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Old 06-10-2012, 03:44   #1
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Solar Panels, Shade Losses..solutions?

I'm trying to put together a system and seeking advice on how best to minimize losses due to shade.

So, Assuming:

- array of around 600W
- shade cover is random in distribution and, at worst, will cover 20% of the total area (mast, rigging and maybe a wind generator)
- cost is not an issue (yet)


How best to arrange the system to minimize losses due to shading?

1) From what I read, 6 x100W panels would likely have less loss than 2 x 300W. Is this, on balance a reasonable statement?

2) Would it be better to have 6 x PWM controllers? i.e. one for each panel? (rather than a mass of diodes?)

3) Or would a single MPPT controller's efficiency make up for the voltage losses in the diodes?

4) Forget about the shade problems and find a way to squeeze in another 100W panel to make up for the losses?

5) What other combo would work better?
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Old 06-10-2012, 04:39   #2
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Re: Solar Panels, Shade Losses..solutions?

1) yes
2) Probably not.
The problem is the high self consumption of good MPPT controllers.
As the shade often effects one side 2 controllers are worth considering. This also gives some redundancy.
3) I would not fit any extra diodes
4) an extra 100w will give more gain than the differences in the controller options.
5) the most important factors are fit the most watts you can. Try and get them in the places that get the least shade. If fitting a MPPT regulator get a good one.
If you have lots of shade lower your expectations of the output, nothing can make up for shade.
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Old 06-10-2012, 04:48   #3
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Re: Solar Panels, Shade Losses..solutions?

Neelie, I bought 3 by 170 watt panels from china, and added two of them to my existing 170watts of panels and have too much power!! Sold one of the 170 watt panels and have the two wind gennies tied off, permantly.
Three by 150 amphr batteries are always full by lunchtime, even in full cloud.
Running a danfoss fridge 24hrs, lots of lights, computers, stereos etc..

Have a single 40 amp, tracker mppt, cost about 400 uad but is great! Forget the wind gennies?

Buying poly crystalline panels minimises shading losses, mono's dont like shading?
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Old 06-10-2012, 05:11   #4
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Re: Solar Panels, Shade Losses..solutions?

Quote:
Originally Posted by surfmachine View Post
Buying poly crystalline panels minimises shading losses, mono's dont like shading?
Keith.
Mono and poly panels have very similar shade tolerance.
Amorphous solar panels are more shade tolerant, but need to be considerably larger for the same output, limiting their usefulness on a boat.
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Old 06-10-2012, 08:41   #5
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Re: Solar Panels, Shade Losses..solutions?

Noelex: Thanks for your input/advice .. can I ask you to expand a bit with a few dumb questions.

2) Probably not.
The problem is the high self consumption of good MPPT controllers.
As the shade often effects one side 2 controllers are worth considering. This also gives some redundancy.
What about PWM controllers? Do they have the same self consumption? I was thinking 6 small PWM controllers would isolate the shaded panels.

3) I would not fit any extra diodes...So if the panels are wired in series into a single MPPT, would not the output of the good panels be absorbed by the shaded panels?

4) an extra 100w will give more gain than the differences in the controller options... and also will account for most of the losses due shade?.. I agree, I think this is the most cost effective "solution"

5) the most important factors are fit the most watts you can. Try and get them in the places that get the least shade. If fitting a MPPT regulator get a good one. Can't really control where the shade happens, its up to the wind and sun angles.. and I can't do anything about the mast and rigging.

For sure, I will get the best quality controller possible. I was wondering if a single MPPT controller was going to be better than multiple small PWMs.

If you have lots of shade lower your expectations of the output, nothing can make up for shade. My expectations are already lowered - I was wondering just how much lower they needed to be.

thanks!!
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Old 06-10-2012, 08:49   #6
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Re: Solar Panels, Shade Losses..solutions?

Quote:
Originally Posted by surfmachine View Post
Neelie, I bought 3 by 170 watt panels from china, and added two of them to my existing 170watts of panels and have too much power!! Sold one of the 170 watt panels and have the two wind gennies tied off, permantly.
Three by 150 amphr batteries are always full by lunchtime, even in full cloud.
Running a danfoss fridge 24hrs, lots of lights, computers, stereos etc..

Have a single 40 amp, tracker mppt, cost about 400 uad but is great! Forget the wind gennies?

