Solar Panel Combinations and Orientation Options

[GILow]

Hello Cruisers,

I have realised that there are two ways of installing the solar panels on our boat, using the existing frames that originally supported pair of mostly defunct 80W panels.

In both cases I should be able to get a bit under 300 Watts of solar installed, which, on my (Conservative) calculations, will be adequate for our needs.

I can use either two panels with their longer axis running fore and aft, each panel around 140 watts, OR, I could use four smaller panels, each around 70 watts with their longer axis across the boat, but with the panels two to a side on the frame, and butted up to one another.

I occurs to me that the four panels may be smarter as they would be less affected by shade, at least, I THINK that is the case. For the record I would be planning to use something from the Kyocera range of panels if I can.

I would like to use the existing structure as:

a) it is there already.
b) panels on the structure provide a lovely shade for the after deck.
c) the structure is sturdy and keeps the panels well out of the way, above head height, clear of all rigging.

HOWEVER:

The structure is bifurcated by the rear stay (12mm) and supports the radar and Aerogen wind generator, both of which have the potential to shade the panels in many conditions.

Some rather sad MSPAINT art attached to show the two options. Which would you choose please?


Matt

P.S. here's a link to a photo of the boat that also shows the support system at the stern, and shows the problem with the radar and windgen.

http://www.cruisersforum.com/forums/...ture18892.html

[sailorchic34]

Hum, Boy the wind genny and radar are not ideally situated for the solar panels.

2 or 4 panels will be shaded similarly, so I would just use two panels and be done with it.

But to do it right and give most bang for the buck I would rework that whole back end and put the panels behind the radar and wind genny. Or move the radar to the mast and wind genny to the side in front of the panels

This as the mast will block the panels anyway, but it gives you at least 180 degrees without shadows. As it stands now, the panels will be shaded quite a bit by the genny. Maybe sell the wind genny and put another panel over the davits behind the radar.

[GILow]

Hi Sailorchic,

Not great, is it?

I did consider moving the panels aft to the dinghy davits, but one of things I really like about the current setup is that the weight is kept (relatively) close to the centre of the boat. Canoe stern boats are supposed to be susceptible to hobby-horsing, so I am keen to centralise all weight. I moved the battery bank from the stern to midships for this reason.

As for selling the Aerogen...? Not in a million years. The power that thing puts out is absolutely breathtaking. It's a pain, but worth it in my books. Seriously, I don't know why they are not more popular.

But you make an interesting point about moving the radar... or the Aerogen. I will give that some thought if I can't get enough power from the panels. But oh dear, that would be a lot of work, with other unexpected downsides I am sure.


Matt

[sailorchic34]

Agree that you want to keep the weight inboard. Sort of looked like the the wind turbine could live about 1/4 the way back from the front of the wind cloth and still clear the boom/sail. That would give you 180 degrees clear, which is what you need. I've also seen one at the top of the mast once, but that would be fun installing and not all that great either

The radar is less of a problem as it's pretty low to the panels and the sun would be above it by about 10 am, which is good. But where the wind turbine is will shade the panels to 11 am and after 2 pm, so you could loose 35-40% of the daily charge depending on how the boat lays at anchor.

Of course if you only anchor the boat so the bow faces north, your good most days then ...

From personal experience shading the panels is a problem at anchor. My boom extends way back, so I have to move it out to starboard at anchor as my panels are on port and aft rails.

Even your insulator on the back stay will cause some shading, but not too bad.

[Scott Berg]

We 'tack' twice a day at anchor using the preventer to clear the panels on the hardtop... We can see the panel output go up 30% or more when unshaded!


Sent from my iPhone using Cruisers Sailing Forum

[GILow]

Originally Posted by Scott Berg

We 'tack' twice a day at anchor using the preventer to clear the panels on the hardtop... We can see the panel output go up 30% or more when unshaded!

For my understanding, what degree of shading is causing that sort of drop? The shade from a few stays, or significant eclipsing of the panels by something bigger, like the boom/sail cover or mast?

Matt

[StuM]

Originally Posted by sailorchic34

Of course if you only anchor the boat so the bow faces north, your good most days then ...

In the Southern Hemisphere?

[sailorchic34]

Originally Posted by GILow

For my understanding, what degree of shading is causing that sort of drop? The shade from a few stays, or significant eclipsing of the panels by something bigger, like the boom/sail cover or mast?

Matt

A single stay is not too bad, Though an insulator on the stay can hurt. But the mast, boom for some of us, is a bugger. As the cells are in series, shading even 1/2 of one cell can drop that panels output 30%-40%, though depends on type of panel and number of bypass diode's.

Looks like your panels articulate in one direction. That will help some

[sailorchic34]

Originally Posted by StuM

In the Southern Hemisphere?

DOH.... Point taken..

[socaldmax]

Originally Posted by sailorchic34

Hum, Boy the wind genny and radar are not ideally situated for the solar panels.

2 or 4 panels will be shaded similarly, so I would just use two panels and be done with it.

But to do it right and give most bang for the buck I would rework that whole back end and put the panels behind the radar and wind genny. Or move the radar to the mast and wind genny to the side in front of the panels

This as the mast will block the panels anyway, but it gives you at least 180 degrees without shadows. As it stands now, the panels will be shaded quite a bit by the genny. Maybe sell the wind genny and put another panel over the davits behind the radar.

Exactly!

[socaldmax]

Originally Posted by GILow

For my understanding, what degree of shading is causing that sort of drop? The shade from a few stays, or significant eclipsing of the panels by something bigger, like the boom/sail cover or mast?

Matt

If you stuck your hand in front of one panel, the total output from your system would probably drop 40-50%. If the stay goes completely across one panel, you might lose as much as 20-25%. It takes very little shading to lose a disproportionate amount of power.

[GILow]

OK, so in that case which combination of panels is likely to be least affected? The two 140's running fore and aft, or the four 70's running laterally?

Matt

[GILow]

Originally Posted by sailorchic34

I've also seen one at the top of the mast once, but that would be fun installing and not all that great either

That would be an absolutely INSANE amount of weight to put at the top of a mast.

And as for servicing, voltage drop in the cables, conflict with nav lights, antenna, halyards... the list goes on. Maybe on a very short aft mast on a ketch or something, but nope, even that strikes me as plain silly.

Matt

[socaldmax]

Originally Posted by GILow

OK, so in that case which combination of panels is likely to be least affected? The two 140's running fore and aft, or the four 70's running laterally?

Matt

I would try to mount the 2 140 watt panels as far aft, as high as possible and as far outboard as possible. This would give you the least amount of shading from the stay, provided you moved the radar and wind generator.

[GILow]

OK, look, thank you for the suggestion, but it is not really answering my question.

Sorry if that sounds narky , but really, I don't want to move all that stuff, I am very happy where it is.

It is a well thought out arrangement that was designed with safety and practicality foremost, unfortunately, this put the efficiency of the solar lower down the priorities (I suspect the solar was very much an after-thought, years after the event as it were.) All in all, I am happy with that order of priorities.

I accept that it is not ideal, but what I am trying to figure out if two 140s or four 70s are going to be the "least worst" solution.

Matt