Originally Posted by roland stockham
Hi all. Need advice on size of solar panels
. I am leaving the boat
on hard standing for 6-9months and there is no electric
available. In the Carribean so lots of sun. I don't have anywhere to put large panels
so a full setup is out.
What would be the right size panel to keep 700Ah of lead acids up. No loads running but how much extra would you reckon the run the bilge
pumps on a 35ft?
I have a little 5watt panel but that will only run a radio
, gives about 150ma. I think I need 2-3a @13.4v, that's about what the charger
runs at when everything is charged which is 25-40W. But, given that the 5W panel actually on produces about 2W I am a bit stuck on sizing! Don't want to overdo it and cook the batteries
When you say "lead acid", do you mean flooded (as opposed to AGM
Are you talking about panels connected directly to the battery
, without a controller/regulator in between?
If so, ask your battery
manufacturer. The panel will need to offset the self discharge, which is significant for flooded batteries and depends on the composition of the plates (antimony vs calcium). I estimate you will need in the order of one amp times 12 hours a day just to offset self discharge.
You can make your own estimate by first charging
the batteries to 100% (ie when accepted amps at manufacturer-specified absorption voltage drop to manufacturer specified value, say 1or 2% of 700 = 7 to 14 amps. Then use a shorepower charger to keep the batteries at float voltage and measure the amps going in to the batteries. Multiply those amps by 13 or so and get the rating in W of the panel you want.
All that said, given that these days you can get a proper Victron solar
controller for US$105, there is no need to walk the fine line between undercharging and overcharging the batteries by not having a controller.