Can improving Power Factor help your Energy Bill?

***Update - 4/21/09: An Electrical Engineer friend of mine just send me the most detailed technical and economic analysis I've seen on the topic of residential power factor correction devices.  Check it out after you read the blog below if you are really interested:  NLCPR: Power Factor correction

Part of our goal with the Mapawatt Blog is to review the best products that can save energy and water in your home.  Product developers know that as energy costs rise, consumer's budgets get tightened, and people start to care more about their environment (the trifecta of sustainable drivers), those consumers are going to want products that help them save energy.  But do all these products live up to their claims?

One of these products is a power factor correction device and can be seen here.  This product claims:

Residential customers throughout North America could see a realized savings of 8% - 10% typically and as much as 25% on their electrical usage (and thus power bills).

However, I'm not buying it.  There are two great resources on-line that address this same issue.  One is from the National Institute of Standards and the other is a blogger I've been reading for 4 years and has a great section on electricity, Michael Bluejay. Both of these resources say power factor correction really wont help on your residential bill.  It can make a difference for certain industrial users who may be billed by the Utility for peak demand, but this is another story (and it is addressed in the Bluejay article).

To go a little deeper, the formula for Power Factor (PF) is below:

PF = Real Power (Watts) ÷ Apparent Power (VA)

- or -

Watts = PF*Amps*Voltage = PF * Apparent Power

The power factor correction devices are said to improve the second half of the above equation, the Apparent Power.  However you don't pay your utility for Apparent Power.  You pay them for Real Power (Watts).  Apparent Power is defined as the total power in an AC circuit, both dissipated AND returned! (scroll to the bottom of this link to view the power triangle and description of Apparent, Real and Reactive power).  This means that if you currently have a poor power factor, your  Apparent Power is higher, but all this means is that you are returning more unused electrons to the utility!  But since they only charge you for used electrons (dissipated electrons = Real Power = Watts) you don't give a hoot about your Apparent Power!

Let's take an example of 2 completely identical motors sitting side by side.  Both of these motors have the exact same efficiency and operate at 1.2 kW. The first motor doesn't have a power correcting device.  The second motors does have PF correcting device.

  • Motor 1: 1.2 kW motor, connected to a 120 V circuit, PF = .7
  • Motor 2: 1.2 kW motor, connected to a 120 V circuit, PF = .999 (this has the Power Factor correction device, thus the excellent PF!)

Using the equation above we can show the amps (current) that will be dissipated in motor 1:

1.2 kW = .7 *120V * A → A= 14.29

And we can do the same thing for motor 2:

1.2 kW = .999*120V*A → A=10.01

But this doesn't mean you'll pay less to the utility!  All this shows as that your power factor increases (gets better) your amperage decreases, but the Real Power (Watts =  what the utility charges you) stays the same!  Therefore no matter your power factor, in residential settings the utility is still going to show that you took the same amount of Real Power off of the power lines, so that is what you pay.

I would like to see more info from the manufacturers of these devices on how improving PF helps save you Watts!  Basically, your utility doesn't really care what your Power Factor is, so I want to see some evidence on how this device impacts your energy bill.

One more thing!  On the product's website there are many customer testimonials.  NEVER believe customer testimonials.  Especially on things like energy saving devices or products that claim they can improve your gas mileage.  The reason people believe these testimonials is because they can't see electricity flowing through their home, so they just take the product's statements at face value.  Even if the "customer" really said the things about the product, how do you know they aren't mentally insane and or compulsive liars?

Also, if your energy bill goes down the month after you install this, how do you know its not just because you didnt have your AC or lights on as much?  You dont! Only believe data and analysis from trusted web sources (Mapawatt, Rocky Mountain Institute, Energy Star, Michael Bluejay, etc.).

