DC converters

ws9876
ws9876 Solar Expert Posts: 448 ✭✭✭
in General Solar Power Topics #1
DC to DC converters are getting more common these days ..... is this a good way to go
if you want to mix old and new panels..???
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: DC converters

    Mixing old and new panels is only a problem if the specifications are too far off (greater than 5% or 10% depending on your tolerance for efficiency losses). For parallel connections the Vmp is the key figure. For serial connections the Imp is it.

    As far as I know, DC to DC converters are meant to operate with constant Voltage in to supply constant Voltage out (usually 24 to 12, or 12 to 24). They are not designed to work with the variations of Voltage and current found in solar panels and would have no way of adjusting a 26 Vmp panel to work with a 18 Vmp panel.

    However, National Semiconductor used to make a "Solar Magic" box (some other companies have similar devices - NS has recently sold their product design) which were supposed to adjust a panel's Voltage to match that of others in the array if shading occurred. I'm not sure how far "out of spec" they could handle or how efficacious they'd be for constant re-alignment of Voltages, but they are more along the lines of what it sounds like your asking after.

    If you do have to run mismatched panels the most sure-fire way is to use separate charge controllers of the MPPT type; one per different panel set. Not the cheapest, but it will maximize the potential harvest.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #3
    Re: DC converters

    A little more specific?

    http://www.power-one.com/renewable-energy/products/solar/string-inverters/aurora-optimizer/series

    If you are talking about per panel MPPT optimizers you might as well go with a direct to AC microinverter.

    http://www.power-one.com/renewable-energy/products/solar/string-inverters/aurora-micro/series
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: DC converters

    ws9876,
    i think you are a bit confused here as dc to dc converters are not gt inverters or controllers and have nothing to do with pvs be they old or new. they are inverters whose output is rectified and filtered to derive a specific dc voltage other than the original dc voltage.

    wow, you guys chime in fast.:D8)
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: DC converters
    niel wrote: »
    ws9876,
    i think you are a bit confused here as dc to dc converters are not gt inverters or controllers and have nothing to do with pvs be they old or new. they are inverters whose output is rectified and filtered to derive a specific dc voltage other than the original dc voltage.

    wow, you guys chime in fast.:D8)

    Actually the optimizers are DC-DC converters, just not a standard voltage to voltage DC to DC converter. They are limited input to output voltage range buck-boost DC to DC converter with MPPT frontend. The limited range of voltage translation gives them high conversion efficiency.

    All panels in a series string must produce the same current. In a normal operation the output current tolerance variation (+/-5% or so) between panels will cause weaker panels to operate a little voltage below their MPP point while stronger panels to operate a little past their optimum MPPT point. The optimizers go for individual panel true MPP point and adjust its output voltage to the series string to match the current of panels series stack. Keep in mind the central inverter is hunting for the overall MPP point at the same time.

    Problem is they are about 80% of the way, guts wise, to a full GT microinverter. In my opinion, the bang for the buck is not there.
    I am also not convinced that having multiple MPPT interactions will not cause MPPT stability problems with the central inverter that will end up wasting more power in MPPT wandering then the optimizers are suppose to improve.
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