Solar Panels for multiple batteries

[Bulldog]

My electrician has let me down again!

So, I've convinced myself that I can DIY a couple of solar panels to maintain my batteries and - hopefully - run a small fridge. I have two 8D's that are starting batteries and two 12V's for my house.

I am really inexperienced at this stuff but am so tired of being blown-off and let down by mechanics, fiberglass guys, etc. Does anybody have any recommendations?

Thanks!

 

[rslifkin]

Doing just the house batteries is easy. Also charging the start batteries will require one of 3 solutions: Either DC-DC chargers, ACRs, or separate small solar panels and controllers for the start batteries.



Personally, I don't see much need to worry about solar charging for my start batteries. It would be very unlikely for my boat to sit more than a few days unplugged from shore power with the engines or generator getting run to top off the start batteries. And nothing draws from my start batteries, so they should stay topped off just as well as if they were totally disconnected.

 

[Bulldog]

Thanks. I forgot to mention that boat lives on a mooring and I do not have a genset.
I was actually thinking of small, separate panels and controllers for all four batteries. Would probably cost me more for the hardware but huge savings in labor.
Thoughts?

 

[rslifkin]

I assume the 2 house batteries are tied together in parallel? If so, I'd probably do a big set of panels and controller to charge those (sized to keep up the fridge, etc), then a pair of small panels with small controllers for the start batteries. The start battery panels can be pretty small, as they just need to keep the batteries topped off.

 

[DavidM]

DIY solar is not that difficult. I would first read the articles in the Library section on designing and installing solar panels, some of which I wrote

Your small fridge will consume 50-75 amp hours daily and other routine DC loads such as lights, water pump, device charging, etc will add maybe another 25 Ahs. So figure on needing a max of 100 Ahs of solar input daily to balance it out.

Roughly speaking unless you are in a high latitude or winter situation a solar panel will put out about 25% of its wattage rating in amp hours daily. This takes into account sun angle, cloudy days, etc. So that means you need about 400 watts to balance your DC loads. You can get by with less if you have good sized batteries and cruise to a different location every few days letting the engine alternator recharge your batteries.

Now you have to find a location on top that isn't shaded by the bimini, radar arch, etc. I assume your boat has an aft hard roof over the cockpit. This is probably the only place to mount hard panels but you will get shading from the bimini at some sun angles. The other way is to put flexible panels on top of the bimini sewed through the grommet. But I am not a big fan of flexible panels.

Then buy a couple of 200 watt, 24 volt nominal panels. Mount them with Z brackets to the deck using 5200 or thickened epoxy. Wire the two in parallel (to minimize shading effects) with #8 wire to where you plan to mount the solar controller. Choose a place close to the batteries.

You will need at least a 40A controller. Renogy and Victron make good ones. Connect the #8 cable to the input terminals of the controller and wire the output to the batteries with #8 as long as the batteries are within 5' of the controller. Otherwise use bigger wire. Make sure to put a 40A fuse in the positive cable near the batteries.

Good luck with your project.

David

 

[Bulldog]

Thanks David! This is great information. I think that you had actually helped me with solar panel recommendations to trickle charge my batteries over the winter through my shrinkwrap. Your recommendations have worked really well. Now I am ready for a more permanent solution.
Thanks again!
Paul.

 

[DavidM]

Glad your through the shrink wrap charging worked well for you Paul.

I now see that you may be talking about leaving the boat on a mooring with the fridge on and wanting solar to keep up with that load. In that case the 25 Ah daily for miscellaneous loads goes away and the fridge may use 50 Ah or less with no door opening, adding warm food, etc. So you can probably get by with 200 watts of solar.

So you might try adding a single 200 watt panel mounted cross wise on your cockpit roof to minimize shading. I would still run #8 gauge wire with a 40A controller in case you want to double it up later . But solar panels are relatively cheap so maybe go for two 200 watt panels.

David

 

[koliver]

Glad your through the shrink wrap charging worked well for you Paul.

I now see that you may be talking about leaving the boat on a mooring with the fridge on and wanting solar to keep up with that load. In that case the 25 Ah daily for miscellaneous loads goes away and the fridge may use 50 Ah or less with no door opening, adding warm food, etc. So you can probably get by with 200 watts of solar.

So you might try adding a single 200 watt panel mounted cross wise on your cockpit roof to minimize shading. I would still run #8 gauge wire with a 40A controller in case you want to double it up later . But solar panels are relatively cheap so maybe go for two 200 watt panels.

David

My experience with a fridge, on a mooring, with a pair of 160w solar panels, at 49° N, is positive. My panels can be raised to lay horizontally out from the upper railings, but still provide adequate amperage hanging vertically from those same railings, one pointing to Starboard, one to port.
My fridge draws <3 amps when running, so unattended, in our normally cool weather, not more than a 25% duty cycle, so <3x24x25% = <18AH.
In your home waters, you should be good with what David has suggested above. Go to Florida, not so much.

 

[Bulldog]

Thanks David. I will give this a shot with a single 200W panel as I'd like to save some roof space for a paddle board. I will let you know how it works.

Thanks again!
Paul.

 

[Bulldog]

My experience with a fridge, on a mooring, with a pair of 160w solar panels, at 49° N, is positive. My panels can be raised to lay horizontally out from the upper railings, but still provide adequate amperage hanging vertically from those same railings, one pointing to Starboard, one to port.
My fridge draws <3 amps when running, so unattended, in our normally cool weather, not more than a 25% duty cycle, so <3x24x25% = <18AH.
In your home waters, you should be good with what David has suggested above. Go to Florida, not so much.

Thanks Keith. All of this info is really useful. I will keep all updated.

Paul.

 

[Bulldog]

I would not recommend walking on solar panels at all.

