mixed panels

jchamp
jchamp Registered Users Posts: 22
Can I mix monocrystal and amourphous panels on the same system as long as they are 12v?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    In general, you can parallel different types of panels without problem as long as:

    1) proper series fuse in each panel (string) to prevent fire
    2) realizing, that the Vmp of the parallel string will probably be set by the Vmp of the lowest panel (reduces overall power production)--see next two bullet points.
    3) PWM controllers will not be affected by the "lowest common Vmp".
    4) MPPT controller output will be negatively affected.

    The normal rule is parallel panels with Vmp's that are about the same. Series connect panels with Imp's that are about the same.

    As always, the devil is in the details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: mixed panels

    I'm actually doing this with my small array. I started with a 45 Watt Harbor Freight kit, then added a few Amorphous panels from Northern Too. Finally added a 130 Watt Kyocera Crystaline panel. All are playing well together. I have another 45 Watt HF kit in my garage that's been collecting dust and awaiting installation. Also have another 130W Kyocera panel in shipment. At this point, I'll only buy Crystaline panels as they have a smaller footprint, and I've moved beyond the hobby/test phase.

    2862.jpg

    The good news is the panels I've purchased earlier will work with the better panels I'm buying now. I'm using two different MorningStar controllers (10L & ProStar 30M), both are PWM types, and also work well together.
  • jchamp
    jchamp Registered Users Posts: 22
    Re: mixed panels

    I am still growing and want to know if my 30 amp controller will hold all my new panels? I have 3 / 100 watt panels in paralle and want to add 2 more 90 watt panels in the same paralle. That will be 480 watts on the 30 amp sunforce controller useing # 10 tray wire. Thanks;
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels
    BB. wrote: »
    The normal rule is parallel panels with Vmp's that are about the same. Series connect panels with Imp's that are about the same.

    OK, I'm a newbie... I'll bite... what's considered "about the same"?

    In my particular case, I've got:
    (4) old Siemens M55's (17.4 Vmp, 3.15 Imp)
    (6) Golden Genesis PV-120E's (16.9 Vmp, 7.10 Imp)

    If I didn't know any better (and I don't yet!), I'd wire the 4 Siemens in two parallel strings (17.4 Vmp, 7.30 Imp, per string, right?) essentially creating 110W panels, to mix with the 120W panels. (I plan on 24V strings)

    Is this "about the same" enough to mix with the Golden Genesis panels, or should I just stick with two charge controllers (I plan on getting an Outback CC, but I could leave the Siemens panels on an old Trace C40)

    Since I'm a newbie, I'll go one step further and ask... what's the proper way to test the output of a PV panel... the Siemens panels might be 15 or 20 years old, and the Golden Genesis are probably 10? years old, so I bet these don't match their nameplate ratings anymore, and maybe some tests are due. I realize I can measure single panel open circuit voltage and amperage, but my Fluke meter is fused at 10A, so I can't measure open circuit Amps of panels in series... I'm got an Amp clamp, but it's AAC only... what do most people do, just buy a Hall effect AC/DC amp clamp?

    Just wondering...

    Thanks,
    -Norm.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    My 2 cent estimate--within about 10% of Vmp and/or Imp... And remember that the 10% difference most likely for a MPPT based solar charge controller, will mean the panels with the 10% (or x%) higher Vmp or Imp will effectively be derated down from their original Watt rating by 10% (x%).

    There are other issues too... For example, if Vmp of the panel with the lower voltage is below the battery+solar charge controller voltage requirements (i.e., battery equalize charge of 15v+controller 1-2 volt drop = Vmp ~17 volts minimum)--that a panel with Vmp of 15.3 volts will probably not supply any current for a flooded cell battery being equalized at 15 volts since most controllers require more than 0.3 volt drop to operate correctly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jchamp
    jchamp Registered Users Posts: 22
    Re: mixed panels

    I'm sorry Bill, I though I was getting this. your post went right over my head. I have 3 / 100 watt panels and I want to hook up 2 more 90 watt panels in parallel with them. I have 7 / 105ah batterys my controller is a 30A sunforce, Is my 480 watts to much for this controller? Please hit me with something simple and thanks for your patience.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: mixed panels
    jchamp wrote: »
    I'm sorry Bill, I though I was getting this. your post went right over my head. I have 3 / 100 watt panels and I want to hook up 2 more 90 watt panels in parallel with them. I have 7 / 105ah batterys my controller is a 30A sunforce, Is my 480 watts to much for this controller? Please hit me with something simple and thanks for your patience.

