Panel mismatch question

Marbil146Marbil146 Registered Users Posts: 4
Im a newby here with an old solar system in my RV that has been reliable for the past 12 years,it consists of two Unisolar 64W panels and a Specialty Concepts Mark 111/15 control monitor system.....Now,I have been searching in vain for another Unisolar 64 panel just to add a little more to the existing system,to take it close to the 15 amp max of the controller,and as they are no longer produced,would like to add around 64 watts in a glass panel,but there seems to be voltage difference of 16.5 to 17.4 between the panels....question....would I be ok adding this glass panel in parallel with the my two amorphous style panels,and would there be any other problems I would encounter?
I don't want to get into the expense of wholesale changes,just add a little wattage to the existing system.Thanks in advance.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panel mismatch question

    Welcome to the forum.

    It depends on the exact specifications of the two panel types. A small Vmp difference (less than 10%, less than 5% for preference) won't be any problem. Basically panels are current sources, and will try to produce their maximum current while the Voltage can fluctuate. Under charging conditions, the Voltage is "pulled down" to battery Voltage anyway. This means a 4 Amp 16.5 Volt panel will produce up to 4 Amps @ battery charging Voltage and a 5 Amp 17.5 Volt panel in parallel with it would produce 5 Amps at that same Voltage.

    If the Voltages are too far apart, as in the case of using a "12 Volt" panel with a "24 Volt" panel on a 12 Volt system, you will lose a large amount of the power potential from the higher Voltage panel. But its current output will be the same.

    I don't blame you for wanting to add a bit more, as those 16.5 Volt panels could be a bit low for a 12 Volt system once they get hot (Voltage drop from heating). But probably most of the charging is done before that happens anyway.
  • Marbil146Marbil146 Registered Users Posts: 4
    Re: Panel mismatch question

    Thanks for the quick reply,I see you're a fellow BC er........so just to clarify since I'm an old fart snowbird...if I add for example a Solartech 85w with a MVP 17.9 to my 2 Unisolar 64 w panels MVP 16.5 all together in parallel that I'm ok? Even when one is multicrystilline and the others are amphorous panels?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panel mismatch question
    Marbil146 wrote: »
    Thanks for the quick reply,I see you're a fellow BC er........so just to clarify since I'm an old fart snowbird...if I add for example a Solartech 85w with a MVP 17.9 to my 2 Unisolar 64 w panels MVP 16.5 all together in parallel that I'm ok? Even when one is multicrystilline and the others are amphorous panels?

    No worries. Panel types don't matter in terms of electrical output, and the Vmp difference between them is roughly 8%. That extra panel ought to kick in another 4 to 5 Amps.
  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Panel mismatch question

    In your case, using your present controller (it appears to be a "shunt pv array current to ground behind a blocking diode" type controller) Vmp (as long as the voltage is high enough) will not affect each other... Each panel in parallel will output its maximum current into the controller/battery bank.

    The "optimum" Vmp for a solar panel on a 12 volt battery bank is around 17.5 to 18.6 volts or so--To low (as Marc/Cariboocoot says), and a hot panel/cold battery bank may not supply full charing current. Much above 18.6 volts or so, and the extra voltage (and panel wattage) is simple "wasted".

    At some point you may want to update the charge controller so something a bit newer (a shunt controller will tend to heat the wiring and controller unnecessarily--heat is damaging to almost everything).

    Also, the UniSolar panels are about 1/2 the efficiency (watts per square foot) as typical glass panels+crystalline solar cells--So if you are running out of roof space, new panels to replace the UniSolar will about double the output current/wattage.

    However, if all is working well and you don't need the extra room, keep the UniSolar panels. Do note that glass solar panels use very thin glass (around 1/8 inch) and they are very easy to crack the glass if not treated like any window glass (they are tempered glass--a bit stronger, but if broken, the entire panel will shatter--and be just another piece of modern art).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Marbil146Marbil146 Registered Users Posts: 4
    Re: Panel mismatch question

    I want to thank you guys for your prompt answers to my questions,so this morning I put in an order for the Solartech 85w and a Morningstar prostar PS-15m controller,to Northern Arizona Wind & Sun.
  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Panel mismatch question

    Watch Customs charges--Can be a nasty surprise (FedEx and UPS tend to charge a bit of money too for brokerage fees).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel mismatch question

    My last UPS experience was a $30 bite... just for the document filing IIRC...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panel mismatch question
    westbranch wrote: »
    My last UPS experience was a $30 bite... just for the document filing IIRC...

    Was that with or without the 12% HST?

    There have been so many instances where the importation fees exceed the value of the item, and the Gov't collecting from the top has no reason to change anything.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel mismatch question

    that was just the bite for their FEE, taxes & duty on top of that!
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Marbil146Marbil146 Registered Users Posts: 4
    Re: Panel mismatch question

    No problem I'm in Casa Grande wintering so no worries until I hit the border.Should be here tomorrow and with the discount the shipping was easy to take.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel mismatch question

    Just keep the bill for when you cross back into 'the North' the CBSA guys will want to see it
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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