 

[firehoser75]

Paul,
Sorry to hear about your issues with getting good advice and good work done from "professionals".
I installed a solar system on both of the boats I have owned with good results.
However, there are some things it is good to take into consideration when installing a new solar system. First, is shading. Your panels will not produce anywhere near their rated output even if partially shaded. The more area that is shaded and/or the longer period of the day where they are shaded (even partially) will have a larger impact, so panel placement is important. Second, especially since you do not have a generator, more panel capacity is better than just sizing for the minimum. I have not heard of anyone saying, "I installed too much solar". Unless you purchase your components with "future expansion" in mind, it is always less expensive and easier to put in the max panels you have space for to start with. Here in BC and areas north where I cruised, we would get rainy days or heavy cloud cover, and sometimes heavy fog for most of the day (only sun for a couple of hours later in the day), and having a larger panel capacity is very helpful on those days.
On my Nordic Tug, I installed 2 panels totalling 570 watts, and most days (late spring to early fall) my batteries get back to 100% (fully recharged - back to float) by 2 PM or so. My electrical use consists of an 8 cubic foot RV style fridge/freezer, an Engel portable freezer, LED lights, AIS on 24hrs for anchor alarm, other small loads like recharging phones, etc. I feel I could have "gotten away" with a 400 watt system, but the cost savings would have been minimal, and there would have been more days where I did not reach a full recharge (possibly resulting in having to replace the batteries more often, eating up any savings?). Last item, buy an MPPT controller and not the PWM type. They cost a bit more, but are a lot more efficient.
Good luck.

 

[NWSeadog]

I second firehoser's comments.

 

[CPD]

Were it me, knowing available space for Solar Panels is likely the largest constraint (and expense), I would maximize and dedicate the Solar Panels through an MPPT Controller to your House Bank. Include a connection from the House Bank through an Auto Charge Relay (ACR) to also charge your Start Batter(ies) once the House Bank voltage sufficiently rises.
Chris

 

[Bulldog]

Thanks Tom. I appreciate your comments - especially regarding the MPPT controller. I will be ordering everything this week and plan to start with 200 Watts. My current strategy is to just maintain my batteries. If I feel that I can get away with it, I will experiment with running my fridge as well. If it doesn't go well, I will plan to add an additional panel. My primary concern is space on my cockpit roof as I will also be storing two SUP's. If I need the space for another panel I guess I can move SUP's to my rails. Thanks again!

 

[vancouvertechie]

You did not mention the size of your house batteries and I am assuming they are 8Ds as well. What is important is how your batteries are wired either in series or parallel to get your total amp hours or AH. From there you can download a usage spreadsheet and calculated your total amp hours. With flood or AGM it is recommended to take your batteries down to 50% of the capacity. Also you didn't mention your inverter type. I would run a controller to for each panel to offset for shadows. It only takes 10% of shade to knock the panel's performance down 50%.

 

[kchace]

Thanks Tom. I appreciate your comments - especially regarding the MPPT controller. I will be ordering everything this week and plan to start with 200 Watts. My current strategy is to just maintain my batteries. If I feel that I can get away with it, I will experiment with running my fridge as well. If it doesn't go well, I will plan to add an additional panel. My primary concern is space on my cockpit roof as I will also be storing two SUP's. If I need the space for another panel I guess I can move SUP's to my rails. Thanks again!

From your signature it sounds like you keep your boat on the Merrimack, I do too. I’ve built my solar up in steps from 100w PWM to 320w MPPT. Be happy to share war stories with you.

Ken

 

[TheAtomicDog]

I can recommend this youtube channel as a pretty good source of info. You might find something useful here:

https://www.youtube.com/channel/UCoj6RxIAQq8kmJme-5dnN0Q

 

[Barrie]

We have a great company here in Ontario Canada called Solacity.
https://www.solacity.com/. I have outfitted my previous boat with solar and about to start my new one. Great service and knowledge transfer. Check out the rv and marine kits and the education link. Prices have also dropped. Good luck
Barrie

 

[Bulldog]

From your signature it sounds like you keep your boat on the Merrimack, I do too. I’ve built my solar up in steps from 100w PWM to 320w MPPT. Be happy to share war stories with you.

Ken

Hi Ken. Yes. Correct. I am on a mooring at the AYC. I think I recognize your boat! Are you on a mooring just upriver of Cove marina? I would really appreciate any input that you have. Where do you store boat for the winter? I am at Yankee Landing.

 

[Birdman]

I can recommend this youtube channel as a pretty good source of info. You might find something useful here:

https://www.youtube.com/channel/UCoj6RxIAQq8kmJme-5dnN0Q

That YouTube guy is absolutely GREAT!! He has some great simple beginner guides, as well as a bunch of advanced stuff, tests/companies available panel brands.... I would watch a bunch of his stuff before buying anything.

Battleborn brand LiPo4(the new lithium technology) batteries are also a great addition for house batteries on a boat. 4 of these batteries will run your AC system all night long. Of course they are about $1k EACH, but a good investment if your going to live aboard. (I know that’s not the case for this thread, but worth mentioning for others...).

 

[kchace]

Hi Ken. Yes. Correct. I am on a mooring at the AYC. I think I recognize your boat! Are you on a mooring just upriver of Cove marina? I would really appreciate any input that you have. Where do you store boat for the winter? I am at Yankee Landing.

Yes I’m actually on a mooring that Cove Marina manages. For winter it’s Kazmiera. Stop by sometime.

Ken

 

[Bulldog]

Yes I’m actually on a mooring that Cove Marina manages. For winter it’s Kazmiera. Stop by sometime.

Ken

Thanks Ken. I will definitely do that.

Best,
Paul.