Over-paneling Victron MPPT controllers.

[Maast]

You might want to add something like: When overpaneling, since unused power from a panel raises the input voltage if you hit the maximum input power limit the panel voltage will start rising towards their VOC voltage.

Or words to that effect.

 

[MattiFin]

Could be intentional. That is called a crowbar, and is common in power supplies (some manuals warn to use a diode when charging batteries for that reason.)
Transistors would be damaged if voltage went too high, and this would prevent it.

Buck converter - Wikipedia

en.wikipedia.org

AFAIK this is the exact reason for Isc limit on Victron.
Controller protects itself from panel over-voltage by shorting the input to ground. This works well as long as the Isc is limited to value that controller can handle.

Victron manual is bit of a mess indeed: it wouldn't make sense to short the panel in case of battery overvoltage alone as the MPTT controller should be able to adjust the battery current to zero anyways..

 

[FilterGuy]

MidNite told me in an email I could essentially Overpanel a classic 150 all I wanted, just don't allow the array to exceed VOC. The controller will only use what it can use and the rest is wasted. And That the excess would not dissipate as heat, it just simply wouldn't be used. But now reading @SpongeboB Sinewave 's comments I'm second guessing my decision.

24v system with Present array: 2565w 3s3p (VOC 116.4 / Isc 29.13). Plan is to double that with same panels to a 3s6p (VOC 116.4 / ISC 58.26). I realize it would be more effective with a second scc, but my understanding from midnite was it won't hurt the classic 150 as long as I don't exceed VOC .

The most heat will be generated when the controller is maxing out the current to the battery. In this case, the controller will adjust the input current to match the need. If there is more wattage available than what is going into the controller, the current point will not be at the max powerpoint and the energy will not be created. (The controller does not dissipate the excess)

The midnight is one of the best all-purpose controllers on the market. I would not be too concerned about over-paneling it. However, since it is going to be running at its max output a lot of the time, it becomes important to follow the recommendations on ventilation and spacing.

Note; While developing my resource on over-paneling, I contacted Midnite and talked to one of the support techs about this. He told me the same thing you were told. However, he also pointed out that having a 2nd controller in order to get all of the power out of the panels has the added benefit of redundancy.

In the latest version of the over-paneling resource, I added a page specific to the midnight classic. (I added specifics on a few other controllers as well) I also added a page about the value of redundancy of controllers.

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

 

[MrM1]

The midnight is one of the best all-purpose controllers on the market. I would not be too concerned about over-paneling it. However, since it is going to be running at its max output a lot of the time, it becomes important to follow the recommendations on ventilation and spacing.

Thank you for your response, AND Thank You for all the resources you have created and posted on this forum

I realize this is a Victron specific thread on the more general idea of over paneling and your resources for that, but what can you say about some of the All-in-One units and their SCCs as to over paneling. Is there any guidance out there for them? We are about to install a fully off grid Growatt Low Frequency SPF 12kw DVM MPV 250 unit in the next few months. Again the we plan is to over panel with the goal of capturing more energy in mornings / afternoons and on cloudy days.

I reached out to Signature Solar whom, while not the manufacturer, I would consider one of the 2 or 3 US based support contacts for the units. Perhaps you could shed some additional light on their response to me and / or find their response valuable in your Over-Paneling Guide update

This from Signature Solar as an email to me about Over Paneling the Growatt 12kw and how the two PV inputs work for the MPPT SCC (PV1 and PV2).

(Me) Page 10 of the Manual - Indicates There are 2 PV input connections for the 12k version, but there is very little or no explanation of why or how they are used. I assume this has to do with MPPT tracking? Are there MPPT settings found in the charge controller section of the controller parameters? Not finding much about this or Array arrangement.
These models are essentially 2 6kw units combined into one. Each MPPT controller can handle 7000W from the array and the settings will be determined by total input.

(Me) We want to over panel the setup, but the manual in the specs only lists the inverter is rated for a 7000w array. Why is this a limitation? If we keep the array input under 250vdc wouldn't any over current just simply not be used? We would like to over panel because we have seen about a 15% drop off in rated power from an array on average here in FL on other off grid systems. Would like to build out a 8000w or 10,000w array for cloudy days, and to maximize power harvest in the mornings and afternoons.
As long as you do not exceed the VOC/VDC you can have more than 7000W of power generated from your panels, however it will not be inverted so it will be wasted.

 

[FilterGuy]

Thank you for your response, AND Thank You for all the resources you have created and posted on this forum

I realize this is a Victron specific thread on the more general idea of over paneling and your resources for that, but what can you say about some of the All-in-One units and their SCCs as to over paneling. Is there any guidance out there for them? We are about to install a fully off grid Growatt Low Frequency SPF 12kw DVM MPV 250 unit in the next few months. Again the we plan is to over panel with the goal of capturing more energy in mornings / afternoons and on cloudy days.

