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!

Tags:

apparent power

customer testimonial

michael bluejay

power factor

real power

ripoff report

Comments

Anonymous (not verified) Mon, 04/18/2011 - 19:12

I came across this website this morning, http://www.saticsaver.com, that sells PFC devices that simply plug in to an outlet and cover that particular circuit in the house. They have other models as well that look like they can be hard wired. This was the simplest version of a PFC that I have seen. There is a video on the site showing how it "works" and the change it makes on a fridge. Not showing anything about watts consumed, simply showing the PF and Amps of course. I have a background in electrical engineering as a lot of people who commented on this blog seem to as well. I don't believe for a minute that these devices are miracle workers and will save me huge amounts on my electric bill. However, I do believe they can serve a purpose in certain situations and I would be willing to understand more about them in that context. Whether it is for a generator or my old furnace blower, I would be interested to know if anyone has done a simple test that could show the difference in watts consumed. I wish I had a TED 5000 because I would be willing to drop a hundred bucks or so to try it out.

ckmapawatt Mon, 04/18/2011 - 20:36

So why don't you get a TED 5000? :)

Anonymous (not verified) Tue, 04/19/2011 - 00:46

I wish I could afford all the toys I want in life. I have been using my little Kill A Watt meter for years and it has done well. Just not capable of handling the bigger machinery in the house. I guess if I was going to drop the money for a TED and a PFC device I could just spend the money to replace my furnace blower with a nice, new, efficient ECM motor and be done with it! Then I would not be spending the money on some unproven device. Maybe someone should check with Consumer Reports or one of the other consumer product review groups and ask if they have looked into these devices before.

Anonymous (not verified) Sat, 04/23/2011 - 15:15

I have a workshop powered by solar and battery bank. I also have a Sharp's CV-P10RC (Portable Air Conditioner) I'd like to use to keep it cool. Would power factor correction reduce the size of the inverter needed for start up? The A/C unit's manual lists input power at 1,000 watts, or 9 Amps. When pricing inverters, there is a fair increase, from 1,000W, to 1200 or 1500 watts. I don't know what the initial surge would be to start the portable air conditioner, I wonder if a pf device would allow me to use the 1,000W inverter.

Anonymous (not verified) Thu, 05/12/2011 - 03:42

I have a very rudimentary knowledge of electricity but even so, I think the equation is amps = watts/volts which means that watts = amps/volts. Now, if you are metered by watts, even then the watts will reduce if the amps reduce. This is what I saw when one of these devices was demonstrated. My motor showed 1.3 amps without the device and 0.75 amps with the device. So, don't I save? I would be grateful for an explanation.

Anonymous (not verified) Thu, 05/12/2011 - 07:56

If the formula watt = amp x volts, is correct then if the amps decrease (which the devices do show)there will be a saving in the electricity bill, which we presume measures watts consumed. Am I correct?

ckmapawatt Thu, 05/12/2011 - 13:24

In a purely resistive circuit, like an incandescent light bulb, you are correct. But in other circuits, the formula is watt = (power factor) * amps * volts. So as power factor increases, amps decreases, but the end value remains largely unchanged.

ckmapawatt Thu, 05/12/2011 - 13:27

Guys, I don't want to be rude, but are you even reading the post? I put up the equation: Watts = PF*Amps*Voltage. Please go back and read the post, as I address this exact issue!

Anonymous (not verified) Sun, 05/15/2011 - 17:45

Chris, excuse my ignorance which I admitted initially. To be blunt, I must say that I have read your post but my question remains the same - how does PF enter the equation? If watt = amp x volts , it follows that if amps decrease then the watts decrease and my bill decreases

ckmapawatt Mon, 05/16/2011 - 01:26

Anwar, please reread the post and my comment again. Where do I say that watt = amp x volts? In the post, I say that watt = power factor x amp x volts. You are incorrect in saying that watt = amp x volts, unless you have a purely resistive circuit.

blog