Solar: 6-95W vs 2-275W? Boom Shadow

[Sumner]

Here are the pictures without having to go to the links...





Having that arch sure is handy. Good luck on the mod and post pictures of the end result,

Sum

[noelex 77]

Originally Posted by KStepman

When there is, the panels that I have chosen will each have 60 cell modules running lengthwise (fore and aft) on the panel, each with bypass diodes. Thus any shadow from the boom will affect only one, and at most six modules, for only a 2% to 10% loss in energy. At least that is the theory. We shall see if reality agrees.

The rigid panel do not have bypass diodes for each cell. 8 bypass diodes would be typical. So a shaddow effecting one cell will shut down 1/8 of the panel.
This also reduces the voltage of the panel by 1/8. Depending on how they are wired this means there this can also create problems matching a panel in full sun with the panel that has shade. The Vmp of the 2 panels is very different.

[KStepman]

Will do. Thanks.

[KnuckleDragger]

Regarding the boom casting a shadow when at anchor, just swing the boom out to the appropriate side and tie it off with a "preventer". Easy peasy...

[KStepman]

Originally Posted by noelex 77

The rigid panel do not have bypass diodes for each cell. 8 bypass diodes would be typical. So a shaddow effecting one cell will shut down 1/8 of the panel.
This also reduces the voltage of the panel by 1/8. Depending on how they are wired this means there this can also create problems matching a panel in full sun with the panel that has shade. The Vmp of the 2 panels is very different.

Each of the 30V solar panels that I am getting have 60 modules (arrayed 6x10).
Am I in error in thinking that each module has bypass diodes?
The two panels will be connected in parallel to an MPPT Controller, which I believe will equalize any difference between the two due to shadow, I believe.

[noelex 77]

Originally Posted by KStepman

Each of the 30V solar panels that I am getting have 60 modules (arrayed 6x10).
Am I in error in thinking that each module has bypass diodes?
The two panels will be connected in parallel to an MPPT Controller, which I believe will equalize any difference between the two due to shadow, I believe.

I did not see the brand of panel you are getting, but typically a 60 cell rigid panel will have 8-10 bypass diodes. Not 60.

The MPPT will pick the maximum PowerPoint for the combined effects of the panels. If one panel is in shaddow and the other is not the ideal MPP voltage will be different for the two panels.
Because they are connected together in parellel the input voltage for the panels must be the same, so a compromise voltage must be chosen.
This is another one of the reasons that output from a shaded solar panel is much less than you would expect from the amount of shaddow.

If one bank of solar panels is likely to consistently experience different conditions ( often port and starboard ) it is sometimes worth using two MPPT controllers so the two banks can be driven at their MPP voltage.
This increases the cost,( but as each controler can be smaller often the increase is less than expected) and increases the self consumption of the controllers, but can often produce a worthwhile increase in output.

[KStepman]

Originally Posted by noelex 77

I did not see the brand of panel you are getting, but typically a 60 cell rigid panel will have 8-10 bypass diodes. Not 60.

The MPPT will pick the maximum PowerPoint for the combined effects of the panels. If one panel is in shaddow and the other is not the ideal MPP voltage will be different for the two panels.
Because they are connected together in parellel the input voltage for the panels must be the same, so a compromise voltage must be chosen.
This is another one of the reasons that output from a shaded solar panel is much less than you would expect from the amount of shaddow.

If one bank of solar panels is likely to consistently experience different conditions ( often port and starboard ) it is sometimes worth using two MPPT controllers so the two banks can be driven at their MPP voltage.
This increases the cost,( but as each controler can be smaller often the increase is less than expected) and increases the self consumption of the controllers, but can often produce a worthwhile increase in output.

Thank you for that advice. I have been considering the two MPPT controller option. Now I understand it better. The panel manufacturer is LG. Any advice there?

[noelex 77]

Originally Posted by KStepman

Thank you for that advice. I have been considering the two MPPT controller option. Now I understand it better. The panel manufacturer is LG. Any advice there?

I could not find an LG 275w panel. There is a 260w 60 cell LG panel that has 3 bypass diodes. I bit low for a 60 cell panel, but these low numbers of bypass diodes are getting more common.

