Panel shading: parallel vs series

[Kwest364]

Does any combination of parallel vs series for the panels matter at all if they're on the same controller?

Or can panels only be completely unaffected if they're on a different "circuit" and separate charge controller?

[Iceni John]

Originally Posted by Kwest364

Does any combination of parallel vs series for the panels matter at all if they're on the same controller?

Or can panels only be completely unaffected if they're on a different "circuit" and separate charge controller?

I don't quite understand your question!

FYI, I have eight 255W panels in two separate arrays of four panels each, each array wired in parallel to its own combiner box that then feeds its own CC that charges its own bank of batteries. In other words, I have two entirely separate systems running in parallel. Everything's working just fine this way.

John

[Clouse House]

Originally Posted by Kwest364

Does any combination of parallel vs series for the panels matter at all if they're on the same controller?

Or can panels only be completely unaffected if they're on a different "circuit" and separate charge controller?

Parallel vs series does matter.
Running too many in parallel will increase your amperage above what the charge controller can handle. Were as running too many in series will increase your voltage above what your charge controller can handle, on the same note, not running enough in series may cause your charge controller to not even turn on.

For example, the charge controller I chose needs a minimum of 60v in order to function but a maximum of 245v. It also has a maximum amperage of 120. I plan to have 6 panels that produce 41.5-49.35v at 10.96-11.44A. If I run all 6 in parallel I'll produce 41.5-49.35v at 65.76-68.64A. My charge controller can handle the amperage but the voltage is too low, the charge controller wouldn't even turn on. But if I run them in pairs; 2 in series with 3 parallel lines it will produce 83-98.7v at 32.88-34.32A. My voltage has now gone over the 60v needed to activate while dropping my amperage to about 15% capacity. More than enough room to grow in the future.

Also, from my understanding (which is limited) shade has a greater effect on panels that are run in series rather than parallel.

If you have two panels in series and one is shaded it reduces the output of BOTH panels. But if you have two panels in parallel and one is in shade it only decreases the output of the panel in the shade. (Again my understanding is limited)

[flattracker]

My experience with solar on the roof of the "new Crown" is that over-voltage will take out a charge controller as much as over-current. My panels produced up to 29 volts and that was enough to take out cheap charge controllers. Once the controllers get shorted out then the panels will produce over voltage conditions at the batteries.
When you have panels in series, any one panel that gets shaded reduces the current flow from all the panels it is in series with. When connected in parallel shading will affect the ones in shaded but the not shaded ones still produce good power. Parallel connected panels produce more current flow thus requiring thicker wiring at some point. I connected mine in parallel.



When you select your charge controller(s), pick ones that EXCEED the expected voltage and current flow you expect to have. My panels were specked to peak at 26 volts open circuit but exceeded that under load. After a few failures I am getting good results.

[Kwest364]

@ John
My question essentially was: effects of panel shading? When using single charge controller, does any combo of panels in series vs parallel avoid shading V drops? Does shading matter if you have separate charge controller to each panel?

@everyone
My research found:
Parallel panels = best for shade. Even when wired to ONE charge controller, panels all in parallel would be best to combat shading. In a parallel string, when 1 panel is shaded, only the 1 shaded panel is affected; all the other panels in full sun will pull their normal amount of power.

Vs

Series, where every panel is affected by the shaded panel, even if all panels in full sun.

So, it comes down to wiring to hit minimum CC operating V, staying under max V and max A, and staying within the lowest part of the range for input voltages and amps to, ideally, be able to expand bank down the road by starting at the low end of the ranges. The total amount of energy produced by the panels (in Watts) will still be the same, regardless of parallel vs string configurations, correct? Or am I mistaking that?

Knowing that, seems separate charge controllers seem to only be for complete redundancy and backup in case one system goes down. Good idea, but worth doing? Wonder the cost difference. Could be a big range, quality depending. But essentially you'd have to add separate CC, panel fusing/combiner, panel disconnect, wiring from panels, wiring from CC to batteries, and fuses. Assuming separate systems, you'd run either into a common/shared battery bank, or separate batteries altogether (unnecessary?). Seems like a shared battery bank, but different CC and panels would be fine if one goes down that route.


