Mono vs Poly Crystalline Panels

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CATraveler
CATraveler Solar Expert Posts: 98 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
As a future solar user what type of panels would you recommend? My application is mobile (RV) and would consist of 2-3 200W+ panels with MPPT controller. For my application the panels would be mounted flat (5 degrees). Also they will be setup for tilting but that is just for the purpose of cleaning under them. Is flat mounting is a consideration for panel selection?

I thought that the polycrystalline were the current rage do to decreased cost. However I've found some good prices on monocystalline panels.

Here's one article I found on mono panels. http://www.solar-facts-and-advice.com/monocrystalline.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Mono vs Poly Crystalline Panels

    Welcome to the forum.

    In a way you've answered your own question: "However I've found some good prices on monocystalline panels."

    Price per Watt is a big factor in the choice, as there is not a huge difference in efficiency between the two (despite what some people will tell you). This is not the same as crystaline vs. amorphous where it's about a 2X difference.

    But there are other things that must be considered when buying panels, such as do they meet the needs for power, Voltage, and current? If you are using a 12 Volt system like most RV's and you buy big monocrystaline panels that operate at 30 Vmp then you have to buy a more expensive MPPT controller or you lose the power available from the higher operating Voltage. Since an MPPT controller costs more ... up go the total system costs.

    My advice is to not get hung up on the poly vs. mono debate and pick the panels that work for your system needs and budget.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Mono vs Poly Crystalline Panels

    in addition to what coot said, that you should consider allowing the tilting of the pvs to be better aimed at the sun when you are stationary as flat pvs don't always cut it for power collection and can accumulate much dirt and debris further cutting down power production. of course you could also elect to remote mount some pvs so the rv is in the shade while the pvs stay in the sun and can make aiming the pvs easier than going onto the rv roof to make adjustments. unfortunately that also makes theft of the pvs much easier too and in both cases you don't want to just up and leave the site without taking care of the pvs for moving on down the road.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Mono vs Poly Crystalline Panels

    I wonder if anyone has ever attached some of those flexible panels to their RV side awning? It would be interesting to see how many "rolls" they could take before damage occurs.
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #5
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    Re: Mono vs Poly Crystalline Panels

    12V, 440AH AGM. My usage is somewhat vague at this point. I have just installed a Trimetric battery monitor so that I can get a handle on that aspect starting in June, but I have documented the draw of every 12V device. The lights are a total disaster in terms of any conservation and I'll consider LED, etc in the future.

    I have researched 12V panels but the sweet spot is the 200W+ panels in terms of $/watt. So less panel cost and more controller cost but 12V is not off of the table. Another consideration is panel size vs roof space. I can with some equipment changes get 3 of the larger panels on the roof. There will be some early morning/late evening shadows and it is what it is. I'm not really interested in mouting the panels 12" above the roof to avoid RV shadows and it's kinda hard to get them above the trees. :D

    I suspect 2 panels might be adequate, but a third should tip the balance considering flat mounting and the left hand coast, not to mention my daughter is in Redmond, WA.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Mono vs Poly Crystalline Panels

    Quick calculation and I'd say you're right: you need at least 400 Watts and would be better with 600+. The Kyocera 235's are really cheap per Watt just now, but you would need that MPPT controller and they are a bit difficult to manage & mount due to size. With RV's, that is a bigger factor than just about anything else. I often say "put as many panels on the roof as you can fit" for just that reason. :D
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #7
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    Re: Mono vs Poly Crystalline Panels
    Cariboocoot wrote: »
    I wonder if anyone has ever attached some of those flexible panels to their RV side awning? It would be interesting to see how many "rolls" they could take before damage occurs.
    I know someone that would like to invent a way to do that. It would use the awning as extra surface for the panels which would have to roll up independently. Awnings can't always be out due to site limitations (trees etc) and wind.

    I suggested to tow a 12' high trailer for the car, roof panels, pop out panels on the sides, solar tracker, wind turbine and extra batteries. And then he could BBQ under the solar popout. :D
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  • lamplight
    lamplight Solar Expert Posts: 368 ✭✭✭✭✭✭
    #8
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    Re: Mono vs Poly Crystalline Panels

    why go flexible which seems more prone to damage... what about a rigid solar awning of solar panels on a hinge type setup that just pops up... might need some counterweight type setup to make it really ideal. but yes flat on the roof with an easy to change tilt would be more useful more frequently.
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #9
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    Re: Mono vs Poly Crystalline Panels

    Are poly panels better suited for shade? Shading cannot always be avoided with a RV.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Mono vs Poly Crystalline Panels
    CATraveler wrote: »
    Are poly panels better suited for shade? Shading cannot always be avoided with a RV.

    No panels are suited for shade: lack of light = lack of power.

    Mono panels produce the most power per area for direct-on sun. Around 18% efficient tops. Poly panels run about 16% efficient tops, but can pick up "scattered" light better. Amorphous panels are the best at scattered light (think bright but cloudy days) but are about 1/2 as efficient as poly.

    Before anyone starts in on me (again) these are generalities, not absolutes; there are always exceptions.

