I wrote about the Plug and Save power factor correction device last year and I opened with :
I was so surprised when I Googled “Save Electricity” and it turned out to be the second hit. I question the validity of a search engine if a company can simply “game” their search ranking to get high on the rankings and then offer no insight on to how their product works. The device claims “Save Electricity Bills by up to 40%”. This is complete and utter b.s.! So what is the Plug and Save?
I also explained why these power factor correction devices don't work as advertised in residential settings in our post "Can improving power factor help your energy bill?":
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!
When people claim their energy bills have gone down after they install a power factor correction (PFC) device, I always ask how they know it was because of the device, or because of their own behavioral changes, or because of factors outside of their control, like the weather. The only real way to test one of these devices is in the lab, like I advocated in Oct. of 2010 in reply to a comment that said that PFC do reduce line loss:
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.
Luckily this type of test has been done!
WGAL TV in Lancaster, PA did a controlled lab experiment back in 2009 that compared a sample residential electrical circuit consisting of 2 kW of electricity demand (see video below). Their results after running the test for 8 hours with and without a power factor correction device: 17.67 kWH without the PFC device vs. 17.28 kWh with the device. That's a savings of 2.2%. Ideally, I'd like to see this type of test repeated several times, and with several different configurations of electronic devices as the load, but I think this is a great start.
The PFC device may have saved a few percent in electricity, but this is hardly the 40% that Plug and Save once claimed and the 12% energy savings on average that the Zap Box claims.