Overpaneling - right, wrong or indifferent

[emcvay]

Hi,

I've been debating over paneling for a little while now and as someone who's watched many of Will Prowes videos I thought I'd pop in here and toss this out:

If 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?

In my mind there is power available as soon as the sun hits the panels in sufficient amounts to generate something the SCC can use. It then continues, essentially in a bell curve throughout the day until it hits peak and then drops off to nothing. Of course, on a cloudy day this curve might be warped quite a bit as the clouds block out the sun at differing degrees however it still follows a predictable path of a start and finish point and a peak at some point during the day.

A smaller charge controller can only utilize so much power from what is available and a larger one, while able to utilize the same amount of power at lower levels can utilize MORE power at the higher levels.

Setting cost aside and all in one systems aside, on a theoretical basis I see no advantage in using a smaller charge controller over a larger one (if measured in max wattage on the input side). I realize the efficiency calculations will appear to make the smaller unit more efficient but that does not equate to making more power available to charge batteries on a cloudy day.

So, how is it that a 2000w max input charge controller can possibly utilize more power from a 2300w array that say, a 2500w max input charge controller could?

 

[Brucey]

I have a 450/100 scc. Maxes out at 100A (can temp push up to 125A during cloud edging effects).

Has two trackers, each with a further limit of 4kW max each. Currently I have ten aptos 370W and ten Hyundai 300W on them. In the winter with overcast conditions the scc utilization is pretty poor. Not a lot of output. In my next experiment I'm going to put 14 375W Vikram on each tracker. That's 10.5kW of panels on an scc that can generally output 5.6kW max. The reason is to increase my non ideal conditions output. Yes in full sunshine I'll be output limited with the 100A limit. But I'll also be producing more in non direct sun. Not more than if I just got a second 450/100, but making more effective use of a single 450/100.

 

[Mattb4]

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.

 

[Johneb]

I overpanel the inverter not the scc. I have an 8k inverter with 3 scc’s. 150/80. Each scc will have a total of about 3600 watts. This keeps the scc from making magic smoke and provides enough energy to keep the inverter working in the 8k range most of the time.

 

[emcvay]

I overpanel the inverter not the scc. I have an 8k inverter with 3 scc’s. 150/80. Each scc will have a total of about 3600 watts. This keeps the scc from making magic smoke and provides enough energy to keep the inverter working in the 8k range most of the time.

To be clear, the inverter has nothing to do with it but I know some get confused because of AIO systems. Inverter's take DC power and convert it to AC power. It's the solar Charge Controller that takes the power from the solar array and utilizes it to charge the battery bank.

The inverter draws power from the battery bank. Now, yes, if the SCC's are charging the batteries the inverter can draw from the batteries without drawing them down -- ie. utilize the power coming in from the SCC's. However, it doesn't care how much power is being directed at the batteries. It simply draws whatever it needs (in Amps) to provide the correct 120v AC to the items drawing.

Kinda like having a 10kwh battery bank and a 1kw inverter -- the inverter could care less what size the battery is, it only matters what the voltage is (that it's not too high or too low) and if it can draw the needed amperage off the bank (a too small bank may restrict the inverter).

 

[emcvay]

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.

This has been my suspicion all along.

It isn't a case of over paneling producing MORE power, it's a case of spending less (hopefully) on more panels than more (ostensibly) on a larger charge controller.

 

[justoneguy]

It's about the varying solar production
over panelled in the summer under panelled in the winter

 

[Q-Dog]

If you look up at a cloudy sky a couple of times a week and say, "If I had about 20% more panels I would be in good shape," then over paneling might be right for you.

Let's say I have a battery that wants to be charged at 20 amps. So I install a 20 amp solar charger and the correct amount of solar panels and the system works perfectly fine, as long as the sun is good. But on cloudy days the production falls a little short. Over paneling lets you add production on cloudy days without overcharging your batteries on good solar days.

 

[emcvay]

If you look up at a cloudy sky a couple of times a week and say, "If I had about 20% more panels I would be in good shape," then over paneling might be right for you.