    There's a local retailer who parades monocrystaline panels as though they were the Holy Grail of solar power with exaggerated (yet non-specific) claims of how superior they are to poly panels as though you should only ever consider this one type. It isn't true, of course, but they probably offer him the best profit margin. His prices suck too. :p
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #11
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    Re: Mono vs Poly Crystalline Panels

    Does partial panel shading tilt the balance one way or another? It's not uncommon for a RV panel to be mounted near say a AC and have shading on one edge (possibly the shading effects cells in just one bypass diode group).
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
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    Re: Mono vs Poly Crystalline Panels
    CATraveler wrote: »
    Does partial panel shading tilt the balance one way or another? It's not uncommon for a RV panel to be mounted near say a AC and have shading on one edge (possibly the shading effects cells in just one bypass diode group).

    Not for panel type, but it will have differing effects depending on the particular panel, its orientation, and the way the panels are wired. As a rule, panels in parallel will only suffer the loss of the one shaded panel (all or part) as the current from the others will not change and panel Voltage is easily maintained. Series connected panels is a different matter, as knocking out one causes the string Voltage to drop by one panel's worth which means it may be too low to provide charging Voltage at all, even though the other panels still produce their full power.

    Within the panel it depends on how the individual cells are connected, what bypass diodes are included, and how the cell string(s) are oriented in respect to the shading hitting the panel. You can think of each panel being a mini array made up of individual solar cells. Sometimes you can't find the specs on the panel layout, so you have to just hope for the best.
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  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    #13
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    Re: Mono vs Poly Crystalline Panels

    I read somewhere that Mono does better than Poly in the heat of the summer. I run Poly but It was just a cost per Watt pick at the time, both are good! But.... I am In the PNW, jacket weather today!!!:cool:
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  • Crotalus
    Crotalus Solar Expert Posts: 26 ✭
    #14
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    Re: Mono vs Poly Crystalline Panels

    If you have limited real estate, such as a RV as in the original post another way of looking at it is watts per square foot and forget the cost. I have a small 17 foot fiberglass trailer that I was able to put a Sharp 80 watt panel on one of the sides. I then found a 95 watt mono panel from Carmanah that has a smaller footprint. It is also at a higher cost. I was thinking that I could put one of these on the other side in a parallel configuration. However the Sharp NE-80EJEA that I have has a Vpm of 17.3 volts and the Carmanah CTI-95 has a Vpm of 17.5 volts and would probably negate any advantage of using the Carmanah panel. I have also found that Sharp no longer makes the 80 watt panel.

    There are all kinds of things sticking up in the air of a RV that will cast shadows. That makes smaller the better for placement and efficiency.

    One panel is Mono crystalline and the other is Poly crystalline. Which one is a better panel is up to debate as both will provide electricity at a different physical size and dollar cost. And is the real difference the Vpm?

    Just my observation!

    Keith
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: Mono vs Poly Crystalline Panels

    Keith;

    The Sharp and Carmanah panels you mention will work fine together. The Vmp difference is insignificant. Take a look at the Imp ratings of the two panels. The Sharp is probably 4.6 and the Carmanah 5.4 or so. The physical size is probably very similar. You're right that Sharp doesn't make small panels anymore: nothing under 200 Watts.

    The difference between poly and mono is the "orientation" of the crystals, which allows mono panels to produce more Watts per area because the crystals are "all pointed in the same direction" so they get the maximum affect of straight-on sun. Doesn't have much bearing on shading because if you block light from any panel the power goes down.

    The actual construction and orientation of the panel will have more affect on its handling of partial shading than the type of cells used.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
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    Re: Mono vs Poly Crystalline Panels

    "However the Sharp NE-80EJEA that I have has a Vpm of 17.3 volts and the Carmanah CTI-95 has a Vpm of 17.5 volts and would probably negate any advantage of using the Carmanah panel."

    you can parallel these 2 pvs just fine. angles to the sun should be the same. what you would see is an average of 17.4v. it's true it would lower the respective voltage of the 17.5v pv, but it would also raise the lower 17.3v pv to 17.4v. also they are well within the 5% tolerance i like to recommend and bb goes with 10%, but for most intents and purposes these 2 are nearly identical.

    you beat me to it coot.;)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
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    Re: Mono vs Poly Crystalline Panels

    Just trying to save you some work "in honour of", Niel. ;)
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  • Crotalus
    Crotalus Solar Expert Posts: 26 ✭
    #18
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    Re: Mono vs Poly Crystalline Panels

    Is this a great forum or what? You guys are great. I have gotten so much valuable information here. Thanks for the reply. I was trying to show the difference between a mono and poly crystalline panel that I found to be similar. Here is the real differences.

    Sharp
    80 watts Vmp = 17.3 Ipm = 4.63 size in inches 47.2 X 21.1 X 1.8 weight = 20.94#
    Carmanah--- 95 watts Vmp = 17.5 Imp = 5.45 size in inches 40.8 X 20.8 X 1.4 weight = 16.3# - almost 6 1/2 inches shorter

    I ran into this trying to find another Sharp panel. I don't want to go the E-Bay route. I think I will swallow the cost and get the Carmanah panel for my upgrade. It comes from Canada. There are times where I can not park the trailer with the panel facing south. I do have a MPPT controller with a battery temperature probe that works just fine although there is a lot of talk on the forums as to the worth on a small system. We are retired and do a lot of dry camping for days on end and prefer not to use the generator unless it is necessary. It's a fishing lodge on wheels. I have a new, 3 week old Trojan 27TMH battery that I want to keep for awhile. It is rated at 115 amps @ 20 hours.