    This is how I figure it.

    300W + 180W = 480w x .8 = 384W reasonable output (could occasionally peak higher)

    384W @ 13V (battery charging voltage) = 29.5A

    Right on the hairy edge. I'd plan on it getting smoked, and I'd order something bigger. Depending on how the Volt and Amps of your mix of panels works out, you might be better off with a MPPT controller. Maybe the Classic with a high voltage input would be out by the time this 30A one smokes.

    30A sunforce will last a while: when sun rises, Panels start slow charging the battery, you won't have 29amps then. As sun climbs, batteries begin to be charged, and don't suck as many amps, and at noon, you may only be pushing 20A into 90% batteries.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • homerramirez
    homerramirez Solar Expert Posts: 102 ✭✭
    Re: mixed panels

    Don't somke it, fuse it, I have a Sunforce charge controller rated @ 400watts of solar array 30amps max., it could be a good time to upgrade to 24v controller. :cool:

    may I suggest to buy panels and batteries in pairs, you could always have more choices regarding voltage.:roll:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    Jchamp,

    I am sorry--for some reason the rest of your post went right by me... :blush:

    Those panels are certainly close enough to run in series/parallel configurations without much problem.

    I am a bit confused--you talk about wiring the panels to run 24 volts... Is this with a 24 volt battery bank too? Or with a 12 volt bank?

    You should not run 2x"12 volt" panels in series on a 12 volt battery bank with PWM controllers--it will work, but you will be tossing about 1/2 your panels "power/watts" away.

    If you get an Outback (or other MPPT type controller), then "high voltage" solar panel string with a lower voltage battery bank is just fine.

    Regarding the question about how to test panels to see if they are good...

    Simple test (about 80-90% confidence):

    1. Test open circuit voltage with DVM
    2. At noon time on a clear day, set a DVM to 10 amp scale and short the solar panel output--should measure Isc (or more than Imp).
    note added from niel: aim it at the sun with close to the optimal az and el angles for the solar noon of that day. solar noon is directly between your sunrise and sunset times and use the closet place to you that divulges that info. sorry for the two cents in your post bill, but i thought it would be better to see it where it applied.

    One additional test that will catch a few other problems...

    3. Put the DVM on 10 amp scale in series with the solar panel and attach it to a12 volt battery (such as your car battery)... The current should read near Imp in the middle of a clear day.

    1 & 2 are easy and will catch most faults. Test number 3 will find a panel that may have some bad cells.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    BB,

    I didn't mean to confuse things. What I was thinking about when I mentioned wiring for 24V was "Scenario A" below... 55W panels wired in parallel to create "110W" panels, then those wired in series for 24V, along with pairs of the 120W panels also wired in series for 24V, then all of them wired in parallel... clear as mud, eh? Sorry.

    Then I got to drawing it out and thought... why not do "Scenario B"? Well, I probably can't do it that way because an Outback CC wouldn't handle the max voltage, right? What would the Vmp and Imp probably be on these two scenarios?

    Thanks,
    -Norm.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: mixed panels

    a would probably work ok just as long as the current will not be too high on the output end of the cc(should be ok at 24v out. the cc is rated 1200w at 24v output). b has too much voltage for the cc just as you thought.
  • jchamp
    jchamp Registered Users Posts: 22
    Re: mixed panels

    Thanks again for everyones help. I am going to stick with my 12v system and to be safe I just ordered a 45amp controller. Thanks Guys Your the Best.....
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels
    niel wrote: »
    a would probably work ok just as long as the current will not be too high on the output end of the cc(should be ok at 24v out. the cc is rated 1200w at 24v output). b has too much voltage for the cc just as you thought.

    Would the output of "Scenario A" be 6.30Imp @ 33.8Vmp? (lowest Imp and lowest Vmp?) It should only be 940W total at 24V nominal...

    -Norm.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: mixed panels

    jchamp,
    note that for 12v output on the mx60 that it can only output 600w. the increase in power capacity comes from the voltage outputted as the currect capability of the fets stay the same. there is a mod for the mx60 to handle higher current from a software perspective so the fets really can handle more than 60a. if you were to have a 48v output the power handled by the controller would be 2400w.

    storminn,
    in series voltages add and current stays the same, but in parallel currents add and voltage stays the same.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    Norm,

    Assuming 24 volt wiring... A would be:

    Vmp = to lowest panel voltage set = 16.9+16.9= 33.8v

    And since you have sets of panels in series/parallel, the current would be:

