Another Solar Charger setup question

[The Canuck]

Like others, I have been intrigued about a solar kit that will allow our boat batteries to be topped off while we are not at the lake. I have seen some flexible panel kits posted here on the forum, as well as some that have a more permanent solution, but they are typically attached on the boat. As the season is getting closer to beginning (for those not down south), and finding out I need at least one new battery (starter), I am back on the hunt/research for a kit that will top off the batteries and maintain them.

I have used Lake Lites solar dock lites, and have been very impressed. Our lake floods a couple times a year with our gangway going underwater, yet the lights continue to shine at night, both out of water and underwater. So it got me looking back at their website, and I came across a kit that they are offering for dual battery setups. Dual Battery Solar Kit. In reading through the description, and going through some of the different manuals (links not always working), I feel like this might be a nice all in one kit. But I have some questions, which I have sent to the company, but figured I would ask a few here as well.

- Are the dual 20w panels sufficient enough to charge or top off, while also maintaining? I am/was under the impression that more was needed. But knowing they use these kits for boat lifts (assuming they work well), it is essentially the same setup. Solar panel charges a battery that is then used to raise and lower a boat lift. Or in my case, solar panel charges a battery that is then used to start boat, or play music on boat.
- Max Power - 20w
- Rated Voltage - 18 volts
- Rated current - 1.12 amps
- Their description isn't great in that it states you get dual regulators, but then you also have to click the box next to pole length. Are the regulators sufficient? I am assuming they are for the system, but will they truly control the charge/topping off/maintaining based on the description/specs for the unit?
- If you have your boat at the dock and say you are wanting to play some music, is it possible to have the batteries connected to the solar panel (charging) while also playing music? Or is that potentially too much draw or demand in that the regulator is trying to "refill" the battery, but say the battery is depleting quicker.

Whether I use their all in one system, or try to piece something together while using theirs as a template for what to get, I feel like this is a great option (if it works) for those that don't have the ability to have power down at a dock. I would imagine the controller would be mounted in the boat similar to how people have the NOCO charger installed. Then I just have to route the cable along the dock and have the disconnect located close to the controller. As well as remembering to make sure it is disconnected before leaving. lol.

Any input/thoughts would be appreciated.

 

[zackmorris]

I just started going down this rabbit hole.

I have a 36V trolling motor battery and then a 3 battery house / starting battery setup I want to keep topped off as the boat sits in the high & dry.

What I came up with was:

Dual-Battery Solar Charging Setup for Boat​

System Overview​

This setup powers a 12V and 36V dual battery bank on a boat using a single compact 100W bifacial solar panel. It’s designed to trickle charge both systems over extended periods between outings — ideal for weekly boating schedules.

Components​

• Solar Panel:
  BougeRV 100W N-Type 16BB Bifacial Panel
  • 25% cell efficiency, bifacial design (front rated at 100W)
  • Vmp: 23.8V | Imp: 4.2A
  • Compact size: 34" × 23.1" | Weight: 12.9 lbs
  • Estimated real output: ~412.5 Wh/day with 75% system efficiency
• Charge Controllers:
  • Victron SmartSolar MPPT 75/15 → 12V battery
  • Victron SmartSolar MPPT 150/35 → 36V battery
• Batteries:
  • 12V 250Ah LiFePO₄ – currently at 75% SoC
  • 36V 100Ah LiFePO₄ – currently at 50% SoC
• Breakers & Cabling:
  • 25A breaker → Y-split MC4 connectors from panel
  • 25A breaker (12V controller) & 25A breaker (36V controller)
  • 10 AWG and 8 AWG marine tinned wire

---

Charging Performance Estimate​

Battery	Capacity	Starting SoC	Energy Needed
12V	250Ah	75%	~800 Wh
36V	100Ah	50%	~1920 Wh
Total Energy Required	–	–	~2720 Wh

• Daily Energy Generation: ~412.5 Wh/day
  (Florida sun, horizontal mount, 5.5 hrs/day)
• Recharge Time:
  

  ~6.6 days to full charge from current SoC

---

Summary​

With a single 100W bifacial panel and dual Victron MPPTs, this system can safely and reliably charge both battery banks in just under a week. It’s ideal for small- to mid-size marine systems where space is limited but uptime between trips matters.

