How close of a match should new panels be with existing panels?

softdown
softdown Solar Expert Posts: 3,925 ✭✭✭✭
in Solar Beginners Corner #1
Great time to augment panel numbers. Can be expensive to duplicate exisitng panels due to oversize shipping charges etc. So how close of a match should we strive for when adding some panels? Thanks in advance.

Sorry if I seem to be going in different directions. My truck has major, major electrical issues at this time. Backed up sewer as well. Tax time etc.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #2
    I have been told with in 10% my new panels are 260W my old ones are 230W, VMP with 1.5........ I have not had any noticeable issues. Except more and better charging on overcast days..
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  • softdown
    softdown Solar Expert Posts: 3,925 ✭✭✭✭
    #3
    Thanks AMan. Sounds about right. Vmp, I think, tends to either be 12, 24, 36, and maybe 48 volt. We should assuredly match the Vmp range and try to get close on the wattage?
    I wanted to stick with the same manufacturer but the shipping for a few panels was outta sight...for me. Constant unforeseen bills cramp my style.
    Alaska Man wrote: »
    I have been told with in 10% my new panels are 260W my old ones are 230W, VMP with 1.5........ I have not had any noticeable issues. Except more and better charging on overcast days..
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • softdown
    softdown Solar Expert Posts: 3,925 ✭✭✭✭
    #4
    A solar company owner said that the smaller wattage panels will drag down larger wattage panels to the output of the smaller panels. So closer size pretty well equals better.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • scrubjaysnest
    scrubjaysnest Solar Expert Posts: 175 ✭✭✭
    #5
    I can't measure any difference with one or both 80 watt panels connected with the 120 watt panel except in full sun. The 120 watt Vmp is 16.9 runs 17.1 in full sun. The 80 watt panels Vmp is 18.1 and that is what they run in full sun, connected with the 120 watt they pull CC input from 17.1 to 18.1 volts. Under full cloud conditions no measurable input voltage difference to the CC, just more current with the additional panel.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Alaska Man wrote: »
    I have been told with in 10% my new panels are 260W my old ones are 230W, VMP with 1.5........ I have not had any noticeable issues. Except more and better charging on overcast days..

    If you are putting the new panels in parallel with the old ones, then a Vmp match within 5% should give you no problems. You will not get quite the output you get from just summing up the two wattages, but it will be close enough to be economical. If you are using a PWM CC you will not notice the difference in voltage at all.
    If you are putting the new panels in series with the old ones, then the new panel should have a higher Imp than the old ones and that Imp should be within 5% of the old to get the maximum benefit from the new panel.
    Even if the currents are within 5%, putting a single low current panel in series with several higher current panels could leave you with the same output instead of increasing it at all. (If the Imp from the old panels is above the Isc of the new panel, then the bypass diodes in the new panel will be driven into conduction and you will not only get no voltage boost from it, you will actually drop the total string voltage by a couple of volts.
    SMA SB 3000, old BP panels.
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