    Imp = 3 x 7.10 amps (GG) + 2 x 3.10 amps (Smns) = 27.36 amps

    Your nominal power output using a MPPT type charge controller (the derating factor takes into account a lot of different sources for losses--so this would be a reasonable maximum output):

    Pmp=33.8v * 27.36 * 0.77 (overall derating factor) = 712 watts

    If this was a PWM controller and you charged your battery bank at 28.4 volts nominal (no derating of panels taken into account--multiply by ~80% - 90% for typical maximum current output):

    27.36 amps * 28.4 volts = 777 watts maximum into battery bank

    Note, at nominal or high temperatures, the PWM and MPPT controllers will have aproximatly the same power into the battery output...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    Hi BB,

    Thanks so much for your help...

    I'm still a little confused, though... sorry.
    BB. wrote: »
    If this was a PWM controller and you charged your battery bank at 28.4 volts nominal (no derating of panels taken into account--multiply by ~80% - 90% for typical maximum current output):

    27.36 amps * 28.4 volts = 777 watts maximum into battery bank

    So 777W * .85 (between 80% and 90%) = 660W using PWM, as opposed to 712 via MPPT?

    If so, I think I understand now...

    Thanks,
    -Norm.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    If you have panels with Vmp~Vbatt-charging+Vcontroller-drop, then a PWM or a MPPT solar charge controller will produce about the same amount of power (energy into the battery).

    In fact, it is possible the PWM controller will produce more power because it uses a bit less energy to run it internal electronics (an MPPT controller is basically a buck mode switching power supply--so there are more FET's, inductors, and control circuits than in a PWM--so there is more power "wasted" just running).

    Where the MPPT works well is when Vmp>>Vbatt-charging+Vcontroller-drop...

    Vbatt-charging is ~14.2-15.5 volts (depending on battery and which part of the charging cycle the controller is in), and Vcontroller-drop is around 1-2 volts (minimum drop for the controller to operate).

    Vmp rises when the panels are cold (so freezing weather helps raise panel voltage and the MPPT controller maximizes Pmp=Vmp*Imp).

    Also, if your panels are a long distance from the controller+battery shed, you can run the panels at a higher voltage (typically 140 VDC max with Outback and Xantrex--and many others--MPPT controllers) and reduce the solar panel current and use lighter gauge wire (i.e., 17 volts vs 5x17v=85volts=Vmp -- 1/5 the current for the same power where P=V*I).

    However, once a battery bank has approached 80-90% state of charge, both PWM and MPPT type solar charge controllers will begin to reduce the charging current--so neither will harvest "maximum available panel wattage" at this point--and the efficiency of either type of controller really does not matter any more at this point (since both controller types will be "throttling back charge current" at this time).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    Thanks Bill,

    Lots of good info here... thank you!

    Basically, I have an old C40 on the (4) 55W Siemens, but I'm planning on moving the system and adding the (6) 120W GG's, and I was planning on getting an Outback MPPT... so I was trying to figure out if I would be better off running both charge controllers, or just run the one MPPT with a mix of panels... trying to figure out how much the mix of panels might hurt my power output...

    So, if I'm absorbing all this stuff correctly... if I plan on running 24V nominal strings with a 24V battery bank, it sounds like I might be better off keeping the C40... (maybe not even get an MPPT?)

    However, I run into mixed panel situations often, so I wanted to learn more about them. I have a friend up the road that I'd like to help out, he has a mis-mash of panels... four different types, in two different locations (four on his roof, and two others 45 feet up a tree). In his case, he has a 12V battery bank (eight L16's) and all the panels are wired in parallel at 12V nominal, to an MX60. The panels on the roof are shaded at different times than the panels up the tree... I know this isn't good, and I suspect since they are wired in parallel, they are pulling down the output of the panels in the tree (but I didn't do it!).

    So I wanted to try and calculate for him what the difference in production would be if he ran with two charge controllers, and sorted out the wiring so the panels in the tree are at 24V (or 48V, he plans to add two more panels up there) for less voltage drop over the 80 foot one-way run of #6 that he has now. He plans on keeping his 12V FX inverter (and he's got mostly 12VDC loads), so it sounds like he could maybe run the panels in the tree at 24 or 48V into the MX60 and then get a cheaper PWM controller for the panels on the roof, run them at 12V and maybe he'd be better off? I've got the specs for all of the panels except the ones in the tree (he's trying to find the paperwork)...

    Thanks for all the help,
    -Norm.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    Running "24 volt" panels (really Vmp ~ 34-36 volts) on a 24 volt string with a short run to the panels from the charge controller/battery shed--it is probalby a wash which one you choose.