    Thanks again!

    Keith
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #19
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    Re: Mono vs Poly Crystalline Panels

    yes, the mono is more efficient and therefore less area for the same watts.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #20
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    Re: Mono vs Poly Crystalline Panels
    niel wrote: »
    ...what you would see is an average of 17.4v. it's true it would lower the respective voltage of the 17.5v pv, but it would also raise the lower 17.3v pv to 17.4v...

    While these panels are so close there is no real difference, I believe in parrallel they work at the voltage of the lower panel, hence you can't put some 30V panels in parrallel with some 37V panels and have them work at 33.5V...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #21
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    Re: Mono vs Poly Crystalline Panels
    Photowhit wrote: »
    While these panels are so close there is no real difference, I believe in parallel they work at the voltage of the lower panel, hence you can't put some 30V panels in parallel with some 37V panels and have them work at 33.5V...

    Combined output voltage would depend on the load applied. No load, and the open circuit voltage would go to that of the higher voltage panel. As load is applied, at first only the higher voltage panel would supply current, then as the load is increased, the combined voltage would be reduced to the point where the second, lower voltage panel would begin feeding current into the load as well.
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  • Jim45D
    Jim45D Solar Expert Posts: 102 ✭✭
    #22
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    Re: Mono vs Poly Crystalline Panels

    OK, you guys....now is as good as anytime to show the RV system I have devised. It's still in the building phase of the frame members. 1" aluminum rails running between panels. Hinged at the bottom, and tilted to my latitude for winter and summer. Listed are the various items with specs. For what's it's worth, panels 3 & 4 are on a old satellite dish mount (already on the RV) ran with a 12 volt motor, on a 34 amp hr. Concorde AGM battery via a Flexcharge timer. It will track the equivalent of 15° (moving the 15° once per hour) every hour from 10:00 am thru 4:00 pm. Thus returning to the easterly position at 7:00 pm, via microswitches. A month ago I was worried about mono vs poly, watts vs watts, and the loses involved. As the old story goes~in 6 months the panel you wanted, but couldn't afford is now obsolete, gone by the wayside, not mfg. any longer.....or in my case when I purchased the 87 watt Kyocera a month ago...well, they won't sell just one panel any longer. You have to buy a pallet of 20.

    I decided after that senario that I would quit wishing and planning, and get the dog by the ears so to speak. All of you have been an inspiration on this site, and I have learned more here than anywhere else. Thanks guys, especially BB, Niel, and Coot, and I can't forget Vtmaps, nor Icarus either, or the rest of you.. In the meantime, please feel free to chastise me on my math formulas, after all I got them from you guys. Check it over....and see if I'm almost right! The only drawback that I have at present time is the 2k Heart inverter I purchased. However, that will change to a lesser degree in the near future.

    I still have to get on the roof of the RV twice a year, but it isn't too bad. Incidently, FYI~ each panel will be wired as it's own entity to the combiner box with #8, then paralled down to the CC, about 5' with #6, and then to the batteries with #4, roughly 2.5'. Each panel will be fused with a 10 amp fuse. Darn it, I have almost exceeded the Morningside 45 PMW specs. However, there's a little headroom, and as we all know what I have specified won't happen in 115° temps, or better on the roof 6 months out of the year.

    This particular installation has been on going for just 2920 plus day's, and ++++ days, and it's still going! A few more days won't matter. Get it right~ as the old saying goes...."why buy a pig when just for a few cents more you can go whole hog", or "for a few pennies more, why not go first class." It doesn't matter with me. It'll be right, or it won't be done! Besides, buying a little half pig.....one may get shysted. Keep up the good work guys. I will keep you posted.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #23
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    Re: Mono vs Poly Crystalline Panels
    Photowhit wrote: »
    While these panels are so close there is no real difference, I believe in parrallel they work at the voltage of the lower panel, hence you can't put some 30V panels in parrallel with some 37V panels and have them work at 33.5V...

    Actually, on a PWM controller they'll function at battery Voltage; putting out their Imp @ whatever V the battery is at.
    With an MPPT controller the controller will adjust the "load" and therefor find the best V point for charging and the panel Vmp's really don't enter in to it. In your example the 30V panels may well operate above their Vmp if connected to an MPPT controller, as they are capable of operating up to Voc (with a reduction in current) and will do so if that's the power point the controller chooses.

    A couple of tenths of a Volt difference in Vmp? You can get that between two of the exact same panels on the same system. Nothing to even bother thinking about.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #24
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    Re: Mono vs Poly Crystalline Panels

    Hey Jim,

    Now that you've got the system up and running you should be able to compare the preliminary calculations against real-world results and see how close the formuli come to predicting performance.

    Or, "We know what it should do but what does it really do?" :D
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