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:solarea...@solareagle.com>
*To:* RE-wrenches <mailto:re-wrenches@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
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