I wrote an introduction to power factor correction devices a few years ago and then last year we showed you a test done by a news station proving that power factor correction doesn't work .
For Xcel Energy residential customers, whole-house power factor correction boxes will not help you save money on your electric bill. The science behind this process is a bit complicated (but I’ll do my best to explain in very broad terms).
It is true that power factor correction devices do reduce the current “upstream” of the devices (i.e. appliances), and therefore reduce line losses. However, the devices have no impact on energy consumption other than reducing line losses. We bill our residential customers based solely on energy use and do not charge a power factor penalty when their power factor is low. Therefore, there is no impact on our customers’ energy bills.
So while these devices may provide other benefits for residential customers, such as prolonging the life of equipment, they do not save on energy bills.
My title may be a bit misleading, as the boxes may lower electric bill by 1 percentage point (due to lower line losses if there are many inductive loads in the home), but the manufacturers and marketers of these devices are flat out wrong when they claim huge energy savings due to these devices. Thankfully a utility has helped confirm out position!