Solar advice: one big panel or 2 smaller panels?

[sparrowhawk1]

I have a friend that did exactly this. 30 volt panel cheap 20a Chinese mppt controller. The panel is rated at 8 amps and he normally gets over 16 amps( at 12 volts nominal) Peak. Needless to say he is very happy. Several benefits to the 30v panel are less sensitive to shading , it starts putting out amperage much sooner in the morning and later in the evening , it puts out a little bit on cloudy days, and most importantly it was much cheaper to buy one big panel than two small ones. And he can easily expand in the future by getting another controller and another panel at whatever voltage he wants.

[sparrowhawk1]

PS I have the multi-panel 18 volt( 12 volt nominal system) and to get that 16 amps it takes up more real estate. But I do have redundancy and I think if one panel out of 4 is completely shaded it would be better than the 30 volt with 1/4 shaded but I don't have any testing to prove it. I also bought them off Craigslist so I got a good deal. Otherwise it would cost a lot more.

[john61ct]

Originally Posted by sparrowhawk1

I think if one panel out of 4 is completely shaded it would be better than the 30 volt with 1/4 shaded

For sure, always, as long as they are in parallel not series.

[StuM]

Originally Posted by sparrowhawk1

I have a friend that did exactly this. 30 volt panel cheap 20a Chinese mppt controller. The panel is rated at 8 amps and he normally gets over 16 amps( at 12 volts nominal) Peak. Needless to say he is very happy.

If it is rated at 8 amps @ 30 Volts, that's 240 Watts. You should expect a peak of over 16 Amps at the start of bulk charging with any system of that size. Nothing to be overly happy about there.

[sparrowhawk1]

Originally Posted by StuM

If it is rated at 8 amps @ 30 Volts, that's 240 Watts. You should expect a peak of over 16 Amps at the start of bulk charging with any system of that size. Nothing to be overly happy about there.

Well actually most standard panels are rated at 17.5 volts so 240 would be just under 14 amps. But he was really happy because the price was much cheaper and it took up a lot less room than a standard 36 cell panel or a 72 cell panel which most large "18"volt panels are. They're basically two 36 cells in one frame. Actually after wrighting that I realize with an mppt controller you would probably get at least 16 amps for the same wattage. And one more benefit I forgot, you can use smaller wire. And it's getting to the point where the wire costs as much as the solar panel!

[Ding Duck]

My suggestion is to go for the big panel 265w/30V. Check with your MPPT Manuf manual, but was looking at a Victron MPPT and they don't actually start charging until solar input is Battery Volts +5V. This was for a MPPT75 & MPPT100 Blue Solar Charge controller. So I don't think it would be suitable for the 18V Panel (Using this controller). Irrespective, you may find you get a bit better output in low light conditions compared to the 18V panel
Otherwise I tend to agree with the redundancy argument, particularly if you likely to encounter hail.
Cheers

[skipgundlach]

Current panels are rated at hail in sizes and speeds you're unlikely to encounter.

That doesn't mean you can't break the glass - but you have to work pretty hard at it.

I was talking a couple of days ago to an installer; he told of guys standing panels up and hitting golf balls at them to no avail, unscientifically testing how difficult it was to break it...