red31 wrote:
NinerBikes wrote:
Calculate your daily amp usage first, then buy panels. 1 to 1.5 watts per amp you use per day.
I don't understand this math.
If I used 40 ah/day and bought a 60 watt panel I'd be loosing ever day unless I was in S AZ in June!
I stand corrected... 1 to 1.5 watts per amp/hr capacity of the battery.
If you use 40 amp/hrs a day, you will most likely need to replace 40amp hours, in a 6 to 8 hour solar recharge period. You therefore need about 7 amps per hour charge rate= 42 amp hours in 6 hours, plus losses experienced during the charge period in the form of parasitic losses.
To get 7 amp hours rate, you'll probably need about 130 watt poly panel, or a 140 or 150 watt mono cell panel. Throw in cloudy days, and not a full 7 hours without shade or clouds, and your margin of error eats into the charging. This is why some folks just hit the generator first thing in the morning with a good dry camping charge controller like an Iota, Progressive Dynamics or Boondocker brand charge controller. The generator and low charge level of battery is most efficient, for the amount of gas burned in the generator over a short time period of 1 to 2 hours, then they let the solar charger do the part it does best, topping things off at lower amp hour ratings, doing a finish charge.
Some folks, like RJfishing, start with 190 or 200 watts of panel, fabricate a bracket they can mount 2 panels on at 100 watts each, and aim it at the sun 2 or 3 or 4 x a day, which really maximizes the harvest or yield of energy from the sun by aiming directly at the sun for the most efficiency.
