75 Watt Solar Panel
what is the volts of 75watts Solar Panel?
am having a 75 watts siemens solar panel and is giving me 12.89volts during bright light, i wanted to know can this be used to charge 100Am/hr battery?
mmmm 12.89 volts is a bit low for charging a standard lead-acid battery (and you want to use a deep-cycle/rv battery for this, not just a plain car battery); ideally, you want 13.5-14.0 volts. this slight overage is needed to break the internal resistance of the battery in order to get it fully charged. personally, i’d take it to a car store that offers testing, your meter may be a little off, and most reputable shops calibrate theirs.
not being fully charged is death at a young age for lead-acid batteries. a car battery is made with very thin plates, which warp easy when they get hot, like from being drained fast for a long time or being charged too fast. an rv or deepcycle battery has thicker plates that can stand the drains better for long periods.
however, comma, you do not want to let these things get drained and stay that way. they stop working fast if you do. if it isn’t fully topped off, have it be charging.
a 100 Amp-hour battery can give you 1 amp for 100 hours, or 100 amps for 1 hour. they work their best when they are delivering 10% of max, in this case 10 amps for 10 hours. what’s that mean in watts?
P power (in watts)
—————-
I * E ( I = current, in amps; E = electromotive force, in volts)
cover the one you are want with your thumb, you now have the formula to figure it out. in this case, we’re looking for watts, I times E, 10 amps * 120 volts = 1,200 watts. you could hook up an inverter and run a toaster with that; I have. coffeepots and drills, too. this is about the same power you will get from a 15 amp receptacle in your house!
using it is all fine and dandy, yeah, but let’s see how long it would take for your panel to recharge that thing:
if you use 10 amps from the battery for 1 hour, you’ve used 1200 watt-hours of electricity, or 1.2 kilowatts. 1200 divided by 75 is 16….. hours of full sunlight needed to refill it!. wait! i say! remember what i said earlier about a battery having internal resistance? actually, we need to double that…
and keep in mind, too, you are only going to get peak sunlight 4 hours a day most places. 32 / 4 = 8 days of sunlight to replace the juice from running a blow dryer for 45 minutes. or, you could wire 7 more panels in series and get it done in 1 day. getting a clue why whole-house Solar Systems are so ’spensive? 
mind, there are many other things you could do to charge the battery than just solar; a small wind turbine if you are in a good location is wonderful! wind and solar are two great tastes that go great together
I have made a waterwheel that drove a standard car alternator. used 12vDC for the lights and an inverter for everything else. on days where i used so much even that wouldn’t get it back fast enough, i actually hooked my car to the battery bank with jumper cables.
there’s a lot of good books on the subject available, one of my favorites is “be your own power company” by jim cullen. there’s a lot on the amazon link below.
hope i didn’t make things more unclear for you!