Power Factor Correction – How and Why

April 13, 2011


Earlier this week I attempted to explain power factor through an analogy using beer. I promised you that I’d follow it up with an explanation of how to correct power factor and why it’s a good financial decision to do so. So let’s recap a little with a vocabulary refresher:

Tap = Utility company – supplying the power to the mug
Beer mug = Load (in this case, for the sake of simplicity, we’ll say the load is one motor)
Beer = Real Power – actually used by the motor
Froth = Reactive Power – not used by the motor, power lost

Refreshed? Ready? Let’s go!


I could go into a few no-cost/low-cost ways to improve a facility’s power factor but to be honest, they are all pretty weak. The low-hanging fruit of power factor correction might save you a handful of singles on the next utility bill and that’s just not significant enough for me to dwell on.

So I’m skipping right to the good stuff. Capacitors! If you’re anything like me, you just got a little bit excited and asked yourself “Oh man, I wonder if I can still remember all the capacitor color coding rules?! First, second, multiplier, tolerance!” I just read that last sentence aloud – I pray to the heavens that you are nothing like me. Anyhow, back to the task at hand.

If your beer mug is has capacity for 100 kW but only needs 80 kW for it to operate sufficiently (aka give you a tingly sensation) then we’ll say your beer mug has 20 kW of froth. Which would *kind of* look like this (pretend it’s a mug… I’m working with what little royalty-free photos I can find):

80% Beer - 20% Froth (Might not be to scale, dont hate.

A capacitor acts like a second mug that you can move all your froth into for storage. The capacitor allows you to move 80 kW of beer into the mug and the other 20 kW is stored in the second mug. As the second mug fills up with froth, the froth settles and turns back into golden, liquidy beer that can be supplied to the original mug (or new mugs!) when it’s needed. Which looks more like this:

Hardly any froth at all .. Image from http://www.sxc.hu

This means that all the beer flowing from the tap (utility) is used and power loss is reduced drastically because all your froth is being used eventually. Your mug still may only need 80 kW of power, but now your second mug (capacitor) is charged up and can supply all that power that’d previous been lost to another load – like the beer mug your friend next you needs to have filled.

Sad, empty glass - Image from http://www.sxc.hu

So, now that we know that a capacitor uses a higher percentage of the power provided from the utility and allows your facility to supply power to more loads and more consistently, let’s talk about why this is good financially.


Poor power factor is penalized by most utility companies. If they are supplying you with 100 kW of power and you’re only utilizing 80 kW, they get mad and make you pay. Why? Because it costs money for the utility company to ensure it’s creating enough energy at all times that your facility can get 100 kW – and you’re not using it all! So they are going to charge you for the 100 kW and THEN tack on a fee for inconveniencing them for no reason. If you install a capacitor that bumps your power factor up to 97% and you start using 97 kW of the 100 kW supplied by the utility, they’ll drop that penalty fee for being wasteful.

Also, poor power factor typically contributes to shorter equipment life. I still have not found a way to relate this to beer since froth doesn’t seem to have any adverse affects on the longevity of a beer mug. But stay with me here… you’re almost a power factor guru now so I can drop the analogy for a second. As poor power factor continues and gets worse, equipment can experience voltage drops. Once these voltage drops become excessivee, overheating and premature failure of motors and other equipment can occur. By allowing for premature equipment failure occur, we’re throwing money at fixing a symptom of poor power factor rather than investing in fixing the problem. That makes sense, right?

So let’s recap this business case:

1. You’re not getting charged for froth you can’t drink. This translates to less money wasted on power that’s never used.
2. You can fill more mugs than you could before. This translates to making more widgets with the same power cost.
3. Your mugs last longer. This translates into less money wasted on replacing equipment, lower operational costs.

Less waste, potential for more production, and lower bottom line – can you argue with that? Probably not.

What did you think of The Art of Explaining Power Factor and [title]? These posts were an exercise in relating technical concepts to those who do not speak energy efficiency as their primary language. I would love your feedback – and do not hesitate to be critical if you feel so compelled. I constantly strive to become better and better at relating to others through communication so any constructive criticisms you have are welcomed.

Please share in the comment section below.

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3 Comments on “Power Factor Correction – How and Why”

  1. Mark W. Says:

    While reading this post I was reminded of my brother’s installation of a new natural gas furnace a few years ago. The new furnace works OK but it wasn’t properly sized for the house. He had an 80K BTU unit installed which is more capacity than necessary. He would have been much better off with a 60K BTU furnace which would have been more energy efficient with better temperature control and probably resulted in longer life. Bigger isn’t always better. It’s not power factor but the closest correlation I could easily come up with.


  2. Madam Energy Says:

    Mark, I can see the correlation. Kind of like the somewhat inappropriate cliche: “bigger isn’t always better – it’s how you use the tool.”


  3. Mrunalini Says:

    Thanks for such a wonderful , Simple & exciting explaination


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