MPPT? (untouched out of the box)

Unloaded my voltage is 130v on both strings of PV. Loaded it drops between 94v and 107v

Any help will be much appreciated.

MPPT Controllers solar

screenshot-2020-03-09-172524.png (26.5 KiB)

screenshot-2020-03-09-172532.png (33.5 KiB)

screenshot-2020-03-09-172620.png (48.1 KiB)

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Answer 1 · 2020-03-09T18:44:38Z

Matthias Lange - DE answered · Mar 09, 2020 at 06:44 PM

I think you problem is that you have only one US2000B module.
A single module can be charged/discharged with 25A (continuous - 100A max for 1 minute).

So the BMS is limiting your PV power.
For your setup you should use 4 modules as it is recommended in the guide(you mentioned you followed!?):
https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

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Warwick Bruce Chapman commented · Mar 09, 2020 at 10:23 PM

This what I posited too, but I cannot explain the 3300W?

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mauromartini commented · Mar 10, 2020 at 05:21 AM

That’s the obvious answer. However it does not make sense. I am getting more that 25A but less than 30A from the PV. Also - once the battery is full why would the output from the PV matter as it is going directly to AC and grid?

I did certainly follow the setup instructions but as you pointed out I am short a few batteries (cost)

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Matthias Lange - DE ♦ mauromartini commented · Mar 10, 2020 at 06:13 AM

PV current ≠ battery current (MPPT output)

Do you have a screenshot of the MPPT output voltage/current at the same timestamp?

@warwick I think at the time you see at the screenshot there was a (big) load running at the AC OUT of the MultiPlus.
So all the available PV power goes straight into the Multi and the loads.

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Answer 2 · 2020-03-10T10:00:27Z

danepb answered · Mar 10, 2020 at 10:00 AM

I have seen this before.

If you set your ESS SOC to 95%, see if that changes anything. I have noticed with a pylon if the SOC is set to 100%, the MPPT does throttle the unit, even when feed in excess power is enabled.

This is due to the battery voltage and the need of +-0.3V over the absorption voltage to feed back the excess power.

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mauromartini commented · Mar 10, 2020 at 10:21 AM

Ok thanks @DanePB. Would that mean I need to rather use the ESS Optimized (without battery life)

Little new to this.

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mauromartini mauromartini commented · Mar 10, 2020 at 12:59 PM

If so it did not help.

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Answer 3 · 2020-03-10T13:03:35Z

danepb answered · Mar 10, 2020 at 01:03 PM

I use the ESS Optimized (with battery life).

Give it a try

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mauromartini commented · Mar 11, 2020 at 09:22 AM

@DanePB This works and I quickly got up to 3700w (slightly cloudy day) but as soon as Battery Life kicks in it drops down to about 60w.

So I retried it without battery life and set the SOC to 95% (think I forgot to 1st time) and seems to be working now!

It seems to be constantly charging and discharging the battery (top 5%) is that going to damage the battery?

Thank you very much

*Update: seems that it is when ESS #1 is active that the PV drops right down.

Another thing I tried is to disable the DVCC while on keep batteries charged. Is there any implication to not use the DVCC?

@warwick

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Warwick Bruce Chapman mauromartini commented · Mar 11, 2020 at 11:00 AM

DVCC is compulsory with ESS and Pylontech.

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mauromartini Warwick Bruce Chapman commented · Mar 11, 2020 at 06:17 PM

Yes correct. Compulsory according to the manual. Reading the manual is not the problem. I need to get max yield or my spend on solar is partly wasted

Question still stands - what is the implication (other than the obvious stated in the manual that battery warranty may be void) of not using DVCC?

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Warwick Bruce Chapman mauromartini commented · Mar 12, 2020 at 06:00 AM

I don’t know. But if you find out, please let me know.

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Answer 4 · 2020-03-10T14:36:23Z

nigelfxs answered · Mar 10, 2020 at 02:36 PM

Surely I should be getting at least 3800w out of the max 4200w? Is there anything I am missing?

The rated solar power is based on "ideal" conditions with 1000W/m^2 illumination from the sun.

Your actual solar production is also affected by the mounting angle, mounting direction, temperature and your location (latitude). It is also worth checking that there is no shading of any part of the panels.

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Warwick Bruce Chapman commented · Mar 10, 2020 at 03:15 PM

I would agree with that, were it not for seeing a very clear flattening off as a result of throttling on the graphs. The peak potential of the panels is not being reached.

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nigelfxs Warwick Bruce Chapman commented · Mar 10, 2020 at 06:33 PM

Another possibility is thermal limiting if mounted without proper ventilation.

The "flattening off" of the current curve could also be due to clouds? I have also seen similar odd graphs when a shadow just catches the edge/corner of a panel. It's easy to overlook the potential impact of panel shading, especially as seasons change. I once had temporary shading from a tall crane from a neighbouring construction site!

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mauromartini nigelfxs commented · Mar 10, 2020 at 06:47 PM

At first it did actually get very hot (still only up to about 3350w). After that I put a small fan and it is barely warm now.

On the days in question there were no clouds at all. Perfectly clear.

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Answer 5 · 2020-03-10T16:13:44Z

aaronsb answered · Mar 10, 2020 at 04:13 PM

What's your DVCC maximum charge current set at? Can you post a graph of DC voltage/amperage for the same time period of your battery as well?

