MASSIVE Overpaneling -MPPT input current

[glandpuck]

Over paneling was a concept first used for grid tied inverters because they operated at higher voltages and were designed to allow for over paneling to be more productive during the day. And this was based on simply taking power and directing it to the local main panel or out the the grid. Nothing fancy, just harvest and dump. So adding the over paneling feature was easy to do and sold more panels and gave more of the utility approved output for a longer period of time in the day. Period, end of story on over paneling.

Now, for an MPPT charge controller, over paneling or coming near the Voc limits, ie. flying close to the sun is completely un necessary and of little to no long term benefit.

The MPPT controller charging a low voltage battery bank takes advantage of the software algorithm once the input voltage gets about 22 volts over that of the batteries. It receives the input voltage and current and then modifies these to allow more current to flow into the batteries AT A LOWER VOLTAGE, NOT A HIGHER VOLTAGE. And with a lithium battery bank, the BMS of the batteries actually controls the input voltage and amps to charge and discharge that are presented to it by the MPPT output.

Rather than "overpanel", you would be better off aiming your panels optimally for PV collection at more hours in the day.

 

[squowse]

Why would the controller blow before the fuse if the fuse is before the controller?

the components are faster to respond to over current, The fuse just interrupts and prevents a fire. The MPPt have an internal but its not replaceable as the componenets will already be blown. Just to prevent fire/further damage.

 

[timselectric]

Anyone wanna experiment and try out their favourite SCC?

Already have.
I ran for several months with 85a worth of solar panels connected to an 18a SCC.
With no concerns or issues.

 

[underdog5004]

Already have.
I ran for several months with 85a worth of solar panels connected to an 18a SCC.
With no concerns or issues.

Yeah over paneling with amperage is way more tolerable than over paneling with voltage.

 

[timselectric]

Yeah over paneling with amperage is way more tolerable than over paneling with voltage.

Overpaneling only involves amperage.
VOC is non negotiable. Never exceed it.
Voltage is pushed.
Amperage must be drawn.

 

[Zsiger]

Already have.
I ran for several months with 85a worth of solar panels connected to an 18a SCC.
With no concerns or issues.

Thanks Tim!

Can You please write a short info about your setup?
Panels configuration, SCC, battery bank...

 

[timselectric]

Thanks Tim!

Can You please write a short info about your setup?
Panels configuration, SCC, battery bank...

At that time I had 98 240w and 250w panels. 8 strings of 10 and 2 strings of 9 .
SCC is built-in to the Growatt AIO. And I think I had about 19kwh of battery capacity.

 

[Zsiger]

At that time I had 98 240w and 250w panels. 8 strings of 10 and 2 strings of 9 .
SCC is built-in to the Growatt AIO. And I think I had about 19kwh of battery capacity.

Sounds pretty nice. And your paralell string capeable of 85Amp max? Wow.
Your SCC never had any problem with that huge overshooting on max Isc?
Does your growatt ever pull the max power it is capeable of? Did you ecperienc any warnings, errors because of the higher PV array Isc?

 

[MrThisIsME]

Confused here.
Is this the "house burned down" thread continuation?

 

[timselectric]

And your paralell string capeable of 85Amp max?

Yes

Wow.
Your SCC never had any problem with that huge overshooting on max Isc?

No, because it doesn't care what is available. Only what it can use.
Amperage isn't pushed, it must be drawn.

Does your growatt ever pull the max power it is capeable of?

Every day.

Did you ecperienc any warnings, errors because of the higher PV array Isc?

No, it doesn't know what is available. Only that it can have all that it wants.

 

[timselectric]

Confused here.
Is this the "house burned down" thread continuation?

If you understand how things work. You can make them work for you.

 

[Zsiger]

Confused here.
Is this the "house burned down" thread continuation?

Why so?

 

[timselectric]

Why so?

I think that they were just making a joke.

 

[Zsiger]

I think that they were just making a joke.

Oh!
Hope not.
I have no problem with joking, but now here for real experience. I don't want to try any setup that have any chance to demage my equipment.

 

[timselectric]

Oh!
Hope not.
I have no problem with joking, but now here for real experience. I don't want to try any setup that have any chance to demage my equipment.

I completely understand. Safety is always my top priority.

 

[Vigo]

I don't know enough about PWM controllers to comment comfortably.
But I can definitely see how overpaneling could be a problem for them.
Their ability to switch on and off the current is limited by what the parts they are made of can handle.

So not in response to you in particular, because a whole essay in response to one person always feels like an attack and this is no attack, but..

Im talking above my pay grade but i wasn't talking about PWM controllers specifically, just the action of PWM in general. As far as i know an mppt is basically a switch mode power supply with a fancy control scheme, but ultimately it is just PWM'ing into and out of an inductor.

If you had an mppt like our Growatts that has a 450v limit and 18a limit, in order for any single 'on' pulse of the input switching to stay under that 18a limit, the mppt input circuit would have to stay at or above 25ohms (450v / 18a = 25ohms). IF the input transistors and the inductor/s they feed had less than 25ohms, then the only thing keeping that first 'on' pulse below 18a is the current limit of the array.

In reality i suspect the resistance of that input circuit is far less than 25ohms (an inductor sitting at 0v is just a piece of wire, very low ohms), which means the 'instantaneous' current flow when the input transistors are 'on' would be far higher than 18a. 18a would be an average or continuous max, but the instantaneous max is unstated.

So if my understanding of the above is correct, the REAL limit to overpaneling is probably based on how cautious (aka short) those first pulses of the input switching is. If the control scheme always starts out with the briefest pulse its capable of, it should be able to handle an array WAY over the 18a max (or whatever) because even if the array is capable of 95a, 95a for one microsecond still isnt long enough to heat up (and physically distort) the transistors to failure. But if the mppt's initial pulsewidth of the input switching is too long, then the transistors will pop before the control scheme even has a chance to make the subsequent pulses shorter.

Again i am NOT an electrical engineer, this is just what my brain can come up with as a possible explanation for why there is a theoretical limit to overpaneling, and it comes down to operating temp of the input circuit devices, which is determined by amps, ohms, and time. Amps is limited by your array, ohms is fixed within a certain range (which is unknown to us), but time is determined by how long the controls leave the transistors on. So how the controls manage pulsewidth should be the deciding factor between which MPPTs can handle severe overpaneling, and which ones cant. That's my theory as a car mechanic and basic electrical instructor who's reaching FAR beyond his actual training.

 

[Robert Mate]

It seems there are (at least) two definitions of 'over panel' (Never over volt mppt input from pv)
-- For pv sys w/ battery --

1) A system is designed & built in such a way that the batteries are fully charged each average day & mppt's specs are never exceeded.
Then more pvs are added (for rainy, cloudy, etc. days) so batteries are fully charged each day & mppt's specs are never exceeded & any excess pv power is not used.

2) A system that has a mppt's max pv amp input in excess of what that mppt could use to charge batteries. In that case, never exceed mppt's spec pv amp limit.

 

[timselectric]

There's only one definition for overpaneling.
Connecting more available amperage than the SCC can utilize, most of the time.
The reason for overpaneling are the times when it can utilize it.