PF penalty of Solar building

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mpcarnahan

Member
Location
Pittsburgh PA
Facts:
100kW PV on Office Building
Approx 40% of bldg. usage
Utility bill shows much lower kWh (because of solar)
But kVARh stays the same (since solar inverters generate only real power >.99pf)
Utility 'sees' "imbalance" in PF. (imbalance is only on their side of the meter, because client producing some of their own kW)

Problem:
They apply penalty for imbalance in PFM (pf multiplier) of 1.46
They take 1.46 x kW peak demand of 87 to make it 127kW "adjusted" demand.
At $7/kW demand fee, that's $280 additional fees for using solar... in one month.

Solutions:
?
Can a capacitor reduce the kVAR in a bldg. where its really not off balance in the first place and they're aren't that many induction loads?
Even if it could, Solar power goes up and down with the sun, clouds, etc. Wouldn't the capacitor have to react in conjunction with that?
 

Carultch

Senior Member
Location
Massachusetts
Facts:
100kW PV on Office Building
Approx 40% of bldg. usage
Utility bill shows much lower kWh (because of solar)
But kVARh stays the same (since solar inverters generate only real power >.99pf)
Utility 'sees' "imbalance" in PF. (imbalance is only on their side of the meter, because client producing some of their own kW)

Problem:
They apply penalty for imbalance in PFM (pf multiplier) of 1.46
They take 1.46 x kW peak demand of 87 to make it 127kW "adjusted" demand.
At $7/kW demand fee, that's $280 additional fees for using solar... in one month.

Solutions:
?
Can a capacitor reduce the kVAR in a bldg. where its really not off balance in the first place and they're aren't that many induction loads?
Even if it could, Solar power goes up and down with the sun, clouds, etc. Wouldn't the capacitor have to react in conjunction with that?

If the power factor is poor because of loads that behave like capacitors, which is expected when motor loads are minimal and the dominant loads are computers / modern lighting, adding a capacitor bank for power factor correction is going to be counter-productive. Capacitor banks for power factor correction are built with lagging inductive loads in mind, such as motors.

Power factor correction is a good idea for this problem, but make sure it is the correct kind of correction.
 
Last edited:

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Many commercial scale grid interactive inverters can be programmed to deliver a specified reactive VA, allowing them to correct your power factor as seen by POCO.
Although I do not know if they can be set for either leading or lagging reactive current.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Many commercial scale grid interactive inverters can be programmed to deliver a specified reactive VA, allowing them to correct your power factor as seen by POCO.
Although I do not know if they can be set for either leading or lagging reactive current.

What he said.

My first step would be to consult the inverter manufacturer.
 

mpcarnahan

Member
Location
Pittsburgh PA
I know I've seen utility scale inverters that have reactive power compensation, but I can't say i've seen them in the commercial 10-60kW transformerless options, like Fronius SYMO or Solectria's PVI's.

On the capacitor reply above, if the capacitor delivers kVAR to the induction loads, doesn't that reduce what the utility company is providing to the building, thus lessening the reactive power delivered? Which is what we want, right? Sry, I've never dealt with PFC's except to tell homeowners not to buy the damn things.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I know I've seen utility scale inverters that have reactive power compensation, but I can't say i've seen them in the commercial 10-60kW transformerless options, like Fronius SYMO or Solectria's PVI's.

On the capacitor reply above, if the capacitor delivers kVAR to the induction loads, doesn't that reduce what the utility company is providing to the building, thus lessening the reactive power delivered? Which is what we want, right? Sry, I've never dealt with PFC's except to tell homeowners not to buy the damn things.
Hawaii is requiring non-unity power factor settings in new GTIs for domestic use. Fronius already has models that meet that requirement and other manufacturers are likely to follow suit as quickly as their engineers can support it.

