Solar panel wattage recommendations

[Stickinthemud57]

I am planning a three-night cruise and considering purchasing a flexible solar panel and charger kit. The idea is to attach the panel to my bimini top. I do not plan to leave it on the boat as a matter of course.

I have two deep-cycle marine batteries, and power demands are low on my boat. I can hand-start the kicker, all my lights are LED, there is no AC, cooking can be done on a butane hotplate or propane Magma grill. I have a couple of 50-watt Crockpot lunch warmers that will probably come into play.

For a short trip like this, a solar panel may be completely superfluous.

So, will a 100-watt unit do it for me, or should I consider something with more punch?

Feel free to recommend a system if you are so inclined.

[Starscream]

Without refrigeration, I don't see any need for more than 100W.

We have a 100W solar system and we do multi-day voyages with 5 on board at 45N latitude or so. No fridge, but LED cabin lights, computers & cellphones & tablets, anchor lights, pressure and waste-water systems, autopilot & chartplotter, air pump for the toys, multiple fans for those hot nights at anchor.

I highly recommend adding an ACR relay to your system. That way the solar panels charge both batteries regardless of the battery selector position. It makes management of two batteries super-simple, because there isn't any management. If there's sun, or the main motor is on, then both batteries are charging, all the time. We have two dual-purpose batteries, and the ACR makes things so simple that I just leave the switch on position 1 all season long.

[wakataka]

It all comes down to how much you use the crock pot. That will pull a lot of amps. Otherwise I think you''ll be fine with a 100w panel. I cruise with just one deep cycle battery providing the house loads for lighting, water pump, charging electronics, and running radios. I do tend to get most of the charging from the outboard when cruising but I pull out the solar panel when I'm going to be at anchor or on a dock without power for more than couple of days. I've got a second start battery that stays fully charged and a Yandina combiner to manage the two.

I use a 100w flexible solar panel that I tie down to the sliding hatch cover on my 26x. It feeds through a Renology Voyager charge controller (https://www.amazon.com/Renogy-New-Voyag ... r=8-2&th=1). I use the same charge controller with a little 5w maintainer panel to keep the battery topped up when the boat is not in use (https://www.amazon.com/gp/product/B07W9 ... =UTF8&th=1). These components have worked flawlessly for 4 years.

I should probably knock on wood now.

I recently bought one of these that I think may come handy on the boat.

https://www.walmart.com/ip/Bluetti-Port ... =101209423

It uses lithium iron phosphate batteries which do not have the potential to self-combust like lithium ion does. Having seen videos of lithium ion batteries self igniting I just sleep better without a big block of lithium ion batteries on the boat.

[KingRichard]

Piggy back everyone else. 1 big deep cycle and a little charging from the kicker is enough a for a couple of days with normal-ish loads. I have a 100 amp solid panel that I never take, too bulky. This year I'm planning on a 50w flexible mounted to the sliding hatch. Partly because I can leave it hooked-up & mounted, and partly because I don't want to be on the boat long enough to need any more power.

[LakeMac26C]

I have a solar panel rated at 100W on my 26C. I do not do any long term sailing or have any heavy loads. My problem is with the charging circuit. The OP hooked up the PWM charger to both batteries in parallel. It ended up almost killing the weaker battery. I now have a switch that manually controls the charging of one or the other battery. Not ideal, but each battery is reliable now.

Considering the talk about ACR, isolators and such, could I recommend a dual battery charger instead? I'm thinking of buying this one. It's a lot cheaper than the other options and without the drawbacks. I know it's not name brand (or even a name that's likely to be around for the long term), but it should maintain two batteries independently.
https://www.amazon.com/EPEVER-Battery-C ... 138&sr=8-2
I'm also buying a pair of MC4 solar panel extension wires because my boat is under a tarp for the season and the solar panel is completely shaded.

