Mono- or Multi-Crystalline? What say Ye?

[MarkJ]

Right-o I'm sure this has been asked before but I want condensed, good knowledge from you smart-bums


Should I buy Mono-Crystalline or Multi-Crystalline solar pannels?

Thanks for your kind thoughts


Mark

[GordMay]

I think you have to compare specific examples (products) of each technology.

Generally:

Single Crystal Silicon cells are more expensive, more efficient, and work better in hot weather & low light conditions.

Poly/Multi-Si cells are less expensive & less efficient.

Multicrystalline panels, while having lower efficiencies than single crystal panels, can nonetheless have the same wattage per square foot as some single crystal panels, because the cells can be rectangular, filling all of the available surface without the gaps left by round or octagonal cells.

[mesquaukee]

Gord May sums it up.
One point which may be important should be added about multicrystalline panels. When a small shadow say from rigging occludes part of the panel the output is less affected than the single crystal panels.

[MarkJ]

Thanks guys.





Mark

[GordMay]

Originally Posted by mesquaukee

Gord May sums it up.
One point which may be important should be added about multicrystalline panels. When a small shadow say from rigging occludes part of the panel the output is less affected than the single crystal panels.

Thanks. I hadn't heard that; thinking it was more a matter of individual cell connection strategies. Can you tell us (or direct us to) more?

[mesquaukee]

It is from an article I read more than 10-15 years ago. It was either in Cruising World, Sail, Practical Sailor or ?????.
It has something to do with how all the little bits in the panel are hooked together in a multicrystalline panel. Sorry I couldn't be more helpfull.

[GordMay]

Originally Posted by mesquaukee

... It has something to do with how all the little bits in the panel are hooked together in a multicrystalline panel. Sorry I couldn't be more helpfull.

Originally Posted by GordMay

Thanks. I hadn't heard that; thinking it was more a matter of individual cell connection strategies. Can you tell us (or direct us to) more?

Originally Posted by mesquaukee

... One point which may be important should be added about multicrystalline panels. When a small shadow say from rigging occludes part of the panel the output is less affected than the single crystal panels.

Ah - thought so.

[mesquaukee]

Okay it took a while. My brain is taking longer and longer accessing files.
Here it is why multicrystalline panels tolerate shadows from rigging better.
This is a simplified explanation.
Each cell in a panel produces 0.5 volts. To be able to overcome the resistance in connecting wire and create a potential difference to “force” current into a battery a series of 32-36 cells are strung together to give a 16-18 volt panel.
Single Crystal Panel
Shading one cell cause a greater voltage drop than 0.5 volts. The rest of the cells have to overcome the resistance in that “dead” cell. A further reduction in voltage. The voltage difference between the panel and the battery is what “drives” the charging process. The “3 volt” differential is now for;
- 1 shaded cell, 2 volt differential, 2/3 the charge rate.
-2 shaded cells, 1 volt differential, 1/3 the charge rate
-3 shaded cells, 0 volt differential, zero rate of charge
Multicrystalline Panel
There are numerous parallel series of cells. Anywhere from 10 to 50 or more parallel series of 32-36 cells. All the parallel series of 32-36 cells are interconnected. If the shadow of a rigging line crosses the panel the “dead” cells are bypassed by rerouting the current to the other cells in the parallel circuits. There is some loss in output.

[44'cruisingcat]

Geez, not another mono vs multi topic!

My understanding is that monocrystalline panels will produce more power per area, multi is more shade tolerant.

Which to get? If your panels are only rarely shaded, mono will give more output.

[MarkJ]

Originally Posted by 44'cruisingcat

Geez, not another mono vs multi topic!

It was 2 years ago mate!

Look at the posting dates

[Mark Johnson]

When I got my solar panels, some years back, (11 and 14 years ago), I went with mono crystalline, because of available deck space. The top of the line mono panels, were more expensive, but WAY smaller for the same wattage, than ANY multi crystalline panels! I have not researched them lately, however. Look up the specs and see if it is still true...

Regarding shade tolerance... I have used only mono crystalline panels on my boats since the 70s, so have no basis for comparison, but this is how mine handle it... A VERY dark shadow from something "close" like the boom, really knocks down their performance. This is why I spread my panels about the boat, and added Schottky, one way, BLOCKING diodes in the + wires. (Not to be confused with BYPASS diodes in the panels) "Bypass" diodes are to prevent backflow issues within the panel, where as my "blocking" diodes prevent backflow between panels. I go under the assumption that one panel will be totally shaded most of the time, so a slight V loss from the diodes is a better option, in my application, than not having them. IMO...

Regarding cloudy days... we sized our array so that they produce TWICE our daily need on a good sunny day. This way they STILL bring our batteries all the way back up on really cloudy days. It just takes until sundown, rather than by 10:00 AM! ONLY on the very darkest of threateningly overcast days, do we need to crank the engine. (about 10 times per year)

On white/cloudy, overcast, but "bright" days, that still require sun glasses, we get about the same performance as clear, sunny days!

Far away shadows from rigging have little or no effect.

Mark

[James S]

Originally Posted by MarkJ

It was 2 years ago mate!

Look at the posting dates

So what did you get ...and are you happy with it/them?

[MarkJ]

Originally Posted by James S

So what did you get ...and are you happy with it/them?

I got Mono-Crystaline.
I still havent got them on top of davits/arch so there is still some significvant shading by the bimiini.

2 x 120 watts gives me an max of about 13 amps whent he battery is low and the moring sun hits the panels at say, 10.30am. (13 amps is not often. Average would be 9 amps)

Normally my battery bank, 330 amp hours is full - or 90% full and the light flashing by 11am. But I don't think its 100% before 2 or 3pm.

I would like a bigger battery bank but couldnt fit larger batteries in the well 440 was what I was aiming for.

Like Mark Johnson said its good to have more panels than you need. yesterday was cloudy with thick cloud and I was a bit naughty charging up a few inverter things. Today has significant thick cloud because of a tropical wave so I started the engine for 30 minutes at 9am.

Currently getting 6 amps under cloud but thin sun casting a shaddow, with 10% shading.

I think when one is dealing with it everyday we get to know it so well that very few mistakes are made.

Get the things that need to be charged doing so in mid afternoon as the batts are full and theres extra solar power going to waste.

And if you watch TV&DV Player via an inverter at night whilst running the freezer and computer then you better have one hell of a set up!






Mark