If customer has a net capacitive PF that can cause stabilty problems for POCO and cannot be reliably used to offset net inductive customers.
 

pv_n00b

Senior Member
Location
CA, USA
This is not an uncommon, but is often overlooked, result of PV in commercial applications. There are two types of PF sources, displacement and harmonic. The one most people mean when they talk about PF is displacement, the difference in phase between the voltage and current waveforms. Harmonic PF has both the voltage and current in phase but harmonics distort the current waveform.

Displacement PF is caused by reactance, harmonic PF is caused by harmonic distortion and it is usually from electronic power supplies that use PWM to provide DC power. I'm not sure utilities are measuring harmonic PF, someone please let me know if you know for sure of a utility that is doing it. It's not easy to measure where displacement PF is very easy to measure.

As far as I know adding a PV system will not effect harmonic PF but it can make displacement PF, as seen by the utility, worse.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Displacement PF is caused by reactance, harmonic PF is caused by harmonic distortion and it is usually from electronic power supplies that use PWM to provide DC power. I'm not sure utilities are measuring harmonic PF, someone please let me know if you know for sure of a utility that is doing it. It's not easy to measure where displacement PF is very easy to measure.

As far as I know adding a PV system will not effect harmonic PF but it can make displacement PF, as seen by the utility, worse.

Simple to measure bad power factor from either cause: Displacement and distortion both cause the product of the RMS voltage and the RMS current to be different from the actual power, which is the integral of the instantaneous product of voltage and current.
When the low PF is caused by distortion, there is no phase angle that can be used to characterize the reason for the discrepancy. But given a meter that can both measure real power (easy to do mechanically or digitally) and measure RMS voltage and current (another easy measurement) you know how poor the power factor is.
What is hard to know is which of the two is causing how much of the measured poor power factor.
If measuring displacement power factor is somehow easier, you could just take the difference between that and total.

For billing purposes POCO does not care about the reason. For network operation, they need to know on an overall network basis what is distortion and what is displacement so that they can figure out whether capacitor banks will help. And for that they use a power analyzer, not just a power meter.
 
Hawaii is requiring non-unity power factor settings in new GTIs for domestic use. Fronius already has models that meet that requirement and other manufacturers are likely to follow suit as quickly as their engineers can support it.

If customer has a net capacitive PF that can cause stabilty problems for POCO and cannot be reliably used to offset net inductive customers.

Had an interesting conversation a few weeks ago with the engineer on a medium sized PV system. We were talking about adding some extra conduits for communications to provide for the possibility that in the future, the POCO can access the inverters to tailor the PF to their needs at any given time. I admit to being a bit unclear on this however. I generally dont think of a source as having or being able to control PF. Ill have to cogitate on that a bit.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Had an interesting conversation a few weeks ago with the engineer on a medium sized PV system. We were talking about adding some extra conduits for communications to provide for the possibility that in the future, the POCO can access the inverters to tailor the PF to their needs at any given time. I admit to being a bit unclear on this however. I generally dont think of a source as having or being able to control PF. Ill have to cogitate on that a bit.
Some inverters do indeed have the ability to change their power factor.
 

Carultch

Senior Member
Location
Massachusetts
I wasnt doubting that, just saying I dont understand the electrical theory of a source being able to "provide" power factor. I'll have to educate myself a bit.

Maybe "provide" isn't the best term here.

What such an inverter does, is it intentionally adjusts the current timing relative to the voltage cycles such that it has a non-unity power factor, to correct for the prevailing imbalance of premises loads.
 

pv_n00b

Senior Member
Location
CA, USA
Simple to measure bad power factor from either cause: Displacement and distortion both cause the product of the RMS voltage and the RMS current to be different from the actual power, which is the integral of the instantaneous product of voltage and current.
When the low PF is caused by distortion, there is no phase angle that can be used to characterize the reason for the discrepancy. But given a meter that can both measure real power (easy to do mechanically or digitally) and measure RMS voltage and current (another easy measurement) you know how poor the power factor is.
What is hard to know is which of the two is causing how much of the measured poor power factor.
If measuring displacement power factor is somehow easier, you could just take the difference between that and total.