[Russ]

could I recommend a dual battery charger instead? I'm thinking of buying this one.
https://www.amazon.com/EPEVER-Battery-C ... 138&sr=8-2

That's an interesting controller. I've been using an ACR with success. My start battery is dedicated to the motor and the house is isolated. The solar charging is connected to the house and when the voltage goes up to 13.8 or whatever the ACR is set to, it will charge both batteries simultaneously. Both my batteries are identical so I'm not worried about dissimilar charging.

That dual battery controller might be especially useful when batteries are dissimilar. However, at that price is it smart enough to handle different chemistry batteries? At that price point, it's probably a decent controller for the job.

[Stickinthemud57]

^^^

Thanks for pointing me to that.

Question, though - I have two batteries connected by an A-B-Both switch. Would it work hook the solar charger to one of the batteries then set the switch at "Both"? These are identical batteries purchased on the same day, and the solar charger would be not be used for daily maintenance charging - just when I am on a several-day excursion.

[Starscream]

^^^

Thanks for pointing me to that.

Question, though - I have two batteries connected by an A-B-Both switch. Would it work hook the solar charger to one of the batteries then set the switch at "Both"? These are identical batteries purchased on the same day, and the solar charger would be not be used for daily maintenance charging - just when I am on a several-day excursion.

Yes, that would work while the sun is out. After a few days of low sun, or shading, there's a risk that both batteries run down though. The ACR really is the best way to handle two batteries. That way if you leave the battery position on 1, only one battery will run the risk of running down at night or long periods of overcast. The ACR really is set-it and forget-it.

[Stickinthemud57]

I see, I think. It sounds like you are saying that if the cells are not sending enough voltage to the batteries that they might be draining them, correct?

[Jimmyt]

I see, I think. It sounds like you are saying that if the cells are not sending enough voltage to the batteries that they might be draining them, correct?

Shouldn’t. He appears to be saying that if your battery switch is using battery one (lights, frig, crockpot, induction cooker, tv, etc - all using battery one), and the sky is overcast, the solar won’t be able to keep up with the load. But, you’ll only drain the battery you’ve selected on your A-B switch.

If you have a proper solar setup, your solar panels will not put a load on your batteries.

[Starscream]

I see, I think. It sounds like you are saying that if the cells are not sending enough voltage to the batteries that they might be draining them, correct?

No, solar panels have diodes that prevent draining of the batteries. I'm saying that if you leave your battery switch on BOTH, and connect with a dual-bank solar charge controller, then everything is fine as long as the sun shines. But if your battery switch is on BOTH, then if there are any loads on the batteries like LEDs for USBs, or the AUTO lights on a bilge pump, or anchor lights, fridge, or whatever, then both batteries will be drawn down during the no-sun times.

With the ACR, you can leave the battery selector on 1 (or 2 if you prefer), and any dark-time loads will only draw down one battery, and as soon as the sun starts shining then the ACR will charge both batteries anyway, even though the selector is on 1. You can sleep soundly knowing that battery 2 will be fine in the morning, even if you forgot where you left the battery selector and left a heavy load on all night.

Personally, I will never put my battery switch to BOTH. If I do, I know that at some point, probably the most inconvenient, I'll forget and later on I'll find that BOTH batteries were drained by something that I forgot to turn off.

[Stickinthemud57]

Thanks for that clarification. Makes sense.

I, too, am averse to the "both" option. I added a second battery about a year after replacing the original, and wired them in parallel. About a year after that, both died. I came to learn that this was bad practice because if one battery goes bad, it pulls the other down with it.

I think if I get a solar panel (still not sure I need it on the short cruises I currently do), I will use it to keep the reserve battery topped off. Meanwhile, I have other sources such as power banks and even my boombox that can charge my cell phone if need be.

I am going to try to keep use of electronics to a minimum, the idea being to leave tech behind for a few days.

[wakataka]

I've used this battery combiner for 4 years without any hiccups. One thing I really like about it is that there is no current draw from the batteries when there is no charging current. That's not true for all ACR relay's. With one of these, you don't need the two circuit solar controller. The combiner will route current to the battery most in need of it and prevent a bad battery from pulling down a good one.

https://cdn.shopify.com/s/files/1/0588/ ... 1668118244