by walt » Thu Apr 05, 2007 1:19 pm
If solar is your only power source, I think you probably need more than a trickle charger. Here is my example (Im fairly conservative on my power usage)
Per week, my power usage might be:(this is basically one day per week of using the boat)
Stereo 4 amps * 6 hours = 24 amp hours (I have two almost teenage boys - woops forget to add in the laptop which gets used to watch DVD)
depth guage .25 amp * 6 hours = 2 amp hours
Other insturments 2 amp hours
lights 3 hours * 1 amp = 3 amp hours
Pump .4 hours *2.5 amp = 1 amp hours
Note - pump assumes its on for only 24 minutes per week
Total consumption = 32 amp hours
Over a week, lets say I get 6 hours of good sunlight per day (42 hours per week) and my derated solar panel output is .04 amps per panel peak rated watt (ballpark, this would be about .8 amps for a 20 watt panel - all sorts of assumptions could vary this but its probably not that far off).
amp hours consumed = amp hours generated
32 amp hours = 42 hours * PPP * .04 amps/PPP
PPP = 19.04 watts - ie, I need a about a 20 watt peak power panel
Note also that for a panel this size, you should get a charge controller. Since your in a cold climate, Id make sure the charge controller had temperature sensing. The battery voltage is a fair amount higher when it gets very cold and if the charge controller is mounted fairly close the battery, it will compenate for the temp and keep the battery fully charged during the winter.
Ive had this sort of set up on a boat stored outside near a lake which gets 3 foot of ice during the winter and just leave the battery in the boat. Havnt had any problems for a few years of doing this.
Note also that if you run your outboard, you can also suppliment your battery charge. My 8 hp is supposed to put out 60 watts which I assume is about 5 amp. So every hour I run the outbourd, I would get an additional 5 amp hours. You would not want to charge the battery full time with 5 amps but likely for as much as a motor gets used (assuming your more likely to be sailing than motoring) your probably not at much risk for any damage to the batteries.