Advice on Solar Panels

[Stella Karuna]

I am considering installing solar panel and would like to put them on the roof UNDERNEATH the racks rather than on them. However, I have been reading that even a small amount of shade can severely reduce the output as the shaded cells act as a barrier to current flow.

Any advice?

cheers Bill

 

[Levitation]

Go above...
Besides which, going underneath will severely limit raising the hatch for ventilation...

 

[CaptMac]

As I understand it, some panels do better than others under partial blocking. All of them suffer loss in output - the Kyocera panel we're using is better than most. You could test it during install - try it both ways before permanant mounting? I suspect you'll be dissapointed - especially on cloudy days. We already lose over 20% just because we don't angle them correctly to the sun....

I'm curious...are you looking to keep the sport rack free for mounting things above? I've wrestled with that too - and have thought I should have hinged the panels on the top of the rack so I could swing them up, in the middle and put kayaks on the side when in transit...

Mac

 

[Stella Karuna]

Hello Captain Mac:

We seem to have got a few of the bugs out since we visited with you. The neutral protect bug is still haunting us although it appears that replacing the starter battery may have fixed the problem...hopefully. The wallace stove has been replaced after our near meltdown.

Tell Linda that we got the Burgee and love it. Great workwomanship.

As you suspected, I would like to keep the racks free for stuff like a bike.

cheers Bill

 

[jimackert]

I'd like to bring this topic up for discussion again. I've noticed on some of the solar equiped Ranger Tugs and Cutwaters at the boat shows here in Florida the panels are installed in partial shade. One Cutwater 28 had the panel mounted partially under the radar dome. A Ranger Tug had the panel mounted under the rack. I've always been told that even a single cell in the panel if shaded blocks the current flow for all the other cells. Even a little shade can cut the current flow by around 80%, or so I thought. Am I missing something here? Are these a new type of panel that works in shade?

 

[Levitation]

You are not missing a thing.
Each cell only produces a small amount of voltage. Like the batteries in your flashlight a string of cells are wired in series to raise the voltage to what we need. Drop off the voltage from a cell or three due to lack of sunlight and the total voltage drops below useable levels - just like having one weak battery in the string of 2 or 3 or 4 in your flashlight..

Worse than that, the voltage being produced by each of the working cells in a given string on a solar panel has to pass through the loafing or comatose cells in the shade. When cells are in the shade their internal resistance rises rapidly slowing or totally stopping the flow of electrons from the working cells wired in series with it. (like a cheap string of Christmas tree light bulbs we all remember with great fondness from our childhood)

Then two or more strings are wired in parallel to increase the current produced by a given panel. Now by clever use of a different pattern of series and parallel connections and some bypass diodes you can reduce the voltage drop and blockage of electron flow due to a shaded cell. But it is only a partial solution. And ineffective when the shade from the sports rack cuts completely across the panel.

 

[knotflying]

Denny is correct in his explanation. You want as much direct sun as possible. However, I will say that even when I have the boat covered with a white tarp and all the electrical draws from equipment that stays on regardless of turning off power as well as my airhead fan, my batteries are always topped off and receive a charge from the panel. Albeit, the draw is small from these items, my point is I am getting a fairly good charge with a tarp covering the panel.