The 75% figure on the starting / house bank is an aggressive depletion estimate, as it recharges on the cruise home. It was just an added safety as the boat sits outside. The real goal is to keep my 36V battery charged and ready since it currently relies shore power to charge.

 

[Zackdadams]

Just keep in mind, solar is not as efficient as you think.

I use it on many different scenarios, and it can be hit or miss.

Cloudy days or weeks can kill your charging.

Let us know your results.

 

[The Canuck]

I've unfortunately had to put things on hold for the moment. Before that, I reached out to another solar company (that happens to be Canadian) to see if they could build something. While they definitely could, and I think the components might be a little better (no idea - but they would be using a Victron Controller and their own solar panel), the biggest hurdle was my desire for a quick-connect, similar to the Lake Lite setup. My thought being while I personally don't mind having to potentially unclip or remove something from a battery, I am thinking more for my wife or kids when they get older. If she is down at the lake for a girls weekend, I want it to be as easy as possible for her to disconnect essentially the solar panel from the battery. Or hook it back up when she leaves. I think the screw style connection would work well, as I haven't seen anything else that is an easy connection that also provides some water-proofing.

Because this other company builds systems that are not designed to be connected and then disconnected, but more stationary on a sailboat or something larger, they didn't give me the confidence through email that we were on the same page. I think my referencing the Lake Lite system to them may have deterred them a bit, which is a shame, as their pricing was 1/3 less. That and having to ship the system would have in the end potentially been about the same pricing.

@Zackdadams Since we are down at the lake only on the weekends, I am not as worried or I don't think I am as concerned about allowing enough time to top the battery off. It's just to keep things topped off during the week when we are not there. Have you run into situations where you are not getting any charge, very little, or actually doing harm to your system with the solar? Curious to know more about your different scenarios.

@zackmorris have you hooked up your system yet, or that is what you are planning? Will you mount it to your dock, or what is your thought on mounting. I assume with the bi-facial panel, it will be set up so it gets some sort of reflection off of the water or other surface.

 

[zackmorris]

I've unfortunately had to put things on hold for the moment. Before that, I reached out to another solar company (that happens to be Canadian) to see if they could build something. While they definitely could, and I think the components might be a little better (no idea - but they would be using a Victron Controller and their own solar panel), the biggest hurdle was my desire for a quick-connect, similar to the Lake Lite setup. My thought being while I personally don't mind having to potentially unclip or remove something from a battery, I am thinking more for my wife or kids when they get older. If she is down at the lake for a girls weekend, I want it to be as easy as possible for her to disconnect essentially the solar panel from the battery. Or hook it back up when she leaves. I think the screw style connection would work well, as I haven't seen anything else that is an easy connection that also provides some water-proofing.

Because this other company builds systems that are not designed to be connected and then disconnected, but more stationary on a sailboat or something larger, they didn't give me the confidence through email that we were on the same page. I think my referencing the Lake Lite system to them may have deterred them a bit, which is a shame, as their pricing was 1/3 less. That and having to ship the system would have in the end potentially been about the same pricing.

@Zackdadams Since we are down at the lake only on the weekends, I am not as worried or I don't think I am as concerned about allowing enough time to top the battery off. It's just to keep things topped off during the week when we are not there. Have you run into situations where you are not getting any charge, very little, or actually doing harm to your system with the solar? Curious to know more about your different scenarios.

@zackmorris have you hooked up your system yet, or that is what you are planning? Will you mount it to your dock, or what is your thought on mounting. I assume with the bi-facial panel, it will be set up so it gets some sort of reflection off of the water or other surface.

Im installing the panel flat on the t-top. I won't be getting any of the bifacial benefits- perhaps some marginal gains from light bleed through according to online sources. I picked the panel due to its size and mono-facial performance, it just happened to be bifacial.

The rest of the equipment comes in today and i'll be installing it next week when I make it over to the marina. I'll be sure to post pics and results once it's on.

