Solar Panels for Trolling Motor

[StarTed]

I'm having trouble keeping my trolling motor batteries charged up, especially when out on the water for more than 1 day with no or not enough power to recharge the batteries. As a result I'm planning to install a couple of solar panels on top of my boat. I built an aluminum canopy to replace the bimini top that was shot.

The panels I ordered are 210 watts from Continuous Resources and will need to be connected in series for the 24 volts needed for the batteries. I would have gone with a 36 volt system but an extra battery would take up too much space.

The size of each panel is around 59 X 27 inches. These panels are capable of putting out almost 10 amps each. Wiring them separately for 12 volts for each battery would require 2 controllers so I'm opting for a series arrangement.

I have some questions and concerns.

How do I mount these solar panels so the shocks from cruising won't damage them?

I'm thinking of making up some kind of folding arrangement so I can fold them over each other with the solar surfaces facing each other. That way the top panel will be upside down with cushioning along the edges. Will it be strong enough that way?

My top is 48" wide before it begins curving and the back flat area is around 35". I expect one panel to hang back over the top when in use but not while travelling down the road if I use a hinged arrangement.

Does anyone have any experience doing something like this?

Thanks in advance.

 

[mike_i]

I don't want to burst your bubble but I doubt the panels are going to keep your batteries fully charged. Don't count on the panels generating 10 amps. That rating is with the panels mounted in the optimum position in relation to the sun. Mounting the panels flat will diminish the efficiency a lot.

 

[StarTed]

Thanks Mike,

I appreciate the input.

I'm already aware of their inability to keep my batteries fully charged the way I use and store the boat. I've already had 2 new batteries fail after 3 months of use so I'm trying to reduce or eliminate that problem. If I can get a quarter of that output I'll be happy.

Fully discharging the batteries is very hard on them so my goal to to keep the charge somewhat higher until I can recharge them through dependable power. I would have to run my generator around the clock to recharge them. That is not an option for me.

Anyway, if they don't meet my needs on the boat I can always use them on my motorhome.

These solar panels are designed to give some output during overcast days. My hope is that they'll work on top of my boat. keeping the battery drain lower. At least I should gain some more knowledge about today's solar panels.

My old solar panel that I carried on top of my backpack many years ago to charge the batteries for my camcorder worked for a week's backpack trip. It's output dropped greatly when not directly facing the sun but it kept those batteries functioning.

New batteries ran my trolling motor for over 2 days before they went dead. After that the batteries never worked as well.

I'm trying to avoid buying new batteries that often.

Thanks again for your input.

 

[gm280]

Okay, wasn't this exact same idea posted on here not that long ago? Sure seems like it.

The quick short real answer is, buy a small gas powered generator to charge your batteries and happy boating. So many think solar panels will do the job and learn that just isn't happening. Sounds great on the drawing board, but reality doesn't come close. A small generator will do what you are looking for and probably cost way less to set up as well... JMHO

 

[StarTed]

Thanks GM280,

I guess I don't know how to search because I couldn't find that post.

I already have a Honda 2000IS and know that would work but CO in a boat is an issue. At least they make us post a sticker in the boat to that effect. I also know that CO is only slightly lighter than air so it can hang around easily. Then there's the issue of where to put it for transportation and while it's running. Real estate is limited. I wouldn't really want it on top of the cabin due to its weight and difficulty moving and starting it.

My solar panel that I bought in the '80s for the backpack trip dropped to around 1/10tth the output when not directly pointed at the sun. I thought that they've greatly improved from that time. At least their sales hype claim to have improved in that regard.

A friend has a couple solar panels mounted flat on top of his motorhome and claims to have good success using it. I am hoping to see some improvement.

At least I'm going to give it a try since I'm one of those that has to experiment with something. I just thought that some others have already done that and could give me some pointers such as mounting problems to avoid and potential damage from pounding waves.

I'll be measuring the output and monitoring the results. The 2 panels are rated for a total of 420 watts so even 1/10th will still be 42 watts at 24 volts for a little over 1 amp. I don't know how much the trolling motor draws because it varies all over when anchored. I suspect it's around 30 amps average. The plug in charger is 20 amps total so each battery usually charges at around 10 amps. 100 amp-hour batteries should charge in around 10 hours for most of the charge. That makes it 100 hours for a 1 amp charge rate. That would be around 10 days to charge them up.

