Electronic – Why do power companies never bother residential customers about power factors


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?

Best Answer

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.


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.