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Can Solar Panels Be At Different Angles?

Veteran52

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May 18, 2020
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I currently have 5 solar panels all facing South at a fixed 45 degree angle from vertical. I'd like to add one more panel. I want to change 3 panels to 28 degrees from vertical to maximize the winter sun, and change 3 to face South at 78 degrees from vertical to maximize the summer sun. Obviously the current from 3 of them going to the collector box will always be lower then the other 3 at any given season. Is there any electrical reason I can't do this? I can't have 6 panels in my space as is, because of some panels shading others in the winter. If I can't do this I'm stuck with 5 panels.
 
How do you have your panels wired, series or parallel? With them pointing in different directions, any in series would likely be "shaded" at some point and greatly reduce the output of the rest of the series.

So, there is no reason you cannot do this, but there is definitely a better way of doing it.
 
If you break them into 2 charge controllers, 3 on each, this is certainly a viable way to go. Ideally, you want charge controllers that communicate with each other to coordinate a leader/follower to avoid conflicts with them having different voltages.
 
If you break them into 2 charge controllers, 3 on each, this is certainly a viable way to go. Ideally, you want charge controllers that communicate with each other to coordinate a leader/follower to avoid conflicts with them having different voltages.
Since all 6 panels would feed into a common collector box I assume the various voltages would be fixed at whatever voltage level by the time it gets to the SCC. The SCC would not see the different voltages going to the collector box would it?
 
All panels in one string should be oriented identically.
Multiple strings wired in parallel should each have the same number of panels, but each string can be oriented differently.
Works great, even wired to a single MPPT.
The manufacturers got around to testing what the thinking hobbyist/installer already knew, and confirmed that. (The determined only a couple % or so loss compared to all same orientation on a single MPPT.)

That said, if one of those strings has significant shading, the current vs. voltage curve may have multiple humps in it. In that case, only some MPPT successfully find the global maxima and don't quit searching on a local maxima.

If all your panels are in parallel, all the above still applies; your strings are just one panel long.
 
All panels in one string should be oriented identically.
Multiple strings wired in parallel should each have the same number of panels, but each string can be oriented differently.
Works great, even wired to a single MPPT.
The manufacturers got around to testing what the thinking hobbyist/installer already knew, and confirmed that. (The determined only a couple % or so loss compared to all same orientation on a single MPPT.)
That said, if one of those strings has significant shading, the current vs. voltage curve may have multiple humps in it. In that case, only some MPPT successfully find the global maxima and don't quit searching on a local maxima.
If all your panels are in parallel, all the above still applies; your strings are just one panel long.
I'm not sure if I'm understanding this. It sounds like if I have 1 string of 3 at one angle and another string of 3 at another angle I'm ok with running both strings into one MPPT. Is this correct? I have a Renogy 40 Amp MPPT controller.
 
I'm not sure if I'm understanding this. It sounds like if I have 1 string of 3 at one angle and another string of 3 at another angle I'm ok with running both strings into one MPPT. Is this correct? I have a Renogy 40 Amp MPPT controller.

Yup. Works great.
The Voc of a panel hardly changes with illumination. Same goes for Vmp.
So if one string of three is orthogonal to the sun and the other is at 45 degrees to the sun, their Vmp differs slightly but not enough to make much difference. Any old MPPT wil find the peak.

If one string has a panel shaded, MPPT might run voltage down until it finds the peak power of the unshaded string of 3, not realizing that by pulling voltage lower it would only slightly reduce power output of that string and also get peak power from the string of 2 unshaded panels. Some MPPT do find that, some don't.

But without major shading, should be fine with any charge controller.
Beyond two strings in parallel you're supposed to fuse each string according to label requirements.
 
Yup. Works great.
The Voc of a panel hardly changes with illumination. Same goes for Vmp.
So if one string of three is orthogonal to the sun and the other is at 45 degrees to the sun, their Vmp differs slightly but not enough to make much difference. Any old MPPT wil find the peak.
I'm curious about the science behind this. So what happens if I run my current setup with 3 panels at 45 degree angle from vertical and just 2 panels at 78 degrees from vertical instead of 3, into my one MPPT? Do I suffer major loss of power, or potential damage to the controller? Why do both strings have to be exactly the same number of panels? With a parallel panel set up the voltage is the same whether 2 or 3 panels per string, right? Only the amps would be different?
 
If you put a string of 2 panels in parallel with a string of 3 panels, Voc will be 2x the Voc of a single panel, because the string of 3 will be pulled down to the voltage of the string of 2.
A PV cell is just a forward biased diode. As voltage is increased, current leakage through it increases massively. You simply can't increase the voltage on a PV panel more than a few 10ths of a volt. The string of 2 will carry all the current it generates from the sun, plus virtually all the current generated by the other string (or strings) of 3 panels in parallel with it. Maybe overheat and fail.

If the panels survive, the MPPT controller will pick a suitable voltage where it harvests power from the 3S || 2S setup. That will kind of work OK. But when MPPt is not drawing current, the short string will clamp Voc.

Not such a problem with 3 illuminated and string of 3 with 2 illuminated, 1 shaded. The shaded panel is still a bunch of diodes that can hold off considerable voltage with little leakage of current.