Let's say I have a battery that wants to be charged at 20 amps. So I install a 20 amp solar charger and the correct amount of solar panels and the system works perfectly fine, as long as the sun is good. But on cloudy days the production falls a little short. Over paneling lets you add production on cloudy days without overcharging your batteries on good solar days.

I don't dispute that - but the question was: If 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?

The answer as far as my 30 years in DC power (telecom) and 15 years in solar remains the same: over paneling does not produce more power than properly sizing the charge controller for the array (which in my book means a charge controller that can handle/utilize all the possible power on the coldest most perfect day in the winter.

I don't dispute that adding more panels isn't a good idea for low light production, I only dispute the logic that utilizing a charge controller that is under rated for the expected solar array will produce MORE power than a properly sized one.

For example, if designing a system, why would anyone over panel the design? To me it makes far more sense to properly size the charge controller for the array all things being equal. After all, I can find a use for the extra power in summer that I'll get (and in my case that's more power tools being used, more freezer power to use etc -- heck, maybe even a mini split for AC).

 

[emcvay]

It's about the varying solar production
over panelled in the summer under panelled in the winter

Not sure what you mean by that -- other way around I'm guessing. Over in the winter would be way over in the summer if one assumes the same power consumption (I don't).

For me, more power in the winter just means more power for me to make use of No generator run time, more power tools for building, more late night music, TV whatever not to mention a freezer that I don't run in the winter (because I no longer need to since I no longer live there in the winter and spend less time off grid in the winter) etc etc.

 

[Q-Dog]

For example, if designing a system, why would anyone over panel the design?

I just gave you an example why.

 

[SunDave]

Hi emcvay,
Setting up a perfect system without cost constraints is easier than having cost constraints. That you can see.

But considering there are cost constraints in the real world, it is often cheaper to "over-panel" than "over inverter\scc". In the over panel scenario, you are often getting more watts for your $. Not more watts vs. the best possible scenario. You do indeed use more of your current inverter that way since not all days are full sun. Even the days that are full sun, you make more power on both sides of solar noon, only chopping off that last bit at high noon.

So if you have a system, and have $1,000 dollars to "improve" it in a hypothetical scenario, it is worth at least considering going the panel route vs. non.

 

[SunDave]

Also, as others have pointed out, over-paneling can produce power when you need it most. You don't often need that last little bit of power on a full sun day, but you often need more power on cloudy days.

So while you are absolutely technically correct that you will be more optimal with a perfect setup. The real world use case for the theory holds up very well.

 

[outboard1196]

I don't dispute that - but the question was: If 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?

The answer as far as my 30 years in DC power (telecom) and 15 years in solar remains the same: over paneling does not produce more power than properly sizing the charge controller for the array (which in my book means a charge controller that can handle/utilize all the possible power on the coldest most perfect day in the winter.

I don't dispute that adding more panels isn't a good idea for low light production, I only dispute the logic that utilizing a charge controller that is under rated for the expected solar array will produce MORE power than a properly sized one.

For example, if designing a system, why would anyone over panel the design? To me it makes far more sense to properly size the charge controller for the array all things being equal. After all, I can find a use for the extra power in summer that I'll get (and in my case that's more power tools being used, more freezer power to use etc -- heck, maybe even a mini split for AC).

For me, over panelling gives me consistent output. My 70A charge controller puts out a constant 70A all day no up and down as the clouds move about on most days it's not raining / overcast. Sure I'm leaving energy on the table.

 

[HarryN]

If you think about the power load use over the course of the day, it might make sense to consider to add panels facing multiple directions than to worry about the panels facing just one direction.

Most people are short of power first thing in the morning and very late afternoon vs mid day.

Think about where the sun is an hour after sunrise and an hour before sunset. That is where you will gain the most value.

 

[emcvay]

Again, I don't dispute all that's been said. My point is about absolutes only. It's a theoretical question. Either over paneling produces more power than properly built systems with the correct charge controller (not inverter, it has nothing to do with it) or it does not. It doesn't.