Anything to add or that I missed?

[Dbacks2k4]

Originally Posted by Kwest364

My research found:
Parallel panels = best for shade. Even when wired to ONE charge controller, panels all in parallel would be best to combat shading. In a parallel string, when 1 panel is shaded, only the 1 shaded panel is affected; all the other panels in full sun will pull their normal amount of power.

Vs

Series, where every panel is affected by the shaded panel, even if all panels in full sun.

So, it comes down to wiring to hit minimum CC operating V, staying under max V and max A, and staying within the lowest part of the range for input voltages and amps to, ideally, be able to expand bank down the road by starting at the low end of the ranges.

Knowing that, seems separate charge controllers seem to only be for complete redundancy and backup in case one system goes down. Good idea, but worth doing? Wonder the cost difference. Could be a big range, quality depending. But essentially you'd have to add separate CC, panel fusing/combiner, panel disconnect, wiring from panels, wiring from CC to batteries, and fuses. Assuming separate systems, you'd run either into a common/shared battery bank, or separate batteries altogether (unnecessary?). Seems like a shared battery bank, but different CC and panels would be fine if one goes down that route.


Anything to add or that I missed?

Sometimes you can get two smaller controllers for less $ than one larger one. Plus the redundancy factor. They're not redundant (aka failover) to each other though. Loss of a CC still loses half your solar. And now you have two components which could fail. A "pick your poison" type of scenario.

But I think you've mainly hit the nail on the head that you want as many smaller strings/series in parallel as you can get to minimize shading impact. The layout of the series on the roof is most important here I'd think.

[rossvtaylor]

I think you've got a good understanding of the differences and the impact of shading. I will add one thing, though, to factor into the pros/cons. A series string will reach a voltage high enough to start providing charge earlier in the day...and keep that up later in the day. And during cloudy days, a series string will often outperform a parallel string just because of the voltage differences. A friend even gets some charging at night in a WalMart or Home Depot parking lot. But yes, they are more prone to shading influences.

Modern large panels with bypass diodes are less severely impacted by shading, so the problem some smaller or cheaper panels have (where a single large leaf could shut down an entire panel) is avoided. But I evaluated a system in India where they installed a single panel...I think they were 80W or so...on every pole in a long string, right below the power lines. It turned out that the 1-inch wide shadow of the overhead lines bisected the panels when the sun was overhead and that completely shut down each panel's production.

[BriteLeaf]

Originally Posted by rossvtaylor

I think you've got a good understanding of the differences and the impact of shading. I will add one thing, though, to factor into the pros/cons. A series string will reach a voltage high enough to start providing charge earlier in the day...and keep that up later in the day. And during cloudy days, a series string will often outperform a parallel string just because of the voltage differences. A friend even gets some charging at night in a WalMart or Home Depot parking lot. But yes, they are more prone to shading influences.

Modern large panels with bypass diodes are less severely impacted by shading, so the problem some smaller or cheaper panels have (where a single large leaf could shut down an entire panel) is avoided. But I evaluated a system in India where they installed a single panel...I think they were 80W or so...on every pole in a long string, right below the power lines. It turned out that the 1-inch wide shadow of the overhead lines bisected the panels when the sun was overhead and that completely shut down each panel's production.

Yes it matters.
I have four 235 watt panels for a total of 1140 watts.
My charge controller can handle 60A.
My panels are rated for 12, 24, 36, and 48V.
Each voltage(coming to the charge controller) is only rated to handle so many watts coming in.
I have a 24V system, so due to my controller only being able to handle 900 watts at 24V I have to have two panels tied in series with one another, and the other two panels tied together in series, and then those two sets of panels are wired together in parallel.(I think I have that right).

