[RE-wrenches] Power Factor

Thu Jul 30 14:17:22 PDT 2009

R. Walters wrote:
> Power factor expresses the time difference  between voltage peak and 
> current peak on each of their sine waves. If both current and voltage 
> waves are "in time", (their wave peaks match up) power factor is 1. If 
> one is ahead or behind the other, it's not. Think about an electric 
> motor: we hit it with a voltage wave, and a fraction of a second 
> later, it actually moves, and the current wave happens. There is a 
> little lag there. Resistive loads like lights have very little lag, 
> and big electric motors coming up to speed can have horrible PF.

This definition of power factor only applies for linear loads with only 
inductance or capacitance (with resistance) and is called "Displacement 
Power Factor (DPF) and you will  see that on some power meters.

For non-linear loads, like battery chargers or computer power supplies 
without PF Correction,  the current waveform (on an O-scope) looks 
nothing like a sine or cosine wave.   The current "spikes up" at the AC 
voltage peaks.  It actually *looks like* it might be in phase, BUT the 
current and the voltage do NOT look the same.  It's non-linear.  Lower 
than 1.0 power factor for sure.

For a grid tie inverter, resistive heater or any load that has a PF of 
1.0,  the current and voltage waveform will both look exactly the same 
AND there will be no phase shift.   They are both linear and all current 
and voltage is in phase at every point in the AC cycle.

So, because of the different ways of specifying PF, it is always best to 
think of Power Factor as being the ratio of real (in phase) power, or VA 
to reactive power (VARS or "Volt Ampere Reactive").   That will work in 
all cases. (Real Vs. Apparent power is the same thing).   Apparent power 
is what you get when you multiply
your RMS meter's Voltage by the RMS current and is called VA Volt 
Amperes)   V x A will be the highest measured number, that is unless the 
PF = 1.0 in which
case both will measure the same.

Some of that measured VA, or apparent power will be "in phase" and is 
the "real" or "true" power.  Some of that VA may be reactive, (inductive 
or capacitive that is) and is the "out of phase" portion.  Capacitive 
and inductive reactance is ALWAYS 90 degrees out of phase in current and 
voltage.... It's just a matter of how MUCH of your power is 0 degrees 
phase shift and how MUCH of that VA is  + or - 90 degrees out of phase.  
If  ALL of the current is in phase with the voltage, then
the power factor is 1.0.   That is, if you lay them on top of each 
other, they will look the same on an oscilloscope if power factor = 1.0

It can get way more complicated that this too, but that's basically it.  
Feel free to add to this.

boB

power meters.

> There is much more to it, with reactance, "real" and "imaginary" 
> numbers?!, etc. but basically, we wrenches need to know that everybody 
> wants  Power factor to be close to 1.
> Obviously there isn't PF on DC, and it is my understanding that most 
> inverters can operate at most power factors. 
> Not 100% sure, but I think GT inverters would help not hurt the PF 
> problem in most situations.
>
> Correct me on any and all of this, Oh fellow wrenches,
>
> R. Walters
> Solarray.com
> NABCEP # 04170442
>

