[RE-wrenches] power factor

[Exeltech]

Hello Todd,

The short answer to your "is this a concern?" query, is "no".

Reactive power is one of the more complex aspects of electric power, and
certainly one of the most misunderstood.  It can and does involve inductive
loads (e.g. motors), capacitive loads (e.g. some types of power supplies),
and non-linear loads (e.g. switch-mode power supplies, dimmers, etc.).

You likely know (or should know) "power factor" is the ratio of real power to
reactive power consumed by a load.  Grid-tie inverters generate "real" watts,
which are then coupled to the grid.  When a reactive load in your home is
consuming power, and you provide real watts to the load from the inverter,
this changes the ratio of real to apparent power consumed by the load as
seen by the utility company.

Dividing real power by apparent power results in a unit-less value between 0
and 1 that describes this ratio.

Let's say a load in your home is consuming 1,200 real watts, and 1,250
apparent watts.  This results in a power factor of 1200/1250, which equals
0.96.  Pretty darn good.

Next, your grid-tie inverter provides 1,000 real watts back to the utility company,
which in turn is 1,000 real watts that the utility company no longer needs to
provide to the load described above.  Thus the net "real" power consumed as
seen by the utility is now 1,200W - 1,000W = 200W.

This means they sell only 200 watts to power your load, but the "apparent"
power aspect is still there.

End result?

200 real watts / 1250 apparent watts yields a power factor of 0.160.  Terrible by
any power company standards, yet you've removed 1,000 watts from the grid.
This is the value that will be displayed on your meter.

Efforts are underway by EPRI and others to help create standards for future
generations of grid-tied inverters capable of generating "reactive" power (where
volts and amps are out of phase with each other) to help mitigate this effect.
I'm a member of the committee working toward that goal.  (No, we're not there
yet. It'll take time.)

This is a very difficult topic to discuss and explain.  Hopefully this helped.

Like Tom Cruise said at the end of "Top Gun" .. "It's complicated."


Dan



--- On Mon, 5/7/12, toddcory at finestplanet.com <toddcory at finestplanet.com> wrote:

From: toddcory at finestplanet.com <toddcory at finestplanet.com>
Subject: [RE-wrenches] power factor
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Monday, May 7, 2012, 9:46 PM




wrenches,


i have a question about my home's system. i was one of the first net metered systems in our area, so the utility company installed a fancy dual register meter which also displays kvar/power factor.


when selling 1 kW today the power factor was .40 and the kvar was 2.37.


this sounds horrible. question: is this a concern?


todd









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