Overpaneling - right, wrong or indifferent

[ricardocello]

woke up from nap to reports from wife that tv and fridge were dark.

Off topic: It could be worse, wife and daughter woke me up a few weeks ago to tell me the septic tank alarm was going off.

On topic: I've gone from being over-paneled, to under-paneled, and in the spring I'll be way over-paneled again when I add 15 more.

Over-paneling bothers me because I could be getting more kWh.
Under-paneling bothers me because I could have more panels.
No such thing as "just-right" because seasons change.

 

[Brucey]

Off topic: It could be worse, wife and daughter woke me up a few weeks ago to tell me the septic tank alarm was going off.

On topic: I've gone from being over-paneled, to under-paneled, and in the spring I'll be way over-paneled again when I add 15 more.

Over-paneling bothers me because I could be getting more kWh.
Under-paneling bothers me because I could have more panels.
No such thing as "just-right" because seasons change.

Yeah just need this snow to melt and then can move from this heavy 3x overpanneling on the 450/100 back to lightly underpanelled (260A worth of SCC).

 

[Zwy]

production is clipped by every SCC, if it's limit is reached.

That's why I said that peak production is the only exception.

It wouldn't have fallen that quickly, if overpaneled.
But it also wouldn't have gotten as high of a peak.

Which produces more, 10Kw of panels with enough charge controllers to pull every watt possible or a 10Kw of panels with a pair of 4Kw charge controllers?

The thing is your roof didn't get larger when you installed solar panels on it. It is a fixed area and only a limited amount of panels can be installed on it. Same with ground mounts, the area is the same. One has to add more mounts to install more panels. There are limitations on how large one can build arrays. My OCD array is limited by space constraints which is why it is missing one panel. I have used the best areas for solar arrays already, the rest will get more shading. Everyone here has limitations whether it is space, financial, a spouse, laws and regulations.

 

[RV8R]

It is about cost. If you leave that out than buying more SCC's or larger capacity SCC's would maximize panel production. Over panelling maximizes SCC value.

,,, Otherwise this would be my array;




If ya gotta ask , ya can’t afford it !!

 

[timselectric]

Which produces more, 10Kw of panels with enough charge controllers to pull every watt possible or a 10Kw of panels with a pair of 4Kw charge controllers?

You are missing the point of overpaneling.
Overpaneling gives you more overall production, from the same amount of MPPT's.
Of course, more MPPT's with more PV, gives even more overall production.

 

[ricardocello]

One reason you might not want more MPPTs is that the current has to go somewhere, either directly to loads, or to batteries.
At some point, too many MPPTs means you hit the limit on recommended battery charge current.

So I guess you can push it a little. If your batteries say 0.3C recommended, 0.5C max, occasionally going to max is ok.
But there is still a limit. Solution? More batteries! $$

Yes, I know Victron has DVCC, which will scale back the power from multiple SCCs intelligently to a max charging rate.
Great feature, but it is just another limit you have to be aware of, where you won’t get all of the PV power you were expecting.

If the system is designed and balanced correctly, you can overpanel and get more power all day without overcharging your batteries.
I’m getting ready to overpanel and not add a new MPPT.

 

[Zwy]

You are missing the point of overpaneling.

I know what the point is.

Overpaneling gives you more overall production, from the same amount of MPPT's.

Not if the MPPT's are large enough to handle the complete output of PV.

See what I did there?

Of course, more MPPT's with more PV, gives even more overall production.

Correct.

 

[Zwy]

One reason you might not want more MPPTs is that the current has to go somewhere, either directly to loads, or to batteries.
At some point, too many MPPTs means you hit the limit on recommended battery charge current.

I've stated it already in this thread. Buy more batteries.

So I guess you can push it a little. If your batteries say 0.3C recommended, 0.5C max, occasionally going to max is ok.
But there is still a limit. Solution? More batteries! $$

Yes, buy more batteries.

Yes, I know Victron has DVCC, which will scale back the power from multiple SCCs intelligently to a max charging rate.
Great feature, but it is just another limit you have to be aware of, where you won’t get all of the PV power you were expecting.

Any charge controller I use has a max charging rate setting.

If the system is designed and balanced correctly, you can overpanel and get more power all day without overcharging your batteries.

Buy more batteries.

 

[Brucey]

You are missing the point of overpaneling.
Overpaneling gives you more overall production, from the same amount of MPPT's.
Of course, more MPPT's with more PV, gives even more overall production.

