Something Interesting About Victron Solar Charge Controllers

[tictag]

I learned something interesting about Victron Solar Charge Controllers (SCC) the other day.

Most SCCs on the market provide two important specifications: Maximum PV Voltage and Maximum PV Power, and you can use these to correctly size your SCC to your PV array. Victron SCCs do not follow this trend, they instead provide a Maximum PV Voltage and a Nominal PV Power, for example, here's the specifications for the Victron SmartSolar 100|30/50:



Note the Nominal PV Power, this is basically the minimum PV power required to generate a 30A/50A charge current e.g. 14.6V x 30A = 438W or 14.6V x 50A = 730W etc.

The Maximum PV Power the unit can handle is actually defined by PV Voc (1) and PV Isc (2) i.e. 100V x 35A = 3,500W (100|30) or 100V x 60A = 6,000W (100|50).

And as you can see from note (3), the unit will simply limit input power if the array is more than 440W/700W etc.

So in theory, you could connect a 3,500W PV array to the Victron 100/30 and, whilst you would obviously be leaving 3,060W on the table (!), it would still be operating within specifications (obviously assuming 100V Voc or 35A Isc isn't exceeded).

Clearly, Victron SCCs have been designed with over-panelling in mind, in fact, the chap I spoke to at Victron about this actually recommended 30% over-panelling to optimise output on cloudy days.

 

[gnubie]

I overpanel my Victron. My array can never exceed the max current available limit on the controller's input so as long as I stay within that (and obviously voltage limits), it's all good with Victron. In summer when the sun is square onto the array I hit the load side current limit daily (50 amps). It limits at that and PV floats up a bit in voltage. I'd be leaving about 400 watts on the table while this is happening. With careful panel selection I could bump the array voltage up a bit more and also just add more panels to get more amps and the Victron would still be happy.

 

[Dzl]

I learned something interesting about Victron Solar Charge Controllers (SCC) the other day.

Most SCCs on the market provide two important specifications: Maximum PV Voltage and Maximum PV Power, and you can use these to correctly size your SCC to your PV array. Victron SCCs do not follow this trend, they instead provide a Maximum PV Voltage and a Nominal PV Power, for example, here's the specifications for the Victron SmartSolar 100|30/50:

View attachment 16343

Note the Nominal PV Power, this is basically the minimum PV power required to generate a 30A/50A charge current e.g. 14.6V x 30A = 438W or 14.6V x 50A = 730W etc.

The Maximum PV Power the unit can handle is actually defined by PV Voc (1) and PV Isc (2) i.e. 100V x 35A = 3,500W (100|30) or 100V x 60A = 6,000W (100|50).

And as you can see from note (3), the unit will simply limit input power if the array is more than 440W/700W etc.

So in theory, you could connect a 3,500W PV array to the Victron 100/30 and, whilst you would obviously be leaving 3,060W on the table (!), it would still be operating within specifications (obviously assuming 100V Voc or 35A Isc isn't exceeded).

Clearly, Victron SCCs have been designed with over-panelling in mind, in fact, the chap I spoke to at Victron about this actually recommended 30% over-panelling to optimise output on cloudy days.

I pretty quickly honed in on Victron as the controller I wanted to use, so most of my research has focused on them. It wasn't until 2 months ago that I realized not every controller determined PV Array limits the way Victron does it (simply Voc and Isc).

Victron has a short article on Overpaneling and sizing I also started a thread on the topic of over-paneling a while back, from many of the comments you can see that a lot of people are unaware of the extent to which Victron SCC's can be overpaneled.

How Victron accomplishes this (and why others do not) is something I'm curious about. The more I learn about Victron the more respect I have for their products, I just wish they would improve their documentation.

My rudimentary understanding from bits and pieces I've gleamed here and there is that Victron Controllers limit charge current by intentionally straying from the maximum power point (maybe all controllers do this, idk), they do this in various situations to limit current. I'm not sure if this is how they deal with substantial overpaneling or if there is another mechanism.


Here are a couple relevant bits and pieces from the Victron Community:
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SmartSolar Maximum input current - Victron Community

community.victronenergy.com

Max power, max voltage and max current are 3 different things, even though P=VxI.

The MPPT has contol over how much power to draw from the PV array - so there is no problem with having a PV array that has a higher max 'power' then the MPPT can use.

The MPPT can easily control power by reducing the charge current delivered the battery, as a result the PV voltage will increase closer to the open circuit voltage and the solar panels will operate at a less efficient point on their power curve.

When assessing the suitability of a solar array for a particular MPPT, the primary specification to check is the maximum PV voltage limit. Ensure that the PV array Voc (open circuit voltage) rating is at least 5 to 10% below the MPPT limit. This is to protect for a scenario with very cold temperature combined with very high irradiance - as the PV Voc rating can be exceeded in the right conditions.

The other specification to check is the maximum PV current limit. Also ensure that the PV array Isc (short circuit current) rating is below the MPPT limit.

Providing these 2 criteria are satisfied, then you can basically install as much 'theoretical' PV power as you want. More PV power is great for overcast days, as you can still have decent solar yield when the solar conditions are unfavorable. Under good conditions the extra power just won't be utilized.

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"Voltage or current limited" - What does it mean? - Victron Community

community.victronenergy.com

Max power, max voltage and max current are 3 different things, even though P=VxI.

The MPPT has contol over how much power to draw from the PV array - so there is no problem with having a PV array that has a higher max 'power' then the MPPT can use.