Just study the Power/voltage curves of PV panels. Mostly what is published is I/V curves, so regenerate those in Excel or the like and then make Power/Voltage curves. Move down the curve from where peak was to 2/3 of that, representing one shaded panel, and see how much power is affected. it'll be noticeable percentage with 1/3 of the panels shaded, less so with my 1/24, 1/12, or 1/8 for my higher voltage strings (more like 1% or 2% in my case)
 
If you put a string of 2 panels in parallel with a string of 3 panels, Voc will be 2x the Voc of a single panel, because the string of 3 will be pulled down to the voltage of the string of 2.
Thank you for the education. I found it very interesting. Now I know the "why" behind what I should not do, even short term. I appreciate it.
 
You could fit a blocking diode in series with the lower voltage string. That will prevent the higher voltage string backfeeding it. Depending on the watts each string produces at any given time the SCC may pull the higher one down to a little above the lower one. The exact point will depend on the light falling on both strings. You may find that the SCC decides to sit up at the Vmp of the higher string when there is more light on it, effectively ignoring the lower set for part of the day.
 
All panels in one string should be oriented identically.
Multiple strings wired in parallel should each have the same number of panels, but each string can be oriented differently.
I'm a bit confused. Does "oriented" mean the same angle, the same direction, or both? If I have 6 panels wired in parallel, all going into a central combiner before going to the SCC, but 3 at 28 degree and 3 at 78 degrees all pointing in the same direction with no shading, is this a problem?
 
Thanks for posting this question, @Veteran52. While not exactly residential I have a similar issue. I have a truck camper with 2 150w panels wired in series and I ordered two more. I was planning on just adding them and end up with 4s. But I'm not sure if I'll be able to get the angle to be exactly the same. The first two are on the cabover which has a slight downward angle which is great. I just park facing south and I'm good. The other location is parallel to the ground.

So with that in mind and having 8 gauge wire(I'm fairly certain) going to the MPPT, 2s2p would be better than 4s. If I'm understanding correctly.

I think I have 2s2p correctly. 4 panels total, with 2 paralleled strings of 2 panels in series. Or would that be 2p2s?
 
Seems like some of these systems are not power hungry enough! So hook up a water heater as an energy dump so you are never even near supplying 100% of your needs. Then, assuming dual MPPT channels, try to maximize each channel either seasonally or by tracking. Dynamic tracking is fine but with shade moving across your field it might be just as well to have each channel fixed on its prime time eg one toward morning max and the other toward afternoon max. Tall evergreens are major influence at one location; the other has no trees at all but offers a N-S roofline so will end up being configured similarly. Love the dual-MPPT scheme.
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If panels in a single string are at slightly different angles (10 degrees or less) not such a big deal; the string will produce current limited to the off-angle panel. Cos(10 degrees) = 0.985

If you have 6 panels in parallel, all can be same or different angles, whether tilt off vertical or rotation for different times of day.
If 2 or more in a series string, those should be same or similar to each other.

For large home system I have fixed arrays at different angles. Mobile you may be limited to what you can carry, so manually adjusting would increase production. Tilting toward one side of the vehicle, and moving vehicle once during the day to switch from morning to afternoon sun should boost production 50%

4s vs. 2s2p - key is open circuit voltage on a freezing morning. Check voltage limits of MPPT, also current/power. Only some may be safe for the electronics, and some may be more efficient than others.
 
If you have 6 panels in parallel, all can be same or different angles, whether tilt off vertical or rotation for different times of day.
If 2 or more in a series string, those should be same or similar to each other.

Interesting! Do you know if someone published results for eg 3 parallel strings (one east for morning, one south for day, one west for evening) on one MPPT and how it does on various days? Ideally comparing vs 3 MPPT?
 
Interesting! Do you know if someone published results for eg 3 parallel strings (one east for morning, one south for day, one west for evening) on one MPPT and how it does on various days? Ideally comparing vs 3 MPPT?

Here's a thread where I posted link to SMA's paper:


Their drawing shows 3 different orientations, but their charts appear to be results for two. That's good enough to confirm and make a decision.
 
Yup. Works great.
The Voc of a panel hardly changes with illumination. Same goes for Vmp.
So if one string of three is orthogonal to the sun and the other is at 45 degrees to the sun, their Vmp differs slightly but not enough to make much difference. Any old MPPT wil find the peak.

If one string has a panel shaded, MPPT might run voltage down until it finds the peak power of the unshaded string of 3, not realizing that by pulling voltage lower it would only slightly reduce power output of that string and also get peak power from the string of 2 unshaded panels. Some MPPT do find that, some don't.

But without major shading, should be fine with any charge controller.
Beyond two strings in parallel you're supposed to fuse each string according to label requirements.
All of these questions relate to the angle of orientation to the sun. I have a strange roof ... does it matter, if, say, I have a single string of 2, both on the exact same pitched roof, no shade, but one is mounted vertically, the other horiontally. Picture an L on the same side of barn roof. I would guess not, but I learned about polarization in school, have no idea if it applies to solar panels. Thanks!!
 
All of these questions relate to the angle of orientation to the sun. I have a strange roof ... does it matter, if, say, I have a single string of 2, both on the exact same pitched roof, no shade, but one is mounted vertically, the other horiontally. Picture an L on the same side of barn roof. I would guess not, but I learned about polarization in school, have no idea if it applies to solar panels. Thanks!!

If the two panels are in series, "2s", they should be close to the same orientation.
When sun is off-angle, a panel produces less current. With two in series, you will get the lower current of what each can produce.

I figure it is to the first order just area presented to the sun, sine or cosine of angle.

There is probably a second order effect of sun at an angle glancing off glass (part of that is polarization, light from sun is polarized at all random angles, but reflection vs. transmission at glass depends on polarization.
 
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