[rossvtaylor]

Originally Posted by BriteLeaf

Yes it matters.
I have four 235 watt panels for a total of 1140 watts.
My charge controller can handle 60A.
My panels are rated for 12, 24, 36, and 48V.
Each voltage(coming to the charge controller) is only rated to handle so many watts coming in.
I have a 24V system, so due to my controller only being able to handle 900 watts at 24V I have to have two panels tied in series with one another, and the other two panels tied together in series, and then those two sets of panels are wired together in parallel.(I think I have that right).

With respect to you, I think you're confusing things. Panels aren't rated for different voltages like that...they will have an output voltage rating. True, the voltage will vary with sunlight strength but systems are designed around the max voltage output. Some smaller panels only put out 12-14V but most larger ones put out 30-40 volts. So your series string will add those voltages and you need to keep the total voltage below the panel input voltage limit of your charge controller.

If you have a 60A charge controller it should handle a lot more than 900W. What you need to check are the max input voltage and current (amperage) rating of the charge controller, the max voltage and output current of each panel, and then configure the panel strings so that the controller limits aren't exceeded.

[scloughcarroll]

Not sure if this was already mentioned, but I know that my panels (100W renogy 12V) include Bypass Diodes within each panel, so if a leaf or something is shading a cell or section of the panel the whole panel does not go down, just the cells in series with that diode.

Helpful overall regardless as to your setup

[Kwest364]

Originally Posted by rossvtaylor

A series string will reach a voltage high enough to start providing charge earlier in the day...and keep that up later in the day. And during cloudy days, a series string will often outperform a parallel string just because of the voltage differences

How is that the case? I thought panels pull watts, and voltage and amps are irrelevant to overall harvested energy production. Same as batteries and amp hrs: doesn't matter if it's 12V @ 400ah, 24V @ 200ah, or 48V @ 100ah, it's all 4,800 Wh of stored energy capacity.

So, a 100 W panel should pull the same amount of energy regardless of it's voltage or amps, right?
25V x 4A = 100 W vs 10V x 10A = 100 W also. So, the energy harvested should be 100W regardless.


But you're saying, voltage does make a difference? I intuitively thought that with batteries (that amp hrs was total measure of energy content, rather than Wh, which is a more accurate measure), but it matters with panels?

[Rwnielsen]

Originally Posted by Kwest364

How is that the case? I thought panels pull watts, and voltage and amps are irrelevant to overall harvested energy production. Same as batteries and amp hrs: doesn't matter if it's 12V @ 400ah, 24V @ 200ah, or 48V @ 100ah, it's all 4,800 Wh of stored energy capacity.

So, a 100 W panel should pull the same amount of energy regardless of it's voltage or amps, right?
25V x 4A = 100 W vs 10V x 10A = 100 W also. So, the energy harvested should be 100W regardless.


But you're saying, voltage does make a difference? I intuitively thought that with batteries (that amp hrs was total measure of energy content, rather than Wh, which is a more accurate measure), but it matters with panels?

Some panels a rated at 12 volts whereas larger panels have an open circuit voltage of around 40 volts. I think that's what you mean (?)

[rossvtaylor]

Originally Posted by Kwest364

How is that the case? I thought panels pull watts, and voltage and amps are irrelevant to overall harvested energy production. Same as batteries and amp hrs: doesn't matter if it's 12V @ 400ah, 24V @ 200ah, or 48V @ 100ah, it's all 4,800 Wh of stored energy capacity.

So, a 100 W panel should pull the same amount of energy regardless of it's voltage or amps, right?
25V x 4A = 100 W vs 10V x 10A = 100 W also. So, the energy harvested should be 100W regardless.


But you're saying, voltage does make a difference? I intuitively thought that with batteries (that amp hrs was total measure of energy content, rather than Wh, which is a more accurate measure), but it matters with panels?

You're right on the math. But with charging to occur, the charge source (the panels) needs to have a voltage higher than the battery voltage. In a series string, the higher voltage of the string will result in it starting to charge earlier in the day.

Say, for example, your 36V panels are all in parallel and at 9:45 am they get enough sun for their output voltage to climb to 26V...higher than the 24V battery bank and charging can start. But if the panels are arranged in a series string, the added voltage means the array output voltage will get to 26V earlier in the day and remain above the battery voltage later in the day. It takes less solar energy for the strings (and the array) to output a voltage high enough to exceed the battery voltage.