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mauromartini commented · Mar 10, 2020 at 06:55 PM

It is not limited at all.

Correct one needed?

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screenshot-2020-03-10-205414.png (120.8 KiB)

Answer 6 · 2020-03-11T09:50:54Z

petajoule answered · Mar 11, 2020 at 09:50 AM

I'm not sure I understand the problem here.

You write you have a MPPT 15/70-Tr.

I assume you do have a MPPT 150/70-Tr. I also assume you have a 48V system. The MPPT is able to charge with 70A max.

48V * 70A = 3360W

You get 3350W - where is the problem?

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Warwick Bruce Chapman commented · Mar 11, 2020 at 10:57 AM

70A charge current is not the constraint in this case because feed in is enabled and the battery is fully charged.

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mauromartini commented · Mar 11, 2020 at 06:12 PM

@PetaJoule you are assuming dc output.

I am referring to PV yield. Panels are 4200w and my mppt is 4000w rated.

I actually got up to 3700w today turning DVCC off

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petajoule mauromartini commented · Mar 11, 2020 at 06:49 PM

@warwick @mauromartini

Yes, I am referring to the DC output. Because all energy going into the MPPT, has to come out eventually. If that doesn't happen, the MPPT would start to glow (which would also be "energy coming out"). And vice versa: energy that can't get out should not come in. Therefore the SmartSolar limits excess energy in.

How does energy "come out"?

The SmartSolars are first and foremost chargers with a certain capacity. That capacity is mentioned in the second number of the model type. In this case 70 => 70Amps.

It's completely irrelevant if the battery is full or not, 70A is the maximum output of the thing. If there is a voltage of - say - 52V, then the power output is 52 * 70A max. If you like to vex your Pylontech, you can push 3700W @ 57V - of course.

These 70A is - in fact - the single hard current limit of this particular MPPT model. (the even harder voltage limit for PV in is the other number in the model name - 150V which - if higher - will even destroy the MPPT)

If the battery is sitting there, full at 57V and your Inverter (Quattro, Multi) is sucking 4000W, the MPPT can provide them (see below).

---

The 150/70 is not "rated 4000W". That is the "nominal PV power" it has been designed for IF you use a 48V system. That's more or less a point of orientation. Of course you can add more PV power (which you do) or less.

Therefore this "nominal PV power" depends on the battery voltage, because as we know the 70A is a fixed given, 70A * Vbat ~~ "nominal PV power". Keep P_in and P_out balanced. (else glow)

So:

If you want the questionable joy of seeing your MPPT pushing 4000W, all you need to do is to

a) have all panels clean, not shadowed, in optimum angle tilted towards the sun on a very sunny, but not hot day in a region with at least 1000W/m² irradiance

b) have your DC output voltage at 57.143V

maybe c) configure your MPPT to still blast away (and not limit) with 57V V_bat.

That would be fun - especially for the Pylons - but I still do not understand where the problem is. You want to destroy your pylons or you want to be with your MPPT output as near to your theoretical PV output (Wp - the p is for "peak") as possible?

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Matthias Lange - DE ♦ petajoule commented · Mar 11, 2020 at 07:27 PM

Thumps up! :)

@mauromartini The absorption voltage for the Pylontech batteries is 52V, so the maximum power you can get from the MPPT is 52Vx70A=3640W.
The Victron MPPT has an efficiency of 98%(if I remember correctly), so from PV-power to battery-power you lose 2%.
3640W+2%=3713W max. PV-power you can get in your system.

But as I sad in my first answer, as long as there are no loads running at the AC OUT of the MultiPlus, the single battery module will limit the charging current from the MPPT to 25A (52Vx25A=1300W)

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Warwick Bruce Chapman petajoule commented · Mar 11, 2020 at 07:36 PM

Like! Thanks @PetaJoule, some useful lessons in there.

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mauromartini petajoule commented · Mar 12, 2020 at 08:27 AM

@PetaJoule Thanks. Some good info here. Suppose it is me being uneducated in this.

Why then when I put the ESS into Optimized with battery life, I get 3600w odd (wasn't full sun). However when SOC #1 is started the system get limited to about 60w?

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mauromartini commented · Mar 12, 2020 at 08:25 AM

The problem is I have 4200w of panels and a 4000w MPPT so I am wasting power.

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petajoule mauromartini commented · Mar 12, 2020 at 09:19 AM

No, you aren't "wasting power". Or - in my opinion - you aren't wasting enough power.

First off, you do not have 4200W of PV power.

You have 4200Wp (Watt-peak of PV power) that is 4200W under optimum conditions. Usually, it's a good idea to oversize the PV array, because most of the time you actually do not have optimum conditions, so many installations are designed to sacrifice their theoretical peak power (which is shaved off) for a more continuous delivery of PV power throughout the year.

See also https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/

and there "Oversizing PV array". It's actually something we do extensively in customer installations on a regular basis. Quite frankly, it's bad system design if you would scale your installation for peak conditions only, because then you would have designed your installation correctly for 5% of the time and wrongly for 95% of the time.

Second, as I already mentioned in my longer text, you do not have a 4000W MPPT. You have a 70A MPPT.

So I think, the problem is merely a difference between (false) expectations and reality.

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mauromartini petajoule commented · Mar 12, 2020 at 11:39 AM

@PetaJoule Thanks for clarifying. Appreciate the feedback.

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PV Throttling

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