Can anyone explain how power factor relates to power consumed vs. cost per kwh?

ratsbew

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I understand that an incandescent bulb has a power factor of 1.0 which means that if it consumes 60W, it will be charged at 60W by your meter.

A LED of CFL bulb might have a power factor of .6-.8. If it consumes 15W does this mean that you are charged 15/.6 = 25W?

Are new high tech bulbs saving energy, but not as much money as you think?
 

CKOD

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Power factor doesnt affect residential customers billing at all currently, in the US. You pay by the watt (hour) not by the VA (hour) Industrial and commercial customers have power factor figured into their bill, and it could benefit them to maintain a good power factor.

The power factor causes "circulating current" which causes resistive losses in your house wiring, which is wasted power, but the actual power used by that should be fairly small compared to the load.

Another way to think of it is, if you put a non polarized capacitor into your AC outlet (thought/explanation only, not actually to be carried out :p ) with the right value you could have 10A @120v flowing though it, but 0 work being done. The 10A flowing would cause I^2R loses in the capacitor and in your household wiring, so that's all you should be billed for.
 

brickbat

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I understand that an incandescent bulb has a power factor of 1.0 which means that if it consumes 60W, it will be charged at 60W by your meter.

That's true.


A LED of CFL bulb might have a power factor of .6-.8. If it consumes 15W does this mean that you are charged 15/.6 = 25W?

No. It could be said to consume 25 volt-amps (VA). But it's pretty much irrelevant because your power meter measures energy in units of kilowatt-hours. So, it's only the wattage of the load that matters. (assuming you are a residential customer of the power company)


Are new high tech bulbs saving energy, but not as much money as you think?

No. A 15W LED of CFL bulb uses 15 Watts. That's all there is to it...
 

gnarly

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Yes, an electricity meter should properly integrate the instantaneous current * instantaneous voltage over time, so it measures the true consumption regardless of the power factor.

A cheap kill-a-watt meter probably doesn't do this, so might read a higher value.

The electricity suppliers don't like power factors less than 1.0, because it causes their distribution systems to be less effective.
 

idleprocess

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It appears that residential consumers pay for the amount of power that the bulb has listed on the packaging, but the bulb itself isn't as good for the environment as you might think because they consume more energy that they are rated at.

This is true - the "apparent load" (the actual power that the utility has to deliver) is greater than the faceplate load. However, given the power factors I've seen it doesn't negate the power savings of most incandescent alternatives.

A typical electro-mechanical electrical meter can't accurately measure for <1.0 power factor, so this inefficiency is not typically billed to residential customers.

A so-called "smart" meter can recognize low power factors and can accurately bill customers for the "apparent load" the utility must meet. Given that utilities have often adapted to the reality of lower power factors amongst residential customers by installing power factor-correction equipment at their substations, this is somewhat opportunistic of them.

Industrial customers have long paid for <1 power factors and usually opt to install correction equipment at their locations.
 

ratsbew

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A so-called "smart" meter can recognize low power factors and can accurately bill customers for the "apparent load" the utility must meet.

Is it common practice for utilities to bill for apparent power?

Is it possible to integrate power factor correction hardware into the confined space inside a LED/CFL base?
 

idleprocess

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Is it common practice for utilities to bill for apparent power?
I gather it's one of the primary reasons utilities install smart meters

Is it possible to integrate power factor correction hardware into the confined space inside a LED/CFL base?
I believe that slightly better (read: slightly more expensive) ballast/driver designs in CFL/LED bulbs considerably improve the power factor.

I'm only familiar with power factor correction gear being used on larger scales - as in for an entire building or piece of equipment that consumes massive amounts of power.
 
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Steve K

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Is it common practice for utilities to bill for apparent power?

Is it possible to integrate power factor correction hardware into the confined space inside a LED/CFL base?

If you check info on the switching power supply chips and controllers, such as the LM3444 LED driver, many of them include PFC (power factor correction) circuits in the application notes. For instance, this is from the first bit of text in the LM3444 datasheet:
"A passive PFC circuit ensures good power factor by drawing current directly from the line for most of the cycle, and provides a constant positive voltage to the buck regulator."

Maybe CFL's don't include power factor correction circuits, but it appears to be a common theme among LED drivers.


regards,
Steve K.
 

SemiMan

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First, power factor has virtually no impact on how much "energy" a device (or your house really) uses. Currently, residential customers are billed only for energy used within their house.

While power factor does increase resistive losses, this is not the big concern of the power companies.

For those who don't know what power factor is, it is a ratio of how current follows voltage over a sinusoidal waveform. For a bulb, a resistive load, it follows perfectly. For a linear power supply, it may only draw power on the peaks of the waveform and hence have a very low power factor. A switching supply/LED driver may be somewhere in the middle.

The issue for the power company is that they must size their systems not only for the power to be delivered, but for the peak VA delivered. That increases the cost of the generating equipment, distribution system (transformers), etc. A 1.0PF makes for the cheapest system.

Semiman
 

ratsbew

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I reran the test with a CFL bulb and its power factor was about .18...much worse than my LED bulbs.

One interesting thing I've come to realize is that it is possible to overload a powerstrip even if the rated Wattage of all loads is under the rated limit of the powerstrip.
 
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AaronG

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I reran the test with a CFL bulb and its power factor was about .18...much worse than my LED bulbs.

One interesting thing I've come to realize is that it is possible to overload a powerstrip even if the rated Wattage of all loads is under the rated limit of the powerstrip.

Are you sure about that? That seems very low. How did you measure it?

Also power factor correction is usually pretty easy to integrate, although it does cost a little more.
 