>
>
> On Jul 30, 2009, at 9:19 AM, boB Gudgel wrote:
>
>> Ron Young wrote:
>>> Ok, so all seem to be in agreement more or less. How do I break it 
>>> to British Columbia Hydro? :-|
>>>
>>> I think they must be misunderstanding what they are asking for but 
>>> the question is in the section for PV and on the same line as the 
>>> total output in Kwh of the PV. Power Factor %
>>
>> It was most likely just  a trick question.
>>
>> You're gonna fool them, though !   :)
>>
>>
>> boB
>>
>>
>>
>>>
>>> I'll contact them and see where this goes but I don't fully 
>>> understand what power factor is which will make it hard to argue my 
>>> case. My understanding is that it is the difference between what the 
>>> utility supplies to a residence vs. the actual loads being used by 
>>> that residence expressed as a percentage. 
>>> I came across the following course offering by SEI that discusses 
>>> Power Factor with reference to PV:
>>>
>>> POWER FACTOR AS IT RELATES TO SOLAR INSTALLATIONS Presented By: 
>>> Michael Smith of Alpine Management Systems 
>>>  
>>> This session will deal with power factor: What is power factor?  
>>> What causes low power factor?  Why improve your power factor? This 
>>> session will explain the role of power factor correction as it 
>>> applies to solar installations. There are currently over 67,000 KVAR 
>>> installations in 26 countries resulting in phenomenal energy savings 
>>> with a corresponding reduction in greenhouse gas emissions. Session 
>>> includes several KVAR installations and the resultant savings. 
>>> http://www.solarenergy.org/workshops/docs/industry08_trainingdetails.pdf
>>>
>>> Ron
>>>
>>> On 30-Jul-09, at 7:43 AM, Wind-sun.com wrote:
>>>
>>>> There is no such thing as a power factor for DC or for panels.
>>>>  ..................................................................................................
>>>> Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
>>>> Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
>>>> ..................................................................................................
>>>>
>>>>     ----- Original Message -----
>>>>     *From:* Ron Young <mailto:solareagle at solareagle.com>
>>>>     *To:* RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
>>>>     *Sent:* Wednesday, July 29, 2009 5:45 PM
>>>>     *Subject:* [RE-wrenches] Power Factor
>>>>
>>>>     Can anyone point me in the direction to find the power factor for
>>>>     Sanyo HIT N 205 panels? The utility is requesting it on a net
>>>>     metering interconnection application.  
>>>>     Ron Young
>>>>     earthRight Products - Solareagle.com
>>>>
>>>>
>>>>     
>>>> ------------------------------------------------------------------------
>>>>
>>>>     _______________________________________________
>>>>     List sponsored by Home Power magazine
>>>>
>>>>     List Address: RE-wrenches at lists.re-wrenches.org 
>>>> <mailto:RE-wrenches at lists.re-wrenches.org>
>>>>     <mailto:RE-wrenches at lists.re-wrenches.org>
>>>>
>>>>     Options & settings:
>>>>     
>>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>>>
>>>>     List-Archive: 
>>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>>>
>>>>     List rules & etiquette:
>>>>     www.re-wrenches.org/etiquette.htm
>>>>     <http://www.re-wrenches.org/etiquette.htm>
>>>>
>>>>     Check out participant bios:
>>>>     www.members.re-wrenches.org <http://www.members.re-wrenches.org>
>>>>
>>>> _______________________________________________
>>>> List sponsored by Home Power magazine
>>>>
>>>> List Address: RE-wrenches at lists.re-wrenches.org 
>>>> <mailto:RE-wrenches at lists.re-wrenches.org> 
>>>> <mailto:RE-wrenches at lists.re-wrenches.org>
>>>>
>>>> Options & settings:
>>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>>>
>>>> List-Archive: 
>>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>>>
>>>> List rules & etiquette:
>>>> www.re-wrenches.org/etiquette.htm 
>>>> <http://www.re-wrenches.org/etiquette.htm>
>>>>
>>>> Check out participant bios:
>>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org>
>>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> List sponsored by Home Power magazine
>>>
>>> List Address: RE-wrenches at lists.re-wrenches.org 
>>> <mailto:RE-wrenches at lists.re-wrenches.org>
>>>
>>> Options & settings:
>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>>
>>> List-Archive: 
>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>>
>>> List rules & etiquette:
>>> www.re-wrenches.org/etiquette.htm
>>>
>>> Check out participant bios:
>>> www.members.re-wrenches.org
>>>
>>>   
>>
>> _______________________________________________
>> List sponsored by Home Power magazine
>>
>> List Address: RE-wrenches at lists.re-wrenches.org 
>> <mailto:RE-wrenches at lists.re-wrenches.org>
>>
>> Options & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> List-Archive: 
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> www.re-wrenches.org/etiquette.htm
>>
>> Check out participant bios:
>> www.members.re-wrenches.org
>>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
>   