Victron 100/20 sizing questions

[woodlecj]

Victron solar experts.

New to this game. I bought the Victron 100/20, which is rated for 290W (12V), but wonder if it’s large enough. Right now I have 2 100W panels, but would like to add two more 100W panels. The 100W are rated Voc 24.3 and Imp 4.91. So if I series string them all, I’m right under 100V and only 5A, but I exceed the 280W rating. Is this controller not capable of four 100W panels? I don’t think series/parallel buys me anything either as its still 400W of solar. Those 75/10 systems must be quite small!

This is just a 12V shed system that has no power right now.

Thanks,

 

[400bird]

How cold does it get where you are? PV voltage increases when it's cold and the rated voltage is at 25°c

At 97.4 VOC, you're too close for comfort unless you live on the equator.

I'd do 3 in series and call it a day. That is assuming all 3 panels have the same specs, sounds like you've purchased them in 2 batches.

Going over the amp limit is fine, and I believe Victron publishes a max spec that is something like double what the unit can actually use.

 

[FilterGuy]

At 20A the controller can put out ~ 12Ax20A = 240W when the batteries are low and ~13VX20A=260W when the batteries are in the flat part of the charge curve.

Lets assume your panels perform at 85% of their rated power (This might be overly generous). In that case 4 100W panels would produce 4 X .85 x 100w = 340W. This is significantly over what the controller will let through, but there is still some value in over paneling a controller. Please review this resource:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

Three panels would produce 3 X 100W x .85 = 255W. Three panels would work well and would not result in very much clipping of the power.

Panel Arrangement.

With a 100/20 controller, the array VOC of 3 panels would be 3 x 24.3 = 72.9V. This is low enough that it would probably be safe in even the coldest situation. However 4 panels in series would be 97.2V. This would be problematic in even slightly cool weather so I would not do 4 in series. Instead, for 4 panels, I would do 2 strings of 2 in series.

 

[woodlecj]

How cold does it get where you are? PV voltage increases when it's cold and the rated voltage is at 25°c

At 97.4 VOC, you're too close for comfort unless you live on the equator.

I'd do 3 in series and call it a day. That is assuming all 3 panels have the same specs, sounds like you've purchased them in 2 batches.

Going over the amp limit is fine, and I believe Victron publishes a max spec that is something like double what the unit can actually use.

I'm in eastern PA, so winter sun angle is pretty crappy. It can get to 0F on a rare instance, but mostly winter is 20-40F. Do I worry about the one 0F day?

 

[FilterGuy]

Going over the amp limit is fine, and I believe Victron publishes a max spec that is something like double what the unit can actually use

I have not seen that.... but what I have seen in the victron specs is a limit on the array Isc current. It turns out that in some cases, this becomes the limit for overpaneling. I tried to get Victron to explain when hos the Isc comes into play, but they declined to answer.

 

[FilterGuy]

Do I worry about the one 0F day?

YES!!! There is a good chance you will blow out the charge controller if you have 4 panels in series. However, 3 panels in series should be fine.

Please review this resource:

Adjusting Solar Panel Voc for temperature

When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...

diysolarforum.com

 

[woodlecj]

At 20A the controller can put out ~ 12Ax20A = 240W when the batteries are low and ~13VX20A=260W when the batteries are in the flat part of the charge curve.

Lets assume your panels perform at 85% of their rated power (This might be overly generous). In that case 4 100W panels would produce 4 X .85 x 100w = 340W. This is significantly over what the controller will let through, but there is still some value in over paneling a controller. Please review this resource:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

Three panels would produce 3 X 100W x .85 = 255W. Three panels would work well and would not result in very much clipping of the power.

Panel Arrangement.

With a 100/20 controller, the array VOC of 3 panels would be 3 x 24.3 = 72.9V. This is low enough that it would probably be safe in even the coldest situation. However 4 panels in series would be 97.2V. This would be problematic in even slightly cool weather so I would not do 4 in series. Instead, for 4 panels, I would do 2 strings of 2 in series.

Thanks for the responses. Let me try to understand what you said. So 2 series = 50V roughly, and 2 parallel = 10A, so I am under spec for this unit, but still can't use 4 panels; correct due to total watts? Sorry to be dense. Maybe I should send it back and get the 100/30 model.

 

[FilterGuy]

Thanks for the responses. Let me try to understand what you said. So 2 series = 50V roughly, and 2 parallel = 10A, so I am under spec for this unit, but still can't use 4 panels; correct due to total watts? Sorry to be dense. Maybe I should send it back and get the 100/30 model.

You can probably use 4 panels but you won't see a huge gain with the 4th panel. Much of the time the controller will be at it's output current limit so it will not pass through the full power the 4 panels could be producing. (This is called clipping). Please review the over paneling document I linked to above.

Victron limits overpaneling through their Array Isc limit. For a 2S2P array, the array Isc will be 2 times the panel Isc. I looked up the 100/20 and it's Isc limit is 20A. I don't know what the Panel Isc is, but you are probably OK.

 

[woodlecj]

Isc = 5.21A. I'm reading that doc right now. Good read! Sounds like I could use all 4 panels. Since I'm in a northern latitude in the winter, I could use all the help I could get from it and don't mind wasting power by clipping in the summer.

