Victron SCC's and oversizing of PV array

[Kiwi2000]

Having recently upgraded from Epever SCC's I had always thought in terms of their 1.5 times max of oversizing of PV relative to the max output of the SCC.

But I was playing around with Victron's MPPT calculator recently and it seems like they are happy with substantially oversizing the PV array relative to the SCC.

This page here explains their reasoning...

Matching solar modules to MPPT charge controllers - Victron Energy

Life used to be so simple; in a 12V battery system you took a ‘12V’ solar module, watched carefully that the maximum PV current would not exceed the charge controller maximum current and the system would work. Unfortunately due to the fact, that with PWM controllers the PV module is not feeding...

www.victronenergy.com

"You can now for example add the same type of modules in parallel later without the need to change the MPPT charge controller. This reduces costs to a minimum, whilst still increasing the yield!"...

..."The big advantage in doing this is that you will now produce the maximum controller output at a lower irradiation. As module prices decrease, this is an effective option"

Sure you need to keep under max voltage but you could add in more strings in parallel and substantially overpanel the SCC in terms of watts.

I have already tried this approach with one array and like the results. 1200 watts of PV feeding to a 100/50 SCC on a 12v system. 6 200w panels in a 3S2P arrangement.

Advantages are a more consistent output during the day. Also more consistent in cloudy weather. Each day I have collected around the same kwh regardless of the different weather conditions.

As such I think it'll be more consistent production throughout the year getting closer to the southern hemisphere's winter months of June and July. Instead of having ample surplus production during the summer months and struggling getting towards winter.

It's not that I'm just throwing away potential summer production. I can build my system to max out what the busbars and cabling and batteries can handle under good blue sky production and yet cloudy weather production isn't far off that as well.

What I am noting is the SCC running much warmer than the others because it's at its max amperage output for hours straight compared to the others that only hit their max output around the middle of the day.

Have any others have been doing this with Victron SCC and have the controllers handle it fine over a longer term?

 

[chrisski]

What I am noting is the SCC running much warmer than the others because it's at its max amperage output for hours straight compared to the others that only hit their max output around the middle of the day.

I notice this also. I do not expose my MPPT to the sun or it will heat too much and derate, producing 3/4s the wattage.

Have any others have been doing this with Victron SCC and have the controllers handle it fine over a longer term?

Perhaps twice a month I set mine up overpanneled. I’ve done this for two years.

I have a 75/15 that I have on a 24 volt system that maxes out at 15 amps and 410 watts. I have not seen degradation. I use up to 900 watts of panels, 300 watts to a string.

If this were used everyday, I’d add another SCC and throttle production back to 75%, for example max 10 amps through each SCC. I would not want it running warm day after day year after year.

 

[Kiwi2000]

If this were used everyday, I’d add another SCC and throttle production back to 75%, for example max 10 amps through each SCC. I would not want it running warm day after day year after year.

I'm curious to see what happens and am just going to let it run like this indefinitely. Broken cloudy days which is very common where I live will give it cool down periods and also when reaching float earlier in the day won't stress it so much anyhow.

If it does die a premature death, I'll just replace it with say a 150/70 and limit output to 50 amps. The bigger unit should run cooler like that.

 

[noobie]

I had wondered about this, like how much can you over panel? According to the manual for the 250/100, it says max short circuit current of 70A

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

The 250/100 says it can support 5800W which at exactly 250V would be 23.2A
A more realistic/safer voltage of around 220V maybe you are at around 26A or so

So if they say you can go up to 70A, it does seem to support a very large and over sized array.
BUT, if you had something that could produce 90A short circuit current and plug it in to a single 250/100 SCC, then it may damage the controller.
"A PV array with a higher short circuit current may damage the controller."
70A on one set of cables from your array seems pretty crazy though.

And although the SCC would only pull its max amperage, the cables surely should be rated for the max short circuit current. Which would require over sized wires.

 

[chrisski]

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I had wondered about this, like how much can you over panel? According to the manual for the 250/100, it says max short circuit current of 70A

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

The 250/100 says it can support 5800W which at exactly 250V would be 23.2A
A more realistic/safer voltage of around 220V maybe you are at around 26A or so

So if they say you can go up to 70A, it does seem to support a very large and over sized array.
BUT, if you had something that could produce 90A short circuit current and plug it in to a single 250/100 SCC, then it may damage the controller.
"A PV array with a higher short circuit current may damage the controller."
70A on one set of cables from your array seems pretty crazy though.

And although the SCC would only pull its max amperage, the cables surely should be rated for the max short circuit current. Which would require over sized wires.

I think 70 amps of of short circuit panels allows that a large number of strings to be fed by different parallel strings to keep the MPPT output maxed out or clipped for a situation where someone may want to keep a maximum output from the MPPT, rather than maximize production from the same amount of panels.

If someone wanted to level 2 charge a car 4500 watts throughout a sunny day with this 250/100 without having a larger battery pack as a buffer, three parallel strings could be built facing South East and West to take advantage of the sun.

I have a much smaller Victron 75/15 SCC that I Have 900 watts of panels. My goal is to have 230 watts pushed by the SCC throughout the day so that 230 watt load will run for up to 10 hours with a 1200 wh battery pack. I set 300 watts of panels up South, 300 Watts East, and 300 Watts West, and throughout the day, my panels keep the load going for a total of around 2.3 kWh, but the potential for 900 watts of panels in a South Orientation is much more than that.

I have not seen any Victron documenting of what this max short circuit amperage exactly is. I define it as a sum off all the ISC of the parallel strings. I could very well be wrong.

 

[Samsonite801]

I have not seen any Victron documenting of what this max short circuit amperage exactly is. I define it as a sum off all the VOC of the parallel strings. I could very well be wrong.

I usually see that Victron DOES document max Isc amps on their Specs sheet PDFs ( Max. PV short circuit current - Footnote 2 - A PV array with a higher short circuit current may damage the controller. )...