Electricity Bill - Peak Power 6

[jdogg05]

I was talking to the electrical superintendent at my work. He was talking about VFDs and how they reduce your energy bill because they ramp up the current slowly rather than just applying full power right away. I was then told that this is how energy companies actually bill you: based on your PEAK power during any billing cycle... I don't understand how or why this is? Can someone explain this to me?

 

[cranky108]

One of the problems I've seen in smaller utilities is big customers will try to push back, and the customer agents will typically agree to modify the PF charges. The larger customers will even go to the commission to argue there case. The bottom line is PF charges don't work universally.

And maybe this is more of an issue with some customer types, as I never saw this with what I called the clean industries (there shops were cleaner also).

I don't see those problems now that I work for a utility with more clean industries (more urban), but I think it is also that the utility is also more flexable with the service options, and it is more difficult to make a case herd without it being news worthy (the voters have a larger role).

 

[dpc]

Cranky,

I've seen the same. Many small utilities have power factor penalties in their rate schedules, but in practice they often do not impose them since it is generally their largest customers who would be paying the penalty. This is starting to change around here since BPA has imposed more stringent PF penalties on these utilities.

 

[LionelHutz]

I looked through some of the billing data I had and found that you could save in the $0.80 to $1.20 range per kW by using a VFD to correct the power factor of a motor which has a decent power factor say in the 81-83% range to begin with. This is based on the demand billing where the demands are based on 90% of VA or the kW, whichever is larger which I typically see.

This means you could save around $60 to $90 a month by installing a VFD on a 75kW motor. The accounting guys typically want to see a 2 year payback which means the VFD must cost in the $1440 to $2160 range to justify the installation. The chassis VFD will cost more than this amount.

The conclusion I would reach is that sure you could reduce the demand charges but the savings would never justify installing the VFD. Heck, it's difficult to justify the installed cost of a capacitor bank when the power factor is >80%.

 

[cranky108]

The VFD is required for large impact loads where the motors would cause voltage flicker. Rock crushers, saw mills and the like.

However if the load were constant then a fixed capacitor bank behind the motor switch would be more cost effective.

Another place a low PF happens is in some high energy lighting.