 

[The Canuck]

can't wait to see it, as well as how it performs.

I hadn't seen the "Bouge RV" line of panels and equipment before, but their pricing seems good. You never know these days what brand or company to go with. Maybe its all the same, maybe not.

 

[zackmorris]

can't wait to see it, as well as how it performs.

I hadn't seen the "Bouge RV" line of panels and equipment before, but their pricing seems good. You never know these days what brand or company to go with. Maybe its all the same, maybe not.

I'm sure these panels are all the same questionable quality Chinese stuff. So far the tinned solar 10awg cables have come in and they look good at least.

 

[zackmorris]

Here's my entire shopping list (so far) for those interested:

• BougeRV 20 Feet 10AWG Solar Extension Cable with Female and Male Connector Adaptor, UL Listed, for Solar Panel, 20Ft Red and Black Solar Cable Wire (Pair)
  Quantity: 3
  Link: https://www.amazon.com/dp/B075424L8R

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B0D4F18X27

• Blue Sea Systems 7180 285 Series Circuit Breakers, Surface Mount, 25A DC
  Quantity: 3
  Link: https://www.amazon.com/dp/B005BI50RY

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B073ZHRG9K

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B0D796TF4Z

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B0CJ9DND29

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B0C284QJKL

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 75V 15 amp 12/24-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B075NQQRPD

• Victron Energy SmartSolar MPPT Solar Charge Controller (Bluetooth) - Charge Controllers for Solar Panels - 150V 35 amp 12/24/36/48-Volt
  Quantity: 1
  Link: https://www.amazon.com/dp/B0CKTFRSZ4

 

[FSH 210 Sport]

My two cents and this is not meant to poo poo your set up, its just based on my research and experience.

Typically from my experience solar set ups only get about 60% of their installed wattage in real performance, and you also have to factor in the losses of the battery chargers.

You have lfp batteries which is a huge plus for solar charging since they only need about .5 hours of absorption time as opposed to lead acid which require roughly 8 hours of absorption time. However, if you look at your batteries spec sheet you’ll most likely see that they require 10A’s minimum charge rate. The solar set up you spec’d out only has 4.2A’s of output at 12V. So why the 10AWG and 8AWG wire? Are you going to run more than one 100W panel?

I’m assuming you guys do not have 120VAC at your dock correct?

Seems to me the best bet would be to install an array of at least 500 watts, probably more, then set up a battery bank on your dock for that array to charge. Then have an inverter to provide 120VAC and just have onboard 120VAC chargers, thats a system that doesn’t have to be on your boat, and the quickest disconnect there is, a single 120 volt extension cord. I figure you’d need about 6.5 KWh’s of battery storage to charge your lfp boat batteries from an 80% discharge approx 4.2KWh, and not exceed the 80% discharge of the shore power system.

With Victron IP67 battery chargers running at 25A’s your boats batteries would be fully charged in roughly 3.5-4 hours for the trolling motor bank, and 4.5 hours for the 250ah at a 80% discharge

Or you can do it way cheaper and buy a honda 2200 watt generator and the batteries will be charged in 4.5 hours …from an 80% discharge. If it’s only a 50% discharge it will be much faster.

Edit; If you’d be running five chargers at 25A’s for your LFP batteries (three for the trolling batteries and two for the house batteries) and one at 10A’s for the start battery which I’m assuming is a group 24 then you’d need a Honda 3000 watt battery. Also, I don’t see that you have a Victron smart shunt in the mix, if you have not bought all the two LFP house batteries I’d install a single LFP house battery and see if you really need that much capacity.

 

[zackmorris]

My two cents and this is not meant to poo poo your set up, its just based on my research and experience.

Typically from my experience solar set ups only get about 60% of their installed wattage in real performance, and you also have to factor in the losses of the battery chargers.

You have lfp batteries which is a huge plus for solar charging since they only need about .5 hours of absorption time as opposed to lead acid which require roughly 8 hours of absorption time. However, if you look at your batteries spec sheet you’ll most likely see that they require 10A’s minimum charge rate. The solar set up you spec’d out only has 4.2A’s of output at 12V. So why the 10AWG and 8AWG wire? Are you going to run more than one 100W panel?

