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I recently bought a Kill-a-Watt meter to measure power consumption of my devices. This was just a fun project for me. I put this on my Mac-Mini to see power consumption during various usage states - idle, MATLAB bench mark, starting an application, screen-saver etc. and discovered that the power factor my my Mac-Mini was 0.2 when on standby and .80+ when up and running. However, while shutting down and before login the power factor was .45

I also measured this for my:

Raspberry pi with a 5v 3A power supply (PF=0.68)
Dell Laptop 90W charger (PF=.98)
2006 Compaq Charger (PF=.55)
CFL Table Lamps (PF=.52)
Tube CFL Lamps (PF=.55)
Power PC Late 2005 (PF=)
A 40W Audio Amplifier (PF=.66)
Vacuum cleaner (PF=.97)
Samsung phone charger (PF=.58).

From what I learned in my classes, 0.9+ is a good power factor and utility companies fine industries if they have power factors less than this. But most household equipment seem to have terrible power factors. Yet I have never heard of utility companies fining residential users? Why? Do they correct the power factors at the transformers at our residence? Or is residential usage too meager to bother about?

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  • \$\begingroup\$ the above power factor measurement of various switching power supplies reveals that they are not equipped with PFC circuit \$\endgroup\$ – yogece Oct 14 '13 at 4:40
  • \$\begingroup\$ You've probably forgot to include the PF for Power PC Late 2005. \$\endgroup\$ – sharptooth Oct 14 '13 at 9:43
  • \$\begingroup\$ Yes I did :-) I am yet to measure it. I suspect it will be poor. \$\endgroup\$ – Lord Loh. Oct 14 '13 at 15:13
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    \$\begingroup\$ Are the power factors you are measuring due to inductive or capacitive loading? Typically industrial companies have heavily inductive loading (e.g. motors) whereas I would suspect the devices you list might tend more to the capacitive side. \$\endgroup\$ – Michael Oct 14 '13 at 16:38
  • \$\begingroup\$ I would think the first stage of an SMPS or a power supply would be a transformer - inductive. I may be wrong. \$\endgroup\$ – Lord Loh. Oct 14 '13 at 20:26
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The power factor of residential premises is already pretty good.

From a 2002 report on power factor correction, we get the following snippet about power factor correction in the tenant spaces (offices, apartments) of a commercial building, vs. the utility parts (elevator lifts, HVAC):

If we were to take an example of a typical commercial building, the main switchboard is split into two separate sections; a house services section and a tenant section... [snip]

The house section normally houses the circuit breakers for the central air conditioning plant, lifts, house lighting and power. As will be highlighted in Section 7, motors account for a decrease in power quality and thus a reduction in power factor. In this particular instance it would be a valid exercise to consider the benefits of power factor on this section of the installation. In most instances power factor correction is installed providing immediate cost savings to the base building owner.

As the tenant power is on a separate bus, they also have the opportunity to consider power factor correction. In most instances the tenant supply usually consists of general lighting and power with some supplementary air conditioning. The power factor for these installations is generally greater than 0.90 and as such there is no significant benefit in installation PFC units. In addition, these tenants are usually metered at a kWh rate that does not consider the power factor of the installation for billing purposes.

The bulk of electricity in houses is used to either heat things up (space heaters, ovens, cooktops, water heaters) or cool things down (air conditioners, refrigerators.) These either have intrinsically good power factor (heating elements are resistive, i.e. p.f. 1.00) or they come with power factor correction in-built (air conditioners.)

The things you measured are mostly electronic devices, so they have poor power factor, but they also don't draw much power compared to the heating/cooling devices listed above.

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Contrast this with industrial sites, where a large part of the load is AC induction motors with rated power factors between 0.80 to 0.90 (and less than that if they're less than fully loaded.) There can be 10 MW worth of induction motors in a decent size plant - I know of ore crushing and grinding mills which are driven by a 10 MW induction motor each.

It is much more cost effective to target such induction motor installations before targeting consumers.


In response to Lord Loh.'s comments:

Consumers (and small businesses) generally have no incentive to improve power factor. In Australia, at least, billing is by kilowatt-hours (real power) and the power factor is not considered in the bill.