I reached out to Signature Solar whom, while not the manufacturer, I would consider one of the 2 or 3 US based support contacts for the units. Perhaps you could shed some additional light on their response to me and / or find their response valuable in your Over-Paneling Guide update

Hmmm.... I looked up the manual and it just talks about 2 inputs. It does not say they are separate MPPT controllers. (A lot of these all in one units have two inputs on a single MPPT controller) However, the email from Signiture indicates 2 controllers. I just sent an email to Growatt-China asking about this but I doubt I will hear back before monday.

Meanwhile, this is what they said about the 3000W units: (My questions are in black, Their response is in red)

The SPF 3000 TL spec says this:

Solar Charger:
Max PV Array Power...........................4000W
MPPT Range @ operating Voltage.....120VDC - 250VDC
Max PV Array Open Circuit Voltage....250VDC
Maximum Solar Charge Current..........80A

Questions:
1) Is the "Is the Maximum Solar Charge Current" the maximum current the charger will send to the battery? (I believe it is, but want to confirm)
Yes，the maximum current the charger will send to the battery
2) Is the Max PV Array Power a hard limit or is that just the max wattage the controller will send to the battery?
A hard limit

I have noticed that the All-in-one units seem to be more restrictive about over-paneling than stand-alone controllers. I do not know why that is.

 

[FilterGuy]

I reached out to Signature Solar whom, while not the manufacturer, I would consider one of the 2 or 3 US based support contacts for the units.

The Growwatt North America website gives this email for support contacts: usa@ginverter.com

However, whenever I send a technical question to that email, it gets forwarded to china by the USA rep. He forwards it to is a list:

marco.liu@growatt.com
owen.liu@growatt.com
zhiwei.yu@growatt.com

I have seen replies from Owen.liu@growatt.com but not the others.

 

[MrM1]

So do you think the 7000ws on the 12kw unit is a hard limit for the total input or for each PV input (7000 PV1 and 7000 PV2)

 

[FilterGuy]

So do you think the 7000ws on the 12kw unit is a hard limit for the total input or for each PV input (7000 PV1 and 7000 PV2)

I think it is a hard limit per MPPT..... but I am not sure if there is one or two MPPTs. I sent an email to them asking about this.

 

[MrM1]

Thx. Based on what Sig Solar wrote me there are 2 MPPTs in the large low frequency inverters. And each can handle its own 7000w array. Will be interesting what answer you get back

 

[PVorBust]

If you dig into them, a lot of the MPPT controllers have limits like this. They are typically 30-50% more than the rated charging power.
It turns out that Victron has a limit to....but the limit is hidden in the Max Isc spec.

the best conclusion I can draw is that it's an economic limit, not an electrical limit.
Once you pass 150~200% panel capacity, you should increase SCC capacity to make the most of it.

 

[FilterGuy]

the best conclusion I can draw is that it's an economic limit, not an electrical limit.
Once you pass 150~200% panel capacity, you should increase SCC capacity to make the most of it.

There definitely is a practical limit to over-paneling, but the manufacturers insist there are electrical limits.

 

[FilterGuy]

Thx. Based on what Sig Solar wrote me there are 2 MPPTs in the large low frequency inverters. And each can handle its own 7000w array. Will be interesting what answer you get back

Well....... Growatt said there are 2 MPPT controllers.... but a limit of 3500W each for a total of 7000W. That implies they don't support any over-paneling beyond the 7000W. It is frustrating that the Growatt documentation is so bad, but the mixed messaging between the documentation, Growatt support, and the distributers is infuriating.

My guess is they can be over-paneled at least 30%, but my guess does not help much if you try it and smoke the unit.

 

[MrM1]

Well....My guess is they can be over-paneled at least 30%, but my guess does not help much if you try it and smoke the unit.

Thx. Yes that is disappointing.

What would cause the unit to smoke if I never exceed 250voc? I'm trying to wrap my head around it. I was planning a 4s4p of 370w panels (5920w) at a VOC of 189.8vdc and an Isc of 44.28a Per PV input on the Growatt 12kw. But as the watts of the array start rising in full sun, is there something unique/odd that happens to the VOC /Isc if the SCC is not able to use the power?

Looks like some SCCs smoke and some don't? Trying to understand why that would be.

 

[Hedges]

An SCC could draw maximum current from an overpaneled PV array and hurt itself. Or it could monitor current and never exceed what it can handle, even if Isc exceeds that.

Heat is created in SCC from IR drop through components like inductor, diode, transistor. MOSFET have very low on resistance, so most of their power dissipation comes while transitioning between on and off. The voltage during steady-state operation would swing between Vmp and zero, with Imp (or whatever lower current it is limited to by SCC wattage rating), dissipating energy J = 1/2 x V x I x falltime (during each transition.) Higher frequency switching dissipates more power, but allows smaller inductor (lighter, less expensive) less ripple in output.

