Overpaneling. How much is too much?

[Dadoftheturkeykids]

I know this has been discussed many times here, and reading into it I think the general conclusion is;

Overpanel as much as you want, just don't go above the voltage limits of your charge controller.

Is this true? What if I doubled the input but stayed under voltage?
I want to know if I can put two 545w panels in series on my 40amp solar charge controller charging a 12v battery bank.

(I am aware of the losses, and aware that if I were to have a 24v bank, it would fit the
CC parameters perfectly)

This would be temporary until I can afford to buy 4 more controllers (i have 4 currently)
or a suitable 24v inverter. As of right now I only have a 12v inverter, but have 8 of these panels I want to utilize/mount now.

SCC- RichSolar 40a mppt (100v max)
Panels- Trina 545w (37.9 VOC)

If I series 2 panels together that would give me 75.8voc @ 17.24a, which is way more than my controller can feed to my battery bank, but will it have any negative impact on my controller?

 

[MisterSandals]

If I series 2 panels together that would give me 75.8voc @ 17.24a, which is way more than my controller can feed to my battery bank, but will it have any negative impact on my controller?

Thats pretty typical over paneling that quite a few people do.

Just be mindful that with a value priced SCC and operating it 100% (40A), I would expect a reduced lifespan. It will run hotter but you might be able to mitigate the heat with improved ventilation and air circulation.

Its like running you car at redline all the time, a shortened lifespan is the likely result.

Higher quality SCCs (like Victron) can run at elevated charge rates and temps based on results i've seen posted here.

 

[MichaelK]

Just doing the math for two panels, assuming charging starts at ~12.5V, then (545W X 2 panels)/12.5V = 87A. Even with 85% de-rating, that's still ~74A. With a tier-1 controller like Midnight, those extra amps would just be clipped off. With a budget-oriented controller like RichSolar I can't honestly tell you what will happen? Maybe it will clip like it's supposed to, or maybe it will actually melt?

In any case, wasting almost half of your amps doesn't seem like a productive use of those panels? What might be feasible right now is virtual tracking. Maybe three panels, each wired in parallel. One would face East, one faces South, and the third West. That way, only one panel will be at full power at any time of the day, but you are likely to be putting out 40A continuously from 8am till 4pm.

 

[Dadoftheturkeykids]

Thats pretty typical over paneling that quite a few people do.

Just be mindful that with a value priced SCC and operating it 100% (40A), I would expect a reduced lifespan. It will run hotter but you might be able to mitigate the heat with improved ventilation and air circulation.

Its like running you car at redline all the time, a shortened lifespan is the likely result.

Thank you, your car example makes quite a bit of sense. Maybe I'll just run dead leads for the moment and bring them online as I buy more controllers. Would have been ideal to run 4 pairs of leads as opposed to 8, joys of a 12v system I guess lol.

In any case, wasting almost half of your amps doesn't seem like a productive use of those panels? What might be feasible right now is virtual tracking. Maybe three panels, each wired in parallel. One would face East, one faces South, and the third West. That way, only one panel will be at full power at any time of the day, but you are likely to be putting out 40A continuously from 8am till 4pm.

I like your thinking, and it sounds like totally something I would try if I had the land space for a groundmount, but my applicable area is really only on my roof which faces north/south

 

[danrclem]

Let me see if I'm understanding this right. It's ok to over panel the amperage of a controller if person has a quality charge controller as long as the voltage guidelines are followed?

 

[MisterSandals]

It's ok to over panel the amperage of a controller if person has a quality charge controller as long as the voltage guidelines are followed?

The SCC pulls the amps.

Its like my 2W nightlight that pulls (2W / 120V = .0166A). This nightlight is plugged into a 15A receptacle (which is part of a 200A household), which is connected to an "even bigger" grid.

 

[DJSmiley]

Yes, but you are limited in the current as well. PV input has limits for both voltage AND current.

A MPPT works by tracking the maximium power point. This also can result in lowering the voltage to get a higher amps (20V x 5A is still more power than 40V / 2A).. thats the principe of a MPPT.

If you exceed the PV input current, you can fry the mosfets.

A Victron SmartSolar 100/30 for example has a max PV input of 100V, and a PV Short circuit current of 35A.

In a 12V setup thats around 400W max charge current. However you can overpanel significantly (altough it might not make sense but you get the point). I personally would not recommend overpanneling over 50%, but there is no problem/damage (apart from not able to use the surplus pv)

Example:
4 panels of 40V / 10A each in a 2P2S config: output is 80V / 20A and you're good.
Same 4 panels in parallel: 40V / 40A.. NOT good since it's exceeding the MPPT PV input current
Same 4 panels in series: 160V / 10A.. NOT good since it's exceeding the MPPT PV input voltage

With a 100/30A you, in theory, can put safely a 90V / 34A panel on it (3060Wp) and still be safe. As said, completely useless since, in a 12V setup, it only can use about 400W and you leave 2600W unused and those panels don't exist, but you get the point.

