Power factor correction, explained
If your electricity bill has a line for reactive power or low power factor, you are paying for power that does no useful work. It is one of the few charges you can remove almost completely.
What power factor means
Motors, compressors, fans, pumps and some lighting draw two kinds of power: real power, which does the work, and reactive power, which the equipment needs to run but which does no work itself. Power factor is the ratio between them. A power factor of 1 means all the power drawn is useful.
The more reactive power a site draws, the lower its power factor, and the more current the network has to carry for the same useful output.
How to tell if you are paying for it
Larger business connections in Ireland can be charged for reactive power when the power factor is low. Look for a reactive power, kVArh or low power factor line on the bill. Sites with heavy refrigeration, compressors, ventilation or motors are the most likely to see it.
How correction works
Power factor correction equipment, usually capacitor banks installed at the main board, supplies the reactive power locally so the site no longer draws it from the network. Sized correctly, it removes the reactive charge and can reduce losses and heat in the site's own cables.
It is sized from measured data. Monitoring the site's power factor through the day, before buying equipment, avoids under- or over-correcting.
Common questions
Does my business need power factor correction?
If your bill shows reactive power or low power factor charges, almost certainly. If it does not, correction will not reduce your bill.
How much can power factor correction save?
Typically the whole reactive power charge on the bill, plus small reductions in losses. Check what the charge has cost you over the last twelve months: that is roughly the annual saving.
What is a good power factor?
Close to 1. Most sites aim for 0.95 or higher.
Want this applied to your building?
Start with an energy audit. If you spend over ten thousand euro a year on energy, the SEAI grant covers most of the cost.