We often compare energy loss in PV wiring (less for higher voltage strings) with loss due to efficiency of SCC (higher for high voltage strings). Also, high voltage strings saves money on copper wire. However, copper doesn't wear out (unless so hot the insulation gets damaged.) Shifting inefficiency to SCC in order to save money stresses SCC more. Over-paneling exacerbates that.

When overpaneling, could be worth aiming for a more efficient operating voltage of SCC so it generates less heat. At least, if you're in a hot climate.

If you overpanel by aiming half your array SE and half SW with a 90 degree angle between them, area presented toward sun is 0.7 times as much. That means you can over panel to 1.4x without exceeding electrical specs of SCC (most of the time; there is more area to capture extra light reflected off nearby clouds under certain conditions.)

With 90 degree angle, 5kW would be fully paneled for 3500W input. With an acute 60 degree angle, 7kW would be full paneled.
At 90 degrees each subarray has 45 degree angle to horizontal, isn't losing much from sun below horizon (but objects causing shading get in the way.)
At 60 degrees, more of panel's daily out put is lost to sun not above horizon.

 

[FilterGuy]

Looks like some SCCs smoke and some don't? Trying to understand why that would be.

I do not know why. In discussing this with Victron, they said there are times when the input is short-circuited....but would not elaborate on why or when this would happen. In addition, I have noticed the AIO units tend to be more restrictive than stand-alone chargers.

On the AIO units, it could be a heating problem. With the SCC, AC-DC charger and inverter all working at once, there could be a significant amount of heat generated. By limiting the PV wattage, it limits the time where the SCC is operating at it's max to a very short period.

 

[curiouscarbon]

time-offset overpaneling as @Hedges mentioned seems pretty clever to me.

if i lived in a cylindrical roof building like barracks then maybe i could overpanel by having a continuous curve and maximize overpaneling and minimize SCC wear and tear ?

then the strings would operate at the SCC max throughout the entire solar day but be overpaneled from the spec

 

[FilterGuy]

An SCC could draw maximum current from an overpaneled PV array and hurt itself. Or it could monitor current and never exceed what it can handle, even if Isc exceeds that.

Heat is created in SCC from IR drop through components like inductor, diode, transistor. MOSFET have very low on resistance, so most of their power dissipation comes while transitioning between on and off. The voltage during steady-state operation would swing between Vmp and zero, with Imp (or whatever lower current it is limited to by SCC wattage rating), dissipating energy J = 1/2 x V x I x falltime (during each transition.) Higher frequency switching dissipates more power, but allows smaller inductor (lighter, less expensive) less ripple in output.

We often compare energy loss in PV wiring (less for higher voltage strings) with loss due to efficiency of SCC (higher for high voltage strings). Also, high voltage strings saves money on copper wire. However, copper doesn't wear out (unless so hot the insulation gets damaged.) Shifting inefficiency to SCC in order to save money stresses SCC more. Over-paneling exacerbates that.

When overpaneling, could be worth aiming for a more efficient operating voltage of SCC so it generates less heat. At least, if you're in a hot climate.

If you overpanel by aiming half your array SE and half SW with a 90 degree angle between them, area presented toward sun is 0.7 times as much. That means you can over panel to 1.4x without exceeding electrical specs of SCC (most of the time; there is more area to capture extra light reflected off nearby clouds under certain conditions.)

With 90 degree angle, 5kW would be fully paneled for 3500W input. With an acute 60 degree angle, 7kW would be full paneled.
At 90 degrees each subarray has 45 degree angle to horizontal, isn't losing much from sun below horizon (but objects causing shading get in the way.)
At 60 degrees, more of panel's daily out put is lost to sun not above horizon.

If panels at different angles are put on the same controller, be sure to put blocking diodes between them.

 

[MrM1]

We are working on a re design now with different angles for the Growatt 12kw 250 with 2 mppt trackers
Pv1 input - 190v voc
- 4440w 4s3p facing south
- 1480w 4s1p facing east

Pv2 input - 190v voc
-4440 4s3p facing south
- 1480 4s1p facing west

For a total array of 4s8p on 2 4s4p sections each going into pv1 and pv2 respectively.

Still a bit hi for the 7000w total of the Growatt but

Hoping this might work?

And would we need a blocking diode for that? What are they? What do they do? (sorry for my ignorance)

If still too large we can either sell off some panels Bc we got a deal or get a second scc

 

[FilterGuy]

And would we need a blocking diode for that? What are they? What do they do? (sorry for my ignorance)

Will does a good job of describing it in this video

However, if the Growatt has two separate MPPT controllers, they are not needed.

 

[Hedges]

If panels at different angles are put on the same controller, be sure to put blocking diodes between them.

Is Voc of an off-angle or shaded panel greater than Vmp of a panel receiving direct sun?
If so, no need for the diode.

In actual operation, not standard tests, the one in full sun would be hotter, reducing its Vmp further.