I don't argue there may be reasons to do it (financial is the only real reason I can see and then it's actually kinda dubious when amortizing the project over it's life.

absolutely technically correct

 

[SunDave]

Yes, in theory, over paneling leaves watts on the table.

In reality, if you use your scenario of a bigger charge controller you are gaining in absolute watts produced and losing in usable watts per dollar.

 

[SunDave]

Some of the discussion will get lost in translation because of scenario dependency as well.

For example, an off-grid person may need the watts in the winter, where a grid tied person may be looking for overall watts. In each scenario, where you spend your dollar can maximize the systems performance for you personally.

 

[Mattb4]

Strictly as a personal preference I favor under paneling an AIO or SCC. But that is because I buy inexpensive and do not trust the Duty cycle of the units ratings.

 

[blackbear199]

agree why what others have stated.
i have 2 arrays on 2 controllers at my camp.

2x410w panels on a 40a epever
2x545wpanels on a 60a epever

i did this beacause of the space where i could put the panels.i wanted to use every amount i could.
i am a bit over the 150% over paneling recommendation.
i am using 8 12v in parallel and wanted to my charge to be around 10-12 amps per battery.
why i went with the above setup.
i am not quick charging my bank so it shud last longer.
it also gave a backup as should one array shut down i still have the other.

but i get to bulk charge earlier in the day and its holds it at float until late in the day so every evening my bank has cycled and is full.

 

[Johneb]

Strictly as a personal preference I favor under paneling an AIO or SCC. But that is because I buy inexpensive and do not trust the Duty cycle of the units ratings.

I underpanel the 150/80 scc to prevent magic smoke which is more likely in winter. Colder temperatures/cloud edge production. I also set the scc for 75amps instead of 80 for further protection from over production leading to said magic smoke . I prefer an added scc over over paneling one. Can be less costly.

 

[SenileOldGit]

I have 12kW of panels. I have only been getting from 1.5 kWh to 3kWh per day for the past week in the U.K., and I am using Tomato Energy night time electricity at 5p per kWh to charge my 15kWh batteries from 1am to 5am, and I use the batteries during the day to power my house. I now know that buying more panels is pointless for me.
I would have to have 90kW of panels to generate even 10kWh of electricity on misty, short days, like we've had in the U.K. for the past few weeks. I would have no garden space left, and it would cost me tens of thousands of pounds to buy.
Whereas right now I am paying from 80p to 90p per day for my electricity, and that's only during November to February. The rest of the time, it's all free.

 

[timselectric]

I only dispute the logic that utilizing a charge controller that is under rated for the expected solar array will produce MORE power than a properly sized one.

The real question is, who's saying this for you to dispute?
Hopefully Noone.

 

[GRMRC]

Hi,

I've been debating over paneling for a little while now and as someone who's watched many of Will Prowes videos I thought I'd pop in here and toss this out:

If 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?

In my mind there is power available as soon as the sun hits the panels in sufficient amounts to generate something the SCC can use. It then continues, essentially in a bell curve throughout the day until it hits peak and then drops off to nothing. Of course, on a cloudy day this curve might be warped quite a bit as the clouds block out the sun at differing degrees however it still follows a predictable path of a start and finish point and a peak at some point during the day.

A smaller charge controller can only utilize so much power from what is available and a larger one, while able to utilize the same amount of power at lower levels can utilize MORE power at the higher levels.

Setting cost aside and all in one systems aside, on a theoretical basis I see no advantage in using a smaller charge controller over a larger one (if measured in max wattage on the input side). I realize the efficiency calculations will appear to make the smaller unit more efficient but that does not equate to making more power available to charge batteries on a cloudy day.

So, how is it that a 2000w max input charge controller can possibly utilize more power from a 2300w array that say, a 2500w max input charge controller could?

STC. If you don’t get/need 1,000 W/m^2 to “max out” your SCC then you over panel so more days than not your SCC can produce “max” power.

 

[emcvay]

The real question is, who's saying this for you to dispute?
Hopefully Noone.

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.