CFL lamps, bad power factor

mike95490mike95490 Solar Expert Posts: 9,014 ✭✭✭✭✭
Yow !!

When the utilities start to complain, I guess it's bad.

excerpt: Every CFL light contains a small ac-dc power supply with reactive components in it that will affect the CFL’s power factor (PF) – that is, the load presented to the ac line. The closer the PF is to 1, the better. A load with low power factor (<.85) draws more current and is less efficient than a load with a high power factor for the same amount of useful power. The higher currents required by the lower PF devices mean increased energy lost in the grid due to such things as I2R losses. These power losses don’t show up directly on our electricity bill, but the utilities sure see the effects.

So, when wired up to a standard off-grid, whole house inverter, do the inverters give any total PF readout, or do they keep pumping out extra power till something gives ? What happens at night, when all the CFL's are on, and no heavy appliances? Anyone have troubles, or use a kill-o-watt on a string of CFL's ?
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gen: ,


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: CFL lamps, bad power factor

    now that's interesting mike so i decided to check one i have here. it's a ge 20w energy smart cfl. i measured the following with my kill-a-watt.
    now calculating v x i=w i get 30.825w.
    they sure do draw more and an inverter would be pressed into a bit extra because of the pf if one doesn't compensate for it.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: CFL lamps, bad power factor

    I can't test a string of them,, but checking a few,,, they seem to draw 13 watts, .16amp 20 va, PF 65. 121.3 vac. (Rated 14 watts)

    What does this mean to me in the real world?

  • RCinFLARCinFLA Solar Expert Posts: 1,327 ✭✭✭
    Re: CFL lamps, bad power factor

    You pay for true power (I*V*pf.) not appearent power (I*V)

    Bad power factor does result in higher IR loss due to higher current but this is usually only a factor for high wattage items like central air conditioner and pump motors.

    Bad power factor is a concern to power company because it creates more transmission losses.
  • BB.BB. Super Moderators, Administrators Posts: 31,048 admin
    Re: CFL lamps, bad power factor
    RCinFLA wrote: »
    You pay for true power (I*V*pf.) not apparent power (I*V)

    Not quite a true statement for everyone...

    Businesses (as I understand) typically pay for "true power" for their monthly billing--but their "reservation/max power" is billed in kVA (apparent power).

    For the typical business customer in California, roughly 1/2 of their power costs are the Monthly kWhr charges. And the other 1/2 are the kVA reservation charges.

    So, it is very easy to see a large office building (lights, computers) could be significantly impacted if the majority of their lighting has a PF of 0.5 (the peak kVA charges would be 2x vs kWhr charges).

    Also, from what I remember some 30 years ago--large users (such as oil refineries) will have a PF meter on their billing too... Basically, the cost was $$kWhr/PF -- So the effective charges where for kVAhr (apparent power) and not KWhr (or true power).

    Next--we in California are now starting to get "Smart Meters" installed. I have seen a couple places where it has been mentioned that Smart Meters will be billing kVAhr--not kWhr. And it was going to be recommended that homes may need PF correction hardware to bring their inductive loads back near unity Power Factor (i.e., 1.00).

    The ugly part is that while it is relatively easy (and cheap) to correct PF for the typical induction motor (such as a well pump, A/C pump and fans)--it is not easy (at least the little bit I know and understand) to correct PF of non-linear electronic loads (i.e., older computers, CFLs, dimmer circuits, possibly older microwaves, etc.).

    And the issue is the same for utilities--pumps, motors, etc., bad power factors are relatively easy and cheap to correct at their distribution points (near customers--such as we can see in the central valley of California where there are banks of capacitors that are typically switched on during the summer when well pumping and A/C loads are the heaviest).

    However, any non-linear PF issues (such as CFL's)--cannot be--and (I would guess) the harmonic energy is eventually converted to waste heat during transmission/transformer conversion.

    I think I have seen in a couple places that lighting was responsible for some 1/3 of the electric consumption in the US (may be one of those urban legends too)--so the mass conversion to CFL/electronic ballasts may be a pretty huge issue for power companies (and eventually) for the consumer.

    What does it mean in the "real world" for the Utility Grid--basically transformers and wiring must be sized to the load/PF... So, if you have a string of CFL's (or other devices) with a PF of 0.5, then the wiring and transformer basically have to be twice as large and they distribution system losses could be 4x larger (I^2 * R losses) because of this (increased infrastructure costs and increase of wasted energy costs to the utility.

    Supposedly--there may also be other issues if the majority of lighting goes "electronic"... For example, these devices (including power supplies and such) are basically "constant power" devices... Or, in English-- P=I*V... So if V goes up, I goes down (to keep P=constant). And if V goes down, I will go up.

    This is a "negative resistance". It would be possible to setup a resonance condition in the grid... You get some heavy loads and/or generator failure--voltage starts to drop, and current increases (negative resistance because of active loads)--causing the voltage to plunge even faster... The utility pumps more current in to bring back up the voltage--and now the current drops. And the voltage will overshoot it regulation set-point. Classic feedback for an oscillator.

    I don't know enough about the US grid to know if this is a real issue or not--but I have read a few discussions where this issue has been raised.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: CFL lamps, bad power factor

    One of the issues talked about in a previous thread was having a purely inductive load. Some inverters will actually shutdown if this occurs. It's also mentioned in the instructions included with inverters (all kinds of good info in those!).

    I haven't tried it, but a friend has. He wired 10 CFL bulbs to his inverter. The string would light up, shutdown, light up, etc. By removing some of the bulbs, the inverter would power up properly, then he could add more bulbs one at a time.

    The instructions say if this occurs, 'simply add a resistive load to prevent the load from being purely inductive'. Great, got to waste energy to get it to work!

    So rather than use the big inverter (parasitic load being left on anyway), I'm taking care of lighting by zones, with cheap independent inverters. Here's how I wired up my living room:

    I didn't use my Kill-A-Watt (not sure how well it would work with a MSW), but I did measure the total current used in the circuit with a clamp-on DC meter. I had two 20 Watt CFL bulbs, and a 400 W MSW inverter. Total current was 3.40 Amps x 12V = 40.8 Watts. That also includes the inverter losses. Can't complain.
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