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# I am building three 60watt solar panels. How many deep-cycle batteries do I need to get the most out of the panels? Answered

I am building three 60watt solar panels. How many deep-cycle batteries do I need to get the most out of the panels?

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Also, be cautious around terms like "Maximum current" or "short-circuit current" and "open-circuit voltage" or "maximum voltage" as these terms cannot be used to determine the power output.

Think of it like a water wheel: If you load it down sooo much that the wheel stops turning and all you have is torque, then no work is done. Just tention on everything. Likewise if you do not load it down at all, and the wheel spins freely, no torque or tension is created and no power is harnessed. Solar panels are the same way, there is a "sweetspot" the manufacturer generally specifies to get the rated 60W of power extracted. That is another reason why you should use a special charging circuit, and have enough batteries that can take at least a day to charge.

Thanks for the quick reply! I will probably be running either lights, computer, or whatever I can squeeze out of it. I realize this is a big difference in voltage but my thinking was this.. How many 60 watt panels can you have without damaging the battery and how many batteries could you use with this setup without charging too slowly? As you can tell I'm pretty new at this lol. Perhaps a little more planning on my part is needed.

You should avoid hooking batteries directly to the output of the panel, too much sun and fully charge batteries will result in over charging, and when it is darker or the panels are facing away from the sun or during night, the batteries will actually discharge back into the cells! A charging circuit will eliminate so many problems.

How do you plan on using the power? Are you powering lights just after sunset until morning? In that case you need to make sure your panels can generate enough energy in the day to power some amount of lights over the night, and that about of energy you will need to calculate how many batteries it takes to store that.

Well, the short answer is "depends."
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It depends on if the batteries are new or used, how much use they will see, how big they are, and if they are standard/flooded, gelled or AMG.
I fairly complete discussion of the different battery availability can be found at, http://www.windsun.com/Batteries/Battery_FAQ.htm
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I've never bothered to do any math for it (just use what I have around), but a 40watt 12V panel was more then enough to maintain charge, for a used Group27 battery in summer, but not enough in winter (in Minneapolis).
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Just make sure you have a charge controller and you won't need to worry about over-charging your batteries.

most solar panels are 12V I will asume the battery will be 12V. 60W per panel seem excessive most are 20 watts at best.. So 60 w times 3 180 watts 180/ 12 euals the amps 15 amps. One battery should be more than enough. most batteries are in range of 80-100 amp hours.

Each panel will be made up of 36 .5 volt cells, which makes it 18 volts. The web site I am getting the build off of is solartechtown.com. He said it was a 60 watt panel, so I have been going off of that. I ended up finding a good deal on cells and decided to make 3 panels instead of 1. My original intention was to use this as a back up when the power goes out but I would also like to use it for whatever I can until that happens. If you have any suggestions on what this type of setup might be good for I will surely take your advice. I would also like to say that I really appreciate you taking the time to write me.