    If you are getting the Outback MPPT controller anyway--It would probably be better just to swap everything over to the new MPPT controller (fewer items to watch/control/maintain).

    The comparison between MPPT and PWM controller in a 24v/24v system is -- in theory -- on a very cold day and warm batteries you can see upwards of a 30% improvement in power over PWM... However, that is probably the best case senario--and a real system may be 1/2 that (just guessing, I do not own a battery charge controller and I do not live in a extreme climate).

    The two places that MPPT work very well is when you wire your panels for Vmp>>34volts... You 1) gain the ability to reduce current through your PV to Controller wires (smaller awg, longer runs, less losses, depending on how you set them up) and 2) the ability to run "hot panels" with "cold batteries" (Vmp falls when hot, battery voltage rises when cold--it is possible that in extreme climates, that your Vmp will not be enough to equalize the cold storage batteries on a hot/windless day).

    I don't have time right at this moment to look at where you are from--and to look at Vmp Hot/Cold vs wire drop + controller drop--the math is not hard... Vmp= Vmp@77F - xx volts per degree F (or degree C)... Use your cold temperature to figureout Voc-cold, and your hot temperature+solar heating of xx degrees for Vmp hot (vs battery temperature/required charging/equalization voltage).

    And see where your installation will fall.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    Thanks Bill,

    I live about 2 hours west of Seattle, at sea level. The climate is not what I would call "extreme" (I've lived in Maine, this is very mild by comparison).

    The average min temp here in winter is 31F, the average max high in summer is 76F...

    Thanks again,
    -Norm.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    You should be fine with either controller running 24/24. But it never hurts to double check and do the math--always a good education for when you help the next person on the board with similar questions (and I can let others type those long/wordy responses that I am so infamous for :roll: ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: mixed panels

    in general a 10% boost overall in current is what is found on mppt, but if one always has the state of charge on the batteries in the upper last portion of the charge the benefit isn't really there for mppt current gains even if in a cold climate. at those stages of charge (acceptance and float) the controller is throttling back so the gain occurs in the bulk charge area. many do use the mppt controllers for the reason of the higher pv voltages to overcome wiring losses and then reduce downward at the best possible power point to charge the lower voltage battery(s). i know many don't go into this lower bulk portion of the charge very much for more battery life cycles and i'm not going to criticize their decision to get more cycle life, but they could be losing some of the benefit from an mppt charge controller too if their intent was to use one primarily for the boost current.
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    OK, I realized a confusion of mine...

    I looked up the specs for the Siemens M55 modules, and the temp. coefficient for Voc is -0.077V/°C... so BB... you're saying if my minimum temperature here is, say 20°F/-6.6°C, then:

    25°C-(-6.6) = 31.6°C difference... 31.6*0.077V = 2.43V, so I add this to the 21.7Voc to get 21.43Voc max... what I might see from these panels on a 20°F day?

    Thanks,
    -Norm.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mixed panels

    Yep...

    Except a math error:
    25°C-(-6.6) = 31.6°C difference... 31.6*0.077V = 2.43V, so I add this to the 21.7Voc to get 21.43Voc max...
    Voc@20F = 21.7v + 2.43v = 24.13 volts

    Xantrex has a neat online calculator for their GT inverter series... I use it because it has a whole bunch of solar panel brands/models listed and I can just plug in the numbers to get the Voc-max and Vmp-min.

    The only thing is you have to divide the voltage numbers by the number of panels to get the single panel Voc/Vmp (if that is what you need). They also list PTC (a more reasonable average panel output--not the STC marketing wattage).

    I have compared the Xantrex calculations against my own installation (a Xantex GT 3.0)--and they seem to be very close to what I see on my system.

    -Bill

    PS: Remember you are calculating Voc--that matters when the controller is unloaded (battery full). Vmp will set the power output under optimum conditions (Pmp=Vmp*Imp).

    Remember there is a smaller second order effect of temperature on current... While Vmp goes up as temperature drops--Imp goes down.

    But, Imp is much less temperature sensitive so it is pretty safe to ignore the temperature effect on current.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • StorminN
    StorminN Registered Users Posts: 12
    Re: mixed panels

    Whoops! It figures I'd get part of it right and mess up on the simple addition... ha!

    Thanks for all the help, BB... talked to my friend with the mis-mash of panels, he said he has the specs on all of them now... I'm headed over there tonight to work on his system and get all the info...

    Thanks,
    -Norm.