I’m assuming you guys do not have 120VAC at your dock correct?

Seems to me the best bet would be to install an array of at least 500 watts, probably more, then set up a battery bank on your dock for that array to charge. Then have an inverter to provide 120VAC and just have onboard 120VAC chargers, thats a system that doesn’t have to be on your boat, and the quickest disconnect there is, a single 120 volt extension cord. I figure you’d need about 6.5 KWh’s of battery storage to charge your lfp boat batteries from an 80% discharge approx 4.2KWh, and not exceed the 80% discharge of the shore power system.

With Victron IP67 battery chargers your boats batteries would be fully charged in roughly 3.5-4 hours.

Or you can do it way cheaper and buy a honda 2200 watt generator and they batteries will be charged in 3.5-4 hours.

I have shore power, but it requires having the boat pulled to a work rack and having them plug it in.. or pull it the day before and plug it in.

I'd rather just have it slow trickle for a top off between uses.

I went with the thicker wire in case I add more panels later. Roof space is getting limited on the boat right now.

If it's able to give me a 20-30% boost on the 36v in a week, thats enough to be worth it.

 

[Zackdadams]

On my work trailer, I have 4x 100w panels.
40A Charge Controller, 200AH battery, 3000w Pure Sine Wave inverter.

This setup produces on average a 10-15A charge.

It sits in full sun 24/7/365.
90% of the time I keep a 95+% charge.

During stormy, overcast weeks, the battery drains down to 25% or less, which requires shore power to bring it back up.

I love solar.
My point was you do all the math you want, but it never equals real world use case scenarios.

The more panels, the better.

My 2 cents.

 

[FSH 210 Sport]

I have shore power, but it requires having the boat pulled to a work rack and having them plug it in.. or pull it the day before and plug it in.

I'd rather just have it slow trickle for a top off between uses.

I went with the thicker wire in case I add more panels later. Roof space is getting limited on the boat right now.

If it's able to give me a 20-30% boost on the 36v in a week, thats enough to be worth it.

Okay, but the batteries require a 10A minimum charge rate correct? I didn’t see which batteries you’ve got in your shopping list so I can’t go and look at their spec sheet.

 

[zackmorris]

Okay, but the batteries require a 10A minimum charge rate correct? I didn’t see which batteries you’ve got in your shopping list so I can’t go and look at their spec sheet.

I have epoch lifepo4s, and my onboard noco is a 5x2. I've trickled them off a noco 2 as well.

edit: the 5x2 and 2a trickle were on the 12v ones.

The 36v has only seen the epoch AC charger, which outputs 15a. I dont see anything in the specs that are requiring 10A charge rate.

36V 100Ah Heated & Bluetooth LiFePO4 Battery

Get the best performance with our 36V 100Ah LiFePO4 Battery. It features internal heating for sub-zero charging, Bluetooth connectivity, and an IP67 rating. With a built-in smart battery management system, overcharge and overdischarge protection, and high & low temperature disconnects, this...

www.epochbatteries.com

 

[FSH 210 Sport]

I have epoch lifepo4s, and my onboard noco is a 5x2. I've trickled them off a noco 2 as well.

edit: the 5x2 and 2a trickle were on the 12v ones.

The 36v has only seen the epoch AC charger, which outputs 15a. I dont see anything in the specs that are requiring 10A charge rate.

36V 100Ah Heated & Bluetooth LiFePO4 Battery

Get the best performance with our 36V 100Ah LiFePO4 Battery. It features internal heating for sub-zero charging, Bluetooth connectivity, and an IP67 rating. With a built-in smart battery management system, overcharge and overdischarge protection, and high & low temperature disconnects, this...

www.epochbatteries.com

Thanks for the info…

Their web page lists a “compatible” charger of 15A.


In their charging recommendation settings it states 50% of the battery capacity which would be 50A.


The compatible charger and charge rate are the same for the 12.8V battery.

I wrote to them a minute ago asking for clarification since their listed specs don’t agree with the compatible charger.