 

[MisterSandals]

As said, completely useless since,

I appreciate your other points but it is not "completely useless". In low light situations like early morning, late afternoon or even overcast, more panels will get you more power (up to the limit of course).

 

[DJSmiley]

I appreciate your other points but it is not "completely useless". In low light situations like early morning, late afternoon or even overcast, more panels will get you more power (up to the limit of course).

Fully agree, I do recommend overpaneling, since the max of the panels is most of the time not archieved.

There is a sensible limit to the amount of overpaneling. In the example I posted (3000Wp) thats not making sense (unless you want to charge with moonlight)... Generally, I wouldn't hesistate to overpanel by like 30-40% to coop with shade/overcast, seasonal differences and so on.

On a 12V setup, I use a 20A MPPT for 300-320Wp of panels, and only recommend a 30A if you have like 350-500Wp (or if the customer wants to pay the additional price for only a few % gain, 95% of the time, the solar output is way below the max panels rating.)

 

[Dadoftheturkeykids]

Thanks for the input guys. I have a lot better understanding of overpaneling already.

My conclusion:
*Never exceed the max voltage input of the charge controller
*Exceeding max PV input parameters (watts)
is fine, but stay away from the max voltage limit, as it will shorten the life of the controller
*Overpaneling is good for panels in various directions to utilize all hours of sun, also for overcast/cloudy days
*Solar panels do not push current, the charge controller draws the needed current from the panels dependent on the load

 

[noobie]

The SCC pulls the amps.

Its like my 2W nightlight that pulls (2W / 120V = .0166A). This nightlight is plugged into a 15A receptacle (which is part of a 200A household), which is connected to an "even bigger" grid.

Victron seems to state a limit. For example the 250/100 SCC it says max of 70A short circuit current. But it's due to the reverse polarity protection:
"A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array."

It seems like you're safe to go crazy, and could theoretically connect panels that could produce 200A short circuit current(ignoring proper wiring size to handle 200A) and the SCC would be fine, assuming you don't reverse the polarity.

 

[MisterSandals]

and the SCC would be fine, assuming you don't reverse the polarity.

Yep, and like most other things, like a scissors, its up to the user to not stick them in your eye or bludgeon your heart.

 

[danrclem]

With a 100/30A you, in theory, can put safely a 90V / 34A panel on it (3060Wp) and still be safe. As said, completely useless since, in a 12V setup, it only can use about 400W and you leave 2600W unused and those panels don't exist, but you get the point.

Does a 12V setup using about 400W apply to all chargers or just this particular one. Would a 24V setup be 800W and a 48V setup be 1600W?

 

[MajicDiver]

If you exceed the PV input current, you can fry the mosfets.

On what basis do you make that statement? I would like to propose a friendly challenge for you to explain how that can occur or point to a reference that does. Unless you are thinking about the issue with reverse polarity mentioned earlier in this thread and at length in other threads.

 

[zanydroid]

It seems like you're safe to go crazy, and could theoretically connect panels that could produce 200A short circuit current(ignoring proper wiring size to handle 200A) and the SCC would be fine, assuming you don't reverse the polarity.

The other standard limit is to not have aggregate input ISC exceed the max output charge current. That should alleviate concerns about available current wrecking the FETs, since they anyway need to pass close to this when the panels are close to battery pack voltage

 

[MajicDiver]

The other standard limit is to not have aggregate input ISC exceed the max output charge current.

With respect to “standard” I’m not sure what you are saying? I’m assuming you are talking about a specific make/model? My inverters certainly do not have such a limit.

 

[zanydroid]

With respect to “standard” I’m not sure what you are saying? I’m assuming you are talking about a specific make/model? My inverters certainly do not have such a limit.

Standard in the sense that some forum regulars flog it. I vaguely think it is alluded to in some random Voltronic or Victron document.

I think it does make sense.

And it is often expressed as a rule for SCC. On inverters/AIO the power path is more complicated but there could likely be similar rules of thumbs.

 

[MajicDiver]

could likely be similar rules of thumbs.

I would be interested to see this list of rules of thumb.

 

[zanydroid]

I would be interested to see this list of rules of thumb.

I haven't seen it written down. But I think you can generalize the SCC rule to an AIO where the MPPT output can go multiple directions after the high voltage bus. Either the path to the battery or through the inverter has a similar max current rating to the SCC (obviously the first case is analogous the SCC situation). Now, I don't know if you can actually add those two and say that's the maximum safe current.

Where it gets tricky is that the SCC rule of thumb is for low voltage 12V/24/48V/what-have-you batteries. The HV bus has much lower current than this. Also, there are many more stages of transisters & whatnot in an AIO than a SCC, and some of the ones unique to AIOs might be ... upset ... with too much available current from the solar panels.

(Also, on the SolArk the MPPTs have a max ISC listed, dunno if it's for reverse polarity or what. It's lower than the max charging current)

 

[carlosspicyweiner]

Guess the waste of panels is relative? I was lucky to get 18 x 315w panels for nothing, and have no use at the moment for 12 of them - so why not over panel the crap out of my systems? (keeping under voltage/current of course)