However, Ergon Energy (the distribution authority in Queensland, Australia) is trying to drive power factor correction in small businesses. They are doing this by offering incentive payments for businesses who want to participate.

The reason for pushing PFC to small businesses is not to increase efficiency, in the sense of saving a few dollars on the power bill, but rather to mitigate the exorbitant price of power at peak demand. To wit:

The aim of the Queensland Government funded project is to use incentive payments to reduce peak demand by a total 4.7 MVA, with subsequent customer savings and carbon emissions reduction.

Because of the way the electricity market works, at peak period the marginal price of electricity (the price for Ergon to buy "one additional kilowatt") can be in the range of $1,000/kWh. So by shaving 4.7 MVA off the peak demand, they are actually saving thousands of dollars ($10,000? $100,000? $1,000,000?) per day.

With savings like that, offering businesses an incentive to voluntarily install PFC is a no-brainer.

There is also the nice effect of decreasing the MVA loading on infrastructure like transmission lines and transformers, so that Ergon can get the most capacity out of those assets before they need to be upgraded. Simplistically, deferring a $1M project by one year allows you to earn 5% interest on that $1M, so this is another significant saving.

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  • \$\begingroup\$ Also, kind of implied in this answer: households don't make up any kind of significant part of the electrical power consumption on the large scale. Household lighting has a sub-single digit percentage and even in summertime when everybody's home with the AC on, household power consumption is still usually below 10%. And it's distributed among orders of magnitude more users. Administrating that many users for so little potential gain is deemed just not worth it. \$\endgroup\$ – user36129 Oct 14 '13 at 6:07
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    \$\begingroup\$ Is that really true, @user36129 ? Wikipedia says that in 2008, 36.2% of electrical energy consumption in the US was residential. en.wikipedia.org/wiki/… (I agree with your broader point that it probably isn't worth the administrative costs.) \$\endgroup\$ – Doug McClean Oct 14 '13 at 7:07
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    \$\begingroup\$ I'd also expect the residential power factors to be partially leading, partially trailing, and most certainly uncorrelated. \$\endgroup\$ – MSalters Oct 14 '13 at 8:57
  • \$\begingroup\$ @DougMcClean ah, thanks for the wiki, I was wrong then. I guess I had the wrong statistic in my head. Also, MSalters, there is no real leading or trailing phase shift as a cause of residential power factor as most of the distortion (which would be a better term) is from switching power supplies, not from phase-shifted loads. \$\endgroup\$ – user36129 Oct 14 '13 at 9:13
  • \$\begingroup\$ I have my doubts about PFC and savings to the customer. It appears to me that better PFC saves the Power Cos a lot of money. The Power Cos can bill the customers for Watts and not the VA (reactive power sent back). Unless the Co is fining for poor power factor, the customer seems to have no incentive to correct it. Do I have my facts wrong? Does PFC benefit the customer financially or otherwise? \$\endgroup\$ – Lord Loh. Oct 14 '13 at 15:25
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Utilities do care about power factor to residential buildings, but hassling them about it is more trouble than it's worth due to the relatively light load compared to serious industrial customers.

Instead, the utilities hassle your legislators. It is logistically easier and much more cost effective for them to get laws passed to require certain power factors from devices commonly used by residential customers than to try to enforce or charge for low power factors from those customers directly. In the EU, for example, any electronic device drawing more than some specified amount of power (used to be around 70 W if I remember right, but I think the threshold has been lowered recently) must have a power factor above some limit to get CE certification. More and more electronic devices start with switching power supplies that do active power factor control, partially as a result of such laws emerging worldwide.

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    \$\begingroup\$ Demanding PFC via law is the real answer on what is happenning here, especially in the EU, where heating with electricity is less common, and the incandescent light bulb is frowned up (via law). \$\endgroup\$ – PlasmaHH Jan 30 '15 at 15:32
  • \$\begingroup\$ @PlasmaHH: … frowned upon. \$\endgroup\$ – Incnis Mrsi Aug 28 '16 at 18:42

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