Solar panels will keep your batteries happy and even run appliances, like a fridge, when on a swing mooring or away from a marina. They need to be appropriately sized,located to catch the sun,not overshadowed, with good multi stage controllers, adjustable for battery type, so they won`t cook the batteries and will record amps generated. Controllers have direct connections for an appliance, giving supply when the batteries are full and not when the batteries get low.Controllers have a one way diode to prevent reverse draining of batteries at night.
For safety we put a fuse in the + line just before the panel lead goes onto the battery. We have 90watts (giving 7amps per hour in theory but not in practice) of panel to each of our (2) 200 amp hour batteries, and a 25 w panel (5-10 watts would have done) for the genset 150amp battery.
Some boats use a relay to cut panel charge when the engine alternator is generating, I didn`t, it doesn`t seem to be a problem.
Have an air gap under the panels to dissipate heat build up, don`t mount them flat on the deck.Remember if they are in the sun they are generating,you can put them to sleep by covering the panel over if you need to work on the wiring.
Success is sun dependant. Australia gets plenty; in SF recently I suggested panels to a friend, he felt there wasn`t enough sun, I think there is. Charged batteries last longer and perform better. Panels,mostly from China,are getting cheaper; our only manufacturer closed (like Solyndra). Select panels and regulators carefully, research and plan fitting,using the internet. Wet type batteries need regular top up,especially if your regulator has an equilization phase.
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-- Edited by BruceK on Thursday 5th of January 2012 06:39:36 PM