Solar coonections, serial or parallel w shading

[jbinbi]

I am planning on putting 2 50W panels on my dodger, on either side of the centerline, and 2 100 W panels on my bimini, again either side of the centerline.

The boat faces South on the mooring about 90% of the time. The boom is normally left in the middle, and is long enough to cover most of the bimini. When boat is on mooring, except when sun is from the South, the mast/boom will be shading 2 panels on one side more than the other.

Both panels have a VOC of about 20-24V.

I don't want to buy 4 controllers, was hoping to maybe just use 2. How would you configure these? Both port panels from bimini and dodger into 1 controller, same for stb ones, or stb and port of bimini into 1 controller and same from dodger into 2nd? Series or parallel into each controller?

[dkenny64]

I would suggest 2 controllers.. port and starboard.
connect the panels on each side in parallel.( ideally the panel have close to the same out voltages). use MPPT controllers. not PWM.
this way you get the most power from the sun from either side.
this can work work with 1 or 2 house banks and if you use a 3rd controller, for a starter battery


-dkenny64

[jbinbi]

Thanks. I am curious about the parallel. No panel will have the same output, I figured might be better to have 2 panels in series and have the volts add? Agree on putting each sides panels together. Just wondering if serial or parallel?

[dkenny64]

any shading on any panel kills the total output. try it. put 2 in series.. shade 1 cell on either panel. watch the output..
-dkenny64
fyi I have 4 panel on each side(port and starboard). each side are in parallel. these charge my 2 house banks. I added a 3rd controller to charge the start battery(from either panel bank).
-dkenny64

[jbinbi]

so you are saying that if each panel can put out 20V max, and one panel is shaded and putting out only 3v and the other panel is putting out 10v, they won't add to 13V? Why would they work in parallel and not series? sorry to be dense, not understanding this..

[HeywoodJ]

More important than shading, when connecting in series Imp must match, in parallel Vmp should be close.

With the same Voc a 50W panel will have an Imp about half that of the 100W panel. Panels in series can only pass the current of the lowest rated panel, so you are effectively derating the 100W panel to 50W, and doing so permanently and under all conditions. The only way to run panels with different current ratings is in parallel (or to separate controllers). The Vmp values in parallel should be close, the array will run at the lower Vmp value, and you can calculate the derating of a higher Vmp by the simple ratio of the voltages (to a reasonable first approximation).

[SV Confianza]

Gone with the Wynns did the best video I’ve seen to show the difference between series and parallel with shading. https://youtu.be/1qD3mN8VotQ

[HeywoodJ]

The video is good as far as it goes, but as with most of this type of demonstration it assumes matching panels. The OP has specifically asked about mismatched panels and that’s a whole different story.

For the proposed layout and mismatched panels parallel is the only option with one controller or one controller per side. The only series option is to series the two 50W panels and the two 100W panels, but the differing shading from being on opposite sides of the boom will limit production to the least irradiated panel in the string.

[jbinbi]

Optimum operating on the 100W is 19V, on the 50W, it is 20.3, so pretty close.

[jbinbi]

In speaking with canvas maker, it looks like the boom only overhangs the bimini by a few inches. So I could put 2 200 W panels across the bimini. Panels long dimension would be mounted across the bimini, not fore/aft.

I am not sure this would as efficient from a shading point of view. Each panel would probably always have shade unless the sun was directly behind, and even then, some as the backstays would make some shadow. I would think if mounted fore aft on each side of the boat, one might have much less shade?

[wrwakefield]

We have 3 panels; one 135w panel above the bimini [came with the boat], and we installed two 165w panels on the stern dinghy davits on our ketch.

To mitigate the effects of partial shading I installed an individual Victron Smartsolar controller for each panel [3 controllers.] I found the cost for 3- 15A 75V controllers proportionate to one larger capacity controller that could accommodate the combined output of all all 3 panels. So, aside from wire, out of pocket costs were more or less equal, but the output is quite optimized with the individual controllers.

In case this is useful.

Cheers! Bill

PS: I have been tracking stats for a few years now, and need to update this earlier article which contains many more details if you are interested.

[jbinbi]

Having 4 controllers is a no go. The smallest victron is 75/15, my panels are 20/5. Each controller is $120. So 2 controllers I think, unless there is some other reasonable quality say 50/5 MPPT for like $50ish....