PV panel orientation?

Do any of you have PV systems where the panels sit at different orientations? How did your installer handle it:

a) One single tracker inverter.
b) One multi-tracker inverter.
c) Two single tracker inverters, one for each orientation.
d) No clue.

I have most of my panels facing south at 20 deg and 6 panels facing south on a angled sloped roof which make them slightly leaning west. The installer said it would not matter much I think he said 1 or 2%. I have a 5.16k Sunpower system with a Sunny boy Sunpower label.

D no clue

It depends completely on what direction each set of panels will be facing and how much the light will be different. Are there any shade issues with where the panels will be going, too? And how much more will it cost to have a system installed that will track each array independantly?

If it were me, I'd go with micro-inverters, but then I'm biased since my system uses them.

I'm not familiar with any inverters that can track multiple arrays - do you know specifically what make/model?

For Gonewild's setup, I'd have to guestimate more than 1-2%... how much power do you typically generate on a clear day? Is the 5.16kW the DC rating?

I have panels in two different orientations; aka "planes". As long as your panel strings (those connected in series) don't cross planes, it shouldn't matter. This was according to my inverter company tech-rep (Fronius). They said any mis-match effect would be small relative to normal daily variations.
I installed these myself and later added more panels with the Enphase microinverters; which like drees, I'm now biased towards.

sparky said:

I have panels in two different orientations; aka "planes". As long as your panel strings (those connected in series) don't cross planes, it shouldn't matter.

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Could you explain what is meant by "cross planes"?

When you connect strings in series across these different "planes", am I correct in thinking that performance of the entire array diminishes to that of the worst performing string? This is what I'm worried about most. I get some really nice sun on the south facing roof at a time when I'm worried significant shadowing will fall on the panels to the east (though I must say that I have yet to go up on the roof late in the day to see what actually happens).

My vendor is fundamentally opposed to micro inverters on the basis of introducing multiple potential sources of failure and his reckoning that in the not too distant future micro-inverters will be built into panels, making separate ones obsolete and difficult to obtain replacements for.

mwalsh said:

sparky said:

I have panels in two different orientations; aka "planes". As long as your panel strings (those connected in series) don't cross planes, it shouldn't matter.

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Could you explain what is meant by "cross planes"?

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He means that as long as the panels face the same direction (IE, sparky's are angled south, just at different angles of 5* and 20*)

mwalsh said:

I get some really nice sun on the south facing roof at a time when I'm worried significant shadowing will fall on the panels to the east (though I must say that I have yet to go up on the roof late in the day to see what actually happens).

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Can you get us a picture of your roof along so we can see what you're referring to? Google or Bing bird-eye view will work.

mwalsh said:

My vendor is fundamentally opposed to micro inverters on the basis of introducing multiple potential sources of failure and his reckoning that in the not too distant future micro-inverters will be built into panels, making separate ones obsolete and difficult to obtain replacements for.

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The Enphase micro-inverters have a standard 15-year warranty - 5-years longer than most company's inverters. Most central inverters have fans built in to cool them off - a common failure mode from what I year - I would try to opt for an inverter that is fanless. He is right that eventually micro-inverters will be integrated into panels (and Akeena's Andalay panels already have Enphase micro-inverters integrated in them), but with so many different PV panel manufacturers out there, I think they will always sell them as a standalone unit. Not to mention that they have shipped over 250,000 micro-inverters already - were they to stop supporting existing installations they would generate so much bad press that no one would recommend them any more.

Edit: Looks like you found the Wind&Sun forums - you'll get good advice there.

mwalsh said:

Could you explain what is meant by "cross planes"?

When you connect strings in series across these different "planes", am I correct in thinking that performance of the entire array diminishes to that of the worst performing string? This is what I'm worried about most. I get some really nice sun on the south facing roof at a time when I'm worried significant shadowing will fall on the panels to the east (though I must say that I have yet to go up on the roof late in the day to see what actually happens).

My vendor is fundamentally opposed to micro inverters on the basis of introducing multiple potential sources of failure and his reckoning that in the not too distant future micro-inverters will be built into panels, making separate ones obsolete and difficult to obtain replacements for.

Click to expand...

By "cross planes" I meant that if you have 4 panels in a string and two of them face south and two face east that's sub-optimal; but just for that string. This is analogous to shading of one panel of your array. It impacts the output from the string it's connected to but not the rest of the array. My understanding of reason for this effect is the panel current is
typically reduced when shading occurs but the voltage is mostly unaffected. The inverter can handle this with its MPPT algorithm as long as all string voltages are mostly constant.
Not sure if this helps or further confuses.

I disagree with your installer about the microinverters. They distribute risk, are very reliable and allow easy upgrading of your array.

OK, you posted a good pic in the W&S forum, I'll copy my reply here:

Definitely go with two separate inverters. You'll lose a lot of power from the south facing array once in the afternoons once the sun stops hitting the east facing array.

If you really want to opt for only one inverter, just install on the south facing roof and forgo the panels on the east facing roof.

If you later decide that you still want more power, then you can add panels to the east facing roof on a separate inverter then.

How many kW can you fit on the south roof? (what panels are you looking at?)

sparky said:

By "cross planes" I meant that if you have 4 panels in a string and two of them face south and two face east that's sub-optimal; but just for that string.

I disagree with your installer about the microinverters. They distribute risk, are very reliable and allow easy upgrading of your array.

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Oh, I get it (or at least I think I do). So as long as I have the 2 strings to the south and the 1 string to the east as their own entities....then not a problem?