I look it at this way. Had 20 panels on my 450/100. That's enough to max out in full sun. Realized winter yield is garbage in overcast conditions. Doubled up on panels. Doubled my overcast day output. Now I will be limited at 100A on a sunny day. But that's very rare. So instead of hoping for a jackpot golden hour or two I try and gather all day, slow and steady.

I could have bought a second 450/100 instead of panels. Which would help me in summer peaks. But would have done nothing for my low winter production.

Now I need to deploy more sccs to handle the peak production possible, but at the time it made more sense to buy more panels versus more scc. I guess if in doubt more panels which will increase your daily output first, then more scc to handle rarer full sun conditions. Without a budget then get panels and more scc at the same time.

 

[ricardocello]

I've stated it already in this thread. Buy more batteries.
Yes, buy more batteries.
Buy more batteries.

I admire the consistency of your messaging.

Any charge controller I use has a max charging rate setting.

Sure, but can you arbitrarily assemble N of them and have them coordinate the maximum charge rate?
That's a Victron feature.

But if others can do that I'd like to know, perhaps two 18kpvs in parallel will coordinate all the MPPTs to limit charge current?

 

[Brucey]

Any charge controller I use has a max charging rate setting.

DVCC takes into account loads as well. So for example with 100A scc if set at say 60A for a smaller battery bank, it will allow the sccs to power loads, while limiting charge to batteries to 60A. Without DVCC the scc would be limited to 60A of production in total at all times.

 

[Q-Dog]

Limiting the output of a SCC is not really that different from overpaneling. Change my mind.

 

[Brucey]

Limiting the output of a SCC is not really that different from overpaneling. Change my mind.

I would agree but with DVCC you aren't necessarily limiting max solar production (assuming you have loads in addition to the batteries to be charged).

 

[Q-Dog]

I would agree but with DVCC you aren't necessarily limiting max solar production (assuming you have loads in addition to the batteries to be charged).

Oh, I agree. I have DVCC implemented with my own setup.

 

[timselectric]

It's pretty simple.
If you only need more production in low light conditions (morning, evening, or cloudy), overpaneling will take care of it.
If you want more production at peak sunshine, then you need more SCC's.

 

[Brucey]

Oh, I agree. I have DVCC implemented with my own setup.

I would say dropping your charge controller max output is more like simulating what you'd see in peak sun with more panels in terms of "clipping". It's not doing anything to add extra pv output in non ideal conditions.

 

[RV8R]

Hi @emcvay

Glad you decided to stick around.

you install a solar array or string that can produce more power than the charge controller can utilize how can that possibly provide MORE charging power to the battery bank than just installing a larger charge controller that is properly sized for the array?

Depends ,,, If you rig the question or throw out responses of “Real World” scenarios rather than theory you will get the answer “You Want”.

My question to you would be what is more important ,,, “Power” or “Energy” which is banked in the batteries? Do larger SCCs waste more energy?

I think, an over panelled smaller SCC, given the right “scenario” could provide more “energy left in the tank” when the sun goes down than a larger SCC;

Crappy weather

Better panel placement to capture more sun’s energy (same size array - but setup for crap weather)

Difference in SCC efficiency & idle

Etc

 

[Zwy]

Limiting the output of a SCC is not really that different from overpaneling. Change my mind.

I came back into the office to post exactly this point.

Take Brucey and his blue 450/100. 4.5Kw of panels so 4500W of max charging.

Reduce output amps to 50A. It is now overpaneled. Sure, it will hit max charge rate and hold it for more hours. But will it produce more Kwh by the end of the day?

 

[Brucey]

I came back into the office to post exactly this point.

Take Brucey and his blue 450/100. 4.5Kw of panels so 4500W of max charging.

Reduce output amps to 50A. It is now overpaneled. Sure, it will hit max charge rate and hold it for more hours. But will it produce more Kwh by the end of the day?

Except in my case I had 6.7kWp on the 450/100.

Now I'm running 15kWp on the 450/100.

Output has doubled (the amount of time where I've had direct sunlight in last two weeks is pretty minimal versus overall solar conditions). If I needed that peak "clipped" output I'd need an additional scc.

What you're describing by limiting scc output isn't the same as adding panels.

 

[Zwy]

Except in my case I had 6.7kWp on the 450/100.

Now I'm running 15kWp on the 450/100.

