Overpaneling - right, wrong or indifferent

[Mattb4]

Not sure if you are reading his question correctly. I believe he is assuming the same number of panels for a both smaller or larger rated controller. Over-paneling any controller will result in some amount of increased power generation as it will max out longer and do better on cloudy days. However, if a controller is already over=paneled and you instill a larger or second controller, that will then produce more. as you won;t be clipping at the peak.

I guess you do not understand ironic humor. As a strictly mathematical based question being able to utilize more watts from a panel when conditions warrant (larger SCC and enough load) is going to produce more. However my joke was math is not everything.

 

[Brucey]

I find it pretty incredible that you are getting 110% of rated power on just a 70 degree day (in Washington no less), let alone after 14 years. I'm also curious as you how you are measuring it.

Maybe with cloud edge effects.

 

[Texas-Mark]

Maybe with cloud edge effects.

He said on sunny days. <shrug>

 

[GRMRC]

LOL

I was hoping to keep who I am a little bit less obvious but I've had many argue with me on this to the point of getting downright, well, silly would be polite.

I'm a youtuber (though no where near Will's level of subs/views) who concentrates on other things than just power related things but as someone who has built his own solar power system and upgraded it a few times and lived with it full time (though I do not right now) I often make videos on solar.

I've made the point a couple times that while I cannot argue with the reasoning behind over paneling, strictly speaking putting in a larger SCC will in fact generate more power. It's simple math.

Anyway, there are many who allow their emotions and personal anecdotal experience cloud their arguments. I get why people do it, might even agree to the reasoning (in fact I've said I can't argue against it in a lot of cases) but from a strictly mathematical standpoint it doesn't make sense -- at least when total power produced can be the issue.

You are missing your calling with that utube thing. With the arguments you are making you clearly should a university professor where theoretical arguments are taught to students.

 

[GRMRC]

I find it pretty incredible that you are getting 110% of rated power on just a 70 degree day (in Washington no less), let alone after 14 years. I'm also curious as you how you are measuring it.

Maybe he posted a youtube video on how he measures it.

 

[Texas-Mark]

I guess you do not understand ironic humor.

Humor aside, I thought your answer was saying yes to "will over paneling produce more power than having a properly sized SCC for the array." To which I disagreed somewhat. As someone else noted, it depends on several factors. An over-paneled controller in a mostly cloudy area may never clip, and thus would not produce more than a having a "properly sized contoller".

 

[emcvay]

OK, 1sty thanks for all the great responses -- even the professor one I've been called that before

Does theory matter? Sure. If in fact the SCC is the deciding factor given the same conditions and same array then yes, even on a wintry day when it's cloudy and drizzling in Seattle the larger SCC will produce more power. Period. It may cost more (not part of the question) but it WILL produce more given the conditions explained.

I'm not hear to debate if over paneling has a place, nor whether or not it costs more or less per kwh. Just (in this thread anyway) whether or not a solar charge controller that is sized to accept all of the power a solar array can provide it under peak conditions would produce less, or more, power that one undersized.

Since my two part question confused some let me try this instead:

Morningstar rates their TriStar MPPT charge controllers this way: Max Recommended Solar PV Input* ~ 130% of Nominal Max Ouput Power(60 Amp models shown above)

This give this note: * The PV array power rating may exceed the controller’s Max Nominal Output Power specification. The controller will limit battery current and prevent damage. Array oversizing should be considered on a case by case basis. See our array string

So the:
TriStar MPPT45 is rated for a 24v system at 1200w output / 1560w input
The TriStar MPPOT60 is rated for a 24v system at 1600w output / 2100w input.

Given an array size of 2000w and all other things considered which charge controller would provide the most useable power in low light conditions?

Note: I'm using this SCC because it's the 2nd one I installed on my system in early 2011 (changing from a PWM controller I'd originally installed to MPPT) and I knew they made a few different rated versions of it. I could, however, do the same with other brands.

