Charge Controller Limitation

[caymaanedge]

I have 1140watts of Solar and an MPPT which will handle 1200watts @ 12v. I am considering adding another array of 3-panels, 570watts. I know at full sun the MPPT will limit the power generation, but at anything less than that, which is 95% of the time, I will see a bump of output up to 50%.
Is this a mistake? Downside?
I don't want to add another controller right now and adding three more panels is very easy.

Thanks!

 

[Texas-Mark]

Some have recommended having some panels face East and some West to extend the solar time instead of wasting it during peak hours.

 

[Bob142]

I have 1140watts of Solar and an MPPT which will handle 1200watts @ 12v. I am considering adding another array of 3-panels, 570watts. I know at full sun the MPPT will limit the power generation, but at anything less than that, which is 95% of the time, I will see a bump of output up to 50%.
Is this a mistake? Downside?
I don't want to add another controller right now and adding three more panels is very easy.

Thanks!

What's the make and model of the MPPT?
How are your current panels wired together?
How do you propose wiring in the additional 3 panels?

 

[12VoltInstalls]

There’s another thread recently with calcs for overpaneling without hurting your charge controller. Get the specs for your SCC and read that thread to figure out if you’re ok or not.

Spreading the load over the day with separate facing arrrays has worked for me to get bulked up early in the day and still be at full charge near sundown. I suspected it would help me but was surprised by how good it works.

 

[caymaanedge]

Victron MPPT 150/85
Currently I have 6-190watt 12v panels 3S2P
Hadn't given wiring any thought yet....
VOC 24.3v
9.36amps

 

[Bob142]

Make sure you do not exceed the 150V input. Read this as it should be helpful (there's a section on Oversizing a PV array):

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

 

[Wellbuilt]

All most a 3rd is a lot but I don’t think it will kill the cc .
My controler is rated for 4000 watts and I have 4500watts no problem
I think less power = less heat = longer life .
But I know guys that have 18 panels hooked up 5400 watts and it works fine .
You can always just turn a string off in the summer when you are getting full power from the son .
In the winter I get about half power any ways

 

[jamiko]

You could buy another MPPT and just put the new string on it.

 

[caymaanedge]

So this is what it says

Determining the maximum PV open circuit voltage​

First look at the datasheets of the solar panels to see what their maximum open circuit voltage is. Then multiply that by the number of panels that are in series in the array. The result of the multiplication must not be higher than the Maximum PV open circuit voltage as listed on the MPPT Datasheet. Make sure to take into account the coldest expected temperature. The colder it is, the higher the open circuit voltage on a PV array will be.

Determining the maximum PV short circuit current​

Get the maximum PV short circuit current from the PV Panel datasheet. Multiply by the number of panels in parallel in the array. Having more panels in series does not change the number.
The result of the calculation may not exceed the Max PV short circuit current as specified in the MPPT Datasheet.

Current Data 3S2P
Max OV Open Circuit Voltage 24.3*3=72.9v MPPT Max 150v
Max PV Short Circuit Current 10.15*2=20.3amp MPPT Max 85amps

https://www.victronenergy.com/upload/documents/Datasheet-Blue-Solar-Charge-Controller-MPPT-150-70-&-150-85-EN.pdf

So this lead me to believe I could run up to a 5S2P, 6S2p, 3S3P etc. and be under those limits.
Where does the 1200watts @ 12v or 2400watts @ 24v come into play?

 

[jamiko]

So this lead me to believe I could run up to a 5S2P, 6S2p, 3S3P etc. and be under those limits.
Where does the 1200watts @ 12v or 2400watts @ 24v come into play?

If your battery system is 12V then you are limited to 1200 watts solar. If your battery system is 24V then you can go up to 2400 watts solar. What is your battery system voltage? You also need to stay under 150V VOC for your MPPT controller which could only be 120V depending on minimum estimated outside temperature in your area.

 

[Bob142]

So this is what it says

Determining the maximum PV open circuit voltage​

First look at the datasheets of the solar panels to see what their maximum open circuit voltage is. Then multiply that by the number of panels that are in series in the array. The result of the multiplication must not be higher than the Maximum PV open circuit voltage as listed on the MPPT Datasheet. Make sure to take into account the coldest expected temperature. The colder it is, the higher the open circuit voltage on a PV array will be.

Determining the maximum PV short circuit current​

Get the maximum PV short circuit current from the PV Panel datasheet. Multiply by the number of panels in parallel in the array. Having more panels in series does not change the number.
The result of the calculation may not exceed the Max PV short circuit current as specified in the MPPT Datasheet.

Current Data 3S2P
Max OV Open Circuit Voltage 24.3*3=72.9v MPPT Max 150v
Max PV Short Circuit Current 10.15*2=20.3amp MPPT Max 85amps

https://www.victronenergy.com/upload/documents/Datasheet-Blue-Solar-Charge-Controller-MPPT-150-70-&-150-85-EN.pdf

So this lead me to believe I could run up to a 5S2P, 6S2p, 3S3P etc. and be under those limits.
Where does the 1200watts @ 12v or 2400watts @ 24v come into play?

Interesting. I've never seen a Victron MPPT datasheet list maximum solar array input power before. Typically they list nominal PV power which I've always equated to the the max power the charge controller can deliver to your battery. You can over panel safely as long as you follow the rules stated above, but your charge controller can only deliver 85A max to your battery bank. For example, 85A x 14.4V = 1,224W. Your model caps the power at 1,200W.

 

[caymaanedge]

Interesting. I've never seen a Victron MPPT datasheet list maximum solar array input power before. Typically they list nominal PV power which I've always equated to the the max power the charge controller can deliver to your battery. You can over panel safely as long as you follow the rules stated above, but your charge controller can only deliver 85A max to your battery bank. For example, 85A x 14.4V = 1,224W. Your model caps the power at 1,200W.

I guess I thought the 150/85 was for input, 150v Max and 85amp Max. You're saying the 85amps is the max the controller can put into the batteries, which does equate to a little more than 1200watts.

 

[Bob142]

I guess I thought the 150/85 was for input, 150v Max and 85amp Max. You're saying the 85amps is the max the controller can put into the batteries, which does equate to a little more than 1200watts.

This confuses people all the time. Especially because the max input current is the same as the charge current. Here's a blurb right from Victron's site:

"In our MPPT model names, for example MPPT 75/50, the first number is the maximum PV open circuit voltage. The second number, 50, is the maximum charge current."

Solar Charge Controllers - Victron Energy

Get the highest attainable efficiency from sunlight, even if it is limited, with the solar charge controllers from Victron Energy. Find a dealer nearby.

www.victronenergy.com

 

[Wellbuilt]

Yes a max of 1200 watts only give you about 80% of rated power and that is at noon on a good sun day .
My panels are 3 in series @295 watts for 885watt total but the max power I see is around 750 watts and that
is for a short time I get 700watts for 4 hour in good sun.
Then there is the nec 20% rule