# What size solar panel needed?

Discussion in 'General Electronics Chat' started by mrel, Oct 23, 2012.

1. ### mrel Thread Starter Active Member

Jan 20, 2009
97
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Hello
Have 6 volt 1.3 ah gel cell .
what is smallest amp size solar panel can use to full charge this battery?
mrel

2. ### Dodgydave Distinguished Member

Jun 22, 2012
4,999
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6V X 1.3 Ah= 7.8 Watt panel, so a 6V 10W would do.

3. ### Bernard AAC Fanatic!

Aug 7, 2008
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Might want to boost V to about 10 OC, 7.5 V / .7 @ about 100 mA. SC. This assumes a light or no load and no time limit stated.

4. ### Audioguru New Member

Dec 20, 2007
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Ther output of a solar panel is rated on when it is outdoors pointing at (or following) the sun at noon on a sunny day in summer.

In the morning and in the afternoon and evening the output is much less.
Guess what happens to the output on a cloudy day or at night?
Even a window reduces its output.

5. ### ErnieM AAC Fanatic!

Apr 24, 2011
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1,606
You want to put in as much (or more really due to charge efficiency) as you take out. Is this a daily load? What percentage of capacity are you using each charge/discharge cycle? How long is the sun available?

AFAIK a gel cell is based on the lead-acid type. Even "deep discharge" types should not be drained completely each cycle, if you want them to live. 50% is max, 25% is more reasonable.

So, assuming your daily load is 25% of capacity, your charge efficiency is 80%, and you have 5 hours of daylight to charge you'll need:

(1.3 AH ) * 25% / 80% / 5 hours = 0.8 Amps

Again, derate the current a cell produces by 80% so that brings us back to a 1 amp output.

I hope I've spurred some thoughts about how your system is being specified.

6. ### mrel Thread Starter Active Member

Jan 20, 2009
97
1
So are you saying to full charge this battery 6 Volts @ 1.3 ah battery need .800ma solar panal ,what is solar panal voltage need to full charge ths battery.
mrel

7. ### mrel Thread Starter Active Member

Jan 20, 2009
97
1
So are you saying to full charge this 6 volt 1.3 AH battery is to get a solar panel that is 7.5 volts at 100 ma solar panel is that right.
mrel

8. ### THE_RB AAC Fanatic!

Feb 11, 2008
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People have give you good numbers and calculations but YOU need to give more info, mainly; how much current your devices uses up and how fast you need to charge the battery!

You can charge a 1.3Ah battery at 60mA, but it will take a few days and won't be a perfect "full" charge. And that is if nothing else is draining power (like your device). Personally for a 1.3Ah battery and low current drain device I would use a panel of about 300mA to 400mA. But then, I live somewhere very sunny.

9. ### Bernard AAC Fanatic!

Aug 7, 2008
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No, I said 10 V, OC, which will drop under load. Or a panel that will hold 7.5V under a load of 100 mA; this is bare bones- re read THE_RB's post.

10. ### ErnieM AAC Fanatic!

Apr 24, 2011
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Nope, use the 1 amp number. The reason being the current is typically spec'd with an Irradiance 1000 W/m2, but 800 W/m2 is something typically expected. I omitted this point.