I tend to go out for 2 to 3 days at a time so maybe I can make it through the 3rd day. It's also important to me to extend the lives of the batteries. Having them under a small charge rate should reduce sulfation.

It's worth a try to me.

 

[Scott Danforth]

there are dozens of threads where someone wants to put solar panels on a boat to keep batteries charged to power a trolling motor

not one of them has ever worked. either get a gas powered trolling motor or a small genny

on a boat, unless you have an active array to keep them aimed at the sun, expect between 5-10% power output.

 

[StarTed]

Thanks Scott,

That's some useful information. I was wondering what percentage to expect. I'm not trying to recharge the batteries, just prevent them from dying and sulfating before I can properly recharge them.

 

[Scott Danforth]

you would be better off with a few of the lithium ion battery jump packs and use them to re-charge the batteries.

to prevent sulfating the plates, get one of the non-charging solargizer maintenance kits. it pulses the battery with its own juice, however at about a 14volt level. just enough to keep the crud knocked off the battery plates.

however hard to beat a 2kw inverter duty genny. they run at about 52 db for noise (about as quiet as a whisper in church) and weigh less than a 24 pack of beer

 

[gm280]

StarTed, if you will, please come back on here and post your results, either way, since it does seem you are going to try it anyway. A true response would help with future endeavors for others. I ask that because we do get that exact same question on here a few times over the year. And a true results posting will certainly help others with the same ideas...

Thanks and hope for your success.

 

[StarTed]

Scott and gm280,

Thanks for the comments.

I looked into Lion batteries. They're too expensive at this time. Just under 1K each is a little steep for my blood at this time.

I use my boat mainly for fishing and my trips are usually for 2 to 3 days. I use my pickup and sleep in the back unless it's too hot, then I take the motorhome and run its generator and AC. Charging the batteries a little in the evening from a generator just isn't doing the job. It might be enough on top of the solar panels.

I don't even have a radio other than the marine vhf one that doesn't get turned on where I go. I like the peace and quiet. That said, the solar panels will be mounted and given a try. I was mainly interested in other people's experiences with mounting and durability due to the shocks from hitting waves. My boat is a river jet boat so it rides hard.

I made the aluminum top so I feel confident It can support a couple solar panels.

The pictures show the framework I bent and welded, the front entry door open and a side view after completion. I did all the metal and fabric work. By the way, the top can be detached from the boat but I don't plan to ever do that.

I'll keep you posted.

I like to think I'm an Ameri"can" not an Ameri"can't".

 

[dingbat]

Scott and gm280,

I like to think I'm an Ameri"can" not an Ameri"can't".

I'm a firm believer in the nothing is impossible but... as an engineer, part of the job is to evaluate the feasibility of a project.

Calculating the outcome isn't rocket science. Simple in/out calculation.

What is your storage capacity in Ah?
What is your consumption in Ah?
What is the charge rate of the panel?

We also know there is a direct correlation between deep of discharge (DOD) and life expectancy.

Battery life expectancy plummets once you past 75% discharge. A number of sources list 80% DOD as a death sentence. Ideally you want to stay under 50% discharge.

Obviously if your killing batteries as quickly as stated, your discharging past the 80% figure. This suggests that you have to reduce / or supplement your DOD by 30% to significantly improve battery life.


From the numbers you've posted so far, it sounds like you expect to pump a quart of water an hour into a 20 gallon tank with a 15 gallon an hour leak and expect a different outcome.

 

[StarTed]

Thanks dingbat for your much in depth response. I think you're right on.

One change I plan to make is to use my Tohatsu 9.8 when I need to go over 5 (half way up) whatever that is in current. I can use it and the 80# Ultera together. I could also use drift socks to slow it down. Maneuverability gets to be an issue when trying to troll slowly in a cross wind or tail wind. I often like to run around 0.6 mph for walleye with a bottom bouncer. Anchoring can also use lots of energy at times.

There's no easy answer. I'm just trying to keep from deep discharging my batteries. Just want a little more time.

There's no substitute to field trials once I can get in the ball park.

Is there a voltage reading that would tell me when I reach the 75% discharge?

