What is the power factor of a pv system and the factors affecting it ?

Is the pv system are unity function and if so why do some pv systems have reactive power ?

Comments

  • BB.BB. Posts: 28,040Super Moderators, Administrators admin
    Are you asking about Grid Tied Inverter type systems?

    If so... The first thing to uinderstand is that AC powered systems only have unity power factor (PF = 1.0) if the loads are purely resistive (heating elements, filament lamps, etc.) or are Power Factor Corrected power supplies (the input section of the power supply is designed to draw current "in phase" with the voltage).

    Most other loads have an Inductive element to them (some sort of coil, inductor, or motor windings) that causes the device to draw current delayed with respect to the AC sine wave voltage (or have a "non-linear" current draw, like a diode rectifier charging a capacitor for a typical computer power supply--Only drawing current near the top of the sine wave voltage).

    https://en.wikipedia.org/wiki/Power_factor

    For typical residential systems... The utility meter only "measures" true power. The reactive power component is "ignored". For commercial utility meters (typically large installations like oil refineries and such), the utility will also measure the reactive power/power factor and charge a penalty for poor power factor (more or less increase the bill by 1/PF x larger). So, for some utility customers (typically with lots of induction motors), it is worth correcting the power factor to near 0.95 or so to reduce their power bills (with motors, using a parallel "motor run" type capacitor will correct poor inductive power factor). Poor PF computer power supplies cannot be "corrected" with a capacitor (need new/redesigned PF Corrected power supplies to fix).

    With Grid Tied Inverters, they are (where) designed to inject power "in phase" with the AC voltage. That is PF=1.0 ... However in "real life", the typical home has a PF in the range of ~0.80 PF, so the "reactive power" is still supplied by the utility. I have seen new design GT Inverter (specifications) that can be programed to supply a PF of up to (or down to) PF~+.- 0.80 .... This means now the GT inverter can also supply some of the reactive current too and the utility is not "burdened" with supplying the reactive current "for free" (and helps reduce current demands on the utility network).

    Does this make any sense? It is a complex question.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Posts: 2,300Solar Expert ✭✭✭✭✭
    Very good explanation indeed, it gets complicated trying to explain what may be common to those familiar with electrical terminology to translate to others without such a background, the vernacular explanation is superb, good work @BB ;
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • jonrjonr Posts: 1,098Solar Expert ✭✭✭✭
    While a phase shifted inverter is good for the utility, it's probably bad for you (it causes more inverter current flow and losses).  Also, it won't fix non-linear load PF (an increasing problem).
  • BB.BB. Posts: 28,040Super Moderators, Administrators admin
    From the utility's point of view, they are supplying reactive current for free (their generators, their distribution system, their transformers).

    For a GT inverter to supply reactive current the wiring and inductors need to be roughly 1.25x larger (more current). (1/.80 pf}

    Other than a percent or so of extra loses from more current flow, it is pretty much near free for the GT inverter to supply reactive current.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Posts: 1,098Solar Expert ✭✭✭✭
    I wouldn't call buying a 25% larger inverter free.    But if the utility looks more favorably on grid-tie because of power factor correction, that's a good thing.
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