Solar advice: one big panel or 2 smaller panels?

[Emouchet]

I would go with 2 panels, mounted in parallel.
Chances are shading will only go to 1 panel at a time, allowing the other one to continue working full speed.
18v or 30v output does not matter since you will be using an MPPT controller.

[newhaul]

A good coat of wax makes it easier to keep clean and helps the rain do that to.

[kmacdonald]

Two panels and two charge controllers. Redundancy.

[Philip St1]

I went with 16-25 watt panels myself. If one is shaded or broken (I will be walking on the big roof it is mounted in), I lose only a little. More money up front, but also easier to replace when the time comes.

[Copacabana]

Originally Posted by Emouchet

I would go with 2 panels, mounted in parallel.
Chances are shading will only go to 1 panel at a time, allowing the other one to continue working full speed.
18v or 30v output does not matter since you will be using an MPPT controller.

Actually, they way the two would be positioned wouldn't keep one out of the shade of the backstay.

I understand the benefit of redundancy (2 panels and 2 controllers), but I think I'm going to go with simplicity - one panel, one controller, simpler wiring. I still have two 45w panels on their own controller for redundancy.

[john61ct]

Originally Posted by skipgundlach

Most modern panels have diodes which will split the input stream. Shading a cell only affects a portion of the entire panel

AFAIK any shading at all, even a schmear of bird poop, has a drastic effect on total panel output, and on the whole string of panels if wired in series.

Diodes or not, they only help a bit.

​On this topic, I am looking for US retail suppliers of (or willing to ship in) gear using the new embedded "MPPT on each cell string" ICs from Maxim.

Jinko "Eagle MX" is one line.

Others mentioned on Maxim's site are Trinapeak, and "ET COM"?

[IMACSS]

Hi,
Couple of good points for me so thanks.

I like the idea of 2 panels due to:
1. The redundancy issue - would hate to be stuck without ANY solar power input
2. The ability to compare output individually - probably only find the need when something goes wrong and I suspect a problem - somewhere.
3. Handling / protection etc etc

Of course the above may be a trade-off against the efficiency so has to be carefully considered.

I would also like to suggest (perhaps because I am not understanding the Voltage figures quoted) that consideration be given to the size of the MPPT controller to ensure that it is not working too close to its capacity.

Again thanks for the discussion topic as I am learning all of the time here.
Imac

[john61ct]

At least with the Victron BlueSolar MPPTs, going over on the current side is no problem.

For example, with the 75/10 model (V/A), you could feed it with 3 panels @4.5 open-current Amps.

In the rare event they actually put out close to their rated output, the peak current above 10A will be wasted.

But the Average amps going to your bank in more normal conditions will be higher.

However, don't exceed the rated Voltage, so three 26 Voc panels in series would risk damaging the controller. Three 19V would be fine.

[emcmia]

I would concur with the higher voltage/larger panel approach.
You might check out Sun Electronics in Miami Lakes (Miami area) - sunelect.com. I have had very good experience with them and they have many domestic US and a couple international distribution centers for their very low cost PV related products. (I have no relationship other than as a customer).

[john61ct]

That would be https://sunelec.com/

[smac999]

20a controller seems on the small side for 280w. Might just make it. But could be throwing power away on the sunny days

Also keep in mind that 20a rating is room temp. And probably drops as it gets warmer.

[Pelagic]

Are failures in quality made panels common?

No moving parts, waterproof connectors, anodized frames, I think they must have a high reliability factor.

[Dadrock33]

BEWARE the flexing!!! Recommend the 2 panels, biminis aren't sturdy enough to stabilize the one panel and that flex will break'em down . . . . add to that the shading and you're putting all your eggs in one basket . . just my $0.02

[Copacabana]

Originally Posted by Dadrock33

BEWARE the flexing!!! Recommend the 2 panels, biminis aren't sturdy enough to stabilize the one panel and that flex will break'em down . . . . add to that the shading and you're putting all your eggs in one basket . . just my $0.02

It's going over the bimini, but mounted on an SS frame. No flexing.

[newhaul]

Originally Posted by Dadrock33

BEWARE the flexing!!! Recommend the 2 panels, biminis aren't sturdy enough to stabilize the one panel and that flex will break'em down . . . . add to that the shading and you're putting all your eggs in one basket . . just my $0.02

We are talking about rigid panels not flex panels here . They don't flex. (Rigid are better imo just look at the warranty difference. Same manufacturers. Usually 20 year on rigid but 5 year on flex.)