[RE-wrenches] power factor

Darryl Thayer daryl_solar at yahoo.com
Tue May 8 06:37:09 PDT 2012


I have found that many inverters will have a poor power factor when producing low power, and the power factor improves with load.  if there are other things on your load it can effect the power factor./   I have also seen very low power factor when motors run unloaded.  I remember a gas dryer with no clothes and the power factor was 0.24

Power Factor is like a spring, a piece of equipment will draw current like compressing a spring and then send it back, so the utility has current flowing in the wires but no net work or no kWh  
DT 

________________________________
 From: "toddcory at finestplanet.com" <toddcory at finestplanet.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org> 
Sent: Monday, May 7, 2012 11:47 PM
Subject: Re: [RE-wrenches] power factor
   
excellent replies to yes, a complicated issue. i think i finally understand this. thank you kent and dan! 
  
todd 
  
  
  
On Monday, May 7, 2012 9:02pm, "Exeltech" <exeltech at yahoo.com> said:

 
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 
>
>> 
>
>>    Sent from Finest Planet WebMail. 
>-----Inline Attachment Follows-----
>
>
>_______________________________________________List sponsored by Home Power magazineList Address: RE-wrenches at lists.re-wrenches.orgOptions & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette:www.re-wrenches.org/etiquette.htmCheck out participant bios:www.members.re-wrenches.org       Sent from Finest Planet WebMail._______________________________________________List sponsored by Home Power magazineList Address: RE-wrenches at lists.re-wrenches.orgOptions & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette:www.re-wrenches.org/etiquette.htmCheck out participant bios:www.members.re-wrenches.org   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20120508/79509ff5/attachment-0004.html>


More information about the RE-wrenches mailing list