 

[emcvay]

Humor aside, I thought your answer was saying yes to "will over paneling produce more power than having a properly sized SCC for the array." To which I disagreed somewhat. As someone else noted, it depends on several factors. An over-paneled controller in a mostly cloudy area may never clip, and thus would not produce more than a having a "properly sized contoller".

hence a point I made elsewhere -- they would both provide the same power. They will both received less than their rated capacity and provide the same amount of power. The larger SCC only comes into play (in terms of which produces more power) when the array produces more power than the smaller one can utilize and so it starts clipping it off while the larger one WILL use that power.

 

[Gttnsun]

even on a wintry day when it's cloudy and drizzling in Seattle the larger SCC will produce more power. Period

I disagree

 

[emcvay]

I disagree

And you would be correct if the solar array does not produce more than the smaller SCC could utilize. I should have been more clear on that one.

On a cold cloudy wintry day if the array still produces more than the smaller SCC can take in and use, the larger one wins.

Someone mentioned being 80% over paneled. That could actually cause this condition

 

[Gaijin2]

emcvay, your argument is unnecessarily argumentative. You asked for answers, then reject them all.

So let's start with your premise: can a 500 watt panel with a 400 watt SCC ever produce more power than a 400 watt panel with a 400 watt SCC, when used solely under ideal test conditions? No. In that one very specific, ludicrous test case which will pretty much never happen, you are correct.

Now, for everyone else who lives in the real world and is trying to make valid decisions with their dollars: can a 500 watt panel with a 400 watt SCC ever produce more power than a 400 watt panel with the same 400 watt SCC? Of course it can, all the time, every day, any and every time the test conditions are less than ideal. Which is almost always.

Panels rarely produce their full rated wattage. Especially in winter, or on cloudy days, or with a slight bit of shading, or (on and on and on). So the case of a "perfectly matched" SCC to panel ratio is fantasy land. You're either wasting energy by overpaneling, or wasting dollars by over-powering your SCC. Adding a few panels can boost your winter production or daily production under less-than-ideal conditions, helping you meet minimum wattage requirements. If you need a system that delivers at least 2,000 watts throughout the solar day, you'd be a fool to panel that with 2000 watts of panels. This should be obvious to you, I'm sure it is obvious to you, but for some reason you insist on arguing a point that's irrelevant in real life, but which for your sake I've already acknowledged as correct.

In reality, there is no such thing as a perfectly matched system, there are compromises made in every design. Overpaneling is a valid technique to increase your overall kWh generation throughout the year, WITHIN A GIVEN BUDGET, if space permits; you will occasionally waste energy at perfectly optimized times but you will gain more energy during suboptimal times. With unlimited money, of course you should build a gigawatt system with gigawatt SCCs, so that argument is theoretical, pointless, and futile. We are all in agreement that unlimited bugets should yield unlimited power so if a D-cell battery stores more energy than a AA battery, then rest assured that we all agree with you. But that doesn't make a D-cell battery the right choice for every situation when space and weight are a consideration, which (outside of laboratory test conditions) they always are considerations.

Summing up: if you're arguing that 400 = 400, we agree with you; we just wonder why you're so adamant about it. If you're arguing "overpaneling is always a bad idea", we all disagree with you, for patently obvious reasons.

 

[Gaijin2]

I disagree

I agree with your disagreement. You stated it in two words, where it took me six paragraphs. Well done.

 

[AntronX]

TriStar MPPT45 is rated for a 24v system at 1200w output / 1560w input
The TriStar MPPOT60 is rated for a 24v system at 1600w output / 2100w input.
Given an array size of 2000w and all other things considered which charge controller would provide the most useable power in low light conditions?

Whichever one that has least conversion loss at 200w input (low light = 10% of rated). Assuming both SCC designs are identical except 45A version uses less mosfets then 45A SCC will make tiny bit more power and energy at low light simply due to less switching loss (but it may have some more resistive loss in the inductor). This is really splitting hairs. You want more cloudy weather energy harvest? Get more panels.

 

[Gaijin2]

And you would be correct if the solar array does not produce more than the smaller SCC could utilize. I should have been more clear on that one.