[sck5]

On having panels that can be tilted to catch the sun - My own experience (and that of the great majority of long time cruisers informally surveyed in Rodney Bay) was that having panels securely and rigidly attached is better than having a tilt function which will rarely be used after a couple of days. Most people don't stay on their boats 24-7 and even if they do they are not constantly running up to adjust the solar panels for optimal angle. Better to fasten them properly as close to horizontal as you can and then be happy with what you get.

BTW your neighbors in the anchorage will thank you if you forgo the wind generator and get another solar panel instead. Besides, isn't one of the things we look for in a "good anchorage" a lack of strong winds?

[donradcliffe]

Originally Posted by KnuckleDragger

Regarding the boom casting a shadow when at anchor, just swing the boom out to the appropriate side and tie it off with a "preventer". Easy peasy...

+1 for the cheap and easy solution! We kept our boom to one side at anchor for 15 years--first because the mainsheet interfered with our canvas, then to keep the bimini panels in the sun.

[Sumner]

Originally Posted by noelex 77

....The MPPT will pick the maximum PowerPoint for the combined effects of the panels. If one panel is in shadow and the other is not the ideal MPP voltage will be different for the two panels.

Because they are connected together in parallel the input voltage for the panels must be the same, so a compromise voltage must be chosen.
This is another one of the reasons that output from a shaded solar panel is much less than you would expect from the amount of shadow.

Our panels on both boats are out in the open so the effects of shading haven't been a big concern of mine, but you guys got me interested in it and I was surprised what a big deal it can be.

Here is a pretty good video that shows the effects of shading...

solar cell shading problem illustration - YouTube

Originally Posted by sck5

On having panels that can be tilted to catch the sun - My own experience (and that of the great majority of long time cruisers informally surveyed in Rodney Bay) was that having panels securely and rigidly attached is better than having a tilt function which will rarely be used after a couple of days. Most people don't stay on their boats 24-7 and even if they do they are not constantly running up to adjust the solar panels for optimal angle. Better to fasten them properly as close to horizontal as you can and then be happy with what you get.....

I agree with the above 99% especially if the boat is on the water all of the time. I did change....



...our panel arrangement on our Mac so that I can tilt the one 40 watt panel and that was due to the fact that the Mac is on a trailer with the bow to the south and I can have that 40 watt panel facing south in the winter where the trailer sits. I still wouldn't need to do that to keep the batteries topped off since there are the 160 watts on the other two panels, but thought at some time I might want to take those panels off when we weren't using the boat to prevent possible wind damage to them.

On our Endeavour the panels...



...will not tilt, but are back beyond the boom and we also keep the boom off to one side while anchored on both boats,

Sum

[KStepman]

Originally Posted by sck5

On having panels that can be tilted to catch the sun - My own experience (and that of the great majority of long time cruisers informally surveyed in Rodney Bay) was that having panels securely and rigidly attached is better than having a tilt function which will rarely be used after a couple of days. Most people don't stay on their boats 24-7 and even if they do they are not constantly running up to adjust the solar panels for optimal angle. Better to fasten them properly as close to horizontal as you can and then be happy with what you get.

BTW your neighbors in the anchorage will thank you if you forgo the wind generator and get another solar panel instead. Besides, isn't one of the things we look for in a "good anchorage" a lack of strong winds?

I agree with your first observation about fixed vs adjustable, especially as each of the panels I am installing are 39" x 65". I am attaching them in classic cruiser fashion: using 150% more mounting brackets, when 100% was tested in 140kt winds.

However, on your second point, about wind generator noise, and vibration below, largely true of the past, but with some of the new units, like the Super Wind, to name one, they are quiet, above and below decks. My objection is why have something that potentially dangerous aboard, if it is not needed. I will let you know.

[Bash]

Originally Posted by KnuckleDragger

Regarding the boom casting a shadow when at anchor, just swing the boom out to the appropriate side and tie it off with a "preventer". Easy peasy...

+1. We call it the "shadow preventer."

(+1 as well on going with fewer, bigger panels. Makes for a better "solar bimini." You'll thank me when it rains.)