CKOD

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Are you sure about that? That seems very low. How did you measure it?

Also power factor correction is usually pretty easy to integrate, although it does cost a little more.
Power factor is one thing, the complete crap non-sinusoidal, harmonic filled current waveform is another. Also, when 4 packs of CFLs are selling for under $4 even a $0.05 component is a significant hit in the profit margin.

Some of the more expensive dimmable CFLs may incorporate it because its not a huge percent of the part cost then, but if its $4 for a 4 pack vs $6 for a 4 pack of bulbs that have all the same info on the "lighting facts" label, what is the average consumer gonna get?
 

brickbat

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I reran the test with a CFL bulb and its power factor was about .18...much worse than my LED bulbs....

Hopefully the OP can jump back in and conform this, but I wonder if that 0.18PF was measured on a dimmable lamp, while it was dimmed to a pretty low setting... (It was stated that way in another related thread)
 

Scotty2014

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I have recently started work for a small company that, amongst other things, resells and installs Power Factor Correction equipment. The customers are small medium businesses who consume over $ 1000 of power per month.

I have only just started studying Power Factor correction. I am not an electronics engineer.

We have just over 200 installed sites for a small scale Automatic Power Factor corrector.

A few of these customers are billed in kVA. There appears to be no question that p.f. correction saves kVA.

Most of our customers are small, and so they are billed in kWh. They do not care about kVA savings.

My boss, and the company, claims that, on average across all kWh billed customers, the device we install saves around 15% of kWh. This claim is supported with (a few) graphs of individual customer's kWh usage comparing kWh prior to installation of the p.f. correction device, with kWh post installation.

The problem I have, as has also been posed here in this thread, is that having looked at dozens of web sites and technical bulletins that discuss power factor, almost none of the theory discusses p.f. correction as being able to bring kWh savings.

Yet, our firm's experience, and the few pieces of individual customer analysis of power bills, indicates that p.f. correction does, for consumers who are billed in kWh, bring kWh savings ranging from 10% to 20%.

I would like to understand how this can be?

The only explanation I can think of is that an appliance with a low p.f. (say 0.6) must need more kWh than the same appliance needs once the p.f. corrected (to say 0.95).

Does anyone have anything to add (or detract) from this rationalisation? Can someone point me to some science which discusses kWh savings from p.f. correction?


Scott.
 

brickbat

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...My boss, and the company, claims that, on average across all kWh billed customers, the device we install saves around 15% of kWh. This claim is supported with (a few) graphs of individual customer's kWh usage comparing kWh prior to installation of the p.f. correction device, with kWh post installation...

Correcting power factor won't cause a 15% reduction in kWh usage.

So, your boss appears to relying on a post hoc ergo propter hoc fallacy.

IOW, something else changed after your PF doo-dad was installed that resulted in real energy savings.

That, or he's just a liar.

Keep in mind that correcting PF can result in a tiny saving in energy consumed because losses in the conductors in the building are reduced a tad. But no way would this be 15% in any real-world installation.
 

JWP_EE

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When the power factor of a device is 1 the load is purely resistive and the current used by the device is in phase with the voltage. When the power factor is less than 1 the current is out of phase with the voltage. The power consumed by the device can be calculated by the voltage times the current times the COSINE of the phase angle between the voltage and current. This phase shift of the current happens because the load looks resistive and partly inductive or capacitive.

The power system that delivers the power will see the same resistive losses for a given current whether the end device is resistive or not. But the cost to the customer is only for the real power delivered. The power delivery system is usually tuned to be just resistive. This is why you see large capacitors on the power poles in industrial area the have motor driven devices... motors are inductive.

Besides the loses in the delivery system that cost the power company money the out of phase currents distort the voltage sinusoidal wave form which can cause problems. So the power company likes to see a unity power factor.
 

SemiMan

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Scotty,

These devices are a complete and absolute scam. Likely breaking some law for even promoting them as they are known to be a scam, it's well documented, and there is no engineering reason why they would improve energy usage that much.

Even large customers are not charged purely on KVA (at least not normally). What they are is essentially penalized for poor PF, and the penalty usually is related to how large their operation is and how far from unity. There are several tiers.

Have you opened up on of those SCAM BOXES? Odds are all that is inside if $10 of capacitors in an off-the-shelf plastic electrical box.

Semiman
 

Anders Hoveland

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I can explain the concept of what the power factor is very simply. In normal alternating current, the voltage and current (amperes) increase and decrease together. When the power factor is less than 1, that means the voltage and current are out of synch. Most electric devices cannot utilize all the power if the voltage and current waveforms are not in the same phase. All that extra current does little good if the voltage is not high enough (at that precise instant), and similarly extra voltage does little good if the current is not high enough at the same time. Effectively what that means is that a portion of the power simply goes through the electrical device being powered and is returned to the generator. This is very wasteful, and electrical current is lost to resistance in the power lines also. When it is the electrical device that has a power factor lower than 1, that means the device is not adequately suited to fully utilize the alternating current that is in perfect voltage-current alignment, basically with the same effect.

Most meters for residential customers only charge for the amount of power actually used, but if you are using devices that have a low power factor, what that effectively means is the utility company will have to generate more power to supply you with the power you are using.



Is it possible to integrate power factor correction hardware into the confined space inside a LED/CFL base?
When a wave of power passes through an inductor (such as a transformer), the current will trail the voltage. Typically the solution to correct this wave distortion is to pass the current through a capacitor, which basically has the opposite effect. That is the reason electrical utilities install so many capacitor boxes at electrical substations.
 
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