I have created a solar setup in my shed i have 2x.5w solar panels i am hoping to charge my 55ah car battery how long would it take to charge the battery and how many watts could i used a day
I don't think so, but if it did, it would take a very long time. You need enough wattage or amps to push the power in the battery and 3w may not be enough. You would be better off with a small 2v battery, maybe the type they use for emergency lights. I would use a sealed battery for this type of setup because car batteries are designed for heavy charging with alternators from 60 amps and up.
Quite a while. I am assuming you are using 2 volts as your buss power. The small panels were intended as a float charge for batteries to keep them from discharging over a period of time. 3 Watts means only /4 Amp. Normally when I do slow charging of batteries, I am using right around amp, and that takes about a week to bring up a battery that was discharged past 80 percent capacity. When you factor in losses from corrosion, battery self discharge, and loose connections, you will likely want to add more panels. using your 55Amp/hour battery, a amp charger running constant in a perfect world would take 55 hours. Real world, probably closer to 64 to 72 hours. That for simplicity is 5 Watts constant charge power. Now you are using /5 of that with your current setup. so 5 times longer, whichh puts you in the 300 hour range of real world, or 220 hours of perfect world. This time of year, you may have about 8 hours worth of charging light, which puts you at close to a month. Don't fret. If you are using it for lighting in a shed, Power LEDs and tethering some of the inexpensive LED lights to the 2 volt source will give you plenty of light for a very long time, the panels will help some, but you will likely need to put the batteries on a charger, or you can build a gas powered 2 volt generator easily enough. Charge it up only when needed.
To charge a 2V lead acid battery, you pretty much have to put almost 24V across it and it's only 50% efficient at charging so if your solar panel does put out 3W, you can expect 3/24/2 or /6th of an amp in usable charging. Therefore, from a flat battery, it would take 55*6 or 880 hours to charge the battery. If you assume about 6 hours of usable sunlight per day, that would be 47 days not taking into consideration the normal leakage that lead acid batteries have. It's quite likely that the leakage rate will be greater than the charging rate and the battery will never charge. You'll need a bigger solar panel.
