Solar panel: single or array?

[TiggerToo]

I am thinking about putting some solar panels on board. The best place (short of building a gantry) would be to put some semiflex on top of the sprayhood. Question: as the boom will often cast a shadow on one side or another, would it better to put up two separate ones (with matching diodes) rather than one single one?

Any ideas?

 

[Hepne]

Tigger Too
I have installed four 30 watt solarpanels wired in series with bypass diodes on my sprayhood in order to avoid the shadow problems. The array which in full sun give over 80 volts, is connected to a MPPT charge controller which supply the correct charging voltage to the batteries. I have had this system for two years now, and its functioning very good. Due to wiring in series and the resulting high voltage, it even give a little charge on a rainy day.
I can post further details and diagrams tomorrow, no I have to prepare our easter lamb steak.
Kind regards John J.

 

[Stemar]

The only practical position for solar panels on Jissel is on the hatch garage, directly under the boom. I was strongly recommended to get two smaller panels rather than one big one. With the PWM controller I have, they needed to be in parallel so a shadow on one wouldn't take the other down. It may be different for an MPPT controller, but my first thought would be to put them in parallel.

 

[RichardS]

The only practical position for solar panels on Jissel is on the hatch garage, directly under the boom. I was strongly recommended to get two smaller panels rather than one big one. With the PWM controller I have, they needed to be in parallel so a shadow on one wouldn't take the other down. It may be different for an MPPT controller, but my first thought would be to put them in parallel.

This is the setup that I have as well with my MPPT controller as I get enough volts even in parallel to activate it early each day.

Richard

 

[GHA]

This is the setup that I have as well with my MPPT controller as I get enough volts even in parallel to activate it early each day.

Richard

It's been said on here that series is a good idea for victron mppt controllers to get the panel voltage 5v above battery voltage earlier and gain some more charging time. Which is wrong, with 36 cells the panel voltage will go up enough to turn on the regulator before the panel will put anything more than few mA into the batteries. Parallel is fine in the respect.

 

[Graham376]

I am thinking about putting some solar panels on board. The best place (short of building a gantry) would be to put some semiflex on top of the sprayhood. Question: as the boom will often cast a shadow on one side or another, would it better to put up two separate ones (with matching diodes) rather than one single one?
Any ideas?

Semi flexible panels on a flexible surface are likely to have short life. Any location with shadow needs panels in parallel rather than one larger one, no diodes needed. If possible, rigid panels on guard wires would be a better bet.

 

[lustyd]

It depends on the shadow. A good panel will have diodes so if there’s a shadow on one side you still get output from the other but at half the voltage. With my two panels if I use them parallel then any shadow makes one panel useless whereas in series a small shadow gives me 3/4 capacity.

 

[Hepne]

Tigger Too
Ref to my posting yesterday.

I have plans of installing a new hard sprayhood/dodger. For testing and preliminary use I mounted the solar panels on top of the old canvas sprayhood using wood backing on the underside of the canvas, screwed to the aluminium tube frame. I have a snap shackle on the main sheet and to minimize shadows from the mainsail boom I move the main sheet from the traveller to the toe rail, when not used. I have had another boat with solar panels on a targa aft, but I disliked that and wanted to try something else on this boat. There are pros and cons of everything, but all in all I am content with having the solar panels on the sprayhood.
The reasoning behind connecting the panels in series is the assumption that the panel array will reach the minimum charging voltage with less light than panels connected in parallel. Living in Norway with dark winters I wanted the panels to charge earlier in the spring. I have not done any comparative test on whether the total charging power actually is better with connecting in series vs in parallel, but I read articles that convinced me before I made it.
To check the effect of shadowing and the effect of the bypass diodes, I did a simple indoor test only involving measuring of voltage. (see picture).
I was in the boat this morning, the sky was cloudy and there was hail and snow. Despite this the solar panel array had between 60 and 76 volts. The charge controller was in the middle of its boost cycle with 14,4 V. (Note that the BM1 show an erroneous higher voltage). The current is low as can be expected with fully charged 3 x 100AH AGM batteries.

I have used the following components in my system:

4 no off Sunbeam system 30W Tough flexible flushmounted solar panels.

1 no off MPPT controller from Scherer,
type: CS 1024-MPPT
Battery voltage 12 V 24 V
Maximum effect 130 W 260 W
Maximum supply 150 V 150 V
Maximum charge 10 A 10 A

5 no off SCHOTTKY barrier rectifiers from ON Semiconductor, type: MBR10100G (10 Amp 80 to 100 Volt).
(The schottky rectifiers have much lower resistance than traditional diodes).

1 no off watertight connection box with screw connection rail.

Kind regards
John J.

 

[ryanroberts]

I plan on sticking one of these under the boom - half cell, so one side is decoupled from the other. Semi flex panels are pricey and have terrible lifespans unless amorphous, which has terrible efficiency.

495W JA Solar Mono Half Cell Panels - High Power Mono PERC - Silver Frame

 

[lustyd]

The two halves of panels are almost always independent these days, that's what the diodes are for, hence my comment above. I think you'd have to really try to get a panel without this!

 

[neil_s]

It depends on what you want from your solar panels. I have one 30W panel on the hatch garage. I usually get one night/day a week on the boat where I use Autohelm and laptop, radio and lights. The solar panel always fully recharges the batteries for next time.

 

[TiggerToo]

Thanks everyone, for all these detailed replies!

 

[scrambledegg]

Trouble is, every issue raised has been contradicted.
Panels in series or parallel, single panel or multiple panels, diodes or no diodes, mppt or not. hatch garage, sprayhood or guard rails.
Take your pick.

 

[lustyd]

Trouble is, every issue raised has been contradicted.

Very probably because none of this matters as much as the forum likes to think it does. Modern panels have diodes built in so there's really no downside to series connections as long as you remain within the limits of your controller. Parallel allows you to connect more panels to a controller without going over voltage but may require larger wires. The reality is that most installations are small enough that a modest MPPT will handle the load either way so as long as you have matching panels you're all good. For larger, more serious installations a bit more thought might be needed, but for the vast majority it's not that hard. Same with battery capacity threads, it's utterly pointless that every single poster is told to go and work out their consumption when the answer is actually "how big is your budget and battery box?"

 

[Norman_E]

On a sprayhood space is limited and panels are subject to some flexing, which damages them over time. Its best to fit multiple small panels for that reason alone. I fitted 4 small panels onto a bimini, where I could have fitted two larger ones, just because tha smaller sized ones would be subject to less flexing due to wind. Do not fit any panel in a place where the frame makes a hard point beneath it.

 

[lustyd]

Do not fit any panel in a place where the frame makes a hard point beneath it.

Agree with everything you say, just adding that you missed "because it might catch fire" at the end there. Some scary pictures on Facebook forums, and stories of molten plastic dripping into the cockpit from the bimini/sprayhood!

 

[noelex]

When considering the pros and cons of connect the solar panels in series or parallel don’t forget the third option of using multiple controllers.

 

[GTom]

I am 500+miles from my cheapo panels ATM but pretty much think they got diodes built in. Curious though if putting them in parallel would be better if one is partially in the shade.

 

[lustyd]

If they have diodes then you're better off in series because half of the shaded panel might give you 9V on an 18V panel. That 9V won't contribute anything useful on its own but added to 18V it would.