The MPPT can easily control power by reducing the charge current delivered the battery, as a result the PV voltage will increase closer to the open circuit voltage and the solar panels will operate at a less efficient point on their power curve.

When assessing the suitability of a solar array for a particular MPPT, the primary specification to check is the maximum PV voltage limit. Ensure that the PV array Voc (open circuit voltage) rating is at least 5 to 10% below the MPPT limit. This is to protect for a scenario with very cold temperature combined with very high irradiance - as the PV Voc rating can be exceeded in the right conditions.

The other specification to check is the maximum PV current limit. Also ensure that the PV array Isc (short circuit current) rating is below the MPPT limit.

Providing these 2 criteria are satisfied, then you can basically install as much 'theoretical' PV power as you want. More PV power is great for overcast days, as you can still have decent solar yield when the solar conditions are unfavorable. Under good conditions the extra power just won't be utilized.

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And an interesting question posed but not answered:

SmartSolar Maximum input current - Victron Community

community.victronenergy.com

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[gnubie]

Stepping off Vmp is both a method and a consequence of current limiting.

 

[HRTKD]

tictag, thanks for pointing this out. I was wondering about that and now I'm thinking that maybe the 100/50 controller I was planning to get is too much controller for my array. I have been using the Victron MPPT Calc spreadsheet to pick the right controller. It says the 100/50 is "Accepted", while the 100/30 is 30% over paneled and still "Accepted".

I'm planning to implement a 2s2p array configuration. Each panel has the following specifications.

Temperature coefficient of Voc: -0.33% °C​

Temperature coefficient of power: -0.23% °C​

Temperature coefficient of Isc current: ±0.05% °C​

NOCT (nominal operating cell temperature): 45 ° C (± ° C)​

Maximum Power Output: 200 Watts​

Max Operating Voltage (Vmpp): 21.052 Volts​

Max Operating Current (Imp): 9.50 Amps​

Open Circuit Voltage (Voc): 24.335 Volts​

Short Circuit Current (Isc): 9.87 Amps​

Module Efficiency: 17.3%​

If I'm calculating the array right, I end up with the following (rounded) numbers:
Total watts: 800
Volts: 50
amps: 20

Should I step down to the 100/30 controller?
Should I add two more panels to the array? 2s3p?
Or, is the 100/50 and the array just fine and I'm worrying too much?

 

[tictag]

With a nominal output of 440W, whilst the 100|30 will work just fine (array Isc = 19.74A, array Voc = 48.7V, is well within specs) you will be leaving quite a lot 'on the table' on Sunny days i.e. 360W left 'on the table' (800W - 440W = 360W), that's 55% over-panelling. You'd be killing it on cloudy days! but would be loosing out somewhat on sunny days. With 800W of panels already, I personally would go for the 100|50.

Should I add two more panels to the array? 2s3p?

There's nothing wrong with adding a couple more panels but this is a system design choice. For example, if you are only consuming say 1,000Wh per day, then having 1,200W of PV generating 4,800Wh per day will have your batteries charged by 0700hrs then sit idle for the rest of the day! Generally speaking you want to be generating what you consume every day, leaving your battery to supply your loads at night and for however many days autonomy you have budgeted for.

 

[Dzl]

tictag, thanks for pointing this out. I was wondering about that and now I'm thinking that maybe the 100/50 controller I was planning to get is too much controller for my array. I have been using the Victron MPPT Calc spreadsheet to pick the right controller. It says the 100/50 is "Accepted", while the 100/30 is 30% over paneled and still "Accepted".

I'm planning to implement a 2s2p array configuration. Each panel has the following specifications.

Temperature coefficient of Voc: -0.33% °C​

Temperature coefficient of power: -0.23% °C​

Temperature coefficient of Isc current: ±0.05% °C​

NOCT (nominal operating cell temperature): 45 ° C (± ° C)​

Maximum Power Output: 200 Watts​

Max Operating Voltage (Vmpp): 21.052 Volts​

Max Operating Current (Imp): 9.50 Amps​

Open Circuit Voltage (Voc): 24.335 Volts​

Short Circuit Current (Isc): 9.87 Amps​

Module Efficiency: 17.3%​

If I'm calculating the array right, I end up with the following (rounded) numbers:
Total watts: 800
Volts: 50
amps: 20

Should I step down to the 100/30 controller?
Should I add two more panels to the array? 2s3p?
Or, is the 100/50 and the array just fine and I'm worrying too much?

To properly answer the question we need to consider battery bank voltage.

If your array is roughly 800W / 50V / 20A you are good to go with either controller on the PV input side. The output side depends on your battery bank voltage.

30A Controller	50A Controller
12V nominal 12V x 30A = 360W (45%) 13.5V x 30A = 405W (50%)	12V nominal 12V x 50A = 600W (75%) 13.5V x 50A = 675W (85%)
24V nominal 24V x 30A = 720W (90%) 27V x 30A = 810W (100%)	24V nominal 24V x 50A = 1200W (150%) 27V x 50A = 1350W (170%)

* Percent values = Controller output power as a percent of PV array power at STC

If I were in your shoes I would go with the 50A controller if you have a 12v battery bank, you would be slightly overpaneled but it might be ideal for real world conditions. If you have a 24v battery bank I would go with the 30A controller or add 2 more panels and go with the 50A controller.

 

[HRTKD]

I will have a 12v, 560 Ah battery bank. Thanks for the feedback. I'll stick with the 100/50, which gives me room to grow from four to six panels.