Shade on solar panels

[hotponyshoes]

Does anybody have experience with the ETFE type solar panels?

Basically I have two 12v batteries on a boat, I want to keep the charge topped up when not in use. They will both be isolated but one of them may be running a bilge pump occasionally.

I am pretty restricted on mounting space for the solar panel(s) as the boat has a sliding sunroof.
If I use the thin flexible type panels I can mount them on the roof behind the sunroof and when it opens it will slide over the top of them.
Obviously I wont get any power from them when the sunroof is open but I really only want them so the batteries are fully charged at the start.

The issue is I can not find completely flat solar panels. They all have a moulded outlet for the cable exits.
So, if I fit 2x 50w panels they are large enough for the outlet blocks to be out of the way when the roof is open.
But to do this about 1/4 of each panel will be shaded/under a radar arch.

I believe the etfe type cope with shading better than the traditional type but I dont have any experience with this?

Power wise, I am sure one 50w panel would be plenty to keep both batteries topped up even if the shade cost 50% of the output.

I am thinking of 2 because then I could wire them in series so should still get plenty of voltage if the shade lowers it on each panel.
I am not sure if the 12/24v charge controllers will cope with that though as the ones I have looked at so far look like they might base the output charging voltage on the input voltage which might be a problem?

 

[voipio]

The individual elements or "cells" in a silicon-based solar panel have an open circuit output voltage of around 0.5 to 0.6V, so a large number connected in series, typically 36, are required to generate sufficient output voltage to be usable in a 12V system. 36 "cells" in series normally result an open circuit output of around 21V, and a Vpmax (max power voltage) of around 17V. If even a single "cell" is shaded, it stops being a donor of current, and instead goes into reverse polarity. By how much depends on the current being passed by the whole panel, and whether individual cells have reverse voltage diodes fitted across them. A consequence of this is that shading can have a huge impact on the amount of power the solar panel is able to deliver. Shading of just one "cell" can result in a 50% reduction in the delivered power.

See e.g.:

https://midsummersolar.co.uk/en/fre...cles/26-the-effect-of-shading-on-solar-panels

 

[Justme]

10% shading does not reduce output by 10% more like 50%.

 

[hotponyshoes]

But will it still work?
If I have two 100ah batteries to keep topped up?
One will be completely isolated so it's just the self-discharge to compensate for.
Bilge pump one will depend how much it rains!

If I wire 2 in series to get 40v or so and had 1/4 of each panel in the shade could I feed that into a charge controller as a single input so that's got enough voltage to charge the 2 batteries independently?

 

[MCKDAVID]

if it's just for battery top up / trickle charging, would wind be another option. What about one of the whirlygig type hanging off the stern, or is the mooring too calm?

 

[voipio]

But will it still work?
If I have two 100ah batteries to keep topped up?
One will be completely isolated so it's just the self-discharge to compensate for.
Bilge pump one will depend how much it rains!

If I wire 2 in series to get 40v or so and had 1/4 of each panel in the shade could I feed that into a charge controller as a single input so that's got enough voltage to charge the 2 batteries independently?

It would be better to wire the two panels in parallel to the charge controller, and try to locate them so that only one panel gets shaded at any time.
It's better to have 50% of possible output, for a given sun angle, than 10%.

 

[hotponyshoes]

if it's just for battery top up / trickle charging, would wind be another option. What about one of the whirlygig type hanging off the stern, or is the mooring too calm?

Wind might be an option I suppose,
It's in a drying harbour so no flow at all really.