Charging Batteries with Solar Panels

[danamul1977]

Im hoping to be able to charge my batteries with some array of solar power (when in the north woods), and not need a panel that is as big as my boat to make it work. Looking for some advice as to the practicality of doing this, to just get me by through a week vacation of using a trolling motor. I'm looking for what size panels I would need to be able to charge two batteries, using one and letting the other one rest. Then switching between the two. How long would say 40 watt solar panel take to charge a trolling motor battery, or is it just to slow to be worth it? I've never tried any of this so if anyone has any advice I would really appreciate it. ty

 

[UncleWillie]

Re: Charging Batteries with Solar Panels

A typical auto sized Battery has a capacity of ~100Ah.
Assuming 12.5 volts that would be 1250 Watt hours.
Also assuming 100% efficiency, 40 watts into 1250 Watt hours yields ~32 hours.
Assuming typical efficiencies, and that you will not be completely discharge the battery dead flat, 32 hours would be a reasonable estimate.

The solar panel will only deliver the 40 watts under a clear blue sky, at noon, with the panel pointing directly at, and tracking the Sun.
You could expect to get the equivalent of 5 to 6 hours of this kind of Sun if you sat with the panel for 8 hours a day to keep it pointing directly at the Sun.

So you should expect to get one battery charged every 6 to 7 days if you are diligent.
If there are any clouds in the sky during that week, all bets are off! :grumpy:

To be practical you are going to need that panel that is as big as the boat as a minimum!

 

[KD4UPL]

Re: Charging Batteries with Solar Panels

Willie has the math right. You need a bigger panel. The most economical size is the most common. They are roughly 40" wide and 64" long and put out about 250 watts. These panels can usually be bought for about $1 per watt ($250).
One of these, oriented 180 degrees south and angled to the sun would charge a typical group 27 batter in a day or two.
They put out 30 volts so you will need a charge controller that is MPPT. This stands for Maximum Power Point Tracking. Never mind what that means, the point is it allows a 30 volt solar panel to properly charge a 12v battery. A minimum rating of 20 amps would be required for the charge controller, slightly more would be better. A controller like this will cost around $200. Blue Sky and Morningstar are two names to look at.

 

[danamul1977]

Re: Charging Batteries with Solar Panels

So my best bet would be 200 watt or more panel, or getting a generator (and maybe upsetting the other campers:mad-new I don't think there to loud. I would love to make the solar thing work but it might just not be reasonable. I could prob mount a few 100w panels on the boat but with rain/clouds, the generator is sounding better to me. Any thoughts on what I should do.

Thx to UncleWillie and KD4UPL that was great info.

 

[UncleWillie]

Re: Charging Batteries with Solar Panels

If this is just for a week once a year, you already have a reasonably quiet generator at the camp site.
It is called the truck. Attach the battery to the trucks electrical system and it will charge the battery.
Driving the truck to town for supplies will speed up the process but just idling for a few hours will also work.
You will burn about the same amount of gas as a generator, maybe a gallon an hour, but you will not have to actually spend money on the generator.

On the other side, if you want the generator for more than just charging batteries or you plan on doing this more than once or twice a year, the generator may be justified.
Plus, it even works when it is cloudy. :joyous:
You mention "The North Woods" and I assume it is not the North Woods of sunny Arizona. :facepalm:

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[Scott Danforth]

Re: Charging Batteries with Solar Panels

I was going to mention using the truck. get a few battery break aways, a pair for the truck and a pair for the boat. then you could always jumpstart the truck from the boat battery if needed

SMH SY175 Series 2 AWG 175A Breakaway DC Power Connector | 263-115

 

[danamul1977]

Re: Charging Batteries with Solar Panels

I was going to mention using the truck. get a few battery break aways, a pair for the truck and a pair for the boat. then you could always jumpstart the truck from the boat battery if needed

SMH SY175 Series 2 AWG 175A Breakaway DC Power Connector | 263-115

Ya, no im talking about northern wisconsin , It has so many lakes, pretty awesome place to fish/camp. I've redone a 1983 375v ranger, and want it to be ready for spring :cold:
Well that might be a great idea I never even thought of that. I pretty much go to town every day anyway (a good hour of driving should about do it). Im not sure if the larger batteries would fit in the truck, but ill also have to look into the Breakaway's, I never used those but that might be the way to go also. I'd like to get up there 2-3 times a year for maybe for a week or less. Great ideas tyvm

 

[Scott Danforth]

Re: Charging Batteries with Solar Panels

use the breakaways, run battery cables to the back of the truck under the bed. Then when you need to run to town, throw the batteries in the bed of the truck and hook them up. also, if you ever need a winch back there, the breakaway can be used to run power to a winch. (They make hitch mounted winch brackets)

Where in Northern Wisconsin?

 

[danamul1977]

Re: Charging Batteries with Solar Panels

use the breakaways, run battery cables to the back of the truck under the bed. Then when you need to run to town, throw the batteries in the bed of the truck and hook them up. also, if you ever need a winch back there, the breakaway can be used to run power to a winch. (They make hitch mounted winch brackets)

Where in Northern Wisconsin?

Vilas County, around Eagle River, that hole area has great north woods and lakes. The Indians spear a lot of our big walleyes, but the musky fishing is pretty great. Heard the DNR stunned a 72" musky on the lake I go to, but who knows the way stories go :suspicious:


So I can hook up more then one. Im gonna have to figure out how to run more then one wire through the alternator. It must charge slower if I had 2 in the back and one under the hood? not really sure how many "watts" the alternator puts out, but im sure I can figure that all out, and that sounds like the thing to do. I wonder if that would put stress on, and burn the alternator out faster (any thoughts on that)?

 

[UncleWillie]

Re: Charging Batteries with Solar Panels

...So I can hook up more then one. I'm gonna have to figure out how to run more then one wire through the alternator. It must charge slower if I had 2 in the back and one under the hood? not really sure how many "watts" the alternator puts out, but I'm sure I can figure that all out, and that sounds like the thing to do. I wonder if that would put stress on, and burn the alternator out faster (any thoughts on that)?

Your alternator is At Least 65 Amps (800W) and could be over 100A. (1200+)
Two or more batteries in parallel will charge just fine together.
You only need to run One Wire from the battery. Just The Positive.
A short wire from the Batteries to the body of the Truck is the Negative.

 

[danamul1977]

Re: Charging Batteries with Solar Panels

Your alternator is At Least 65 Amps (800W) and could be over 100A. (1200+)
Two or more batteries in parallel will charge just fine together.
You only need to run One Wire from the battery. Just The Positive.
A short wire from the Batteries to the body of the Truck is the Negative.

Very good, I think I was over thinking it. Thats what im going to do. Thank U to everyone for the help on this. Should make my life easier..

Someone just mentioned using a product called Stay-n-Charge. Ill have to read up more on this but that looks promising.

 

[UncleWillie]

Re: Charging Batteries with Solar Panels

Don't forget the 50/100Amp Circuit Breaker that is required on the Battery End of the Cable to protect the Battery/Alternator/Cable from overload.