Solar panels for Battery Charging

[Sharphooks]

Yo, Gents

I do a lot of boat camping and camper camping miles away from plug-in power. Seems like a good scenario for investigating solar panels

Anybody have any info on these (are they efficient for the amount of sun we get on an annual basis...as in, not too much...??) What wattage capacity would be typical to top off two 12 V batteries?

I just got real lucky and picked up a house on the water so my boat's tied to a dock instead of sitting in a driveway. But I learned the downside of leaving a boat in the water---I left the auto-bilge pump switch "on" when I went on a trip---came back and the bilge was dry but my house battery was dead. Seems like a solar panel might be applicable?

yes, I can leave the boat plugged in to shore power but I'm uncomfortable doing that for extended periods of time (cords strung down a long dock, live cords near water etc, a the trickle down unit that works fine but is continually WARM (right on the verge of being hot)

So that's why I'm thinking solar panel

Any experiences or comments you guys can share?

thanks

 

[Sharphooks]

Big help, High5--

Especially like the power-requirement calculator on that website

thanks!

 

[TenMile]

Hey Sharphooks,

I have 2 solar setups that I run so can give you some advice.

One system is on my boat for battery charging like you have described. Mine is an 85w panel that puts out about 4.2A in full sun. That is generally more than enough power to keep the batteries topped off, fridge running etc during the summer months. For batteries, I have 2 x 6V golf cart batteries as a house system (225Ah capacity) and 1 x 12v start battery. I have set up a second system at the family cabin -- it's much larger and consists of 4 x 6V batteries and 3 x 125W panels with a 45A charge controller and 2000W inverter -- that system puts out 21A in full sun and can recover the system from overnight use in about 3-4 hours of sunlight.

Some things I can suggest for a boat setup:
- 2 x 6V batteries generally have more capacity than 2 x 12V batteries of the same size
- you need a charge controller and don't skimp here -- the Morningstar Sunsaver mentioned above is very good and has a temperature compensating sensor on it
- get as large a panel as you can fit on your boat -- larger panel means batteries charge faster
- don't waste your money on the roll-up panels -- they are very expensive and generally have low output power
- panel needs to face south (if possible) and be 100% free of any shadows -- even a small shadow from an antenna or rod will cut the output of a panel by 60-80% -- the size of the shadow is not proportional to the output loss.
- get yourself an ACR system -- combines both your house and start batteries while the system is charging, but separates them while the system is not charging so you will always have your start battery fully charged
- get yourself a battery monitor that monitors voltage and Amps in/out and will report on your battery State of Charge. I have 2 of the Trimetric 2025 units on the boat and at the cabin -- these things are great because they tell you your ACTUAL usage and real time % charged state of your battery without any guess work. I'd recommend getting this unit first before you invest in panels and controllers. That way, you can measure your 12v usage over a typical day which helps you then calculate the size of panel you need (otherwise it's just guesswork).
- Wiring is very important -- oversized wire works much better than undersized as you lose quite at bit of power in a 12v system if your wiring is undersized.

Final bit of advice -- read this article. It's very very long but full of extremely useful tips for how to design your system. If you want the cheat sheet -- skip to the very end and he summarizes.