Solar charging specs
I've used solar panels since 1997. Currently have 331 watts of panels installed going to six Optima batteries in boat and travel trailer. Here are some things to know. Lead acid batteries wet cell open or sealed or AGM or require a minimum of 14.4 volts and 10 amps to fully recharge properly in a reasonable length of time. Two amps will work if steady for 48 hours or more in a multistage charger that tapers and adjusts the charge and voltage as necessary per time. Best done with shore power 3 or 4 stage charger or alterator with regulator rated for more than 10 amps running coninuously. Anything less than 10 amps or done in starts and stops like motor use will refresh, or replace some capacity but not fully recharge and will shorten your battery's life by reducing the number of cycles with which it can be recharged due to lead sulphate buildup on the plates. If you only want to keep a fully charged battery at or near maximum charge, then the total of solar sources plus engine operations should be more than your actual draw down. Your energy budget should include engine start, navigation lights, cabin lights, spotlights. Be especially aware of many things that draw phantom current because although turned off, they are still on to retain memory or have instant on features. Cell phone recharging, VHF, weather and FM radios, TVs, laptops,ipods, etc. If your solar charging panel, in amps, is more than 1% of your battery's capacity in amps, then you need a solar regulator to avoid overheating, overcharging the battery which also shortens battery life and boils off fluid. Solar panels are best wired directly to the battery terminals with a fuse in the positive lead. Do not lead the panel to a switch that can be turned off. The impedance of the switch reduces your throughput and leads to a situation where the batter is not being charged if the switch off is forgotten or overlooked. In figuring the effectiveness of your charging system, only figure in 5 hours per day of solar panel maximum output due to sun angle through the atmosphere and angle of incidence reducing the output of the panel.Keeping the surface of the panel clean is important. Face it toward the sun if at all possible. Hazy or overcast, or heavy pollution days wil reduce the effectiveness of the panels. Maximum rated output is seldom achieved during the high heat of summer or the extreme cold of winter as temperature affects the charging capacity of the solar panels. Some panels are still sold that have only a 10 or 11% efficiency. The current best have efficiencies of 15% or better. My first panel was a Unisolar flexible 11 watt panel for the boat which stil functions well for it's intended purpose of keeping a battery charged while the battery is not being used,that has already been fully charged with a 3 stage AC charger. For serious use of active systems I use Kyocera multicrystalline rigid panels because they are 15% efficient, guaranteed for 25 years, and can be found for less cost than others that are not guaranteed for as long and are less efficient. High cost does not mean high quality, but may only reflect local demand and supply or seller's greed. A decent price currently for a efficient solar panel is between $5.15 and $5.50 per watt. Hope this helps.