Output has doubled (the amount of time where I've had direct sunlight in last two weeks is pretty minimal versus overall solar conditions). If I needed that peak "clipped" output I'd need an additional scc.

Output should double as you added more panels.

Output would double by adding the same number of panels with another charge controller, it would be the same production on a cloudy day too.

The only thing different is overpaneling might hit max input if it isn't "cloudy enough".

If I keep beating it into your head, you might understand. "Maff' is hard."

What you're describing by limiting scc output isn't the same as adding panels.

Yes, you are overpaneling the charge controller as output is throttled, the same as having twice the number of panels the 450/100 can pull at max charge setting.

 

[Zwy]

DVCC takes into account loads as well. So for example with 100A scc if set at say 60A for a smaller battery bank, it will allow the sccs to power loads, while limiting charge to batteries to 60A. Without DVCC the scc would be limited to 60A of production in total at all times.

I just put whatever the panels can produce on the DC bus and the inverters take what power is needed for the loads. It isn't rocket science. You are claiming the DVCC is some special thing, it isn't.

I admire the consistency of your messaging.

You are welcome.

Sure, but can you arbitrarily assemble N of them and have them coordinate the maximum charge rate?
That's a Victron feature.

I run max charge rate on both SCC's in my house. The SCC's put all power on the DC bus and it goes where it needs to go, either battery or loads. No coordination, the SCC's just put out what can be pulled from the array.

But if others can do that I'd like to know, perhaps two 18kpvs in parallel will coordinate all the MPPTs to limit charge current?

You can add diversion loads if the battery isn't big enough. Heating/cooling, hot water. Those are just different forms of battery/energy storage. I never seem to have a problem finding a place for peak power to go.

 

[akitawpo]

I have two 6000Xps in parallel. One of the MPPT has 8 550watts panels in series / 4,400 watts. The limit on that MPPT is 4000 watts. The good thing about it is I get high solar production in the early mornings and late in the afternoons. Also, if you take into account that real solar production is around 85% of the rated output, over paneling compensates for that "loss". On a good day at 10:30am I've seen it pegged at 4000watts on that MPPT.

 

[Brucey]

Output would double by adding the same number of panels with another charge controller, it would be the same production on a cloudy day too.

The only thing different is overpaneling might hit max input if it isn't "cloudy enough".

If I keep beating it into your head, you might understand. "Maff' is hard."

We are using the same math. In my previous post I cover budget as a factor. In an unlimited budget scenario then having enough ssc capacity to capture every Watt of possible panel output is the theoretical "best" solution (lightly underpanelled so that peak pv output never hits scc max output)

Post in thread 'Overpaneling - right, wrong or indifferent' https://diysolarforum.com/threads/overpaneling-right-wrong-or-indifferent.96921/post-1323409

"I look it at this way. Had 20 panels on my 450/100. That's enough to max out in full sun. Realized winter yield is garbage in overcast conditions. Doubled up on panels. Doubled my overcast day output. Now I will be limited at 100A on a sunny day. But that's very rare. So instead of hoping for a jackpot golden hour or two I try and gather all day, slow and steady.

I could have bought a second 450/100 instead of panels. Which would help me in summer peaks. But would have done nothing for my low winter production.

Now I need to deploy more sccs to handle the peak production possible, but at the time it made more sense to buy more panels versus more scc. I guess if in doubt more panels which will increase your daily output first, then more scc to handle rarer full sun conditions. Without a budget then get panels and more scc at the same time."

 

[Brucey]

I just put whatever the panels can produce on the DC bus and the inverters take what power is needed for the loads. It isn't rocket science. You are claiming the DVCC is some special thing, it isn't.

There is a difference between dvcc controlling max charge rate to batteries while allowing additional pv to power loads, versus what you get by limiting charge rate on the scc itself. Nothing magical, but different and can allow for significantly more pv output even with a small battery system. It doesn't matter to you and I because we aren't battery limited, where enabling dvcc makes sense.

 

[ricardocello]

There is a difference between dvcc controlling max charge rate to batteries while allowing additional pv to power loads, versus what you get by limiting charge rate on the scc itself. Nothing magical, but different and can allow for significantly more pv output even with a small battery system. It doesn't matter to you and I because we aren't battery limited, where enabling dvcc makes sense.

It matters to me because I am battery limited at 15 kWh!

I know, I know, buy more batteries, sheesh.
For me right now: Install Panels first, more batteries second, additional SCCs third.
I suspect all of us have a different priority at any given moment in time.