Help connecting solar cells to be 12 V

Question

I just purchased a lot of 40 solar cells each with 1.8 W, 0.5 V, and 3.6 A. This gives a total of 72 W. Ideally, I would like to connect the cells in a manner to yield 12 V. I know I can connect two sets of 20 cells (series) in parallel for 10 V and 7.2 A, or all 40 in series for 20 V, 3.6 A. I'm fairly certain there is no possible way to yield 12 V with factors of 40. I know I can use 24 cells in series to get 12 V, but then I won't be able to use the 16 other solar cells. I considered a DC-DC "buck" converter to convert from 20 V to 12 V, but I couldn't find any with a high enough current output.

I think I may have a way to connect the cells to get 12 V, but I'm not sure it would work. This circuit is going beyond what we are currently (pun intended) learning in my high school physics class. So would this work: One group of 23 cells in series. This gives a voltage of 11.5, an amperage of 3.6, and a power output of 41.4 Watts. Another group of 17 cells in parallel, 0.5 V, 61.2 A, 30.6 W. Then both groups would be connected in series. From what I understand (which could be completely wrong), the voltages would add to 12 V and the power would be 72 Watts. What I don't understand is what happens to the amps. I can calculate from P=VA that the amperage would be 6. I'm just confused as to how 61.2 A and 3.6 A could combine somehow and make 6 A (which makes me think that this might not work).

So does anyone think that this might work? If it won't, can I please be pointed in the right direction?

Answer 1

I'm guessing that you got those panels as a kit or a pack all together. They intended for you to use 36 of them in series for a "12" volt panel and 4 extra for the oops I broke it or screwed up as they are very fragile to work with

Now why 36 for a-12 volt panel? Because that's what almost everyone does! It will give you 18 volts OPEN voltage, but a little less when in an actual circuit. So why so high for a 12 volt battery? Well you will lose some voltage through line loss, about .7 to 1 volt for the diode to prevent night time reversal of the batteries back into the panel. Then There is the fact that most 12 volt batteries attached to solar panels are actually closer to 15 volts when fully charged (lead acid) (actually 14.4 volts, but ocassionanally a charge controller might do an equalizer charge that can be up to 15 volts). So the fact is you need the higher voltage.

So depends on your need, but your best bet is to use all panels in series!

Good luck

Answer 2

It doesn't work that way.

If you connect two groups in series, the output current you get is the lowest of the current from either group. Thus you'd get 12 V (11.5 + 0.5), but only 3.6 A.

Secondly, solar cells don't give maximum output all the time -- only under ideal conditions. Likely most of the time you'll get much less output than you expect. W

The best approach is to connect equal numbers in series (or in parallel) to generate a 'reasonable' voltage, and then use a DC/DC converter to convert that (varying) voltage to the one (12 V ?) that you want. Perhaps 4 paralleled groups of 10 in series might be a good starting point.