For billing purposes POCO does not care about the reason. For network operation, they need to know on an overall network basis what is distortion and what is displacement so that they can figure out whether capacitor banks will help. And for that they use a power analyzer, not just a power meter.

It's unfortunate that in the electrical industry we use the same term, Power Factor, to describe two completely different phenomena that have no relationship other than the use of the name.

It's important to use the correct terms. The vector product of the RMS voltage and the RMS current is the apparent power. The apparent power can be broken down into the vector sum of the real power component and the reactive power component. If the current and voltage waveforms are in phase the apparent power and real power are the same, and the reactive power is zero. These are all vector quantities with a magnitude and direction.

With harmonic distortion PF there is no reactive power component. Even if the current waveform is very distorted the power is still 100% real. The calculation of harmonic distortion power factor is not a vector and unlike displacement PF cannot be negative. It's a scalar quantity between 0 and 1 that is inversely proportional to the total harmonic distortion.

The utility might not like having to provide the harmonic components in the current and make a customer put in harmonic filters but it's a separate issue from supplying or sinking reactive power. It is possible to have harmonic and displacement PF issues at the same time but they are still completely different phenomena.
 
Maybe "provide" isn't the best term here.

What such an inverter does, is it intentionally adjusts the current timing relative to the voltage cycles such that it has a non-unity power factor, to correct for the prevailing imbalance of premises loads.

Sure, but one must employ some "tricks" to get the impedance on the inverter output to be what you want when you want, that is the more complex part. I suspect it involves some fancy use of the inverters internal inductors and capacitors (I havent read the article yet, been working longs days, havent had enough mental energy to digest).
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It's unfortunate that in the electrical industry we use the same term, Power Factor, to describe two completely different phenomena that have no relationship other than the use of the name.

It's important to use the correct terms. The vector product of the RMS voltage and the RMS current is the apparent power. The apparent power can be broken down into the vector sum of the real power component and the reactive power component. If the current and voltage waveforms are in phase the apparent power and real power are the same, and the reactive power is zero. These are all vector quantities with a magnitude and direction.

With harmonic distortion PF there is no reactive power component. Even if the current waveform is very distorted the power is still 100% real. The calculation of harmonic distortion power factor is not a vector and unlike displacement PF cannot be negative. It's a scalar quantity between 0 and 1 that is inversely proportional to the total harmonic distortion.

The utility might not like having to provide the harmonic components in the current and make a customer put in harmonic filters but it's a separate issue from supplying or sinking reactive power. It is possible to have harmonic and displacement PF issues at the same time but they are still completely different phenomena.

Overall, I find your analysis (the math) less than compelling and only marginally useful.
Your last paragraph is fine though. Both reactive power and harmonic power end up being a strain on the generating equipment even though they do not necessarily increase the fuel requirement. :)

1. If you are talking about a "vector product", you need to specify which one: dot product, which is a scalar, or cross product, which is a vector.
The cross product of two parallel vectors is zero, so you do not want to use that one. But it is a vector.
What gives you the cos(theta) term you need is the dot product. But it is scalar, so the idea of it being composed of two vector components is not terribly useful either.
And for apparent power, you actually want the scalar product of the scalar RMS amplitudes. Then you draw that as a vector of that magnitude with the appropriate decomposition into real and reactive components.
As concluded in another mega-thread the reactive power does not numerically correspond to any real (even cyclical with net zero) transfer of energy.
There can be the equivalent of reactive power in distortion power factor in that certain current harmonics may transfer power to and from POCO with a net of zero even if they are in phase with the voltage fundamental.

2. It seems a lot simpler to me to use the analysis I described in passing, namely that the apparent power is the product of the RMS current and RMS voltage. That works for both displacement and for distortion power factor. You have to recognize that the RMS current is not in fact a sine wave, so the relationship of RMS to peak and average will not be what you are used to. But there are meters that will measure both and their product is the apparent power.
The real power (average power in one direction over a single cycle) can be determined ONLY by an integral of the instantaneous product of current and voltage over one or more cycles.
In the case of displacement power factor the real power can be derived from the apparent power in terms of the cosine of the phase difference.
In the case of distortion power factor, its relationship to the apparent power can only be predicted if you know the amplitude and phase of all of the harmonics of both voltage and current. Often you can still approximate the voltage as a pure sine wave, but not always.
 