I still might have to press harder on the micro-inverter idea though. The shadow from that chimney could pretty well kill the one string on winter afternoons, if I extend it out as far as the installer suggested, and I don't really want that!

sparky said:

By "cross planes" I meant that if you have 4 panels in a string and two of them face south and two face east that's sub-optimal; but just for that string. This is analogous to shading of one panel of your array. It impacts the output from the string it's connected to but not the rest of the array. My understanding of reason for this effect is the panel current is
typically reduced when shading occurs but the voltage is mostly unaffected. The inverter can handle this with its MPPT algorithm as long as all string voltages are mostly constant.

Click to expand...

Right, but just a slight clarification - for each string/array, the total current flowing through each panel must be the same, not the voltage - those just add together.

If you look at the volt/amp/power graphs for a panel (just about all spec sheets for panels include this), you will notice that they have a knee in them where power output will be highest. Slight variations in volts/amps won't change panel output significantly.

The MPPT algorithm in the inverter will attempt to find that knee.

As long as light is hitting a panel, usually the optimal voltage of the panel will remain fairly constant. As the intensity increases, current goes up.

So now let's add a panel which is no longer getting full sun and can no longer push full current - this means that the current drops on the other panel - voltage will rise somewhat to offset the drop in current, but it's no longer optimal and at a certain point, panel voltage won't go any higher.

drees said:

How many kW can you fit on the south roof? (what panels are you looking at?)

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Looking at the Sunpower Serengeti E13/228, 228w each. Currently proposed as 10 panels (lower row), 8 panels (middle row), and 4 panels (top row), two strings of 11, for a system size of 5.01kw.

I was going to suggest dropping the two from the northern end (where the chimney shadow is) and putting them over on the east with 4 additional for another string of 6. Total system size then....5.9kw.

drees said:

So now let's add a panel which is no longer getting full sun and can no longer push full current - this means that the current drops on the other panel - voltage will rise somewhat to offset the drop in current, but it's no longer optimal and at a certain point, panel voltage won't go any higher.

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So I need to find out what time the shadow from my roof peak and own chimney falls onto that east facing roof in the afternoon, right? If it happens late enough into the day that I won't be making that much production anyway, then it's not an issue?

It's not worth sticking on an additional 20% of panel if they are going to be on the same string but on a completely difference facet.

You will be lucky to get any increase in total output at all - it will likely be marginal.

And IMO, don't stick panels where they will be getting shade where +-2-3 hours from solar noon in winter - unless you are using micro-inverters. Your installer should be able to tell you how much shade you will be getting at that time of year.

mwalsh said:

So I need to find out what time the shadow from my roof peak and own chimney falls onto that east facing roof in the afternoon, right? If it happens late enough into the day that I won't be making that much production anyway, then it's not an issue?

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No, it will be an issue nearly all the time with panels facing both south and east. You might have a couple hours a day where it doesn't significantly affect output, and the farther away from summer you get, the worse it will be.

OK, you've got me convinced....separate inverters, micros, or just panels to the south.

mwalsh said:

OK, you've got me convinced....separate inverters, micros, or just panels to the south.

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Have a look at the other thread referenced in the W&S forum where a fellow had an 8 kW array installed on multiple facets with some shade issues. Lots of good data there. His array is under-performing by about 30% from expected.

Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

Edit: It is performing 30% worse than expected - in contrast, my install is currently performing better than expected (by about 10%, but hard to tell for sure as it's only been 4 months) - and most installs seem to do the same.

I now have quotes from four different PV installers. Three of them are projecting AC kWh output about 15% in excess of what the California Solar initiative calculator shows. The fourth installer projects about 5% under the CSI prediction (their derating). Does anyone know how 15% outperformance could be possible? All are microinverter systems. I've asked them to 'splain themselves.

DeaneG said:

I now have quotes from four different PV installers. Three of them are projecting AC kWh output about 15% in excess of what the California Solar initiative calculator shows. The fourth installer projects about 5% under the CSI prediction. Does anyone know how this could be possible? I've asked them to 'splain themselves.

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It sounds to me like the 3 optimistic installers will say anything to convince you to buy from them. These are tough times for solar installers, so getting the sale is paramount. The installer giving you a 5% under estimate wants you to be HAPPY after the sale. I'm guessing the first 3 will hand you the keys and good luck getting ahold of them later....

EXPECT to get the 5% under value, and then be pleasantly surprised when you get more than that. It's MUCH better than expecting a lot and being let down month after month when the generation numbers don't match your unrealistic expectations.

If the prices were all close, I'd go with the one honest guy over the 3 hype-sellers. JMHO.

Jimmydreams said:

It sounds to me like the 3 optimistic installers will say anything to convince you to buy from them...

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Agreed but one of them is willing to warrant that 15% higher kWh output for 15 years! It'll be interesting to read his email response to my doubt.

The 15% higher guys are using Sunpower 225's or 230's, or a Del Solar 230. The 5% under guy is Akeena using Westinghouse 175W panels with integrated Enphase.

DeaneG said:

Agreed but one of them is willing to warrant that 15% higher kWh output for 15 years! It'll be interesting to read his email response to my doubt.

The 15% higher guys are using Sunpower 225's or 230's, or a Del Solar 230. The 5% under guy is Akeena using Westinghouse 175W panels with integrated Enphase.

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Interesting! That guarantee would be interesting to see.

I WILL say that I have SunPower 225's and I LOVE 'em. SunPower is a little more expensive, but if you're the type of person who will keep an eye on solar production often (as I do with my system), then you might want to consider the extra $$ for SunPower as your satisfaction will last a LONG time. :mrgreen: If you're the 'set and forget' type, then maybe the extra $$ for SunPower won't generate much 'solar satisfaction'.

Good luck on your decision!