Buying poly crystalline panels minimises shading losses, mono's dont like shading?
Keith.
Keith, Thanks.

I think my daily power consumption may be more than yours. Interesting idea to ditch the wind gennies.. maybe its because you're close to the equator and there is not much wind there?

I was thinking of installing one 400W wind gennie but that will also be a source of shade, so I am re-considering after reading your advice. Plus they are noisy buggers.
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Old 06-10-2012, 09:19   #7
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Re: Solar Panels, Shade Losses..solutions?

Quote:
Originally Posted by neelie View Post
Noelex: Thanks for your input/advice .. can I ask you to expand a bit with a few dumb questions.

2) Probably not.
The problem is the high self consumption of good MPPT controllers.
As the shade often effects one side 2 controllers are worth considering. This also gives some redundancy.
What about PWM controllers? Do they have the same self consumption? I was thinking 6 small PWM controllers would isolate the shaded panels.

3) I would not fit any extra diodes...So if the panels are wired in series into a single MPPT, would not the output of the good panels be absorbed by the shaded panels?

4) an extra 100w will give more gain than the differences in the controller options... and also will account for most of the losses due shade?.. I agree, I think this is the most cost effective "solution"

5) the most important factors are fit the most watts you can. Try and get them in the places that get the least shade. If fitting a MPPT regulator get a good one. Can't really control where the shade happens, its up to the wind and sun angles.. and I can't do anything about the mast and rigging.

For sure, I will get the best quality controller possible. I was wondering if a single MPPT controller was going to be better than multiple small PWMs.

If you have lots of shade lower your expectations of the output, nothing can make up for shade. My expectations are already lowered - I was wondering just how much lower they needed to be.

thanks!!
Non MPPT controlers have quite small self consumption but there is no need advantage (from an effeciency point of view) of having more than one controller. The panels will be wired up in parallel and as long as the panel voltage is above the battery voltage the panel will contribute some current to the battery. If the voltage of one panel falls below the battery voltage it will contribute no current, but it will not block or prevent the other panels working (there may be a very tiny power absorption by the shaded panel, but this will be very small).

The only difficulty with shaded and full sun panels effects MPPT controllers. The maximum power point is different for shaded and full sun panels. If these panels feed one controller the controller has to pick one input voltage as a compromise. With a good MPPT controller this does not cause any problems, but some of the advantage of MPPT is lost.
MPPT regulators can be used with solar panels in parallel. In fact that is how mine are wired. There is a lot of debate about series/ parallel connection of panels with an MPPT controller on a boat and frankly I am still unsure which is best.

If we compare a single MPPT and non MPPT in an installation like yours with the solar panels in parrallel both systems will give very similar performance. Maybe a couple of percent advantage to the MPPT set up.
More (even 6) non MPPT controllers will not help in fact it would be worse.
Two good MPPT controllers will be slightly better, but only by another couple of percent.
6 MPPT controllers would be very similar or maybe slightly worse.
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Old 06-10-2012, 09:27   #8
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Re: Solar Panels, Shade Losses..solutions?

Neelie,

I think Noelex and I respond similarly to these questions, I would say the same things he did above. To your requests for amplification:

2. PWM controllers operate solely on battery SOC. When the battery voltage it high they open a switch to disconnect the panels from the batteries, when the voltage drops they close it again. No point in having multiple PWM controllers from the perspective of getting charge into the batteries. May need multiple to deal with all the current, get better cost, or to have redundancy. PWM controllers really don't take much power

MPPT on the other hand controls on both panel conditions and battery conditions. They have voltage converters to match panels to batteries, and those voltage converters are not 100% efficient.

3. Series connections are really problematic if one of the panels in series will have shade and another won't. Pretty much all panels you can buy have bypass and blocking diodes already installed, which is why you don't need additional diodes. But (big but), if your shade is diffuse then the shaded panel may be able to reach full voltage with low current. If that happens the unshaded panel will get blocked, so you lose a lot of its output. If there is a hard shade line on a panel then it will likely not make voltage, which would allow other panels in the series to open the bypass diodes. Go parallel for panels that may be in different shade conditions.

And as I was typing this I see Noelex replied with much the same.
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Old 06-10-2012, 11:38   #9
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Re: Solar Panels, Shade Losses..solutions?

There's an interesting piece by Nigel Calder in the September Sail magazine that supports the previous advice.