I have options but some of them are not very desirable due to too much additional effort while fishing.

 

[gm280]

Talking tail winds and cross winds, you may need to install a sail...lol

Ha, by all means don't let others talk you out of, or in to, any idea. We only offer verifiable facts. YOU have to determine if those facts can be mitigated and over come. And the only way to prove that one way or the other, is to try it. But understand math doesn't lie. Numbers in and numbers out have to balance...always!

Now with that stated, as far as mounting such solar cells to withstand a rough going, how about a bolt system with rubber and spring inserts to absorb the bumps. Kind of like they do with trolling motor mounting setups. Don't direct bolt the panels down tight. Run a long bolt through a rubber cylinder type mount with an outside spring around the rubber mount. Then it will hold the panels tight, but allow for bounding without transferring that stark movements to the panels. Like a shock-absorber. In fact check to see if they already have such smaller type shock-absorbers so you can just buy them instead of trying to manufacture them.

If you ever used a newer model chainsaw, they actually have such shock absorbing type setup on them. Mimic that setup and the panels won't be as effected from the rough ride... Just an idea!

 

[dingbat]

Is there a voltage reading that would tell me when I reach the 75% discharge?

 

[Scott Danforth]

Here is some reading on some of the other similar threads (remember, these are old threads and should not be posted in)

https://forums.iboats.com/forum/other/non-boating-technical-topics/10531022-solar-battery-charger

https://forums.iboats.com/forum/gen...6-seeking-advice-solar-powered-trolling-motor

https://forums.iboats.com/forum/boa...trolling-motors/10521085-solar-panel-question

https://forums.iboats.com/forum/boa...rger-mounted-on-boat-allow-more-trolling-time

 

[StarTed]

Thanks gm280 for the thoughtful input. I have some shock mounts lying around but they may be too light and/or too old.

I'll be sure to install some kind of shock mounting.

Thanks dingbat for the table. I'll make a copy and keep it in the boat. I'll also install a voltmeter on the batteries that is readable to me. The voltmeter on the trolling motor is''t readable to me.

Also thanks Scott for the links. I read them and find them informative and also what I already know. I've read up a lot on the latest solar panels. If the hype is close there has been lots of improvements made to capture more energy when the solar panels aren't directly aimed at the sun. Of course aiming them directly at the sun gives the greatest output (what's given as the rating).

The 2 panels I'm getting are monocrystalline and the controller is MPPT to maximize the output.

I'm a retired meter electrician so I plan to install metering equipment. An ammeter and a voltmeter at the minimum. Since this is DC I shouldn't need a wattmeter.

When I get started I'll take pictures and keep you posted. I know the solar panels will get better later but a current update won't hurt.

 

[bruceb58]

420W using an MPPT controller will give you 420/28=15A. With a 30% penalty for being flat mounted, that would be 10.5A. This is all charging a 24V battery

Use this site to determine the number of equivalent sun hours.
https://www.wholesalesolar.com/solar...n-hours-us-map

During your peak month, you will get around 4.8 x 10.5A= 50AH...with a 24V battery

Hopefully you don't have anything that will cast shade on your panels like antennas.

 

[StarTed]

Thanks bruce for your input.

50AH would be great. I expect it'll be less than that.

No, there won't be anything above the panels.

I understand that solar panel output decreases as temperature rises. The extra hours during the summer may be a wash.

They will be used during the winter month weather permitting.

I'm still waiting for the panels.

 

[bruceb58]

I have 700W on the roof of my travel trailer...flat mounted. What I told you is what I see with my panels and controller. I have a Victron MPPT solar controller on mine. It has built in bluetooth so I can see the stats of what it is delivering every day.

As far as temperature, if your boat is on the water and you have any kind of breeze blowing, that will go a long way to help your output. Your biggest problem is the latitude you are at as the optimum angle is steeper than what I would need.

 

[StarTed]

Thanks bruce for the additional information.

I'm thinking 2 ammeters would be desirable. one for the solar output and the other for the trolling motor input. One voltmeter on the batteries should do unless I measure each battery independently. Two voltmeters would eliminate voltage loss in the lead between the batteries. I'll probably connect to different terminals on the batteries to eliminate losses in the connections there.