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!

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I have a question... I'm not looking to save money on my electric bill, but instead am looking to 'extend' the use of my electrical service. I'm in a condo, and am limited to 100amp service because of the size of the conduit coming into my unit. However, I recently completed a renovation, and am now testing the limits of my electrical service because of additional loads (a 30 amp electric oven, 40 amp induction cooktop, 60 amp hottub, etc.). So, I'm looking to squeeze some extra juice out of my 100 amp service to prevent tripping up my electrical. Will a power factor correction device work for my intended use?
Chris, So there is no savings in energy (coal, n.g., etc) that can be quantified by increasing the PF of a given load. The only "savings" is not having to bring additional generation on line to provide the additional current required for the higher amount of VA associated with a lower PF and this "savings" does not translate to energy consumed by this given load. Am I getting there?
ckmapawatt's picture
I believe that's it!
I need help with the energy balance. Neglecting losses, I believe utility company gernerators produce VA-h energy which is equivalent to a given quanity of coal. Am I correct here? If so, consider the following: If an inductive laod with a pf of 0.7 requires 1 VA-h to do 0.7 Watt-h of work and 1 VA-h requires X lb of coal to be burned, but 0.7 Watt-h requires 0.7 X lb. of caol, where did the 0.3 lb of coal go?
Chris, Thanks. So if a motor load is say 10 watt (real power) and the PF results in 15 VA (total power)then the utility burns the amount of coal to produce 10 watt and not 15 VA. If this is true then the utility only burns coal to statisfy the real power watt demand regardless of PF and resultant VA, neglecting losses? Right?
ckmapawatt's picture
Rob, the amount of coal burned is going to be the same if you are producing the same qty of VA-h. In the case of poor power factor, .3 lb is burned and the electrons it created (through the turbines) that are not converted to useful energy (watts) are left on the line waiting to be used. Improving power factor just means you are more efficient in transporting electrons to do useful work.
Sir In all power factor improvement articles, the efficiency(watt loss/kvar) of compensating device is not taken into account. What if the compensating device consumes more energy than it can save upstream?
ckmapawatt's picture
Not necessarily. The utility has to create all 15 VA, but only 10 watts is used. That means the other electrons are still floating on the line waiting to be used up. This is why utilities punish industrial plants with poor PF. The utility has to create the power (thus meaning they have to activate assets like peaking natural gas plants) to supply power to the industrial user, but because the industrial user has a poor PF not all the power is being used. Note that no energy is wasted, the only thing that is wasted is the utilities time and effort to actuate the plants that could be idle if PF was better.
can someone tell me how my electric meter calculates or reads my power factor?
It's easy. Your electric meter doesn't care about power factor.


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