By the power of the sun...

[Project_Mayhem]

I'm in the market for a 50-100w solar panel and am having trouble deciding where to mount it. I can mount a 50w on the port side of the stern rail. I have the throttle control mounted there and almost never dock on that side. This mounting option would allow the panel to be angled towards the east (or towards the sky) just like one of my neighbors

I could also fit a 50w on my bow rail. There's always a chance that it will bump into the abandoned boat's rail next to me if the wind picks up while docking. Wiring is a longer run but this panel would be facing east

The other option would be a 100w panel hanging off of the back of the stern rail facing North or straight up. In either case I would make the panel pivot on the rail.

Our power requirements are pretty minimal - LED lights, outboard starter, two speaker stereo (more like a one speaker load because they're 8 ohms), occasional phone charging, etc. We're using the boat 2-3 times a week at the moment.

1) Which option would gather more power across all weather conditions?
2) For those of you who've had solar panels mounted on the railings, what are the pro's and cons for each location?
3) What did you learn after having a panel installed for a while?

 

[dlochner]

1) Which option would gather more power across all weather conditions?

The panel which gets the most direct unshaded sunlight will produce closer to its rated capacity. The panel should face to the south and be angled at roughly your latitude, i.e, if you are at 45°N then the panel should be about at 45°. Flat will also work, but be less efficient.

 

[jeepbluetj]

I had 160W on the stern of my C-30 on tiltable mounts. I wouldn't have wanted one on the side, and definitely not on the bow.

So I'd say your 100W on the stern sounds the best for me, and if it hangs off the end wouldn't affect the operation of the boat much.

 

[thinwater]

Cabin top. Yes, less output, but it's not in the way. Most boats have too much rail clutter.

 

[DArcy]

I have 2x 123W panels fixed above my Bimini currently putting out 75 watts with partial cloud cover, angled about 10 deg North, at 45 deg North latitude just after noon.
Not great performance but they are about 30 deg from perpendicular from the sun at the moment, it's not full sun and I am a long way North. Real world, this is about what I would expect. I get about 150~175 Watts with full sun and angled South at 45 deg North latitude. So figure about 50% of rated output for a few hours per day if you can angle the panels towards the south. Outside peak hours you will still get some charging but it does taper off and it is not always sunny.

 

[Project_Mayhem]

I'm leaning more towards the 100w stern rail mount. The boat actually faces Southeast. Panels could have a clear view NW, flat or SW with mast and folded up bimini shadows at various times of the day. As far as power generation goes, how does this sound?

 

[dlochner]

Nigel Calder estimates daily solar output to be 3 times the nominal panel rating. In this case, it would be 300 watt hours a day or about 25 amp hours a day on average. However, because of charging inefficiencies not all of that power will end up back in the battery. Assuming you have a couple of Flooded Lead Acid Group 24 or Group 27 batteries that should be enough power to keep the batteries reasonably close to 100% SOC if you start with fully charged batteries. It might be stretch to recharge deeply discharged batteries.

AGM batteries would die a rapid death because this is not enough power to bring them back to 100% SOC each day.