Anode

Member
Location
Washington, USA
Facts:
100kW PV on Office Building
Approx 40% of bldg. usage
Utility bill shows much lower kWh (because of solar)
But kVARh stays the same (since solar inverters generate only real power >.99pf)
Utility 'sees' "imbalance" in PF. (imbalance is only on their side of the meter, because client producing some of their own kW)

Problem:
They apply penalty for imbalance in PFM (pf multiplier) of 1.46
They take 1.46 x kW peak demand of 87 to make it 127kW "adjusted" demand.
At $7/kW demand fee, that's $280 additional fees for using solar... in one month.

Solutions:
?
Can a capacitor reduce the kVAR in a bldg. where its really not off balance in the first place and they're aren't that many induction loads?
Even if it could, Solar power goes up and down with the sun, clouds, etc. Wouldn't the capacitor have to react in conjunction with that?


Like others have said, the inverter should be programmable to adjust power factor. This will in turn reduce the efficiency of power harvest, but it will reduce the imbalance with POCO on power factor.

I have always come back to this short article: https://www.gses.com.au/wp-content/uploads/2016/03/GSES_powerfactor-110316.pdf
 

pv_n00b

Senior Member
Location
CA, USA
GoldDigger, just because two completely different things have the same name does not make them the same. It's unfortunate that the folks working in harmonics who wanted a term for a new rating they came up with for harmonic distortion chose a term already in use to describe phase shift and it confused people. Not much else I need to say, harmonic distortion has nothing in common with phase shift between voltage and current other than being called by the same name. :slaphead:
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
GoldDigger, just because two completely different things have the same name does not make them the same. It's unfortunate that the folks working in harmonics who wanted a term for a new rating they came up with for harmonic distortion chose a term already in use to describe phase shift and it confused people. Not much else I need to say, harmonic distortion has nothing in common with phase shift between voltage and current other than being called by the same name. :slaphead:
Harmonic distortion and phase shift have nothing in common. (Although you can argue that both can be completely characterized from the Fourier transforms of the two waveforms!)

Poor power factor caused by harmonic distortion and poor power factor caused by phase shift have a lot in common, namely the basic definition of power factor that applies perfectly well to both cases.

You may still argue that power factor should not have been chosen in the first place as a figure of merit for non-linear loads that are connected to an AC power grid. On that ground, the Total Harmonic Distortion, and other weighted figures from various harmonic amplitudes form perfectly useful figures of merit for non-linear loads already. However they do not, by themselves, provide any measure of the relative amount of "non-useful" current through the load, as characterized very well by power factor.

If you think that the definition of displacement power factor involves cos(theta), IMHO you are wrong. The definition of PF is based on the ratio of two quantities with dimensions of Volts time Amps, and from that definition it can be proved that it is equal to cos(theta) for the special case where both current and voltage are pure sine waves.
 

Carultch

Senior Member
Location
Massachusetts
GoldDigger, just because two completely different things have the same name does not make them the same. It's unfortunate that the folks working in harmonics who wanted a term for a new rating they came up with for harmonic distortion chose a term already in use to describe phase shift and it confused people. Not much else I need to say, harmonic distortion has nothing in common with phase shift between voltage and current other than being called by the same name. :slaphead:

Power factor is not ultimately a different concept in the two cases. Low power factor is still due to a mismatch between the actual value of average power (based on instantaneous volts*instantaneous amps integrated), and the product of RMS Volts & RMS Amps that doesn't consider each function's own nuances.

It is just that there are different reasons for a power factor of non-unity, whether it be due to a phase shift of the two waveforms, or due to different shapes of the two waveforms.
 
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