He studied panel shading and found that his test 80 watt 32 cell panel's output was reduced by 65-80% if 75% of a single cell was shaded (shading only 2.5% of the total panel surface).

The determining factor for a panel was the percentage that the most shaded cell was shaded. Thus a thin shadow line across multiple cells from rigging was less bad than a single cell mostly shaded.

Output from unshaded panels wired in parallel were not affected by a shaded panel. When wired in series, a shaded panel impacted all panel output.

Diodes in a panel will isolate a shaded cell but the total panel's voltage still falls such that the panel may not be putting out a charging voltage and contributes nothing.

His conclusion is that you should use many solar panels wired in parallel and consider using a boost regulator to get the voltage up.

Carl
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Old 06-10-2012, 11:55   #10
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Re: Solar Panels, Shade Losses..solutions?

Quote:
Originally Posted by CarlF View Post
There's an interesting piece by Nigel Calder in the September Sail magazine that supports the previous advice.

Output from unshaded panels wired in parallel were not affected by a shaded panel. When wired in series, a shaded panel impacted all panel output.


His conclusion is that you should use many solar panels wired in parallel and consider using a boost regulator to get the voltage up.

Carl
Carl, thanks. Even after reading thousands of posts about series vs. parallel, it's always the simplest that makes sense, and always has.
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Old 07-10-2012, 05:44   #11
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Re: Solar Panels, Shade Losses..solutions?

Noelex, Dsanduril, Carl F and STu Jackson...

Thank You All.

I think I see the light.

So in general, the "better" setup for shade loss mitigation would be 6 x 100 W panels wired in parallel?

Am I correct in assuming that an MPPT will not provide enhanced efficiencies because at best the total output voltage will be panel voltage.. say around 17V or so?

So, this means I should be looking for a high quality PWM?

CArl F... whats a boost regulator?.. and who makes them?
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Old 07-10-2012, 06:52   #12
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Re: Solar Panels, Shade Losses..solutions?

I have made some tests with hard shade vs. soft one. Huge differences. Go test this for yourselves. In our installation a shroud shade cutting across the whole panel seems to give next to nill loss.

BTW Different thread but I noticed losses from poor panel angle (fixed panels) at least as detrimental as hard shades.

Cheers,
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Old 07-10-2012, 17:49   #13
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Re: Solar Panels, Shade Losses..solutions?

Neelie, my mppt, 40 amp controller is wonderful, it always outputs the proper voltage for my batteries, regardless of volts out from the panels. It does the boost, desulphation, trickle activities automatically and can switch on the anchor lights at night.
It is a computer controlled dc to dc converter, no voltage loss or minimal, converts 17 volts at 18 amps to 13.6 volts at 20 amps for the batteries!
Never got full batteries with the old switch controller, this one even puts out 15amps in full,deep cloud!
Dont need the wind gennies as very hard to regulate them!
I use heaps of power, 600w will be heaps?

Best money I spent on electrics?
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Old 07-10-2012, 22:57   #14
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Re: Solar Panels, Shade Losses..solutions?

So timely,
I'm after the same information and my research is similar to that being discussed.
I am about to order 6x 50 watt 17v panels to be run in parallel.
I'm now trying to figure the best way to control them. As there will be shade on 1 or 2 of 4 often.
I've read that solbian supples a voltage boosters that can be placed on each panel (for their 8 watt unit) I'm not sure if they regulate a specific Voltage out?
I was thinking if their was something like that placed at each panel and then Controlled by 1 MPPT unit?
Or break in into port starboard using 2 MPPT controllers?

Thoughts?
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Old 08-10-2012, 08:32   #15
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Re: Solar Panels, Shade Losses..solutions?

Surfmachine... Thanks!.. Ive been reading some more and have come to the conclusion that MPPT is likely the better option. If not, it wont be worse. What brand/model is your controller?
And are you in Padang? I used to visit there years ago.

Mischief - My thinking now also is 2 x MPPT as much for for redundancy as anything else. Perhaps you may consider a different combo than a simple port and stbd config? Depending on shade patterns with your rig, wind gennie, or whatever.

Cost wise? By the time the arch and frame fabrication, wiring and installation costs are added in - the cost of an extra MPPT is but a drop in the ocean. So one may as well start out with the best quality electronics.

Anyhow, thanks to all the knowledgeable advisers. I am grateful for your generosity in sharing your knowledge.
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