Ok - I wrote this big long post and got carried away - If you just want an answer I would say no more than 24v panel.

If you want to know why, read on...

(BTW - I am not a solar expert - I have just read and absorbed what I have - there may be some factual nuances incorrect)

I have been hesitant to jump in because solar power is "science" and the scientists get picky over the details. But most explanations around are beyond us mortals and the scientists get involved and confuse us even more...

but I will try to make a simple explanation -

First you must understand the Volts X Amps = Watts

So Watts / Volts = amps

These definitions are not science but are for clarity

Volts - consider this as Pressure - the ability of electricity to "push" electrons

Amps = How many (volume?) of electrons I am pushing

Watts - Because it is a formula consider this as "power"

Your

battery has about 12.2 volts worth of cells. To push electrons into your

battery you need greater than 12.2 volts. You can't just raise voltage to 1,000v and charge your battery in 5 minutes - The battery can only accept electrons so fast or it heats up too much further increasing resistance (resistance is bad) and further deteriorating acceptance. (oh and it will blow up)

Amps are sort of like volume - You'd like to have plenty of volume available so that the battery will accept them as fast as it can.

Generally in bulk phase ~14.8 volts is good and as many amps as your system can produce. The battery basically will take only what it can.

(I won't talk about the final stages of

charging (float) except to say that it's like filling a pitcher with

water. As you get close to the rim you slow down the tap so you can fill precisely to the rim without spilling)

So now onto

solar panels. Each cell produces a voltage and an amperage and many, many cells are wired together.

What happens when we wire them together. If we wire in series (plus to minus) voltage is doubled and amps is the same. If we wire in parallel (plus to plus) voltage is the same and amps are doubled.

Think about watts = power. If we double the cells we should double the power. So 12 volt cell and 1 amp capacity

1 cell = 12 X 1 = 12w

2 in series = 24 X 1 = 24w

2 in parallel = 12 X 2 = 24w

So now a trick. Solar cells do not produce power when shaded. So a 12 v panel actually is wired so that under full sun they produce 17 volts typically. Then when some of the cells are shaded the panel is still putting out 12v.

So the smart guys figured it out. If I built circuits that always kept the output voltage at 14.8 when the panel "is producing" 17v I could lower the voltage and get more amps!

This first link shows a couple of graphs that describe another bit and that is the power output is not linear with sunlight - there is a "peak efficiency zone" fancy controllers take advantage of this to find the peak efficiency voltage and keep the panel there.

Solutions - Techniques to Maximize Solar Panel Power Output
So Is more volts better? The downside of more volts is high voltage (big "pressure" makes big sparks if shorted and we humans aren't super tolerant of high voltages). counter intuitively high voltages can "push" amps down smaller wires - that's why home electricity is routed around at 440+ and stepped down near your house.

Likely your choices will be 12/24/48v

panels.

Remember - Power is a function of the number of cells which equates to area of the total panel so there is no magic. You can't get a higher voltage panel of the same size as a lower one and magically get more watts. You get lower amps with higher volts.

But the advantage is if the panel gets shaded the likelihood of partial shading won't drop the panel voltage below 14.8v (needed to push into the battery).

You charge controller is rated at

360w @ 12 volts -and-

30 amps

This makes sense

360w /12v = 30a for 12 volt

panels
So what if you opt for 24v = Remember there is no free lunch for the same dimension panel half of the cells are wired to the other half in series - there is only so much power (volts X amps) per area square.

So the same dimension panel is likely

360 /24 = 15a

You are in the 75w range for panels

75 / 12 = 6 amps

75 /24 = 3 amps

Remember you want 14.8 volts and max amps. The peak voltages of these panels is likely to be 17 and probably 34.

But your fancy controller will reduce the voltage to 14.8 all the time and maximize the amps. Your 24v panel will be outputting 14.8v (though the charge controller) and putting out around 5 amps - BTW your 12 v panel is also operating at 14.8v and around 5 amps (higher voltage = lower amps)

I would not go higher than 24v - That's just my paradigm. The wire between the panel and the controller will have 34v and that's enough for me.

Also if you think the panel will get 50% shaded than 24v panel should still give you (marginally) a

charging voltage (although 1/2 the amps are gone) the 12 volt panel will be outputting 6 volts - not enough to "push" the electrons.

To be honest - If I had a giant battery bank and was pushing towards 30 amps of solar (360w+) I would go for 24v (maybe)

For 75w

single panel I probably would go 12v. However that's probably just my paradigm. The

MPPT controller probably loves 24v panels.

This next link has articles about maximizing solar output - basically says get an MPPT controller - and dives into some science.

Sorry for the long lecture and to the scientists - be gentle...

http://www.sunforceproducts.com/Supp...lectricity.pdf