And there is the completion of the argument in a nutshell. The solar array will rarely ever produce as much as the "perfectly matched" SCC could utilize. So if you've got an extra $400 to improve your system's performance throughout the year, buying a few more panels will almost certainly add more to your annual kWh production than buying a larger-capacity SCC would. That's all.

 

[Texas-Mark]

So the:
TriStar MPPT45 is rated for a 24v system at 1200w output / 1560w input
The TriStar MPPOT60 is rated for a 24v system at 1600w output / 2100w input.

Given an array size of 2000w and all other things considered which charge controller would provide the most useable power in low light conditions?

In low light conditions (no clipping), it will probably be a wash.

However, given those two controllers, I would opt for the second one because it can output up to 60 amps, and thus can charge the battery faster (provided there is enough sun) and where the other could be clipping due to the over-paneling.

 

[Supervstech]

If you ASSUME a battery bank that can charge at as high a rate as possible, then having a larger controller makes sense.

However, overpaneling solves a few issues.
Cost aside, overpaneling solves full day charging by providing max amps as early as possible, and as long as possible. Larger controllers require larger solar production to begin charging.
Overpaneling solves if the max charge current of the battery bank is say 150A, then having two 100A chargers will not be able to safely charge the bank.
Where, two 75A chargers both overpaneled will provide the 150A max input as long as the sun is capable of producing the watts.
Also, with grid tie, the power company limits what you are able to build. The max output is locked. So, overpaneling makes the absolute best sense by producing the max wattage into the system for the longest time.

So… ignoring costs, I have provided three indisputable reasons for overpaneling.

Feel free to tackle them.

 

[Brucey]

hence a point I made elsewhere -- they would both provide the same power. They will both received less than their rated capacity and provide the same amount of power. The larger SCC only comes into play (in terms of which produces more power) when the array produces more power than the smaller one can utilize and so it starts clipping it off while the larger one WILL use that power.

I'll have some data for you starting tomorrow regarding overpanelling. I'm going to double the panels on my 450/100 from 10 per tracker to 20. Because I never hit the theoretical max of maybe 30kWh a day from 6.7kW of panels. Best I've got is 18kW in a day.

So in my case, I expect to double my scc output, without buying another 450/100 for $1100. Because my winter utilization is garbage. That's where overpanelling makes sense to me. Getting a second 450/100 for winter would be a total waste. Better to spend that money on more panels for winter production.

 

[emcvay]

"can a 500 watt panel with a 400 watt SCC ever produce more power than a 400 watt panel with the same 400 watt SCC? "

That isn't the question. It's quite the reverse.

I'm not trying to be argumentative and haven't disagreed with everyone at all. I've agreed that cost may be a factor (only said I'd have to do some research to see how much), that if the array never produces more than the smaller SCC can utilize than both would provide the same etc etc.

I'm just surprised at the responses I guess.

I have no problem with theoretical discussions as they do pertain to the real world in one way or another. It doesn't mean one way is correct or one way isn't, nor does it have to do with what's less expensive, more costly, more effective use of an array etc etc. It's just a question on, which is more capable. My Morningstar example makes that clear.

"If you need a system that delivers at least 2,000 watts throughout the solar day, you'd be a fool to panel that with 2000 watts of panels. This should be obvious to you, I'm sure it is obvious to you, but for some reason you insist on arguing a point that's irrelevant in real life, but which for your sake I've already acknowledged as correct."

I'm neither disagreeing with that, nor arguing against it -- and my system is way over built though I didn't over panel. My 2400+ watts of solar can get my 9.7kwh batteries back up to full charge usually within an hour of good sun. I've sized it intentionally to keep me charged up during the winter. I'm not arguing that at all.

Ans for those asking how I know what my panels are producing, I've only just moved into the somewhat modern world and using the ap on my new SCC to see what's being produced. I've seen it run as high as 672w off my 615w array. However, over the years I've seen their voltage run high as well and they are poly panels which are known to produce better than rated under good conditions. Is the SCC reporting incorrectly? Could be but in the end, I don't usually worry about it anyway as my system charges very fast.

