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jsmvanwyk avatar image
jsmvanwyk asked

MPPT Throttling

Good day

I have 2 x 48/5000/70 Multiplusses . I have 1 x 150/100 MPPT with 18 x 315W Canadian Solar's facing due East, connected to this giving a maximum of 5.6 kWp. I have also added recently a 250/100 MPPT with 12 x 355W Canadian Solar giving me about 4.22 kWp which is directly facing West.

The East facing MPPT and panels receives full sunshine very early in the morning (I am based in South Africa, Pretoria). I have noticed that it appears as if the system is throttling my MPPT to between 3200-3400 Watts. I sometimes see it spike up to 4kW but it never sustains it there. My curves are not bell shaped either and are more like chopped bell shapes with a level shape around these 3200-3400 values. I have no shading that blocks the light until about 1:30 pm in the afternoon. I thought that this might be an issue due to the installation but we have gone through it with a fine tooth comb and everything physically checks out. Which left me to believe it is probably ESS throttling my system. I have added load to the system and I have feedback to the grid enabled and no matter what I do I just can't get more out of the system.

I notice exactly the same behavior in the afternoon when maximum sun is available, it maxes it out at around 2700W and has almost identical curves to the issue described above, that it is flat lining it around this value.

My Multiplusses are both microprocessor 26 on version 430 connected in Master/Slave

I have feedback enabled to the grid

My CCGX is on ver 2.20

Both my MPPT's are on ver. 1.37

I have measured my results against 3 different design packages and even drawn in accurate shading etc. and the gap is substantial. I am "missing" at least 30%-40% of potential PV generated. Now I know one can't rely 100% on these values and if there was around a 15%-20% difference I might have accepted it, but 30%-40% is substantial.

I really would appreciate any thoughts that you might have on what could be the issue as I have seen somewhere else that ESS might be limiting the potential of inverting to 80% of the available power and if so that would explain it....but is there a way around it?

Below are the graphs


MPPT Controllers
1541452364057.png (70.1 KiB)
1541452396247.png (79.0 KiB)
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5 Answers
wkirby avatar image
wkirby answered ·

How are your PV modules configured? I mean are they 2S 9P or are they 3S 6P for instance?

I am thinking about what your array voltages are. If the array voltage is dropping to low under high power, then that could limit your output power.

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jsmvanwyk avatar image jsmvanwyk commented ·
Hi,

thank you.

the MPPT 150/100 (18 panels) is configured in 6 strings into one combiner box

the MPPT 250/100 (12 panels) is configured in 4 strings into one combiner box


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porcini avatar image
porcini answered ·

What batteries do you use? What's the VE.Bus state when the carger limits? Is the MP-Setup an one-phase-configuration in an 1-phase-grid?

The 2nd image looks like it would change from bulk to absorption OR limit power because of TEMPERATURE. Is the charger getting warm?

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jsmvanwyk avatar image jsmvanwyk commented ·

HI, I have a Redflow ZBM 10kWh battery. Bulk and absorption states starts early in the morning around 6:30am and then will only go into float at night.

It is a master slave combination with both MPPT's connected to the same bus and yes, it is a one phase system. re. Temperature, It is not getting warmer than other MPPT's I've seen.




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jsmvanwyk avatar image jsmvanwyk jsmvanwyk commented ·

Ultimately what I notice is that if I switch off either one of the MPPT's then the other actually ramps up to provide more throughput. Which makes me wonder why they don't deliver more as I have feedback enabled and at least while charging the battery I should be seeing much higher throughput.


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wkirby avatar image
wkirby answered ·

Right, so turning a MPPT off allows the other one to work at full power, which suggests that there is no problem with the controllers. This is very useful information.
Like you say, something else is limiting the power.
So, what grid code is set for the MultiPluses? I'm not 100% certain about this, but some grid codes may dictate a maximum feed-in power and the Multipluses are feeding in the maximum allowable power for that grid code. In the UK, domestic limit (G83 grid code) is 16 Amps (~4KW). Maybe SA grid code is something similar.

So, if your batteries are full and the Multipluses are feeding in maximum allowed, then your PV power will be limited. Put a big load (kettle) on and see if your PV output increases.
Does your geyser get powered from the MultiPluses?

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jsmvanwyk avatar image
jsmvanwyk answered ·

Hi

The grid code is as below. I also attach a graph with the input current that shows my feedback seems to max out at around 17A.



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jsmvanwyk avatar image jsmvanwyk commented ·

Here's the current fed back..

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PeterM avatar image
PeterM answered ·

Did you ever find out whats limiting your PV output? Perhaps some issue to do wuth having 2 MP's feed to grid? Maybe only one is doing s and the other not?

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