Solar Panel Query

[Porthandbuoy]

I have room on top of the solid doghouse for a long 100W solar panel. The downside is it will invariably be partially shaded by the boom & sailcover when on the mooring.
Would I be better off fitting 2 x 50W solar panels in parallel? One would always be 'in the clear', the other partially shaded

 

[geem]

Yes

 

[Porthandbuoy]

A nice concise answer.

 

[Never Grumble]

Some of the more expensive flexible ones claim to be able to handle shaded sections, to what extent I have no idea, but I am just about to fit one, one less pair of wires to route.

 

[geem]

Some of the more expensive flexible ones claim to be able to handle shaded sections, to what extent I have no idea, but I am just about to fit one, one less pair of wires to route.

I know some panels have blocking diodes between banks of cells such that if that bank of cell is shaded it removes it from the panel circuit. Only aware of these on expensive panels. The problem is that you only have so many cells and diodes so if the voltage drops as a result of shading you won't be doing much charging. Seems cheaper and better to split the panels in two and some redundancy as well

 

[VicS]

I know some panels have blocking diodes between banks of cells such that if that bank of cell is shaded it removes it from the panel circuit. Only aware of these on expensive panels. The problem is that you only have so many cells and diodes so if the voltage drops as a result of shading you won't be doing much charging. Seems cheaper and better to split the panels in two and some redundancy as well

By-pass diodes are probably what you are thinking of.
A blocking diode is the one that stops current flowing backwards through the panel at night (although the controller will usually do that anyway)

 

[geem]

By-pass diodes are probably what you are thinking of.
A blocking diode is the one that stops current flowing backwards through the panel at night (although the controller will usually do that anyway)

Correct, thankyou. Suffering from a bit of brainfade. Got covid?

 

[William_H]

I know a centralised boom hanging on the topping lift looks neat but I have found on my little boat it is far better to leave the boat with boom and sail dropped onto the cabin top and off to one side. This to save wear on the traveler system which gets a work out with every roll of the boat when moored. This might solve problem of shade of the panel. ol'will

 

[Stemar]

Would I be better off fitting 2 x 50W solar panels in parallel? One would always be 'in the clear', the other partially shaded

This is exactly what I did on Jissel. It worked fine and our two 20w panels could keep up with out needs at anchor (no fridge)

 

[pyrojames]

I have a bigger setup with 2x 135W panels. I get better performance from them in series with an MMPT controller. I suspect 2x50W in series with an MMPT will give the best results.

 

[Stemar]

I have a bigger setup with 2x 135W panels. I get better performance from them in series with an MMPT controller. I suspect 2x50W in series with an MMPT will give the best results.

If both are equally exposed series is best, but if one of a set of series panels is even partially shaded, my understanding is that it will bring the other down with it. In parallel, you get one shaded, and not doing much, but the other can still do its stuff. When I was shopping for my panels 10 or so years ago, the seller confirmed that two panels wired in parallel was the way to go on the hatch garage.

 

[lustyd]

Modern panels usually have two bypass diodes so if one is shaded or even half of one it makes no difference, you get power from all the bits in the sun You only lose power if voltage drops below battery+5V which is generally one full panel or two half panels to make 18V. In practice I've not seen it make a huge difference parallel or serial so generally connect mine however is convenient for the position and wiring since mine are movable and I have various extension leads for them