 

[FilterGuy]

Maybe I should send it back and get the 100/30 model.

If that is an option and you don't mind the extra cost, getting the 100/30 might not be a bad idea.

 

[400bird]

I have not seen that.... but what I have seen in the victron specs is a limit on the array Isc current. It turns out that in some cases, this becomes the limit for overpaneling. I tried to get Victron to explain when hos the Isc comes into play, but they declined to answer.

I should have clarified, I meant you could go over the mathematical amp (isc) limit. Ei the solar amperage input to get to the rated output (in this case 20 amp output)

 

[ShaneC]

Isc = 5.21A. I'm reading that doc right now. Good read! Sounds like I could use all 4 panels. Since I'm in a northern latitude in the winter, I could use all the help I could get from it and don't mind wasting power by clipping in the summer.

2S2P arrangement would work best then. You could even add more but there's not much point unless you're really trying to max out the charge controller in winter which would be hard anyway.

 

[mikefitz]

Just to clarify the issue with cold. The panel V oc is specified at 25 deg C. As it gets colder the panel Voc increases so four series panels in cold conditions will exceed the 100 volt limit of the controller. The V oc Inreases by about 4% for every 10deg C below 25C.
Edit, sorry, should have looked at all the comments, this has been discussed.

Mike

 

[Q-Dog]

I ran 800 watts of panels through a Victron 100/20 at 24 volts for a couple of months. On a clear, sunny day the controller would shut down after 30 or so minutes of putting out 19.8 amps continuously, I assume to protect itself. It never gave me any errors, just would stop charging for a few minutes at a time until it cooled down a bit. I put a fan on it and that eliminated most of the shutdowns. Went back to 6 panels because I didn't really see enough gain in clouds to justify pushing it so hard in good sun, plus the shutdowns and the fan were cutting into my output in good weather.

I eventually installed a bigger controller, and more panels, and then more panels.

 

[Pi Curio]

I have not seen that.... but what I have seen in the victron specs is a limit on the array Isc current. It turns out that in some cases, this becomes the limit for overpaneling. I tried to get Victron to explain when hos the Isc comes into play, but they declined to answer.

I found this to be very informative.

Victron MPPT SmartSolar 100/20 - Victron Community

community.victronenergy.com

Worth mentioning that some Victron SCCs have lower charging amps but higher Isc tolerance. For instance, a 150/35 has a tolerance of 40A Isc.

Best,
D.

 

[Pi Curio]

I ran 800 watts of panels through a Victron 100/20 at 24 volts for a couple of months. On a clear, sunny day the controller would shut down after 30 or so minutes of putting out 19.8 amps continuously, I assume to protect itself. It never gave me any errors, just would stop charging for a few minutes at a time until it cooled down a bit. I put a fan on it and that eliminated most of the shutdowns. Went back to 6 panels because I didn't really see enough gain in clouds to justify pushing it so hard in good sun, plus the shutdowns and the fan were cutting into my output in good weather.

I eventually installed a bigger controller, and more panels, and then more panels.

Merely curious, did you try lowering the charging current to say, 17-18.5A on 100/20?

 

[FilterGuy]

I found this to be very informative.

Victron MPPT SmartSolar 100/20 - Victron Community

community.victronenergy.com

Worth mentioning that some Victron SCCs have lower charging amps but higher Isc tolerance. For instance, a 150/35 has a tolerance of 40A Isc.

Best,
D.

That thread talks about short-circuiting the input. Other threads on the Victron Community site say the same thing. What no one has been able (or willing?) to explain is why a controller would ever short-circuit the input. It seems to me that if they want to protect from over-charging, they could just turn off the inputs.

 

[Pi Curio]

Victron solar experts.

New to this game. I bought the Victron 100/20, which is rated for 290W (12V), but wonder if it’s large enough. Right now I have 2 100W panels, but would like to add two more 100W panels. The 100W are rated Voc 24.3 and Imp 4.91. So if I series string them all, I’m right under 100V and only 5A, but I exceed the 280W rating. Is this controller not capable of four 100W panels? I don’t think series/parallel buys me anything either as its still 400W of solar. Those 75/10 systems must be quite small!

This is just a 12V shed system that has no power right now.

Thanks,

As others have previously said and I agree, in terms of the SCC Voc and Isc limits 2s 2p would probably be the best panel configuration to be able to use all 4 panels and not worry about the Voc at all.

The part about the 400W array, it depends really.

In my case where my panel is flat mounted vertically, I consider a 400W panel to be a perfect match for my 100/20.


Best,
D.

 

[woodlecj]

Thanks for all of the replies. A lot of good info to digest! On another note:

Very excited today! Hooked up my 2 100W panels in series and would hit 245W at times! Also I hit absorption at 14.2V on Lifepo 12V/100ah battery, don’t I want to hit 14.6, then fall back to adsorption? I’m using the standard Victron Lifepo profile.

 

[pollenface]

The most I got from my 100/20 in 12v is about 256w output (300w panel).

Also I hit absorption at 14.2V on Lifepo 12V/100ah battery, don’t I want to hit 14.6, then fall back to adsorption? I’m using the standard Victron Lifepo profile.

Standard Victron Lifepo4 profile is 14.2v with 2hrs absorption