12v or 24v

[jp.beauchemin71]

Just wondering if there is any difference between wiring 2 24v (100w) panels in parallel or wiring 2 12v (100w) in series. I need 24v in the end.

[Sailmonkey]

Yes there is, the series vs parallel part.

You've already got your answer.

[Paul Elliott]

Panels in parallel are more tolerant of shading (which can be a problem on a sailboat). Panels in series may let you use lighter gauge wire, but if one panel gets shaded the power from the other panel gets "blocked" and you get very little output. If both panels are clear of shading then series is often the better choice.

If you connect the panels in parallel, you will need a solar regulator/controller that will step up the voltage to your required 24V. Step-up controllers are less common, but they do exist. Genasun makes some.

[newhaul]

Originally Posted by jp.beauchemin71

Just wondering if there is any difference between wiring 2 24v (100w) panels in parallel or wiring 2 12v (100w) in series. I need 24v in the end.

Yes with what you posted here there is a big diference.
With 2 100 watt 12 volt panels in series you have 100 watts at 24 volts.
wiring 2 24volt 100 watt panels in parallel you end up with 200watts at 24 volts.

[a64pilot]

But a Watt, is a Watt regardless of voltage isn't it? So either way it's 200 W at 24V?

[jp.beauchemin71]

The weird thing is both 12v and 24v panels are the same physical size. Both rated at 100w just one model is 12v and the other is 24v

[evm1024]

Originally Posted by newhaul

Yes with what you posted here there is a big diference.
With 2 100 watt 12 volt panels in series you have 100 watts at 24 volts.
wiring 2 24volt 100 watt panels in parallel you end up with 200watts at 24 volts.

100 watts at 12 volts is 8.33 amps

100 watts at 24 volts is 4.16 amps

qty 2 100 watt panels give 200 watts regardless of voltage.

2, 100 w 12 volt panels:

- in series gives 24 volts at 8.33 amps for (24 * 8.33) 200 watts
- in parallel gives 12 volts at 16.66 amps for (12 * 16.66) 200 watts

2, 100 w 24 volt panels:

- in series gives 48 volts at 4.16 amps for (48 * 4.16) 200 watts
- in parallel gives 24 volts at 8.33 amps for (24 * 8.33) 200 watts

[evm1024]

Originally Posted by jp.beauchemin71

The weird thing is both 12v and 24v panels are the same physical size. Both rated at 100w just one model is 12v and the other is 24v

Nothing weird about it. The panel is composed of a number of cells that are arranged to give the speced voltage.

Remember that watts = voltage * current and that:

in series, voltage adds and current stays the same
in parallel, voltage stays the same and current adds.

This is true regardless of if we are talking solar panels, solar cells, battery banks, battery cells.


For solar panels power (in watts) is a function of how big the panel is. (Of course the cell technology, light spectrum, etc all have their effects but we can ignore that for the moment.)

The voltage of the panel is purely a function of the way the cells are connected.

[noelex 77]

Yes, there is a very important difference.

Due to some silly convention/nomenclature, panels rated as 24v typically have 60 cells. 12v panels typically have 36 cells.

The astute members of Cruisers Forum skilled in higher maths will have noticed that 60/2 does not equal 36 .

The result of this silly convention is that 12v panels have a voltage suitable for charging 12v batteries, but 24v 60 cell panels do not have enough voltage to ideally charge 24v batteries. This misunderstanding can cause an expensive mismatch.

So two 12v panels in series are OK for a 24v house bank, but one 24v pannel, or two 24v in parallel are not a great option. Two 24v panels in series are OK providing the solar controller can cope with the higher levels and input voltage.

[evm1024]

Yes, of course the complicating factors are that 12 v panels are not really 12 volts....

I came across this photo that shows a single panel and then 2 panels in series or parallel. Please ignore the power(w) legend as that it does not apply to the curves.

The text points out that the actual power of the 2 panels is "still" only the product of voltage times current.

[jp.beauchemin71]

Thanks everyone for the great info. Think i'll go with 2 12v panels in series. It seems to be the better way to go. plus as a bonus its a tiny bit cheaper

[a64pilot]

I don't think you will get as much useable power with panels in series