I’ll wager a guess they come back with 15A is the minimum charge rate. Every other LFP battery I’ve looked at has a minimum charge rate of 10A.

My concern for you is that you’re not charging the house batteries with enough current…

 

[Zackdadams]

@FSH 210 Sport Are you saying that even with 2A trickle charge the batteries won't stay topped off?

Had to do a little research, and looks like you are correct.
Can actually damage the lithium batteries over long term, interesting.

 

[zackmorris]

I know for a fact that the 12v 100AH lifepo4 batteries from them charge just fine on a 2A noco.

We'll find out this week on the 36v one!

 

[Zackdadams]

Oh it'll charge it, it just says over long term it will damage the battery.

I think the takeaway is if you're going to do a solar trickle charge setup, go lead acid or AGM?

My neighbor is an electrical engineer for NASA, he builds the batteries that gets sent to the International Space Station.
I'll pick his brain over this subject later.

 

[zackmorris]

Oh it'll charge it, it just says over long term it will damage the battery.

I think the takeaway is if you're going to do a solar trickle charge setup, go lead acid or AGM?

My neighbor is an electrical engineer for NASA, he builds the batteries that gets sent to the International Space Station.
I'll pick his brain over this subject later.

Can you explain why it would harm it? I would understand if I wasn't using a MPPT that did lifepo4 compatible charge phasing (such as a constant low amperage trickle) it would harm the battery, but why would just a low amperage charge do it?

I'm not doubting your feedback-- genuinely trying to learn.

 

[FSH 210 Sport]

Can you explain why it would harm it? I would understand if I wasn't using a MPPT that did lifepo4 compatible charge phasing (such as a constant low amperage trickle) it would harm the battery, but why would just a low amperage charge do it?

I'm not doubting your feedback-- genuinely trying to learn.

It has to do with how the electrolyte works… and the lithium ions, they need a certain amount of ooomph to push them back to the other node. As I said before, every lfp battery I have investigated has stated 10A minimum charge current. These batteries can handle up to .5C or 50% of the Ah capacity.

Yeah your 2A charger will charge the battery sort of.. but my educated guess will be that you will lose capacity of the battery, and probably permanently. LFP batteries have some no go zones that if exceeded will be permanently damaged.

Again, when I look on their web site it states “compatible charger” that is 15A in size.

I have not heard back from them yet.. will let you know when I do.

In lead acid batteries the minimum charge rate 10-13% of the rated Ah, but, that has more to do with electrolyte mixing to get rid of stratification, which, will lead to an eventual decrease in capacity, but in lead acid batteries that is recoverable. It also has to do with the amount of amperes being pushed through plates of a certain size to keep the plates clean.

 

[Zackdadams]

Here's what my rocket scientist neighbor said:

Me: Mind if I pick your brain for a minute? A friend is putting together a solar charger on his T-top boat. He has a 36V lithium battery for his trolling motor. He thinks one 100 watt panel will provide enough to keep the battery charged in between use. Thoughts? If he provides less than 10 amp charge, can it damage the batteries?

Engineer: "I think he will fine depending on how hard and the rest time for recharge. On my 12V system, I typically use about 250W on a trip. So if he used the same, it would be 750W. His panel should output about 700W/day. That is while his is fishing too (in the sun obviously). So if it rests 2 days he'll be good."

Me: I thought I read somewhere that lithium batteries can be damaged over long term with a trickle charge?

Him:" ON trickle charging... That is correct, however, modern day BMS system prevent trickle charging. The ones I use I can set the hysterisis on how far down a cell need to discharge before letting it charge again.

BTW - using multiple batteries in a lead acid system works fine because when lead is full, it still passes current on to the next cell. When Lithium is full, it stop all current flow."

Me: He's putting together a nice Victron system.

Him:" I like Victron. What panel is he using?... (I linked it)

I used connectors from that company (Brouge) and they seem to be fine (so far). I think the dividing line is between the flexible (not having good packaging) and the rigid (better packaging, less flexibility for install). That panel looks like it rigid, so that is probably the right answer.

Me: Sounds like it has your stamp of approval, thanks

Him: Yep, looks like a good system.