You are absolutely correct that changing the voltage (by stringing in series) doesn't change the wattage output, it just lets the array exceed the battery voltage with less energy. So, whether that's a cloudy day or nighttime lighting in a parking lot or earlier/later daylight the output voltage will be higher than a parallel string. It won't be a lot of power, so it may not be worth worrying about, but it's something to consider.

[Clouse House]

Originally Posted by rossvtaylor

You're right on the math. But with charging to occur, the charge source (the panels) needs to have a voltage higher than the battery voltage. In a series string, the higher voltage of the string will result in it starting to charge earlier in the day.

Say, for example, your 36V panels are all in parallel and at 9:45 am they get enough sun for their output voltage to climb to 26V...higher than the 24V battery bank and charging can start. But if the panels are arranged in a series string, the added voltage means the array output voltage will get to 26V earlier in the day and remain above the battery voltage later in the day. It takes less solar energy for the strings (and the array) to output a voltage high enough to exceed the battery voltage.

You are absolutely correct that changing the voltage (by stringing in series) doesn't change the wattage output, it just lets the array exceed the battery voltage with less energy. So, whether that's a cloudy day or nighttime lighting in a parking lot or earlier/later daylight the output voltage will be higher than a parallel string. It won't be a lot of power, so it may not be worth worrying about, but it's something to consider.

I was under the impression that although voltage does vary with sun intensity/shading it varied only a small amount. And that amperage was what varied the most throughout the day.
For example: A panel rated at 48V at it's lowest point might produce only 41V with next to no amperage. But the voltage would drop no lower than 41V.

[rossvtaylor]

Originally Posted by Clouse House

I was under the impression that although voltage does vary with sun intensity/shading it varied only a small amount. And that amperage was what varied the most throughout the day.
For example: A panel rated at 48V at it's lowest point might produce only 41V with next to no amperage. But the voltage would drop no lower than 41V.

True. It only varies a small amount after it reaches its peak, which is does rather quickly because the increase in voltage is logarithmic (so it doesn't spend much time at the lower voltages). Once at its peak, the voltage remains fairly constant and current increases. I haven't read that a 48V panel won't have a voltage potential below 41V and I've seen (in practice) low voltages in low irradiance situations. In such a case, the series string will reach a charge voltage with less light. But like I said, it's not much of a difference and probably not worrying about...that log increase in voltage means you may only see it in really low-light situations. My friends Yvan and Sylvie Lacroix get some charging at night in parking lots, but it's a bit of a novelty more than practical charge energy.

[Kwest364]

Originally Posted by rossvtaylor

You're right on the math. But with charging to occur, the charge source (the panels) needs to have a voltage higher than the battery voltage. In a series string, the higher voltage of the string will result in it starting to charge earlier in the day.

Say, for example, your 36V panels are all in parallel and at 9:45 am they get enough sun for their output voltage to climb to 26V...higher than the 24V battery bank and charging can start. But if the panels are arranged in a series string, the added voltage means the array output voltage will get to 26V earlier in the day and remain above the battery voltage later in the day. It takes less solar energy for the strings (and the array) to output a voltage high enough to exceed the battery voltage.

You are absolutely correct that changing the voltage (by stringing in series) doesn't change the wattage output, it just lets the array exceed the battery voltage with less energy. So, whether that's a cloudy day or nighttime lighting in a parking lot or earlier/later daylight the output voltage will be higher than a parallel string. It won't be a lot of power, so it may not be worth worrying about, but it's something to consider.

Exactly the type of explanation I was looking for. Thank you. Do you think it's worth leaving panels as they are? Or worth wiring up differently? It has been working with no problems, but I'm guessing it's worth it, especially long term and easier on equipment to run the proper voltage input range for CC, which is 36V-72V @ 24V system (3P2S = 72V 15A) vs the current wiring of 2P3S (108V 10A).

Worth hassle of pulling panels off and rewiring?