 

[Brucey]

I'm neither disagreeing with that, nor arguing against it -- and my system is way over built though I didn't over panel. My 2400+ watts of solar can get my 9.7kwh batteries back up to full charge usually within an hour of good sun. I've sized it intentionally to keep me charged up during the winter. I'm not arguing that at all.

OK so your only using about 2.5kWh overnight?

 

[emcvay]

Again, I'm not arguing that there is a place for it, nor if it works for you. I'm surprised this is an issue for so many.

It is merely a mathematical question that's been answered. No. Overpaneling will not produce MORE power than using a solar charge controller that is built for the array (meaning, slightly larger than the array wattage). So a 2100w input SCC with a 2000w array can and will produce more of that 2000w than one sized at say 1500w -- or my earlier example of 2300w array with a 2k SCC vs a 2.5k scc.

Of course, if the array only produces 1000 watts they both will only be able to use that 1000w so neither will produce more. Certainly the smaller of the two will not utilize more of that 1000w somehow, than the larger of the two.

As for larger SCC's requiring more starting amps I do see that anywhere on Morningstar's data sheet, or others for that matter. They can and do provide power at even the smallest amounts once the voltage and the amperage is high enough to begin charging the batteries.

 

[emcvay]

I'm using around 75-80ah overnight typically. I don't actually track wattage, I convert to it for all those that do. I use (when it's hooked up but I've made changes so it isn't at the moment) a Tri-Metric meter set to amps, soc and volts.

So, yes, to be fair, I'm getting some small charge when the sun begins to hit the panels and it isn't until I get full sun that the battery banks gets full quickly but I said 'in good sun' - maybe I should say 'in full sun' or 'peak solar'.

Even in the winter (and I'm near the Canadian border on the north slope of a hill) when I get very little solar production, I can get the batteries back up quickly. That's why I sized my system over the way I did.

 

[Brucey]

As for larger SCC's requiring more starting amps I do see that anywhere on Morningstar's data sheet, or others for that matter. They can and do provide power at even the smallest amounts once the voltage and the amperage is high enough to begin charging the batteries.

The victron 450/100 and 200 have a startup voltage of 120V.
Midnite hawkes bay 90 and 120 and barcelona need 220V.
Not sure on the startup voltage for Schneider 600V sccs

 

[emcvay]

So in my case, I expect to double my scc output, without buying another 450/100 for $1100. Because my winter utilization is garbage. That's where overpanelling makes sense to me. Getting a second 450/100 for winter would be a total waste. Better to spend that money on more panels for winter production.

And I wouldn't disagree with your reasoning here.

 

[Kiwi2000]

Why do that when you could just add a larger SCC to handle the additional power in the summer and run a mini split with the extra wattage?

This is something I'm constantly thinking of. It won't reduce winter production over the day or at peak (actually, if you hit peak it will INCREASE winter production which you want).

But would your battery bank and wiring handle the increasing amps?

Your battery bank will ultimately have a maximum charging rate.

Let's make an example that's easy to understand. Say you only have a single 12v 100Ah battery to charge. And it has a max charge rate of 50 amps. So 50 amps is the most you would ever want to charge with so you get a 50 amp SCC. 50 amps at 13v is around 660 watts so you get yourself a 660 watt PV array.

This way you have not overpanelled the SCC.

However you now find that you only get 50 amps of charging in the middle of a cloudless day. Most of the time you are receiving much less than 50 amps.

So you decide to parallel in another 660 watt PV array on the same string going to the same SCC. You have now overpanelled it by 200%. Result is you are now receiving 50 amps of charge more consistently from day to day and for a much longer period of the day.

 

[emcvay]

Morningstar TriStar's have this: **PV Voltage must be greater thanVbattery + 1 Volt to start charging

So for a 24v nominal bank it's +1 from what? 27.2v for LiFePo4's -- and it's the same regardless of the size of the SCC.