I'm not saying this doesn't work, but I am saying that I need more evidence, and until I see more evidence, I think your and my money can be spent on better energy savings

I'm not the only site questioning the validity of Power Factor correction devices.  Open4Energy has a great review of Power Factor correction devices and another post on Energy Saving Scams.  I should note that it is in their "scam" section!

enjoyed our post? let others know: 


Oh i have bouht one recently.So you are saying my money is wasted
ckmapawatt's picture
oh well... that is rigth my friend... power factor correction is only great in industries cause they pay if they dont reach the required power factor... but for a residential, its another story... we dont pay such bill (power factor)...
A Tampa company that has been in biz a full 6 months is offering a "lifetime" warranty on their metal magic box.
ckmapawatt's picture
What's the name of the company?
PF correction may make a VERY small savings to an individual home. It will also result in very small savings for industrial users who do not pay a penalty for excess KVAR. If you have a PF of .7 then 30% of your VA is being returned to the utility on the neutral. This will infact spin your electrical meter backwards. Residential or industrial meters do not differentiate between power coming and going. It spins in whatever direction the power is flowing. As far as the savings that are realized are concerned, if you reduce the current flowing through a piece of wire from 10 amps to 8 amps you will in fact find that the wire has less loss, most of this loss is associated with heat on the conductors. What you can save is the power associated with the difference in heat generated in the wire with 8 amps versus the heat generated at 10 amps. The heavier loaded the wire is for it's size will impact the amount of heat generated by that 2 amps of power. Once of the major reasons utilities run power factor correction is that they are not covered by the NEC like we are when it comes to conductor size. NEC will not allow residential, commercial or industrial users to install smaller wire due to power factor correction being installed, the power company however can take advantage of this. So by reducing the PF, they reduce the current draw through their lines which reduces the losses of heat in the lines. This in turn allows the lines to be smaller and hopefully to reduce the total output of the generation facility. You will never save enough money at the residential level to justify the cost of the hardware. Your electrical equipment may last longer, however that will be hard to quantify. I am not an engineer, however I did stay at a Holday Inn express one time. :)
The power factor does matter and I do have a MS in Electrical Engineering. If your load is inductive, the load will still dissipate the same amount on the resistive portion of the load (i.e. Ohms), but the inductive load will reflect power on the lines in your home and be dissipated on the lines and other resistive loads. Using a capacitor in parallel (or solid state design) with the inductive load will result in a purely resistive load, you also must place the capacitor close to the inductor to reduce the mentioned line loss. The capacitor has to be efficient itself in order to capitalize on the inductive line loss savings. Now the actual savings is going to also depend on how much of the load is inductive and how many. Most average homes could save from this. A very small amount of refrigerators (heat pumps, water pumps etc...) actually have power factor correction.
ckmapawatt's picture
You're right. I think I have finally realized that the extra electrons on the line (resulting from a poor PF) reduce efficiency of the wire...but now my question is how much does this really have an impact? The sellers of PFC devices would have us believe it is 20-40%, but I think it is closer to 2-5% (if that). As you say, most new appliances already have some form of power factor correction. The only solution to this issue seems to be to build to identical houses right next to eachother (so they experience the same weather). Or build two model homes in a temperature chamber. And have a PFC device on one and see how much it saves when you run them through the exact same test scenarios.
Your right in questioning the % savings, as each home is different with different electrical equipment. You could do a quick look around your own home and take note of all the inductive loads, which most likely are going to be AC motors. If possible find the current draw and whether it has power factor correction built in and measure the entire house current (peak and low loads). Using the average power factor ~ .85 for most large household motors/pumps/generators for each inductive load along with its respective current and the measured house current would allow you to calculate the wasted power, therefore finding the potential impact on your power bill. In order to be more accurate a person would have to measure the house load for 1 week 24hrs a day during each season as well as each major inductive load. You could also find the power factor of each load device and the efficiency of the PFC capacitor.
I have a question reguarding the article. It is pertaining to Active and Reactive power (Start Up Surge), It is a known fact that inductive motors require more power at start up than the motor actually needs to run, if a motor is rated to run at 5 amps and the demand coming across your meter is 2 or 3 times more than that, what happens to that wasted energy, If it is not used it goes back to the grid or power company. but you don't receive any credit for it. Isn't true that inductive motors can run and perform well on less power draw than is listed on the label example a 5 amp moter could run and perform on say 3 amps drawn from the meter (reduce the load that crosses your meter you will reduce your bill). I think if people can use thier power more efficently will help with the over all cost. Also what percentage of your electric is Reactive Surges we there are inductive motors throughout the house and they engage all the time. Please respond thanks Calvin


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