Looking At Solar

Bad Obsession · Mar 28, 2016

Soloban solar panel paired with a Genasun GV-10 solar controller. That will take care of it. Go big for the panel, 100 watts. You will have all of the power you need and some.

The best part, put the solar panel on your bimini. It is out of the way, easy to remove, and works great.

Capt jgw · Mar 28, 2016

Charging in place by whatever means is better than hauling the battery in and out. Handling the battery can stir up sediments from the bottom and short it out, not to mention what lifting it can do to your back. Might be moot in a trailer boat though, I'm sure bouncing down the highway doesn't help either.
A small solar panel would be ideal though, you can hook it up any number of ways to make it easily removable, and once you consider it "paid for", the output is free.

centerline · Mar 28, 2016

I beleive bigger is better when it comes to solar, cuz it doesnt really cost that much more.... if you are building the system yourself.
But for a minimum size panel for battery charging/ maintaining, i would never go with anything less than a 35watts... but with 100-140 watts you will never be without power for extended cruises, unless you feel the need for refridgeration, in which case you will need to go twice that amount.

There are some that claim to maintain a battery on a 5 or 10 watt panel, but this only shows they arent using the boat/battery much.
A charger that is too small may work if there is very little usage from the battery, but if ii gets used like most of us use our boats, the small charger can actually cause damage to the battery because it takes too long to charge back up...and its very likely they are pulling the battery down too low to begin with.

sesmith · Mar 28, 2016

Ok, some suggestions so far for big panels. Now someone correct my math if I'm wrong, but Greengas says he has a group 27 battery. That's about 80 amp hours of supply. If he only depletes it to 75% worst case, that's only 20 amp hours of usage.

A 40 watt 12v panel from Solar Blvd (where I usually get my solar panels and accessories), has a max charging current of 2.33A. If he gets an average of 8 hours charging, on a summer day at 2 amps, that would recoup 16 amp hours. If he isn't running the battery down that far on a daily basis, that 40 watt panel would be more than sufficient. If he's a weekend user, and had all week to recoup the battery, he could get by on less.

Edit: just reread his post. he said he goes out twice a month. If I were him, I'd carry an extra group 24 for a backup, and recharge with a much smaller portable panel during the off weeks (at least 15 -20 watts)...don't forget the controller to avoid overcharging.

walt · Mar 28, 2016

FYI, I used to windsurf at Aurora res so am familiar with that lake. No gas motors allowed and its a small lake maybe on the order of 1.5 miles in diameter. You can only use electric motors there but there isnt any where to motor to anyhow..

I come to the same conclusion - 40 watt would be all that is needed and if you take a trip later where you have a gas outboard, the 40 watt will be huge overkill (unless you have a fridge or spend a lot of time on a computer looking at forums/FB).

Another way to look at the numbers:

Trolling motor uses 45 amps at near full thrust (which is barely enough for that boat).
Use the trolling motor for 1/3 of an hour (20 minutes) each time you go sailing, go sailing three times a week.
So your amp hours used per week is 45* 1/3 * 3 = 45 amp hours.

A rule of thumb for solar is that you would get .2 to .3 amp hours per panel watt per day. Since you are at Aurora res where its likely to cloud up each afternoon, use .2 amp*hour / (watt *day)

You are charging the battery for 7 days so..

Power use = power generated
45 amp* hours = (.2 amp * hour/watt*day) * solar panel watts * 7 days
Solar panel watts = 45/(.2*7) = 32 watts minimum and on average. Solar daily fluctuations might be 70% or more, weekly fluctuations will be much smaller.

You must have a charge controller with the panel - the Genasun is a great choise (I dont think you need any more than the GV-5).

Any sort of shading - even what seems unimportant - does really bad things for the solar output. The only really good place on the sailboat for the panel is the top of the mast.. LOL.. second best is off the back. If you put the panel on your pop top cover and under the boom.. you just wasted a bunch of cash.

Also, take a look at the other sailboats at Aurora. Do you see any with large panels hanging off the back or are they there to sail to the boats potential. The heavier the boat, the more the panel and its weight dont matter. But you have a light boat, if you want it to sail to its potential, you have to keep it light. An option if you keep the boat mast up in that upper parking lot is larger panel that only goes on the boat when its in the parking lot, the panel goes in your car when your sailing.

Stu Jackson · Mar 28, 2016

Pretty much.

There's this: https://handybobsolar.wordpress.com/

And then there is Sumner's excellent material, do a search on Sumner and read his website.

Good luck, no more luggin'!

And it's called a controller, not a charger. It controls the solar panels' output to maintain the proper charging voltage to your batteries. Works almost the same in concept as a shorepower charger. Different thing, different name.

walt · Mar 28, 2016

Greangas, Im also wondering how you use the trolling motor? At Aurora, I know there are some boats out on moorings plus the mast up parking lot and you can not use a gas motor at all. How long do you actually run the trolling motor?

We sailed at Aurora last year with the Hobie club, the picture is from May back up in the coves.

RussC · Mar 28, 2016

Here's Another link with some good info (below). I'm using (above) a 30w unit and it's working even better than I'd hoped. cost, by doing my own fab work on mounts etc, was about $160.00
http://www.captaincurran.com/2014/10/diy-how-to-install-solar-panels-on-boat.html

Stu Jackson · Mar 28, 2016

Here's a link that includes a contribution by Sumner:

http://forums.sailboatowners.com/in...do-sailing-expertise.177963/&highlight=sumner

sesmith · Mar 28, 2016

walt said:
Another way to look at the numbers:

Thanks for the better explanation. We came to the same conclusion, but I overestimated (by a quite a bit) the solar panel output. Just call me overly optimistic

walt · Mar 28, 2016

I probably underestimated it. You see that rule of thumb estimate on the internet sometimes out to several decimal points for a parameter that has huge variations day to day, season to season, location, temp, battery charge state (with MPPT which that Genasun has). Another range I saw somewhere was .25 to .5. Denver normally has thunderstorms in the summer - might cloud up for some of the best solar hours of the day so I used .2. I just measured .32 for that rule of thumb number with a 20 watt panel and that Genasun GV-5 for my sailboat sitting in the yard (Arizona) with some partial shading from the house, power line and the end of the mast.

Benny17441 · Mar 28, 2016

Are there any others in the place that you keep the boat who are using solar panels successfully?

JohnShannon · Mar 28, 2016

10 A controller?? the panels put out 2.6A max. Also the wires from the panel/controller only need to be sized for 3A so 12AWG is maybe overkill. How quickly do you need to recover your 20AHr? I suspect 40W panel is also a bit of overkill. A smaller panel is cheaper, and cheaper to ship, mount ....

JohnShannon · Mar 28, 2016

Well a 20W panel will give you about 1A for 5 hrs a day. That is 35Ahr a week and your consumption 20Ahr a week. However if you are happy I am happy, a 40W panel will recover the battery sooner which is a good thing.